Heat Transfer Coefficient Distribution of W and Broken W Turbulators at High Reynolds Numbers

Abstract

An experimental and numerical study of the convective heat transfer enhancement provided by two rib families (W and Broken W) is presented, covering Reynolds numbers (Re) between 300,000 and 900,000 in a straight channel with a rectangular cross section (AR = 1.29). These high Reynolds numbers were selected for the current study since most data in the available literature typically pertain to investigations at lower Reynolds numbers. The objective of this study is to assess the local heat transfer coefficient (HTC) enhancement (compared with a smooth channel) and the overall thermal performance, taking into account the effect of increased roughness on the friction factor, of a group of W-shaped turbulators over a wide range of Reynolds numbers. Furthermore, the effects of increasing the rib spacing on the thermal performance of the Broken W configuration are presented and discussed. The numerical results are compared against heat transfer measurements obtained using the transient liquid crystal (TLC) method. The research shows that for the Broken W turbulators, increasing the Reynolds number is associated with an overall decrease of the thermal performance while the thermal performance of the W configuration is relatively insensitive to Reynolds number. Nevertheless, the Broken W configuration delivers higher thermal performance and heat transfer compared with the W configuration for the range of Re investigated. The Broken W configuration with a pitch spacing of 10 times the rib height was shown to provide the optimal thermal performance in the configurations investigated here.