Shell and tube heat exchangers are one of the most popular types of heat exchangers used in industries today due to their efficiency in adjusting the temperature of substances. They are versatile in that they can handle different materials, they are easy to clean, and come in a variety of sizes and applications. A shell and tube heat exchanger uses a cylindrical shell with bundles of tubes in its interior. The fluid inside the shell exchanges heat with the fluid inside the tubes without ever touching or mixing.
How the parts of a heat exchanger are arranged and utilized will depend on the temperature, pressure, and types of fluid. Choosing high-quality parts and the proper design for a specific function will ensure maximum efficiency for the heat exchanger. Design options include straight or U-tube, single or double tubesheet, fabricated or machined channels, and more. To know more about these options, read on.
Tubesheet Design in a Shell and Tube Heat Exchanger
Enerquip’s tubesheets are round, flat plates made from stainless steel (304L or 316L) or other alloys, including duplex, AL6XN and Hastelloy. Holes for the tubes are drilled into the tubesheets. The primary function of tubesheets is to support the tubing and isolate them. Since tubesheets are in contact with both fluids on the shell side and the tube side, they must have corrosion resistance and be sealed tightly to prevent fluids from gaining contact.
Because quality matters, we handle each tube-to-tubesheet joint with care. We roller expand tubes into grooved tubesheets. Typically, tubesheets less than 1.5” thick receive single sealing grooves and those thicker are double-grooved.
The tube-to-tubesheet joints can also include seal welding or strength welding when requested.
Once the tubes are seal welded in place, the tubesheet face is polished (if required) to the specified finish for enhanced stability and contamination prevention.
In order to protect against the potential of cross contamination from the shell side utility fluid and tube side process fluid, double tubesheet designs are a good option. What’s the difference between a single tubesheet and double tubesheet design? Keep reading.
Double and Single Tubesheet Designs
In a double tubesheet design, a second outer tube sheet is added to further seal and separate the tubes and the shell. The gap between the tubesheets allows for differential radial thermal expansion, minimizing stress on the tube-to-tubesheet expansions. The gap also allows for easy leak detection.
In a single tubesheet design, leakage from between the tubesheet and the tubes can occur, leading to cross-contamination of process and utility fluids. In a double tubesheet design, in the event of a leak in a tube-to-tubesheet joint, shell-side fluids would flow out into the gap between the two tubesheets, instead of leaking into the channel. Leaks can easily be detected and fixed sooner.
Standard Practice for Pharmaceutical Manufacturing
Enerquip exchangers are fabricated with multiple measures to ensure proper hygienic design and production. All our pharma grade exchangers are made with double tubesheets to minimize the risk of cross-contamination of process fluids between the shell and tubes. The gap between the tubesheets helps to minimize stress on the tube to tubesheet expansions and allows for leak detection.
Pharmaceutical units also include roller expanding and seal welding of the tube-to-tubesheet joints on the face of the outer tubesheet per ASME BPE. The roller-expanded and seal-welded surfaces are then polished to the specified finish for all the wetted surfaces.
Double Tubesheet Design Applications
Double tubesheets are crucial for the safe operation of many heat exchanger applications. In recent years, power plant condensers have even made use of double tubesheet designs. And water treatment facilities use double tubesheets to prevent contamination of their treated and demineralized water from the raw water they used in their condenser steam space.
Both straight tube and U-tube style heat exchangers can utilize the double tubesheet design for added safety and security.
Straight Tube – This type of heat exchanger uses tubesheets that are either welded directly to the shell or floating inside the shell. In a welded construction, an expansion joint may be necessary to allow for differential thermal expansion between the tubes and shell.
U-Tube – As the name indicates, the tubes inside the shell are u-shaped. The tubes start at the top of the tubesheet, make a u-shaped bend, then come back to the bottom. The U-tube design does not require an expansion joint because the tube bundle is free to expand or contract.
The ability of thermal regulating equipment like heat exchangers, condensers and immersion heating devices to heat and cool substances efficiently and safely make them an indispensable tool in industrial processes. Choosing the right equipment to fit your production operations will help greatly in ensuring your process and product quality.
More from the Enerquip Blog
- Pharmaceutical-Grade Shell & Tube Heat Exchangers from Enerquip
- Heat Exchanger Material Selection based on Common Criteria
- Five Important Qualities to Look for in Pharmaceutical Process Equipment
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- Preventing Cross Contamination in Your shell and tube heat exchangers
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