EFFECT OF TUBE-TAPE CLEARANCE ON HEAT-TRANSFER FOR FULLY-DEVELOPED TURBULENT-FLOW IN A HORIZONTAL ISOTHERMAL TUBE

This paper presents the effect of tube-tape clearance on the heat tran sfer for a fully developed turbulent flow in an isothermal tube. Tests were performed on 15 different tapes; they include 3 twisted tape rat ios each with five different widths. Results have demonstrated that as the tube-tape clearance decreases, the heat transfer enhancement incr eases. For the case of twist ratio of 3.6, the tape widths have result ed in almost 17% difference in the enhancement. On the other hand, for the cases of twist ratios of 5.4 and 7.1, the enhancements were 9% an d 4%, respectively. For practical design of thermal systems, operating under turbulent flow condition, small twist ratio and tight-fit tape are desirable in order to obtain a reasonably high heat transfer enhan cement. The heat transfer for twist ratio of 3.6 and loose-fit tape sh ows nearly the same enhancement as the case of the tight-fit tape for the same twist ratio. Such behavior indicates the presence of an optim um tape width, and such width is a function of the twist ratio and Rey nolds number.