Liquid crystal technique application for heat transfer investigation in a fin-tube heat exchanger element

Abstract

The use of thermochromic liquid crystal technique (LeT) and true-colour image processing system in heat transfer modelling is described. Experimental procedure, led on rig at Technical University of Gdansk, cover full-field flow patterns in heat exchanger element (flat plate with fine-tubes in-line, staggered and with vortex generators) describing local heat transfer coefficient and Nusselt number on the surfaces. Also the dependence of average heat transfer and pressure drop on Reynolds number and geometrical parameters is investigated. Nomenclature: H -height ofthe channel [m] k, -conductivity ofthe air [WzmK] k, -mean conductivity ofthe liquid crystal package and plate [WzmK] L -the length ofthe channel in the main flow direction [m] M -pressure drop [Pa] r, -Hue ratio coefficient (ratio of number of pixels for the hue range considered) [ -] T" -temperature of air [K] T, -temperature of plate on waterside [K] T, -temperature of surface (liquid crystal yellow-green isotherm temperature) [K] U -inlet mean velocity [m/s] Ot -thickness ofthe liquid crystal package and plate [m] p -air density [kg/m'] v -viscosity of air [m'zs]