CONDENSATION HEAT TRANSFER IN CONCURRENT, STRATIFIED TWO-PHASE FLOW THROUGH HORIZONTAL INTERNALLY FINNED TUBES WITH CONSTANT WALL TEMPERATURE

摘要

In this paper, the condensation heat transfer of turbulant saturated steam in horizontal tubes with radial, internal longitudinal fins has been considered. Saturated steam cocurrently enters the tube as a two-phase flow and stratifies. The effect of interfacial shear stress the axial variation of saturated steam temperature as well as the variation of free surface condensate level at the bottom of horizontal tube and condensate accumulated in the space inter fines, have been determined. The governing equations in the regions such as condensate layer flow over the tube internal surface, condensate flow over the fins themselves, condensate accumulated at the bottom of the tube and the condensate in the space between the adjacent fins have been derived subject to their specific conditions, respectively. The resulting intercoupled equations have been solved numerically by special procedure. Finally to verify the effect of the internal fins upon overall heat transfer coeflicient a case has been considered that the tube has low longitudinal fins arranged in equal angular positions in the periphery of tubes (90°), in which the ratio of the height of the fins to the radious is 0.4. The results of our calculations shows that the heat transfer coefficient increased up to 43% compared with the tube without fins.