In many conventionally designed heat exchangers, efficiency is limited due to a small temperature difference at the heat exchange surface. For instance, in a shell and tube exchanger, liquid usually flows through the tube. The outer layer of liquid has greater exposure to the walls of the tubing, therefore it experiences higher heat transfer than liquid in the core and can form a barrier, sharply inhibiting thermal exchange. This can happen for a variety of reasons, but low velocity is the most common one.
To maximize efficiency in these applications, one option Campbell-Sevey can recommend is the use of static mixers or turbulators within heat exchangers.
A static mixer consists of a rod with mixer elements, such as half-circle discs, to agitate the fluid. The flow of liquid is directed radially toward the pipe walls and back to the element, regardless of velocity. As a result, fluids are completely mixed to eliminate differences in temperature and improve thermal transfer.
One notable element to consider when adding static mixers is that pressure drop will be higher. The team at Campbell-Sevey can help you determine how that may affect your system based on your process.
Twisted Tape Turbulators
Twisted tape turbulators are a cost effective way to enhance the heat transfer in the tubes for some of these applications as well. Unlike a static mixer, twisted tape turbulators are thin, flat metal sheets in a helical shape. They are inserted into the tubes and break up the laminar flow of fluids, enhancing heat transfer efficiency.
The larger the temperature difference is at the heat exchange surface, the more efficient the heat exchanger is, and the smaller the heat exchanger can be, reducing capital cost. Additionally, whether you use static mixers or twisted tape turbulators, both can help extend equipment life by eliminating hot and cool spots that can cause thermal stress.
For more information on improving your system and heat exchanger efficiency, contact the team at Campbell-Sevey.