Lesson 4 - Convection

Finally, we can bring it all together and introduce the equation for the rate of heat transfer by convection.

Recall that for heat transfer by conduction we used Fourier’s equation:

Fourier’s equation can be applied to heat transfer across the boundary layer between the solid and fluid interface and the bulk fluid in steady state conditions. In conduction, we had resistance to heat flow governed by the thermal conductivity, k, the thickness of the layer, B, and the temperature difference.

The film heat transfer coefficient we just described considers the thermal conductivity and thickness of the boundary layer, as well as the geometrical shape of the heat transfer environment and fluid flow parameters. Therefore, we can write for convection a modified Fourier equation applied to heat transfer across the boundary layer between the solid and fluid interface and the bulk fluid:

Where

q is the rate of heat flow, measured in Js^-1(W) 

A is the surface area, measured in m² 

h is the film heat transfer coefficient in Wm^-2K^-1

T_w is the temperature of wall or pipe, measured in K 

T_∞ is the bulk temperature of the fluid past the boundary layer, measured in K 

Later in this lesson, we will look at an example using this equation.