École Nationale Supérieure de
Techniques Avancées

Abstract

This study deals with the variation of heat fluxes due to a change in prescribed temperatures in a fluid system under natural or forced convection in the particular case of strongly temperature-dependent viscosity. We consider the heat transfer from the fluid load to the cold walls of its container or any cooled immersed structure. Because of the strong increase in viscosity at low temperature, an almost solid layer forms and sticks to the cold walls. This phenomenon appears in particular in glass melting processes in which the heat flux absorbed by the structures and the thermic state of the fluid are determinant in the scaling and design of enduring and fitted melting crucibles. We focus on the understanding of the effect off temperature-dependent viscosity on scaling laws between heat flux and characteristic parameters of the system, using a Vogel-Fulcher-Tammann model for the viscosity. It is shown that the heat flux may, in particular operating conditions, become independent from the prescribed cold temperature of the walls. We also show that an increase in the heating temperature of the fluid load can lead to unusual growth of the heat flux, caused by further fluidizing of the load. Theoretical results are validated by numerical simulations and experimental data.