Research On Enhancement Of Flat-plate Solar Collector Pipes Heat Convection By Multiple Interlocked Rings Wire Coil Inserts

According to statistics, building energy consumption ratio can account for thewhole society is close to30%. In building energy consumption, heating energy accountsfor about45%, in recent years, solar central heating system has become an importantresearch direction, heating collector is the most important part of the whole solar energyheating system, and large-scale solar thermal system adopts flat solar collector as thecollecting heat equipment, but the flat solar collector efficiency remains to be improved.Experimental investigation of heat transfer, friction factor and thermal performanceof multiple interlocked rings wire coil solar water heater with various cyclomaticnumbers has been conducted and the results are compared with plain tube collector andtwisted tape tube for the same operating conditions. Isothermal pressure drop tests andheat transfer experiments under uniform heat flux conditions have been carried out.Within the range of investigated parameters, the Nu in the double interlocked rings wirecoil insert collectors has been found to increase by68.4%~200.7%, whereas thepressure drop increased by238.7%~794.6%, as compared to plane collectors. Nu andpressure drop of three interlocked rings wire coil insert collectors is106.1%~272%,470.8%~906.8%. A performance comparison between twisted tape insert, doubleinterlocked rings wire coil insert and three interlocked rings wire coil insert has shownthat three interlocked rings wire coil insert tube perform better than plain tube, twistedtapes tube and double interlocked rings wire coil insert tube in the low Reynoldsnumber range: Re=240～2300. Given calculation formula of Nu and f with influencingfactors by regression analysis. Through total enhancing heat transfer evaluation formulaPEC analysis, multiple interlocked rings wire coil PEC values were greater than1, andgreater than twisted PEC values. Analysis enhancement heat transfer mechanism aboutmultiple interlocked rings wire coil by field synergy principle, the number of fieldsynergy values Fc of multiple interlocked rings wire coil is increased substantially, the speed field and temperature field of pipe with multiple interlocked rings wire coil has agood synergistic effect.With the Fluent software as a tool for numerical simulation, velocity field andtemperature field distribution of multiple interlocked rings wire coil pipe is presented.The velocity field and temperature field of multiple interlocked rings wire coil pipe haschange significantly compared with plain tube, and has shown that three interlockedrings wire coil insert tube perform better than double interlocked rings wire coil inserttube. Studies have found that the angle between the velocity vector and the temperaturegradient vector changed significantly also shows that the velocity field and temperaturefield of multiple interlocked rings wire coil pipe has a good synergistic effect. Multipleinterlocked rings wire coil can increase the fluid velocity and disturbance on fluid flowpatterns. Destroy the fluid boundary layer, and promote the core fluid and the boundaryof fluid mixing, makes the pipe fluid temperature distribution is uniform, Convectiveheat efficiency is increased.In this research, through experiment and numerical simulation and field synergytheory analysis found that the heat transfer effect of three interlocked rings wire coilpipe is better than other pipe. The analysis can prove that multiple interlocked ringswire coil can strengthen convective heat transfer between the working medium and pipewall of the flat-plate solar collector and improve the flat-plate solar collector’scollection efficiency.