Performance of series connected heat exchangers with liquid circuit on loop.

The series connected heat exchangers - configured either as an arrangement of gas-gas,gas-liquid or liquid-liquid heat exchangers- are widely used in the process industry andair-conditioning where they can be found in a variety of heat (cool) recovery, in heating andcooling applications. The design of heat exchangers follows the conventional designprocedures for compact heat exchangers, and involves computation of excanger dimensionsto yield a prescribed heat exchanger efficiency and pressure drops for fluid streams.This paper describes a procedure for calculating the performance of series connectedheat exchangers, when heat tranfer fluid has been looped between heat exchangers. The heatexcanger system consists of heat (cool) recovery heat exchanger(s), pre-heater(s) or precooler(s) and a main heat exchager to heat or to cool a main stream to the aim temperature.The heat excangers are connected with the looped fluid circuit. The connecting fluid flow ratehas to be determined to achieve optimum heat or cool recovery.The following considerations has to be almost always made when the heatexchangers is designed for the application,- Heat transfer requiremments- Costs- Physical size- Pressure drop characteristicsIn the main stream the heat transfer requirements for temperatures must be met in theselection or design of any heat exchanger. The way with which the requirements are met,depends on the relative weights placed on costs, physical size or pressure-dropcharacterristics. Economic plays a key role in the design and selection of heat exchangerequipment, and the engineer should bear this in his mind when embarking on any new heattransfer design problem.For the used heat exchangers the presented procedure gives the looped fluid flowrate, with which the best possible heat recovery efficiency is achieved. In the other hand theprocedure gives the performances for heat exchangers to achieve the end temperature of themain stream.