Thermal control system and method
View Patent ↗A system for improving the thermal efficiency of a thermal control loop in which refrigerant after compression and condensation is applied to an evaporator employs a subsidiary counter-current heat exchange intercepting refrigerant flow to maintain the quality of the refrigerant by exchanging thermal energy between the input flow and the output flow from the evaporator. The same principle is effective, with particular advantage when small connections have to be made, in systems using mixed phase media and using the concept of direct energy transfer with saturated fluid.
1. A temperature control system employing a two-phase refrigerant and a compressor/condenser loop having an input and output for circulating refrigerant at a controllable temperature to and from a load evaporator having input and output terminals and a thermal capacity, the temperature control system including a subsidiary flow circuit for enhancing the performance of the system, comprising:
a subsidiary heat exchanger coupled between the flow from the output of the compressor/condenser loop to the load evaporator input, the subsidiary heat exchanger having a smaller thermal capacity than the thermal capacity of the load evaporator, said subsidiary heat exchanger comprising:
a first flow path including an input receiving flow from the compressor/condenser loop and an output therefrom coupled to the evaporator input,
a second flow path in parallel thermal exchange relation along the length of the first flow path, the second flow path including an input to the subsidiary heat exchanger from the evaporator output on the same side as the input flow received from the compressor/condenser loop, and
an output from the subsidiary heat exchanger coupled to the compressor input,
a thermo-expansion valve disposed in the first flow path between the output of the compressor/condenser loop and the input to the first flow path of the subsidiary heat exchanger;
a sensing element for the thermo-expansion valve responsive to the pressure of the output flow in the second flow path from the subsidiary heat exchanger; and
a pressure dropping device in the first flow path downstream of the subsidiary heat exchanger and upstream of the load evaporator, said pressure-dropping device introducing a pressure differential driving the counterflows of fluid in the first and second flow paths through the subsidiary heat exchanger and configured such that the temperature difference between the first and second flow paths through the subsidiary heat exchanger approximates the difference between the boiling temperature of the refrigerant in the load evaporator and the temperature of the refrigerant at the compressor input.
2. The system of claim 1 , further comprising a subsystem in the compressor/condenser loop for providing a combined flow at controllable temperature to the evaporator, said subsystem including a first direct flow control for providing a selected proportion of hot gas flow from the compressor and a second derivative flow control for providing a selectively expanded and cooled flow from the condenser, subject to the proportion provided by the first direct flow control and a mixing circuit receiving the first and second flows for providing a combined flow therefrom to the evaporator via the subsidiary heat exchanger.
3. In a thermal control system using the different thermal transfer characteristics of the phases of a two-phase refrigerant and including a refrigeration loop of operative elements incorporating a compressor, a condenser, and an expansion device in sequence, the refrigeration loop being in thermal communication with an evaporator comprising the load to be cooled, the evaporator having a nonlinear heat transfer coefficient in response to localized refrigerant quality variations, wherein quality is expressed in terms of the proportion of vapor mass to total mass, the system comprising:
a subsidiary heat exchange loop disposed between the expansion device and the evaporator, comprising:
a heat exchanger comprising a first flow path coupling the expansion device to the evaporator on one side and a second flow path coupling the output from the evaporator to the compressor on the other side,
a differential pressure device in the coupling between the heat exchanger output and the evaporator input selected to lower the temperature of flow to the evaporator,
a pressure sensing device responsive to the pressure in the output line from the heat exchanger to the compressor input, wherein the pressure sensing device is configured to control the operation of the differential pressure device in the refrigeration loop to provide a temperature difference between the first and second flow paths.
4. The system of claim 3 , wherein the refrigeration loop comprises a thermo-expansion device including a vapor confining sensing bulb responsive to the temperature of the refrigerant being returned to the compressor from the heat exchanger, the sensing bulb having an internal fluid selected to have a chosen vapor pressure to approximate that of the refrigerant used in the cooling cycle.
5. The system of claim 3 , wherein the differential pressure device in the coupling between the counter-current heat exchanger output and the evaporator input is selected to provide a temperature change approximating the superheat of the evaporator.
6. The system of claim 3 , wherein the refrigeration system includes a system for mixing refrigerant media in expanded at least partially vapor phase after condensation and the same refrigerant in pressurized gas phase, including a mechanism for mixing the two different phases for application to the evaporator of given thermal capacity, wherein the subsidiary heat exchange loop is disposed between the mixing mechanism and the evaporator.
7. The system of claim 6 , wherein the pressurized gas phase has substantially greater energy content that the expanded vapor phase and wherein the subsidiary heat exchange loop stabilizes the entire thermal control system for effecting relatively small incremental temperature changes.