Conjugate jet impingement heat transfer investigation via transient thermography method

Investigating the conduction-convection coupling, the present study is focused upon measurement of conjugate heat transfer ensuing jet impingement on a 15-mm-thickmetallic plate. Based on a rapid change in jet temperature and using time-accurate infrared thermography, a transient measurement methodology is developed toward acquisition of heat transfer coefficients. The new technique is shown to have comparable levels of Nusselt number and effectiveness accuracy, all while significantly reducing the number of consecutive measurements and their duration. To highlight the significance of the conjugate effect, different plate materials (copper, steel, and Inconel) are employed to differ the solid thermal conductivities, resulting in Biot-number variations. The plate surface heat transfer is studied at two injection Reynolds numbers (34,000 and 37,000) and for two nozzle-to-plate distances (two and five jet diameters). The changes in slabmaterial conductivity reveal small but quantifiable differences in heat transfer coefficients (up to ∼20% locally and 9% globally). Furthermore, constituting an upper bound and lower bound, respectively, it is observed that all conjugate Nusselt number distributions lay within the two limits of isoheat flux and isothermal boundary condition cases.