HEAT TRANSFER IN GRADIENT TURBULENT BOUNDARY LAYER

Effect of pressure gradient on heat transfer in turbulent boundary layer is constantly investigated during creation and improvement of heat exchange equipment for energy, aerospace, chemical and biological systems. The paper deals with problem of steady flow and heat transfer in turbulent boundary layer with variable pressure in longitudinal direction. The mathematical model is presented and the analytical solution of heat transfer in the turbulent boundary layer problem at positive and negative pressure gradients is given. Dependences for temperature profiles and coefficient of heat transfer on flow parameters were obtained. At negative longitudinal pressure gradient (flow acceleration) heat transfer coefficient can both increase and decrease. At beginning of acceleration zone, when laminarization effects are negligible, heat transfer coefficient increases. Then, as the flow laminarization increases, heat transfer coefficient decreases. This is caused by flow of turbulent energy transfers to accelerating flow. In case of positive longitudinal pressure gradient, temperature profile gradient near wall decreases. It is because of decreasing velocity gradient before zone of possible boundary layer separation.

DESIGN AND STUDY OF EXCHANGERS WITH PRESSURE GRADIENT HEAT INTENSIFIERS

This paper is presented the numerical study of local heat transfer in the turbulent boundary layer with longitudinal pressure gradient. The study is based to free software with open source code (Salome and Code_Saturne) has been based by RANS approach and empirical models of turbulence. Validation of mathematical models and software is based by collation numerical results with the results of experimental study of fl ow characteristics in a turbulent boundary layer of longitudinal pressure gradient and high turbulence intensity (Epik E. Ya., NASc of Ukraine). The validation had a high qualitative coincidence of the fl ow characteristics determined as a result of the simulation with experimental data. We designed two constructive schemes of heat exchangers for air. This study presents a calculation plan for these heat exchangers. Results of the study are showed that the use of gradient heat exchange intensifi ers leads to an increase in the heat transfer coeffi cient from air to 17 %.