Finned-tube heat-exchanger costs

The least costly way to add such a cooler is to transfer the heat from the rinse sump to the ambient air via a small external finned-tube heat exchanger. 

Figure 10-144. Approximate relationship of the overall coefficient fouled, and the fouling factor of inside tubes for predicting the economical use of finned tubes in shell and tube units. (Used by permission Williams, R. B., and Katz, D. L. Performance of Finned Tubes and Shell and Tube Heat Exchangers, 1951. University of Michigan. Note For reference only, 1950 costs.)...

Low-fin tubes (Mfi-in-high fins) provide 2.5 times the surface per lineal foot. Surface required should be divided by 2.5 then use Fig. 11-41 to determine basic cost of the heat exchanger. Actual surface times extra costs (from Table 11-14) should then be added to determine cost of fin-tube exchanger. 

Design an air-cooled heat exchanger to cool water under the following conditions. The design ambient air temperature is 35°C (95°F). The tubes to be used are steel tubes [thermal conductivity = 25 Btu/ (h)(ft2)(°F), or 43 W/(m)(K)] with aluminum fins. The steel tube is 1 in (0.0254 m) outside diameter and 0.834 in (0.0212 m) inside diameter. The inside heat-transfer coefficient and the fouling coefficient hs are each 1000 Btu/(h)(ft2)(°F) [5680 W/(m2)(K)]. Heat-exchanger purchase cost is 22 per square foot for four-tube-row units, 20 per square foot for five-tube-row units, and 18 per square foot for six-tube-row units. 

Double pipe heat exchanger c/s inside c/s with inner tube finned. Total area bare tube area = 5-10 1. Increase in area by selection of fins and tube length. Duplication of units not allowed in this correlation. FOB cost 30000 at 3 total heat transfer area, n = 0.14, range 0.1-20. L+M = 2.57. L/M = 0.35-0.37. Alloy FOB factors in c/s outside jacket c/s X 1.00 s/s X 1.85-2.65 unfinned central s/s tube X 2.1. Alloy FOB factors for tubes and jacket s/s X 5.5. Pressure factor 6 MPa X 1.10 7 MPa X 1.25. 

Separate externai superheater. This is most desirable in cases where a large amount of superheat is needed. Superheaters are often made with finned tubes, which give a less costly heat exchanger than one with bare tubes for this duty. 

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