- Detailed heat transfer measurements are done using a transient liquid crystal technique for an array of in-line air jets (four rows with each row having twelve jet holes) impinging orthogonally on a pinned target surface with three different spent-air crossflow orientations. Measurements are done at four jet Reynolds numbers ranging from 4850 to 18300. Pin of 0.635 cm in diameter (equal to the jet diameter) and 0.3175 cm in height are inserted on the target surfaces in two different patterns (239=207 pin and 115=55 pin). The results show that jet Reynolds number has a strong effect on local heat transfer coefficient. The local and averaged heat transfer coefficient increases with an increase in jet Reynolds number. The crossflow direction also influences the local heat transfer coefficient. A pinned surface may produce a higher or lower heat transfer coefficient than a smooth surface, depending on the spent-air crossflow direction. The pinned surface results are comparable with the existing rough surface data. Copyright 2002 Taylor & Francis.