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عنوان مقاله [English]
"Shell and tube heat exchanger with helical baffles" is one of the new technologies used to improve the performance of common heat exchangers with segmental baffles. Although the advantages and efficiencies of these baffles are known well and they have been used in many developed countries, however, scientific and technical information concerning them have rarely been published.
In this article, after introducing some present technologies to improve the performance of shell and tube heat exchangers, the advantages of using helical baffles are pointed out. Then some relations for computation of correction factors of heat transfer and pressure drop coefficients are presented on the basis of developed method of Bell-Delaware. It is shown that the product of two correction factors of the "change in the cross flow characteristics" and "the turbulence enhancement", at about a 42-degree angle, reaches the maximum value about 1.4.
By using those relations and on the basis of Rapid Design Algorithm, a relation is presented for helical baffles that relate the heat transfer coefficient directly to pressure drop and heat transfer area. Design method is presented by using of this relation.Finally a comparison is made between helical and segmental baffles in an industrial unit, and the effects of application of tube inserts are studied. In comparison with a unit with segmental baffles, it is found that the heat transfer coefficient was 36% higher and pressure drop was 10% lower in a system with helical baffles.