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Heat Exchanger Basics--Shell&Tube Heat Exchangers
Jul 19, 2017

Heat exchangers are widely used in various plant processes to transfer energy without mixing the related substances. As integral parts of comfort and process heating and cooling applications, they perform efficiently and effortlessly for years. We would like to share a little knowledge about heat exchangers and how they operate and hope it could help their users apply these devices more appropriately and cost effectively.

Each of the major types of heat exchanger: shell&tube, spiral, and plate are described and discussed here.

Shell&tube heat exchangers

The shell&tube heat exchanger is probably the most common type found in industry. It is widely used in the process industries as well as in many types of HVAC equipment. Uses for these workhorses of heat transfer include heat removal in chillers, condensers, and reboilers, process stream cooling, and as critical parts of evaporative cooling and refrigeration systems.

Shell&tube units consist of bundles of round tubes installed in cylindrical shells. Components include the head, tube bundle, and shell. They can be built to any diameter or length. Tube bundles are typically hydrostatically tested. Many are ASME-designated as pressure vessels. The shell is a cylinder of seamless or rolled and welded pipe with a bolting flange at each end. Carefully placed holes in the tube sheets accommodate the tubes. Baffles help create the turbulence needed for heat transfer.

Shell&tube heat transfer technology has remained essentially the same over the years. Most recent developments include enhanced surface tubes that let units achieve approach temperatures of as small as 2-3 deg F. True counterflow construction is now commonly used to avoid heat-transfer limiting pinch points. Finally, some units feature double-wall construction, essentially a second tube within each tube. Double-wall construction offers significant leak protection and safety, though at higher cost.

Equipment comes in many design variations. Straight tube and U-tube configurations are popular. Compact U-tube units save space, feature removable, replaceable bundles, and are more frequently found in HVAC applications (although today some are finding their way into process situations). Fixed, straight-tube arrangements are more often specified in process situations because they can handle higher pressures and are easier to clean mechanically. Among other configurations is the straight tube, floating tubesheet unit, which features a removable tube bundle, a stationary tubesheet at one end, and a floating head at the other end to accommodate differential expansion and relieve stresses.