Numerical simulation and experimental validation of dynamic liquid-return characteristics of refrigerant-lubricating oil mixtures in accumulator of room air-conditioner.

Room air-conditioners adopt accumulators to supply vapor refrigerant and liquid refrigerant-lubricating oil mixture to the compressors, and the excessive or insufficient liquid mixture returning to the compressor may respectively lead to liquid slugging or oil starvation, resulting in compressor damage. Optimization design of the accumulator based on accurate simulation is an effective way to appropriately regulate the liquid return rate. The purpose of this paper is to develop a model for accumulator simulation and to validate it by experiments. In the model, the mass and energy conservation equations for both vapor phase and liquid phase within the accumulator cavity are established to reflect the flow processes in two phases; the equations for calculating the refrigerant dissolution and desorption rates are formulated to describe the flow process of vapor-liquid interphase; the pressure balance equations based on flow path divisions are formulated to reflect the flow processes in the inlet and outlet pipes. An experimental rig is built to measure liquid return rate, oil return rate and height of liquid level of the accumulator, and the validation results show that the mean absolute deviations between predicted and experimental data of those three parameters are 6.3 %, 8.7 % and 4.6 %, respectively. By using the model, the structural parameters of the oil bleed hole for a room air  onditioner accumulator with a rated cooling capacity of 3.5 kW were optimized, and the optimization results indicate the reasonable ranges for the diameter and the height of oil bleed hole are 0.65–0.92 mm and 15–30 mm, respectively.