The Numerical Analysis Of Convercation Transfer Across Cylinders And Non-circular Tubes

Cylinders and non-circular tubes not only play a theoretical role in experimental and theoretical research,but also have attracted attention in practical engineering in recent years with the enhancement of engineering technology and material optimization,and the characteristics of non-circular tube heat transfer strongly are also widely concerned and explored in practical engineering.Because the theoretically large space is an infinite distance,in practice,both the workload and the precision must be considered in the simulation.When the model is established,the limited boundary will inevitably have a certain influence on the heat transfer,and the influence of the boundary needs to be considered.Therefore,firstly,in the large-scale Reynolds number,different scale models are used to simulate the convection heat transfer across a single tube of forced convection across the tube and compared with the existing experimental results of references.Then,the suitable numerical simulation methods were determined for different ranges of Re.Finally,the experiment of the non-circular tubes were limited in the past,they all adopted a relatively limited range of Re numbers.The numerical simulation of non-circular tube convection heat transfer results in a larger experimental Reynolds number range,obtained its flow and heat transfer characteristics,and analyzed the non-linear phenomenon.This article gets the following results:1?Select six scale models with H/d=6,H/d=8,H/d=10,H/d=12,H/d=14,and H/d=16.The comparison of the flow field and temperature diagram simulated by the forced convection flow across a single tube and the comparison between the average Nu number of the numerical simulation and the experimental correlation yields:when Re<100,in the H/d=6 to H/d=16 model,the simulation results are approximately the same as the experimental results,and the model with H/d=6 can be selected;when100<Re<10~4,each The proportional model has shown a gradual increase in correlation with experimental correlations.The vorticity distances presented by H/d=14 and H/d=16 are approximately the same,so H/d=14 and H/d=16 are more reliable;When Re?10~4,it can be considered that the H/d=16 proportional model can be used as a forced convection model in which a large space fluid traverses a single circular tube.The numerical simulation of the accurate proportional model of the fluid traversing a single tube in a confined space to an infinite space is obtained.2?The direct numerical simulation,large eddy simulation,and Reynolds stress model were used for numerical simulation,and the numerical results were compared with the experimental results.It was concluded that in the range of relatively large Re numbers,which numerical simulation method is optimal.Under the grid of this paper,when Re<10~4,the DNS can give very good results,and the points where the local Nu rise appears.When 10~4?Re<10~5,the LES results are very good.When Re>10~5,the RSM is good.This paper mainly adopts the non-steady two-dimensional model,where the fluid is air and Pr=0.7,the Nusselt number under the conditions of fluid flow heat transfer and Reynolds number is nonlinear.When Re<100,the average Nu does not change with time;when 100<R?300,Nu oscillates regularly with time;when10~4?Re<10~5,Nu oscillates gradually intensified with time,the oscillation presents a nonlinear law.When Re?10~5,alternating detached vortices appear again,and Nu returns to relatively stable oscillations no longer violently with time.3?The numerical simulations of convective heat transfer around a non-circular tube at 4 different angles are performed in a range of Reynolds numbers that are larger than the experimental Re range.Through the simulation of the flow field and temperature field,to analyze the effect of wake vortex and shape etc.of non-circular tube on heat transfer.When Re?5×10~4,The different angles of square tube placed in the flow field gradually reduce the effect of drag and average Nu.When 10~4?Re?10~5,The ratio of drag and average Nu of the resistance of vertical elliptical tube and horizontal elliptical tube tends to be linear.