Oil recovery mechanism
The oil recovery mechanism effectively separates and recovers oil from refrigerants with lower specific gravity using a gas-liquid separator and oil separator, enhancing refrigeration system efficiency and maintenance by preventing oil obstruction.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- MAYEKAWA MFG CO LTD
- Filing Date
- 2024-12-18
- Publication Date
- 2026-06-30
Smart Images
Figure 2026106591000001_ABST
Abstract
Description
Technical Field
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[0001] The present invention relates to an oil recovery mechanism.
Background Art
[0002] In a refrigeration system, the liquid-phase refrigerant generated by passing through a compressor and a condenser cools the air inside the refrigerated warehouse by exchanging heat with the air inside the warehouse when passing through the evaporator.
[0003] By the way, for example, in Patent Document 1 below, a configuration including an oil sump for recovering oil accumulated at the bottom of a heat exchanger functioning as an evaporator is disclosed in a flooded cooler using an ammonia refrigerant.
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] However, when the specific gravity of the oil is smaller than that of the refrigerant, it has been difficult to effectively recover the oil.
[0006] The present invention provides an oil recovery mechanism that can simply and effectively recover the oil contained in the refrigerant of the evaporator. <An oil recovery mechanism according to one aspect of the present invention is an oil recovery mechanism for recovering oil from a refrigerant mixed with oil that has a lower specific gravity than the refrigerant, and comprises: a gas-liquid two-phase line through which the refrigerant flowing out of the evaporator flows, connected to the downstream end of an evaporator; a gas-liquid separator connected to the gas-liquid two-phase line downstream of the evaporator, which separates the refrigerant flowing out of the evaporator into a liquid phase and a gas phase; an oil recovery line connected to a portion of the gas-liquid separator located above the lower end, through which oil contained in the refrigerant in the gas-liquid separator is discharged; and an oil separator provided below the portion of the gas-liquid separator connected to the oil recovery line, which stores the oil flowing through the oil recovery line.
[0008] In this embodiment, since the specific gravity of the refrigerant is greater than that of the oil, two layers of liquid are stored in the gas-liquid separator, with the refrigerant in the lower layer and the oil in the upper layer. In this case, since the oil separator is located below the connection point (oil discharge opening) to the oil recovery line within the gas-liquid separator, when the oil in the upper layer reaches the same height as the oil discharge opening, it is discharged from the gas-liquid separator through the oil discharge opening. The oil discharged from the gas-liquid separator is stored in the oil separator. In this way, the oil remaining as supernatant in the gas-liquid separator can be flowed into the oil separator by the weight of the oil itself, so that oil can be removed from the main refrigerant flow path even while the refrigeration system is in operation. As a result, the obstruction of heat transfer of the refrigerant by oil is suppressed, making it easier to maintain cooling efficiency. In particular, as in this embodiment, by providing an oil separator downstream of the evaporator, oil is recovered from the low-pressure, two-phase gas-liquid refrigerant that has passed through the evaporator. This allows for the easy and effective recovery of oil contained in the refrigerant.
[0009] In the oil recovery mechanism according to the above embodiment, it is preferable that the gas-liquid separator is connected to a first gas return line through which the gas phase refrigerant of the refrigerant that has flowed into the gas-liquid separator flows toward the compressor's intake, and that the upper end of the oil separator is provided with a second gas return line connected to the first gas return line, through which the gas phase refrigerant present in the oil separator flows toward the first gas return line. According to this embodiment, the refrigerant that has entered the oil separator along with the lubricating oil and has become gaseous flows through the second gas return line to the first gas return line. As a result, the gaseous refrigerant discharged from the oil separator can be combined with the gaseous refrigerant discharged from the gas-liquid separator in the first gas return line and then returned to the refrigeration unit.
[0010] In the oil recovery mechanism according to the above embodiment, it is preferable that the oil separator is provided with a heater for heating the inside of the oil separator. According to this embodiment, heating the inside of the oil separator by the heater makes it easier to change the refrigerant mixed with the oil inside the oil separator into a gas phase. This allows the refrigerant to be effectively discharged into the second gas return line.
[0011] In the oil recovery mechanism according to the above embodiment, it is preferable that the gas-liquid separator is provided with a first gas return line through which the gas phase refrigerant of the refrigerant flowing into the gas-liquid separator flows toward the compressor's intake, the lower end of the oil separator is provided with an oil return line connected to the first gas return line and through which the oil present in the oil separator flows toward the first gas return line, and the oil return line is provided with an oil return valve that switches between communication and disconnection between the oil separator and the first gas return line. According to this embodiment, the oil separator and the first gas return line are switched on and off by opening and closing the oil return valve. This allows the lubricating oil in the oil separator to be returned to the first gas return line.
[0012] In the oil recovery mechanism according to the above embodiment, the oil recovery line is provided with an oil recovery valve that switches between communication and disconnection between the gas-liquid separator and the oil separator, and a control unit that controls the opening and closing of the oil return valve and the oil recovery valve. Preferably, the control unit opens the oil recovery valve and closes the oil return valve during cooling operation, while closing the oil recovery valve and opening the oil return valve after defrosting operation to melt frost adhering to the evaporator. According to this embodiment, during cooling operation, the oil return line is shut off by the oil return valve, and the oil separator and the gas-liquid separator are maintained at the same pressure, making it easier for the oil remaining as supernatant in the gas-liquid separator to flow into the oil separator due to the weight of the oil itself. On the other hand, the temperature rise caused by defrosting increases the pressure in the first gas return line and the oil separator compared to cooling operation. When the compressor is operated in this state, the refrigerant in the first gas return line is drawn towards the compressor, creating negative pressure in the first gas return line, including the connection point with the oil return line. Also, because the pressure in the oil separator has increased due to the effects of defrosting, a differential pressure is created between the oil separator and the first gas return line. By opening the oil return valve in this state, the oil in the oil separator is drawn into the first gas return line. As a result, the lubricating oil is returned to the refrigeration unit along with the refrigerant. This eliminates the need for separate oil recovery work, thus improving maintainability.
[0013] In the oil recovery mechanism according to the above embodiment, a second gas return line is provided at the upper end of the oil separator, which is connected to the first gas return line and through which the gaseous refrigerant present in the oil separator flows toward the first gas return line, and a gas return valve is provided in the second gas return line that switches between communication and blockage between the inside of the oil separator and the first gas return line, and it is preferable that the control unit opens the gas return valve during cooling operation and closes the gas return valve after defrost operation. According to this embodiment, by closing the gas return valve after defrosting, it is easier to return the lubricating oil in the oil separator to the first gas return line through the oil return line.
[0014] In the oil recovery mechanism according to the above embodiment, the evaporator has a coil filled with a liquid-phase refrigerant, and the refrigerant is preferably carbon dioxide. According to this embodiment, by using a so-called full-liquid type evaporator, it is easier to lower the supply temperature of the refrigerant to the evaporator when carbon dioxide is used as the refrigerant. This makes it easier to maintain an extremely low temperature inside a refrigerated warehouse. [Effects of the Invention]
[0015] According to each of the above aspects, the oil contained in the refrigerant can be recovered simply and effectively.
Brief Description of the Drawings
[0016] [Figure 1] It is a schematic configuration diagram of a refrigeration device according to an embodiment. [Figure 2] It is a front view of an evaporator according to an embodiment. [Figure 3] It is a cross-sectional view of the evaporator corresponding to the line III-III in FIG. 2. [Figure 4] It is a configuration diagram showing an evaporator and a gas-liquid separator according to an embodiment.
Embodiments for Carrying Out the Invention
[0017] Next, embodiments of the present invention will be described based on the drawings. In the embodiments and modification examples described below, corresponding configurations may be denoted by the same reference numerals and the description thereof may be omitted. In the following description, expressions indicating relative or absolute arrangements such as "parallel", "orthogonal", "center", "coaxial", etc. not only strictly represent such arrangements, but also represent states in which they are relatively displaced with tolerances and angles or distances that can obtain the same function. Further, in the present embodiment, "opposite" includes not only the case where the orthogonal directions (normal directions) of two surfaces coincide with each other, but also the case where the orthogonal directions intersect.
[0018] [Refrigeration System 1] FIG. 1 is a schematic configuration diagram of the refrigeration system 1. The refrigeration system 1 shown in FIG. 1 is an ultra-low temperature refrigeration system 1 used for storing fish such as tuna and bonito (hereinafter referred to as refrigeration objects). The refrigeration system 1 includes a refrigerated warehouse 10, a refrigeration device 11, a defrosting device 12, and a control unit 13.
[0019] [Refrigerated Warehouse 10] The refrigerated warehouse 10 allows items to be frozen to be brought in and out through an entrance / exit (not shown), and stores the frozen items that have been brought in at a predetermined temperature range. In this embodiment, it is preferable that the inside of the refrigerated warehouse 10 be maintained at an extremely low temperature (-45°C or lower).
[0020] <Refrigeration unit 11> The refrigeration unit 11 cools the inside of the refrigerated warehouse 10 by exchanging heat between the refrigerant and the air inside the warehouse 10. In this embodiment, carbon dioxide (CO2) is used as the refrigerant. However, other refrigerants (for example, ammonia (NH3) or alternative fluorocarbons) may be used in the refrigeration unit 11.
[0021] The refrigeration system 11 comprises a refrigeration unit 20, an evaporator 21, a gas-liquid separator 22, and an oil separator 23. The refrigeration unit 20, the evaporator 21, and the gas-liquid separator 22 are arranged in order in the direction of refrigerant flow in the refrigerant main flow path 25.
[0022] The refrigeration unit 20 is a so-called direct expansion type condensing unit. The refrigeration unit 20 receives mainly the gas phase of the two-phase gas-liquid refrigerant that has passed through the evaporator 21, and generates high-pressure liquid phase refrigerant by compressing and heat exchanging (condensing) the gas phase refrigerant. The upstream end of the supply line 30 is connected to the outlet of the refrigeration unit 20. The supply line 30 constitutes part of the main refrigerant flow path 25. The liquid phase refrigerant generated in the refrigeration unit 20 flows through the supply line 30 toward the evaporator 21. An expansion valve 31 is provided in the supply line 30.
[0023] The refrigerant discharged from the refrigeration unit 20 contains lubricating oil (refrigeration oil). The lubricating oil is used to lubricate the compressor (not shown) installed in the refrigeration unit 20. In other words, the main refrigerant flow path 25 contains the lubricating oil that flows out with the refrigerant when it is discharged from the compressor's outlet. The lubricating oil used has a lower specific gravity than the refrigerant and is incompatible with the refrigerant, however, if it separates in the evaporator 21 or the gas-liquid separator 22 and accumulates at the top, a compatible lubricating oil may be used.
[0024] The evaporator 21 cools the air inside the storage unit by exchanging heat between the liquid-phase refrigerant supplied from the refrigeration unit 20 and the air inside the storage unit. The downstream end of the supply line 30 is connected to the inlet of the evaporator 21. In other words, the liquid-phase refrigerant is supplied directly to the evaporator 21 through the supply line 30 without passing through the gas-liquid separator 22. When carbon dioxide is used as the refrigerant, the temperature of the refrigerant at the inlet of the evaporator 21 is set to a temperature near the triple point of carbon dioxide (for example, -55°C), but not below the triple point (-56.6°C).
[0025] The upstream end of the gas-liquid two-phase line 32 is connected to the outlet of the evaporator 21. The gas-liquid two-phase line 32 constitutes part of the refrigerant main flow path 25. The gas-liquid two-phase refrigerant used to cool the air inside the chamber in the evaporator 21 flows through the outlet of the evaporator 21 to the gas-liquid separator 22 via the gas-liquid two-phase line 32. The detailed configuration of the evaporator 21 will be described later.
[0026] The gas-liquid separator 22 is located at the downstream end of the gas-liquid two-phase line 32. The gas-liquid separator 22 separates the gas-liquid two-phase refrigerant discharged from the evaporator 21 into a gas phase refrigerant and a liquid phase refrigerant. A first gas return line 35 is connected to the gas-liquid separator 22. The first gas return line 35 constitutes part of the refrigerant main flow path 25 and connects the gas-liquid separator 22 to the refrigeration unit 20. Of the gas-liquid two-phase refrigerant that flows into the gas-liquid separator 22, the gas phase refrigerant flows towards the inlet of the refrigeration unit 20 (compressor suction port) through the first gas return line 35.
[0027] A liquid return line 36 is connected to the gas-liquid separator 22. The liquid return line 36 connects the portion of the supply line 30 located between the expansion valve 31 and the evaporator 21 to the gas-liquid separator 22. In this embodiment, the liquid return line 36 keeps the evaporator 21 and the gas-liquid separator 22 in constant communication. Of the refrigerant that flows into the gas-liquid separator 22, the liquid phase refrigerant flows towards the supply line 30 through the liquid return line 36. That is, the liquid phase refrigerant flowing through the liquid return line 36 merges with the liquid phase refrigerant flowing through the supply line 30 and is then supplied back to the evaporator 21. Furthermore, because the evaporator 21 and the gas-liquid separator 22 are constantly in communication through the supply line 30 and the liquid return line 36, a flow of liquid phase refrigerant from the evaporator 21 to the gas-liquid separator 22 is also possible. The detailed configuration of the gas-liquid separator 22 will be described later.
[0028] The oil separator 23 stores the lubricating oil contained in the refrigerant. The oil separator 23 is formed as a cylinder with its vertical direction as the axial direction, and comprises a container with both its upper and lower ends closed. The oil separator 23 is positioned below the gas-liquid separator 22.
[0029] The oil separator 23 is connected to an oil recovery line 40, an oil return line 42, and a second gas return line 43.
[0030] The oil recovery line 40 connects the gas-liquid separator 22 and the oil separator 23. Specifically, the upstream end of the oil recovery line 40 is connected to a portion of the gas-liquid separator 22 that is below the connection portion of the gas-liquid two-phase line 32 and above the connection portion of the liquid return line 36. The downstream end of the oil recovery line 40 is connected to the upper part of the oil separator 23. The oil separator 23 is located below the connection portion of the gas-liquid separator 22 with the oil recovery line 40. Therefore, the lubricating oil present in the gas-liquid separator 22 flows towards the oil separator 23 in the oil recovery line 40 due to its own gravity (head difference between the gas-liquid separator 22 and the oil separator 23).
[0031] An oil recovery valve 51 is provided in the oil recovery line 40. The oil recovery valve 51 switches between communication and disconnection between the gas-liquid separator 22 and the oil separator 23 through the oil recovery line 40. A check valve 50 (non-return valve) is provided in the portion of the oil recovery line 40 located downstream of the oil recovery valve 51. The check valve 50 allows the flow of fluid (mainly lubricating oil) from the gas-liquid separator 22 to the oil separator 23 and suppresses the flow of fluid from the oil separator 23 to the gas-liquid separator 22.
[0032] The oil return line 42 connects the oil separator 23 and the first gas return line 35. Specifically, the upstream end of the oil return line 42 is connected to the portion of the oil separator 23 located below the connection portion of the oil recovery line 40. In the illustrated example, the upstream end of the oil return line 42 is connected to the bottom wall portion of the oil separator 23. The downstream end of the oil return line 42 is connected to the first gas return line 35. The oil return line 42 is provided with an oil return valve 52. The oil return valve 52 switches between communication and disconnection between the oil separator 23 and the first gas return line 35 through the oil return line 42. The oil return line 42 may also be provided with a temperature sensor 54 for detecting the temperature inside the oil return line 42.
[0033] The second gas return line 43 connects the oil separator 23 and the first gas return line 35. Specifically, the upstream end of the second gas return line 43 is connected to the portion of the oil separator 23 located above the connection portion of the oil recovery line 40. In the illustrated example, the upstream end of the second gas return line 43 is connected to the top wall portion of the oil separator 23. The downstream end of the second gas return line 43 is connected to the portion of the first gas return line 35 located upstream of the connection portion with the oil return line 42. The gaseous refrigerant present in the oil separator 23 flows through the second gas return line 43 toward the first gas return line 35. The second gas return line 43 is provided with a gas return valve 53. The gas return valve 53 switches between communication and disconnection between the oil separator 23 and the first gas return line 35 through the second gas return line 43.
[0034] A heater 55 is provided on the outer surface of the oil separator 23 and the oil return line 42. The heater 55 heats the inside of the oil separator 23 and the oil return line 42, making it easier to vaporize the liquid phase refrigerant contained in the lubricating oil.
[0035] <Evaporator 21> Figure 2 is a front view of the evaporator 21. Figure 3 is a cross-sectional view corresponding to line III-III in Figure 2. As shown in Figures 2 and 3, the evaporator 21 comprises a fin module 80, a refrigerant flow path 81, and a warm brine flow path 82. In this embodiment, the evaporator 21 is a so-called full-liquid type evaporator 21. A full-liquid type evaporator 21 is one in which heat exchange is performed between the liquid phase refrigerant and the air inside the chamber when a predetermined amount of liquid phase refrigerant is filled in the refrigerant flow path 81.
[0036] The fin module 80 is equipped with multiple fins 90. Each fin 90 is made of a material with excellent thermal conductivity, such as aluminum. Each fin 90 is formed in a thin plate shape with the thickness direction being the direction that intersects the vertical direction (hereinafter referred to as the X direction). Each fin 90 is arranged with spacing in the X direction. Air inside the chamber can pass between adjacent fins 90.
[0037] As shown in Figure 3, each fin 90 has a first refrigerant pore row 91, a second refrigerant pore row 92, and a warm brine pore row 93. In each fin 90, the corresponding refrigerant pore rows 91 and 92 and the warm brine pore rows 93 overlap each other when viewed from the X direction. Therefore, in the following description, the details of the refrigerant pore rows 91 and 92 and the warm brine pore row 93 will be explained using one fin 90 as an example.
[0038] The first refrigerant hole rows 91 and the second refrigerant hole rows 92 are arranged alternately with a gap between them in a direction that intersects the X direction when viewed from above (hereinafter referred to as the Y direction). Adjacent first refrigerant hole rows 91 and second refrigerant hole rows 92 constitute a pair of refrigerant hole sets 94. Therefore, in this embodiment, multiple refrigerant hole sets 94 are arranged in the Y direction.
[0039] The row of holes 93 for warm brine is provided between adjacent rows of holes 91 and 92 for refrigerant that constitute a single row of holes 94 for refrigerant. In this case, the row of holes 93 for warm brine is not provided between adjacent rows of holes 94 for refrigerant. However, the row of holes 93 for warm brine may be provided alternately for all rows of holes 91 and 92 for refrigerant.
[0040] The first refrigerant hole row 91 comprises a plurality of first refrigerant holes 95. The plurality of first refrigerant holes 95 are arranged in a straight line with spacing in the vertical direction. Each first refrigerant hole 95 penetrates the fin 90 in the X direction. Each first refrigerant hole 95 is a round hole formed with the same diameter D1. The plurality of first refrigerant holes 95 constituting the first refrigerant hole row 91 are arranged at equal intervals.
[0041] The second refrigerant hole row 92 comprises a plurality of second refrigerant holes 96. The plurality of second refrigerant holes 96 are arranged in a straight line with spacing in the vertical direction. Each second refrigerant hole 96 penetrates the fin 90 in the X direction. Each second refrigerant hole 96 is a round hole formed with a diameter D1 equivalent to that of each first refrigerant hole 95. The plurality of second refrigerant holes 96 constituting the second refrigerant hole row 92 are arranged at equal intervals. Note that the shape of each refrigerant hole 95,96 is not limited to a perfect circle, but can be changed as appropriate to an elliptical shape, etc.
[0042] In the first row of refrigerant holes 91 and the second row of refrigerant holes 92 that constitute a single refrigerant hole set 94, the first refrigerant holes 95 and the second refrigerant holes 96 are arranged with a half-pitch offset in the vertical direction. Specifically, the arrangement pitch of the first refrigerant holes 95 (the distance between adjacent first refrigerant holes 95 in the vertical direction) and the arrangement pitch of the second refrigerant holes 96 (the distance between adjacent second refrigerant holes 96 in the vertical direction) are equal. Furthermore, in the first row of refrigerant holes 91 and the second row of refrigerant holes 92 that constitute a single refrigerant hole set 94, the first refrigerant holes 95 and the second refrigerant holes 96 are arranged in a staggered (alternating) pattern when viewed from the X direction. However, the arrangement pitch of the multiple refrigerant holes 95 and 96 that constitute each refrigerant hole set 91 and 92 can be changed as appropriate.
[0043] The row of warm brine holes 93 comprises a plurality of warm brine holes 105. The plurality of warm brine holes 105 are arranged in a straight line with spacing in the vertical direction. Each warm brine hole 105 penetrates the fin 90 in the X direction. Each warm brine hole 105 is a round hole formed with a diameter D2 smaller than the diameter D1 of the refrigerant holes 95, 96. In this embodiment, the diameter D1 is set to, for example, 15.88 mm, and the diameter D2 is set to 12.70 mm. It is preferable that both diameters D1 and D2 are set in the range of 9 mm to 16 mm. The shape of the warm brine hole 105 is not limited to a perfect circle, but can be changed as appropriate to an elliptical shape, etc. In this case, it is sufficient that the opening area of the warm brine hole 105 is smaller than the opening area of the refrigerant holes 95, 96. Also, the warm brine hole 105 and the refrigerant holes 95, 96 do not necessarily have similar shapes.
[0044] Each of the warm brine holes 105 constituting a row of warm brine holes 93 is arranged at equal intervals. In this embodiment, the arrangement pitch of each warm brine hole 105 is greater than the arrangement pitch of the refrigerant holes 95 and 96. That is, the number of warm brine holes 105 constituting the row of warm brine holes 93 is less than the number of refrigerant holes 95 and 96 constituting the rows of refrigerant holes 91 and 92. In the illustrated example, the warm brine holes 105 are located between vertically adjacent first refrigerant holes 95 in the first row of refrigerant holes 91, and between vertically adjacent second refrigerant holes 96 in the second row of refrigerant holes 92. Therefore, each warm brine hole 105 is surrounded by four refrigerant holes 95 and 96.
[0045] As shown in Figures 2 and 3, the refrigerant flow path 81 constitutes a part of the main refrigerant flow path 25. The refrigerant flow path 81 is connected to the downstream end of the supply line 30 via an inlet header (not shown). On the other hand, the refrigerant flow path 81 is connected to the upstream end of the gas-liquid two-phase line 32 via an outlet header (not shown). The refrigerant flow path 81 is equipped with two coils (first coil 110 and second coil 111) for each row of refrigerant holes 91 and 92. Each coil 110 and 111 is a tubular material (heat transfer tube) having an outer diameter that can be pressed into each refrigerant hole 95 and 96. That is, the outer diameter of each coil 110 and 111 is formed to be equivalent to the diameter D1 of each refrigerant hole 95 and 96. In the following, the coils 110 and 111 provided in the first row of refrigerant holes 91 will be used as an example to explain the details of the coils 110 and 111, and the second row of refrigerant holes 92 will be given the same reference numerals as the coils 110 and 111 provided in the first row of refrigerant holes 91, and its explanation will be omitted.
[0046] Each coil 110, 111 penetrates the refrigerant holes 95 facing each other in the X direction between adjacent fins 90, and extends upward in a meandering manner in the X direction by being folded back on both sides in the X direction relative to the fin module 80. The lower end of each coil 110, 111 is connected to the inlet header. The upper end of each coil 110, 111 is connected to the outlet header. Each coil 110, 111 extends parallel to the same first row of refrigerant holes 91, forming a so-called double-circuit structure (parallel structure).
[0047] As shown in Figure 2, the first coil 110 comprises a first straight section 110a, a second straight section 110b, a first folded section 110c, and a second folded section 110d. The second coil 111 includes a third straight section 111a, a fourth straight section 111b, a third folded section 111c, and a fourth folded section 111d.
[0048] The first straight section 110a is assembled in a state where it is in contact with the inner periphery of the first through-hole 95a by being press-fitted into the first through-hole 95a of the first refrigerant hole 95. The first straight section 110a is provided between adjacent fins 90 so as to penetrate each of the first through-holes 95a that are facing each other in the X direction. The second straight section 110b is assembled in a state where it is in contact with the inner periphery of the second through-hole 95b by press-fitting it into the second through-hole 95b which is adjacent to the first through-hole 95a above the first refrigerant hole 95. The second straight section 110b is provided so as to penetrate each of the second through-holes 95b that are facing each other in the X direction between adjacent fins 90.
[0049] The third straight section 111a is assembled in a state where it is in contact with the inner periphery of the third through-hole 95c by press-fitting it into the third through-hole 95c, which is adjacent to the second through-hole 95b above the first refrigerant hole 95. The third straight section 111a is provided between adjacent fins 90 so as to penetrate each of the third through-holes 95c that are facing each other in the X direction. The fourth straight section 111b is assembled in a state where it is in contact with the inner periphery of the fourth through-hole 95d by press-fitting it into the fourth through-hole 95d, which is adjacent to the third through-hole 95c above among the first refrigerant holes 95. The fourth straight section 111b is provided so as to penetrate each of the fourth through-holes 95d that are facing each other in the X direction between adjacent fins 90.
[0050] In this embodiment, the first refrigerant holes 95 consist of two through-holes (first through-hole 95a and second through-hole 95b) through which the first coil 110 (first straight section 110a and second straight section 110b) passes, and two through-holes (third through-hole 95c and fourth through-hole 95d) through which the second coil 111 (third straight section 111a and fourth straight section 111b) passes, arranged alternately. In the following description, the first through-hole 95a and second through-hole 95b will be referred to as the first hole set 115, and the third through-hole 95c and fourth through-hole 95d will be referred to as the second hole set 116. In this case, the first refrigerant hole row 91 will consist of the first hole set 115 and the second hole set 116 arranged alternately in the vertical direction.
[0051] The first folded portion 110c is provided on one side (-X side) in the X direction relative to the fin module 80. The first folded portion 110c connects the X-direction ends of the first straight portion 110a and the second straight portion 110b, which are provided in the same first hole set 115. The second folded portion 110d is provided on the other side (+X side) in the X direction relative to the fin module 80. The second folded portion 110d connects the other end in the X direction of the second straight portion 110b provided in one first hole set 115 and the first straight portion 110a provided in another first hole set 115 located, for example, above the first first hole set 115.
[0052] The third folded portion 111c is provided on one side in the X direction relative to the fin module 80. The third folded portion 111c connects the X-side ends of the third straight portion 111a provided in one second hole set 116 and the fourth straight portion 111b provided in another second hole set 116 located, for example, below the first second hole set 116. In the illustrated example, the third folded portion 111c wraps around the outside of the first folded portion 110c. The fourth folded portion 111d is provided on the other side in the X direction relative to the fin module 80. The fourth folded portion 111d connects the other ends in the X direction of the third straight portion 111a and the fourth straight portion 111b, which are provided in the same second hole set 116. In the illustrated example, the second folded portion 110c wraps around the outside of the fourth folded portion 111d.
[0053] Brine (antifreeze) used for defrosting the evaporator 21 flows through the warm brine channel 82. In this embodiment, the brine used is a material with a freezing point lower than the triple point of carbon dioxide, such as an HCFO-based brine.
[0054] The warm brine channel 82 is a tubular material (heat transfer tube) having an outer diameter that can be pressed into the warm brine hole 105. That is, the outer diameter of the warm brine channel 82 is equivalent to the diameter D2 of the warm brine hole 105 and smaller than the outer diameter of each coil 110, 111. The warm brine channel 82 penetrates the warm brine holes 105 facing each other in the X direction between adjacent fins 90, and extends upward in a meandering manner in the X direction by being folded back on both sides in the X direction relative to the fin module 80. Specifically, the warm brine channel 82 comprises a straight section 82a, a folded section 82b on one side, and a folded section 82c on the other side.
[0055] The straight section 82a is assembled in contact with the inner periphery of the warm brine hole 105 by press-fitting it into the warm brine hole 105 or the like. The straight section 82a is provided between adjacent fins 90 so as to penetrate the warm brine holes 105 that are opposite each other in the X direction. The one-sided folded portion 82b is provided on one side in the X direction relative to the fin module 80. The one-sided folded portion 82b connects the one-sided ends in the X direction of one straight portion 82a and a straight portion 82a located above the first straight portion 82a. In the illustrated example, the one-sided folded portion 82b is provided so as to straddle the second hole set 116 in the vertical direction. The other-side folded portion 82c is provided on the other side in the X direction relative to the fin module 80. The one-side folded portion 82c connects the other end in the X direction of one straight portion 82a and a straight portion 82a located, for example, below the first straight portion 82a. In the illustrated example, the other-side folded portion 82c is provided so as to straddle the first hole set 115 in the vertical direction.
[0056] Figure 4 is a configuration diagram showing the evaporator 21 and the gas-liquid separator 22. In Figure 4, the gas-liquid separator 22 is shown in cross-section. As shown in Figure 4, the evaporator 21 of this embodiment is positioned within a height range that includes at least a first height T1 and a second height T2 set lower than the first height T1. The first height T1 is the height from the lower end Ta of the refrigerant flow path 81, and is the height at which the liquid phase refrigerant sufficiently fills the refrigerant flow path 81 in the evaporator 21. In this embodiment, the first height T1 is set to, for example, 80% of the total vertical dimension of the refrigerant flow path 81 (dimension from the lower end Ta to the upper end Tb) from the lower end Ta of the refrigerant flow path 81.
[0057] In this case, it is preferable that the first height T1 be 90% or less, in that a predetermined amount of liquid-phase refrigerant can be filled into the refrigerant flow path 81 (in that it is possible to suppress the flow of more than a predetermined amount of liquid-phase refrigerant into the gas-liquid separator 22 and the return of the liquid-phase refrigerant to the compressor).
[0058] The second height T2 is the height from the lower end Ta of the refrigerant flow path 81, and is the height (lower limit height) at which the evaporator 21 is filled with the liquid phase refrigerant necessary to perform the predetermined cooling. In this embodiment, the second height T2 is set to, for example, 70% of the overall vertical dimension of the refrigerant flow path 81 from the lower end Ta of the refrigerant flow path 81. In this case, it is preferable that the second height T2 be 60% or more in order to secure the effective area of the refrigerant flow path 81. However, the first height T1 and the second height T2 can be changed as appropriate.
[0059] <Gas-liquid separator 22> The gas-liquid separator 22 includes a housing 120, an inlet passage 121, a gas discharge passage 122, a liquid discharge opening 123, an oil discharge opening 124, a baffle plate 125, a first liquid level sensor 126, and a second liquid level sensor 127. The housing 120 is a container for separating the gaseous-liquid two-phase refrigerant and lubricating oil that have passed through the evaporator 21. That is, the housing 120 stores two layers of liquid, with the liquid phase refrigerant separated from the gaseous-liquid two-phase refrigerant as the lower layer and the lubricating oil as the upper layer. The housing 120 is positioned adjacent to the evaporator 21 in the horizontal direction. The housing 120 is positioned within a range that includes at least a first height T1 and a second height T2 in the vertical direction. In this embodiment, the housing 120 is positioned so as to straddle the first height T1 and the second height T2 in the vertical direction.
[0060] The housing 120 comprises a cylindrical portion 120a, a bottom wall 120b, and a top wall 120c. The cylindrical portion 120a is formed as a cylinder with its vertical direction as the axial direction. The bottom wall 120b closes the lower end opening of the cylindrical portion 120a. The bottom wall 120b is located between the lower end Ta of the refrigerant flow path 81 and the second height T2. The top wall 120c closes the upper end opening of the cylindrical portion 120a. The top wall 120c is located above the upper end Tb of the refrigerant flow path 81. However, the top wall 120c may be located below the upper end Tb of the refrigerant flow path 81, as long as it is located above at least the first height T1.
[0061] The inflow channel 121 constitutes the downstream end of the gas-liquid two-phase line 32. In other words, the inflow channel 121 is part of the refrigerant main channel 25. In cross-sectional view, the inflow channel 121 is formed in a downward L-shape. The inflow channel 121 comprises an inflow penetration portion 121a, a hanging portion 121b, and a closing portion 121c.
[0062] The inlet penetration 121a penetrates the upper end of the cylindrical portion 120a. Specifically, the inlet penetration 121a extends along the upper end Tb of the refrigerant flow path 81. However, the inlet penetration 121a only needs to be provided in the portion of the cylindrical portion 120a that is located above the first height T1. The tip of the inlet penetration 121a is located on the axis O of the housing 120.
[0063] The hanging portion 121b extends downward along axis O from the tip of the inlet penetration portion 121a within the housing 120. The lower end of the hanging portion 121b is located below the second height T2. In the illustrated example, the lower end of the hanging portion 121b reaches the lower end of the cylindrical portion 120a. Multiple inlets 129 are formed at the lower part of the hanging portion 121b, connecting the inside and outside of the hanging portion 121b. The inlets 129 allow the gas-liquid two-phase refrigerant flowing through the inlet channel 121 to flow into the housing 120. Multiple inlets 129 are arranged at intervals in the vertical direction and in the circumferential direction of the hanging portion 121b.
[0064] In this embodiment, at least a portion of the hanging portion 121b is immersed in the liquid phase refrigerant stored in the housing 120. That is, at least some of the inlets 129 formed in the hanging portion 121b open into the liquid phase refrigerant stored in the housing 120. In the illustrated example, the uppermost inlet 129 is located below the first height T1. The lowermost inlet 129 is located below the second height T2. However, it is sufficient that any of the multiple inlets 129 are located below the first height T1.
[0065] The occluding portion 121c closes the lower end opening of the hanging portion 121b. Therefore, the inflow channel 121 does not open in a position facing the bottom wall 120b. The occluding portion 121c is positioned away from the bottom wall 120b and faces the liquid discharge opening 123.
[0066] The gas discharge passage 122 constitutes the upstream end of the first gas return line 35. In other words, the gas discharge passage 122 is part of the refrigerant main passage 25. In cross-sectional view, the gas discharge passage 122 is formed in an L-shape. The gas discharge passage 122 comprises a discharge penetration portion 122a and an upright portion 122b.
[0067] The discharge penetration 122a penetrates the cylindrical portion 120a at a position opposite the inlet penetration 121a. The tip of the discharge penetration 122a is located inside the housing 120. The upright portion 122b extends upward from the tip of the discharge penetration portion 122a. The upper end opening of the upright portion 122b opens upward above the inflow passage 121. That is, the upper end opening of the upright portion 122b opens above the upper end Tb of the refrigerant passage 81. The gaseous refrigerant present in the housing 120 flows into the gas discharge passage 122 through the upper end opening of the upright portion 122b. The opening position of the gas discharge passage 122 can be changed as appropriate, as long as it is above the first height T1. In this case, it is preferable that the opening position of the gas discharge passage 122 is above the first height T1 and above the baffle plate 125.
[0068] The liquid discharge opening 123 constitutes the upstream end of the liquid return line 36. The liquid discharge opening 123 penetrates the bottom wall 120b in the vertical direction. The upper end opening of the liquid discharge opening 123 opens upward at the lower end inside the housing 120. That is, the upper end opening of the liquid discharge opening 123 opens in a portion located below the second height T2. Liquid phase refrigerant from the refrigerant present inside the housing 120 flows into the liquid discharge opening 123 due to its own gravity (head difference between the gas-liquid separator 22 and the inlet portion of the refrigerant flow path 81).
[0069] The oil discharge opening 124 constitutes the upstream end of the oil recovery line 40. The oil discharge opening 124 is provided by penetrating the portion of the cylindrical section 120a that is located below the portion connected to the inflow passage 121. The oil discharge opening 124 is located in the vertical center of the cylindrical section 120a. Specifically, the oil discharge opening 124 opens into the housing 120 at a position of first height T1. In other words, the oil discharge opening 124 opens into the housing 120 in a portion located above the uppermost inlet 129 among the multiple inlets 129. Lubricating oil that remains as the supernatant of the liquid phase refrigerant inside the housing 120 flows into the oil discharge opening 124. The lubricating oil that flows into the oil discharge opening 124 flows to the oil separator 23 by its own weight (gas-liquid separator 22, oil separator 23 and head difference). The oil discharge opening 124 only needs to be formed at a position higher than the second height T2.
[0070] The baffle plate 125 has the function of preventing liquid-phase refrigerant flowing into the housing 120 through the inlet 129 from reaching the gas discharge passage 122. In this embodiment, a plurality of baffle plates 125 are provided at vertically spaced intervals at the upper end of the hanging portion 121b (the portion located above the inlet 129). The gas discharge passage 122 described above opens above the baffle plates 125 within the housing 120. Each baffle plate 125 is formed in a skirt shape (conical shape) with an outer diameter that gradually increases towards the bottom. The baffle plates 125 are attached to the hanging portion 121b so as to partition the inside of the housing 120 in the vertical direction.
[0071] The baffle plate 125 has multiple through holes (not shown) that penetrate it vertically. Each through hole connects the space below and above the baffle plate 125 within the housing 120. The through holes in each baffle plate 125 are spaced apart so that they do not overlap each other in a plan view.
[0072] The first liquid level sensor 126 detects that the liquid level (liquid phase refrigerant and lubricating oil) inside the housing 120 is at a first height T1. The second liquid level sensor 127 detects that the liquid level inside the housing 120 is at the second height T2. Each liquid level sensor 126, 127 may be a contact type (float type, electrode type, etc.) or a non-contact type (ultrasonic type, etc.).
[0073] <Defrosting device 12> As shown in Figure 1, the defrosting device 12 circulates brine between itself and the evaporator 21 during defrosting of the evaporator 21. In other words, the refrigeration system 1 of this embodiment can be switched between a cooling mode, in which the inside of the refrigerated warehouse 10 is cooled via the evaporator 21 by the operation of the refrigeration device 11, and a defrosting mode, in which frost accumulated on the evaporator 21 (fin module 80, etc.) is removed when the refrigeration device 11 is stopped. The defrosting mode is performed periodically, for example, after the refrigeration device 11 has been driven in cooling mode for a predetermined time. However, the switch from cooling mode to defrosting mode may be performed manually or based on changes in the internal temperature during cooling mode.
[0074] The defrosting device 12 is connected to the evaporator 21 via a brine supply line 140 and a brine return line 141. Brine, adjusted to a desired temperature by the defrosting device 12, flows through the brine supply line 140 toward the evaporator 21. In this embodiment, so-called warm brine, adjusted to a temperature higher than the refrigerant temperature (for example, around 25°C), can be supplied. The upstream end of the brine supply line 140 is connected to the defrosting device 12. The downstream end of the brine supply line 140 is connected to the lower end (upstream end) of the warm brine flow path 82 via an inlet header (not shown).
[0075] The brine return line 141 carries the brine used for defrosting in the evaporator 21 toward the defrosting device 12. The upstream end of the brine return line 141 is connected to the upper end (downstream end) of the warm brine flow path 82 via an outlet header (not shown). The downstream end of the brine return line 141 is connected to the defrosting device 12.
[0076] <Control Unit 13> The control unit 13 shown in Figure 1 comprehensively controls the operation of the refrigeration system 1. The control unit 13 is realized by a hardware processor such as a CPU executing a computer program (software) stored in a memory unit. The control unit 13 controls the flow of refrigerant and lubricating oil by switching the opening and closing of the oil recovery valve 51, oil return valve 52, and gas return valve 53 according to the operating mode of the refrigeration system 1. In addition, the control unit 13 controls the liquid level of the evaporator 21 (refrigerant flow path 81) by adjusting the opening degree of the expansion valve 31 and the output of the refrigeration unit 20 based on the liquid level of the gas-liquid separator 22 detected by the liquid level sensors 126 and 127.
[0077] <Operation method of refrigeration system 1> Next, the operation method of the refrigeration system 1 described above will be explained. The following explanation will describe the operation in cooling mode, defrost mode, and oil recovery mode, respectively.
[0078] <Cooling Mode> As shown in Figure 1, in cooling mode, the control unit 13 opens the oil recovery valve 51 and the gas return valve 53, and closes the oil return valve 52. That is, in cooling mode, the inside of the gas-liquid separator 22 and the inside of the oil separator 23 are in communication through the oil recovery line 40, and the first gas return line 35 and the inside of the oil separator 23 are in communication through the second gas return line 43. On the other hand, in cooling mode, the communication between the first gas return line 35 and the inside of the oil separator 23 via the oil return line 42 is blocked. When the refrigeration system 11 is operated in this state, the liquid phase refrigerant discharged from the refrigeration unit 20 is supplied directly into the evaporator 21 (refrigerant flow path 81) through the supply line 30. The refrigerant flowing into the refrigerant flow path 81 flows upward while meandering in the X direction. The liquid phase refrigerant flowing into the refrigerant flow path 81 then exchanges heat with the air inside the chamber passing between adjacent fins 90 via the fins 90, etc. In other words, the evaporator 21 cools the area around it by absorbing heat of vaporization from the surroundings as the refrigerant in the refrigerant flow path 81 vaporizes. As a result, the air inside the storage area is cooled, and the inside of the refrigerated storage area 10 is maintained at the desired temperature.
[0079] The refrigerant, after heat exchange with the air inside the chamber, becomes a gas-liquid two-phase system and is discharged from the evaporator 21 into the gas-liquid two-phase line 32, before flowing into the gas-liquid separator 22. Specifically, the refrigerant flowing through the gas-liquid two-phase line 32 passes through the inflow channel 121 and then flows into the gas-liquid separator 22 (housing 120) through the inlet 129. Of the refrigerant that has flowed into the gas-liquid separator 22, the gas phase refrigerant flows into the gas discharge channel 122 through the upper end opening of the upright section 122b and is discharged from the gas-liquid separator 22. The gas phase refrigerant that has flowed into the gas discharge channel 122 flows through the first gas return line 35 and is returned to the refrigeration unit 20. The gas phase refrigerant returned to the refrigeration unit 20 is converted back into liquid phase refrigerant in the refrigeration unit 20 and then supplied to the evaporator 21.
[0080] On the other hand, of the refrigerant that flows into the gas-liquid separator 22, the liquid phase refrigerant is stored in the housing 120. In the refrigeration system 1 of this embodiment, the evaporator 21 and the gas-liquid separator 22 are arranged within a height range including the first height T1 and the second height T2. Furthermore, the evaporator 21 and the gas-liquid separator 22 are constantly in communication with each other through the gas-liquid two-phase line 32 and the liquid return line 36. That is, in cooling mode, the inside of the evaporator 21 (inside the refrigerant flow path 81) and the inside of the gas-liquid separator 22 (inside the housing 120) are maintained at the same pressure. In this case, the liquid phase refrigerant stored in the gas-liquid separator 22 is returned to the evaporator 21 due to the head difference between the gas-liquid separator 22 and the inlet portion of the refrigerant flow path 81. Specifically, the liquid phase refrigerant stored in the gas-liquid separator 22 flows into the liquid discharge opening 123 through the upper end opening of the liquid discharge opening 123. Subsequently, the liquid phase refrigerant is returned to the downstream side of the supply line 30, beyond the expansion valve 31, via the liquid return line 36. The liquid phase refrigerant returned to the supply line 30 merges with the liquid phase refrigerant supplied from the refrigeration unit 20, and is then returned to the evaporator 21.
[0081] In this embodiment of the refrigeration system 1, the inside of the evaporator 21 (inside the refrigerant flow path 81) and the inside of the gas-liquid separator 22 (inside the housing 120) are maintained at the same pressure. Therefore, the liquid level of the liquid phase refrigerant in the refrigerant flow path 81 is equal to the liquid level of the liquid phase refrigerant in the housing 120. In other words, the liquid level in the refrigerant flow path 81 can be determined based on the liquid level in the housing 120. In this embodiment, the liquid level in the refrigerant flow path 81 is adjusted by controlling the opening degree of the expansion valve 31 based on the liquid level in the housing 120.
[0082] Specifically, based on the detection result from the first liquid level sensor 126, the control unit 13 determines that the liquid level in the housing 120 has reached a first height T1, and reduces the opening of the expansion valve 31 and lowers the output of the refrigeration unit 20 (low output mode). In low output mode, the control unit 13 determines that the evaporator 21 is filled with a sufficient amount of liquid-phase refrigerant and reduces the amount of liquid-phase refrigerant supplied to the evaporator 21. On the other hand, based on the detection result from the second liquid level sensor 127, if the control unit 13 determines that the liquid level in the housing 120 is less than the first height T1 and has reached the second height T2, it increases the opening of the expansion valve 31 and increases the output of the refrigeration unit 20 (high output mode). In high output mode, if the control unit 13 determines that there is a risk of insufficient liquid phase refrigerant necessary for normal operation in the evaporator 21, it increases the amount of liquid phase refrigerant supplied to the evaporator 21. In low output mode, the opening of the expansion valve 31 may be set to 0.
[0083] In this way, the control unit 13 adjusts the opening degree of the expansion valve 31 and the output of the refrigeration unit 20 based on the detection results from the liquid level sensors 126 and 127, thereby maintaining the liquid level of the gas-liquid separator 22 between the first height T1 and the second height T2. As a result, the liquid level of the liquid phase refrigerant filling the evaporator 21 is maintained within the desired range (the range between the first height T1 and the second height T2). By maintaining the liquid level of the gas-liquid separator 22 between the first height T1 and the second height T2, during the cooling mode, at least some of the inlets 129 formed in the hanging portion 121b open into the liquid phase refrigerant stored in the housing 120.
[0084] Furthermore, lubricating oil is retained in the gas-liquid separator 22 as the supernatant of the liquid phase refrigerant. In other words, two layers of liquid are stored in the gas-liquid separator 22, with the refrigerant in the lower layer and the oil in the upper layer. In this case, since the oil separator 23 is located below the connection point (oil discharge opening 124) to the oil recovery line 40 of the gas-liquid separator 22, when the oil in the upper layer reaches the same height as the oil discharge opening 124, it is discharged from the gas-liquid separator 22 through the oil discharge opening 124. In cooling mode, since the oil recovery valve 51 is open, the oil discharged from the gas-liquid separator 22 flows towards the oil separator 23 through the oil recovery line 40 due to the head difference between the gas-liquid separator 22 and the oil separator 23. As a result, the lubricating oil contained in the refrigerant is stored in the oil separator 23.
[0085] Furthermore, the lubricating oil flowing into the oil separator 23 may contain refrigerant (mainly liquid-phase refrigerant) that has flowed from the gas-liquid separator 22 along with the lubricating oil. Heaters 55 are provided in the oil separator 23 and the oil return line 42, and the liquid-phase refrigerant contained in the oil separator 23 is heated by the heaters 55 and vaporized before being discharged from the oil separator 23 through the second gas return line 43. The gaseous refrigerant that flows into the second gas return line 43 merges with the gaseous refrigerant discharged from the gas-liquid separator 22 in the first gas return line 35 and is then returned to the refrigeration unit 20.
[0086] <Defrost Mode> In defrost mode, the defrosting device 12 is operated with the refrigeration unit 20 stopped. In defrost mode, brine adjusted to the desired temperature by the defrosting device 12 passes through the evaporator 21, warming the evaporator 21 and removing frost that has accumulated on it. Specifically, the brine flowing through the brine supply line 140 flows into the upstream end of the warm brine flow path 82 via the inlet header. The brine that flows into the warm brine flow path 82 flows upward while meandering in the X direction. The heat from the brine flowing through the warm brine flow path 82 warms the warm brine flow path 82 and the fins 90, etc. This melts the frost that has accumulated on the warm brine flow path 82 and the fins 90, etc. The water generated from the melted frost falls through the gaps between adjacent fins 90. This removes frost from the evaporator 21. In addition, the defrost mode is performed with the oil recovery valve 51 and gas return valve 53 open and the oil return valve 52 closed, similar to the cooling mode.
[0087] In this embodiment, the row of holes for the warm brine 93 is arranged between the rows of holes for the refrigerant 91 and 92 that constitute the refrigerant hole set 94, so that the warm brine channel 82 and the refrigerant channel 81 are located in close proximity. Therefore, the heat of the brine flowing through the warm brine channel 82 is also transferred to the refrigerant channels 81 which are located on both sides of the warm brine channel 82 in the Y direction. Consequently, the refrigerant flowing through the refrigerant channel 81 is efficiently heated by the brine. In this case, for example, the latent heat of condensation when the liquid phase refrigerant flowing through the refrigerant channel 81 evaporates and then condenses again can heat the refrigerant channel 81 and the fins 90. This makes it possible to melt frost that has accumulated on parts located around the refrigerant channel 81 by utilizing the latent heat of condensation of the refrigerant. As a result, it is easier to achieve the desired defrosting performance while keeping the brine temperature relatively low. Therefore, it is possible to suppress the evaporation of moisture present around the refrigerant channel 81 by the heat of the brine and suppress frost formation in locations other than the evaporator 21. The defrost mode may be terminated after the defrost device 12 has been operating for a predetermined time, or it may be terminated when the refrigerant pressure in the refrigerant flow path 81 is detected and rises to a predetermined pressure.
[0088] <Oil recovery mode> In this embodiment, the oil recovery mode is performed after the defrost mode ends and before the cooling mode starts. In the oil recovery mode, the refrigeration unit 20 is operated to supply liquid phase refrigerant to the evaporator 21, and the lubricating oil stored in the oil separator 23 is returned to the refrigeration unit 20.
[0089] In oil recovery mode, the control unit 13 opens the expansion valve 31 and the oil return valve 52, and closes the oil recovery valve 51 and the gas return valve 53. That is, in oil recovery mode, the first gas return line 35 and the inside of the oil separator 23 are in communication through the oil return line 42. On the other hand, in oil recovery mode, the communication between the inside of the gas-liquid separator 22 and the inside of the oil separator 23 through the oil recovery line 40 is blocked, and the communication between the first gas return line 35 and the inside of the oil separator 23 is blocked through the second gas return line 43. In this state, when the refrigeration system 11 is operated, the liquid phase refrigerant discharged from the refrigeration unit 20 is supplied to the evaporator 21 (refrigerant flow path 81) through the supply line 30, similar to the cooling mode.
[0090] Incidentally, when defrosting is performed using the defrost mode described above, the temperature of the refrigerant present in the refrigerant flow path 81 rises, causing the pressure in the refrigerant main flow path 25 and the oil separator 23 to increase. When the oil recovery mode is performed in this state, the refrigerant in the first gas return line 35 is drawn towards the refrigeration unit 20 (compressor), creating negative pressure in the first gas return line 35, including the connection point with the oil return line 42. Since the pressure in the oil separator 23 has increased due to the effect of the defrost mode, this differential pressure causes the lubricating oil present in the oil separator 23 to flow into the first gas return line 35 through the oil return line 42 during the oil recovery mode. Therefore, the gaseous refrigerant and lubricating oil present in the oil separator 23 are returned to the refrigeration unit 20 together with the gaseous refrigerant flowing through the first gas return line 35.
[0091] The operation time for the oil recovery mode may be a predetermined time based on a timer (not shown). The control unit 13 may also determine whether to switch from the defrost mode to the oil recovery mode based on the detection result of the temperature sensor 54 (temperature in the oil return line 42). That is, the control unit 13 may allow switching from the defrost mode to the oil recovery mode when the temperature in the oil return line 42 is higher than a predetermined temperature (for example, -50°C). If the temperature in the oil return line 42 is lower than the predetermined temperature, there is a possibility that liquid phase refrigerant is present in the oil return line 42. Therefore, by prohibiting switching to the oil recovery mode when the temperature in the oil return line 42 is lower than the predetermined temperature, it is possible to suppress the inflow of liquid phase refrigerant into the first gas return line 35 through the oil return line 42.
[0092] As described above, the refrigeration system (oil recovery mechanism) 1 of this embodiment includes a gas-liquid two-phase line 32 connected to the downstream end of the evaporator 21 through which the refrigerant flowing out of the evaporator 21 flows, a gas-liquid separator 22 connected to the gas-liquid two-phase line 32 downstream of the evaporator 21 and separating the refrigerant flowing out of the evaporator 21 into a liquid phase and a gas phase, an oil recovery line 40 connected to the portion of the gas-liquid separator 22 located above its lower end and through which lubricating oil contained in the refrigerant in the gas-liquid separator 22 is discharged, and an oil separator 23 provided below the portion of the gas-liquid separator 22 connected to the oil recovery line 40 and storing the lubricating oil flowing through the oil recovery line 40. In this configuration, since the specific gravity of the refrigerant is greater than that of the lubricating oil, two layers of liquid are stored in the gas-liquid separator 22, with the refrigerant in the lower layer and the lubricating oil in the upper layer. In this case, since the oil separator 23 is located below the connection point (oil discharge opening 124) to the oil recovery line 40 within the gas-liquid separator 22, when the lubricating oil in the upper layer reaches the same height as the oil discharge opening 124, it is discharged from the gas-liquid separator 22 through the oil discharge opening 124. The lubricating oil discharged from the gas-liquid separator 22 is stored in the oil separator 23. In this way, the lubricating oil that remains as a supernatant liquid in the gas-liquid separator 22 can be flowed to the oil separator 23 by its own weight, so that the lubricating oil can be removed from the refrigerant main flow path 25 even while the refrigeration system 1 is in operation. As a result, obstruction of refrigerant flow by lubricating oil is suppressed, making it easier to maintain cooling efficiency. In particular, as in this embodiment, by providing the oil separator 23 downstream of the evaporator 21, lubricating oil is recovered from the low-pressure, two-phase gas-liquid refrigerant that has passed through the evaporator 21. This allows for the easy and effective recovery of lubricating oil contained in the refrigerant.
[0093] In the refrigeration system 1 of this embodiment, a first gas return line 35 is connected to the gas-liquid separator 22, through which the gaseous phase refrigerant flowing into the gas-liquid separator 22 flows toward the compressor's intake. At the upper end of the oil separator 23, a second gas return line 43 is provided, which is connected to the first gas return line 35 and through which the gaseous phase refrigerant present in the oil separator 23 flows toward the first gas return line 35. With this configuration, the refrigerant that has entered the oil separator 23 along with the lubricating oil and has become gaseous flows through the second gas return line 43 to the first gas return line 35. As a result, the gaseous refrigerant discharged from the oil separator 23 can be combined with the gaseous refrigerant discharged from the gas-liquid separator 22 in the first gas return line 35 and then returned to the refrigeration unit 20.
[0094] In the refrigeration system 1 of this embodiment, the oil separator 23 is provided with a heater 55 that heats the inside of the oil separator 23. With this configuration, the inside of the oil separator 23 is heated by the heater 55, which makes it easier to change the refrigerant mixed with the oil inside the oil separator 23 into a gas phase. This allows the refrigerant to be effectively discharged into the second gas return line 43.
[0095] In the refrigeration system 1 of this embodiment, the lower end of the oil separator 23 is connected to the first gas return line 35, and an oil return line 42 is provided through which the lubricating oil present in the oil separator 23 flows toward the first gas return line 35. The oil return line 42 is provided with an oil return valve 52 that switches between communication and disconnection between the oil separator 23 and the first gas return line 35. With this configuration, the oil return valve 52 can be opened and closed to switch the communication between the oil separator 23 and the first gas return line 35. This allows the lubricating oil in the oil separator 23 to be returned to the first gas return line 35.
[0096] In the refrigeration system 1 of this embodiment, the oil recovery line 40 is provided with an oil recovery valve 51 that switches between communication and disconnection between the gas-liquid separator 22 and the oil separator 23. A control unit 13 is provided to control the opening and closing of the oil return valve 52 and the oil recovery valve 51. The control unit 13 opens the oil recovery valve 51 and closes the oil return valve 52 during cooling operation of the evaporator 21 (cooling mode), while closing the oil recovery valve 51 and opening the oil return valve 52 after defrost operation (defrost mode) to melt frost adhering to the evaporator 21. With this configuration, in cooling mode, the oil return line 42 and the first gas return line 35 are disconnected, and the oil separator 23 and the gas-liquid separator 22 are maintained at the same pressure. This makes it easier for the lubricating oil that remains as supernatant in the gas-liquid separator 22 to flow into the oil separator 23 due to the weight of the lubricating oil itself. On the other hand, the temperature rise due to the defrost mode increases the pressure in the first gas return line 35 and the oil separator 23 compared to the cooling mode. When the oil recovery mode is performed in this state, the refrigerant in the first gas return line 35 is drawn towards the compressor, creating negative pressure in the first gas return line 35, including the connection point with the oil return line 42. Also, because the pressure in the oil separator 23 has increased due to the effects of the defrost mode, a differential pressure is created between the oil separator 23 and the first gas return line 35. By opening the oil return valve 52 in this state, the lubricating oil in the oil separator 23 is drawn into the first gas return line 35. As a result, the lubricating oil is returned to the refrigeration unit 20 together with the refrigerant. This eliminates the need for separate lubricating oil recovery work, thus improving maintainability.
[0097] In the refrigeration system 1 of this embodiment, the second gas return line 43 is provided with a gas return valve 53 that switches between communication and disconnection between the oil separator 23 and the first gas return line 35. The control unit 13 opens the gas return valve 53 when the evaporator 21 is in cooling mode, and closes the gas return valve 53 after the defrost mode is activated. With this configuration, closing the gas return valve 53 after the defrost mode makes it easier to return the lubricating oil in the oil separator 23 to the first gas return line 35 via the oil return line 42.
[0098] In the refrigeration system 1 of this embodiment, the evaporator 21 has coils 110 and 111 filled with liquid-phase refrigerant. With this configuration, by using a so-called full-liquid evaporator 21, it is easier to lower the supply temperature of the refrigerant to the evaporator 21 when carbon dioxide is used as the refrigerant. This makes it easier to maintain an extremely low temperature inside the refrigerated warehouse 10.
[0099] (Other variations) While preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Additions, omissions, substitutions, and other modifications are possible without departing from the spirit of the present invention. The present invention is not limited by the above description, but only by the appended claims. In the embodiments described above, a configuration was described in which the second gas return line 43 is connected to the first gas return line 35, but the configuration is not limited to this. The second gas return line 43 may be connected directly to, for example, the refrigeration unit 20. In the embodiment described above, the oil separator 23 is equipped with a heater 55 for heating the inside, but the heater 55 is not an essential component.
[0100] In the embodiment described above, a configuration was described that includes an oil return line 42 connecting the oil separator 23 and the first gas return line 35, but the configuration is not limited to this. The lubricating oil stored in the oil separator 23 may be recovered separately, or it may be returned to the refrigeration unit 20 via a separate line from the first gas return line 35. In the embodiment described above, an oil recovery valve 51 was provided in the oil recovery line 40, but the embodiment is not limited to this configuration.
[0101] In the embodiment described above, a configuration was described in which valve switching control is performed after the defrost mode, but the configuration is not limited to this. In the embodiments described above, the case in which a full-liquid evaporator is used was explained as an example, but the configuration is not limited to this. The type of evaporator can be changed as appropriate. In the embodiments described above, the refrigeration system 1 installed in the refrigerated warehouse 10 was described as an oil recovery mechanism, but the configuration is not limited to this.
[0102] In the above-described embodiment, a configuration was explained in which the refrigerant supplied to the evaporator 21 is adjusted based on the liquid level of the liquid phase refrigerant in the gas-liquid separator 22 (inside the housing 120), but the configuration is not limited to this. The evaporator 21 may also be supplied with refrigerant using a separate refrigerant pump or the like. In this case, the layout of the gas-liquid separator 22 relative to the evaporator 21 can be changed as appropriate.
[0103] In the embodiment described above, a configuration was described in which defrosting is performed by brine flowing through a warm brine channel 83 assembled in the fin module 80, but the configuration is not limited to this. Defrosting may also be performed by using a separate heater or by spraying brine or water onto the fin module 80. In the embodiment described above, a configuration was described in which the supply line 30 is connected to the evaporator 21 without going through the gas-liquid separator 22, but the configuration is not limited to this. The supply line 30 may also be connected to the evaporator 21 via a surge tank such as a gas-liquid separator. In this case, the liquid phase refrigerant supplied from the refrigeration unit 20 is temporarily stored in the surge tank before being supplied to the evaporator 21.
[0104] Furthermore, without departing from the spirit of the present invention, the components in the embodiments described above can be replaced with well-known components as appropriate, and the modifications described above can be combined as appropriate. [Explanation of Symbols]
[0105] 1: Refrigeration system (oil recovery mechanism) 13: Control Unit 21: Evaporator 22: Gas-liquid separator 23:Oil separator 32: Gas-liquid two-phase line 35: First gas return line 42: Oil return line 43: Second gas return line 51: Oil recovery valve 52: Oil return valve 53: Gas return valve 55: Heater 110: Coil 111: Coil 124:Oil drain opening
Claims
1. An oil recovery mechanism for recovering oil from a refrigerant that has been mixed with oil that has a lower specific gravity than the refrigerant, A gas-liquid two-phase line through which the refrigerant flowing out of the evaporator is connected to the downstream end of the evaporator, A gas-liquid separator is connected to the gas-liquid two-phase line downstream of the evaporator and separates the refrigerant discharged from the evaporator into a liquid phase and a gas phase. An oil recovery line is connected to the portion of the gas-liquid separator located above the lower end, and from which oil contained in the refrigerant within the gas-liquid separator is discharged. An oil recovery mechanism comprising: an oil separator provided below the connection portion of the gas-liquid separator to the oil recovery line, which stores the oil flowing through the oil recovery line.
2. The gas-liquid separator is connected to a first gas return line through which the gaseous phase of the refrigerant that has flowed into the gas-liquid separator flows toward the compressor's intake. The oil recovery mechanism according to claim 1, wherein the upper end of the oil separator is provided with a second gas return line which is connected to the first gas return line and through which the gaseous refrigerant present in the oil separator flows toward the first gas return line.
3. The oil recovery mechanism according to claim 2, wherein the oil separator is provided with a heater for heating the inside of the oil separator.
4. The gas-liquid separator is provided with a first gas return line through which the gas phase refrigerant, of which has flowed into the gas-liquid separator, flows toward the compressor's intake. At the lower end of the oil separator, an oil return line is provided, which is connected to the first gas return line and through which the oil present in the oil separator flows toward the first gas return line. The oil recovery mechanism according to any one of claims 1 to 3, wherein the oil return line is provided with an oil return valve that switches between communication and shutoff between the oil separator and the first gas return line.
5. The oil recovery line is provided with an oil recovery valve that switches between connecting and disconnecting the gas-liquid separator and the oil separator. The system includes a control unit that controls the opening and closing of the oil return valve and the oil recovery valve, The oil recovery mechanism according to claim 4, wherein the control unit opens the oil recovery valve and closes the oil return valve during cooling operation, and closes the oil recovery valve and opens the oil return valve after defrosting operation to melt frost adhering to the evaporator.
6. At the upper end of the oil separator, a second gas return line is provided, which is connected to the first gas return line and through which the gaseous refrigerant present in the oil separator flows toward the first gas return line. The second gas return line is provided with a gas return valve that switches between communication and disconnection between the oil separator and the first gas return line. The oil recovery mechanism according to claim 5, wherein the control unit opens the gas return valve during cooling operation and closes the gas return valve after defrosting operation.
7. The evaporator has a coil filled with a liquid-phase refrigerant, The oil recovery mechanism according to any one of claims 1 to 3, wherein the refrigerant is carbon dioxide.