Heat exchangers selection criteria

Note 1 The vendor shall notify the purchaser if the criteria for minimum temperature rise and velocity over heat exchange surfaces result in a conflict. The criterion for velocity over heat exchange surfaces is intended to minimize waterside fouling the criterion for minimum temperature rise is intended to minimize the use of cooling water. The purchaser will approve the final selection. 

Given the large variety of process heat transfer problems and the heat exchanger configurations available, the engineer must select a type and design that satisfy several criteria. These are listed approximately in the order of their importance, though in any individual case one criterion or another may move up or down in the list of relative importance. 

But with the establishment of thermoeconomic isolation plus the use of the correction factors mentioned above, minimization of the cost per transfer unit Yx becomes a precise criterion. It has already been shown above how the optimum value of the length and diameter of the tubes is obtained—as well as the optimum number of tubes per pass. Further synthesis of such heat exchangers results from minimizing YXrfAoptfUopt with respect to material and geometric selection factors. 

Criteria for selection of a molten salt for transport of heat should inelude criteria to assure ehemical plant safety. In most cases, this criterion is not expected to have a significant impact on the choice of molten salt. The transport of heat imposes two technical criteria on the choice of the salt (1) thermally stable at very high temperatures and (2) compatible with the materials of construction used for piping and heat exchangers. These criteria require selection of fluoride salts that are thermodynamically very stable. This required characteristic also makes exothermic chemical reactions with chemical process reagents unlikely in practical systems. 

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