×
The submission system is temporarily under maintenance. Please send your manuscripts to
Go to Editorial ManagerBoth surface extension and nanofluid methods were used to enhance the heat transfer in a double pipe heat exchanger under turbulent flow conditions. Aluminum oxide nanoparticles were used with different concentrations(0.6-3 g/l)in hot water to increase the heat transfer rate on smooth tube and circular fins tube for a range of Reynolds number4240-19790. The simulation was also performed to predict the heat transfer coefficient and temperature profile for selected conditions in which COMSOL Multiphysics is used. The experimental results revealed that the heat transfer enhancement by both circular fin and nanofluid exhibited an increasing trend with Reynolds number and nanofluid concentration. The conjoint effect of Al2O3 of 3 g/l concentration and circular fin provided largest heat transfer enhancement of 53% for the highest Re investigated. Simulation results showed reasonable agreement with the experimental values of heat transfer coefficient. The simulation showed that the presence of nanofluid on finned surface influenced the temperature profile indicating the increased heat transfer rate.
The process of increasing the heat transfer coefficient, resulting in enhancing system efficiency, is known as heat transfer enhancement. Enhancing heat transport is both economically beneficial and a considerable energy conservation problem. To improve heat transfer, many passive components are utilized within tubes, including wire plugs, enhanced surfaces, rough edges, twisted tape inserts, and liquid additives. This study evaluated twisted tape inserts, which are highly effective passive devices. Considering its numerous advantages, such as effortless maintenance, uncomplicated operation, and straightforward production. The twisted tape inserts within the tube generated a vortex and swirling flow. The interior convective heat transfer process is significantly improved. A summary of various twisting tape additives that can boost performance.
Numerical and experimental investigation on the turbulent enhancement convective heat transfer inside slot and plain dimples tubes with internal twisted tape were performed in this study. An experimental rig was constructed and instrumented to evaluate the heat transfer enhancement and pressure drop at this surface. Air was used as working fluid, and steam was used as a heating source where constant wall temperature condition of (135C?) was achieved. Heat transfer and pressure drop data were obtained from four configuration tube. The test facility was capable for providing turbulent flow with Reynolds number varied from 4000 to 15000. Thermal and hydrodynamic flow pattern was numerically studied using commercial code FLUENT15. The average heat transfer of the experimental results was in good agreement with the numerical ones. The result depict that the slot dimple tube with twist tape and plain tube with twist tape give high enhancement in heat transfer relative to plain tube due to increase in area of heat transfer. The average enhancement ratio for slot dimple tube with (TR =4 and 8) are (1.204 and 1.202) respectively .This indicates that 15.5-20.4% of heat transfer area can be saved at the same pumping power for present cases configuration compared with the plain tube heat exchanger.
Numerical and experimental investigations were carried out on the effect of the vortex generators on the flow field and heat transfer from duct heaters. The flow Reynolds number ranging from 32000<Re<83000 with a constant heat flux of 43.09426._x000D_ In the numerical investigation, Fluent package (6.3) was used to solve the steady, (3-D), continuity, momentum and energy equations where the standard (k-?) model was used to remedy the turbulent effects. Theoretical results show that the presence of VGs would save 27% of heaters power. The effects of two areas of VGs were looked at a small circle cross section vortex generator (SCCSVG) and a big circle cross section vortex generator (BCCSVG) of similar shapes (where)._x000D_ The experimental results showed that there were an enhancement in heat transfer with the presence of VGs and heat transfer depends on VGs’ areas. The BCCSVG was the better one of enhancing heat transfer by (2.76%-4.11%). Additionally, the increase of area of VGs, number of rows for VGs and the distance between each two rows of VGs and the heaters are the most effective parameters in improving the performance of heat transfer.