Heat transfer and fluid flow in rectangular fin and elliptic tube heat exchangers under dry and dehumidifying conditions

Experimental and numerical analyses were carried out to study the thermal-hydraulic and mass transfer characteristics of four-row rectangular fin and elliptic tube heat exchangers having a major/minor axis ratio of 2.83. Four types of rectangular finned configurations have been investigated for various inlet frontal velocities ranging from 1 to 6 m/s under dry and dehumidifying conditions: two staggered tube arrangements with fin heights of 7 mm and 10 mm, respectively; and two in-lined tube arrangements with fin heights of 7 mm and 10 mm, respectively. The results indicated that the sensible Colburn factory j_s and the friction factor ∫ for the wet coils are, respectively, 56-71% and 2-16% higher than those for dry coils. In addition, a two-dimensional fin efficiency analysis for rectangular fins with elliptic tubes was presented for a wide range of air relative humidities and Biot numbers. It is shown that the fully wet fin efficiency is lower than that of the dry fin by 20% and 31% with respect to fin heights of 7 and 10 mm.