Individual Tube Transfer Coefficients in a Segmentally Baffled Shell and Tube Exchanger

Abstract

A review of the literature pertaining to shellside heat transfer coefficients in segmentally baffled cylindrical shell and tube heat exchangers has been made. It is shown that this work has dealt mainly with bundle average transfer coefficients and these studies have been correlated to give empirical equations which allow similar exchangers to be designed yet do not predict the effect of the geometric parameters on the flow distribution. A review of the literature relating to work carried out on heat exchangers using a mass transfer analogy has also been made. It is demonstrated that the mercury mass transfer analogy is the best of the methods so far developed for this approach. Following the work of Williams (2) and Haggart (6), a reliable system of renewing a mercury transfer surface in situ has been developed. This transfer surface has been installed in an exchanger similar to that used by Williams but employing air instead of nitrogen as the shellside fluid, and the results obtained from this exchanger are compared with the results of Williams. The exchanger was of 5 ¼ I.D and consisted of 80 tubes of 3/8” O.D.. Baffles were manufactured to give cut downs of 18.4%, 31%, and 43.7% of the shell diameter at a baffle spacing of 3.86”. Gaskets were employed to prevent tube-to-baffle and baffle-to-shell leakage. A completely new analysis, using statistical methods where appropriate, has been made of the results of Bergelin et al. (1) and Williams (2) with particular reference to the individual tube results obtained by Williams. The results of this analysis are presented in the form of tube groups which are independent of flowrate, and from this, it is shown that the 31% baffle cut down gives the most even transfer of the three baffle cut downs studied.