Simultaneous heat transfer enhancement and pressure loss reduction for finned-tube bundles with the first or two transverse rows of built-in winglets

Heat transfer enhancement and pressure loss penalty caused by a single row of winglets built in the first transverse row of tubes, are compared between “common flow up” (“toe-out”) and “common flow down” (“toe-in”) winglet configurations. For the three-row tube bundle in a staggered arrangement, the “toe-in” winglet-pairs bring about 5-15% increase in heat transfer enhancement and 2-10% increase in pressure loss penalty, in comparison with fin-tube bundles without winglet. In the present authors' previous paper [K. Torii, K.M. Kwak, K. Nishino, Heat transfer enhancement accompanying pressure-loss reduction with winglet-type vortex generators for fin-tube heat exchangers, International Journal of Heat Mass Transfer 45 (2002) 3795-3801], “toe-out” winglet-pairs built only in the first transverse row of three-row tube bundle in a staggered arrangement successfully increased heat transfer by 10-30%, and simultaneously reduced pressure loss by 34-55%, for the Reynolds number (based on two times channel height) ranging from 350 to 2100. In the present paper, the front two rows of the “toe-out” winglet-pairs were applied for a three-row tube bundle in a staggered/in-line arrangement, for comparison. Heat transfer and pressure loss in the staggered arrangement were increased by 6-15% and by 61-117%, respectively, in comparison with the case of the single transverse row of the “toe-out” winglet-pairs. The corresponding increases for an in-line arrangement with two rows of winglets were 7-9% and 3-9%, respectively.