Oil separator and oil return mechanism for ejector-type direct expansion (DX) evaporators.

Abstract

A system and method for improving the refrigeration capacity of a direct expansion refrigeration system with a vapor separator and a vapor ejector is provided. After throttling in the expansion device, the liquid and vapor mixture enters the inlet separator. The vapor separator flashes the warm refrigerant liquid at high temperature and pressure to a lower pressure, generating vapor that powers the ejector. The cooled refrigerant liquid then passes to the evaporator coil inlet. The vapor, along with refrigerant vapor from the evaporator outlet, passes to the ejector. The ejector sends the oil, vapor, and liquid refrigerant to the oil separator, which returns the oil to the compressor and sends the liquid and vapor refrigerant to the evaporator.

Description

[Technical Field]

[0001] The present invention relates to a refrigeration system using a direct expansion evaporator. [Background technology]

[0002] Refrigeration cycles use refrigeration oil to lubricate, cool, and seal the internal moving parts of the compressor. Even with good oil separation, small amounts of oil are carried throughout the system by the refrigerant and tend to collect in the evaporator suction header. It is important to remove this oil from the evaporator and return it to the compressor. Oil return is usually accomplished when the refrigeration cycle employs hot gas defrost; however, not all systems are equipped with hot gas defrost. Summary of the Invention

[0003] Ejector-type direct expansion (DX) evaporators offer up to 38% increased cooling capacity compared to conventional DX evaporators. This increased cooling capacity is achieved by recirculating liquid refrigerant from the suction header to the distributor via the ejector, with superheated vapor exiting through the upper suction connection, just like conventional DX evaporators. This can lead to problems with refrigeration oil being recirculated and potentially accumulating within the evaporator coil tubing. The objective of this invention is to mitigate this potential problem by separating and collecting the refrigeration oil from the refrigerant downstream of the ejector and intermittently returning the collected oil to the suction connection.

[0004] The foregoing summary and the following detailed description of the preferred invention will be better understood when read in conjunction with the accompanying drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a diagram of a standard direct expansion refrigeration system. [Figure 2] This is a diagram of a direct expansion evaporator (ejector-type DX evaporator) whose cooling capacity is enhanced by a steam ejector. [Figure 3] FIG. 1 is a schematic diagram of an ejector-type DX evaporator with an oil separator / collector at the outlet of the ejector according to one embodiment of the present invention. [Figure 4] FIG. 1 illustrates an oil separator / collector according to one embodiment of the present invention. [Figure 5] FIG. 10 illustrates a secondary ejector bridged between the outlet port and the LC, according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0006] Figure 1 shows a typical standard direct expansion (DX) refrigeration system. High-pressure, cooled refrigerant from the high-pressure receiver passes through a thermostatic expansion valve and distributor into the evaporator. The thermostatic expansion valve opens and closes based on the superheat of the outlet vapor. Its purpose is to generate superheated vapor (superheat ≥ 6°F) to ensure dry suction for the compressor. However, this does not actually occur. Unevaporated liquid tends to leak out of the evaporator, resulting in a decrease in superheat, which closes the thermostatic expansion valve and reduces the refrigerant flow rate. This reduces refrigeration capacity. Additionally, a suction trap, as shown in Figure 1, is required to trap the liquid and ensure dry suction for the compressor.

[0007] The DX system mentioned above also uses a distributor to distribute liquid to all evaporator circuits, but is sensitive to mal-distributions. Uneven distribution can result in excess liquid exiting some circuits, causing superheat to drop below target. This forces the thermostatic expansion valve to raise the superheat back up to target, but at the cost of reduced capacity.

[0008] Figure 2 illustrates a portion of a DX refrigeration system that replaces the portion of the DX refrigeration system illustrated in Figure 1 enclosed within the dashed line. Specifically, the portion of Figure 2 includes an ejector-type DX evaporator (U.S. Pat. No. 11,493,245 and U.S. Application Serial No. 18 / 350,739, both of which are incorporated herein by reference in their entireties). The ejector is a refrigerant vapor-powered fluid enthalpy pump that recirculates refrigerant liquid (L1) from the bottom of the suction header back to the side port of the distributor, as shown. This results in the evaporator operating in an "overfeed" condition, increasing cooling capacity, while the fluid exiting the suction connection is superheated vapor with no liquid entrainment, as in a conventional DX system.

[0009] Referring to FIG. 2, high-pressure, cooled refrigerant is fed to an expansion device 3. The outlet 5 of the expansion device 3 is connected to the inlet 9 of an inlet separator 11 via a refrigerant line 7. The inlet separator 11 delivers the vapor flash gas received from the expansion device to the inlet 31 of an ejector 33. Meanwhile, liquid refrigerant is delivered from the outlet 15 of the inlet separator to the inlet 17 of a distributor 19 via a refrigerant line 16. The distributor's multiple outlets 21 are connected to an evaporator coil 25 via a refrigerant line 26, delivering refrigerant liquid to the evaporator inlet 23 of the evaporator coil 25. While an evaporator coil is used in this example, any type of evaporator can be used in the present invention. Both superheated vapor and unevaporated liquid are produced at the outlet 27 of the evaporator coil 25. The superheated vapor is delivered to a suction trap and / or compressor via a refrigerant line 29, and the unevaporated liquid is delivered to the liquid inlet 35 of the ejector 33 via a refrigerant line 30. Sensors 100 measure the temperature and pressure of the superheated steam and communicate this to a controller 102 to determine if superheat has been achieved. Based on the superheat determination, the controller 102 opens or closes an expansion device.

[0010] Meanwhile, the ejector 33 uses the flash gas received from the outlet 13 of the inlet separator 11 to pump / entrain unevaporated liquid through the refrigerant line 18. The entrained refrigerant liquid and excess flash gas are supplied from the outlet 37 of the ejector 33 to the distributor 19 through the refrigerant line 46.

[0011] FIG. 3 is a schematic diagram of an ejector-type DX evaporator similar to that of FIG. 2, but with an oil separator / collector 301 according to the present invention installed at the outlet of the ejector 33. This invention is necessary for returning oil to the compressor in ejector-type DX evaporators without hot gas (HG) defrosting. The ejector DX circuit is bottom-feed, allowing oil to be returned during hot gas defrosting. In this case, hot gas is pumped from the suction connection to the suction header and directed to the coiled tubing. Condensate formed during defrosting is discharged through the circuit to the distributor and ultimately exits through the side port of the distributor. Refrigerant oil in the coiled tubing is also forced out of the side port of the distributor along with the condensate and hot gas.

[0012] However, in ejector-type DXs without HG defrost, the recirculation of liquid refrigerant from the suction header can cause oil to accumulate in the coil tubing, and there is no active means to return the oil. This invention is specifically intended for such applications, and separates, captures, and intermittently returns refrigeration oil to the suction connection, as shown in Figure 3.

[0013] FIG. 4 illustrates an oil separator / collector 301 according to an embodiment of the present invention. The oil separator / collector 301 has two chambers: an upper chamber (UC) 303 and a lower chamber (LC) 305, where a hollow float 6 return resides. The oil separator also has an inlet port 311, an outlet port 313, and an oil return line 315 at the bottom. The inlet port 311 of the UC 303 receives vapor, liquid refrigerant, and oil from the primary ejector 33, as shown in FIG. 3. The UC 303 is equipped with a long dip tube 317 leading to the LC 305. The liquid / oil, being denser than the vapor, flows quickly through the dip tube 317 into the LC 305. This is a separation or stratification technique that moves the denser oil / oil-rich refrigerant to the bottom of the LC 305 and the lighter refrigerant to the top of the LC. Meanwhile, the vapor enters the secondary ejector 319, as shown. The secondary ejector 319 bridges (connects) the LC 305 and the oil separator outlet port 313. The secondary ejector 319 (described below) is steam-driven, and its intake pipe 321 is connected to the top of the LC 305 as shown. As the steam-driven fluid passes through the secondary ejector 319, liquid is drawn from the top of the LC 305, and the gas-liquid mixture is discharged through the outlet port 313 to the side port of the distributor, as shown in Figure 3. Due to the low fluid movement within the LC 305, the denser oil / oil-rich liquid remains at the bottom of the LC 305, and the liquid level gradually rises. When the oil-rich refrigerant level rises within the LC 305 and exceeds approximately 75% of the height of the float 307, the float rises due to buoyancy and opens. As the float rises, a small amount of oil is expelled from the bottom orifice 309 and flows to the suction connection.

[0014] The present invention is particularly suitable for use with a liquid refrigerant having a lower density than refrigeration oil, such as ammonia refrigerant and FES#1 compressor oil with a specific gravity of 0.87.

[0015] A schematic diagram of the secondary ejector is shown in Figure 5. The function of the secondary ejector 319 is to remove oil-free liquid refrigerant (if present) from the top of the LC 305. This is done using motive vapor and operates at a very low pressure drop, preferably 0.5 psi or less. The secondary ejector 319 is equipped with an annular passage 323 to increase the vapor velocity, and liquid refrigerant is drawn in through a central inlet pipe 321 connected to the top of the LC 305. The typical mass flow entrainment ratio for this unit is 2 to 3. This ratio exceeds the entrainment ratio of the primary ejector 33 to prevent liquid refrigerant from flooding the UC 303.

[0016] The effectiveness of this oil separator 301 is that the liquid refrigerant / oil mixture tends to be drawn into the LC 305 through the long dip tube 317, while the vapor moves quickly out the ejector port to the outlet. The lighter liquid refrigerant then rises to the top of the LC 305 by gravity, while the oil / oil-rich refrigerant tends to migrate to the bottom. The addition of a secondary ejector 319 allows the lighter liquid to be skimmed off the top of the LC 305, while allowing sufficient settling time for the oil to separate and collect at the bottom.

[0017] When a sufficient amount of oil accumulates, buoyancy causes the float valve to rise, allowing the oil to drain through an orifice to the suction connection.

[0018] Several prototypes have been built, including full-size prototypes capable of handling steam flows of over 1 lb / min and liquid flows of over 2 lb / min, which are the maximum flow rates expected from a large capacity (e.g., 50TR) evaporator coil.

[0019] As will be appreciated by those skilled in the art, various modifications can be made to the above-described preferred embodiments without departing from the spirit of the present invention. Accordingly, it is not intended that the present invention be limited to the particular embodiments disclosed, but rather that modifications be encompassed within the spirit and scope of the invention as disclosed herein and within the scope of the claims to be interpreted in their broadest reasonable terms based on the present specification. [Explanation of symbols]

[0020] 3 Expansion device 5 Expansion device outlet 7 Refrigerant Line 9 Inlet to inlet separator 11 Inlet side separator 13 Inlet side separator steam outlet 15 Inlet side separator liquid outlet 16 Refrigerant line 17 Distributor inlet 18 Refrigerant line 19 Distributor 21 Distributor outlet 23 Evaporator inlet 25 Evaporator 26 Refrigerant line 27 Evaporator outlet 29 Refrigerant line 30 Refrigerant Line 31 Ejector steam inlet 33 Ejector 35 Ejector liquid inlet 37 Ejector liquid outlet 39 Refrigerant Line 41 Outlet side separator inlet 46 Refrigerant line 57 Refrigerant line 100 Superheat Sensor 102 Controller 103 Refrigerant line

Claims

1. 1. An apparatus for improving the performance of a direct expansion refrigeration system, comprising: an inlet separator adapted to be connected to an outlet of an expansion device of the direct expansion refrigeration system; an evaporator connected to the liquid outlet of the inlet-side separator; an ejector connected to the vapor outlet of the inlet-side separator; a first refrigerant line connecting a first outlet of the evaporator and a liquid inlet of the ejector; a second refrigerant line connecting a second outlet of the evaporator and a compressor; an oil separator connected to an outlet of the ejector; a third refrigerant line connecting the first outlet of the oil separator and the compressor; a fourth refrigerant line connecting the second outlet of the oil separator and the evaporator; the inlet-side separator is configured to simultaneously and continuously supply refrigerant vapor to the ejector and refrigerant liquid to the evaporator; the ejector is configured to supply oil, refrigerant vapor, and refrigerant liquid to the oil separator; The apparatus, wherein the oil separator is configured to supply oil to the compressor and supply refrigerant vapor and refrigerant liquid to the evaporator.

2. the oil separator comprising a vertically disposed tube having an upper chamber and a lower chamber; the upper chamber having an upper chamber inlet port and an upper chamber outlet port; The lower chamber has a float located above an oil return outlet; the upper chamber is connected to the lower chamber by a dip tube; the dip tube is configured to pass oil, liquid refrigerant, and liquid refrigerant into the lower chamber; The apparatus of claim 1 further comprising an inlet pipe for the secondary ejector for passing liquid refrigerant from the lower chamber to the secondary ejector.

3. 3. The direct expansion refrigeration system of claim 1, wherein the inlet separator and the ejector are combined to form an integrated refrigerant recycling device.

4. 4. The direct expansion refrigeration system of claim 1, further comprising a heat exchanger connected to the expansion device by the refrigerant line for cooling the refrigerant in the refrigerant line.

5. 5. A direct expansion refrigeration system according to claim 1, wherein the heat exchanger is a condenser or a gas cooler.

6. a refrigerant line connecting the expansion device, the inlet separator, the evaporator, and the compressor in this order; an ejector connected to an outlet of the inlet-side separator and an outlet of the evaporator; an ejector outlet connected to an oil separator; Equipped with the oil separator having a first outlet configured to return oil to the compressor and a second outlet for supplying liquid refrigerant and vapor refrigerant to the evaporator; The inlet separator is configured to simultaneously and continuously supply refrigerant vapor to the ejector and refrigerant liquid to the evaporator.

7. the oil separator comprises a vertically disposed tube having an upper chamber and a lower chamber; the upper chamber having an upper chamber inlet port and an upper chamber outlet port; The lower chamber has a float located above an oil return outlet; the upper chamber is connected to the lower chamber by a dip tube; the dip tube is configured to pass oil, liquid refrigerant, and liquid refrigerant into the lower chamber; 7. The direct expansion refrigeration system of claim 6, further comprising an inlet pipe for the secondary ejector for passing liquid refrigerant from the lower chamber to the secondary ejector.

8. 8. The direct expansion refrigeration system of claim 6, wherein the inlet separator and the ejector are combined to form an integrated refrigerant recycling device.

9. 9. The direct expansion refrigeration system of claim 6, further comprising a heat exchanger connected to the expansion device by the refrigerant line for cooling the refrigerant in the refrigerant line.

10. 10. A direct expansion refrigeration system according to any one of claims 6 to 9, wherein the heat exchanger is a condenser or a gas cooler.

11. 1. A method for increasing the refrigeration capacity of a direct expansion refrigeration system, the method comprising: removing liquid from an outlet of the evaporator and sending it to an ejector; removing refrigerant vapor from an inlet separator disposed upstream of the evaporator and sending the refrigerant vapor to the ejector; using the ejector to warm the refrigerant liquid received from the evaporator together with the vapor received from the inlet separator; supplying liquid refrigerant, vapor refrigerant, and oil from the ejector to an oil separator; supplying oil from the oil separator to a compressor; supplying liquid refrigerant and vapor refrigerant from the oil separator to the evaporator; A method that simultaneously encompasses both.

12. allowing the oil to settle below the level of the liquid refrigerant in a lower chamber of the oil separator; using a secondary ejector disposed in an upper chamber containing the vapor refrigerant; 12. The method of claim 11, further comprising: using the vapor refrigerant in the secondary ejector as a driving force to draw liquid refrigerant from the lower chamber into a supply line of the secondary ejector, thereby transferring the liquid refrigerant and the vapor refrigerant from the oil separator to the evaporator.

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