Effects of Transient Heating on Two-Phase Flow Response in Microchannel Heat Exchangers

Abstract

Two-phase microfluidic heat sinks promise high heat flux cooling at reduced pumping power compared to pumped liquid microchannel heat sinks. However, flow instabilities caused by bubble nucleation and expansion severely reduce heat transfer performance of two-phase microfluidic heat sinks. This study probes the governing physics of bubble nucleation and expansion by comparing the effects of pulsed heating to steady-state heating in a single microchannel. Pulsed heating at 8 Hz causes an increase in the average hotspot temperature of as much as 8°C compared to steady-state heating. Upstream and downstream temperature response does not vary significantly between heating conditions. The results correspond well with thin-film evaporation models for bubble growth. This study provides insight for designing two-phase microfluidic cooling system subjected to transient hotspots.

MEMS Vaporazing Liquid Microthruster: A Comprehensive Review

“…The interest in a pulsed heating strategy has continuously increased in recent years for thermal management applications. Miler et al [48] experimentally characterized transient phenomena in a water-fed single microchannel heat exchanger during pulsed heating (frequency f s = 8 Hz and pulse duration t s = 31 ms). The authors observed that low-frequency/highduration pulsed heating leads to an increase in the average hotspot temperature.…”

A diamond made microchannel heat sink for high-density heat flux dissipation

“…Regarding the experimental research under nonuniform heat flux, the wall temperature cannot be simply calculated based on the one-dimensional heat conduction equation, so the heat transfer coefficient cannot be obtained. Therefore, most of the previous studies that are relevant to the present work [11,13,14] directly presented the measured wall temperature as the indicator of the cooling performance of heat sinks at given conditions. The wall temperature, however, reflects the conjugated effects of both fluid convection and wall conduction on the cooling performance.…”

“…Placing the hotspot near the outlet can effectively reduce the CHF. In addition, some experimental efforts have explored the flow boiling instabilities [11], flow maldistribution [12,13], transient behavior of heat transfer [14,15] under nonuniform microchannel heating. These studies provide a basis for understanding the physical mechanism of heat transfer in microchannels under nonuniform heating conditions.…”

Local measurement of flow boiling heat transfer in an array of non-uniformly heated microchannels

“…Maldistribution was caused by a local increase in two-phase pressure drop due to boiling, which diverted single-phase liquid to other locations; this effect was most pronounced for a hot spot at the inlet. Transient non-uniform heating situations have also been investigated [19,21].…”