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Abstract
This article presents an experimental study of friction factor and heat transfer coefficient for a vertical liquid up-flow of R134a. A flat aluminium multiport extruded tube composed of 11 parallel rectangular channels ( 3.28 mm×1.47 mm) with hydraulic diameter of 2.01 mm was used. Mass flux ranges from 28 to 800 kg m −2 s −1 and heat flux from 0.84 to 22 kW m −2. Working pressure is around 2000 kPa and inlet subcooling around 70 K. The results were compared with those found in the literature for conventional tubes and mini-channels, and discussed.
Highlights
New environmental policies on global warming require that emissions of gases with significant greenhouse effect should be decreased
This work presents experimental friction factors and heat transfer coefficients obtained with a single-phase liquid flow in such mini-channels, in preparation for a future two-phase flow study
Harms et al [7] have studied single-phase water flow in horizontal rectangular mini-channels made of silicium and found friction factors very close to the predictions of Shah and London, whereas their transition from laminar to turbulent flow took place for a Reynolds number of about 1500
Summary
New environmental policies on global warming require that emissions of gases with significant greenhouse effect should be decreased. The use of mini-channel heat exchangers (hydraulic diameter about 1 mm) contributes to achieve this purpose thanks to higher heat transfer coefficients, thermal efficiency and a lower required fluid mass. This work presents experimental friction factors and heat transfer coefficients obtained with a single-phase liquid flow in such mini-channels, in preparation for a future two-phase flow study. Harms et al [7] have studied single-phase water flow in horizontal rectangular mini-channels made of silicium and found friction factors very close to the predictions of Shah and London, whereas their transition from laminar to turbulent flow took place for a Reynolds number of about 1500. Yan and Lin [8] measured friction factors in laminar and turbulent flows significantly higher than the predictions of the Poiseuille and Blasius equations The authors impute this to entry length effects or to tube roughness. The dimensions are l 1⁄4 3:28 Æ 0:02 mm, h 1⁄4 1:47 Æ 0:02 mm and Ra < 1 lm, yielding Dh 1⁄4 2:01 Æ 0:06 mm
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