Experimental measurement of single-phase liquid heat transfer in a curved microtube using thermochromic liquid crystal
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abstract
2015, Avestia Publishing. The present work is to experimentally investigate the single-phase liquid heat transfer using un-encapsulated Thermochromic Liquid Crystal (TLC) technique. To the best of the authors' knowledge, this work is the first trial of using the TLC with a micro-curved tube. The objective of experiment was not met, however in this paper; we are reporting the experimental challenges to be considered in future studies. The experiments are conducted on two sizes of 90 bended microtubes with hydraulic diameters (Dh) of 1.194 mm and 0.838 mm, respectively. The radius ratios, defined as the ratio of curvature radius of the test tube and its hydraulic radius (2Rc/Dh), are 6.8 and 9.1 respectively. The dielectric fluid FC-72 is selected as the working flow. The inlet temperature maintains around 37C and Re number varies from 4000 to 5500. The uniform heat flux (q'') is applied to the microtube surface varying from 5 to 7 kW/m2. Un-encapsulated TLC is coated on the curved microtube surface for surface temperature measurement, and the tube surface temperature map is then illustrated. The stream-wise local Nu numbers against the Re number and heat fluxes for both microtubes are presented. It is found that the heat transfer coefficient in the curved portion of microtube enhanced by Dean Vortices. The maximum local Nusselt number appears at the turning angle between 40 and 60.
