Numerical Study On Turbulent Convective Heat Transfer Of N-heptane Under Supercritical Pressures

A general numerical scheme, which incorporated accurate transport and thermodynamic property calculations based on a modified corresponding-state method and the fundamental thermodynamic relationships with the Soave-Redlich-Kwong (SRK) equation of state, was developed in this paper. A comprehensive numerical investigation of the turbulent convective heat transfer with a typical hydrocarbon fuel, n-heptane, under supercritical pressures, a physical process closely related to engine cooling technique in rocket and hypersonic propulsion systems, was systematically conducted. The present fundamental numerical study focuses on the effects of many key parameters, including the inlet pressure, inlet velocity, wall heat flux, and the inlet fluid temperature, on the supercritical heat transfer processes. Results indicate that under supercritical heat transfer processes, heat transfer deterioration could occur once the wall temperature or the fluid temperature in a large near-wall region reaches the pseudo-critical temperature, and increasing the fluid pressure would enhance heat transfer. Since the ratio of Grashof Number and the Reynolds number square is very small, it's concluded that the influence of buoyancy force could be ignored under the investigated condition. Variations of the Nusselt number were further elucidated and compared with those obtained from the available empirical formula. The conventional empirical Gnielinski expression could only be used for supercritical heat transfer predictions of n-heptane under very limited operational conditions. It is found in the present numerical study that a supercritical heat transfer expression for CO2, H2O, and HCFC-22 applications can generally be employed for predicting the supercritical heat transfer coefficient of n-heptane when the inlet velocity is higher than 10 m/s.