### Overall Heat Transfer Coefficient

#### Learning Outcomes

At the end of this module, you will be able to:

- determine thermal resistance due to convective boundary layer
- develop an expression to determine overall heat transfer coefficient
- calculate rate of heat transfer using overrall heat transfer coefficient

In this module, we will first use the concept of thermal resistance for convective heat transfer. This is similar to what we learnt in a previous module for conductive heat transfer.

Knowing how to calculate thermal resistance both due to conduction and convection, we will now examine overall heat transfer when we have both these modes of heat transfer present in a system. For example, to determine the rate of heat transfer from hot water flowing in a steel pipe into the surrounding atmosphere, we follow the path of heat transfer as it encounters: first, convective boundary resistance in the fluid flowing inside the pipe, second, conductive resistance through the steel pipe, and third, convective boundary resistance in air that surrounds the pipe. Thus, the overall heat transfer involves three resistances to heat transfer. In the next video we will learn how to calculate an expression for an overall heat transfer coefficient that involves all three resistances encountered in the path of heat transfer.

Recap

In this module, first, we learnt how to calculate thermal resistance due to convective boundary layer in a fluid. Next, we developed an expression to determine the overall heat transfer coefficient. Overall heat transfer coefficient is the most used parameter when designing heat exchange equipment underscoring the importance of this concept.