Introduction to Food Engineering

Heat Exchangers

Learning Outcomes

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

1. conduct an energy balance on a tubular heat exchanger
2. derive an expression to determine rate of heat transfer in a tubular heat exchanger
3. to calculate log mean temperature difference between two fluids flowing in a tubular heat exchanger

In this module we will learn about heat transfer in a tubular exchanger, one of the most used equipment in food processing plants. In designing tubular heat exchangers, we encounter two important types of calculations: know how much heat transfers from one fluid to another, and what length of a heat exchanger is required to accomplish a certain amount of heat exchange. In the next video, we will conduct an energy balance on a tubular heat exchanger to determine the amount of heat exchange between two fluids.

In the previous video, we obtained energy balance in a tubular heat exchanger. Next, we will derive an expression to calculate the rate of heat exchange between two fluids flowing in a heat exchanger. This type of heat exchanger can be operated under two different flow conditions, either both fluids flowing in a concurrent (parallel) direction, or in countercurrent direction. The mathematical development will help us understand how the term log mean temperature difference appears when we want to determine the rate of transfer between the two fluids.

Log mean temperature difference (LMTD) is a new concept introduced in this module. To get improved understanding of this concept, in the next video, we will work through numerical examples for different flow conditions in a tubular heat exchanger.

Recap

We learned how to conduct an energy balance between two fluids flowing in a tubular heat exchanger. To design a tubular heat exchanger, we often need to calculate its length. We learned how a mathematical expression for the rate of heat transfer in a tubular exchanger is obtained. We determined log mean temperature difference for concurrent (parallel) and countercurrent flow heat exchangers.