Forced and mixed convection heat transfer from an array of cylinders to a liquid submerged jet

Abstract

The results of an experimental investigation concerning the heat transfer from three cylindrical heaters to a water jet are reported in the form of correlating equations, which express the Nusselt number versus the Reynolds, Prandtl and Grashof numbers and some dimensionless ratios characterising the configuration. As the experienced range of the thermal flux is wide (2·10⁴ ≤ q̇ ≤ 6·10⁵ W·m⁻²), the influence of the free convection, which was shown to be negligible in previous studies, is carefully investigated in the present one. This influence appears still negligible up to the maximum value of q̇ for the heater impinged by the jet; on the contrary it is remarkable for the heaters lying in its wake. Another aspect which is carefully studied is the influence both of the ratios characterising the configuration and of the impingement direction: accordingly the values of these ratios and the kind of impingement which yield the maximum Nusselt number are clearly singled out. The investigation is completed by some visualization experiments which allow us to qualitatively clarify some aspects of the interaction between the dynamic and thermal fields.