In this article, we will take a deep look at the shell & tube heat exchanger pressure drop, why it is important, how to calculate it and what factors affect the pressure drop.
Shell and tube sides of the exchanger
Shell and tube heat exchangers are very popular and widely used in the process industry, thanks to their versatility. They consist of metal tubes passing through another metal enclosure, which is referred to as the 'shell'.
So in shell and tube exchanger, we have two compartments shell side and tube side for housing either one of the hot or cold fluids on either sides of the exchanger. The fluid allocation on either sides is decided based a few factors such as corrosive or fouling nature of a fluid.
Pressure drop on shell side
It is very common to use baffles in the shell side of shell and tube exchanger. They cause the shell side fluid to go across the tubes. This causes 'cross flow' conditions and promotes the overall heat transfer.
But at the same time, the shell side fluid has to overcome the additional obstacles in the form of the tube bundle. This causes turbulence and excess pressure loss on the shell side of the exchanger.
Some times the turbulence is preferred. For example, it is common to place a more viscous fluid on the shell side. The resulting turbulence helps in an improved heat transfer coefficient on the side of the viscous fluid.
Tube side pressure drop
In contrast to the shell side, flow on the tube side is much better streamlined, hence resulting in minimal pressure drop.
The overall tubeside flow gets divided into a number of smaller tubes. Hence the pressure drop on tube side can be further managed by changing the tube size or increase / decrease the number of tubes. Due to the lower pressure drop on tube side, it is preferable for a service where we have a small allowable pressure drop across the exchanger.
Shell & tube heat exchanger pressure drop calculations
Here are some resources to help you with accurate calculations for pressure drop across a shell and tube exchanger.
- This calculator is for shell side pressure drop calculation. You will need to input basic geometrical details of the shell side construction and fluid properties.
- You can use this calculator to determine tubeside pressure drop. The required inputs are - fluid properties, tube size and length.
Note that the linked calculators are for demo. To access the actual working calculators, you will need to create a login on EnggCyclopedia.
- Tutorial - Heat Exchanger shellside pressure drop calculation
- Tutorial - Heat Exchanger tubeside pressure drop calculation
Factors affecting heat exchanger pressure drop
The pressure drop across a shell and tube heat exchanger is mainly a function of the heat exchanger structure and shell & tube arrangement.
When you are designing a new shell & tube exchanger, you can use the pressure drop calculations to verify that the selected design satisfies your process requirement of allowable pressure drop across the exchanger. Otherwise you can change the design parameters to lower the pressure drop and try again.
Here are some factors that you can adjust to manage the pressure drop across shell and tube heat exchanger.
- When you want to lower the pressure drop on shell side, try increasing the baffle spacing. But keep an eye on how it changes the overall heat transfer rate. Increasing the baffle spacing will lower the heat transfer rate. Here are some more details about optimizing the baffle spacing.
- If you have a very limited allowable pressure drop for one fluid, think of putting that fluid on the tube side. If the other fluid (on shell side) is not dirty or corrosive, this may work very well.
- If you have excess pressure drop on the tube side, try increasing the tube size of adding more number of tubes.