Thermal design and operational limits of two-phase micro-channel heat sinks

While the vast majority of published studies on two-phase micro-channel heat sinks have been focused on determination of pressure drop and heat transfer coefficient, very few studies have addressed the operational limits of these devices. This study provided a comprehensive methodology for thermal design of micro-channel heat sinks with saturated inlet conditions. This includes predictive methods for pressure drop and heat transfer coefficient using universal correlations that rely on large databases amassed from numerous sources, and which encompass many working fluids, and very broad ranges of hydraulic diameter, mass velocity, inlet pressure, and inlet quality. This is followed by predictive tools for thermal limits associated with dryout incipience and premature critical heat flux, as well as two-phase critical flow limit. The three limits are combined to define an envelope for acceptable heat sink performance. Using these tools, a parametric study is performed to determine the variation of maximum heat flux with total volumetric flow rate for different combinations of the channel's geometrical parameters for three working fluids, HFE-7100, R134a, and water. Then, the values of maximum heat flux are used to assess corresponding variations of pressure drop and maximum bottom wall temperature of the heat sink. It is shown that maximum heat flux is dominated by different limits for different flow rate ranges, and may be increased significantly, while decreasing bottom wall temperature, by using a large number of small channels. Furthermore, using deeper micro-channels is shown to increase maximum heat flux and decrease pressure drop, while producing a relatively weak adverse effect on bottom wall temperature.