What is the effect of the shell-side and tube-side fluid Reynolds number on the thermal efficiency of a shell and tube heat exchanger?
Most heat exchangers are designed for Reynold's numbers above 5000 so you have fully developed turbulent flow. That gives the maximum overall heat transfer coefficient. If you have lower Reynold's numbers in the laminar flow region, then the heat transfer has more effect from conduction than convection and the thermal efficiency is reduced. The good news is that a heat exchanger designed for heat transfer at higher flows will also work well at lower flows at lower Reynold's numbers because the amounts of heat needed at lower flows are also less and you have plenty of heat transfer area to compensate for reduced efficiency.
