Chimney Design Research Articles

Research and development in solar chimney power plant technologies: a review

Solar chimney power plant seems an alternative source for electrical power generation. The large volume canopy air heated in the system and flow through a small opening of chimney can produce the requisite kinetic energy to run the turbo-generator and generating electrical power. Few laboratory scale solar chimney power plants are running in the world; mostly used for R&D purpose. There is immense opportunity for research and development particularly in large size solar collector system, chimney design and low wind power generators. The present study deals with the comprehensive review of various design, analysis, and material aspects of solar chimney and integrated approaches of the practically realised design reported in previous studies. Some very recent developments in solar chimney power plant technologies are also highlighted.

P072 潜熱蓄熱板を組み込んだ温室換気用ソーラーチムニーの最適設計(メカボケーション学生研究発表セッション)

P072 潜熱蓄熱板を組み込んだ温室換気用ソーラーチムニーの最適設計(メカボケーション学生研究発表セッション)

An experimental investigation of an inclined passive wall solar chimney for natural ventilation

Ongoing investigations into solar chimney development have resulted in constantly evolving new designs. In this study, experiments are carried out with an inclined passive wall solar chimney (IPWSC) model with a uniform heat flux on the active (absorptive) wall. The effectiveness of this design has been examined for the heat flux range of 100W/m2–500W/m2 with a fixed base air gap width of 0.1m and inclination angles of the passive wall in the range of 0–6 degrees. The experimental results show that the inclination angle of the passive wall has no significant effect on the temperature distribution across the air gap width and along the chimney height. On the other hand, the averaged air flow velocity across the air gap width is strongly affected by the inclination angle. The experimental results also show that the IPWSC with 0.7m absorber height and 0.1m air gap width at an inclination angle of 6° and input heat flux of 500W/m2 can produce sufficient ventilation for a 27m3 room based on ASHREA standards. Further, the present experimental results show that the IPWSC design can significantly improve the ventilation performance of a solar chimney in comparison to the conventional chimney design with vertical passive wall configuration. The experimental results are supported by flow visualization experiments and are consistent with scaling predictions.

Simulation and optimization of geometric parameters of a solar chimney in Tehran

An analytical and numerical study for geometrical optimizing of a solar chimney prototype at University of Tehran was performed. A fundamental mathematical model that describes the flow was presented, and the performance evaluation of solar chimney was simulated with operational and geometric configurations. The numerical predictions were validated through comparison with the experimental data of the solar chimney pilot which was constructed in height of 2m and collector radius of 3m. The results show that, the collector inlet of 6cm, the chimney height of 3m, and the chimney diameter of 10cm were the best alternatives for the constructed solar chimney pilot. It is found that the velocity magnitude can be raised to 4–25% in different cases; also the analysis indicated that the height and diameter of the chimney are the most important physical variables for solar chimney design.

Design guideline for application of earth-to-air heat exchanger coupled with solar chimney as a natural heating system

Abstract In the present paper, design of solar chimney (SC) and earth-to-air heat exchanger (EAHE) to meet thethermal need of flat buildings are studied regarding adaptive thermal comfort criteria. Investigation onthe effects of geometric features shows that the design of SC with the air gap and outlet sizes of 0.2 m andalso EAHE with the diameter and length of 0.5 and 25.0 m reveals better performance. Thermal comfortanalysis shows that the SC is capable to power the underground heating system during few hours of thesunny days even at the ambient temperature as low as 08C and the heating demand of 1000 W withoutneeding the auxiliary devices. In addition, the required numbers of SCs and the underground air channelsare strongly influenced by environmental outdoor conditions and heating demand of building and areapproximately calculated by: room volume/50and 2 ð room volume/50Þþ1, respectively. Keywords: Design; earth-to-air heat exchanger; natural heating; solar chimney Received 31 July 2013; revised 23 November 2013; accepted 4 January 2014

Experimental, CFD simulation and parametric studies on modified solar chimney for building ventilation

The solar chimney is a passive solar system which can be used for enhance the natural ventilation and space conditioning of a building. A solar chimney design is modified and installed at CBRI Roorkee (29.87° N 77.88° E), India. A Computational fluid dynamics (CFD) software is used for prediction of velocity and temperature in Modified solar chimney (MSC) and evaluating the Air Change per hour (ACH), which is validated through experimental and theoretical counterpart and found a good agreement between them. From the result of thermal performance analysis, it is found that MSC generates 2.39–7.13 ACH in experimental room in month of May 2013, when outdoor solar radiation was in the range of 250–612 W/m2. Due to this ACH, the room temperature is dropped by 2–4°C as compared to reference room temperature. The parametric study shows that the optimum glass tilt angle estimated by 5 degree for highest performance consideration of MSC. The air gap is optimised by 60 mm and air gap to inlet opening height ratio is optimised by 0.2.

Numerical simulation of turbulent flow mixing inside a square chimney structure of a research reactor

Abstract Numerical simulation was performed to study the turbulent mixing behavior of two opposing flows inside a square chimney structure of a research reactor. The chimney design facilitates drawing pool water in the downward direction and thereby suppresses the upward flow of radioactive water jet to limit the radiation field at the reactor pool top. Analyses were carried out considering a mass flow rate of 750 kg/s for the upward flowing hot water from the core, which corresponds to Reynolds number of 3 × 106. Mass flow ratios of the downward flow and the upward flow were 0.0, 0.05, 0.1 and 0.15. The effects of mass flow ratio, chimney height on the velocity and temperature distribution inside three-dimensional chimney structure was evaluated using CFD code PHOENICS. The effect of temperature difference between the opposing flows on velocity was also analysed. It is observed that increase in downward flow causes the jet height to decrease due to the opposing momentum of downward flow against the upward jet. The effects of chimney height and temperature difference on the jet height are found to be marginal because of dominating inertial force over buoyancy force for the study.

Parameterization Studies of Solar Chimneys in the Tropics

The paper examines the effect of the solar chimney’s stack height, depth, width and inlet position on the interior performance (air temperature and speed at 1.20 m height above the ground) as well as proposes an optimal tropical solar chimney design. Simulations show that the output air temperature remains constant while the solar chimney’s width is the most significant factor influencing output air speed. The solar chimney’s inlet position has limited influence on the output air speed although regions near the solar chimney’s inlet show an increase in air speed. Furthermore, a regression model is developed based on the solar chimney’s stack height, depth and width to predict the interior air speed. To optimize solar chimney in the tropics, the recommendation is to first maximize its width as the interior’s width, while allowing its stack height to be the building’s height. Lastly, the solar chimney’s depth is determined from the regression model by allocating the required interior air speed.

Design and zonal building energy modeling of a roof integrated solar chimney

Roof integrated solar chimneys use solar radiation to heat air and induce natural ventilation through a house. They can improve the performance of roof integrated photovoltaic arrays by removing heat absorbed by the panels, and enhance buoyant free cooling at night. This paper studies an unobtrusive, integrated solar chimney design in a detached single family home. A method for modeling it in the zonal building energy modeling program ESP-r is proposed, to assist in evaluating the design and predicting the thermal dynamics in changing ambient conditions. The model discretizes the solar chimney by dividing it into several zones to better resolve the airflow and heat transfer. Computational fluid dynamics is used to calibrate key model inputs. The results show that with the proposed rooftop design, the chimney airflow is induced mainly by buoyancy forces whenever the temperature difference from interior to ambient differs by more than a few degrees, so there is the potential to provide effective free cooling. A sensitivity analysis evaluates the model's sensitivity to several inputs and assumptions. It confirms that the inside to ambient temperature difference is the most important predictor of ventilation airflow. Solar insolation levels are less important, being significant for less than one third of the time-steps sampled. Sensitivity of modeling results to uncertainty in the calculation of the convection coefficient is explored, showing there is high sensitivity in the prediction of the heat transfer normal to the surface of the roof, but low sensitivity in the prediction of the rate of ventilation airflow through the house and the temperature of the roof surface. The amount of pressure loss in the flow through the vent at the entrance to the chimney is a significant factor for the ventilation flow rate.

The thermal efficiency improvement of a steam Rankine cycle by innovative design of a hybrid cooling tower and a solar chimney concept

In the present work, a dry cooling tower and a solar chimney design are recombined in order to increase the thermal efficiency of a steam Rankine cycle. The rejected heat from the condenser into the dry cooling tower supplemented by the solar radiation gained through its transparent cover are the sources of wind energy generation that is captured by a wind turbine which is located at the beginning of the chimney. In this research a case study for a 250 MW steam power plant of Shahid Rajaee in Iran has been performed. A CFD finite volume code is developed to find the generated wind velocity at the turbine entrance for a 250 m dry cooling tower base diameter and a chimney height of 200 m. Calculations have been iterated for different ambient temperatures and solar irradiances, representing temperature gradient within day length. A range of 360 kW to 3 MW power is obtained for the change in the chimney diameter from 10 to 50 m. The results show a maximum of 0.37 percent increase in the thermal efficiency of a 250 MW fossil fuel power plant unit; which proves this design to be a significant improvement in efficiency of thermal power plants, by capturing the heat that is dissipated from dry cooling towers.

A numerical study of flow and mixing characteristics inside the chimney structure of a pool type research reactor

Numerical studies were performed to examine the effects of flow velocities of opposing streams on the flow pattern and turbulent mixing characteristics in a three-dimensional chimney structure using CFD code PHOENICS. This chimney structure facilitates guiding of the radioactive water from the reactor core (i.e., core flow) towards the side outlet nozzles and simultaneously drawing out water from the reactor pool through the chimney top. The radioactive water flows upward and has a tendency to reach to the pool top through the chimney top which is open for fuel and isotope handling. The chimney design allows drawing out a part of the pool water in the downward direction to suppress the upward flowing radioactive water jet. This downward flow through the chimney is compensated by providing additional core bypass flow to the pool. Analyses were carried out on 1:1 chimney structure and also on 1/6th scaled down chimney model to understand the similarity of behaviour of the model and the prototype. Mass flow rate of upward flowing water (i.e. core flow) is considered to be 750kg/s and core bypass flow is varied from 0% to 15% that of the core flow. In the model study, mass flow rate was varied from 8.33 to 25kg/s and core bypass flow was considered to vary from 0% to 15%. Flow mixing pattern inside the chimney and the non-dimensional stagnation depth was predicted for the model and the prototype. It was observed that there is a good similarity in behaviour of the prototype and model.

Structural analysis of reinforced concrete chimneys subjected to uncontrolled fire

We studied the behavior and residual structural capacity of reinforced concrete chimneys subjected to an uncontrolled fire. We used a combination of a heat transfer finite element model–to obtain the temporal distributions of temperature during the fire event–and the structural model of concrete chimney design provided by the American Concrete Institute (ACI 307–08). This approach allows estimating the reduction in the vertical (axial) strength and moment strength of the chimney both during a fire and post-fire, and gives a direct estimate of the reduction in the safety factors of the concrete chimney. Using this method, we examined the impact of various design parameters on the residual structural capacity of a concrete chimney subjected to an internal fire. An iterative finite element method was also presented as an alternative to the ACI 307 calculations. Moreover, finite element calculations were used to study the role of thermal stresses on the axial strength of the chimney during fire. Our study provides insight into possible failure mechanisms of concrete chimneys damaged due to fire and could suggest possible approaches for minimizing the risk of chimney failure due to an uncontrolled fire.

Analysis of Collapsed Chimney of Balco Power Plant in India

A large under-construction chimney at BALCO Power Plant in central India collapsed on Sep. 23, 2009 under severe stormy weather, causing serious casualties and massive economic losses, while another, similarly built, survived. So far, there has been no strict and scientific analysis on the cause of the accident. In this paper, finite element method is used to simulate the effect of wind loads and the whole collapse procedure based on the investigation of information about the design, the construction, the site related records, etc. The results show that the initial part of the chimney destroyed is the top of the structure (specifically the construction platform and the partial top cylinder wall of the chimney); then the debris from the top fells and crashes the lower part of the structure, eventually leading to the whole structure collapsing. The analysis results are basically consistent with the observation of the debris and the toppling scene and what the witnesses described, and scientifically clarify the actual cause of the chimney collapse. In addition, by comparing the chimney design codes between the USA and China, along with the analysis results, some suggestions are proposed to prevent similar accidents in chimney projects.

Constructal Distribution of Solar Chimney Power Plants: Few Large and Many Small

In this paper, we show how to use constructal design to distribute solar chimney power production on available land area most efficiently. The solar chimney design is used as an example of solar-driven power plant. We found that the power generated per unit of land area is proportional to the length scale of the power plant, as well as to the chimney height, roof radius, and chimney radius. It was also found that the chimney height, roof radius, and chimney radius cannot increase independently and indefinitely. Because of the flow resistances associated with distributing the power over a territory, the land area for each power plant must be finite and allocated optimally. Several patterns of the multi-scale plants on a square area are explored. The global performance of such patterns is greater when more land area is allocated to the largest plant. This performance depends comparatively less on the total land area covered by all power plants.

Analysis of a solar chimney power plant in the Arabian Gulf region

A simplified thermodynamics analytical model for steady airflow inside a solar chimney is performed. A simplified Bernoulli equation combined with fluid statics and ideal gas equation was implemented and solved using EES solver to predict the performance of the solar chimney power plant. The analytical model matched the experimental data and numerical study available in the literature. The developed analytical model was used to evaluate the effect of geometric parameters on the solar plant power generation. The analysis showed that chimney height and turbine pressure head are the most important physical variables for the solar chimney design. The study showed that second-law efficiency has non-monotonic relation with turbine pressure head. The model shows that second-law efficiency and power harvested increase with the increase of chimney height and/or diameter. The developed model is used to analyze the feasibility of solar chimney power plants for the UAE climate which possesses typical characteristics of the Gulf climate. The solar characteristics of the UAE are shown along with characteristic meteorological data. A solar chimney power plant with a chimney height of 500 m and a collector roof diameter of 1000 m would produce at least 8 MW of power. The amount of power produced during the summer would be higher where the demand in the Gulf area is the highest.

Initial Buoyancy Reduction in Exhausting Smoke With Solar Chimney Design

A possible problem in using solar chimney as a natural smoke exhaust system will be identified in this paper. Smoke generated in a fire might not be removed effectively if the glazing walls are heated up due to exposure to solar radiation. It is because the buoyancy of the smoke is reduced initially in the solar chimney. This phenomenon of reducing buoyancy will be discussed. A simple equation of motion on smoke movement was set up. Some of the results of full-scale burning experiments carried out earlier for assessing the fire response of a glass façade system were applied to support the argument. Experiments indicated that smoke would take a longer time to move up when the glazing wall temperature is higher. A better smoke exhaust design accounting the reduction in buoyancy at this early stage of a fire should be worked out.

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/m 2, 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 m 3/h was measured on that day. Thus, an average air flow rate of 177 m 3/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.

Evaluation of Turtle Exclusion and Escapement Devices for Hoop‐Nets

Abstract Baited and unbaited hoop-nets commonly are used to capture catfish in lotic and lentic systems. Turtle bycatch and post-capture mortality has been problematic during catfish surveys in Missouri, USA, most recently in the Gasconade River, Gasconade and Osage counties. We evaluated 3 modified hoop-net designs that would reduce turtle bycatch without reducing catfish capture in the Gasconade River during 15 May–15 July 2006 after pilot study evaluation of 5 hoop-net designs in April 2006. We deployed modified and control-nets in blocks for 48 hours to evaluate differences in turtle and catfish catch rate, as well as abundance, size, and mortality rate of turtle bycatch. The chimney design reduced turtle bycatch by 84% when compared to the control, without decreasing the number or average size of captured flathead catfish (Pylodictis olivaris). Environmental conditions that affected turtle mortality included Secchi disc transparency, temperature, dissolved oxygen, and stream river depth. This is the ...

Theoretical evaluation of the influence of geometric parameters and materials on the behavior of the airflow in a solar chimney

An analytical and numerical study of the unsteady airflow inside a solar chimney was performed. The conservation and transport equations that describe the flow were modeled and solved numerically using the finite volumes technique in generalized coordinates. The numerical results were physically validated through comparison with the experimental data. The developed model was used for airflow simulation in solar chimneys with operational and geometric configurations different from those found in the experimental prototype. Analysis showed that the height and diameter of the tower are the most important physical variables for solar chimney design.

Solar chimney and building ventilation

This study is concerned with the design of a solar chimney to induce ventilation in a building. CFD modelling techniques were used to assess the impacts of inclination angle, double glazing and low-emissivity finishes on the induced ventilation rate. It was found that for a south-facing chimney, an inclination angle of 67.5° from the horizontal was optimum for the location chosen, giving 11% greater efficiency than the vertical chimney, and that a 10% higher efficiency was obtained by using a low-emissivity wall surface.