How to Estimate Heat Transfer Coefficients

Determine if you have convection or forced transfer system. Convection systems allow the heat to "naturally" radiant from hot to cold, while forced transfer systems contain the hot or cold substance under pressure. The two sides of the heat exchanger can be different heat transfer system. For example, a hot water radiator uses forced transfer for the hot water and convection for the air.

Determine the heat transfer coefficients for each substance individually. The best method is to look the values up in a reference table; however, if the exact values are unavailable, you can estimate them based upon air (about 50 W/ m^2 K) and water (about 5,000 W/ m^2 K).

To make an estimate of the overall heat transfer coefficient, first multiply each coefficient by 1, if the substance transfers heat by forced transfer, and by 0.5 if it transfers the heat by convection.

Add the two adjusted coefficients together, then divide by 2 to get the average heat transfer coefficient.

Multiply the average heat transfer coefficient by the heat exchanger's construction material's conductive ratio. A heat exchanger is a device for transferring thermal energy from one substance to another substance. A radiator is a common example. Metals and highly conductive substances can be assumed to have a 100 percent thermal conduction, while more insulating materials, like plastic, will have a lower thermal conduction, in the 85 percent to 95 percent range, depending on thickness.