【正文】 ? singlephase (both shellside andtubeside)。 ? baffles。 ? channel cover。 ? tubes。 here we focus on the application of these correlations for the optimum design of heat exchangers. A followup article on advanced topics in shellandtube heat exchanger design, such as allocation of shellside and tubeside fluids, use of multiple shells, overdesign, and fouling, is scheduled to appear in the next issue. Components of STHEs It is essential for the designer to have a good working knowledge of the mechanical features of STHEs and how they influence thermal design. The principal ponents of an STHE are: ? shell。 shellside design, including tube layout, baffling, and shellside pressure drop。 data needed for thermal design。 畢業(yè)設(shè)計 (論文 )外文資料翻譯 原 文 題 目： Effectively Design ShellandTube Heat Exchangers 原 文 來 源： Chemical Engineering Progress February 1998 學(xué) 生 姓 名： 學(xué) 號： 所在院 (系 )部： 機(jī)械工 程學(xué)院 專 業(yè) 名 稱： 過程裝備與控制工程 1 Effectively Design ShellandTube Heat Exchangers To make the most of exchanger design software, one needs to understand STHE classification, exchanger ponents, tube layout, baffling, pressure drop, and mean temperature difference. Thermal design of shellandtube heat exchangers (STHEs) is done by sophisticated puter software. However, a good understanding of the underlying principles of exchanger design is needed to use this software effectively. This article explains the basics of exchanger thermal design, covering such topics as: STHE ponents。 classification of STHEs according to construction and according to service。 tubeside design。 and mean temperature difference. The basic equations for tubeside and shellside heat transfer and pressure drop are wellknown。 ? shell cover。 ? channel。 ? tubesheet。 and ? nozzles. Other ponents include tierods and spacers, pass partition plates, impingement plate, longitudinal baffle, sealing strips, supports, and foundation. The Standards of the Tubular Exchanger Manufacturers Association (TEMA) (1) describe 2 these various ponents in detail. An STHE is divided into three parts: the front head, the shell, and the rear head. Figure 1 illustrates the TEMA nomenclature for the various construction possibilities. Exchangers are described by the letter codes for the three sections —for example, a BFL exchanger has a bon cover, a twopass shell with a longitudinal baffle, and a fixedtubesheet rear head. Classification based on construction Fixed tubesheet. A fixedtubesheet heat exchanger (Figure 2) has straight tubes that are secured at both ends to tubesheets welded to the shell. The construction may have removable channel covers (., AEL), bontype channel covers (., BEM), or integral tubesheets (., NEN). The principal advantage of the fixedtubesheet construction is its low cost because of its simple construction. In fact, the fixed tubesheet is the least expensive construction type, as long as no expansion joint is required. Other advantages are that the tubes can be cleaned mechanically after removal of the channel cover or bon, and that leakage of the shellside fluid is minimized since there are no flanged joints. A disadvantage of this design is that since the bundle is fixed to the shell and cannot be removed, the outsides of the tubes cannot be cleaned mechanically. Thus, its application is limited to clean services on the shellside. However, if a satisfactory chemical cleaning program can be employed, fixedtubesheet construction may be selected for fouling services on the shellside. In the event of a large differential temperature between the tubes and the shell, the tubesheets will be unable to absorb the differential stress, thereby making it necessary to incorporate an expansion joint. This takes away the advantage of low cost to a significant extent. Utube. As the name implies, the tubes of a Utube heat exchanger (Figure 3) are bent in the shape of a U. There is only one tubesheet in a Utube heat exchanger. However, the lower cost for the single tubesheet is offset by the additional costs incurred for the bending of the tubes and the somewhat larger shell diameter (due to the minimum Ubend radius), making the cost of a Utube heat exchanger parable 3 to that of a fixedtubesheet exchanger. The advantage of a Utube heat exchanger is that because one end is free, the bundle can expand or contract in response to stress differentials. In addition, the outsides of the tubes can be cleaned, as the tube bundle can be removed. The disadvantage of the Utube construction is that the insides of the tubes cannot be cleaned effectively, since the Ubends would require flexibleend drill shafts for cleaning. Thus, Utube heat exchangers should not be used for services with a dirty fluid inside tubes. Floating head. The floatinghead heat exchanger is the most versatile type of STHE, and also the costliest. In this design, one tubesheet is fixed relative to the shell, and the other is free to ―float‖ within the shell. This permits free expansion of the tube bundle, as well as cleaning of