Limited by the structures of the engineering components, sometimes the narrow gap impingement with limited jet-to-target spacing is required in the practical situations. In order to obtain an improved understanding upon the effects of narrow gap impingement on surface heat transfer and to fill gaps in the limited literatures, experiments of multi-jet impingement have been carried out using different jet-to-target distance (0.5D and 1D). Different configurations of jet-array are adopted and the transient thermochromic liquid crystal (TLC) is applied for the acquisition of the heat transfer data. Reynolds number of the jet flow ranges from 2.43×104 to 5.39×104. It shows that the impingement using 90° attack angle with a jet-to-target distance of 0.5D leads to non-uniform distributions of the Nusselt number, especially for the upstream jet-region. According to the experimental results, the jets with the non-orthogonal attack angle and staggered array perform better than the normal ones. Under the same experimental conditions, the staggered jets with 75° attack angle can give higher average Nusselt numbers with fewer fluctuations in the jet region.

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