Paper 1: Natural Convection in the Supercritical Region

Abstract

In the region just above the thermodynamic critical point, the thermodynamic properties vary rapidly with small changes in temperature. The rapid variation of the physical properties exerts a strong influence on the natural convection heat transfer process. Relatively large heat transfer coefficients are experienced in this region.

Consideration of the fundamental equations involving conservation of mass momentum and energy has led to the establishment of a set of significant parameters to be considered in this problem. The derivation is essentially an extension of the work of Sparrow and Gregg (I) and is more adaptable to actual solution of the general variable property problem.

The technique allows for variation in density, specific heat, viscosity, and thermal conductivity. An important step in the development is the use of thermodynamic relationships to obtain derivatives of properties with respect to temperature. A demonstration of the technique is made for Freon 114 using a Martin (2) equation of state along with Sutherland and Bromley equations for viscosity and thermal conductivity, corrected for pressure (3) (4). The use of a reference temperature in the variable property problem is critically discussed.