Local Heat Transfer Measurements in Microchannels Using Liquid Crystal Thermography: Methodology Development and Validation

Microchannel heat transfer governs the performance of the microchannel heat sink, which is a recent technology aimed at managing the stringent thermal requirements of today’s high-end electronics. The microencapsulated form of liquid crystals has been well established for use in surface temperature mapping, while limited studies are available on the use of the un-encapsulated form. This latter form is advantageous since it offers the potential for high spatial resolution, which is necessary for microgeometries. A technique for using un-encapsulated thermochromic liquid crystals (TLCs) in order to measure the local heat transfer coefficient in microchannel geometries is shown in the present study. Measurements were made in a closed loop facility combined with a microscopic imaging system and automated data acquisition. A localized TLC calibration was used to account for a non-uniform coating and variation of lighting conditions. Three test section configurations were investigated with each subsequent configuration arising due to a shortfall in the previous. Two of these configurations are comprised of single wall heated rectangular channels, while the third is a circular tube channel. Validation results are also presented; overall, the methods developed and utilized in this study have been shown to provide the local heat transfer coefficient in microchannels.