Experimental Investigation on Impingement Array Cooling Systems Through IR Thermography

This paper reports the results of an experimental campaign involving heat transfer measurements on the target surface of an impingement jet array. Test were performed with the help of an open loop wind tunnel test rig, housing a model of the cooling system. The model general layout consists of an impingement channel, designed as a straight duct with rectangular section. A side of the channel is a steel impingement plate, while the opposite side acts as the impingement target surface and is composed of an electrically heated Inconel sheet supported by a thin steel plate. The coolant flow is provided by a plenum located upstream the impingement plate. The combined use of an inverter controlled electric fan and four rotary vanes vacuum pumps allows air circulation inside the model. Convective heat transfer coefficient on the impingement target surface is evaluated through a steady-state technique. The temperature of the target surface is measured through IR thermography: the outer side of the target surface is painted with a high-emissivity black coating and is observed by an IR camera; the inner temperature is then obtained through a simple finite difference model of the target plate. In the present work , different impingement layouts were tested (3 < Sx/d < 10, 3 < Sy/d < 20, 2.5 < H/d < 3.33) for different values of jet Reynolds number (2000 < Rej < 19000). Heat transfer results show a good agreement with the existing correlations, thus providing a validation for the adopted measurement technique, and extend the investigation to holes pitch values outside from correlations.