【作者】 王娜；

【导师】 邓先和；

【作者基本信息】 华南理工大学 ， 化学工程， 2014， 硕士

【摘要】 太阳能是新能源可再生资源中最引人注目、开发研究最多、应用最广的清洁能源。我国正加快发展与利用太阳能,以缓解日益紧张的能源问题。太阳能热利用技术在降低常规能源消耗、促进节能减排过程中已发挥并继续发挥着重要的作用。平板型太阳能集热器是太阳能集热器的一种,世界各国都普遍使用。平板型太阳能集热嚣具有节能、高效、易于加工,应用广泛等特点。目前的太阳能集热嚣采用的流道尺寸一般都比较大,在5mm以上,水的体积热容大,加热速度慢,要使水达到预期的水温需要较长的时间,进出口温差小,集热器热损大,高温段的热效率偏低,因此此类集热嚣只能用于低温场合。而本课题把徽尺度传热理念运用于平板式太阳能集热器作为研究内容,希望通过探索和研究,开发出一种适合于太阳能海水淡化等太阳能中温运用场合的非聚焦型太阳能集热器。本文首先设计和建立徽通道平板型太阳能集热器模型,徽通道尺寸确定为0.7mm,透明盖板和吸热板的距离确定为17mm。给定入口流速进行强制对流实验,从平板集热器的能量守衡、瞬时效率和热损失几个方面,对集热器的热性能进行分析,得出瞬时效率随流量的增加而增加,集热器的热损失主要来源于顶部散热。然后对微通道内的传热过程进行分析,通道细长的结构,使水有足够时间与吸热板内壁进行充分的热量交换,吸热板与流体的温差很小,在3℃以内,从而可以达到较高的出口温度值。自然对流循实验是指利用太阳能使水在封闭的集热器系统中由于进出口温差而产生自然循环的过程。在相近的实验条件下,自然对流可达到的最高温度低于强制对流。所以,强制对流能够提高水的传热系数,更容易满足得到较高温度的要求。数值模拟能够从徽观上分析徽通道内的传热状况。根据实验数据进行模拟,得出实验与模拟的一致性。利用数值模拟还可分析徽通道和常规通道内流体传热的特征及区别,发现传热系数、出口温度、阻力系数都随流道尺寸的增加而减小。所以在微通道中,要想办法减小阻力大小,就能进一步提高传热效率。数值模拟还可以分析流道中的速度温度场的分布情况。更多还原

【Abstract】 Solar energy is a kind of new energy. As to renewable clean resources, it is the most remarkable and widely used resource that attracts many researchers’interest. Our country is speeding up the development and utilization of solar energy, to release the present tension of the energy problems. Solar thermal utilization technology in reducing fossil fuels consumption, promoting energy conservation and emissions reduction has been played and continued to play an very important role.Flat-plate solar collector is a kind of solar collectors which is widely used in all countries in the world. Comparing with other solar collectors, flat-plate solar collector has advantages of energy saving, high efficiency, easy processing and wide application, etc. The fluid channel size in solar collector is commonly large, more than5millimeters, so the volume of water heat capacity is relatively large, it needs a longer time to reach the desired water temperature. Also the temperature difference of inlet and outlet is small, heat loss of the collector system is large and thermal efficiency in high temperature range is low. This kind of collector can only be used in low temperature range. In this paper, we have designed a new flat-plate solar collector, applying the concept of micro channels heat transfer into it, wishing to develop a kind of non focusing type solar collectors which can he used in middle temperature occasions such as solar desalination.At first, this paper has designed and built a microchannel flat-plate solar collector experimental equipment. MicroChannel size was determined to be0.7millimeters, the distance between the transparent plate and absorber plate was determined to be17millimeters. Secondly, we conducted the forced convection experiment by giving an inlet water velocity, from the aspects of energy balance, instantaneous efficiency and system heat loss, to analyse the thermal performance of the collector. We founded that the instantaneous efficiency increased with the increase of flux, system heat loss primarily caused by the top part. And then we analysed the heat transfer process in the microchannel, the slender structure made the water have sufficient time to make heat exchange with the wall of absorber plate. The temperature difference between water and absorber plate was small, less than3degree centigrades, resulting in achieving higher outlet temperature. Natural convection cycle experiment refered to the natural circulation process in a closed collector system which due to the inlet and outlet water temperature difference was also studied. Under similar experimental conditions, the highest temperature we got in natural convection experiment was lower than forced convection. It is concluded that forced convection can enhance the heat transfer coeilicient of water, and it is easier to meet the requirement of reaching the high water temperature.Numerical simulation can help to analyse the heat transfer characteristics in the microchannel from microcosmic aspect. The simulation based on experimental data, the results showed consistency of the experiment and simulation. Taking advantage of numerical simulation can also study the characteristics and differences in niicrochanncls and regular channels. It is founded that heat transfer coefficient, outlet temperature and drag coefficient decreased with the increase of the flow channel size. Therefore, in microchannei, it can further improve the effect of heat transfer if we found ways to reduce the resistance. Numerical simulation can also be used to analyse the velocity and temperature field distribution in flow channel.更多还原