Dynamic physical model for a solar chimney

The aim of this research is to investigate the theoretical usefulness of a solar chimney with thermal inertia applied to the Mediterranean climates, offering nocturnal ventilation benefits. A mathematical dynamical model is proposed to evaluate the energy performance of a solar chimney with 24 cm concrete wall as storage surface for solar radiation. The results obtained with the proposed model are coherent with several models response and experiments reported on solar chimneys. As well, the difference of the proposed model to others is the incorporation of an unsteady state and the inclusion of thermal inertia. The results show that for a 2 m height and width of air channel of 14.5 cm, 0.011 kg/s air mass flow rate is obtained for 450 W/m². The 24 cm thickness concrete wall, reaches its greater temperature 2 h later with respect to the maximum ambient temperature, maintaining its temperature over the beginning of the night, so nocturnal ventilation is achieved. The model shows the interest in continuing investigating on this cooling techniques and to built a solar chimney with thermal inertia for future experimental research.     

Analysis of solar chimney power plant utilizing chimney discrete model

The paper presents a mathematical thermal model for steady state airflow inside a solar chimney power plant using modified Bernoulli equation with buoyancy effect and ideal gas equation. The study evaluates the use of constant density assumption across the solar chimney and compares it with more realistic chimney mathematical discrete model that allows density variation across the chimney. The result shows that using a constant density assumption through the solar chimney can simplify the analytical model however it over predicts the power generation. The results show that the chimney height, the collector radius, the solar irradiance, and the turbine head are essential parameters for the design of solar chimneys. The maximum power generation depends on the turbine head and the relation is not monotonic.     

Performance analysis of solar chimney using mathematical and experimental approaches

A mathematical model based on one‐dimensional energy and mass balance across the solar chimney has been developed. The air flow characteristics such as exit velocity and temperature are evaluated with respect to the collector inclination angle, hourly solar radiation, ambient temperature, and wind speed. The model is validated by comparing the performance parameters obtained, with the experimental results and also with the experimental data of different geometrical range and environmental conditions from the literature. An average deviation of 8% for exit air velocity and 1.35% for exit air temperature is obtained for the solar chimney with absorber inclination angle 30°, collector area 0.41 m², and chimney height 0.24 m. The experimental daily average and maximum exit air velocity during the month of April are 0.5 and 0.88 m/s, respectively. The predicted optimum operating conditions are 75° inclination angle, 0.63 m² absorber area, and 0.48‐m chimney height. The maximum average exit air velocity and temperature numerically obtained are 0.64 m/s and 331 K, respectively, when operating with optimum conditions. It is observed that the exit air velocity increases 33% by increasing the absorber area from 0.5 to 3 m² for a solar chimney with 0.5 m height. An increase in exit air velocity of 52% was obtained by increasing the chimney height from 0.5 to 3 m for a solar chimney with 0.64 m² absorber area. A reduction in exit air velocity of 4% was observed for the increment in wind flow over the glass cover from 1.5 to 3 m/s. These results confirm that the solar chimney could be designed based on the predicted monthly performance by the present model.     

Experimental and theoretical performance of a demonstration solar chimney model—Part I: mathematical model development

The solar chimney is a natural draft device which uses solar radiation to provide upward momentum to the in-flowing air, thereby converting the thermal energy into kinetic energy. A study was undertaken to evaluate the performance characteristics of solar chimneys both theoretically and experimentally. In this paper, a mathematical model which was developed to study the effect of various parameters on the air temperature, air velocity, and power output of the solar chimney, is presented. Tests were conducted on a demonstration model which was designed and built for that purpose. The mathematical model presented here, was verified against experimental test results and the overall results were encouraging. © 1998 John Wiley & Sons, Ltd.     

Performance of a solar chimney

A mathematical model of a solar chimney was proposed in order to predict its performance under varying ambient and geometrical features. Steady state heat transfer equations were set up using a thermal resistance network and solved using matrix inversion. Existing correlations of heat transfer coefficients were utilised. Property values for the air flow in the duct were based on mean bulk or film temperatures. The performance of the chimney was evaluated by predicting the temperatures of the glass glazing and the heat-absorbing wall and also the temperature and velocity of the induced air flow in the chimney. The effects of air gap and solar radiation intensity on the performance of different chimneys were investigated. In order to verify the theoretical model, experiments were conducted on a 2 m high×0.45 m wide physical model with air gaps of 0.1, 0.2 and 0.3 m. Experiments were carried out outdoors on the roof and the experimental model exposed to both direct and diffuse solar radiation. Air velocities between 0.25 m s⁻¹ and 0.39  m s⁻¹ for radiation intensity up to 650 W m⁻² were obtained. No reverse air flow circulation was observed even at the large gap of 0.3 m.     

Thermodynamic study of a simplified model of the solar chimney power plant

A simplified model of solar chimney power plant (SCPP) consists of a heating air collector, turbine and chimney. Thermodynamic interpretation of processes occurring in these SCPP components is based on the derived energy and exergy balances. The examples of the energy and exergy flow diagrams show how the SCPP input of 36.81 MW energy of solar radiation, corresponding to 32.41 MW input of radiation exergy, is distributed between the SCPP components. Responsive trends to the varying input parameters are studied. Additionally, the concept of mechanical exergy (ezergy) of air is applied and it allowed for quantitative determination of the effect attributed to the terrestrial gravity field on the component processes of the SCPP.     

A mathematical model of heat-exchange control in solar greenhouses

A mathematical model of the heat exchange process in solar greenhouses is developed on the basis of an analytical approach. The possibility of approximating complicated transfer functions by simpler ones that are suitable for practical calculations is shown.     

Constructal solar chimney configuration

In this study, we describe the constructal-theory search for the geometry of a solar chimney. The objective is to increase the power production over the area occupied by the plant. The ratio height/radius, maximum mass flow rate and maximum power under the constraints of a fixed area and volume are determined. We find that the power generated per unit of land area is proportional to the length scale of the power plant. The analysis is validated by a detailed mathematical model. Pressure losses are reported in terms of the dimensionless length scale of the system, and are illustrated graphically. They indicate that the pressure drop at the collector inlet and at the transition section between the collector and chimney are negligible, and the friction loss in the collector can be neglected when the svelteness (Sv) of the entire flow architecture is greater than approximately 6.     

Numerical simulations of solar chimney power plant with radiation model

A three-dimensional numerical approach incorporating the radiation, solar load, and turbine models proposed in this paper was first verified by the experimental data of the Spanish prototype. It then was used to investigate the effects of solar radiation, turbine pressure drop, and ambient temperature on system performance in detail. Simulation results reveal that the radiation model is essential in preventing the overestimation of energy absorbed by the solar chimney power plant (SCPP). The predictions of the maximum turbine pressure drop with the radiation model are more consistent with the experimental data than those neglecting the radiation heat transfer inside the collector. In addition, the variation of ambient temperature has little impact on air temperature rise despite its evident effect on air velocity. The power output of the SCPP within the common diurnal temperature range was also found to be insensitive to ambient temperature.     

太阳能烟囱制冷系统的研究

通过分析制冷系统和太阳能烟囱热气流发电系统的技术和特点,提出了太阳能烟囱制冷系统.将太阳能烟囱系统与制冷系统相结合进行制冷,可实现制冷不用电.该系统由烟囱、集热棚、蓄热层、涡轮机、开启式制冷压缩机、冷凝器和变速器等组成.介绍了太阳能烟囱制冷系统的结构特点、工作原理以及系统相关参数的计算方法.分析结果表明,太阳能烟囱制冷系统结构简单,运行维护方便,制冷不用电,无污染,具有良好的环境效应,可根据环境温度改变压缩机运行转速调节供冷负荷,能有效解决热带及沙漠地区的供冷及供电问题.     

A mathematical model of thermal performance of a solar air heater with slats

A mathematical model for computing the thermal performance of a single pass flat-plate solar air collector is presented. Air channels were formed by providing metal slats running along the circulated air passage linking the absorber plate by the bottom one in an endeavor to enhance the thermal efficiency of the solar air collector. A mathematical model, therefore, is developed by which the influence of the addition of the metal slats on the efficiency of the solar collector is studied. A computer code that employs an iterative solution procedure is constructed to solve for the governing energy equations to estimate the mean temperatures of the collector. The effect of volume airflow rate, collector length, and spacing between the absorber and bottom plates on the thermal performance of the present solar air heater was investigated. Furthermore, a numerical comparison of the present design with the most common type of solar air heaters is conducted. The results of the comparison have indicated that better thermal performance was obtained by the modified system.     

Analysis of chimney height for solar chimney power plant

Current in solar chimney power plant that drives turbine generators to generate electricity is driven by buoyancy resulting from higher temperature than the surroundings at different heights. In this paper, the maximum chimney height for convection avoiding negative buoyancy at the latter chimney and the optimal chimney height for maximum power output are presented and analyzed using a theoretical model validated with the measurements of the only one prototype in Manzanares. The results based on the Manzanares prototype show that as standard lapse rate of atmospheric temperature is used, the maximum power output of 102.2 kW is obtained for the optimal chimney height of 615 m, which is lower than the maximum chimney height with a power output of 92.3 kW. Sensitivity analyses are also performed to examine the influence of various lapse rates of atmospheric temperatures and collector radii on maximum height of chimney. The results show that maximum height gradually increases with the lapse rate increasing and go to infinity at a value of around 0.0098 K m^?1, and that the maximum height for convection and optimal height for maximum power output increase with larger collector radius.     

A simplified mathematical model for predicting the nocturnal output of a solar still

The production capacity of a solar still which converts saline water to fresh water can be increased by introducing hot feed water into the unit at night. A waste heat source, such as cooling water from a power plant, can be used to preheat the feed. The nocturnal production, i.e. the distilled water produced at night, seems to be influenced by several parameters. However, a simplified mathematical model suggests that the distillate depends only on the initial brine temperature, the drop in brine temperature and the brine depth. This was experimentally verified for different brine depths and for initial brine temperatures up to 150°F.     

A mathematical model for the anodic half cell of a dye-sensitised solar cell

We present a mathematical model of the steady-state current produced by the anodic half cell of a dye-sensitised solar cell (DSC) under both illuminated and non-illuminated conditions. A one-dimensional transport model that describes the transport of charged species via migration and diffusion within the electrolyte filled pores and the porous semiconductor that constitutes the porous anode of the DSC is given. This model is coupled to an interfacial model, developed previously by the authors, that describes charge transfer across the semiconductor–dye–electrolyte interface by explicitly accounting for each reaction at the interface involving dye molecules, electrolyte species, and semiconductor electrons. An equivalent circuit extension to the anode model (in the form of a boundary condition) is developed in order to validate some of the simulation results of the anode model with experimental results obtained from a full DSC specifically commissioned for the study. Parameter values associated with the model are obtained from the literature or experimentally from the specifically commissioned cell. A comparison of the numerical simulation results with experimental results shows a favourable correspondence without the need to fit parameter values.     

The solar cyclone: A solar chimney for harvesting atmospheric water

The Solar Cyclone has been introduced as a means of extracting fresh water from Earth's atmosphere. The conceptual device operates in the fashion of a Solar Chimney; it is composed of a greenhouse for collecting and storing solar energy as heat, with a central chimney that channels an updraft of surface air heated in the greenhouse. An expansion cyclone separator for condensing and removing atmospheric water is placed at the base of the chimney. The separator consists of a strongly rotating vortex in which the central temperature is well below the dew point for the greenhouse air. Power consumed in the expansion and separation is furnished by the motive potential of the chimney updraft. Turbulent flow conditions are established in the expansion cyclone separator to enhance the centrifugal separation. Excess updraft power is used to generate electricity, as is done in the Solar Chimney. The article furnishes a theoretical basis for the feasibility of the Solar Cyclone, suggesting that an experimental study of the separation device would be worthwhile.     

太阳能热风发电系统集热器热物理模型及分析

集热器是太阳能热风发电系统的重要组成部分.文章建立了集热器的热物理模型,分析了集热器各部分的传热过程和集热器效率的计算方法.介绍了集热器热损失的求解方法,即利用热阻法求解和根据经验公式求解.     

A two-dimensional simulation method of the solar chimney power plant with a new radiation model for the collector

A two-dimensional axisymmetric CFD method is proposed for the solar chimney power plant (SCPP), which includes a solar radiation model within the collector, an energy storage model, an air flow and heat transfer model, and a turbine model. Numerical simulation is conducted for the Manzanares pilot plant. Different solar radiation modes in the collector and simulation methods are compared and discussed. Results show that the present two-dimensional method obtains consistent results with the three-dimensional method in the literature and experiment data, validating the feasibility of the proposed two-parallel-plate model for the radiation heat transfer within the collector.     

关于太阳能建筑气流电站的设想

一前言 最早的"烟囱"形太阳能气流电站是由上百吨钢板建造的,其缺陷是大烟囱耗费材料多,在室外日晒雨淋薄钢板容易生锈,使用寿命短.为解决大烟囱经久耐用的问题,则需要投入更多的材料和人力,耗费巨大,成为气流电站推广使用的拦路虎.     

Experimental study for natural ventilation on a solar chimney

Thermal performance of a solar chimney for natural ventilation was experimentally investigated. The experimental model was implemented on full scale and real meteorological conditions, so that experimental results will be compared with the simulation results. The results show that for a maximum irradiance of 604 W/m², occurring around 13:00 h on September 15th, 2007, a maximum air temperature increment of 7 °C was obtained through the solar chimney. Also, a volumetric air flow rate ranging from 50 to 374 m³/h was measured on that day. Thus, an average air flow rate of 177 m³/h was achieved from 0:00 h to 24:00 h. The experimental solar chimney discharge coefficient, C_d, was 0.52. This coefficient is useful to determine the mass flow rate in the solar chimney design. It was observed that the air flow rate through the solar chimney is influenced by a pressure difference between input and output, caused by thermal gradients and wind velocity, mainly.