The Fin Side Flow And Heat Transfer Characteristics Of Circular Tube Bank With The Triangular Wavy Fins

As the key equipment in the process of heat transfer, finned-and-tube heat exchanger used in many cases, it not only led to the development of social economics, but also brought convenience to our life. At the same time, the operation of the fin-and-tube heat exchanger consumes very large amount of high grade energy. In order to raise the utilization of energy and conserving energy, it is necessary to study the heat transfer enhancement technology to further improve the heat transfer characteristics of the fin-and-tube heat exchanger. There are many kinds of the fin type for the fin-and-tube heat exchanger, according to the geometric shape of the fin, they can be divided into the plain fin, the slit fin, the corrugated fin, the shutter fin, and the fin stamped with vortex generators. Air side thermal resistance as the main thermal resistance in the fin-and-tube heat exchanger accounts for 70% to 90% of the total thermal resistance, that is to say, the heat transfer performance plays a decisive role for the heat transfer performance of such heat exchanger. Therefore, the heat transfer performance of the air side should be enhanced further to improve the overall heat transfer performance of the heat exchanger.This paper used numerical method to study the heat transfer performance of the triangular wavy finned tube heat exchanger in this paper. Firstly, the corresponding mathematical and physical model is needed to establish, and then the appropriate fin unit as the computational region is selected, the reasonable grid system in computational region is obtained after checking the grid distribution, the size of the grid number used in the numerical calculation is determined, through the comparisons of the numerical and experimental results the correction of the algorithm is validated. Then using the numerical method to obtain Nusselt number and friction coefficient of the find side at various fin parameters and working conditions. The linear regression method is used to obtain the correlation between Nusselt number and the geometric parameters, and friction coefficient and the geometric parameters.Comparisons of the heat transfer performances of the triangular wavy fin and the plain fin are performed: such as differences between the change rules of the friction coefficients, between Nusselt numbers at different Reynolds number, between the flow fields on the horizontal and vertical section. In order to further reveal the mechanism of heat transfer enhancement enforced by the triangular wavy fin, the relationships of Nusselt number and the friction coefficient vs. the longitudinal vortex intensity and the transverse vortex intensity are reported.The results of the study show that: compared with the plain fin, the local Nusselt number is larger on the surface of the triangular wavy fin and its heat transfer performance is better.Analyzing the flow field within the channel which formed by the triangular wavy fin and the circular tube, it is found that the secondary flow phenomenon is very obvious in the corrugated and wave trough. Because of the channel which formed by the triangular wavy fin and the circular tube can produce longitudinal vortex and horizontal vortex, the longitudinal vortex and horizontal vortex also enhance heat transfer. The Nusselt number, longitudinal vortex intensity and transverse vortex intensity increase with the increase of the fin spacing,the angle of the ripple and the number of the ripple. The friction coefficient decreases with the increase of the fin spacing, the angle of the ripple and the number of the ripple. The average Nusselt number and the friction coefficient of the triangular wavy fin are also higher than the plain fin at the same Reynolds number. The correlations of Nusselt number and the friction coefficient vs. Reynolds number, longitudinal vortex intensity, and transverse vortex intensity are given, respectively.