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5. Heat pumps Fig. 5.17. Thermostatic expansion valve with external pressure compensation – cross-section. 1 – temperature sensor, 2 – membrane, 3 – membrane spring, 4 – ajustting screw, 5 – tappet, 6 – nozzle insert with valve cone (Source: own elaboration) Throttle valves with electrical auxiliary energy. Electronic expansion valves technology has been developed to deal with increasingly complicated requirements. The cost of electronic valves, which includes the regulator, sensors, actuator and the valve, is still high. Electronic expansion valves are therefore mostly found on very large systems. Electronic expansion valves are controlled by temperature or pressure sensors. The electronic regulating unit can be programmed to correct differences in temperature and pressure at any point of the system. Because the electric actuator reacts only to signals from the regulator, there are good possibilities for achieving a lower level of superheating than with a thermal expansion valve (Hadorn, 2015). Thermo-electric throttle valves are equipped with a bimetallic strip. It contains two metal layers with different heat transfer coefficients. If the band is heated, it deforms in proportion to the temperature change. Heating is carried out using a heating wire wound around the strip. In the vapour intake line behind the evaporator, there is a thermistor. The capacity of the expansion valve (the amount of refrigerant flowing through it) is determined by the relationship between the opening and closing times. A regulator controls the opening and closing of the valve in order to reach the correct level of superheating. The inputs to the regulator are the temperature and pressure at the evaporator outlet. The inputs could also be the inlet and outlet evaporator temperatures, as for an electronic valve with a continuous control. 163PDF Image | Heat Pumps 978-83-65596-73-4
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CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
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