Experimental investigation of non-uniform heating effect on flow boiling instabilities in a microchannel-based heat sink

Abstract

Copyright @ 2011 ElsevierTwo-phase flow boiling in microchannels is one of the most promising cooling technologies for coping with high heat fluxes produced by the next generation of central processor units (CPUs). If flow boiling is to be used as a thermal management method for high heat flux electronics it is necessary to understand the behaviour of a non-uniform heat distribution, which is typically the case observed in a real operating CPU. The work presented is an experimental study of two-phase boiling in a multi-channel silicon heat sink with non-uniform heating, using water as the cooling liquid. Thin nickel film sensors, integrated on the back side of the heat sinks were used in order to gain insight related to temperature fluctuations caused by two-phase flow instabilities under non-uniform heating. The effect of various hotspot locations on the temperature profile and pressure drop has been investigated. It was observed that boiling inside microchannels with axially non-uniform heating leads to high temperature non-uniformity in the transverse direction.This research was supported by the UK Engineering and Physical Sciences Research Council through grant EP/D500109/1

Confined bubble growth during flow boiling in a mini/micro-channel of rectangular cross-section Part I: Experiments and 1-D modelling

“…For uniformly heated parallel channels, Qu, Mudawar [14] defined two forms of reversal, Mode 1: coordinated (low frequency) and Mode 2: uncoordinated (high frequency). Bogojevic et al [15] deduced similar behaviour in a group of 40 channels with axially non-uniform heating and uneven flow distribution between channels detected by wall temperature sensors spanning 3 groups of 7 channels. At low heat flux, some channels had subcooled wall temperatures indicating single-phase flow, others were superheated, indicating boiling.…”

“…It is often assumed that the downstream compressibility is infinite, so that the exit pressure is maintained constant by a condenser or open discharge to the atmosphere. Measurements as in Bogojevic et al [15], suggest that fluctuations in the outlet pressure may be of similar magnitude to those in the inlet pressure in a closed system or in an open system with two-phase flow in a long discharge pipe to the atmosphere.…”

“…Mode 1 reversal is difficult to detect in a large array. During the low-frequency fluctuations in inlet and outlet pipe pressures recorded by Bogojevic et al [15], the inlet pressure was always higher than the outlet pressure, which may indicate the absence of coordinated reversals, as opposed to the uncoordinated reversals observed in individual channels. The upstream compressible volume required for Mode 1 reversal is of the order of the channel volume, which could be as small as 1 mm 3 in a single channel experiment.…”

Characteristics of heat transfer and fluid flow in microtube and microchannel using conventional fluids and nanofluids: A review

“…Bogojevic et al [65] investigated experimentally the effects of nonuniform heating on flow boiling instabilities in microchannel-based heat sink using water as the cooling liquid. The results indicate that the onset of boiling caused metastable non-uniform flow distribution, with boiling in some channels and single-phase flow in others, leading to transverse variations in temperature that were less severe when the hotspot was at the downstream position.…”

Boiling two-phase flow and efficiency of co- and counter-current microchannel heat exchangers with gas heating

“…They found that the flow regime and the type of two-phase flow instabilities depended on the q/G ratio and the inlet subcooling conditions. Bogojevic et al [23] also presented an experimental study on the system instability in microchannels with non-uniform heating. They studied the effect of the hotspot location on pressure drop and the temperature profile and found that a system with axially non-uniform heating leads to a high temperature non-uniformity in the transverse direction.…”