| With the rapid development of society,energy conservation and rational utilization has become the theme of sustainable development in today.To improve the efficiency of heat transfer equipment by strengthening the heat transfer,which can effectively alleviate the problem of energy shortages,has been the focus of energy conservation and emissions reduction in the word.Pin-finned tube as a highly effective heat transfer element,with the expansion of the surface and increasing the fluid turbulence,has been widely used in petrochemical,coal chemical industry,metallurgy,ceramics,building materials and other fields.Although the pin-finned tube has been applied in the industry,the research was mainly committed to the shape,size and arrangement of the pin fins.The research parameters,application areas are different,and there is no optimal analysis.Especially for the shaped pin-finned tube applied to enhance the heat transfer and flow characteristics of the gas side with low heat transfer coefficient,there was lack of systematic detailed data which can explain the proper kind of pin-finned shape with the best comprehensive performance.Besides,the heat transfer mechanism was lack of unified understanding.In this paper,the heat transfer and flow characteristics of three different shaped pin-finned tube including circular,elliptical and drop-shaped,were studied by means of theoretical analysis,numerical simulation and experimental verification.The heat transfer and flow characteristics of the pin-finned tube were analyzed theoretically,which can provide the guidance for numerical simulation and experiment.In order to analysis the lateral flow characteristics and heat transfer mechanism,the CFD numerical simulation technique and the naphthalene sublimation experiment were performed for the pin finned tube in a wind tunnel.Orthogonal test design was carried out for the tube with circular pin fins.Nine kinds of circular pin-finned tubes were designed and simulated.The pressure field,temperature field and velocity field distribution on the outer air side of the pin-finned tubes were obtained,and the flow and heat transfer characteristics were analyzed.The results of orthogonal test showed that each cycle number of pin fins and the height of pin fins were significant for the flow and heat transfer characteristics.By the numerical simulation,it can be concluded that the pressure drop of the pin finned tube was about 1.35-2.31 times of the smooth tube,and the total heat transfer coefficient of pin finned tube was about 1.10-1.72 times of the smooth tube under the given range of the Reynolds number.The comprehensive heat transfer of the pin finned tube was better than that of the smooth tube.Under the conditions that the pin fin height was 45 mm,each cycle number of pin fins was 8,the longitudinal spacing was 30 mm,and the radius of pin fin was 5mm,the comprehensive heat transfer was 1.15-1.29 times better than that under the conditions that the pin fin height was 25 mm,each cycle number of pin fins was 4,the longitudinal spacing was 30 mm,and the radius of pin fin was 4mm.The numerical simulations were carried out for three kinds of pin finned tubes with different pin fin shapes.Based on the simulation results of the heat transfer quantity per mass,the heat transfer quantity per area,the total surface heat transfer coefficient,the resistance characteristics and the comprehensive heat transfer performance,it can be concluded that the heat transfer and flow characteristics of drop-shaped pin finned tube was the best,which indicated the use of drop-shaped pin fins can enhance the heat transfer and reduce the resistance simultaneously.Numerical simulations were also carried out for drop-shaped pin finned tubes considering the effect of the pin fin height,each cycle number of pin fins,parent tube height,the number of pin fin cycles,the difference between inside wall temperature and inlet temperature,as well as the inlet air velocity.The field synergy on the air side of the pin finned tube was also investigated.The results showed that the pin fin height of 35 mm was beneficial for the heat transfer quantity per mass,the heat transfer quantity per area,the total surface heat transfer coefficient,the resistance characteristics and the comprehensive heat transfer performance,with the fix of each cycle number of pin fins.With the increasing parent tube height,the performances above mostly decreased first and then increased.The heat transfer quantity per mass,the total surface heat transfer coefficient,the resistance characteristics and the comprehensive heat transfer performance increased linearly with the increasing number of pin fin cycles,while the heat transfer quantity per area decreased with the increasing number of pin fin cycles.The heat transfer quantity per mass,the heat transfer quantity per area,the total surface heat transfer coefficient and the comprehensive heat transfer performance increased with the increasing difference between inside wall temperature and inlet temperature,while the resistance characteristics remained almost unchanged with the increasing difference between inside wall temperature and inlet temperature.The heat transfer quantity per mass,the heat transfer quantity per area,the total surface heat transfer coefficient and the comprehensive heat transfer performance increased with the increasing inlet air velocity,while the resistance characteristics decreased with the increasing inlet air velocity,which indicated that the momentum decreased.The field synergy analysis results showed that drop-shaped pin fins had an obvious superiority in synergy effect on the air side.Naphthalene sublimation experiments were carried out for three kinds of pin finned tubes with different pin fin shapes.The effect of longitudinal spacing,each cycle number of pin fins and circumferential angle on the heat transfer and flow characteristics were investigated.The results showed that circumferential angle of Φ=90° was beneficial for the heat transfer on pin fin surface and parent tube surface under the Reynolds number of 0.5×105-4.1×105 range.The heat transfer coefficients of the three kinds of pin finned tubes increased with the increasing Reynolds number,which were better than that of the smooth tube.The pin fin shape showed great influence on the resistance characteristics.Since the drop-shaped pin fin was close to streamline,the resistance was smaller.Therefore,considering the heat transfer and the resistance characteristics,the pin finned tube with drop-shaped pin fins exhibited better comprehensive heat transfer performance.In this paper,the study on the heat transfer and flow characteristics of the pin finned tubes with different shaped pin fins has great significance to the design and production practice of the pin-finned tubes. |
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