Forced Convection Heat Transfer for Turbulent Flow in a Square Duct with a Rough Wall. Characteristics of a Mean Temperature Field.

Abstract

This paper presents experimental results about a mean temperature field obtained in forced convection heat transfer for a turbulent flow through a square duct with a rough wall. The local Nusselt number on the smooth walls of the rough duct was 1.71∼1.97 times that of the smooth-walled duct. Distributions of the local wall heat flux clearly reflected the secondary flow pattern in the duct. In a half cross section including the smooth wall opposite the rough wall, the distribution of the mean temperature was similar to that of the primary flow velocity. The existence of a temperature inner-law was confirmed there. However, the inner-law did not exist in the half section including the rough wall. In this region, dissimilarity appeared between the distributions of the mean temperature and the primary flow velocity. Based on the transport equations of Reynolds stress and turbulent heat flux, the mechanism of the heat transfer enhancement by the rough wall was examined.