Transfer characteristics of two-row plate fin and tube heat exchanger configurations

The heat-mass transfer analogy, in conjunction with the naphthalene sublimation technique, was used to investigate the transfer capabilities and transfer mechanisms in two-row plate fin and tube heat exchanger configurations. Local and average transfer coefficients were determined from measurements of the mass transferred in an analogical system consisting of a pair of naphthalene plates and an array of spacer disks. The analogical system modeled a typical heat exchanger flow passage. The results were presented in dimensionless form to facilitate their conversion to Nusselt numbers. Different transfer mechanisms were found to be operative on the portions of the fin which are respectively associated with the first and the second rows of tubes. For the portion associated with the first row, the two factors which provided high mass-transfer rates were the boundary layer on the forward part of the fin and a vortex system which develops in front of the tubes. On the other hand, for the portion of the fin associated with the second row, there is no boundary-layer regime, and it is the vortex system alone which is responsible for high transfer rates. At higher Reynolds numbers, the influence of the second-row vortex system is sufficient to cause a near equality in the transfer capabilities of the first-row and second-row fin surfaces.