Study of Heat Transfer of a Concave Surface of Short Annular Channels under Impact Jets

By means of physical and mathematical modeling, convective heat transfer and resistance of an annular channel under jet air impingement on the outer concave surface were investigated. It has been established that, in the studied ranges of variation of geometric and mode characteristics, heat transfer and aerodynamics of short annular channels are determined by the dimensionless parameter A_f, which is the ratio of the total area of the blowout holes to the area of the blown surface. To ensure uniform heat transfer on the concave surface of the channels, it is advisable to use internal perforated pipes with a value of the parameter A_f less than 0.01, and to control heat transfer and intensify it in the required zones, it is possible to use pipes with its higher values. The resistance coefficient of the device decreases with increasing parameter A_f and increases slightly with decreasing Reynolds number. An equation has been obtained for calculating the average heat transfer over the surface, the dimensionless total pressure drop in the device, and the total resistance coefficient in the following ranges of variation of mode and geometric parameters: Re = 873–19.7 × 10³, A_f = (0.94–42.57) × 10^–3, S/d_c = 3.49–24.92, and h/d_c = 4.5–8.1. Assessment of the heat exchange device using the energy efficiency coefficient showed that its optimal value is observed at values of the parameter A_f approximately equal to 0.035–0.040.