Transient behavior of flow boiling in structured microchannels under sudden and highly variable heat loads

Abstract

In practice, heat sinks are sometimes exposed to sudden and irregular or highly variable heat loads. Therefore, here, for expanding micro-pin-fin heat sinks having micro cavities (heat sink code: MD) transient flow boiling characteristics are investigated under sudden and highly variable heat loads. Results are compared with those of conventional parallel channel heat sink (SD). Experiments can be grouped into two categories: (1) For a specified mass flux (G = 200 kg m−2 s−1) and inlet temperature (Ti = 78 °C), different heat loads (150 W, 30 W, 200 W, 150 W and 30 W, respectively) are applied. Every heat load is applied for three minutes, successively. (2) For a given mass flux (G = 200 kg m−2 s−1) and different inlet temperatures (Ti = 36 °C, Ti = 57 °C and Ti = 78 °C), the heat sinks are suddenly exposed to heating power of 200 W for ten minutes. It is deduced that MD increases heat transfer coefficient, decreases pressure drop and enhances thermal response characteristics compared to SD. In whole experimental range, heat transfer coefficient increases up to 11,802%, decrease in surface temperature reaches up to 39.2 °C, decrease in pressure drop reaches up to 4.05 kPa, and time passed for stable thermal conditions reduces from 48 s to 25 s. Decreasing inlet temperature increases thermal performance, however, leads higher fluctuations.