Abstract

The present research is aimed at improving the knowledge and understanding of the physical processes that control heat transfer across the solid-fluid interface, which is very important in order to develop efficient heat exchangers. To achieve this objective, the research has been divided into three phases, which investigated the fundamental physical phenomena from different aspects. The first phase provided the first detailed investigation of the impact of different wall roughness on the turbulent properties in a smooth channel. The results show the different wall roughness has significant effects on the mean streamwise velocity and Reynolds stress distribution. For other turbulent properties, the enhancement was observed near the rough wall, however, it was restricted to the inner region. The second phase provided the first quantitative comparison of the mean and turbulent properties in the presence and absence of wall heating under same operating conditions. The results show that both mean and turbulent characteristics are affected by wall heating. The results also showed that an originally laminar flow becomes turbulent with the addition of heat. However for an originally turbulent flow, addition of heat reduces the magnitudes of the mean streamwise velocity and turbulent properties. The third phase provided the first detailed comparison on the turbulent characteristics with and without a baffle. The results showed a significant enhancement of all turbulent characteristics in the region downstream of the baffle. These results demonstrate that higher turbulence produced by a baffle would be responsible for the enhanced heat transfer rate at the wall