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ISSN Online: 2377-424X

International Heat Transfer Conference 12
August, 18-23, 2002, Grenoble, France

Convective heat transfer models for three-temperatures problems Application to jet impingement and film cooling

Get access (open in a dialog) DOI: 10.1615/IHTC12.1060
6 pages

Sinopsis

We investigated the convective heat transfer characteristics of two different geometries for which a three - temperatures problem was involved: flows temperatures T1 and T2 and wall temperature Tp. The aim was to establish a universal law to model forced convective heat transfer in "3-temperatures" configurations. The first geometry considered was a round free jet of hot air (T1=20°C to 140°C) developing within ambient air (T2=20°C) and impinging on a flat plate (Tp). The heated-thin-foil technique was used jointly with infrared thermography to determinate simultaneously the adiabatic wall temperature Taw and a local heat transfer coefficient h. The wall heat flux could then be linked to the wall temperature through the use of a classical convective law. The results were analysed in terms of local effectiveness and local Nusselt numbers. It was showed that effectiveness was independent of the temperature difference (T1-T2) within the test range. The local Nusselt numbers Nu were independent of the temperature difference as soon as this difference didn't exceed 40°C. The second geometry corresponded to a film cooling geometry. The main flow was parallel to a heated flat plate and was heated so that its temperature T1 could vary from 16°C to 70°C. A secondary flow was injected through perforations in a staggered pattern (9 rows and 8 columns) and formed a thermal shield between the main flow and the wall. The temperature T2 of this secondary flow was 20°C. Infrared thermography was used to measure the local temperature at the wall for different positions. From these measurements, a new heat transfer model linked the wall's local heat flux density to the two reference temperatures T1 and T2 through the use of two local heat transfer coefficients h1 and h2 independent of the flows temperatures.