Heat exchangers are important devices that are used in a variety of industries. As their name indicates, these devices transfer heat in order to accomplish various tasks and create specific conditions. Fuel oil heaters and hot water storage tanks are just two types of devices that function due to having a heat exchanger.
The Heat Transfer Process
The Second Law of Thermodynamics describes how a heat transfer occurs between two fluids. Per this law, heat is only able to flow from hotter to cooler fluids. In order for this transfer to take place, the two fluids need to be at different temperatures and come into thermal contact. This process involves convection in each fluid and then conduction through the wall that separates them.
These devices work by transferring heat between the following types of substances:
- Between two or more fluids
- Between a solid surface and a fluid
- Between solid particulates and a fluid
The Three Types of Heat Exchanger Configurations
There are three different types of heat exchangers. Each one of these tends to be used for a specific purpose:
- Parallel-flow or counterflow configuration
- Cross-flow configuration
- Shell-and-tube configuration
In some circumstances, fluids only need to pass each other once to accomplish a heat transfer. This is referred to as a single-pass heat exchanger. Under other circumstances, fluids need to pass each other more than once. This is referred to as a multi-pass heat exchanger.
Parallel-Flow Heat Exchangers
With parallel-flow heat exchangers, there is one fluid on the tube side and one on the shell side. These are often referred to as shell-and-tube heat exchangers. Both of the fluids will flow in the same direction with this type of heat exchanger. When these fluids enter the heat exchanger, they will do so from the same end. These fluids will also possess a substantial difference in temperature.
Cross-Flow Heat Exchangers
In cross-flow heat exchangers, there is one fluid that will flow through tubes and another one that will pass around the tubes in a perpendicular manner.
Plate and Frame Heat Exchangers
The plate and frame heat exchanger uses metal plates in order to transfer heat between two different fluids. Given this, the plate and frame heat exchangers tend to be more popular than conventional heat exchangers because the fluids come in contact with a larger surface area as they flow over the plates.
The Importance of Regular Maintenance
As with all devices, regular maintenance is necessary in order to ensure that equipment functions optimally. In some instances, corrosion can pose a significant concern. This can obviously wear down parts, which need to be replaced. The shell portion of the heat exchanger, for example, will usually last for over 40 years unless it becomes corroded or is otherwise damaged.
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