Thermal control systems for process tools requiring operation over wide temperature ranges
View Patent ↗A system and method for maintaining the temperature of a thermal transfer fluid at a selectable level within a wide temperature range, so as to operate a process tool in a chosen mode employing at lease two cascaded stages, each operating with a different fluid in a separate refrigeration cycle. By interrelating energy transfers between parts of upper and lower stages, thermal efficiency is maximized and a smooth continuum of temperature levels can be provided. The refrigerants advantageously have vaporization points below and above ambient, for upper and lower stages respectively, and employs the upper stage for a constant refrigeration capacity, controlling the final temperature with the lower stage. The system allows for a further extension of range because the thermal transfer fluid can be heated for some process tool modes as the refrigeration cycles are run at low loads.
1. A refrigeration system employing a low boiling point oil-containing refrigerant that is a gas at ambient temperature, for cooling a thermal transfer fluid to be used in cooling process equipment comprising:
a compressor having a suction input and providing a pressurized refrigerant output;
an oil separator receiving the refrigerant output and returning a substantial part of the oil therein to the compressor input;
a condenser system receiving the pressurized refrigerant output from the oil separator and providing a pressurized liquid refrigerant output;
a counterflow subcooler receiving the pressurized liquid refrigerant as one input and returning suction input refrigerant as a second input;
an excess volume cylinder coupled to receive a restricted flow of gaseous refrigerant from the suction input refrigerant to limit pressure buildup;
a heat exchanger/evaporator coupled to receive pressurized refrigerant and the thermal transfer fluid separately, but in heat exchange relation, and
an expansion valve device coupled to receive the pressurized liquid refrigerant from the subcooler and providing a selected mixture of expanded liquid/vapor to the heat exchanger/evaporator.
2. A refrigeration system as set forth in claim 1 above, wherein the system includes a controller providing commands for the expansion valve device, the expansion valve device including both a solenoid expansion valve and a thermal expansion valve, and wherein the system includes pressure relief elements coupled separately to pressurized gas refrigerant lines and pressurized liquid refrigerant lines.
3. A refrigeration system as set forth in claim 1 above, and including in addition a hot gas bypass valve responsive to input suction temperature and coupling the compressed gas output from the oil separator to the suction input and a desuperheater valve responsive to suction input pressure and selectively coupling pressurized liquid refrigerant to the suction input in the event of suction input being below a selected threshold.