Abstract
Enhancements in heat transfer systems are being applied for recovery of heat in domestic as well as industrial applications in many areas. These are done by generating turbulence and swirl motion in the flow by inserting inserts to reduce the thermal resistance of heat transfer. This paper presents the experimental and numerical results of heat transfer enhancement of cooling of a confined space by inserting twisted tape in a pipe buried in concrete under the floor. The Reynolds number is fixed to 15000. Thirteen cases are considered varying the configurations and designs of twisted tapes and the effects of different types of perforations and slots on twisted tapes are studied. Water as the test fluid flowed in pipe inserted with twisted tapes. Heat is transferred from a heating plate to water along the pipe length through concrete to simulate the heat transfer from a room and the water temperature rise is studied. To validate the experimental results, ANSYS-FLUENT is used as the CFD tool with a Standard k-ε turbulence flow model and the SIMPLE algorithm is implemented. Flow physics behaviour is displayed using velocity and temperature profiles inside the pipe. Insertion of twisted tapes shows that the heat transfer is enhanced due to swirling action, friction and turbulence. The experimental differences in inlet and outlet water temperature validated the CFD simulation results. The temperature distribution on a single twisted tape with increasing twist ratio is found to be the most efficient for heat transfer enhancement of the cooling floor surface with a water temperature rise of 1.62 ºC along a pipe length of 1.8 m.
Highlights
Hydronic systems are used for cooling applications in which the roof and floor surfaces are cooled by flowing cold water through pipes
After the analysis of thirteen cases of smooth and augmented pipes, it was found that twisted tape with increasing twist ratio was the most efficient one for heat transfer enhancement
It removes maximum heat from the confined space than others because it has 8.64% more surface contact with water compared to twisted tape with constant twist ratio, and the intensity of swirl flow increases from inlet to outlet
Summary
Hydronic systems are used for cooling applications in which the roof and floor surfaces are cooled by flowing cold water through pipes. Swirl flows are generated with the help of twisted tapes as these flows increase turbulence and heat transfer area and the rate of heat transfer. Most of the practical applications in industries such as cooling and heating devices, heat exchangers, cyclone separators, This paper was recommended for publication in revised form by Regional Editor Liu Yang agricultural spraying machines, diesel and petrol engines, vortex tubes, gasoline engines, furnaces, etc. Use swirl flow generation for improvement in heat transfer. The twisted tape is one of the best examples of swirl flow generation. The geometrical parameters of twisted tapes are needed to study the design of heating and cooling appliances.
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