Heat Exchanger Tutorial using ANSYS CFX: Here
A heat exchanger is a device used to transfer heat between two or more fluids. The fluids can be single or two phase and, depending on the exchanger type, may be separated or in direct contact. Devices involving energy sources such as nuclear fuel pins or fired heaters are not normally regarded as heat exchangers although many of the principles involved in their design are the same.
In order to discuss heat exchangers, it is necessary to provide some form of categorization. There are two approaches that are normally taken. The first considers the flow configuration within the heat exchanger, while the second is based on the classification of equipment type primarily by construction. Both are considered here.
Classification of Heat Exchangers by Flow Configuration
There are four basic flow configurations:
- Counter Flow
- Cocurrent Flow
- Hybrids such as Cross Counterflow and Multi-Pass Flow
Figure 1 illustrates an idealized counterflow exchanger in which the two fluids flow parallel to each other but in opposite directions. This type of flow arrangement allows the largest change in temperature of both fluids and is, therefore, most efficient (where efficiency is the amount of actual heat transferred compared with the theoretical maximum amount of heat that can be transferred).
In current flow heat exchangers, the streams flow parallel to each other and in the same direction as shown in Figure 2. This is less efficient than countercurrent flow but does provide more uniform wall temperatures.
Crossflow heat exchangers are intermediate in efficiency between countercurrent flow and parallel flow exchangers. In these units, the streams flow at right angles to each other as shown in Figure 3
In industrial heat exchangers, hybrids of the above flow types are often found. Examples of these are combined crossflow/counterflow heat exchangers and multi pass flow heat exchangers. (See for example Figure 4)
Figure 4. Cross/counter flow.