A Flat-plate Solar Collector And Its Application In Wood Drying

As a non-concentrating collector,flat-plate solar collector has now become the world's most widely used solar thermal products.It has the characteristics of large lighting areas,simple structure,reliable operation,low cost,etc.However,in the actual operation when the temperature level is somewhat high,flat-plate collector often has a large heat loss,and it efficiency is low.Based on this,this paper carried out the following theoretical and experimental studies.?1?Development of a mathematical model for a flat-plate solar collector.Using this mathematical model to analyze the structure of the flat-plate solar collector and is performance,including the total heat loss coefficient,instantaneous efficiency,efficiency factor and the heat removal factor etc.?2?Optimization design of a flat-plate solar collector.By means of the iteration calculation,the total heat loss coefficient decreases and then increases with the distance between the cover plate and the heat absorbing plate increased.We set an optimization parameter and then calculated.The results shows that when the distance is 6cm,the collector performance is the best.The material of the cover plate is changed,coating with high transmittance films so that the transmittance is increased from 86.93%to89.72%.Thermal insulation material is 35mm polyurethane plate,which thermal conductivity is 0.024W/?m·??.Laser welding is used to reduce the thermal contact resistance.?3?Experimental test of flat-plate solar collector.The experimental system is set up to test the optimized flat-plate solar collector.The test results showed that the instantaneous efficiency curve intercept is 0.824,increased by 15.1%;the heat loss coefficient is 3.723W/?m²·??,reduced by 24.7%;the efficiency factor was 0.906,increased by 5.3%;the heat transfer factor is 0.888,increased by 5.8%.The optimized collector is named as high efficiency-low heat loss flat plate solar heat collector.?4?Application of flat-plate solar collector in wood drying.Analyzed the process and demand of wood drying,then designed flat-plate solar collecting system,total collector areas are 1013.54m²,storage tank is70.948m³,using electric as auxiliary heating.The system heated the water which temperature is 10?,and then passed into the existing coal-fired boiler heating to 89.11?for wood drying.Using TRNSYS software to simulation,the system annual effective utilization of solar energy 3.502×10⁹kJ,collector efficiency is 64.0%,solar fraction is 40.8%.?5?Simulation of influencing factors on solar wood drying system.Effects of ambient temperature,collector flow rate,tank volume and collector area are simulated and analyzed.It is known that the system is more suitable for the areas with high ambient temperature and high solar radiation.When the tank volume increased from 30m3to 60m3,the efficiency improved 8.8%.Compared with conventional electric power,this system can save 130.4 tons of standard coal per year,reduce 321.5 tons of CO₂,9.8 tons of SO₂,4.9 tons of NO_X,and 88.7 tons of dust.