A General Mills yogurt processing plant in Murfreesboro, Tenn., needed to cool propylene glycol brine for use in different parts of the plant. The company evaluated several evaporator options, including shell-and-tube and shell-and-plate heat exchangers. The plant initially installed twin parallel shell-and-plate exchangers because of the relatively small amount of refrigerant required to charge the circuits. However, due to regulatory and operational issues, the facility later decided to replace the heat exchangers with shell-and-tube units. The decision presented a significant challenge: How could the company get shell-and-tube heat exchangers, which are typically much larger than shell-and-plate exchangers, to fit within the existing limited space?
Enhanced Tube DesignThe plant owner wanted a compact system that would perform efficiently and require a low ammonia charge. Conventional flooded shell-and-tube units with prime-surface carbon steel tubes were too large. After evaluating a number of different vendors and equipment options, the company chose Isotherm Inc., in Arlington, Texas, to develop an effective solution.
Isotherm designed a system that uses various kinds of enhanced tubes along the height of the tube bundle.
“These tubes also have internal ’turbulators’ - twisted tape inserts with a specific pitch that are designed to enhance the inside of the tube,” Ayub said. “This type of tube has shown good nucleate boiling behavior in the presence of strong convective forces.”
By using the enhanced tube design, engineers were able to create an efficient evaporator that fit within the plant’s designated confined space and required a low refrigerant charge, comparable to that of the two original shell-and-plate evaporators.
Isotherm Inc., Arlington, Texas, manufactures heat transfer equipment for refrigeration, petrochemical and industrial process applications. For more information, call (817) 472-9922; visit www.iso-therm.com; e-mail firstname.lastname@example.org.