Oscillating flow in a heat sink with parallel micro channels

The performance of two phase heat sinks can be greatly affected by the coolant flow instabilities. For the applications in electronic cooling system, the micro-channel heat sink usually consists of some parallel channels and common header or manifold, the flow instabilities can be an especially noticeable problem. Flow instabilities will cause a severe reverse flow and subsequent maldistribution of cooling medium in the header. In addition, the instabilities degrade the total heat transfer performance of the heat sink and lead to a remarkable variation of pressure drop. As the cooling medium coming from the upstream pipe is always in two-phase flow state, the common header filled with this coming vapor will serve as a buffer tank. This tank provides significant compressible volume to the downstream heated channels and may lead to sustained pressure and temperature oscillations in the system. In this paper, the periodic reversed flow and maldistribution of fluid in a heat sink with parallel micro channels are studied experimentally. Visualization results are presented simultaneously. The effects of channel size, surface tension and fluid viscosity are considered. The results show that the micro-channel heat sinks are especially susceptible to flow instabilities and fluid maldistribution. The channel size and the surface tension effect on the reverse flow as well. And the heat transfer performance deteriorates when the ammonia reverse flow occurs.