Choosing Between a Straight Tube and U-Tube Heat Exchanger Design

Designing a Shell and Tube Heat Exchanger

Designing a shell and tube heat exchanger involves considering various factors, such as cost, application, and facility limitations. A key decision in this process is choosing between a straight tube and a U-tube exchanger. The tube design is crucial; selecting an inappropriate design can lead to exchanger damage or fouling, which is hard to clean. Both designs are widely used across industries like food and beverage, chemical, and pharmaceuticals, each with its own pros and cons.

The Tubular Exchanger Manufacturers Association (TEMA) classifies exchangers into types, with the BEU model (U-tube design) and the BEM model (straight tube design) being the most common. These models are identical except for the tube design and the rear bonnet. The B-type front bonnet allows access to the tube sheet for cleaning after removal from the piping and is relatively inexpensive. The E-type shell is a popular single-pass design.

Straight tube shell and tube heat exchangers from Enerquip

Advantages of a Straight-Tube Design

The straight tube design, particularly the BEM model, is simple and versatile, suitable for nearly any industry and application. Some companies may prefer other models for higher efficiency, but the BEM design often works as a substitute.

Straight tube exchangers enable pure countercurrent flow, usually without needing a second exchanger in series. In such cases, an F-type two-pass shell with a longitudinal baffle is preferred over the E-type, as the baffle separates the two streams. Countercurrent flow means the hot and cold streams move in opposite directions, ensuring the hot stream is always warmer than the cold stream throughout the exchanger.

In contrast, cocurrent flow involves the hot and cold streams moving in the same direction, requiring the cold stream to always be cooler than the hot stream. This configuration is less efficient, so many manufacturers avoid it.

Cleaning is another key consideration. Straight tubes are the easiest to clean due to their lack of bends. However, some designs make inspecting and cleaning the shell difficult because the tubes cannot be removed from the shell.

U-tube shell and tube heat exchanger from Enerquip

Advantages of a U-Tube Design

While straight tube designs have many benefits, they can be limited in certain areas, making the U-tube design popular. Although U-tubes involve bending, they require only one tube sheet and bonnet, significantly reducing costs.

Straight tubes are susceptible to damage from thermal expansion, as tubes heating at different rates can harm the tube sheet and shell. An expansion joint can mitigate this issue, but it adds cost. U-tube exchangers, connected to the tube sheet and shell at only one end, allow for thermal expansion without damaging the rest of the machine.

U-tube designs also facilitate easy removal of tube bundles for inspection and cleaning of the shell and the outside of the tube bundle.

If you have questions about the most suitable type of exchanger for your application, contact the experts at Enerquip for advice on the best option to meet your needs.