Heat Transfer Enhancement in Dimpled Tubes

Heat transfer is directly proportional to the surface area and the temperature difference. While temperature difference is restricted by the application, so the surface area per unit volume is the only parameter which controls the heat transfer rate. As device having higher surface area per unit volume as compared to conventional channels is frequently used. With the development of variations in the field of fluid flow and heat transfer are increasing. Heat transfer enhancement can be achieved through dimpled tubes. This is an interesting technique in order to obtain more compact and efficient equipment. Tubes with artificial roughness obtained by providing dimples on the external tube surface are competitive in comparison to performance and cost of other enhanced techniques currently employed in turbulent flow. By using dimpled tubes heat transfer is enhanced compared to regular tubes. Enhanced tubes can be used for many applications such as Boilers, evaporators, condensers, Heaters, oil radiators and heat exchangers. This work concentrates on experimental investigation of forced convection heat transfer from dimpled tube with varying diameter and depth of dimples. The results of dimpled tube are compared with the tube without dimple. In the present investigation, heat transfer and hydrodynamics analysis of enhanced heat transfer tube with circular dimples was carried out. The dimples are disposed to form a certain specified depth on tube. Experimental tests were carried out with heating air on the entry side with a constant flow rate. This work accomplished by performing an experimental and numerical investigation using two different types of dimples: 1) circular (spherical) dimples with 4 mm diameter and 4mm depth with inline arrangement, 2) circular (spherical) dimples with 4 mm diameter and 4mm depth with staggered arrangement, 3) circular (spherical) dimples with 8 mm diameter and 4mm depth with inline arrangement and 4) circular (spherical) dimples with 8 mm diameter and 4mm depth with staggered arrangement Dimples were placed on periphery of copper tube with diameter of 4mm and 8 mm with depth of 4 mm. For those configurations the average heat transfer coefficient and Nusselt number ratio were determined experimentally. For circular dimples, heat transfer enhancements (relative to a plain tube) were observed for Reynolds number range from 5000 to 12000.