The effect of liquid phase temperature and concentration on gas ‒ droplet cooling efficiency

•A thermodynamic approach to describe experimental data on the efficiency of film cooling with gas-droplet jets has been developed under the assumption that the temperature and vapor concentration are constant in the vicinity of the adiabatic wall.•Using the values of the total enthalpy of the vapor‒gas‒droplet mixture, experimental data on thermal efficiency were generalized in a wide range of initial conditions.•The efficiency of surface cooling by two-phase jets is significantly (3‒5 times) higher than by the single-phase ones even at relatively low contents of liquid droplets (∼2% by weight) at the inlet. Experimental data on the efficiency of a gas-drop cooling on an adiabatic wall at various temperatures of the external flow and concentrations of the liquid phase were analyzed. Air was used as a gas phase; water was used as a liquid phase. A model for generalization of the measurement results, based on the constancy of temperatures and concentrations of components near the adiabatic wall, as well as the state of vapor phase saturation, is proposed. The distribution of the vapor concentration near the wall is studied, and a generalization of the experimental data on a change in the components of the vapor‒gas‒droplet mixture with variations in temperature and concentration conditions at the inlet is obtained using the asymptotic approach. The parameter of thermal efficiency of cooling, recorded by means of the total enthalpies of the vapor-gas and liquid phases on the wall, in the gap and in the flow core, taking into account the heat of phase transition, allowed generalization of the experimental data in the framework of the asymptotic approach of the Kutateladze – Leontiev theory of film cooling. The obtained relationships on component concentration and efficiency of a two-phase wall jet allow us to evaluate the thermal state of surfaces when they are protected by gas-droplet curtains. It was found that the thermal efficiency parameter of the two-phase curtain can be 3–5 times higher than in the single-phase cooling regime with a relatively low mass content of the droplet phase in the wall film, not exceeding 2% by mass. The obtained relations for the concentration of components and effectiveness of a two-phase wall jet make it possible to estimate the thermal state of surfaces protected by the gas-droplet cooling.