Heat exchangers are essential equipment common in almost all industries. They work by exchanging heat between two fluids, gas or liquid, through a conductive barrier. While the heat exchanger works, these fluids do not come into contact physically. Due to continuous application, there has been a growing urge to develop and improve the effectiveness of heat exchangers.
It has led to a wide range of experiments and investigations to help increase the heat transfer rate while decreasing the cost and size of the industrial apparatus. Therefore, heat exchanger manufacturers in India have come up with double-pipe heat exchangers. This type of heat exchanger has gained much popularity, all thanks to its range of uses and simplicity. But what is it that makes these heat exchangers so unique? Here is a comprehensive guide.
What Are Double Pipe Heat Exchangers?
These are a type of heat exchanger with two pipes, a large and small pipe inside it concentrically. The heat transfer process in this heat exchanger occurs inside the larger pipe. One fluid flows through the inner part of the small pipe while the other fluid flows between the two pipes; thus, the inner pipe acts as a conductive barrier. The shell side of this heat exchanger includes the fluid flow, which passes on the tube side or the inner side.
The double pipe heat exchanger is also popularly known as jacketed u-tube, hairpin, pipe in the pipe and jacketed pipe exchanger. While they can contain a bundle of pipes, the outer pipe must have a diameter of less than 200mm. Sometimes, when there is a need to increase the heat transfer rate between the working fluids, there are longitudinal fins in the inner tube.
The Working Mechanism Of Double Pipe Heat Exchangers
The inner pipe contains the hotter flow, while the outer pipe contains the cold flow. However, that isn’t always the case, the placement of these fluids can sometimes change, but the results remain the same. The double pipe heat exchangers work through conduction. That is when the heat from one flow transfers to the inner pipe wall. This pipe wall is made of a conductive material like aluminium or steel. The flow system in double pipe heat exchangers is counterflow. It means that its fluids move in opposite directions.
These heat exchangers’ design and flow system make them ideal for increased heat transfer coefficient. Moreover, they can also work in a parallel flow system where both fluids flow in the same direction. However, counterflow is usually the most thermally effective.
Double pipe heat exchangers can handle high temperatures and pressures because they can freely expand and have a simple construction. That is why most process equipment manufacturers in Maharashtra use them. When in counterflow, these heat exchangers can also experience temperature cross. That is when the cold flow’s outlet temperature is hotter than the hot flow’s. In some cases, this can be advantageous, while in others, it might not. However, it is worth noting that their other counterparts, like plate heat exchangers, cannot achieve this.
Advantages Of Double Pipe Heat Exchangers
Double pipe heat exchangers are the easiest designs to fabricate, repair and add on to any place. All thanks to their simple design. As a result, they have some unique advantages over some of the most complicated heat exchangers on the market. Some of these advantages include the following:
- They have standardized parts due to their popularity. Thai allows for easy repairs and parts sourcing.
- They can easily handle high temperatures and pressure.
- They have the most flexible designs, allowing for the removal or addition of components.
- They have a small footprint with little maintenance space while maintaining excellent heat transfer.
- Their design allows for more thermal expansion without an expansion joint.
Disadvantages of Double Pipe Heat Exchangers
While this heat exchanger stands out with an excellent heat transfer system, it also has some downsides worth noting:
- The pipes are difficult to clean without disassembling the entire heat exchanger and are easily fouled.
- They have limitations to lower heat transfer duties compared to the other designs.
- They can easily leak, especially when paired with more units.
- Their counterflow system restricts specific applications.
Specifications And Applications
Several custom double pipe heat exchangers are on the market to help meet the various applications and satisfy industrial projects. While using this heat exchanger, it is essential to know the fluid types. The viscous fluid should always be on the shell side because of the availability of space for flow. Therefore, if steam is used as one of the fluids, it’s vital to use pipes for flow.
Before choosing the type of heat exchanger, it’s better first to determine the project specifications. It would be best if you defined the required heat transfer and the inlet and outlet temperatures. All these specifications will help design the perfect pipe pairs for the heat exchanger. While the double pipe heat exchanger design is pretty simple, it would cost more to increase the surface area. Some typical applications of these heat exchangers include the following:
- Sewage treatment
- Heating and cooling in process engineering processes
- Petroleum refining
- Compressors and boilers due to their high temperatures and pressure.
Double pipe heat exchangers have the simplest designs and are perfect for high-temperature and pressure applications. Therefore, they are used in several applications as the first choice for several projects. Moreover, they can serve in both counterflow and parallel flow systems.