ISSN Online: 2377-424X
International Heat Transfer Conference 12
The improved prediction of turbulent convection
Abstrakt
A simple algebraic expression has been devised that predicts without any explicit empiricism the Nusselt number for fully developed turbulent forced convection in round tubes, parallel-plate channels, and circular concentric annuli for arbitrary thermal boundary conditions on the wall(s), all values of Re, and all values of Pr greater than 0.45. A complementary expression for values of Pr less than 1.7 incorporates one arbitrary (empirical) exponent. These two expressions are made up of only four elements: the limiting solution, Nu0, for Pr = 0; a particular solution, Nu1, for Pr = Prt; the asymptotic solution, Nu∞ for Pr → ∞ ; and the parameter, Prt/Pr. Nu0 and Nu1 incorporate some empiricism by virtue of a semitheoretical correlating equation for the
local turbulent shear stress, but the resulting uncertainty in the predicted values of Nu0, Nu1, and Nu is
completely negligible (less than 1%). The greatest uncertainty arises from the necessity of utilizing a
semitheoretical expression for Prt/Pr, but again the resulting uncertainty in Nu is completely negligible (less than 1.5%). A critique is presented for these expressions and their elements in terms of experimental data, numerically computed values, and prior correlating equations.