Two-phase flow in high-heat-flux micro-channel heat sink for refrigeration cooling applications: Part I––pressure drop characteristics

Two-phase pressure drop was measured across a micro-channel heat sink that served as an evaporator in a refrigeration cycle. The micro-channels were formed by machining 231lm wide · 713lm deep grooves into the surface of a copper block. Experiments were performed with refrigerant R134a that spanned the following conditions: inlet pressure of Pin = 1.44–6.60bar, mass velocity of G = 127–654kg/m s, inlet quality of xe,in = 0.001–0.25, outlet quality of xe,out = 0.49–superheat, and heat flux of q 00 = 31.6–93.8W/cm. Predictions of the homogeneous equilibrium flow model and prior separated flow models and correlations yielded relatively poor predictions of pressure drop. A new correlation scheme is suggested that incorporates the effect of liquid viscosity and surface tension in the separated flow model s twophase pressure drop multiplier. This scheme shows excellent agreement with the R134a data as well as previous microchannel water data. An important practical finding from this study is that the throttling valve in a refrigeration cycle offers significant stiffening to the system, suppressing the large pressure oscillations common to micro-channel heat sinks. 2004 Elsevier Ltd. All rights reserved.