Boundaries for heat transfer deterioration onset in supercritical pressure channel flows

Heat transfer deterioration could affect heated channel flows of supercritical pressure fluids in a number of technological applications. Aim of the present study is to provide an indication for the boundaries of the phenomenon onset and to investigate its dependence on the pressure, for three light hydrocarbons: methane, ethane and propane. To reach this goal a parametric numerical analysis is carried out on uniformly heated straight channels varying the species, the inlet reduced pressure, and the enforced heat flux. A parabolized Navier-Stokes solver is used to carry out the simulations, together with Helmholtz energy equation of state and accurate models for the transport properties. Results lead to an unambiguous definition of the threshold value for the ratio between heat flux and specific mass flow rate which identifies the boundary for heat transfer deterioration onset. On the basis of this definition, a correlation for the threshold parameter in terms of reduced pressure is presented for the considered species.