Graphical Solution to Heat Transfer Coefficient

Rating heat exchangers without the use of a computer is time consuming, because it must always be done on a trial and error basis. The task is even more tiresome if the rating method in question is a laborious step-by-step computation, as is required for the correct results. 

A graphical method has been developed which allows prediction of the overall heat transfer coefficient within a limit of 3%. This suggested short cut will, in many instances, make a laborious calculation unnecessary. 

DIRECTIONS FOR USE Line 1 Connect values on w and t scales ith a straightedge. Line 2 Pivot straightedge about point of intersection of Line 1 with the uncalibrated line and connect with tube-size scale. Result is read where Line 2 intersects the hi scale. 

EXAMPLE Determine the coefficient of heat transfer referred to rae externol tube surface when 2,000 Ib./hr. of water at 80° F. flow ide a 1 O.D., 16 BWG tube. 1—Connect w = 2,000 and t = 80 F. with Line 1. 2—Pivot Line 1 about its intercept on uncalibrated line r til it intersects 1 O.D. 16 BWG. 3—Read hj=497. 

This velocity rise increases the average value of the shell-side coefficient, as could be expected. Furthermore, the small leakage rate at a large baffle spacing improves the heat transfer conditions to a certain extent. The increase of the heat transfer coefficient, however, is remarkably constant for very different kinds of fluids and for different shell diameters. 

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