Heat transfer of tubes closely spaced in an in-line bank

An experimental investigation of heat transfer around four cylinders closely spaced in a cross-flow of air has been conducted. The cylinders are settled in tandem with equal distances between centers. Their inline pitch ratio is in the range of 1.15 ≤ cd ≤ 3.4 (c = distance between cylinders' centers, d = cylinder diameter); the Reynolds number ranges from 104 to 5 × 104. It is found that there exists a critical Reynolds number Redc at which the heat transfer behavior changes drastically, and is correlated with the in-line pitch ratio by Redc = 1.14 × 105 (cd)−5.84. Variations of characteristic features of the mean and local Nusselt numbers are discussed in relation to the length of the vortex formation region behind the cylinder.