Experimental investigation and analysis of parametric trends of instability in two-phase micro-channel heat sinks

Abstract

This study explores Density Wave Oscillation (DWO) and Parallel Channel Instability (PCI) in a micro-channel heat sink containing 38 parallel channels having a hydraulic diameter of 316 μm. Experiments are executed using FC-72 as working fluid with mass velocities from 171.2 to 1124 kg/m2s and a fairly constant inlet subcooling of ~15°C. The flow instabilities are reflected in pressure fluctuations detected mostly in the heat sink's upstream plenum. Both inlet pressure and pressure drop signals are analyzed in pursuit of amplitude and frequency characteristics for different mass velocities and over a range of heat fluxes. The analysis is complemented by detailed visualization of interfacial features along the parallel channels using high-speed video. Appreciable confinement of bubbles in individual channels is shown to promote rapid axial bubble growth. The study shows significant variations in the amount of vapor generated and dominant flow patterns among channels, a clear manifestation of PCI, especially for low mass velocities and high heat fluxes. It is also shown effects of the heat sink's instabilities are felt in other components of the flow loop. The parametric trends for PCI are investigated with the aid of three different types of stability maps which show different abilities at demarcating stable and unstable operation.