Experimental and analytical investigation into maldistribution of two-phase flow boiling in mini/microchannel heat sinks

Abstract

Two-phase mini/micro-channel heat sinks have been considered a promising solution for thermal management systems that require efficient dissipation of high heat flux. This is due to their high heat transfer coefficient and ability to minimize temperature gradients along the surface. However, the flow maldistirbution which frequently occurs in parallel mini/micro-channels can deteriorate the efficiency and reliability of the system. In the present study, therefore, how operating conditions influence flow distribution and its underlying mechanism are suggested by measuring flow distribution, heat flux of each channel, and inlet temperature gradient. A heat sink with dimensions of 318 mm in length and 216 mm in width is utilized, containing a total of 16 mini/micro-channels measuring 2 by 2 mm² each. Before performing flow rate measurement experiments for each channel, the relationship between operating conditions and the intensity of parallel channel instability is established by conducting FFT analysis using the inlet pressure. The results of FFT analysis reveal that as the heat flux and inlet temperature increase, and the mass flow rate decreases, the frequency of inlet pressure oscillations decreases and their intensity becomes stronger. The temperature gradient along the inlet plenum resulting from the vapor backflow from the channels to the inlet is also identified. Finally, a parametric study with the variation of heat flux and inlet temperature is conducted to identify key parameters governing the flow distribution. The temperature gradient in the inlet plenum induces flow maldistribution by varying the single-phase length which is related to the temperature in front of channel inlet. The stability map is utilized to identify the operating conditions that can achieve uniform flow distribution in practical applications.