Evaporation of a water layer under local non-isothermal heating

Abstract

• Water layer evaporation under local heating was investigated. • Gas convection effect was several times greater than diffusion and buoyancy of vapor. • Local heating allowed achieving high values of the heat transfer coefficient. • Obtained results were important for the development of new methods of heat exchange enhancement. The evaporative behavior of a water layer and the heat transfer under local heating were investigated. Non-stationary and non-isothermal heat exchange conditions were created by laser heating. The thermal field on the free surface of the layer was registered using thermal imaging technology. Changes in the liquid mass due to evaporation were determined using the gravimetric method. The key factors affecting water evaporation were estimated and the characteristic heat fluxes associated with evaporation, radiation and convection are compared. The effect of free convection in the gas phase on the evaporation rate of the water film is several times higher than the effect of diffusion and buoyancy of vapor. The local heating allowed achieving high values of the heat transfer coefficient and heat fluxes at considerably smaller liquid temperatures and heating area, which is advantageous from an energy point of view. The obtained results were important for the development of new methods of heat exchange enhancement, as well as for the prediction of heat fluxes and hydrodynamic flows and evaluation of non-isothermal, non-stationary and inhomogeneous heat exchange.