Performance study of a novel solar air collector

A novel solar air collector of pin-fin integrated absorber was designed to increase the thermal efficiency. According to experimental results, the average thermal efficiency of twenty-five kinds of pin-fin arrays collector reach 0.5–0.74 compared to the solar transmittance of 0.83 for the glazing. A correlation equation can be put forward to reflect the maximum thermal efficiency (η_max) of twenty-five kinds of pin-fin arrays collectors as function of dimensionless pin-fin span (s/d) and dimensionless pin-fin height (h/d). By theoretical calculation, the mathematic models of thermal efficiency of twenty-six collectors including flat-plate collector are obtained representing the influences of solar irradiation and inlet conditions of air stream on thermal efficiency. In the performance analysis of varying flow rate on PZ7-11.25 pin-fin arrays collector, the correlation equation on heat transfer coefficient is obtained and the efficiency variation vs. air flow rate is determined in this work.     

Integration of solar air collector with phase change material wall for a heating system

可再生能源的高效利用是降低建筑能耗的有效方法。将相变储能墙与太阳能热风相结合,可改善太阳能热风采暖的不稳定性,从而提高太阳能的利用效率。通过试验和ANSYS模拟软件对复合系统的分析,确定相变储能墙体的储热特性和合理用量,研究复合采暖系统的室温变化和传热规律,分析相变储能墙对采暖系统的贡献率。结果表明：与未采暖房间相比,复合采暖系统可以使室内平均温度提高7~15℃,该复合采暖系统具有一定的应用前景;当太阳能空气集热器的送风口温度在37~77℃时,相变材料能够充分利用,相变墙整体的相变比例约为40%,从线性回归比例看,复合采暖效果要比太阳能热风采暖效果好。     

A dimensionless model for the outlet temperature of a nonisothermal flat plate solar collector for air heating

The numerical model proposed by Baritto (2010) for the prediction of temperature distribution in a flat plate solar air heater is presented in dimensionless form and solved for a wide range of turbulent flow operating conditions. A parametric study is performed and the outlet temperature is proposed as a function of the aspect ratios and the mass flow number. The proposed equation shows good agreement with experimental data.     

一种槽式太阳能空气集热器热性能的试验研究

为了研究日光温室用槽式太阳能空气集热器的热性能,基于TracePro光学模拟软件设计了一种槽式太阳能空气集热器,对其进行试验研究,分析了不同因素对集热性能的影响规律。实验结果表明,管中空气流速的变化对集热器集热效率和集热量的影响规律是相同的,在不同的流速下,存在最佳空气流速约为4.4 m/s,使得集热器的集热量和集热效率最大,集热量达到373.2 W,集热效率约为25%,此时集热性能最好。对于不同太阳辐照度,正午时刻之前,太阳辐照度越大,集热器的集热效率越大,正午时刻之后,集热器的集热效率基本保持不变,15:40之后集热器集热效率逐渐减小。当太阳辐照度和管中流速相同时,室外温度越高,集热器集热效率越大,集热性能越好。集热管中空气温度沿着集热管出口方向不断增大,太阳辐照度越大,集热管相同位置空气温度越高。该研究结果可为此种槽式太阳能空气集热器在日光温室的应用中提供参考。     

An experimental study of a forced flow solar collector/regenerator using liquid desiccant

One of the main components of a liquid desiccant cooling system is the regenerator. In a liquid desiccant air conditioner, outside air is dehumidified by liquid desiccant and cooled within the absorber. The diluted desiccant solution thus obtained has to be concentrated for reuse, by passing through the regenerator and the cycle is, consequently, repeated. The regenerator used in this application is a forced parallel flow type solar collector/regenerator. The regenerator has been designed and optimized and the prototype of the solar collector/regenerator has been built and tested. Calcium chloride has been used as the absorbent solution. The results of the tests conducted as a parametric analysis indicate that the air and solution mass flow-rates and the climatic conditions affect the regenerator performance. Furthermore, a comparison between the experimental data obtained and a previously developed model for a forced parallel flow solar collector/regenerator reveals that the experiments are in good agreement with the model predictions. Finally, it was concluded that the proposed solar collector/regenerator performs satisfactorily under the summer conditions of Adelaide, Australia.     

An experimental study on a finned type and non-porous type solar air heater with a solar simulator

The results of experiments performed on two non-porous solar absorber solar air heaters with and without fins have been reported in this communication. The experiments were performed under laboratory conditions. Air heaters with fins are seen to be more efficient in comparison to the air heater without fins for air flow rates ≤0.0388 kg/sec per m². The experimental results have been used to validate a simple theoretical model.     

Comparative study of air heating solar collectors

Three types of conventional solar air heater are designed such that their heat absorbing areas and the pressure drops across them are equal for equal air mass flow rates per unit collector area. The results of thermal performance tests conducted simultaneously on these collectors, under the same environmental conditions, are presented.     

An oriented-design simplified model for the efficiency of a flat plate solar air collector

In systems design, suitably adapted physical models are required. Different modelling approaches for a solar air collector were studied in this paper. First, a classical model was produced, based on a linearization of the conservation of energy equations. Its resolution used traditional matrix methods. In order to improve the possibilities for use in design, the behaviour of the collector was next expressed in terms of efficiency. Lastly, simplified models constructed from the results obtained with the classical linearized model, and explicitly including the design variables of the collector, were proposed. These reduced models were then evaluated in terms of Parsimony, Exactness, Precision and Specialisation (PEPS). It was concluded that one of them (D2), using a low number of variables and of equations, is well suited for the design of solar air collector coupled with other sub-systems in more complex devices such as solar kiln with energy storage.     

Thermal performance of a triple-pass solar air collector

This communication presents a mathematical model for the thermal performance of a triple-pass solar air heater. The model predicts a rise of 4–22°C in the temperature of air (corresponding to efficiencies of 0.37–0.46) during a typical day in Nsukka, Nigeria in April; the predictions have been compared with the reported experimental results of Ezeike [Energy in Agriculture, Vol. 5, pp. 1–20 (1986)]     

Performance of a double pass solar air collector

Double pass counter flow solar air collector with porous material in the second air passage is one of the important and attractive design improvement that has been proposed to improve the thermal performance. This paper presents theoretical and experimental analysis of double pass solar air collector with and without porous material. A mathematical model has been developed based on volumetric heat transfer coefficient. Effects of various parameters on the thermal performance and pressure drop characteristics have been discussed. Comparison of results reveals that the thermal efficiency of double pass solar air collector with porous absorbing material is 20-25% and 30-35% higher than that of double pass solar air collector without porous absorbing material and single pass collector respectively.     

一种开孔被动式太阳能集热器热效率的研究

对一种具有多孔折线型的被动式太阳能集热器的热性能进行实验研究,探讨在受迫奈件下集热器热效率的计算公式。实测过渡季集热器出口温度、进口风速和太阳辐射强度3个参数。通过实验分析,这种折线型太阳能集热器的热效率可达59．4％,并且热效率随进口风速和太阳辐射强度的增加而提高。此外,集热器效率要先于太阳辐射强度达到当天最大值。     

Notes on a solar collector with unique air permeable media

Tests on plate heat collectors reveal that they are highly efficient in transferring heat and thus in increasing the temperature of a stream of air provided that the space between the cover and the bottom of the collector is filled with slit-and-expanded aluminum foil blackened on the one side, which is turned toward the sun. The air stream traverses the collector parallel to the general plane of the foil layers. The high radiant-energy exchange should reduce the cost of heat collectors and hasten wider utilization of solar heat.     

非晶硅太阳能光伏/光热空气集热器性能对比实验研究

文章设计了新型非晶硅太阳能PV/T空气集热器,该空气集热器能够解决传统太阳能PV/T热水器在高温波动情况下,晶硅电池热应力大的问题,同时避免了冬季管道发生霜冻的现象。文章通过实验对比,分析了非晶硅太阳能PV/T空气集热器、单独非晶硅光伏电池和传统太阳能空气集热器的能量效率和[火用]效率的差异。分析结果表明:非晶硅太阳能PV/T空气集热器的平均热效率为45.70%,比传统太阳能空气集热器的平均热效率降低了约25.88%;当空气质量流量增大至0.048 kg/s时,非晶硅太阳能PV/T空气集热器中的非晶硅光伏电池的平均电效率高于单独非晶硅光伏电池,它们的平均电效率分别为4.70%,4.54%;非晶硅太阳能PV/T空气集热器的总[火用]效率高于传统太阳能空气集热器的热[火用]效率和单独非晶硅光伏电池的电[火用]效率,非晶硅太阳能PV/T空气集热器总[火用]效率最大值为7.14%。文章的分析结果为非晶硅太阳能PV/T空气集热器的推广提供了参考。     

The effects of air leaks on solar air collector behaviour

The construction of conventinal solar air collectors and the fact that they will operate with a significant pressure difference between the heated air stream and ambient, suggests that significant quantities of air may leak into or out of them. A search of the literature reveals no consideration of the effects these air leaks may have on the validity of collector efficiency measurements, on the efficiency itself, or indeed what the meaning of efficiency is under such operating conditions. This paper discusses the meaning of collector efficiency when leaks into the collector occur, analyses the effects on efficiency measurements, and solves the collector efficiency for the simple case of a constant leakage rate along the collector. Assuming that air leaking in from ambient can replace deliberate fresh air supply to the load as in building heating, then significant measurement errors are made if air leaks in to the collector are not accounted for. Further, the collector efficiency is increased over the no leak case, so that complex construction methods to make the collector air tight are probably not warranted.     

Modelling and performance of a copolymer solar water heating collector

The performance of a solar flat-plate thermal collector wholly manufactured in a copolymer material is studied. The influence of different parameters of the system such as the insulation thickness, the flow rate and the fluid layer thickness is analysed. Thermal performance, productivity and efficiency of such a solar system is presented for a Mediterranean site. Yearly mean efficiencies are about 56.5% in no wind and about 49.0% for a wind speed of 5 m s⁻¹. The use of polymer materials reduces the collector weight by 50% in comparison with a traditional metal collector, this renders easier installation.     

Performance analysis of a double-pass thermoelectric solar air collector

The thermoelectric (TE) solar air collector, sometimes known as the hybrid solar collector, generates both thermal and electrical energies simultaneously. A double-pass TE solar air collector has been developed and tested. The TE solar collector was composed of transparent glass, air gap, an absorber plate, thermoelectric modules and rectangular fin heat sink. The incident solar radiation heats up the absorber plate so that a temperature difference is created between the thermoelectric modules that generates a direct current. Only a small part of the absorbed solar radiation is converted to electricity, while the rest increases the temperature of the absorber plate. The ambient air flows through the heat sink located in the lower channel to gain heat. The heated air then flows to the upper channel where it receives additional heating from the absorber plate. Improvements to the thermal and overall efficiencies of the system can be achieved by the use of the double-pass collector system and TE technology. Results show that the thermal efficiency increases as the air flow rate increases. Meanwhile, the electrical power output and the conversion efficiency depend on the temperature difference between the hot and cold side of the TE modules. At a temperature difference of 22.8 °C, the unit achieved a power output of 2.13 W and the conversion efficiency of 6.17%. Therefore, the proposed TE solar collector concept is anticipated to contribute to wider applications of the TE hybrid systems due to the increased overall efficiency.     

Experimental study on house cooling and heating with solar energy using flat plate collector

The OSE Project aims at developing the technology to utilize solar energy for heating, cooling and hot water supply on the basis of various technology for energy conservation in buildings. For the first step of this project a solar heating and cooling system with flat plate collectors and absorption refrigeration machine was installed in a house in 1974. This paper reports outlines of the system and operating results.     

西北新农村建筑太阳能主动供暖试验研究

为了降低西北新农村建筑采暖的能耗,改善室内生活环境,通过试验研究了太阳能主动供暖和传统小型燃煤锅炉供暖的西北新农村建筑的室内热环境、空气质量和采暖能耗的差异。研究结果表明:在室外环境最低温度为-16.2℃条件下,太阳能主动供暖建筑室内平均温度和平均辐射温度分别高出对比建筑5.4℃和3.3℃;在天气晴朗情况下,当室外环境的平均温度高于4.2℃且室外环境的最低温度高于-1.6℃时,仅利用太阳能进行供暖即可满足西北新农村建筑的供暖需求;太阳能主动供暖建筑室内CO,NO2,SO2,CO2及可吸入颗粒物PM10的浓度分别是对比建筑的0.45倍、0.48倍、0.56倍、0.59倍和0.5倍;经过分析得到太阳能主动供暖时室内环境温度与散热片内热水温度以及室外环境温度的二元线性关系;太阳能主动供暖的节能率为86.6%。     

An analytic model for the long-term performance of solar air heating systems

An analytic model is presented for the prediction of the monthly and yearly thermal performance of solar air heating systems. The effects of stratification in packed rock bed storage are explicitly taken into account. An expression for monthly solar fraction that depends on the important system and climatic variables is derived, which affords accurate predictions compared to corresponding f-chart calculations. The value of our analytic model, vis-a-vis calculational tools such as f-chart, is discussed. The method is applicable to all solar collector types as well as to load distributions of other than 24 hr/day.     

Design parameters of an active regenerative solar still: An experimental study

In this communication, an analytical expression for the thermal efficiency of an active regenerative solar distillation system has been presented in terms of the design parameters of the solar still, an effectiveness of the heat exchanger, a number of transfer unit (NTU) and the collectors. It is observed that there is a significant improvement (50%) in the overall thermal efficiency, owing to the regenerative effect, which is in an accordance with the experimental results.