PRINCIPLE OF UNIFORMITY OF TEMPERATURE DIFFERENCE FIELD IN HEAT-EXCHANGER

A principle of uniformity of temperature difference field (TDF) in hea t exchangers is advanced. It states that the more uniform the temperat ure difference field, the higher the effectiveness of heat exchanger f or a given NTU and C-r. Analytical and numerical results on the unifor mity of TDF and effectiveness of thirteen types of heat exchangers sho w the validity of the uniformity principle. Its further verification i s given by the asymptotical solution of TDF in terms of a recurrence f ormula of heat transfer area distribution. The analyses of entropy gen eration caused by heat transfer indicate that the uniformity principle is based on the second law of thermodynamics. Two ways, redistributin g heat transfer areas and-varying the connection between tubes, are pr esented for the improvement of the uniformity of TDF and the consequen t increase of effectiveness for crossflow heat exchangers.