Local Heat Transfer Measurements on a Curved Microsurface Using Liquid Crystal Thermography

Abstract

In this paper, local heat transfer measurements in circular mini- and microchannels are presented through the use of unencapsulated thermochromic liquid crystals for local wall temperature measurement Microchannel heat transfer is fundamental to the design of a number of novel technologies in development for thermal control. Measurements are carried out in three different stainless steel tubes with nominal inner diameters of 1.07, 0.51, and 0.25 mm. The working fluids are distilled water and FC-72. A unique localized calibration of the thermochromic liquid crystal material is employed to minimize the effects of lighting nonuniformity and the effect of variable coating thickness. Local heat transfer and frictional pressure drop measurements are presented for the laminar, transitional, and turbulent flow regimes. The results are compared with correlations for both macro- and microchannels in the turbulent regime and show that, considering experimental uncertainty, both correlations are adequate for the experimental range investigated. Overall, the methods developed in this work demonstrate that the unencapsulated forms of thermochromic liquid crystals are a viable approach for temperature measurement in microheat transfer experiments.