In-line finned tube banks are preferred for waste heat recovery applications because they can be cleaned with commercially available on-line soot-blowing methods. However, there is some uncertainty about the heat transfer effectiveness of in-line finned tube banks. It is first demonstrated that the outside heat transfer coefficients of in-line finned tube banks are about 0.7 to 0.8 of those of similar staggered banks if the banks are deep and the Reynolds number is large. It is then shown that the thermal performance of a particular in-line finned tube bank decreases with row number and reaches about 0.25 to 0.35 of the staggered value with seven tube rows. Herein lies the uncertainty. New data are also presented, which show that stagnation regions develop in the wakes behind the tubes in the front rows but do not develop deeper in the bundle. The number of tube rows with the stagnation region decreases with increasing Reynolds number. It is apparent, then, that the heat transfer performance of a particular in-line finned tube bank first decreases with row number, reaches a minimum value that is Reynolds number dependent, and then increases to the asymptotic deep bank value.
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