EJECTOR REFRIGERATION CIRCUIT

Abstract

An ejector refrigeration circuit 1 including: a two-phase circuit 2 including: a heat rejection heat exchanger 12 including an inlet 12a and an outlet 12b; and an ejector 14 including a high pressure inlet 14a, a low pressure inlet 14b and an outlet 14c; the ejector high pressure inlet 14a is coupled to the heat rejection heat exchanger outlet 12b; and an evaporator 18 including an inlet 18a and an outlet 18b; the outlet 18b of the evaporator 18 is coupled to the low pressure inlet 14b of the ejector 14; and the ejector refrigeration circuit 1 further including a vapour quality sensor 20 positioned at the outlet 12b of the heat rejection heat exchanger 12.

Claims

1. An ejector refrigeration circuit comprising: a two-phase circuit including: a heat rejection heat exchanger comprising an inlet and an outlet, and an ejector comprising a high pressure inlet, a low pressure inlet and an outlet, wherein the ejector high pressure inlet is coupled to the heat rejection heat exchanger outlet; and an evaporator comprising an inlet and an outlet, wherein the outlet of the evaporator is coupled to the low pressure inlet of the ejector; and wherein the ejector refrigeration circuit further comprises a vapour quality sensor positioned at the outlet of the heat rejection heat exchanger.

2. The ejector refrigeration circuit of claim 1, wherein the vapour quality sensor is an optical sensor, such as a camera or a microscope.

3. The ejector refrigeration circuit of claim 1, wherein the vapour quality sensor is a dielectric sensor, such as a capacitance probe.

4. The ejector refrigeration circuit of claim 1, wherein the vapour quality sensor is a wire mesh sensor, or an electrical resistance sensor or an electrical impedance sensor.

5. The ejector refrigeration circuit of claim 1, further comprising a controller configured to receive signals from the vapour quality sensor, wherein the controller is configured to adjust the capacity of the ejector based on the received signals to ensure that a required pressure uplift through the low pressure inlet of the ejector is achieved.

6. The ejector refrigeration circuit of claim 5, wherein the required pressure uplift at the low pressure inlet of the ejector is between 1 and 2 bar.

7. The ejector refrigeration circuit of claim 1, wherein the ejector refrigeration circuit comprises a plurality of ejectors connected in parallel.

8. The ejector refrigeration circuit of claim 1, wherein the, or each, ejector is a variable geometry ejector with one or more controllable parameters.

9. The ejector refrigeration circuit of claim 8, wherein the one or more controllable parameters are modified using one or more actuators controlled by the controller.

10. The ejector refrigeration circuit of claim 1, wherein each of the plurality of ejectors are non-variable ejectors each with a flow valve upstream of the high pressure inlet.

11. The ejector refrigeration circuit of claim 10, wherein the controller is configured to control the flow through the one or more of the flow valves.

12. A method of operating an ejector refrigeration circuit, the ejector refrigeration circuit comprising: a controller; a two phase circuit comprising a heat rejection heat exchanger comprising an inlet and an outlet, and an ejector comprising a high pressure inlet, a low pressure inlet and an outlet, wherein the ejector high pressure inlet is coupled to the heat rejection heat exchanger outlet; an evaporator comprising an inlet and an outlet, wherein the outlet of the evaporator is coupled to the low pressure inlet of the ejector, and a vapour quality sensor positioned at the outlet of the heat rejection heat exchanger, wherein the method comprises monitoring the vapour quality in the two phase circuit; providing a signal to the controller indicative of vapour quality; and the controller adjusting a capacity of the ejector in response to the signals indicative of the vapour quality in the two phase circuit.

13. The method of claim 12, wherein the ejector is a variable geometry ejector with one or more controllable parameters, wherein the controller adjusts the one or more controllable parameters using one or more actuators to adjust the capacity of the ejector.

14. The method of claim 12, wherein the ejector refrigeration circuit comprises a plurality of ejectors connected in parallel.

15. The method of claim 14, wherein each of the plurality of ejectors are non-variable ejectors each having a respective flow valve positioned upstream of the high pressure inlet of the ejector, wherein the controller controls the flow through the one or more flow valves to adjust the overall.

Description

DRAWING DESCRIPTION

[0058] Example embodiments of the invention are described below by way of example only and with reference to the accompanying drawing.

[0059] FIG. 1 shows a schematic view of an ejector refrigeration circuit.

DETAILED DESCRIPTION

[0060] The ejector refrigeration circuit 1 shown in FIG. 1 comprises a high pressure, two phase circuit 2 and a low pressure, low temperature circuit 3. The high pressure, two phase circuit 2 comprises a one or more compressors 10a, 10b, 10c forming a compressor unit with an inlet 10d and an outlet 10e.

[0061] The outlet 10e of the compressors 10a, 10b, 10c of the compressor unit is fluidly connected to an inlet 12a of a heat refection heat exchanger 12. The heat rejection heat exchanger may also be referred to as a condenser 12. The outlet 12b of the condenser 12 is fluidly connected to a high pressure inlet 14a of an ejector 14.

[0062] The ejector further comprises a low pressure inlet 14b and an outlet 14c. The outlet 14c of the ejector is fluidly connected to an inlet 16a of a flash tank 16. The flash tank 16 comprises a liquid portion and a vapour portion, wherein the liquid portion and the vapour portion are separated by gravity due to the different densities of the fluids.

[0063] The flash tank 16 further comprises a vapour outlet 16b near the top of the flash tank and a liquid outlet 16c near the bottom of the flash tank 16.

[0064] The vapour outlet 16b of the flash tank 16 is fluidly connected to the inlet 10d of the compressor unit 10a, 10b, 10c. The liquid outlet 16c of the flash tank is fluidly connected to the inlet 18a of an evaporator 18 via an expansion valve 17. The outlet 18b of the evaporator 18 is fluidly connected to the low pressure inlet 14b of the ejector 14.

[0065] In operation a refrigerant, such as carbon dioxide, is circulated through the ejector refrigeration circuit. A low pressure vapour line 24 delivers the refrigerant to the compressor 18 in gaseous form. The compressor 18 increases the pressure of the refrigerant and delivers it to the condenser 12.

[0066] The condenser 12 is configured to transfer heat from the refrigerant to the environments, reducing the temperature of the refrigerant in the process. This reduction in temperature condenses the refrigerant from a vapour to a liquid. In conventional ejector refrigeration circuits, the refrigerant leaving the outlet 12b of the condenser 12 is single phase, liquid, refrigerant. However, in the embodiment shown in FIG. 1, the refrigerant leaving the outlet 12b of the condenser 12 is two phase, liquid and vapour refrigerant. The majority of the refrigerant is liquid, with a small amount of vapour remaining.

[0067] In the ejector refrigeration circuit 1 of FIG. 1, the condenser comprises two fans which are configured to blow air through the condenser to enhance heat transfer from the refrigerant to the environment. It will be appreciated that more or less than two fans can be present.

[0068] High pressure two phase line delivers the two phase fluid to the high pressure inlet 14a of the ejector 14 which is configured to expand the refrigerant to a lower pressure level.

[0069] In the ejector 14, the refrigerant enters through the high pressure inlet 14a and passes into a convergent section. It then passes through a throat section and then a divergent section at the outlet 14c of the ejector 14. The movements from the inlet section, through the throat and then to the divergent section increases the flow velocity and reduces the pressure of the refrigerant. The pressure drop in the refrigerant between the inlet 14a and the outlet 14c of the ejector 14 draws a secondary flow through the low pressure inlet 14b.

[0070] The low pressure, two phase, refrigerant leaves the ejector 14 via the outlet 14c and enters the flash tank 16 through the flash tank inlet 16a. Within the flash tank 16, the refrigerant is separated due to gravity into a liquid portion in the lower part of the flash tank 16 and a vapour portion in the upper part of the flash tank 16.

[0071] The refrigerant in the vapour portion of the flash tank 16 leaves via the vapour outlet 16b and is returned to the compressor unit 10a, 10b, 10c. Meanwhile, the refrigerant in the liquid portion leaves the flash tank 16 via the liquid outlet 16c and is delivered to the expansion valve 17 and then enters the evaporator 18. Depending on the level of expansion achieved by the ejector 14, the expansion valve 17 may not be necessary. In which case a by-pass line (not shown) can be employed.

[0072] In the evaporator 18, heat is transferred from the environment to the liquid refrigerant. This heat causes the refrigerant to vaporise, removing heat from the environment. The resulting refrigerant vapour leaves the evaporator 18 via the outlet 18b and is delivered to the low pressure inlet 14b of the ejector.

[0073] In operation, the pressure drop between the high pressure inlet 14a and outlet 14c of the ejector causes the refrigerant to be sucked from the flash tank 16 through the expansion valve 17 and evaporator 18 to the low pressure inlet 14b. This pressure drop must therefore be maintained at a required amount and so the efficiency of the ejector 14 must also be maintained at an optimum level.

[0074] In conventional systems, the refrigerant in the high pressure circuit 2 between the condenser 12 and the ejector 14 is single phase, liquid, refrigerant. However, having a small amount of vapour in the refrigerant leaving the condenser has been shown to improve the efficiency of the ejector 14.

[0075] However, this must be balanced with the compressor capacity as the more vapour that is present in the circuit, the more work there is to do for the compressors. This may result in more compressors being needed, which would increase the complexity of the refrigeration circuit and reduce the overall operating efficiency.

[0076] There is therefore an optimum amount of vapour, which results in a sufficient increase in the ejector efficiency, without having a significant impact on the compressor workload.

[0077] Conventional ejector refrigerant circuits comprise pressure and temperature sensors which are sufficient for single phase flow. However, given that the flow in the high pressure circuit 2 is two phase, pressure and temperature measurements alone do not provide adequate information to control the system accordingly.

[0078] The ejector refrigeration circuit 1 shown in FIG. 1 comprises a vapour quality sensor 20 at the outlet 12b of the condenser 12. The vapour quality sensor 20 may be an optical sensor such as a camera or a microscope. Alternative, the vapour quality sensor 20 may be a dielectric sensor such as a capacitance probe.

[0079] The ejector refrigeration circuit 1 further comprises a controller 22 configured to receive signals from the vapour quality sensor 20. The controller may also be configured to receive signals from the pressure and temperature sensors (not shown in the FIGURE).

[0080] Based on the signals received from the vapour quality sensor 20, the controller 22 is configured to adjust the capacity of the ejector 14 to maintain the optimum pressure drop to secure the required suction through the low pressure inlet 14b while keeping the amount of vapour to compressors to a minimum.

[0081] The ejector 14 may be a variable geometry ejector comprising one or more actuators for adjusting one or more parameters of the ejector. The actuators are configured to be controlled by the controller 22 based on the signals from the vapour quality sensor.

[0082] The ejector refrigeration circuit 1 may comprise a plurality of ejectors 14 depending on the required level of expansion. The plurality of ejectors 14 can be connected in parallel.

[0083] Each of the plurality of ejectors may be variable geometry ejectors each with one or more actuators for adjusting one or more parameters. The controller 22 may configure each ejector to have the same capacity. Alternatively, the controller 22 may configure each ejector 14 to have a different capacity. A flow valve may be located upstream of the high pressure inlet 14a of each ejector 14. The controller 22 may be configured to restrict the flow through one or more of the valves depending on the required capacity of the ejectors.

[0084] In an alternative arrangement, each of the plurality of ejectors 14 may be non-variable ejectors, each with a flow valve upstream of the high pressure inlet 14a.

[0085] The controller 22 can be configured to restrict flow through the one or more flow valves for each respective ejector 14 of the plurality of ejectors 14. This method can serve as an alternative way adjust the capacity of the ejectors based on the signals received from the vapour quality sensor, instead of using a variable geometry ejector.

[0086] The ejector refrigeration circuit 1 thus ensures optimum pressure drop to ensure sufficient suction through the expansion valve and evaporator, without the need for a pump as in conventional systems. This results in a simplified, more compact, circuit with lower maintenance costs.