Calculation of heat transfer on surfaces furnished with various intensifiers is a complex problem in view of their irregular geometrical features and complex flow pattern caused by these features, a circumstance that adds difficulty in obtaining generalized regularities. Prediction of heat transfer under such conditions is based in the main on empirical relationships. The article demonstrates a possibility of theoretically determining the heat transfer coefficient for turbulent flow in channels with a uniform wall roughness. For such flows, it is assumed that the flow has a uniform and settled structure. For a constant heat flux on the wall, the heat transfer can be evaluated using the Lyon’s integral. The profile of flow velocities, thermal sublayer thickness, and turbulent thermal conductivity are the key parameters in evaluating the heat transfer coefficient. In the model, a two-layer representation of the thermal boundary layer consisting of a thermal sublayer and the flow turbulent core was used. It was assumed that the heat transfer in the thermal sublayer took place over the channel cross section entirely through molecular thermal conductivity (the turbulent component was neglected). The turbulent thermal conductivity in the flow core was determined using the Prandtl mixing length model, which is valid for turbulent fluctuations of both velocity and temperature. The mixing length was calculated with taking into account the influence of vortex structures generated by the roughness. By numerically calculating the Lyon’s integral, the heat transfer coefficient distributions have been obtained for the practically significant ranges of the roughness elements relative height and Reynolds number. The prediction results demonstrate good agreement with experimental data on heat transfer for turbulent flow in a tube with threaded roughness.
И.А. Давлетшин (Wed,) studied this question.