HEAT TRANSFER INVESTIGATIONS OVER THE RIB ROUGHENED WALL USING LIQUID CRYSTAL THERMOGRAPHY

Abstract

In this dissertation work, a methodology has been developed for evaluating the heat transfer coefficient distribution using liquid crystal thermography. The transient liquid crystal technique has been used to obtain the detailed information of local Nusselt number distribution. MATLAB has been used to capture the transient liquid crystal images while using 3-CCD color camera. Subsequently, the hue information of the recorded video frames has been extracted which is being converted into the temperature information of the heating surface while using the calibration curve. A number of TLC calibration tests have been conducted and show similar calibration curves each time, which confirms the repeatability of TLC measurements. Having all temperatures and time values the 1-D heat transfer equation for semi infinite solid is iteratively solved to get the value of heat transfer coefficient of each and every pixel of the test surface. Solid rib with chamfer angle of 0°, 5, 10, 15 and 20° have been used for heat transfer investigations at different Reynolds number i.e. 11,000, 22,000, 33,000, 45,000 and 58,000. The pitch to rib-height ratio set during the experiment was 10 and the rib-height to hydraulic diameter ratio was equal to 0.125. Systematic study of these different configurations of rib geometries have been carried out for single rib and array of ribs. The results show that the local heat transfer is strongly dependent on the rib shape in the region downstream of the rib. In case of a single rib, the heat transfer augmentation by solid rib with chamfer angle equal to 15° at a Reynolds number of 33,000 is around 1.97 times as comparison to smooth surface, which is maximum in all configurations and the solid rib with square cross-section shows minimum heat transfer enhancement. In case of array of ribs, the average Nusselt number (Nux,a) is maximum with solid rib of chamfer angle equal to 20° at a Reynolds number of 33,000. The array of solid rib (cc= 10°) shows maximum heat transfer at Reynolds number of 33,000 as comparison to other Reynolds number and periodicity in the heat transfer distribution has been observed.