열펌프 압축기의 액분사 효과에 대한 수치해석

Abstract

Heat and fluid flow in a heat pump compressor into which liquid refrigerant is injected for the purpose of reducing discharge gas temperature has been numerically analysed. A mechanistic approach encompassing liquid jet breakup and droplet evaporation has been performed to investigate the effects of liquid injection on the spacial and temporal variation of the gas temperature and pressure inside the compressor cylinder. An evaporation model based on kinetic theory is employed for superheated liquid droplets of which the thermodynamic state is close to flash boiling. Various parameters, such as liquid injection mass, time, duration and droplet size, are considered in the present study to elucidate the mechanism and flow field inside the compressor, which could not have been acquired by the typical cycle simulations. As the injection mass is increased, discharge gas temperature is decreased, while the pressure is increased due to the added mass of the injection. For the injected liquid mass corresponding to 15% of the total vapor mass in the cylinder, the discharge gas temperature drops by 22.4 K. It is found that the injection starting time and duration have little effect on the discharge temperature drop. It is, however, observed that the droplet size plays a major role in the evaporation rate of the droplets that determines the degree of the discharge temperature drop.