Study On The Enhancement Limit Of The Internal Flow And Numerical Simulation To Periodic Convection In Ducts With Modified Flow-Inclining Fins

Because heat transfer enhancement can increase the efficiency, reduce the weight and volume of the heat exchange equipment, it receives much attention from the scientific and technical circles continuously. Many approaches have been employed in engineering to enhance heat transfer. Guo and his co-workers proposed a novel concept for enhancing convective heat transfer which is called the Field Synergy Principle (FSP). The core content of the theory is the correspondence between the heat transfer rate and the integral of the dot product of the velocity and the temperature gradient.In the current study, the limit of the heat transfer rate that corresponds to the all-impinged internal tube flow is first analyzed from the view of the FSP. The comparison of the all-impinged heat transfer and the conventional internal heat transfer has been conducted. The potential maximum enhancing ratio for both the laminar and the turbulent flow is discussed. The analysis reveals that the maximum enhancing ratio is 16.9 for the laminar flow and 3.5 for the turbulent flow at the same Reynolds number. Then, numerical simulations have been conducted to study the convection in 2-D and 3-D channels developed according to the FSP. The velocity fields, the temperature, the flow resistance and the heat transfer characteristics have been obtained and the results have been analyzed. The fin angle ranges from 0°to 30°, and the height of the channel is 14mm, 24mm, and 34mm respectively. Effects of the fin angle and the channel height on the thermal performance have been verified for different Reynolds numbers. In the 2-D channel, the effect of the fin thickness has also been studied. The results show that the enhancement effect increases versus the increase of Re number, channel height and the fin angle. To evaluate the enhancement effect reasonably, the assessing method under the same pump power constraint is adopted. For 2-D channel,the fin angleβ=30°is of the best heat transfer effect. But for the 3-D channel, different channel height shows different tendency. For the case of 2H=14mm, the fin angleβ=30°is the best, while for 2H=14mm and 2H=34mm, the fin angleβ=23.2°is the best for the laminar flow andβ=16°the best for the turbulent flow. This tells us that there exists a different optimum fin angle for each channel height.