Heat Transfer During Drop Impact Onto a Heated Solid Substrate

The present paper addresses the theoretical and experimental study of a liquid drop impacting onto a solid heated substrate. The experiments encompass the measurement and evaluation of the instantaneous substrate and contact temperatures, for different impact conditions and various thermodynamic properties of the liquid and target. Initial surface temperatures are varied from the ambient temperature up to slightly above the boiling temperature of the liquids (T_W0max = 120°C), for different surface materials, covering significantly different wall effusivities, thus allowing to validate the model for extreme conditions. The theory is based on the remote self-similar analytical solution of the Navier-Stokes equations in the spreading drop coupled with the energy equation, which allows obtaining a theoretical solution for the flow field and temperature field in the liquid region. An explicit analytical expression is proposed for the contact temperature, which is expressed, not only through the thermal effusivities of the solid and liquid materials and their initial temperature, but also depends on the Prandtl number. The theory predicts a constant value of the contact temperature in the phase when the thermal boundary layer is thinner than the thickness of the lamella. The model is validated by comparison with the experimental data. The agreement is rather good despite the fact that no adjustable parameters are introduced in the model.