The Double-Pipe Heat exchanger Design Calculations formulas

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Heat exchangers can be classified in a number of ways, depending on their construction or on

how the fluids move relative to each other through the device.

Now there will be looked at one particular heat exchanger to go a little deeper into the working principles and the practical utilizations.

A double-pipe heat exchanger consists of two concentric pipes or tubes. The outer tube is called the annulus. In one of the pipes a warmer fluid flows and in the other a colder one.

Due to the temperature difference between the fluids heat is transferred. By the word ‘fluid’ all substances that can ‘flow’ is meant. So the word fluid means not only liquids but also gases. In this part there will be looked at a double-pipe heat exchanger with parallel flow.

This means that the hot fluid and the cold fluid flow in the same directions. There are also counter flow heat exchangers. In this situation the hot fluid and the cold fluid flow in opposite directions.

Schematically a double pipe heat exchanger with parallel flow is drawn in figure.

*A double pipe heat exchanger with parallel flow*

To understand what factors influence the dimensions of this heat exchanger when a certain heat rate is expected some simple equations will be examined.

First a simple heat balance:

The subscript c stands for cold.

But also the next equation is valid: