Arvind Pattamatta

This paper reports the results of an experimental study to investigate the local and average convective heat transfer coefficients from a single jet and a row of jets impinging over an unheated flat plate. A thermochromic liquid crystal technique is used to visualize the temperature distribution on the impingement surface and the semi-infinite approximation methodology is used to extract the local heat transfer coefficients. Measurement of potential core length and turbulence intensity have also been carried out using hotwire anemometry. Results are presented for jet Reynolds numbers 5000, 10,000 and 15,000 with varying separation distances (normalized distance between jet and the target plate (L/D)) of 2, 4 and 6 for four different jet configurations namely, single orifice, single nozzle, a row of orifices and a row of nozzles. A comparison of heat transfer characteristics of the single orifice with the single nozzle and the row of orifices with the row of nozzles is reported. The measured stagnation Nusselt number is found to be correlated to the jet characteristics such as potential core length and turbulence intensity. Correlations are developed for Nusselt number as a function of Reynolds number and separation distance.

This paper reports the results of experimental and numerical studies to understand the heat transfer characteristics of three-dimensional wall jets exiting from a single and a row of circular jet openings over an unheated flat plate. Infrared thermography is employed to obtain the temperature distribution over the target surface, and the semi-infinite approximation methodology is used to estimate the heat transfer coefficients. Single wire constant temperature hot-wire anemometer is used to measure the flow characteristics. Additionally, computational studies have been performed to select a suitable low Reynolds number turbulence closure models among the following models, namely (i) Spalart Almaras (SA) (ii) Realizable k-ε with enhanced wall treatment (RKE-ewt) (iii) k-ω SST and (iv) Reynolds Stress Model with enhanced wall treatment (RSM-ewt) that predicts the experimentally obtained results for heat transfer characteristics accurately. Based on the investigations carried out, it is observed that RKE-ewt turbulence closure model is not only accurate but also faster in the prediction of heat transfer coefficient. Further, it is also seen that for a fixed mass flow rate, and at a given diameter of the jet opening, widely spaced jets show higher heat transfer coefficients. Furthermore, for a row of three-dimensional wall jets correlations based on the numerical results are developed for the Nusselt number for a Reynolds number range of 5000 to 15000.