Heat transfer characteristics of oblique jet impingement liquid film cooling in the forced convection mode

Liquid film cooling by oblique jet impingement is widely used in small liquid rocket engine thermal protection. In this work, heat transfer characteristics of oblique jet impingement liquid film cooling in forced convective mode were experimentally investigated to examine the effect of the impingement velocity and the initial wall temperature. The temperature distribution on the rear surface (opposite to the jet) was recorded by a high-frequency infrared camera, and then the heat flux on the front surface was estimated by solving the inverse heat conduction problem. It was found that the lagging effect by thermal diffusion is nonnegligible and can be well described by the penetration time. In addition, thermal diffusion makes the temperature distribution on the rear surface more uniform than the liquid flow path. In contrast, the heat flux distribution has a clear boundary same as the liquid flow path. The length of the wetting front l_wf can be fitted as l_wf=atⁿ. The constant a and the wetted area A are affected merely by the impingement velocity. The point with the maximum heat flux is located at the impingement point in the forced convective mode rather than the wetting front in the film boiling mode. Inside the liquid film, there is no clear boundary as the film thickness distribution between the thin layer zone and the raised zone, implying the local film velocity determines the heat transfer rather than the film thickness. The cooling power increases with higher impingement velocity and initial temperature difference. The standardization fitting equation shows the effect of the initial temperature difference on the cooling power is more significant than the impingement velocity.