AUGMENTATION OF HEAT TRANSFER DURING CONDENSATION OVER FINNED TUBES

Abstract

The surface condensers are widely used in the refrigeration and air-conditioning, petro chemical and process industries, thermal and atomic power plants and allied industries. Many augmentation techniques, to improve the vapour to coolant heat transfer rate, have been reported in literature. These techniques can reduce the size of condensers in a significant manner. A thorough review of literature shows that the enhancement in condensing side heat transfer coefficient will augment the heat transfer in the surface condensers. The heat transfer coefficient can be enhanced many folds by the simple technique of providing integral-fins over the tube surface. Therefore, an experimental investigation has been planned and carried out to study the augmentation of heat transfer by enhancing the condensing side heat transfer coefficient and heat flux during condensation of the saturated vapour of steam, refrigerant R-12 and R-134a over 14 horizontal tubes including 11 integral-fin tubes with different fin geometries. R-134a is a new environment friendly refrigerant with thermo-physical properties closer to those of R-12. R-134a has zero ozone depletion potential and ten percent global warming potential in comparison to R-12. Hence, R-134a is seen as a suitable replacement of R-12. The investigation was initiated by acquiring data for the condensation of steam, R-12 and R-134a over a plain tube in two experimental set-ups(set-up #1 for steam and set-up #2 for R-12 & R-134a). The results for the condensation over a plain tube established the integrity of each of the experimental set-up. The plain tube results are also used as reference data for the comparison of the performance of other finned tubes.