Q. What is "Piping Symmetry" and what is its importance?
Piping symmetry involves the concept that all fluid users in a branching parallel piping system will get equal flow rates simply due to the piping design. This means that every branch will split flow equally in all directions. In order to satisfy multiple fluid users, this also will require multiple levels of symmetrical branching. In some cases, this type of design may be simple to accomplish and prove beneficial to the stability of the process, but in many cases the design itself may be cost prohibitive as well as space-prohibitive.
There are some other factors which tend to increase the importance of symmetry. If there is a close temperature differential between the primary and secondary fluids in the heat exchanger, then balanced flow rates through the parallel exchangers is more important. In the same sense, if the system is a low pressure system, then the differential pressures have a much greater impact. Once again, balanced flow rates, and a possible symmetrical design become more important.
In the end, the importance of piping symmetry is going to depend on the piping system in question. If your system is typically steady-state with very little variability, then piping symmetry may eliminate the cost of flow measurement and control. The examples we looked at here were for a simple system with only 4 heat exchangers. But if you had 8 heat exchangers, and had to maintain a symmetrical design, you would have to add a third level of splitting. Even more levels would be required for more exchangers. Now, you would be most likely looking at a cost-prohibitive symmetrical design. So analyze the design requirements of the system before jumping head-first into a symmetrical piping design. You might be able to get equal or even better performance from a carefully planned non-symmetrical design.