Exergetic performance assessment of a solar photovoltaic thermal (PV/T) air collector

In this paper, an attempt is made to evaluate the exergetic performance of a solar photovoltaic thermal (PV/T) air collector. A detailed energy and exergy analysis is carried out to calculate the thermal and electrical parameters, exergy components and exergy efficiency of a typical PV/T air collector. Some corrections are done on related heat loss coefficients. An improved electrical model is used to estimate the electrical parameters of a PV/T air collector. Further, a modified equation for the exergy efficiency of a PV/T air collector is derived in terms of design and climatic parameters. A computer simulation program is also developed to calculate the thermal and electrical parameters of a PV/T air collector. The results of numerical simulation are in good agreement with the experimental measurements noted in the previous literature. Finally, parametric studies have been carried out. It is observed that the modified exergy efficiency obtained in this paper is in good agreement with the one given by the previous literature. It is also found that the thermal efficiency, electrical efficiency, overall energy efficiency and exergy efficiency of PV/T air collector is about 17.18%, 10.01%, 45% and 10.75% respectively for a sample climatic, operating and design parameters.     

Experimental study and analysis of air heating system using a parabolic trough solar collector

An experimental study of air heating system was carried out using a parabolic trough collector with a U-tube aluminium heat exchanger. An evacuated tube placed at the focal length of the parabolic trough collected the solar radiations reflected from the surface of parabolic trough. The air was used as a working fluid, which was heated by passing it through a U-shaped aluminium heat exchanger placed inside the evacuated tube. It was found that efficiency of the parabolic trough collector depends on the mass flow rate, solar intensity and use of fins. It was observed that by using fins at a high mass flow rate of 4.557?kg/h, the maximum temperature of 126°C was achieved which is 13.27% more than the maximum temperature obtained without fins. Furthermore, for a low-mass-flow rate of 1.69?kg/h, the maximum temperature obtained was 149°C.     

Thermal performance analysis of the glass evacuated tube solar collector with U-tube

In this paper, based on the energy balance for the glass evacuated tube solar collector with U-tube, the thermal performance of the individual glass evacuated tube solar collector is investigated by analytical method. The solar collector considered in this study is a two-layered glass evacuated tube, and the absorber film is deposited in the outer surface of the absorber tube. The heat loss coefficient and heat efficiency factor are analyzed using one-dimensional analytical solution. And the influence of air layer between the absorber tube and the copper fin on the heat efficiency is also studied. The results show that the function relation of the heat loss coefficient of the glass evacuated tube solar collector with temperature difference between the absorbing coating surface and the ambient air is nonlinear. In the different ambient temperatures, the heat loss coefficient of the solar collector should be calculated by different expressions. The heat efficiency factor will be subject to influence of air layer between absorber tube and the copper fin. Specially, the influence is remarkable when the heat loss coefficient of the collector is large. When the synthetical conductance amounts to 5 W/m K, the solar collector efficiency decreases 10%, and the outlet fluid temperature decreases 16% compared with the case which the air thermal resistance is neglected. And the surface temperature of the absorbing coating increases 30 °C due to the effect of air thermal resistance. So the surface temperature of the absorbing coating is an important parameter to evaluate the thermal performance of the glass evacuated tube solar collector.     

槽式太阳能集热器聚光面能流分布及传热特性

本文运用蒙特卡罗光线追踪法模拟了LS-2型槽式太阳能集热系统的聚光特性,并以此为边界条件,进一步研究传热工质为THERMINOL55合成导热油时该集热器内管壁和管内流体的温度分布特性和传热特性。结果表明,管壁和管内流体温度分布十分不均匀。并考察了不同导热油以及导热油的流速对传热效率的影响工质流速对管壁温度分布影响较大,当太阳直射辐照为1000 W/m^2,导热油入口温度为160℃,流速为0.05 m/s时,吸热管圆周方向最大温差为235℃左右,当流速增加到0.05 m/s时,最大温差减小到142℃左右。     

槽式太阳能集热器传热模型及性能分析

槽式太阳能集热器一维和二维传热数学模型是一组非线性代数方程,为改进求解的稳定性和计算精度,将槽式太阳能集热器一维和二维传热模型的求解看作有约束优化问题,建立了集热器传热过程求解的有约束优化数学模型,应用MATLAB软件优化函数fmincon进行求解。分析了传热流体入口温度及太阳能辐射热流密度变化对集热器性能的影响。采用fmincon函数求解集热器传热过程,计算速度快,计算过程稳定。分析表明,传热流体温度变化对集热器效率的影响大于太阳能辐射热流密度对集热器效率的影响。     

Numerical model of natural convective heat transfer within a solar dryer using an indirect double pass collector

The double pass collector is one of the most efficient means of drying crops because heating of air takes place from both sides of the absorber plate. To investigate the performance, a double pass natural convection solar dryer was fabricated for experimentation; the results were collected and used to develop a validated numerical model using MATLAB. The experiments were undertaken during February–March 2016 in Salem Tamil Nadu, India over 10 sunshine days. The simulation was carried using the developed model under the measured ambient conditions. The results showed that the mathematical model could predict the performance of the double pass collector for a particular ambient condition to an uncertainty of ±5%. This model could be used to optimise the performance of the collector so that we can predict and investigate the actual performance of the collector with the various optimised designs before fabricating the dryer.     

浅述太阳能集热器的选型

结合某工程实例,对目前常用的平板型、玻璃真空管型及热管型等太阳能集热器的优缺点进行了介绍,并对各种太阳能集热器进行了综合评价,根据评价提出了设计中推荐选用水平大热管型集热器的建议。     

Experimental investigation of the solar cooker during sunshine and off-sunshine hours using the thermal energy storage unit based on a parabolic trough collector

A solar cooker based on a parabolic trough collector with thermal energy storage (TES) was investigated. In this experimental set-up, solar radiations were focused on the absorber tube and the collected heat was transferred to the solar cooker by natural circulation (thermosiphon) of the working fluid. The water and thermal oil (engine oil) were used separately as working fluids. Acetanilide was used as the TES material in the solar cooker. In day time, the phase change material (PCM) stored heat as well as transferred it to the cooking pot. In evening time, the stored energy by PCM was used to cook the food. The cooking process was carried out with different foods and with variation in the quantity of food. It was found that the temperature of thermal oil was 10–24°C higher than water as the working fluid. The system was able to cook the food twice a day and the rate of evening cooking was higher as compared with noon cooking. Using thermal oil as the working fluid, the quantity of heat stored by PCM was increased by an amount of 19.45–30.38% as compared with water.     

Thermal performance analysis of evacuated tubes solar air collector in Indian climate conditions

The thermal performance of one-ended evacuated tubes solar air collector is experimentally investigated during the winter season at NIT Kurukshetra, India [29 ° 58^′(latitude) North and 76 ° 53 ^′ (longitude) East]. The collector consists of 15 one-ended evacuated tubes with different lengths of directional inner aluminium tubes (inserted tubes) and a manifold channel, with air used as a working fluid. The inlet air flows through the directional inner aluminium tubes as a result of forced convection. In this experiment, evacuated tubes are used for producing hot air corresponding to different lengths of directional aluminium tubes without using any intermediate fluid. The temperature of the outlet air depends on the air flow rate, length of the directional aluminium tube and solar intensity. The maximum temperature difference between outlet air and inlet air at solar intensity 904 W/m² was found to be 72.7 °C with a flow rate of 5.06 kg/h and length of 0.83 m.     

无筒体旋风除尘器分级效率的实验研究

提出一种去掉筒体的新型结构的旋风除尘器,直接采用锥体进行使用,并将其与有筒体的旋风除尘器进行了分级效率的对比实验研究,结果表明在相同风量下,无筒体旋风除尘器的分级效率高于有筒体旋风除尘器。     

Effect of flat plate collectors in parallel on the performance of the active solar still for Indian coastal climatic conditions

The effect of flat-plate collectors (FPCs) when connected in parallel on, in particular, the heat transfer coefficients and, in general, distillate output and the efficiency of solar still has been studied in the active mode. The solar still has an effective basin area of 1?m² and fixed cover inclination of 30°. Each FPC with an effective area of 2?m² is attached to the solar still. An effective collector inclination of 5° is used. Experiments have been conducted for 24?h in summer for the active solar distillation system at Kakinada (16°.93′N/83°.33′E), India, which has coastal climatic conditions. The aim of the present work is to study the variation in internal heat transfer coefficients with respect to the number of FPCs coupled with the solar still in parallel. It is understood that the heat transfer coefficients depend significantly on the size of the collector. The size of the collector is increased by increasing the number of collectors. It is also observed that this leads to an increase in distillate output but a decrease in efficiency of the solar still.     

Experimental and numerical investigation on thermal and electrical performance of a building integrated photovoltaic-thermal collector system

An experimentally validated computational fluid dynamics (CFD) model of a novel building integrated photovoltaic-thermal (BIPV/T) collector is studied to determine the effect of active heat recovery on cell efficiency and to determine the effectiveness of the device as a solar hot water heater. Parametric analysis indicates that cell efficiency can be raised by 5.3% and that water temperatures suitable for domestic hot water use are possible. Thermal and combined (thermal plus electrical) efficiencies reach 19% and 34.9%, respectively. A new correlation is developed relating electrical efficiency to collector inlet water temperature, ambient air temperature and insolation that allows cell efficiency to be calculated directly.     

Year-round numerical simulation of a parabolic solar collector under Lebanese conditions: Beirut case study

A detailed thermal and optical numerical model is developed to simulate the performance of a small-scale parabolic collector having an evacuated receiver line with selective coating, taking into account different energy balances and interactions with the surrounding. An analytical model is developed to estimate the direct, diffuse and global solar radiation intensities on inclined surfaces. The collector performance model was validated using published experimental data. A year-round dynamic simulation for the collector performance under Beirut climatic conditions was carried out with an economic and environmental analysis. The outlet water temperature could reach a maximum of 114°C in July and 52°C in December by employing a collector of about 6 m² aperture area with 0.01 kg/s water flow rate. The maximum daily thermal energy production is attained in July with 22.267 kWh while January exhibits the lowest thermal energy production with 6.704 kWh per day with a maximum thermal efficiency of 72%.     

Thermal solar water heater with H2O-Al2O3 nano-fluid in forced convection: experimental investigation

This paper describes laboratory experiments with a thermal solar water heater consisting of a flat-plate solar collector and helical coil heat exchanger using Al₂O₃ nano-particles dispersed in water as a working. The experiments were carried out for various nano-particle concentrations, from 0% to 3% (by volume), through forced convection cooling. The experiments were carried out under the climatic conditions of Tanta University, Egypt. The laboratory work has been carried out in actual thermal environment in August 2013. The experiments have an emphasis on the main parameters with impact on the water production temperature. These parameters include the solar radiation, the feed water mass flow rate and the nano-particle volume fraction. The main conclusion is that considerable improvement in the daily solar collector efficiency is obtained with increasing the nano-particle concentration up to 11% for concentration 3% with; this increase in efficiency is bounded by ±10% uncertainty. The outlet water temperature is increased with increasing of nano-particle concentration by 5.46% for concentration 2%. The helical heat exchanger effectiveness is increased by 4.25% for a concentration of 1% with ±13% uncertainty. The helical heat exchanger effectiveness and solar collector efficiency are increased with decreasing the working fluid mass flow rate.     

Numerical analysis on heat transfer characteristics of ionic liquids in a tubular heat exchanger

ABSTRACT

The efficiency of the solar thermal system depends on the performance of the solar collectors. There is a need to operate solar collector at higher possible temperature to attain maximum efficiency limits. However, the performance of the collector system is limited by the heat transfer characteristics of the working fluid called as the heat transfer fluid (HTF). Water is widely used as the HTF in the solar collector, but the major problem of using water as the HTF is its limited operating temperature. The objective of the work is to investigate the heat transfer characteristics of ionic liquids in tubular heat exchanger (HE) suitable for the solar thermal application. The HE was designed for a heat duty of 1?kW based on the thermal transport property of available ionic liquids and the computational fluid dynamics (CFD) analysis was performed. The results indicate that there is only minimal deviation between the assumed and CFD data.     

U型管式全玻璃真空管太阳集热器的热性能

在U型管式全玻璃真空管集热器能量平衡分析的基础上,推导了集热器热损系数、效率因子等性能参数计算公式,其理论计算结果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温和环境温度之差是非线性关系,将两者的计算关系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接触热阻后,采用U型管连接方式不会对热水系统集热器效率造成太大影响。     

Experimental investigation and analysis of the hybrid solar collector

Hybrid solar collector is a new and innovative technique to harness all the spectrum of sunlight and hence generate a system to harness sunlight. This project deals with the fabrication of a parabolic trough which suits the required design of the solar collector. This project deals with the study of heat transfer across the receiver tube and mode of heat transfer across the hybrid solar collector, to optimise the design, to minimise the losses and maximise the heat and photon transfer to the receiver and power generating unit. Our aim is to study the heat exchange process across tube and to prevent the heating of solar panels from the radiations emitted by the receiver tube when light is focused on it and direct the working of solar collector to a maximum efficient way. We consider the radiation spectrum of sun to be of different waves and utilising each component of it – that is, visible and UV (consisting most of photons) and infrared (consisting of heating radiation) – and try to segregate them with the help of a water jacket and bring the temperature of the PV panels to an optimum condition.     

壁挂式太阳能空气集热器最佳供暖方式研究

以采用太阳能空气集热器的供暖系统为研究对象,实验研究了供暖效果的影响因素和改善策略下的运行效果,为更科学合理地进行太阳能空气集热器与建筑集成设计提供参考。     

冲缝吸热板渗透型太阳能空气集热器性能研究

介绍了冲缝吸热板渗透型太阳能空气集热器的结构,建立了传热数学模型。采用Matlab程序对传热数学模型进行求解,模拟研究了结构参数、运行参数对集热器热性能的影响。集热器出口空气温度的实测结果与模拟结果的平均偏差为0.99K,证明传热数学模型准确可靠。集热量随吸热板外表面发射率增大而降低,随集热器出口空气流量、太阳辐射强度的增大而升高,随环境温度的增大先降低后升高。集热器出口空气温度随吸热板外表面发射率、集热器出口空气流量的增大而降低,随太阳辐射强度、环境温度的增大而升高。     

Exergetic performance optimization of an endoreversible intercooled regenerated Brayton cogeneration plant. Part 2: Exergy output rate and exergy efficiency optimization

The exergy output rate and exergy efficiency performances of an endoreversible intercooled regenerative Brayton cogeneration plant are optimized based on the model which is established using finite time thermodynamic in Part 1 of this paper. It is found that the optimal heat conductance allocation of the regenerator is almost zero. When the total pressure ratio and the heat conductance allocation of the regenerator are fixed, it is shown that there exist two optimal intercooling pressure ratios, and two optimal groups of the heat conductance allocations among the hot-, cold- and consumer-side heat exchangers and the intercooler, which correspond to a maximum dimensionless exergy output rate and a maximum exergy efficiency. When the total pressure ratio is variable, there exist two optimal total pressure ratios which correspond to a double-maximum dimensionless exergy output rate and a double-maximum exergy efficiency, also the corresponding exergy efficiency and exergy output rate are obtained. The effects of the total heat exchanger conductance and the consumer-side temperature on the double-maximum dimensionless exergy output rate and the double-maximum exergy efficiency are discussed. It is found that there exists an optimal consumer-side temperature which correspond to a thrice- maximum dimensionless exergy output rate, and the intercooling process is not necessary by taking exergy efficiency as the objective when the consumer-side temperature is high.