Application Study Of Positive Truncated Spherical Vortex Generators In Solar Air Collectors

In order to achieve the global double carbon target,new energy research and application should be vigorously promoted to achieve an early release from the traditional fossil energy sources to the economy and society.Solar air collectors,as a common solar thermal conversion device,can convert solar radiation energy into internal air energy for storage and are widely used for auxiliary heating of buildings,drying of agricultural crops and wood,etc.In order to overcome the limitations of the low heat transfer strength in flat plate solar air collectors,this paper proposes a new type of positive truncated spherical vortex generator,which,due to its own special disturbance structure,can theoretically achieve a greater thermal enhancement effect while at the same time reducing the flow resistance to a certain extent,and can be applied to collectors to improve their performance.Firstly,the feasibility of a positive truncated spherical vortex generator to improve collector performance was experimentally verified by building an indoor experimental rig for vortex generator type solar air collectors.The influence of the four structural parameters of the vortex generator(deflection angle,lateral spacing,longitudinal spacing and height)and the variation of Reynolds number Re on the collector performance were investigated.Based on the experimental data,the least squares method was used to fit the correlation equations between Nu and f and Re and the structural parameters of the vortex generator,and the average prediction accuracy of the two correlation equations was 97.46% and 91.4%,respectively,which were good predictors of the internal heat transfer and flow characteristics of the collector.Secondly,a numerical model of the vortex generator type solar air collector was constructed by Meshing and Fluent software,and the enhanced heat transfer mechanism and flow characteristics of the orthotropic spherical vortex generator were analysed in depth by means of numerical simulations.Based on the experimental results,the number and range of structural parameters of the vortex generator are further expanded and the influence of each parameter on the collector performance is analysed in detail,including eight structural parameters such as deflection angle,lateral spacing,longitudinal spacing,height,circumferential angle,longitudinal alignment angle,staggered alignment ratio and hole opening method.It was found that the first five structural parameters had a significant effect on the variation of collector performance,but the last three parameters did not have a substantial effect on collector performance.Finally,using MATLAB and Design Expert software as tools,the structural parameters of the vortex generator are optimised by the BBD method,the least squares method to establish the link between the input and output values,and the non-dominated genetic algorithm to carry out the optimisation of the vortex parameters,and the optimal combination of the structural parameters of the orthotropic spherical vortex generator and the corresponding optimal value of the collector performance are derived This provides a theoretical basis for the engineering application of this collector.At the end of this chapter,the optimisation results of this collector are compared with similar literature and it is found that the performance enhancement of the collector caused by the new vortex generator designed in this paper is among the best in its class.