加装导流板的真空管热水器流动与换热的数值模拟

针对真空管与水箱连接处冷热水混流、出现随机涡流而影响换热等问题,分别建立了两种加装导流板结构模型.用FLUENT软件对两种导流结构热水器进行三维数值模拟研究,并与原结构进行比较分析,研究了真空管内的对流换热过程以及水箱内流体的分层情况.结果表明:加装导流板后,管口和水箱内的冷、热水混合换热情况得到了改善,增强了管内流体...     

储热式真空管太阳热水器

太阳热水器通常由太阳集热器和贮水箱两部分组成,而闷晒式热水器则将集热器与贮水箱合二为一,构成一种结构比较简单的热水器.若将真空管集热器与贮水箱合为一体,组成的太阳热水器称之为储热式真空管热水器,俗称真空闷晒式热水器.储热式真空管热水器既保留了真空管集热器固有的优良热性能,又可省去附加的贮水箱,其结构紧凑,安装使用方便,外形也比较美观.     

导流板结构对真空管热水器流动与换热的影响

针对真空管与水箱连接处出现随机涡流,不利于换热的问题,建立了真空管内加装导流板结构模型,运用Ansys Fluent软件对加装不同长度、厚度导流板结构的热水器进行三维数值模拟研究。导流板的存在减小了管内及连接处冷热流体的混合,使速度场均匀,流动稳定无扰动,保证了冷热流体的有序流动;特别是在真空管的下半部分,流体由水箱流入真空管处的速度提高,且流动稳定无涡流;加装不同长度导流板后,真空管底部、中部以及接近水箱入口处的水流平均速度提高了20%～313%,大大地增加了真空管下半部,特别是底部的热交换效率。     

上海地区应用全玻璃真空管太阳热水器的经济评估

此文根据已有资料，对全玻璃真空管太阳热水器和煤气热水器的总体使用性能进行了较实际的计算比较。结果表明，上海地区使用全玻璃真空管太阳热水器的年运行费用比煤气热水器节省４２％左右。到达１５年寿命期后，累计寿命期内节省的总费用，又可购买一台新的同型号太阳热水器。这相当于用户一次投资安装全玻璃真空管太阳热水器后，可永久使用。总体效益十分可取。欢迎读者各抒己见，展开讨论。———编者     

插式热管—玻璃真空管太阳能热水器的研制

本文介绍了插式热管－玻璃真空管太阳能热水器研制思路及主要的结构特点,性能参数。对集热元件热管－玻璃真空管的设计做了一般性阐述。     

平板型与真空管型太阳能热水器发展状况分析

分析了平板型太阳能热水器和真空管太阳能热水器的发展状况,对两种热水器的性能进行了比较,同时对它们的发展趋势做出了展望。     

如何选购全玻璃真空管太阳能热水器

全玻璃真空管太阳能热水器具有高效、节能。无污染、安全可靠、使用方便等特点,一年四季均能使用,越来越受到广大消费者的青睐。同时,广大用户也迫切需要了解如何选择和鉴别全玻璃真空管太阳能热水器的知识。为此,本文将有关玻璃真空管太阳能热水器的结构、选材等质量问题作一介绍。1外观质量及加工工艺鉴别太阳能热水器主要由保温水箱、支架、反射板和真空管组成,要求整体美观、外形轮廓流畅。支架应有足够的刚度和稳定性,支架与其它部分连接牢固。支架焊接处焊缝平整无夹渣;水箱外壳圆整、平滑、无划伤;端盖与水箱外壳连接处无明…     

Water-in-glass evacuated tube solar water heaters

Evacuated tube solar collectors have better performance than flat-plate solar collectors, in particular for high temperature operations. A number of heat extraction methods from all-glass evacuated tubes have been developed and the water-in-glass concept has been found to be the most successful due to its simplicity and low manufacturing cost. In this paper, the performance of a water-in-glass evacuated tube solar pre-heater is investigated using the International Standard test method ISO 9459-2 for a range of locations. Factors influencing the operation of water-in-glass collector tubes are discussed and a numerical study of water circulation through long single-ended thermosyphon tubes is presented. Preliminary numerical simulations have shown the existence of inactive region near the sealed end of the tube which might influence the performance of the collector.     

Performance of water-in-glass evacuated tube solar water heaters

The performance of water-in-glass evacuated tube solar water heaters is evaluated using experimental measurements of optical and heat loss characteristics and a simulation model of the thermosyphon circulation in single-ended tubes. The performance of water-in-glass evacuated tube solar collector systems are compared with flat plate solar collectors in a range of locations. The performance of a typical 30 tube evacuated tube array was found to be lower than a typical 2 panel flat plate array for domestic water heating in Sydney.     

全玻璃真空管太阳热水器数值模拟研究

基于FLUENT软件及TECPLOT软件,通过对均匀加热条件下的全玻璃真空管太阳热水器内流场及温度场的数值模拟,研究了热水器的对流换热与传质过程;分析了集热管倾角、真空管双面受热对热水器内流场及温度场的影响和真空管与水箱连接处、垂直等温面上的流体速度、温度分布。结果表明,在真空管与水箱连接处出现随机的涡流和真空管内出现分段的小环流,对传热传质过程不利,特别是对于带反射板的双面受热的集热器,应采取措施确保管内对流换热流动的有序性。建议加装导流板,并初步探讨了导流板的长度,确立了最佳板长模拟结构,为后续的理论研究与试验打下基础。     

Optimal tilt-angles of all-glass evacuated tube solar collectors

In this paper, a detailed mathematical procedure is developed to estimate daily collectible radiation on single tube of all-glass evacuated tube solar collectors based on solar geometry, knowledge of two-dimensional radiation transfer. Results shows that the annual collectible radiation on a tube is affected by many factors such as collector type, central distance between tubes, size of solar tubes, tilt and azimuth angles, use of diffuse flat reflector (DFR, in short); For collectors with identical parameters, T-type collectors (collectors with solar tubes tilt-arranged) annually collect slightly more radiation than H-type collectors (those with solar tubes horizontally arranged) do. The use of DFR can significantly improve the energy collection of collectors. Unlike the flat-plate collectors, all-glass evacuated tube solar collectors should be generally mounted with a tilt-angle less than the site latitude in order to maximize the annual energy collection. For most areas with the site latitude larger than 30° in China, T-type collectors should be installed with a tilt-angle about 10° less than the site latitude, whereas for H-type collectors without DFR, the reasonable tilt-angle should be about 20° less than the site latitude. Effects of some parameters on the annual collectible radiation on the collectors are also presented.     

U型管式全玻璃真空管集热器热效率及性能研究

在能量平衡分析的基础上，建立了U型管式全玻璃真空管太阳能集热器热效率方程，推导了集热器热损系数、效率因子等性能参数的计算公式，理论计算热效率与实验数据吻合良好。计算分析表明，真空管热损系数与吸热管和环境温差并非线性关系，将其关联式按环境温度分段整理将使计算结果更接近实际；涂层发射比对集热器的热效率影响较大，降低涂层发射比是提高集热器效率的有效途径；采取适当的措施降低吸热管与肋片间的接触热阻后，采用U型管连接方式不会时热利用系统集热器效率造成太大影响。     

全玻璃真空管太阳能热水器影响因素的数值模拟研究

利用热能工程专业基础知识和场协同原理,结合计算流体力学配套商业软件,对反光板、倾斜角度、辐照强度、集热管尺寸和水箱大小等因素,影响全玻璃真空管太阳能热水器的传热传质特性进行了数值模拟研究和可视化分析,通过数值模拟研究给出了全玻璃真空管太阳能热水器的的最佳条件。     

Thermosyphon heat-pipe evacuated tube solar water heaters for northern maritime climates

Under transient climatic conditions previous research has reported that evacuated tube solar water heaters (ETSWHs) with heat-pipe absorbers are the most effective solution for collection of solar energy. The cost of such systems is greater than the mass produced “water in glass” evacuated tube solar water heater mainly manufactured in China. Previous studies have reported that the costs of solar water heating can be reduced through the adoption of thermosyphon fluid circulation. Well designed thermosyphon systems are as effective as pumped systems but with lower capital and running costs. To investigate if costs could be reduced and performance levels maintained, outdoor testing of three thermosyphon heat-pipe ETSWHs primarily designed for pumped fluid circulation was carried out under a northern maritime climate. Experimental data from a year’s side by side monitoring of two thermosyphon ETSWHs (both with the same area of 2 m²) was collected and used to validate a correlation based on a modified version of the f-chart design tool between the observed and expected performance for both systems. The R² value between measured and predicted monthly solar fractions was greater than 0.99 for both systems. The R² value between measured and predicted diurnal solar fractions was calculated as greater than 0.95 for both systems. The only difference between the two was that one utilised internal heat-pipe condensers whilst the other used external ones. The system with internal condensers was found to be 17% more efficient. A simplifying assumption of a constant temperature rise across the collectors reduced the calculations required to predict the performance of thermosyphon heat-pipe ETSWHs and was also statistically significant. To determine if the assumption was valid for other thermosyphon heat-pipe ETSWHs with different collector parameters a third system with internal condensers an area of 3 m², a heat removal factor (F_R) of 0.816 based on the absorber area and a collector loss coefficient (F_RU_L) of 2.25 W m^?2 K^?1 was assembled and its performance monitored, when the same assumption was applied the R² value between the measured and predicted daily solar fractions was calculated as 0.96 experimentally demonstrating that this relationship was still statistically significant for another heat-pipe thermosyphon ETSWH with different collector parameters.     

Comparative studies on thermal performance of water-in-glass evacuated tube solar water heaters with different collector tilt-angles

To performance comparative studies, two sets of water-in-glass evacuated tube solar water heater (SWH, in short) were constructed and tested. Both SWHs were identical in all aspects but had different collector tilt-angle from the horizon with the one inclined at 22° (SWH-22) and the other at 46° (SWH-46). Experimental results revealed that the collector tilt-angle of SWHs had no significant influence on the heat removal from solar tubes to the water storage tank, both systems had almost the same daily solar thermal conversion efficiency but different daily solar and heat gains, and climatic conditions had a negligible effect on the daily thermal efficiency of systems due to less heat loss of the collector to the ambient air. These findings indicated that, to maximize the annual heat gain of such solar water heaters, the collector should be inclined at a tilt-angle for maximizing its annual collection of solar radiation. Experiments also showed that, for the SWH-22, the cold water from the storage tank circulated down to the sealed end of tubes along the lower wall of tubes and then returned to the storage tank along the upper wall of solar tubes with a clear water circulation loop; whereas for the SWH-46, the situation in the morning was the same as the SWH-22, but in the afternoon, the cold water from the storage tank on the way to the sealed end was partially or fully mixed with the hot water returning to the storage tank without a clear water circulation loop, furthermore, such mixing became more intense with the increase in the inlet water temperature of solar tubes. This indicated that increasing the collector tilt-angle of SWHs had no positive effect on the thermosiphon circulation of the water inside tubes. No noticeable inactive region near the sealed end of solar tubes for both systems was observed in experiments.