Analysis Of Fluid Flow And Heat Transfer Characteristics Of Semicircular Spiral Channel With Winglet Vortex Generator

The semi-circular spiral channel has the advantages of compact structure,good heat transfer effect,and strong carrying capacity,and has a wide range of applications in industrial production.The reactor is a common industrial equipment that completes the process of aggregation,digestion,hydrogenation,sulfide and contraction.It is widely used in chemical industry,medicine,agriculture,food and dyeing industries.Because the reactor is usually accompanied by heat absorption and heat releasing reactions during the work,and the fluctuation of temperature is an important factor affecting the quality of the product.Therefore,the semi-circular spiral channel can be used as a heat transfer jacket of the reactor to ensure that the best reaction conditions can be achieved during the process,thereby obtaining the best reaction effect.This article uses a numerical simulation method to analyze the effects of the length,area,quantity and arrangement method of the vortex generator on the flow and heat transfer characteristics.Selecting the semi-circular spiral channel as the calculation area,the divided grid independence verification was performed.The numerical simulation results were compared with the experimental results to verify the accuracy of the numerical simulation method.Finally,the overall performance of the semi-circular spiral channel are compared and analyzed.The results showed that:（1）The triangular winglet vortex generator is installed on the inner wall of the semi-circular spiral channel.After the fluid flows over the vortex generator,a pair of longitudinal vortices in opposite directions will be generated behind the vortex generator,which changes the original flow field structure of the semi-circular spiral channel.This pair of longitudinal vortices can induce the fluid to continuously scour the boundary layer on the surface of the semi-circular spiral channel,thin the boundary laye,decrease the thermal resistance,and hence the improvement of the heat transfer performance of the semi-circular spiral channel.（2）When the length-to-height ratio of the vortex generator is 1.6,the average Nu of the semi-circular spiral channel is the largest,which is increased by 15.5%～20.9%compared with the semi-circular spiral smooth channel,and f is also increased by 27.3%～45.6%.When the length-to-height ratio of the vortex generator is 2.77,the comprehensive heat transfer performance of the semi-circular spiral channel is the best.This is because when the length-to-height ratio of the vortex generator is 2.77,although the heat transfer performance is not significantly improved compared with that of the vortex generator with the length-to-height ratio of 1.6,lower flow resistance can be obtained.（3）When the vortex generator area is S₄=74.92mm²,the average Nu of the semi-circular spiral channel is the largest,which increases by 14.96%～16.24%compared with that of the vortex generator area S₁,but f also increases by 38.02%～52.4%.When the area of the vortex generator is S₄and Re is 4000,the maximum JF can reach 1.137.The comprehensive heat transfer factor of the semi-circular spiral channel is the largest when the area of the vortex generator is S₃for Re>6000.（4）With the increasing quantity of vortex generators,the average Nu of the semi-circular spiral channel increases to a certain extent,and so does f.The average Nu and f increases by 24.4%～27.6%and 56.25%～84.57%in the semi-circular spiral channels installed with 27 pairs of vortex generators compared with those installed with 4 pairs of vortex generators.When Re ranges from 4000 to 12000 and the number of vortex generators is 27pairs,the maximum JF of the semi-circular spiral channel can reach 1.19.When Re is in the range of 14000～16000,the comprehensive heat transfer factor of the semi-circular spiral channel installed with 13 pairs of vortex generators is the largest.（5）The value of Nu/Nu₀of the vortex generator with a longitudinal distance of 31.41mm for the staggered arrangement is reduced by 0.31%-1.86%,but f/f₀is reduced by 5.1%-5.74%compared with the vortex generator with parallel arrangement.When the longitudinal distance of the vortex generator is 10.47mm and Re is 4000,JF of the semi-circular spiral channel can reach the maximum value of 1.197.The difference in JF between the staggered and parallel arrangements of vortex generators becomes obvious with the increase of Re.