Abstract
The most desirable feature in any thermal equipment is the enhancement of heat transfer. Heat transfer is basically a slow process and is enhanced by adopting passive or active methods of enhancement. In passive enhancement methods, heat transfer is increased without demanding any external power source; while in active method, enhancement in heat transfer demand external power. In this work, a passive enhancement method is proposed and tested to check the extent of heat transfer enhancement noticed. A tube in shell heat exchanger is designed with circumferential fins attached along the length of tube and a spiral insert running inside the tube. One fluid is made to flow inside the tube under the influence of twisted tape and the shell side fluid is running around the tube continuously provoked by fins. Therefore, the hot and cold fluids were estimated to exchange more heat because of thorough mixing initiated in their flow paths. In this work, analysis was made in CFD package by creating a model that simulates experimentations observed in the literature. The results of experiments and results of CFD analysis were compared. Noticing the agreement between the results, the CFD model is given enhancements like circumferential fins and twisted tape to check the enhancement in heat transfer. The velocity and temperature contours were observed at various flow conditions (Reynolds numbers). Based on results of analysis, thermal performance factor is also estimated to check the increment in heat transfer with reference to hydraulic (or flow) parameters.
Highlights
Heat exchangers are used in different processes ranging from conversion, utilization & recovery of thermal energy in various industrial, commercial & domestic applications
Variation of friction factor with Reynolds number in the tube fitted with twist tape and the plain tube are depicted in friction factor graph
It shows that twist tube inserts in a heat exchanger yields higher pressure drops compared with plain tube, because of additional disturbance increases the tangential contact between secondary flow and wall surface of the tube
Summary
Heat exchangers are used in different processes ranging from conversion, utilization & recovery of thermal energy in various industrial, commercial & domestic applications. The need to increase the thermal performance of heat exchangers, thereby effecting energy, material & cost savings have led to development & use of many techniques termed as Heat transfer Augmentation. Saha and Dutta [1] investigated on circular tube with different configurations of inserted tapes of short length, full length smoothly varying pitch & regular spaced twisted tapes for water as working fluid They observed twisted tape is effective in laminar flow. Wang and Sunden [11] [worked on twisted tape in circular tube water as working fluid, their experiment results both inserts effective in enhancing heat transfer in laminar region compared with turbulent flow; twisted tape has poor overall efficiency if pressure drop is considered. They found large number of turns may yield improved thermo hydraulic performance compared with single turn
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