They say you can’t teach an old dog a new trick, but sometimes you can upgrade your dog. Innovations, such as twisted tubes, expanded metal baffles, graphene-coated surfaces, and more are improving heat exchanger and condenser performance, making some upgrades worth considering.
Shell-and-tube heat exchangers have been around longer than anyone reading this article. The heat exchanger offers many advantages. It can be used in condensing, boiling, or single-phase applications; it can be utilized over a wide range of pressures and temperatures; it can be constructed from a variety of materials to meet corrosion and other design requirements; maintenance is fairly simple and straightforward; and it can accommodate various physical orientations.
However, there are some limitations to the design. The conventional shell-and-tube heat exchanger contains baffles on the shell side to provide support and direct flow through a circuitous course across the tubes. The downside is that low-flow areas, or dead zones, result in the vicinity of the baffles where fouling can occur, corrosion can go unchecked, and heat transfer is reduced. The directional changes caused by the baffles also consume energy, and the shell-side pressure decrease can be significant. The classic design is also prone to flow-induced tube vibration, which can ultimately result in failure.
Reinventing Heat Transfer
With these problems in mind, it’s not surprising that engineers have continued to conduct research to enhance the shell-and-tube design, resulting in new technology that improves heat exchanger performance, counteracts fouling problems, saves space, reduces cost, and increases efficiency. One group that is leading the way in this effort is Heat Transfer Research Inc. (HTRI).
Based in Navasota, Texas, HTRI is a research and software development company that tests various exchanger types and heat transfer surfaces. Its staff conducts application-oriented research on equipment and uses these proprietary data to develop methods and software for the thermal design and analysis of heat exchangers and fired heaters. Its research includes physical testing, computational fluid dynamics, and flow visualization.
“HTRI has and continues to investigate new commercialized exchanger types such as plate and shell or helical baffle exchangers,” said Joe Schroeder, senior vice president of technical programs for HTRI.
In the helical baffle heat exchanger that Schroeder mentioned, quadrant-shaped plate baffles are placed at an angle to the tube axis in a sequential arrangement to create a helical flow pattern. The helical flow design improves thermal effectiveness, enhances heat transfer, reduces pressure loss, lessens fouling, and significantly reduces vibration concerns. One manufacturer of the helical style, CB&I, says the design is well proven with more than 1,800 of its HELIXCHANGER heat exchangers in operation worldwide.
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