Numerical Study On Heat Transfer And Flow Characteristics Of Fin And Tube Heat Exchangers And Structure Optimization

With the acceleration of industrialization and the development of economy and society,the demand for energy in industry,business and household areas has increased sharply,and the concept of "carbon neutral carbon peak" and energy conservation and emission reduction came into being.In order to solve the problem of energy shortage,in addition to developing various renewable energy sources,it is necessary to improve the efficiency of energy use.As an important part of the thermal system,heat exchanger is widely used in refrigeration system,heating system and many other fields,it is significant to strengthen its heat exchange performance and reduce resistance loss for energy saving and consumption.Fin and tube heat exchangers,as a kind of high efficiency heat exchanger,has become a research hotspot because of its variable structure and complex flow.Most of the existing researches focused on the conventional base tube type and fin type,but there were few researches on the combination tube type and the special fin type.In this paper,the performance analysis and structure optimization of fin and tube heat exchanger are carried out by CFD numerical simulation method.The main research contents of this paper are as follows:(1)The three-dimensional geometric model and mathematical model of fin and tube heat exchangers were established,and the unstructured meshing of the model was carried out by using Meshing software.Fluent 2020 software was used for calculation,mesh independence was verified,and appropriate mesh number and density were determined.The numerical model was verified from the heat transfer characteristics and flow resistance.The average error between the numerical results and the experimental results was 4.55%and 4.21%,which verified the accuracy of the model.(2)The numerical simulation of a single base tube type showed that the plain fin and tube heat exchanger with elliptical base tube and flat base tube had better comprehensive performance than that with circular base tube.Furtherly,two types of composite tube types,elliptic tube-flat tube and flat tube-elliptic tube were designed.The calculated results were compared with those of a single base tube.The results showed that the elliptic tube-flat tube has the largest j/f comprehensive heat transfer factor.(3)According to the type of fin,two different types of folded fin and circular fin were designed.The heat transfer and flow performance were analyzed,and the calculated results were compared with those of plain fin.The results showed that the Nu of circular fin and fold fin increased by 4.86%and 19.02%,respectively.However,in terms of comprehensive heat transfer performance,the j/f comprehensive heat transfer factor of plain fin was 13.0%and 59.3%higher than that of circular fin and curved fin,which showed the best comprehensive heat transfer flow performance among the three fin types.(4)Based on the geometrical parameters of fin and tube heat exchangers,the influences of fin pitch,tube diameter,transverse tube pitch and longitudinal tube pitch on heat transfer and flow characteristics of fin and tube heat exchangers were studied by combining with temperature,velocity and pressure nephogram.Finally,a set of orthogonal experiments were designed and a set of geometric structure parameters with the best comprehensive heat transfer performance was obtained through range analysis.When the velocity of the inlet is of 1-5 m/s,the j/f comprehensive heat transfer factor of the optimal structure increased by 122.8%on average compared with the original structure.