A. Shell and Tube

(by G. F. Hays)

(a) Tube-side Flow

Fluids on the tube-side of a shell and tube heat exchanger have well defined flow paths and uniform velocity, neglecting the end effects at the entrance and exit of the tubes. The tube-side is the easier side of the heat exchanger bundle to clean. Thus, fluids, which are more susceptible to fouling, should preferentially be placed on the tube-side. Traditionally, the fluid, which is at a substantially higher pressure, has been placed on the tube-side regardless of fouling considerations. This is particularly true for gas-liquid coolers, such as compressor intercoolers and aftercoolers. That practice minimizes the initial cost of a new heat exchanger, but may significantly increase the operating cost due to fouling. Compressor intercoolers and aftercoolers are prime examples of this cost differential. Thus, the total cost of ownership is significantly higher when the higher fouling fluid is on the shell-side.

Cooling water is particularly susceptible to fouling from sources, many of which the designer normally cannot predict. Foulant sources may include water chemistry, airborne contamination, process leaks, biomass and suspended matter. Once-through cooling waters are susceptible to macro fouling; such as zebra muscles and debris from the water source. Open recirculating cooling water is most susceptible to micro fouling. Thus, from a fouling standpoint, cooling water should be placed on the tube-side.