Assessment of pulse-width modulated flow through serial expansion valve/capillary tube arrangements

This paper outlines an experimental and theoretical study on pulse-width modulated (PWM) flow of HFC-134a through serial expansion valve/capillary tube arrangements. The influence of the operating conditions (inlet pressure, duty cycle, and pulse period) and the geometry (valve diameter) on the refrigerant mass flow rate was experimentally evaluated using a purpose-built testing facility with strict control of all relevant variables. Several experiments were carried out and the results used to calibrate an algebraic first-principles mathematical model. A good agreement between the experimental and calculated data was achieved, with more than 85% of the data points falling within the ±15% error band. It was also observed that the model followed the experimental results closely.