Parallel Flow Heat Exchangers
In general, parallel flow heat exchangers considered less efficient than counter flow heat exchangers in terms of transferring heat from one fluid to another. However, there are applications where parallel flow has its benefits, such as when limiting the transfer of heat is recommended.
Another advantage if parallel flow heat exchangers are used is that outlet temperature of the fluid being cooled can reach a limiting temperature. If water is kept above 32 deg F, freezing can be avoided.
While parallel flow arrangement can be beneficial, under certain conditions that reduce the limiting temperature, channeling problems can occur or freeze may be caused at shutdown.
Thus, parallel flow in heat exchangers minimizes the chance of freezing or channeling, but does not eliminate the possibility of either. Adding supplemental heat is recommended to solve these problems.