| Flat plate solar collector has a high efficiency under low temperature conditions,reliable,cost-effective,and easy to combine with the buildings.It has broad space for development in the future of solar thermal utilization.Meanwhile,compared with water as a heat transfer working fluid of solar collectors,solar air collectors can be used in cold conditions,it will not be frozen,without the presence of scaling,corrosion and other problems.It has a wide range of applications in the heating,drying,food processing and other fields.In this paper,combining the advantages of corrugated board structure in high-efficiency heat collection with the effect of vacuum thermal insulation,we design a high-efficiency solar flat plate collector which can be used in cold conditions.We study the process of energy transfer and the calculation of heat transfer coefficient,and calculating the heat loss coefficient and the flow resistance loss of the collector to analyze structural advantages.Design and build a highly efficient solar air collector test platform to test outlet temperature,efficiency and different inlet mass flow rate on thermal performance of the collector,etc.On this basis,through a reasonable simplification,a three-dimensional mathematical model for unsteady air flow within the collector and heat transfer were built.We use Fluent software to study the internal flow field and temperature field of the collectors in numerical simulation.Researches and analysis of the different mass flow of imports,import different temperatures,different seasons,different impact absorber plate waveform flat plate solar collectors,and further series of collector system were simulated.The results show that:(1)When it is non-vacuum,the heat loss coefficient at the top of the solar collector is 17.6 times as much as the vacuum pressure is 0.05Pa.The flow resistance loss of this design is small,a collector unit only 38.02Pa.(2)When the air flow rate is 75m3/h,ambient temperature shocks between 23?-28?,air temperature of the collector unit may raise 16.21?.The instantaneous efficiency of the collector can reach up to 92%in the experiment.(3)With the increase of inlet mass flow,air flow rate increases,the corrugated board disturbance significantly enhanced the distribution of the air flow in its collector cavity more uniform,temperature gradient distance increases,the outlet temperature of the collector and the absorber plate surface temperatures continue to reduce and the collection efficiency increases.When the flow is greater than 75m3/h,outlet temperature will level off.(4)With the increase of inlet air temperature,the temperature of the absorber plate and the air flow path rises rapidly heated uniformly and the temperature gradient is more significant.When the inlet temperature change from-20 ? to 30?,the outlet temperature and the thermal efficiency of the collector were shown a prior increase and then decreasing trend from 0?.(5)The maximum temperature of the outlet is in summer,when the inlet mass flow rate is 12m3/h,the outlet temperature exceeded 40?.The temperature in June reaches a peak,the sine wave plate collector IS 45.83 ? the V-shaped wave plate collector is 45.03 ?;the temperature in spring and autumn were similar between 25?-40?;the minimum temperature of the outlet is in winter,the sine wave flat-plate collector in December is 24.92? the V-shaped wave plate collector is 24.63 ?.(6)The performance of sine wave plate collector is better than V-shaped wave collector,better than the normal plate-shaped collector.When the inlet mass flow rate is 75m3/h,the average solar irradiance is 825.53W/m2 the inlet temperature is 293K,the instantaneous efficiency of the three kinds of collectors was 87.81%,86.68%and 81.45%.(7)In the air flow rate of 12m3/h,a collector unit can raise 45.83 ?,the outlet temperature of the second stage in the two-stage cascade system is 43.27?,the third pole outlet temperature of the three tandem system is 39.6?. |
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