Study Of Heat Transfer Characteristic With Temperature-pressure Coupling Natural Convection Of Solar Chimney Power Plant System With Vertical Collector

In this paper, conduct the energy balance analysis for the solar chimney powerplant system with vertical collector，the calculate formulation of the pressuredifference of the system,the internal energy balance relationship and the energyconversion efficiency was deduced; considering the effects of temperature and pressureto the air within the system, calculates the relationship of the density of the air in thechimney and temperature and pressure, i. e. how the air density changes with height.Through the research, obtain the following conclusions:①The pressure differenceof the inlet and outlet of the chimney passage will increase along with the heightincreasing of the chimney and the temperature difference between the inlet and outletof the chimney;②The solar radiation absorbed by the air within chimney channelcan increase the temperature and decrease the density of the air; on the other hand,with the increasing of the chimney height, the pressure getting smaller,then thedensity also decreased under the influence of the air pressure. Under the combinedeffect of the two, the density of the air constantly reduced with the increase of thechimney height; with the solar radiation intensity increases, the air density decreasesmore obvious;③The heat transfer mechanism of the system is different during theday and night. During the day, solar radiation enters the system through a glass plate, aportion of the heat was absorbed by the air within the chimney,In the meanwhile aportion of the heat was stored up by the heat storage layer. During the night, no solarradiation, the heat stored by the heat storage layer during the day is transmitted to theair within the chimney and the ambient air flow, so the system can be continuous.In the process of numerical calculation, flow condition of the air in runner had been taken into account when boundary conditions were set. A program was importedinto FLUENT to describe the changes of parameters in the system, which wasprogrammed by UDF considering the relation between density and temperature andpressure, and changes of density with height. The pressure field, temperature field andvelocity field were obtained to compare with the simulation results and experimentalresults of the constant air density model. The error between result when consideringthe impact of temperature and pressure on air density with that obtained with theexperimental value was28%,compared with error of41%before doing simulation. Itturned out that the result was more consistent with the experimental data whenconsidering the influence of temperature and pressure on air density. Therefore, thesolar chimney power plants with vertical collectors run in the conditions oftemperature coupled with pressure.The influence of structural parameters on heat transfer and flow characteristicswas analyzed using this method, the following conclusions: With the increase inchimney height and width of the collector plate, the system performance was moreexcellent; when the thickness of the air layer was thinner, the temperature in the flowpassage increased with the increasing thickness of the air layer, but when the thicknessof the air layer reached a certain value and then continued to increase, the temperatureof the air in the flow passage decreased gradually, i.e., the thickness of the air layerexisted an optimum value.The shape of the chimney was also one of the factors affecting the systemperformance, the design of the chimney structure was improved, the convergentchannel took the place of the original tapered rectangular channel, and this structurewas analyzed using numerical methods. The results show：the differential pressure andtemperature of modified chimney channel are bigger than the former, same as air flowvelocity. The temperature difference increases about4K, and the air speed in chimneyis higher than speed of the previous model, and about175%of the previous one.Considering higher air flow velocity carry more energy when the energy aretransformed electric energy through turbine, therefore, we collect tapered chimneychannel to increase the power of system, instead of rectangular chimney channel.