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Local wall temperature mapping during flow boiling in a transparent microchannel

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Original languageEnglish
Article numberTHESCI_5638
Pages (from-to)344-361
Number of pages18
JournalInternational Journal of Thermal Sciences
Volume135
Early online date29 Sep 2018
Publication statusPublished - Jan 2019

Abstract

In this study the local two-phase heat transfer coefficients in a rectangular high-aspect-ratio (a = Wch/Hch = 22) polydimethylsiloxane (PDMS) microchannel with a hydraulic diameter of 192 μm were obtained using wall temperature measurements and fluid saturation temperatures obtained from interpolating inlet and outlet pressure measurements, the latter from integrated silicon ceramic-based pressure sensors located near the inlet and outlet of the microchannel. The experiments used FC-72 liquid with a mass flux of 7.37 kg m-2s-1 with heat fluxes ranging between 3.34 and 61.95 kW m-2. The hydrodynamic and flow boiling characteristics of the microchannel were characterised using high frequency and high spatial resolution infrared thermography, with heat transfer coefficients obtained as function of axial position, lateral position and time, at the inlet, middle and outlet sections of the microchannel base. This enabled the effect of heat flux on local temperature variation, flow boiling heat transfer coefficient distribution and the two-phase pressure drop to be studied. This provided evidence that the two-phase heat transfer coefficient does not increase monotonically with the heat flux, and actually reduces under certain conditions. This decreasing trend of the heat transfer coefficient is shown to depend on the heat flux range and is correlated with vapour-liquid dynamics and liquid film thinning resulting in suspected dryout, observed simultaneously with the temperature measurements. This application of high speed thermography simultaneously with flow visualization additionally enabled more detailed information to be obtained on two- phase flow and bubble dynamics.

    Research areas

  • Flow boiling, Microchannel, ransparent-heating, Flow boiIntegrated pressure, Infrared thermography

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