Comparison of heat transfer characteristics in surface cooling with boiling microjets of water, ethanol and HFE7100

Abstract

The basis of microjet technology is to produce laminar jets which when impinging the surface have a very high kinetic energy at the stagnation point. Boundary layer is not formed in those conditions, while the area of film cooling has a very high turbulence resulting from a very high heat transfer coefficient. Applied technology of jet production can result with the size of jets ranging from 20 to 500μm in breadth and 20 to 100μm in width. Presented data are used in order to validate authors own semi-empirical model of surface cooling by evaporating microjet impingement in the stagnation point. Main objective of this paper was to investigate the physical phenomena occurring on solid surfaces upon impingement of the single microjet in case of three fluids. Intense heat transfer in the impact zone of microjet has been examined and described with precise measurements of thermal and flow conditions of microjets. Reported tests were conducted under steady state conditions for surface cooling by single microjet producing an evaporating film. Obtained database of experimental data with analytical solutions and numerical computer simulation allows the rational design and calculation of microjet modules and optimum performance of these modules for various industrial applications.