Selection of Size and Arrangement

The preliminary surface is calculated by means of equation 16 where  

The first surface selected will be either the same or smaller than the final selection to eliminate the possibility of making a selection that satisfies all conditions but is oversurfaced, a possibility if we started with a larger surface than the final selection. Starting with a smaller surface is accomplished by specifying in the input a which is the maximum acceptable overall heat transfer coefficient. If in doubt about what to specify, use a U that is abnormally high or use the reciprocal of the total fouling factor. 

the surface per exchanger is calculated from equation 17, where  

J Search Standard Tube Count Table For 2 Tube Pass  

Pipe size + thickness TEMA shell I.D. Bundle dia., in. J (20) 

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