Suction condition: Its effect on refrigeration compressor performance

This investigation was carried out to determine the relative importance of the factors affecting volumetric efficiency during the transition from "dry" to "wet" compression when the refrigerant is Freon 12 and the compressor is running at a high speed. Experimental techniques were developed to measure piston leakage and fluctuating cylinder wall temperatures. The development of an electrical analogue and a rotating drum photoformer is described. This analogue was used to calculate the cyclical heat flow between the cylinder wall and the charge. In addition the performance of non-uniform ladder networks was Investigated and the analogue was adapted for various other calculations. These were, (a) To determine the suitability of thermocouple elements with dissimilar thermal properties to the body whose temperature is being measured. (b) To determine the effect of irregularities at the thermocouple junction. This took the form of a small "fin" or "lips" on the thermocouple wire, represented by a 2-dimensional network. The investigation showed that when measuring fluctuating temperatures, large errors could be caused by such a "lip" indicating the unsuitability of peening for such purposes. (c) To investigate the heat transfer between droplets of liquid and an environment of its own vapour when undergoing compression and re-expansion. The effect on volumetric efficiency of the retention of liquid in the cylinder is calculated. It is concluded that the most important process involved is cyclical heat transfer due to alternate condensation and re-evaporation when the cylinder wall temperature falls below the maximum saturation temperature of the vapour. It is shown that "flashing" of entrained liquid has little effect on performance, hut that evaporation of this entrainment from the cylinder wall could cause rapid lowering of the cylinder wall temperature. It is also concluded that liquid deposited on the cylinder walls reduces the rate of condensation on the walls and subsequent re-evaporation. Piston leakage is shown to have little effect on the performance of the compressor during the change from "wet" to "dry" compression