Heat exchanger tube sheets for challenging operations
Tube sheets are used to provide a termination for the tubes within the heat exchanger, while maintaining the design pressure and providing a flat and resealable surface to locate the removable headers. They are generally rectangular or circular in form and, with intermediate supports and fin material, they align the tubes within the heat exchanger.
Learn more about how the different types of heat exchanger tube sheets are used.
What is a tube sheet in a heat exchanger?
A tube sheet in a heat exchanger is a plate with holes drilled in at optimal positions. Tubes then pass through these holes. The tube sheet holds the tubes in place within the heat exchanger to ensure effective heat transfer.
In shell and tube heat exchangers, two plates support the tubes, one on each end. Fluid passes through the tubes while a second fluid (coolant) flows within the shell surrounding the tubes.
Tube sheet types
Heat exchanger engineers can design tube sheets in different ways to support specific and challenging operations.
Fixed tube sheet heat exchangers
Fixed tube sheets are perhaps the most ‘standard’ form of tube sheet. They are used when there are no harsh or challenging operating conditions. It describes straight tubes that are fixed to the shell at both ends.
Double tube sheet heat exchangers
Double tube sheets are used in operations when it’s vital that the substances in the heat exchanger don’t mix. They prevent cross-contamination by providing a void between the two tube sheets in which the leaking substance can evacuate the heat exchanger. This is paired with a detector in the leakage path to raise an alarm.
With a single tube sheet design, the tube-to-tube join at the sheet can allow small amounts of contamination between the tube-side and shell-side fluids. There is no known joining method which completely eliminates the risk of contamination, so instead, heat exchangers that must avoid contamination use a double tube sheet.
A double tube sheet, as it sounds, includes two tube sheets. In the event of a leak, the tube-side fluid collects between the two tube sheets, instead of leaking into the shell where the shell-side fluid is contained.
There are a wide range of operations in which this could be vital.
In some countries, it’s the law for heat exchangers in power plant condensers to use double tube sheets. It prevents the coolant, which often contains a lot of impurities, contaminating the condensate. This could otherwise lead to serious chemical reactions, risking the safety of the plant.
Double tube sheets are also commonly used in generators for marine environments. For example, in submarines.
Floating tube sheets
Floating tube sheets, sometimes referred to as a floating head, have one end fixed to the shell while the other ‘floats’ freely.
This form of heat exchanger tube sheet is important where the product undergoes dynamic temperature changes. This could be a heat exchanger that has a cycle of hot and then cold mediums.
Temperature changes can cause the tubes to expand or shrink. Where both ends are fixed, the pressure on the metal could cause leaks or damage. A floating design prevents stress on the joints by allowing for shrinkage and expansion.
It’s also helping in industries that process substances which leave sediment or other build up. In a floating tube sheet design, the tube bundle can be removed for cleaning or inspection.
Floating tube sheet applications
Floating tube sheets are the most common form of tube sheets used in heat exchangers.
Heat exchanger tube sheets are an essential element, particularly in shell and tube designs. Different designs can help the heat exchanger to function in more challenging operating environments. They can reduce the risk of contamination, adapt to dynamic temperatures or allow for easier cleaning and maintenance.
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