Aerodynamics and Complicated Heat Transfer with the Mixed Motion of Air in the Flat Duct of a High-Temperature Heat Exchanger

The purpose of the research is to study the aerodynamics and heat transfer in the duct of a high-temperature recuperation system. The object of the research is a flat duct with a thickness-to-height ratio a:b = 1:10, length c = 400·a with one-sided heat input to the duct surface, complicated heat transfer and mixed air movement in the duct. The objectives of the research are to determine: (a) average temperatures on the duct surfaces; (b) air temperature distribution along the length of the duct; (c) local and average integral temperature values along the length of the duct; (d) local and average integral heat flow densities on the duct surfaces; (e) local and average integral heat exchange coefficients and Nusselt numbers on the duct surfaces; and (f) pressure distribution along the length and total pressure drop in the duct. The research method is based on conducting a mathematical numerical experiment in a stationary three-dimensional Cartesian formulation and physical modeling of processes on a prototype. It is established that the dominant heat transfer between the duct walls and the air is a complicated convective heat transfer, in which forced convection is affected by free convection. There is a 1.5–2.0-fold difference in the values of the heat flow density on the hot and non-heated surfaces of the duct. Generalizing dependences of Nusselt numbers, temperature pressures and friction resistance coefficients as functions of a dimensionless coordinate are obtained.