ABSTRACT
Our consideration of convective transport has so far been limited to cases where the «ow „eld is laminar. Most transport operations involve not laminar but turbulent «ow. The reason behind this is simple: transport coef„cients in turbulent «ow are often an order of magnitude or more larger than the corresponding coef„cients for laminar «ow. This difference can be traced to a difference in the structure of the laminar and turbulent boundary layers. Unfortunately, we still cannot solve turbulence equations analytically, and numerical solutions are even more dif„cult to obtain than solutions for laminar «ow over spheres and cylinders. Thus, our knowledge of the turbulent boundary layer’s structure is still largely experimental. In this chapter, we will discuss how we represent turbulent «ow, the difference between turbulent and laminar boundary layers, and how this difference leads to changes in the values of the transport coef„cients.
