Forced convection
In forced convection heat transfer, heat transfer coefficient depends on Reynolds’s and Prandtl number. The correlations are of the form

(8)

 is mass flux , m and n are exponents The following correlation is useful for turbulent flow through the pipes,

(9)

(10)

In correlation 9, Reynolds’s number is calculated by mass flux. In the absence of a relation between a physical property of the fluid and temperature, the fluid properties may be evaluated at the average temperature of the fluid.
It is to be noted that there are several empirical correlations available for the convective heat transfer coefficients. The reader must make sure that the experimental conditions of a correlation match with the conditions of the problem before use of a correlation.

Radiation

Heat transfer by radiation occurs in the form of electro –magnetic waves of various wave lengths. We are concerned primarily with flow of heat through gas filled spaces, and specifically with rate of heat exchange between two surfaces.
Stefan’s Boltzmann law states that rate of radiation of heat from a surface is proportional to the fourth power of the absolute temperature. Radiation is the principle mechanisms of heat transfer in high temperature fuel fired furnaces.
The emissive power of a black body  is according to Stefan-Boltzmann  

(11)