Optimal design of a micro-orifice for constant evaporator superheat in a small cooler

Abstract

Abstract We present an optimal design for an orifice in a small cooler. The objective of the optimal design is to maintain constant superheat at the outlet of an evaporator while the flow rate and cooling load are changed. Four parameters are chosen for the optimal design: the diameter of the orifice, the aspect ratio between length and diameter, the entrance angle to the orifice, and the surface roughness. R-123 is used as the refrigerant. We perform a simulation to check the sensitivities of each parameter, and we determine the orifice diameter as the most sensitive design parameter among the four parameters to maintain the constant superheat. To find the optimal orifice diameter, experiments are performed on orifices of various diameters. To simulate the vapor-refrigeration cycle, the inlet condition of the orifice upstream flow is fixed at 3 bar and 60 °C. The superheat is measured at the outlet of the orifice while the cooling loads vary by 60, 80, and 100 W and the flow rate varies by 20–70 mL/min. An orifice diameter of 350 μm is selected as the optimal value to keep constant superheat at the evaporator outlet for various flow rates and cooling loads. The resulting optimal orifice design will be used in a small cooler.