Compression refrigeration machine and compression refrigeration process

Abstract

The invention relates first to a compression refrigeration machine (1) in which a refrigerant (14) circulates in a closed circuit, comprising: an evaporator (2) in which the refrigerant (14), in the liquid state and at a low pressure, absorbs heat from a medium outside the circuit and evaporates; a compressor (5) which compresses refrigerant vapour (15) from the evaporator (2) to a high pressure; a condenser (6) in which the refrigerant vapour (15) from the compressor (5) releases heat to a cooling medium outside the circuit and condenses; a throttle valve (7) which expands the condensed refrigerant (14) from the condenser (6); and pipes (12) for the refrigerant (14) which connect, in succession, the evaporator (2), the compressor (5), the condenser (6) and the throttle valve (7) back to the evaporator (2) to form the circuit. The invention also relates to a compression refrigeration process using a circuit of this type. In order to improve the refrigeration process, according to the invention a partial flow of the refrigerant vapour (15) from the evaporator (2) is recirculated, at the low pressure, into the evaporator (2) before compression.

Description

[0001] Compression refrigeration machine and process

[0002] The invention relates firstly to a compression refrigeration machine in which a refrigerant circulates in a closed circuit with an evaporator in which the refrigerant in the liquid state absorbs heat from a medium outside the circuit at low pressure and evaporates, a compressor that compresses refrigerant vapor from the evaporator to a high pressure, a condenser in which the refrigerant vapor from the compressor releases heat to a cooling medium outside the circuit and condenses, a throttle valve that expands the condensed refrigerant from the condenser, and pipes for the refrigerant that successively connect the evaporator, the compressor, the condenser, and the throttle valve back to the evaporator to form the circuit. The invention further relates to a compression refrigeration process with such a circuit.

[0003] A compression refrigeration machine and a process of the aforementioned type are known, for example, from EP 2 754 978 A1 and are characterized by the continuous cycle of compression, condensation, expansion, evaporation, and recompression of the circulating refrigerant. The refrigeration capacity, particularly of the cooling medium, is controlled by varying the compressor output under given ambient conditions. In this compression refrigeration machine, a refrigerant line carries the liquid refrigerant from a separator located directly downstream of the evaporator back into the evaporator.

[0004] In order to avoid performance losses due to dryout of the evaporator, conventional compression refrigeration machines are "flooded", i.e. filled with more refrigerant - e.g. approx. 1 kg of ammonia per kW of cooling capacity - than would be necessary for complete evaporation. As an environmentally friendly refrigerant, ammonia is therefore only used in large compression refrigeration machines for industrial use, where the higher investment compared to other refrigerants is amortized by the higher efficiency. The background to the invention is known from specialist literature (including VDI Heat Atlas, Berlin 2013) about the flow conditions under which a ring flow occurs in a two-phase flow. Furthermore, the background to the invention is a two-phase distributor with which two phases of a two-phase flow can be distributed in a controlled manner across several outgoing lines.

[0005] Furthermore, AU 2016 101310 A4 discloses in the background of the invention a compression refrigeration machine in which liquid refrigerant is recirculated from the evaporator in the low-pressure region into the evaporator.

[0006] Task

[0007] The invention is based on the object of improving the cooling process.

[0008] Solution

[0009] Based on known compression refrigeration machines, the invention proposes a low-pressure bypass that recirculates a partial flow of refrigerant vapor from the evaporator upstream of the compressor into the evaporator at low pressure. This partial flow increases the vapor flow in the evaporator. By adjusting the partial flow, the expert can expand the available operating conditions with the particularly effective two-phase annular flow, for example, in an evaporator with boiling channels. If the evaporator is operated as a flooded heat exchanger, the expert can additionally recirculate a liquid partial flow into the evaporator.

[0010] A compression refrigeration machine according to the invention preferably has a collecting vessel downstream of the throttle valve, in which a vapor phase separates from a liquid phase of the condensed refrigerant, and a vapor line that receives the vapor phase and conducts it into the evaporator separately from the piping. The vapor phase and the liquid phase can thus be introduced into the evaporator in a controlled manner and used for other purposes. The flow conditions required for the intended application are achieved by a person skilled in the art by selecting, on the one hand, the pressure ratios of high and low pressure or by controlling the mass flow of the recirculated gas phase, and, on the other hand, the compressor capacity.

[0011] Preferably, in a compression refrigeration machine according to the invention, the condensed refrigerant is expanded in the throttle valve to an intermediate pressure between the high pressure and the low pressure and the vapor phase promotes the partial flow into the evaporator as a propulsion jet.

[0012] Preferably, in a compression refrigeration machine according to the invention, liquid refrigerant is recirculated from the evaporator to the liquid phase. The energy not used in the throttle valve is thus utilized for recirculation. Alternatively, recirculation can also be driven by mechanical pumps for the liquid phase and compressors for the vapor.

[0013] The consistent separation of the vapor and liquid phases of the refrigerant in the collection vessel and during recirculation avoids cavitation during mixing processes and subsequent erosion of the components of the compression refrigeration machine according to the invention.

[0014] In a compression refrigeration machine according to the invention, the evaporator preferably has a plurality of boiling channels that are evenly supplied with refrigerant from a two-phase distributor. Such two-phase distributors are generally known. Alternatively, a tube bundle or plate heat exchanger can be used in a compression refrigeration machine according to the invention.

[0015] Preferably, the refrigerant in a compression refrigeration machine according to the invention is ammonia. Ammonia is a natural substance and a proven refrigerant. Alternatively, a compression refrigeration machine according to the invention can be operated with another refrigerant such as methane, propane, or water.

[0016] A compression refrigeration machine according to the invention preferably has a valve in the low-pressure bypass and / or in a refrigerant line that directs the liquid refrigerant from a separator arranged directly downstream of the separator back into the evaporator. Such valves allow the flow of refrigerant through the refrigerant line and the flow of refrigerant vapor through the low-pressure bypass to be controlled independently of one another. Alternatively, one skilled in the art can also use known overflow valves to control the recirculated mass flows.

[0017] A compression refrigeration machine according to the invention preferably has a high-pressure bypass that branches off a partial flow of the refrigerant vapor at high pressure from the compressor upstream of the condenser and feeds it back into the evaporator. Further preferably, the partial flow is expanded to the intermediate pressure by means of a controllable throttle valve, thus adjusting the intermediate pressure. Since the pumping capacities of the vapor and liquid jet pumps do not change proportionally with the intermediate pressure due to the different behavior of gases and liquids, the ratio of the recirculation rates and the mass flows can be regulated.

[0018] A compression refrigeration machine according to the invention preferably has a heating element that heats the liquid, expanded refrigerant from the condenser. Such a heating element can be powered electrically or with heat from the hot refrigerant vapor or another heat source. As the temperature increases, the pressure of the expanded refrigerant increases, and thus, in turn, the pumping capacity of the vapor and liquid jet pumps.

[0019] Based on known compression refrigeration processes, the invention proposes that, after expansion, a vapor phase is separated from a liquid phase of the condensed refrigerant, and the vapor phase is passed separately into the evaporator. The compression refrigeration process according to the invention takes place in a compression refrigeration machine according to the invention and is similarly characterized by the advantages explained above.

[0020] In a compression refrigeration process according to the invention, the refrigerant preferably flows through the evaporator in a two-phase annular flow. The separately introduced vapor phase does not mix with the liquid phase in the evaporator and promotes two-phase annular flow. The refrigerant requirement of the compression refrigeration machine according to the invention, for example, with ammonia as the refrigerant, is less than 0.1 kg / kW of cooling capacity. A corresponding reduction in the refrigerant quantity is also achieved with other refrigerants. The compression refrigeration machine according to the invention is therefore also suitable for smaller applications.

[0021] Examples of implementation

[0022] The invention is explained below using exemplary embodiments.

[0023] Fig. 1 shows a first compression refrigeration machine according to the invention, Fig. 2 shows a second compression refrigeration machine according to the invention, Fig. 3 shows a third compression refrigeration machine according to the invention, Fig. 4 shows a fourth compression refrigeration machine according to the invention, Fig. 5 shows a fifth compression refrigeration machine according to the invention and Fig. 6 shows a sixth compression refrigeration machine according to the invention.

[0024] The first compression refrigeration machine 1 according to the invention shown in Figure 1 has an evaporator 2 with a plurality of boiling channels 3 and a separator 4, a compressor 5, a condenser 6, a throttle valve 7, a collecting vessel 8, a steam jet pump 9, a liquid jet pump 10 and a two-phase distributor 11 as well as pipes 12 connecting these to form a closed circuit and a low-pressure bypass 13 between the evaporator 2 and the steam jet pump 9.

[0025] Ammonia circulates in the circuit as refrigerant 14. The refrigerant 14 flows through the boiling channels 3 under low pressure in a two-phase annular flow: The liquid refrigerant 14 is pressed by the vapor phase against the inside walls of the boiling channels 3, absorbs heat from a medium (here: air) flowing around them on the outside and to be cooled, and expels further refrigerant vapor 15.

[0026] After exiting the boiling channels 3, remaining liquid refrigerant 14 collects at the lower end of the separator 4, the refrigerant vapor 15 is sucked upwards by the compressor 5 and compressed to high pressure and releases the heat absorbed in the evaporator 2 and the energy supplied by the compressor 5 as additional heat to a cooling medium (here: ambient air) in the condenser 6.

[0027] In the throttle valve 7, the liquefied refrigerant 14 is expanded to an intermediate pressure. From the adjoining collecting vessel 8, liquid refrigerant 14 flows from the bottom and refrigerant vapor 15 from the top. The refrigerant vapor 15 is expanded to low pressure in the steam jet pump 9, and the liquid refrigerant 14 is expanded to low pressure in the liquid jet pump 10, thereby drawing in additional liquid refrigerant 14 from the bottom and a partial flow of the refrigerant vapor 15 from the top of the separator 4.

[0028] The liquid and vapor streams exiting the jet pumps are evenly distributed to the boiling channels 3 via the two-phase distributor 11. The compression refrigeration machine 1 operates at a stable operating point with balanced mass flow balances of the liquid refrigerant 14 and the refrigerant vapor 15 and constant liquid levels in the separator 4 and the collecting vessel 8. The mass flow through the throttle valve 7 into the collecting vessel 8 determines the pumping capacity of the steam jet pump 9 and the liquid jet pump 10.

[0029] In the other compression refrigeration machines according to the invention, identical components are designated by the same reference numerals.

[0030] The second compression refrigeration machine 16 according to the invention shown in Figure 2 essentially corresponds to the first compression refrigeration machine 1. Unlike the first compression refrigeration machine 16, the second compression refrigeration machine 16 has a valve 18 in the low-pressure bypass 13 and in the refrigerant line 17 from the separator 4 into the liquid jet pump 10. The valves 18 independently control the flow of the refrigerant 16 through the refrigerant line 17 and the flow of the refrigerant vapor 15 through the low-pressure bypass 13.

[0031] The third compression refrigeration machine 19 according to the invention, shown in Figure 3, again essentially corresponds to the first compression refrigeration machine 1. Unlike the third compression refrigeration machine 19, it has a high-pressure bypass 20 for a partial flow of the refrigerant vapor 15 under high pressure between the compressor 5 and the collection vessel 8. The partial flow through the high-pressure bypass 20 is controlled by a second throttle valve 21 and expanded to the intermediate pressure. The intermediate pressure and the temperature in the collection vessel 8 are simultaneously controlled via the partial flow.

[0032] The fourth compression refrigeration machine 22 according to the invention shown in Figure 4 combines the features of the second compression refrigeration machine 16 and the third compression refrigeration machine 19.

[0033] The fifth compression refrigeration machine 23 according to the invention shown in Figure 5 essentially corresponds to the second compression refrigeration machine 16. Unlike the fifth compression refrigeration machine 23, it has a heating element 24 in the collecting vessel 8. By means of the heating element 24, the temperature, and thus the pressure in the collecting vessel 8, and the pumping capacity of the steam jet pump 9 and the liquid jet pump 10 can be increased.

[0034] The sixth inventive device shown in Figure 6

[0035] Compression refrigeration machine 25 combines the features of the fifth

[0036] Compression refrigeration machine 23 and the third compression refrigeration machine 19.

[0037] In the figures are

[0038] 1 compression refrigeration machine

[0039] 2 evaporators

[0040] 3 Boiling channel

[0041] 4 separators

[0042] 5 compressors

[0043] 6 condensers

[0044] 7 throttle valve

[0045] 8 collection vessel

[0046] 9 Steam jet pump

[0047] 10 Liquid jet pump

[0048] 11 two-phase distributors

[0049] 12 Pipeline

[0050] 13 Low pressure bypass

[0051] 14 liquid refrigerant

[0052] 15 Refrigerant vapor

[0053] 16 compression refrigeration machine

[0054] 17 Refrigerant line

[0055] 18 Valve

[0056] 19 compression refrigeration machine

[0057] 20 High pressure bypass

[0058] 21 throttle valve

[0059] 22 compression refrigeration machine

[0060] 23 compression refrigeration machine

[0061] 24 heating element

[0062] 25 compression refrigeration machine

Claims

Patent claims 1. Compression refrigeration machine (1, 16, 19, 22, 23, 25) in which a refrigerant (14) circulates in a closed circuit with an evaporator (2) in which the refrigerant (14) in the liquid aggregate state absorbs heat from a medium outside the circuit under a low pressure and evaporates, a compressor (5) which compresses refrigerant vapor (15) from the evaporator (2) to a high pressure, a condenser (6) in which the refrigerant vapor (15) from the compressor (5) releases heat to a cooling medium outside the circuit and condenses, a throttle valve (7) which expands the condensed refrigerant (14) from the condenser (6), and pipes (12) for the refrigerant (14) which successively connect the evaporator (2), the compressor (5), the condenser (6) and the throttle valve (7) back to the evaporator (2) to the circuit, characterized by a low pressure bypass (13),which recirculates a partial flow of the refrigerant vapor (15) from the evaporator (2) upstream of the compressor (5) under low pressure into the evaporator (2).

2. Compression refrigeration machine (1, 16, 19, 22, 23, 25) according to the preceding claim, characterized by a collecting vessel (8) behind the throttle valve (7), in which a vapor phase separates from a liquid phase of the condensed refrigerant (14), and a vapor line which receives the vapor phase and guides it into the evaporator (2) separately from the pipes (12).

3. Compression refrigeration machine (1, 16, 19, 22, 23, 25) according to the preceding claim, characterized in that in the throttle valve (7) the condensed refrigerant (14) is expanded to an intermediate pressure between the high pressure and the low pressure and the vapor phase promotes the partial flow into the evaporator (2) as a propulsion jet.

4. Compression refrigeration machine (1, 16, 19, 22, 23, 25) according to one of the preceding claims, characterized in that liquid refrigerant (14) is recirculated from the evaporator (2) into the evaporator (2) with the liquid phase.

5. Compression refrigeration machine (1, 16, 19, 22, 23, 25) according to one of the preceding claims, characterized in that the evaporator (2) has a plurality of boiling channels (3) which are uniformly fed with the refrigerant (14) from a two-phase distributor (11).

6. Compression refrigeration machine (1, 16, 19, 22, 23, 25) according to one of the preceding claims, characterized in that the refrigerant (14) is ammonia.

7. Compression refrigeration machine (16, 22, 23, 25) according to one of the preceding claims, characterized by a valve (18) in the low-pressure bypass (13) and / or in a refrigerant line (17) which leads the liquid refrigerant (14) from a separator (4) arranged immediately behind the evaporator (2) back into the evaporator (2).

8. Compression refrigeration machine (19, 22, 25) according to one of the preceding claims, characterized by a high-pressure bypass (20) which branches off a partial flow of the refrigerant vapor (15) under the high pressure from the compressor (5) upstream of the condenser (6) and leads it back into the evaporator (2).

9. Compression refrigeration machine (23, 25) according to one of the preceding claims, characterized by a heating element (24) which heats the liquid, expanded refrigerant (14) from the condenser (6).

10. Compression refrigeration process in which a refrigerant (14) circulates in a closed circuit, wherein the refrigerant (14) in the liquid state absorbs heat from a medium outside the circuit under low pressure in an evaporator (2) and evaporates, refrigerant vapor (15) is compressed to a high pressure, the refrigerant vapor (15) releases heat to a cooling medium outside the circuit and condenses, and the condensed refrigerant (14) is expanded, characterized in that a partial flow of the refrigerant vapor (15) from the evaporator (2) is recirculated into the evaporator (2) before compression under the low pressure.

11. Compression refrigeration process according to the preceding claim, characterized in that the refrigerant (14) flows through the evaporator (2) in a two-phase annular flow.

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