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.     

Experimental investigation of solar heating and humidification system based on desiccant bed heat exchanger

In this article, an experimental investigation has been made on a solar heating and humidification system. In this system, an evacuated tube solar water heater is connected to the desiccant bed heat exchanger (DBHE) by connecting pipes. The evacuated tube solar water heater supplies required heat to the DBHE for the regeneration of desiccant material. Various types of solid and composite desiccant materials have been used in the DBHE to investigate their effect on the system performance. It has been found that the system obtained its best performance with silica gel with average humidification rate of 0.63?kg/h. The maximum temperature difference of process air has been found as 16°C at the flow rate of 295.2?kg/h.     

Experimental analysis of thermal performance of evacuated tube solar air collector with phase change material for sunshine and off-sunshine hours

An experimental investigation of an evacuated tube solar air collector coupled to a latent thermal energy store for generating hot air when no solar radiation is incident was undertaken. Acetamide was used as a phase change material (PCM). The latent thermal energy store was integrated with the manifold of the solar collector and water was used as the working fluid transferring solar gain to the air being heated. The maximum measured temperature differential between the heated air and the ambient air was 37°C and 20.2°C during conditions of incident and non-incident solar radiation, respectively. This occurred using a circular fin configuration at a flow rate of 0.018?kg?s^?1. The efficiency at low (0.018?kg?s^?1) air flow rates was 0.05–0.50 times less as compared to high (0.035?kg?s^?1) air flow rates. This system has advantages over systems using sensible storage as it can be used after sunset due to better heat storing capacity of the PCM.     

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.     

A comparative performance analysis of solar heat exchangers for solar hot water application under controlled laboratory conditions

The paper presents the experimental performance evaluation of a novel retrofit heat exchanger (‘SolaPlug’) developed for solar hot water storage applications. The performance of this system was compared with a traditional dual-coil (‘Coil’) solar cylinder under controlled operating conditions. The tests were conducted under different solar-simulated conditions with a 30 and 20 evacuated tube collector. The results showed that after a 6-h test period, the average water temperatures within the store for the ‘SolaPlug’ system were 58.8°C and 40.5°C at 860 and 459?W?m^?2, respectively, and for the ‘Coil’ system were 60.5°C and 40.6°C when a 30 tube collector was used. The performance of the ‘SolaPlug’ system was marginally better than the ‘Coil’ system under the low solar input condition. Under high insolation condition, the overall ‘SolaPlug’ system efficiency was found to be 4.3% lower than that of the ‘Coil’ system. The ‘SolaPlug’ heat exchanger rating was 222?W?K^?1.     

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 performance of the solar parabolic trough collector at different flow rates: an experimental study

Currently, the most capable thermal systems based on the solar energy are the concentrating collectors, which are essentially finding applications in power generation and process industries. In the present study, thermal performance of the parabolic tough collector (PTC) is investigated experimentally at different flow rates of working fluid. Mass flow rate is one of the key parameters influencing its performance. Here, PTC is constructed as a simple structure having a non-evacuated tube and tested in tracking and south-facing modes utilising water as the working fluid. The performances in terms of water temperature rise, useful heat gain, collector efficiency are evaluated with and without utilising glazing on the receiver. Results revealed that performance of collector chiefly depends upon the mass flow rate and no considerable change is found when the flow rate of water is more than 0.024?kg/s. Furthermore, small-sized PTC offers slight better performance in the south-facing than the tracking mode.     

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.     

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。     

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。     

太阳能平板集热器关键参数对其热性能的影响

为了提升太阳能在建筑能源供给体系中的比重,形式多样的太阳能集热设备及其系统在建筑领域得到了广泛应用。基于机理分析法,建立了具有单层玻璃盖板的管板式太阳能平板集热器的稳态传热模型。并且针对集热管间距、集热管内径、工质入口温度和工质质量流量等关键参数对集热器集热效率的影响特性进行了数值模拟与分析。结果表明,建立的该稳态传热模型是可行的;此外,在其余参数值保持不变的情况下,减小集热管间距或增加集热管内径均可使集热器瞬时效率增大;增大工质入口温度会导致集热器瞬时效率下降;而增大工质质量流量会提升集热器瞬时效率。这些结论对于太阳能平板集热器在太阳能建筑一体化的实际应用中,具有一定的参考作用。     

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。     

Experimental study on productivity enhancement of an improvised inclined solar still

Experimental studies are carried out on the inclined solar still with baffle plates for enhancing its performance. The baffles placed in the inclined solar still act as a solar collector which helps in increasing the contact time with solar radiation thereby raising the saline water temperature. Experiments are carried out during winter and early summer climate of Chennai, India. Experimental parameters, such as ambient temperature, solar radiation, glass temperature, water temperature and distillate output are recorded. Hourly productivity is found to be higher during sunny days. The estimated production of fresh water through analytical study is 3.50?kg/m² per day for a minimum mass flow rate of 0.0833?kg/min. The actual experimental yield is 2.793?kg/m² per day. Also, the inlet saline water temperature affects the yield and the latter is found to be highest at 48.5°C.     

Experimental analysis of the performance of a solar flat plate water heater with and without internal fins

Generally increasing, an increase in the surface area will increase the heat transfer capability of a solar collector and possibly its efficiency. Conventional solar water heaters have longitudinal fins attached externally to the collector tubes for reaping the benefits of enhanced heat transfer. Attempts have been made towards providing internal fins (spirally grooved copper tubes), in addition to the existing external fins for analysing its influence on efficiency and outlet temperature. Two identical solar water heaters with a capacity of 25?L per day were designed and fabricated, one with a collector with plain (unfinned) internals and another with internal grooving (finned tube). The paper details the temperature profile observed in the two collectors, variation of thermo-siphon mechanism and change in efficiency of the solar water heaters with respect to time. It has been observed that providing internal fins had led to an increase in efficiency of about 4.5% as compared to conventional plain tubes.     

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.     

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.     

Experimental exergy analyses on fabricated parabolic solar collector with/without preheater and different collector materials

This is an experimental work, to get maximum performance by parabolic solar collector (PSC). Three different PSCs are opted with same dimensions for this experimental work; mirror, aluminium and preheater–aluminium collectors. Copper, aluminium, mild steel and brass are selected for various absorber pipe materials. By experimental analyses, fluid temperatures, convective heat transfer coefficients, overall heat loss coefficients, heat removal factors, collector efficiency factors, inlet exergies, outlet exergies, exergy gains and exergy efficiencies are obtained at a range of operating conditions for fabricated PSCs. Exergy analyses are conducted with various fluid flow rates and with different PSCs and then graphs are also generated for these analyses. After analyses, this work can be concluded as – the brass as absorber pipe material and preheater–aluminium sheet combination as PSC are the most excellent to achieve the most favourable performance from fabricated system. This combination gives maximum exergy efficiency which is near about 78%.     

Collector characterisation and heat loss tests on a novel batch solar water heater with CPC reflector for households

ABSTRACT

This solar water-heating unit is an integration of the older concept of batch water heating with the modern trends in solar water-heating technologies i.e. incorporating a concentrator in the design. The concentrator used is the compound parabolic type (CPC) which is a non-imaging device having wider acceptance angle (64°) and supported on a wooden cradle, which comprises the two arms of the parabola. To suppress the heat loss, an air gap has been introduced in the arms of the CPC. The collector is a single larger diameter drum which serves both as an absorber and storage unit positioned at the focus of CPC. The parametric study of the model showed the thermal efficiency of the collector as high as 38% and maximum water temperature attained was 53°C. Heat loss tests performed on the collector on a 24-hr cycle period showed good long time performance estimates. The response time of collector computed and performance characteristic curve plotted to predict system response under any given conditions of solar insolation and ambient temperature.     

A theoretical study of Cu-H2O nano-fluid effect on heat transfer enhancement of a solar water heater

In the present work, an attempt has been made to enhance the heat transfer in a solar water heater by using Cu nano-particles dispersed in water for various concentrations ranging from 0% to 5%. Considerable improvement in the solar collector efficiency is obtained by increasing the nano-particle concentration up to 17.5 for a concentration of 5% and for a mass flow rate ratio of 10. The outlet water temperature increases by increasing the nano-particle concentration up to 8.35% for a concentration of 5% and for a mass flow rate ratio of 5. The study showed that the solar heater collecting area takes into account significant factors for increasing the outlet temperature. An increase in the collecting area of the solar water heater by 6 times could increase the water temperature by 39% for a 5% nano-particle volume fraction. The helical heat exchanger effectiveness is increased up to 65.71 for a concentration of 5% for a mass flow rate ratio of 10.     

Design and development of a solar-based cooker with a mechanical sun tracking system

ABSTRACT

This research paper proposes the design and development of a solar-based cooker with a mechanical parabolic trough sun tracking system. This novel design uses a typical mechanical clock system for the sun tracking. The automated solar tracking system is achieved by a water float linked through a tow pulley to the gearbox. The gearbox is connected to a pulley on the shaft that connected to the dish. The driving weight required by the solar tracking collector system has been estimated. The value of the summation of all loads chosen as the driving load is 1.5?kg with a force of 14.7?N. Experiments have been conducted to measure the temperature at the centre of the parabolic trough for cooking applications, bread baking in particular.