Local Heat Transfer Analysis in a Single Microchannel with Boiling DI-Water and Correlations with Impedance Local Sensors

Mohammadmahdi Talebi, Sahba Sadir, Manfred Kraut, Roland Dittmeyer and Peter Woias
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Mohammadmahdi Talebi: Laboratory for Design of Microsystems, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg, Germany
Sahba Sadir: Institute for Micro Process Engineering (IMVT), Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany
Manfred Kraut: Institute for Micro Process Engineering (IMVT), Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany
Roland Dittmeyer: Institute for Micro Process Engineering (IMVT), Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany
Peter Woias: Laboratory for Design of Microsystems, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg, Germany

Energies, 2020, vol. 13, issue 23, 1-29

Abstract: Determination of local heat transfer coefficient at the interface of channel wall and fluid was the main goal of this experimental study in microchannel flow boiling domain. Flow boiling heat transfer to DI-water in a single microchannel with a rectangular cross section was experimentally investigated. The rectangular cross section dimensions of the experimented microchannel were 1050 μ m × 500 μ m and 1500 μ m × 500 μ m. Experiments under conditions of boiling were performed in a test setup, which allows the optical and local impedance measurements of the fluids by mass fluxes of 22.1 kg · m − 2 · s − 1 to 118.8 kg · m − 2 · s − 1 and heat fluxes in the range of 14.7 kW · m − 2 to 116.54 kW · m − 2 . The effect of the mass flux, heat flux, and flow pattern on flow boiling local heat transfer coefficient and pressure drop were investigated. Experimental data compared to existing correlations indicated no single correlation of good predictive value. This was concluded to be the case due to the instability of flow conditions on one hand and the variation of the flow regimes over the experimental conditions on the other hand. The results from the local impedance measurements in correlation to the optical measurements shows the flow regime variation at the experimental conditions. From these measurements, useful parameters for use in models on boiling like the 3-zone model were shown. It was shown that the sensing method can shed a precise light on unknown features locally in slug flow such as residence time of each phases, bubble frequency, and duty cycle.

Keywords: boiling flow; microchannel; heat transfer analysis; local sensing elements; impedance measurement; local sensing; bubble frequency; flow regime (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2020
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