Heat transfer in a serpentine channel with a series of right angle turns

Abstract

Heat transfer in a two-dimensional serpentine channel with a series of right angle turns was investigated experimentally and numerically. Similar channel geometry can be found typically in heat exchangers, thermal regenerators, and internal cooling passages of gas turbine blades. Heat transfer coefficients were measured in the turbulent regime using the naphthalene sublimation technique. A finite volume based numerical model was developed to predict heat transfer and fluid flow in serpentine channels. The standard k-ε turbulence model was incorporated for turbulence closure. The experimental results were compared with the numerical predictions in the periodically fully developed region. The local heat transfer coefficients were measured in the periodically fully developed region at Re = 18,460 and 32,940. To examine the continuous variation of local heat transfer distributions, heat transfer coefficients were measured throughout the channel surfaces from the entrance to the periodically fully developed region at Re = 32,940. By analyzing the experimental results, it was found that a region where flow impinges reaches the periodically fully developed condition in a relatively long distance from the channel entrance compared with a region where flow recirculates. The thermal field in the channel investigated became periodically fully developed after three flow turns. The numerical model underpredicted the average heat transfer coefficient and the friction factor by 17% and 27%, respectively. By numerical simulation, correlations for the average Nusselt number and the friction factor were developed. It was found numerically that heat transfer is more sensitive to the Reynolds number in a high Prandtl number fluid than a low Prandtl number fluid. The maximum values of the heat transfer enhancement and the friction factor increase were found in the channel with relatively small undulation height (1 through 1.5 times of the channel width).