Enhancement of heat pump performance by pulsation of refrigerant flow using a solenoid-driven control valve

The heating performance of an R410A heat pump system can be enhanced by a pulsatile refrigerant flow in a heat pump cycle. To generate the pulsatile refrigerant flow, a control valve was installed in parallel with the expansion valve located between the outlet of the condenser and the inlet of the evaporator in this system. Intermittent 200-ms openings of the control valve improved the heating performance because of two factors: the ‘pulsation effect’ that enhanced heat transfer and the ‘pushing effect’ that elevated the condensing pressure and increased overall mass flow rate. Heating capacity and COP (coefficient of performance) were increased by 4% and 3.2%, respectively, when the control valve operated at 0.005 Hz and 0.1% duty. In phenomenological view, two-phase invasion is considered when the control valve is operated.