Heat transfer control at impinging pulsed gas-drop flow in the regime of evaporative cooling

Abstract

The experimental results on heat transfer when a pulsed multi-nozzle spray flows onto a vertical surface are presented. The behavior of the effective heat transfer coefficient averaged over time and over the entire heat transfer surface has been studied. The experiments were carried out in the regime of evaporative cooling at a constant temperature of the heat transfer surface T_w = 70°C. The duration of pulses for supplying the liquid phase of the spray τ and their repetition frequency F were varied in the experiments within wide limits: τ = 1–10 ms and F = 0.25–50 Hz. In addition, the effect of droplet phase flow rate on heat transfer was studied by changing the pressure in front of the nozzles (ΔP_L = 0.05–0.6 MPa). Preliminary studies have shown that heat transfer during spray impingement onto a surface can be strongly influenced by the co-supply of air due to turbulization of the wall layer and the return of droplets reflected from the surface. It has been established that the main factor determining the intensity of heat transfer when the spray flows onto the surface is the time-averaged mass velocity of the liquid phase. Using this value, generalization of experimental data on the heat transfer coefficient and the thermal efficiency parameter of a pulsed spray was achieved.