MULTICHANNEL EVAPORATOR

Technical field:

[1] The invention relates to a refrigerant circuit with a compressor (A), a condenser (D), a evaporator (C) and a suction-gas heat exchanger wherein the refrigerant is capillary-tube throttled in two steps, firstly from the condenser to the suction-gas heat exchanger (F) and then from the suction-gas heat exchanger to the evaporator (E).

[2] The purpose of such a circuit is to distribute the refrigerant so that the evaporator is flooded, and that the suction gas at the compressor inlet is overheated. Background art:

[3] Such a circuit is known from DK174179 wherein the suction-gas heat exchanger condenses the vapour which reaches the fluid container so that only pure liquid is conducted further. Simultaneously the heat exchanger regulates the pressure in the container - and thereby regulates the magnitude of the flow of refrigerant to the evaporator. The magnitude of this flow of refrigerant controls the extent of flooding (or overheating) of the suction gas which controls how strong the suction-gas heat exchanger cools the condensate between the two throttling steps. The process is self-adjusting, and when equilibrium is reached, the evaporator is flooded. Brief description of figures

[4] Fig. 1: Compressor (A), 4- way valve (B) wherein the direction of the flow of refrigerant can be changed. Evaporator/condenser (C,D) is symmetrical and connected through two nozzles, e.g. two identical capillary tubes (E,F) which meets in the suction-gas heat exchanger (H), and heat exchanger with the suction line (G).

[5] Fig. 2 shows a regulator for multichannel evaporator/condenser. In the figure there is shown 3 capillary tubes (E) for connection to the evaporator and 2 capillary tubes (F) for connection to the condenser. The suction line (G) is guides through the external jacket (H) which exhibits channels for the capillary tubes.

[6] Fig. 3 shows the temperatures in the suction-gas heat exchanger. Te is the temperature of the suction gas at the inlet of the heat exchanger, and Tx is the "almost" constant temperature at the liquid side. Tc shows how the temperature of the condenser lies with respect to the heat exchanger.

[7] Fig. 4 and 5 show calculations of the circuit in an enthalpy-log(pressure)-diagram.

The refrigerant is R290, the evaporation temperature is -25 ⁰ C and the condensing temperature is 45 ⁰ C. The circuit in fig. 4 has a larger load of refrigerant than the circuit in fig. 5, which pulls the evaporator (EF) further to the left. The line segment CD is enthalpy transferred by the heat exchanger, and the line segment (FG) is the corresponding shift of the evaporator towards lower enthalpy. In fig. 4 the evaporator contains almost 3 times so much refrigerant as the evaporator in fig. 5.

Disclosure of the invention:

[8] The invention differs from DK 174179 in that the liquid container is lacking. Instead the amount of circulated refrigerant is adjusted to the load conditions by binding excess refrigerant in the evaporator. This happens by the excess of refrigerant, through the suction-gas heat exchanger, lowers the enthalpy at the inlet of the evaporator whereby the ratio between vapour and liquid is shifted - so that the density of the refrigerant is increased.

[9] The construction is symmetric and the flow of refrigerant can be changed so that the evaporator and condenser exchange their functions. This provides the opportunity for defrosting of the evaporator - or that the evaporator can be applied for both cooling and heating. The method is independent of the gravitational field and it can function in aeroplanes wherein the system is turned up side down, and in space crafts completely without gravitational field.

[10] The method is self-adjusting and without movable parts, and therefore it can be placed in inaccessible places or it can be embedded completely in insulation foam.

[11] The invention can be applied with all sizes of systems and with most refrigerants - albeit not zeotropic mixtures with large temperature slip, because in this case, the regulation of the enthalpy of the evaporator would imply large fluctuations of the temperature of the evaporator. The new technical means (claim 1):

[12] The throttling means consists of two throttling steps separated by a suction-gas heat exchanger wherein the flow velocity through the suction-gas heat exchanger is so high that liquid and gas are not separated.

[13] The two throttling steps can be established by two nozzles, e.g. two capillary tubes, and the suction-gas heat exchanger by two concentric tubes which fulfil the following two requirements:

[14] The heat transfer property must be sufficient for removing all fluid refrigerants from the suction gas, under all operational conditions.

[15] The flow velocity, at the condenser side, must be so high that liquid and gas are not separated. This is fulfilled at turbulent flow defined by Reynolds 's number being larger than 3000. The technical effect (Claim 1):

[16] The condensate passes the suction-gas heat exchanger as a mixture of liquid and vapour wherein there is thermodynamic equilibrium between pressure and temperature. When the suction gas removes enthalpy from the condensate, some of the vapour condensates - but no significant change of the pressure appears and therefore no change in the temperature either. The suction gas passes the condensate in counter current and is heated to a temperature close to the temperature of the condensate.

[17] This process is self-adjusting

[18] Proof:

[19] When the refrigeration circuit has an excess of refrigerant, this results in a drop in enthalpy at the outlet of the evaporator. The change of enthalpy cannot pass the heat exchanger since the suction-gas temperature after the exchanger is "almost" constant - and the drop in enthalpy will therefore be transferred to the condenser side, where the enthalpy at the inlet of the evaporator drops correspondingly.

[20] A drop in enthalpy at the evaporator inlet implies a larger density in the evaporator - and thereby a binding of the refrigerant - which reduces the cause - which was excess of circulating refrigerant.

[21] Similarly, when the circuit lacks refrigerant:

[22] This causes an increase of the enthalpy at the outlet of the evaporator. The change of enthalpy cannot pass by the heat exchanger because the suction-gas temperature after the heat exchanger is "almost" constant - and the increase in enthalpy will therefore be transferred to the condenser side where the enthalpy at the inlet of the evaporator increases correspondingly.

[23] An increase in enthalpy at the inlet of the evaporator implies less density in the evaporator - and thereby the refrigerant is released - which reduces the cause - which was a deficit of circulating refrigerant.

[24] The construction is symmetrical and the flow of the refrigerant can be changed so that the evaporator and condenser exchange function.

The new technical means (Claim 2):

[25] The invention can easily be extended to regulate systems wherein the evaporator and/or the condenser are partitioned into several sections. [26] The nozzles to and from the suction-gas heat exchanger can be replaced by more parallel nozzles so that there is a separate nozzle for each section in the evaporator/condenser.

The technical effect (Claim 2): [27] The partition into many parallel nozzles does not provide any problems at the collection of refrigerant from many condenser sections, but the distribution of refrigerant to many evaporator sections could be a problem in that some nozzles are supplied much liquid while others are supplied are supplied much vapour. This problem is solved by requirement of a turbulent flow in the heat exchanger which ensures a homogeneous mixture of liquid and vapour, which can then be distributed to many nozzles without problems. Example:

[28] Compressor SC21CNX2 is for R290 and has a power of 750 Watt at the evaporation temperature -25 Celsius and condensation temperature 45 Celsius, corresponding to a flow of mass of 3 gram/second. Both capillary tubes have a diameter of 1 mm and a length 1000 mm, corresponding to a capacity of 27.4 litre of nitrogen per minute.

[29] Fig. 3 shows that the heat exchanger at maximum must transfer 50 % of the refrigeration power, here 400W, at a temperature difference of 30 Kelvin, which requires an area of 90 cm2. The diameter of the suction line is 10 mm, so 90 cm2 corresponds to the surface of about 30 cm of the suction line.

[30] The heat exchanger consists of two concentric copper tubes with length 300 mm. The inner tube is the suction line having an outer diameter of 10 mm, and the outer tube is chosen with an inner diameter of 10.4 mm so that the distance between the tubes becomes 0.2 mm. The opening between the tubes becomes 6 mm2, and from this it can be calculated that Reynolds' number lies in the range 3200 and 6000, which ensures turbulent flow. Summary of advantages of the invention:

[31] It is as simple and robust regulator of refrigerant for systems with flooded evaporator, including multichannel evaporators with several parallel sections.

[32] The direction of flow of the refrigerant can be changed so that the evaporator and condenser changes function.

[33] It does not require adjustment or maintenance and it can be placed at inaccessible places.

[34] It functions independently of the gravitational field and it can be applied in aeroplanes and space crafts.