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太阳能空气集热器中蜂窝结构的试验对比研究 总被引:2,自引:1,他引:1
介绍了一种用于建筑采暖的平板式集热器,针对平板式集热器中透明蜂窝结构抑制对流减少热损失的效应进行试验研究.通过对不同蜂窝盖板的集热器的空晒和抽气试验,发现小尺寸的蜂窝虽然能够抑制对流引起的热损失,但由于遮光和肋面热传导的增加又抵消了因抑制对流而带来的好处.在试验采用的几种蜂窝尺寸中,发现50 mm×50 mm×25 mm的蜂窝为较佳方案;对于相同高度(25 mm)、相同矩形截面(50 mm×25 mm)的蜂窝,在出口空气温度较低时,矩形截面水平放置(50 mm×25 mm)和垂直放置(25 mm×50 mm)给出相近的空气温度;但在出口空气温度较高时.则水平放置时的空气温度比垂直放置时高. 相似文献
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全玻璃真空管空气集热器管内流动与换热的数值模拟 总被引:2,自引:0,他引:2
目前,对于太阳能集热器的数值模拟大多是基于一维、非稳态的简化模型之上。该文采用三维数学及物理模型对插管提热系统的流动与换热情况进行了数值模拟。并对模拟结果进行了实验验证。 相似文献
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对交叉波形吸热板-波形底板空气集热器的盖板与波形吸热板间滞止空气层内的自然对流换热建立物理模型,利用数值方法在进行数值模拟,并对计算结果进行分析优化,揭示了平均板温差,波纹板的高度特征比,几何特征比,集热器倾角等参数对换热的影响。 相似文献
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为提升无盖板型太阳能空气集热器热性能,设计一种条缝射流型太阳能空气集热器,并利用数值模拟和实验验证对其热性能进行分析。集热器内部流动及换热特性的模拟结果表明,利用圆孔和挡片形成的条缝射流能对集热板形成有效覆盖,进而提高进气与集热板的对流换热。射流条缝存在最优结构参数,当圆孔直径为25 mm时,条缝宽度在3 mm处接近最优;集热效率则随挡片直径的增大而增大,是由于射流贴附效应在变强。实验结果表明,条缝射流型集热器的全天热效率稳定且高效。当处理气量为39 m3/h时,该集热器全天热效率稳定在约48%,优于传统的无盖板渗透型太阳能集热器。 相似文献
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高效太阳能空气集热器的研究 总被引:2,自引:0,他引:2
为制作和运输方便,太阳能空气集热器采用单元制作、现场安装的方案.利用优化设计的方法得出太阳能空气集热器的最优结构参数,结合集热器的使用性和加工工艺性,选择集热器单元的结构尺寸和制作用料,提高集热器的热效率、降低制作成本.经对样机使用表明,该太阳能空气集热器安装方便、造价便宜,能够为农业干燥作业提供绿色能源. 相似文献
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本文运用数值模拟的方法,对带有多重V形肋片的平板型太阳能空气集热器的换热与流动特性进行了研究。在雷诺数5 000~20 000范围内,采用RNG k-ε湍流模型,研究了相对肋宽比(W/w)对集热器换热特性的影响规律,并对集热器内部流场进行了分析。研究结果表明,V形肋片增强了空气的对流换热。这是由于流体掠过肋片后,产生旋涡和回流,加强了流体扰动,从而使换热增强。相对其它肋宽比而言,W/w=6时,集热器具有较好的换热效果,努塞尔数为光滑壁面的2.54倍,但肋片的存在导致摩擦损失增加,换热性能因数最大为1.55。 相似文献
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The performance of solar collector systems is optimized for the Beirut climate with respect to the following parameters: angle of tilt and orientation, plate emissivity and number of glass covers. The Beirut hourly ambient temperature, wind speed, wind direction and the monthly averaged hourly and daily global, beam and diffuse radiation are used in the calculation of the useful harnessed energy, collector's efficiency, storage-tank temperature and other relevant parameters.
The optimal thermal performance of the solar collector in Beirut is obtained for a south-facing collector all the year with a slope angle equal to latitude +15° in winter and latitude −15° in the summer. The use of a selective surface of low emissivity in the collector gives a higher useful energy gain of about 25% in summer and 10% in winter as compared with a nonselective plate surface. The collector's daily efficiency, under optimal conditions, varies from 55 to 65% depending upon the month of the year. 相似文献
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The collector is the main element that affects the solar system's performance. The collector's efficiency is affected by its operating temperature. Different levels of heating were considered for a milk-processing factory. The optimal collector type (i.e. the one with the minimum payback period) that can be used for these levels was deduced. 相似文献
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Stephen H. Hale Hans J. Schlereth Stefan Bortnowski 《Energy Conversion and Management》1982,22(4):385-388
A 450 ft ‘site-built’ air collector was completed in February 1981 in Boston, Massachusetss. The collector uses the Airco/Guardian ‘Passive Solar Glass’ with a selective surface coating on the inner lite of the collector's double glazing. This paper discusses the issues and theory that led to the building of the collector and estimates performance for the system. Preliminary data taken in late winter indicates that the system will perform seasonally as predicted. 相似文献
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Cort J. Willmott 《Solar Energy》1982,28(3):205-216
A numerical climatic model for computing total solar irradiance on the surface of a flat-plate collector, positioned at any tilt and azimuth, is described. Owing to a small time-step (one hour), and a quasi-realistic characterization of a collector's environment, the algorithm is able to produce credible estimates of both the climatically “optimal” position and the amount of energy lost to a collector when it is non-optimally positioned. Exemplary computations for Sterling, Virginia and Sunnyvale, California are presented and they suggest that the non-optimal positioning of a collector, e.g. as a simple function of latitude and a few highly summarized climatic-environmental variables, will not, in many cases, produce significant losses of available solar irradiance. In other situations, however, where a collector's horizon is significantly obstructed and/or the climatic environment of the area creates large diurnal or seasonal asymmetries in available irradiance, non-optimal positioning may cause sizeable energy losses. It is also apparent that even moderately sized horizonal obstructions, which are “seen” by a collector, can substantially reduce the amount of available irradiance, relative to an unobstructed horizon. 相似文献
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Blaine F Parker 《Solar Energy》1981,26(1):27-32
The collector efficiency factor which measures the effectiveness of a collector absorber plate in transferring heat to the transport fluid, and the loss factor for air-type collectors, are mathematically derived. These equations provide a method for computing these two factors, which with the effective transmittance-absorptance product, enables one to write the generalized performance equation. The prediction of performance provided by this procedure is particularly useful in comparing performance of different collectors and for studying a specific collector's performance with changes in environment and design parameters which can be controlled to some extent by the designer. 相似文献
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A model is developed for the heat transfer in a flat plate solar collector with a rectangular channel for water or air flow. This 2-dimensional geometry offers the maximum area of contact between the fluid and the collecting surface exposed to the Sun. The analysis yields temperature and heat flow distributions in both dimensions of the collector. Thermal boundary layer development is investigated. Overall efficiencies are calculated for uniform solar heat influx with variable heat losses from the plate. The thermosyphonic effect, due to natural convection, is evaluated and the collector's geometry optimized with respect to this effect. 相似文献
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This paper reports on the experimental performances of flat plate solar collectors tested with a solar simulator under steady-state conditions, in terms of collector efficiency, η, and ratio of temperature difference and solar radiation (Tfi-Te)/IT. Te was the effective heat-sink temperature of the tested collector and could be evaluated from temperatures of the collector's cover, ambient and light source panel (or infrared filter). Techniques for converting values of the collector's parameters, FRULe and FR(τα)e, obtained from the indoor tests to match outdoor results were demonstrated. The adjusted results agreed well with those of the outdoor data in the case of a collector having a flat glass cover. For a collector having a convex plastic cover, the estimated optical efficiency was lower than that of the outdoor result. 相似文献
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A solar collector made of a lattice of fluid conduits embedded within a thin concrete slab is investigated. Such a configuration can be constructed to withstand some mechanical strain by reinforcing the concrete with glass fibers. This collector can be integrated within construction elements of buildings and therefore offers means for low-cost solar energy collection. The geometry of such a collector as well as its characteristic parameters are different from the conventional flat-plate thin-fin collector. Its performance cannot therefore be accurately predicted by assuming a thin-fin behavior. It requires a different and somewhat more involved thermal analysis. In the present analysis, a numerical solution of a two-dimensional cross-sectional slice is expanded in the longitudinal direction by superpositioning such slices in tandem. A parametric study of the relative influence of various operational, geometrical and material parameters is presented. The study provides the tools for a feasibility study of such collectors. Transient characteristics of the collector's dynamic response during a typical summer day with continuous or intermittent radiation are also presented. 相似文献
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A.J. de Ron 《Solar Energy》1980,24(2):117-128
In the modelling of flat-plate solar collectors the dynamic effects have often been neglected. But because the solar collector is inherently exposed to variable weather conditions, its dynamics may be important to the design and control.It is demonstrated that it is not necessary to ignore the dependence of the various temperatures on the location in the direction of flow (which is often done to avoid complications) provided the model is developed in the frequency domain.The linearised model has been verified in the frequency domain by means of a least squares estimator. The verification was performed with a part of a full-size collector, as has been applied in some solar houses, and an artificial sun. It is concluded from the results of the verification that the developed model describes the collector dynamics quite satisfactorily. The differences between the theoretical and estimated heat resistances was about 10 per cent. The verification and estimation procedure proved to be a useful tool for comparing various collectors because the collector has to be fitted with only two temperature sensors.It is shown that the simple models have been discussed in the literature give responses which are not representative of the collector's dynamics. For well-designed collectors a simplified model is derived. Finally, some desirable sampling rates are given. 相似文献
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A prototype collector with parallel-connected evacuated double glass tubes is investigated theoretically and experimentally. The collector has a tubular absorber and can utilize solar radiation coming from all directions. The collector performance is measured in an outdoor test facility. Further, a theoretical model for calculating the thermal performance is developed. In the model, flat-plate collector's performance equations are integrated over the whole absorber circumference and the model determines the shading on the tubes as a function of the solar azimuth. Results from calculations with the model are compared with measured results and there is a good degree of similarity between the measured and calculated results. The model is used for theoretical investigations on vertically-placed pipes at a location in Denmark (Copenhagen, lat. 56°N) and at a location in Greenland (Uummannaq, lat. 71°N). For both locations, the results show that to achieve the highest thermal performance, the tube centre distance must be about 0.2 m and the collector azimuth must be about 45–60° towards the west. Further, the thermal performance of the evacuated solar-collector is compared to the thermal performance of the Arcon HT flat-plate solar-collector with an optimum tilt and orientation. The Arcon collector is the best performing collector under Copenhagen conditions, whereas the performance of the evacuated tubular collector is highest under the Uummannaq conditions. The reason is that the tubular collector is not optimally tilted in Copenhagen but also that there is much more solar radiation “from all directions” in Uummannaq and this radiation can be utilized with the tubular collector. It is concluded that the collector design is very promising—especially for high latitudes. 相似文献