It has to be calculated on cold and hot side, as the value can be different. Therefore, it is significant to manage the pressure drop during thermal design of the exchanger. Why Measuring the Pressure Drop is Crucial for Heat Exchangers. The pressure drop across a shell and tube heat exchanger is mainly a function of the heat exchanger structure and shell & tube arrangement. With. If during the course of thermal design, calculated pressure drop is far more than the allowable pressure drop, the pressure drop becomes a … Generally, heat exchangers are one of those devices where change if pressure is very very negligible compared to the operating pressure in which they are working. Generally, pressure drop in heat exchanger is because of two reasons, 1. ΔP = Pressure drop through the exchanger, per side (Pa) ΔP channel = Pressure drop through the exchanger channels, in between each plate (Pa) ΔP collector = Pressure drop in the inlet/outlet ports of the heat exchanger (Pa). If your referring to how to measure a pressure drop from inlet to out let this is done utilizing pressure gauges at each point.