Study On The Effect Of Ellipsoidal Dimple On Fluid Flow And Heat Transfer Enhancement In Circular Tube

Heat exchangers are often used energy transfer equipment in industrial production,and their heat transfer performance is primarily determined by heat transfer efficiency.A heat exchanger,also known as a heat exchanger carrier,is a device that transports cold and hot fluid heat exchange,mostly for internal heat exchange.In the process of continual updating and development of tube internal increased heat transfer technology,relevant technical measures are constantly improved,and heat transfer efficiency is considerably improved.Due to its high heat transfer efficiency and low pressure drop,experts and researchers have concentrated on the dimple structure as a new type of internal enhanced heat transfer technology.The numerical simulation method is utilized in this work to investigate the effect of ellipsoidal dimples with different arrangements on fluid flow and increased heat transfer in circular tubes.The fluid flow state and heat transfer characteristics are investigated as the attack angle of the ellipsoidal dimple changes.The influence of parameter modifications on fluid flow and heat transfer in the tube is investigated by varying the three dimple parameters of depth d,aspect ratio a:b,and pitch P.The fully formed flow field is simulated using periodic boundary conditions,and the numerical method’s accuracy is evaluated by comparing it to experimental data.The numerical findings of the new ellipsoidal dimple tube are investigated both quantitatively and qualitatively.The following conclusions are obtained from the research:(1)The symmetrical arrangement of adjacent ellipsoidal dimples along the flow direction has higher heat transfer performance,and the longitudinal vortex generated by it causes more severe disturbance in the central area of the fluid,resulting in better comprehensive performance.(2)The model with a dimple attack angle of α=45° has the best comprehensive heat transfer performance.Within the Re calculation range,compared with the smooth tube,the model withα=45° increases Nu by 72.93%～85.55%,f by 46.98%～59.04%,and PEC can reach 1.48～1.61.(3)The change in dimple depth has a significant impact on heat transfer and pressure drop.As the dimple depth increases from 1mm to 2mm,Nu increases by 18.67%～30.47%,and f increases by 53.03%～64.12%.PEC is affected by the increase in flow resistance,and when Re>20000,the PEC of the dimple model with a depth of d=2mm is lower than that of the model with d=1.5mm.(4)As the aspect ratio of the long and short axes of the dimples increases,Nu and f also increase.The model with an aspect ratio of a:b=6:3 has the best comprehensive heat transfer performance.Within the Re calculation range,compared with the model with a:b=4:3,the model with a:b=6:3 increases Nu by 15.83%～18.4%,f by 19.03%～30.76%,and PEC can reach1.50～1.67.(5)As the dimple spacing decreases,Nu and f gradually increase.The model with a dimple spacing of P=6mm has the best comprehensive heat transfer performance.Within the Re calculation range,compared with the model with P=18mm,the model with P=6mm increases Nu by 12.97%～22.06%,f by 22.69%～69.74%,and PEC can reach 1.51～1.68.