Measuring Heat Transfer Coefficients for Microchannel Jet Impingement Using Time-domain Thermoreflectance

Jet impingement heat transfer has become well known for its capability to achieve high heat transfer coefficients (HTCs) on a heated surface, especially in the stagnation region. For this reason, jet impingement mechanisms have become popular topics in heat transfer research and microelectronics. This current study presents the findings of experiments that measure the HTCs on surfaces exposed to hot-spot heating and cooled using water jet impingement at Reynolds numbers up to 6432. The HTCs were found using time-domain thermoreflectance (TDTR) with a water jet on a fused silica (FS) glass substrate coated with a thin-film Hafnium-alloy (Hf). The HTC data are based on a local, micron-sized hot-spot region (generated by the TDTR pump laser) that is translated at different locations relative to the stagnation point. The study shows that at different microchannel regions (relative to the stagnation point) and for different Reynolds numbers for the jet that the TDTR method can detect changes in the HTC. Material is also presented to show how a third heating laser can be used to control and define the hot-spot region independently of the TDTR pump-probe laser, facilitating hot-spot heat fluxes up to 155 MW/m(2) over hot-spot areas ranging between 0.0193 and 0.0246 mm(2).