Excel templates work well for calculation of forced convection heat transfer coefficients, typically based on correlations of Nusselt number in terms of Reynolds number and Prandtl number. Forced convection occurs when a fluid moving past a solid surface with the fluid and the solid being at different temperatures. Newton's Law of Cooling is a simple expression for the rate for convective heat transfer: Q = hA(Ts - Tf), where the parameters are:
- Q = rate of forced convection heat transfer (Btu/hr - U.S. or W - S.I.)
- Ts = the solid temperature (oF - U.S. or oC - S.I.)
- Tf = the fluid temperature (oF - U.S. or oC - S.I.)
- A = the area of the surface that is in contact with the fluid (ft2 - U.S. or m2 - S.I.)
- h is the convective heat transfer coefficient (Btu/hr-ft2-oF - U.S. or W/m2-K - S.I.)
The most difficult part of forced convection heat transfer calculations is typically determination of a good value for the heat transfer coefficient, h. The most common way of determining the heat transfer coefficient for a particular forced convection application is through a correlation for Nusselt number (Nu) in terms of Reynolds number (Re) and Prandtl number (Pr). The definitions of these three dimensionless numbers are shown in the box at the right, where:
- D = characteristic length (diameter for pipe flow)
- V = characteristic fluid velocity
- k = thermal conductivity of the fluid
- rho = density of the fluid
- mu = viscosity of the fluid
Excel spreadsheets to calculate forced convection heat transfer coefficients for several common physical configurations are available at our downloads page.