摘要
The experimental study of natural convection in allglass evacuated tube solar collectors is performed through the experimental platform of the solar-assisted fuel cell system.The experimental facility includes solar collectors with different length and diameter tubes, different coating materials, and with / without guide plates, respectively. Threedimensional mathematical models on natural and forced convections in the solar collectors are established and the experimental data is validated by field synergy and entransy principles. The results of natural convection show that the water temperature increases and thermal efficiency decreases gradually with the evacuated tube length. The thermal efficiency increases when absorption rates increase from 0. 95 to 1. 0 and emission rates decrease from 0. 16 to 0. 06. The thermal efficiency of solar collectors is increased after being equipped with the guide plate, which is attributed to the disappearance of the mixed flowand the enhancement of the heat transfer at the bottom of the evacuated tube. The results of forced convertion indicate that the Reynolds, Nusselt and entransy increments of the horizontal double collectors are higher than those of the vertical single collector while the entransy dissipation is lower than that of the vertical single collector. It is concluded that the solar collectors with guide plates are suitable for natural convection while the double horizontal collectors are suitable for forced convection in the thermal field of solar-assisted fuel cell systems with lowand medium temperatures.
以太阳能与燃料电池耦合系统为应用背景,对不同管长和管径、不同吸收率和发射率和有/无内置导流板3种不同情况下的太阳能集热器进行试验研究.建立太阳能集热器自然对流和强迫对流数值计算模型,并应用场协同和火积理论分析模拟计算数据.自然对流研究表明,随着真空管长度的增加,水箱温度逐渐升高,但集热效率逐渐下降;当吸收率在0.95-1.0范围内升高,发射率在0.16-0.06范围内降低时,集热效率逐渐上升;全玻璃真空管加装导流板后,由于真空管中混流消失和真空管底部强化传热作用而提高了太阳能集热器的热效率.强迫对流研究表明,横双排太阳能集热器的雷诺数、努赛尔数和火积增量均高于竖直单排太阳能集热器;横双排太阳能集热器的火积耗散低于竖直单排太阳能集热器.研究结果表明,在中低温太阳能耦合燃料电池集热场,自然对流宜采用内置导流板太阳能集热器,强迫对流宜采用横双排太阳能集热器.
基金
The National Natural Science Foundation of China(No.51376110,51541604)
the Major International(Regional) Joint Research Project of the National Natural Science Foundation of China(No.61320106011)
