Fork-shaped constructal fin array design a better alternative for heat and mass transfer augmentation under dry, partially wet and fully wet conditions

Abstract

In actual practical situations, the evaporator fins of refrigeration and air-conditioning apparatuses may operate under dry, fully wet or partially wet conditions. Thus in the present study, the optimum design of an array of constructal fork shaped fins operating under partially wet conditions has been determined by using a linear variation of the humidity ratio of saturated air with the corresponding fin surface temperature. The point of separation between the dry and wet portions may be located either in the stem or branch part of the fin and hence, two cases having different governing equations and boundary conditions are analysed in the current study. The optimisation study is done by maximising the total heat transfer rate of the fin array and un-finned surface and the constraints are imposed in such a way that fin material limitations, minimum fin gap requirements as well as space limitations in the radial direction are taken into account. For obtaining the optimum condition, a swarm based meta heuristic algorithm called Firefly algorithm has been employed. Arrays of fork-shaped fin having two and three numbers of branches are analysed in the present study and a comparative study is done with the rectangular fin array. For more compact evaporators, it would be more preferable to select the fin array that results in larger optimum heat transfer rate as well as that having a smaller total length of each fin. An important finding is that the array of fork–shaped fins with two branches give higher optimum heat transfer rate than that from the rectangular fin array in all the cases of different operating conditions. However, no advantage with respect to either higher optimum heat transfer rate or smaller fin length is obtained when the number of branches of fork shaped fins is increased from two to three.