When Designing helical coil heat exchanger, we usually calculating an adequate surface area to handle the thermal duty for the given specifications. However, Fluild friction effects are equally important in heat exchange system design since they determine the pressure drop of the fluids flowing in the system, and as a result, the pumping power of fan work input necessary to maintain the flow. Provision of pumps of fans adds to the caiptial cost and is a major park of the operating cost of the exchanger. savings in exchanger capitals cost achieved by designing a compact unit with high fluid velocites may soon be lost by increased operation costs. The final design and selection of unit will, therefore be influenced just as much by effective use of the permissible pressure drop and the cost of pump or fan power as they are influenced by the temperature distribution and provision of adequate area for heat transfer.