双风道回风式太阳能空气集热器的数值模拟

Numerical Simulation of Double Air Duct Return Air Solar Air Collector

提出一种带半圆形吸热板的双风道回风式太阳能集热器,上层风道是由PC盖板与半圆形吸热板组成的空间,室外空气进入上层风道后,在上层的10个独立小风道中流动;下层风道是由半圆形吸热板和隔热层组成的空间。PC盖板为半透明介质,太阳辐射热量主要由吸热板吸收后,通过对流换热将热量传递给上、下层风道内的空气。上层风道内的空气通过与吸热板进行对流换热以及吸收太阳辐射热量获得热量,其中与吸热板的对流换热占主导。半圆形吸热板增加了空气的扰流,使换热更加充分。对该集热器建立物理模型,利用Fluent软件进行数值模拟。结果表明,对上下层风道进风速度相同工况:太阳能空气集热器的出风温度与进风速度有关,进风速度越大,出风温度越低。当进风速度为0. 5～2. 0 m/s,上层风道的进风温度设定为273 K,下层风道的进风温度设定为291 K时,上层风道的最高出风温度可达374. 47 K,下层风道的最高出风温度可达343. 38 K。上下层风道进风速度相同时,进风速度由0. 5m/s增大到2.0m/s时,集热器的瞬时集热效率随之增大,但增大的幅度逐渐降低。对上下层风道不同进风速度工况:当下层风道的进风速度不变时,上层风道的进风速度越大,集热器的瞬时集热效率越高。当上层风道的进风速度一定时,集热器的瞬时集热效率随着下层风道进风速度的增大先增大后减小。当上层风道的进风速度为2. 0m/s,下层风道的进风速度为1. 0 m/s时,集热效率最高,达63. 08%。当上层风道的进风速度为0. 5 m/s,下层风道的进风速度为2. 0 m/s时,集热效率最低,为41. 87%。

A double air duct return air collector with semi-circular heat absorbing plate is proposed.The upper air duct is a space composed of PC cover plate and semi-circular heat absorbing plate.After outdoor air enters the upper air duct,it flows in the upper10 independent small ducts.The lower air duct is a space composed of semi-circular heat absorbing plate and insulation layer.PC cover plate is a translucent medium.The solar radiation heat is mainly absorbed by the heat absorbing plate,and the heat is transferred to the air in the upper and lower ducts by convective heat transfer.The air in the upper duct obtains heat by convective heat transfer with the heat absorbing plate and absorption of solar radiation heat,in which the con-vective heat transfer with the heat absorbing plate is dominant.The semi-circular heat absorbing plate increases the disturbance of the air and makes the heat exchange more complete.The physical model of the collector is established,and the numerical simulation is carried out by Fluent software.The results show that under the same inlet air speed conditions of upper and lower air ducts,the outlet air temperature of the collector is related to the inlet air speed,the higher the inlet air speed,the lower the outlet air temperature.When the inlet air speed is 0.5 to 2.0 m/s,the inlet air temperature of the upper air duct is set to 273 K,and the inlet air temperature of the lower air duct is set to 291 K,the maximum outlet air temperature of the upper air duct can reach 374.47 K,and the maximum outlet air temperature of the lower duct can reach 343.38 K.When the inlet air speed of the upper air duct and lower air duct is the same and the inlet air speed increases from 0.5 m/s to 2.0 m/s,the instantaneous heat collecting efficiency of the collector increases,but the increase amplitude gradually decreases.Under the different inlet air speed conditions of upper and lower air ducts,when the inlet air speed of the lower air duct is constant,the higher the inlet air speed of the upper air duct,the higher the instantaneous heat collecting efficiency of the collector.When the inlet air speed of the upper air duct is constant,the instantaneous heat collecting efficiency of the collector increases first and then decreases with the increase of the inlet air speed of the lower air duct.When the inlet air speed of the upper air duct is 2.0 m/s and the inlet air speed of the lower air duct is 1.0 m/s,the heat collecting efficiency is the highest,up to 63.08%.When the inlet air speed of the upper air duct is 0.5 m/s and that of the lower air duct is 2.0 m/s,the heat collecting efficiency is the lowest,being 41.87%.