Study of heat transfer in the stagnation region during spray cooling using the inverse heat conduction method

The solution of the inverse heat conduction problem using the Monte Carlo method, Green's function solution equation and the alternative Green's function solution equation are compared. The Monte Carlo method is a simple technique that provides a method of determining the source of error and placement of sensors. However, in comparison with the exact solution, if attainable, the cost is a higher error in the solution. All the three methods use the function specification method in the sense that a functional form for the surface heat flux or temperature is assumed and the parameters defining the function are evaluated by minimizing the error functional. In the alternative method, the functional form also satisfies the boundary conditions which are the unknown quantities in the problem. The input data for this comparison are experimentally measured temperatures in a stainless steel disk subjected to spray cooling.; Spray cooling using an air-water mixture is studied. There are two distinct heat transfer regimes during spray cooling: the wetted and a dry wall regime. These two regimes are connected by a transition regime. The heat transfer mechanism in the wetted regime is due to evaporation on the surface and forced convection by the air flow, whereas in the dry-wall regime, at high temperatures, radiation plays an important part. At temperatures closer to the saturation temperature of the liquid component, in the transition regime, the heat transfer is due to droplet evaporation near the surface and efficient removal of the vapor by the air flow field. This study focuses attention on the transition regime. It is shown that high heat fluxes can be obtained near the saturation temperature in the transition regime. The stagnation flow field superimposed on the impinging surface efficiently removes the vapor. Higher evaporation rates due to local variation of relative humidity and local variation of saturation pressure in the stagnation region results in high heat transfer rates even when the surface is below the saturation temperature corresponding to the ambient pressure.