Chimney Height Research Articles

Power generation quality analysis and geometric optimization for solar chimney power plants

Solar chimney power plant (SCPP) is one of the promising power generation approaches for future applications of solar energy. An unsteady comprehensive mechanism model and a streamlined unsteady mechanism model of SCPPs are derived to analyze the energy conversion and transmission of the system in this paper. The streamlined unsteady mechanism model with concise expressions clearly indicates the correlations among the power output and geometric parameters. Both of the two models are verified by the experimental data from the Spain Manzanares demonstration plant. Moreover, a power quality factor is defined to evaluate the power generation quality of SCPPs both from the points of generation efficiency and power stability. The suitability of the geometric optimization of SCPPs based on the streamlined unsteady mechanism model is finally verified by an example. The coupling optimization results show that there are a strong positive correlation between the chimney height and the power quality factor, as well as a negative correlation between the solar collector radius and the power quality factor. Furthermore, the optimal solar collector height is a quadratic function relation with the chimney diameter, while the optimal thickness of the heat storage layer is little associated with other geometric parameters.

Comparison of measured and simulated performance of natural displacement ventilation systems for classrooms

Children spend the majority of their weekdays in classrooms that often have low indoor air quality and limited financial resources for the initial and running costs of mechanical ventilation systems. Designing effective natural ventilation (NV) systems in schools is difficult due to the intense use of the classroom spaces and the dependence of NV on building geometry and outdoor conditions. Building thermal and airflow simulation tools are fundamental to predict NV system performance in the design phase. These predictions of these tools must be validated (preferably with data from real buildings). This paper presents a set of detailed measurements of buoyancy driven natural DV systems of three classrooms located in two buildings in Lisbon (Portugal). The rooms are located in two educational buildings, a kindergarten and a university, and have different buoyancy driven natural DV systems (with and without chimneys). The experimental measurements are used to validate a three-node DV model implemented on the open-source thermal building simulation software EnergyPlus. The validation results show that the building thermal simulation model tested is able to predict bulk airflow rate with an average error of 16%. In addition, a good agreement is also obtained for the vertical temperature prediction: an average error of 4% corresponding (average deviation of 0.7°C). Analysis of the kindergarten rooms results revealed, that as expected, increasing chimney height from 1 to 4m has a significant positive impact in NV system performance. The performance of natural DV systems depends on the number of thermal plumes in the room. For the same sensible heat load, increasing the number of plumes lowers the average occupied zone air temperature and increases the bulk airflow rate. In light of the complexity of the cases tested, NV with uncontrolled boundary conditions, the results of the comparisons performed between measurements and simulations should contribute to increase confidence in the use of EnergyPlus to simulate buoyancy driven natural DV systems.

A new economic feasibility approach for solar chimney power plant design

Solar chimney power plants have been accepted as one of the promising technologies for solar energy utilization. The objective of this study is to propose an effective approach to simultaneously determine the optimal dimensions of the solar chimney power plant and the economic feasibility of the proposed plant. For this purpose, a two-stage economic feasibility approach is proposed based on a new nonlinear programming model. In the first stage, the proposed optimization model which determines the optimal plant dimensions that not only minimize the discounted total cost of the system, but also satisfy the energy demand within a specified reliability taking into account the stochasticity of solar radiation and ambient temperature is solved using a commercial optimization solver that guarantees finding the global optimum. In the second stage, the net present value of building the plant is computed by deducting the discounted total cost found in the first stage from the present value of revenues obtained due to selling the electricity generated by the plant. The proposed approach is novel because it determines the optimal dimensions of the plant together with its economic feasibility by taking into account the energy demand and uncertainty in solar radiation and ambient temperature. The proposed approach is applied on a study in Potiskum, Nigeria, which reveals that building a plant with a collector diameter of 1128m and chimney height of 715m to Potiskum would be profitable for investors at an annual rate of return of 3% and would provide electrification to about 7500 people with a high level of reliability. The proposed approach is benchmarked with an intuitive approach and an approach that does not consider uncertainty in solar radiation and ambient temperature. The results clearly revealed the value of the proposed approach. Managerial insights on the impact of the efficiency of the collector, the efficiency of the turbine, electricity price, electricity demand, meteorological conditions, and discount rate on the size of the plant and the net present value are obtained through detailed sensitivity analyses.

Development of analytical model for solar chimney power plant with and without water storage system

In a solar chimney power plant (SCPP) system, heated air under the collector rises up through the updraft tower and produces electricity in the turbine generator. An analytical model for a solar chimney was developed to estimate the power output and temperature configuration of the collector. The analytical model was validated using experimental data from a prototype plant in Manzanares, Spain. A water storage system was established under the collector to conserve heat energy during the night. The power of a large-scale SCPP was evaluated according to parameters such as the chimney height, collector radius, chimney diameter and solar irradiation, among others. The power of the large-scale SCPP with and without the water storage system was assessed. The power variation throughout a 24-h period was analyzed according to the depth of the water storage system.

Analytical Modeling and Optimization of a Solar Chimney Power Plant

Wind and solar resources are diluted and intermittent on the earth; their combination allowed increasing their availability and stability. At great scale, the use of Solar Chimney Power Plant (SCPP) technique constitutes a promising alternative to fossil fuel for generating electrical power particularly in rich regions of natural resources such as solar, wind, terrain, built material, water…etc.). Recently, various research works investigate the design and optimization of these systems under operating conditions. The analysis of different studies carried out on (SCPP), allowed to develop a parametric modelization approach in steady state, founded on 1D heat and mass transfer inside the (SCPP) in order to describe, optimize and to assess its performances under the influence of geometric, operating and ambiance conditions using Matlab-Simulink code. From the present simulation results, the (SCPP) appeared feasible since the temperature gradient of the airflow between the inlet and outlet of the chimney attains 13°C and remains constant during operating cycle. The (SCPP) output is strongly influenced by solar radiation intensity, air heater surface, and chimney height. The solar air heater, the tower (chimney) and the (SCPP) efficiencies obtained are 22.6%, 19.2% and 2.6% respectively.

Experimental investigation of solar tower with chimney effect installed in CRTEn, Tunisia

This paper studies the performance of a solar tower power plant (STPP) with chimney effect based on renewable energy proposed for electricity production. That's way, a solar tower prototype was constructed and tested in the Research and Technology Centre of Energy (CRTEn), Borj Cédria, northern Tunisia.The design involves heating air using solar energy and the chimney effect to raise the hot air up the chimney stack. The hot air velocity increases by the use of a convergent nozzle to reach a suitable velocity which can run the wind turbine. The kinetic energy of the hot air is then converted to electricity by the wind turbine.During this study, the influence of the climatic conditions of Borj Cédria site (insulation, ambient temperature) as well as the chimney height and the collector diameter on the amount of electricity production were investigated.The distribution and the evolution of the temperature at different positions of the prototype as well as the electrical energy produced were determined.The results reveal that when the temperatures reach 45 °C, the electric power reaches an average value of about 0.3 W/m2 for a solar tower prototype with 8 m of diameter and 2 m of height chimney.

Lung cancer risk assessment at receptor site of a waste-to-energy plant

The toxicity of particulate matter emitted from waste-to-energy plants, is associated to the compounds attached to the particles, several of which have been classified by the International Agency for Research on Cancer (IARC) in the Group 1 carcinogens. In this paper a modified risk-assessment model, deriving from an existing one, was applied to estimate the lung cancer risk related to both ultrafine and coarse particles emitted from an incinerator whose people living nearby are exposed to. To this end, the measured values of Polycyclic Aromatic Hydrocarbons (PAHs), heavy metals (As, Cd, Ni) and PCDD/Fs (Polychlorinated dibenzodioxins/furans) emitted from an incinerator placed in Italy were used to calculate the Excess Lifetime Cancer Risk (ELCR) at the stack of the plant. The estimated ELCR was then used as input data in a numerical CFD (Computational Fluid Dynamics) model that solves the mass, momentum, turbulence and species transport equations to study the influence of wind speed and chimney height on the ELCR at receptor sites. Furthermore, combining meteorological data (wind speed and direction), and hypothesizing different exposure scenarios on the basis of time-activity patterns of people living nearby the plant, specific risk maps were obtained by evaluating ELCR around the incinerator. Results show that with the increasing of wind speed, the ELCR value downwind at the plant decreases and its point of maximum risk becomes closer to the stack. On the other hand, increasing the stack height decreases the ELCR, moving away from the stack the point of maximum risk. Finally, the risk maps for people living or working nearby the plant have highlighted that the excess risk of lung cancer due to the presence of the incinerator is below the WHO target (1×10−5).

Experimental study on an indoor scale solar chimney setup in an artificial environment simulation laboratory

An artificial environment simulation laboratory (AESL) was built and successfully applied to the experimental study of a solar chimney setup for the first time. A solar simulator and a temperature control system are included in the laboratory to achieve active control of environmental parameters. An indoor scale solar chimney setup with a collector diameter of 1.22m and chimney height of 1m was constructed in the testing area of the AESL. The airflow temperature and updraft velocity were measured for the solar chimney setup with varying radiation intensities and chimney heights. The measured data were used to validate a thermal model for the collector. The thermal characteristics of the solar collector were investigated through the temperature field in the collector. The upper limitations on the collector radius and chimney height were discussed based on experimental results. The experimental work on the basic solar chimney setup performance helped in understanding the thermodynamic characteristics of the solar chimney power plant (SCPP), thereby serving as the basis for the design of large-scale commercial SCPPs.

One-dimensional analysis of compressible flow in solar chimney power plants

A novel theoretical approach for the calculation of the buoyancy driven air flow in all constitutive parts (entrance to collector, collector, turbines, collector-to-chimney transition section and chimney) of a solar chimney power plant is presented in the paper. It consists in the use of one-dimensional model of flow. The flow in the collector and the chimney is considered as compressible, while the flow in entrance to collector, turbines and collector-to-chimney transition section is treated as incompressible. Differential equations that describe the flow in the collector and in the chimney, together with algebraic equations that describe the flow in other parts of the plant are simultaneously solved. As a result, distribution of basic physical quantities, like velocity, temperature, pressure and density, in the collector and the chimney are obtained. The model is tested on two solar chimney power plants: well known Manzanares plant and Enviromission plant. The obtained results are in good agreement with measured results from Manzanares plant known in literature, together with predicted values of turbine power and turbine pressure drop for Enviromission plant. In addition, dimensional analysis of the model equations is performed and the results for mass flow rate, available turbine power, chimney height, etc. are presented. These results can be used as reliable prediction of the performance of solar chimney power plants.

An experimental study on the thermal performance of a solar chimney with different dimensional parameters

For optimizing solar chimney power plant (SCPP) and also reaching to new experimental data, a pilot setup consisting of a chimney with 3 m height and 3 m collector diameter was constructed. Two main effective parameters including absorber material and geometric dimensions were analyzed using thermal and velocity data. In this paper, the main purpose is obtaining new experimental data in these new dimensions. The obtained data will be utilized in our future after studies for achieving a structural dimensional formulation of SCPPs. In fact, there is no comprehensive formula for achieving a precise relationship between the geometric parameters of the SCPPs. The dimension analyses show that the collector entrance distance of 6 cm has the best performance and the corresponding amounts of the chimney diameter and the chimney height are 10 cm and 3 m, respectively. Also, aluminum absorber has more heat transfer rate than iron one and the maximum fluid temperature difference between the collector and the ambient is 27 °C. The maximum air velocity of 1.7 m/s was recorded inside the chimney. In comparison to the chimney with 2 m height, this was about 55.3% higher.

Experimental investigations on turbulent mixing of hot upward flow and cold downward flow inside a chimney model of a nuclear reactor

Experiments were conducted to study the turbulent mixing of hot upward flow and cold downward flow inside a scaled down model of chimney structure of a pool type nuclear research reactor. Open pool type nuclear reactors often use this type of chimney structures to prevent mixing of radioactive core outlet water directly into the reactor pool so that radiation field at the reactor pool top can be kept to a lower limit. The chimney structure is designed to facilitate guiding of the radioactive water towards the two outlet nozzles of the chimney and simultaneously allows drawing water from the reactor pool through the chimney top opening. The present work aims at studying flow mixing behaviour of hot and cold water inside a 2/9th scaled down model of the chimney structure experimentally. The ratio between the cold downward flow and the hot upward flow is varied between 0 and 0.15 to predict the extent of suppression of the hot upward flow within the chimney region for various bypass flow ratios. The Reynolds number of the hot upward flow considered in the experiment is about 1.5×105 which corresponds to a flow rate of about 500lmin−1. The upward jet height and the temperature distribution were predicted from the experiment. It was observed that increase in bypass flow ratio reduces the upward jet height of hot water. Experiments were also carried out by increasing the flow rate to 1000 and 1500lmin−1 corresponding to Reynolds numbers of 3×105 and 4.5×105, respectively. It was observed that the jet height did not vary significantly with changing upward flow rate provided the bypass flow ratio was held constant. Experiments were also done by increasing the chimney height from 500mm to 600mm and no significant change in mixing behaviour of the hot and cold water was observed.

Experimental investigation and CFD simulation studies of a laboratory scale solar chimney for power generation

In this communication, thermal performance of the laboratory type solar chimney for power generation is studied for a warm and semi-arid climate of Kota, India. Mathematical and Computational Fluid Dynamics (CFD) modeling are used to calculate the specific parameters, energetic and exergetic efficiencies. The predicted results are validated through experimental studies and statistical assessment shows that predicted temperatures are observed very close to measured data. The temperature variation along the collector height is also examined. The maximum air temperature and velocity in the collector area are found to be 42.4°C and 12.2m/s respectively at 1400h of the typical day. The maximum solar radiation is measured to be 820W/m2 at 1200h. The maximum ambient temperature is found to be 42°C at 1400h of the typical day.The temperature of the collector surface is approximately 4–6°C higher than the hot air temperature at the peak hours of the typical day. The high energy efficiency is estimated to be 3.5% at 1200h of the day and reduced by morning and evening hours. The exergy efficiency is also low and found to be 8% at the same time.The turbine installation location is decided by the maximum velocity point, which is estimated with the help of CFD simulation as to be 0.25–1m inside the chimney pipe. The effect of chimney height, inlet temperature and the solar radiation is also evaluated and model equation for performance measurements is developed. The diameter of the chimney is very low as 0.2032m and velocity generated at the entry of the chimney (exit of collector) is appropriate to produce small power and it can be used as a small power plant.

Experimental Investigation of a Household Refrigerator Performance Using Chimney-Type Condenser

In this study, the condenser unit was investigated experimentally in order to search for the effect of using chimney on the performance of a household refrigerator charged with 139 g of R134a refrigerant. An experimental design based on chimney-type condenser has been developed, and three chimneys having different size were produced. A series of measurements were conducted over the climatic conditions of Karabuk/Turkey, and results show that the efficiency and energy consumption of the refrigerator vary with the chimney height. Results showed that the best performance observed was for the 170 cm chimney height. Energy consumption of natural convection with chimney was found less than that of natural convection by 5 and 10 % for the loaded and unloaded situations of the refrigerator.

A computational model for a rocket mass heater

A simple one dimensional pseudo-steady computational model of a rocket mass heater is presented. A rocket mass heater is a space heating device that utilizes an insulated “J-tube” to promote complete combustion of burning wood, a steel barrel to act as a heat radiator, and a thermal mass usually shaped into a bench that stores heat from the exhaust before the combustion gases are released to the atmosphere. The gas model is based on fundamental relationships for steady compressible flow through one-dimensional geometry and is coupled to an unsteady finite difference model for two dimensional heat conduction in the thermal mass, which is modeled as a hollow cylinder. The model accounts for detailed heat transfer effects and fluid frictional losses, and is able to predict efficiency, flow rate, and spatial variations in temperature and pressure as functions of key parameters such as burn rate, thermal mass volume and length, duct routing details, and chimney height. Key results demonstrate how insufficient chimney height and narrow barrel clearances can threaten heater performance, how a system damper and increasing duct length can improve heater efficiency, and that axial temperature variation in the mass is small compared to radial gradients.

A Mathematical Model for Determination of Electric Energy Performance of Small Solar Chimney System in Nakhon Ratchasima Province, Thailand

A solar chimney power plant is a simple solar thermal power plant that is capable of converting solar energy to thermal energy in the solar collectors. Then, the generated thermal energy is converted to kinetic energy in the chimney and ultimately to electric energy via a wind turbine and a generator. The purpose of this study is to evaluate the performance of the solar chimney power plant in Nakhon Ratchasima, Thailand in terms of estimateion for the electric energy output. A mathematical model based on the energy balance was developed to estimate the power output of solar chimneys as well as to examine the effect of various ambient conditions and structural dimensions on the power generation. It was found that, the wind speed inside chimney reaches more than 2 times of the value of free wind speed outside the chimney. The solar chimney power plant with 10 m chimney height and 4 m chimney diameter is capable of yearly producing between 1,779-3,647 W and the performance of solar chimney in the range of 9-18% respectively. The highest performance of solar chimney (18%) was appeared in April. It can save the use of conventional sources of energy like oil and natural gas.

3D CFD simulations of air cooled condenser-II: Natural draft around a single finned tube kept in a small chimney

The objective of this study is to investigate the transient 3D numerical simulations of natural convection of air around a circular finned tube (24.9mm OD) kept in a small chimney. The annular plain fins are considered in this study. The effects of fin spacing to fin diameter ratio (0.057mm⩽S/Df⩽0.24mm), chimney height (400–1000mm) and ambient to surface temperature difference (10K⩽Ts⩽65K) on the heat transfer and the driving force have been investigated. The results are presented in terms of the temperature contours, velocity vectors, heat transfer and the driving force. It has been found that the heat transfer coefficient increases with an increase in the fin spacing upto an optimum value (S=8mm) for all the fin geometries, and beyond S=8mm, the heat transfer coefficient decreases. The separation of the thermal boundary layer with a variation in the fin spacing and its effects on the heat transfer and driving force has been shown. For a fixed fin spacing, the heat transfer rate, heat transfer coefficient and the driving force increases with an increase in the fin diameter, however, for Df>41mm, the rate of increase in the heat transfer coefficient reduces. The heat transfer coefficient increases with an increase in the chimney height and it has been found that the effect of chimney height on the heat transfer coefficient is a resultant effect of the air outlet temperature and the driving force generated by the chimney. The base to ambient temperature difference has been varied to observe the temperature sensitivity on the heat transfer coefficient and flow patterns. In the last section, various circular and elliptical tube designs have been investigated, and it is found that, the elliptical tube with minimum ellipticity (b/a=0.33) and circular tube with smallest diameter (7mm) provides better heat transfer coefficient than the other circular and elliptical designs.

Investigation of a Novel Combination for Both Solar Chimney and Solar Tower Systems

The aim of this work was to propose a novel system combines both solar chimney and thermo siphon solar tower systems. To this end, theoretical study to the proposed system was conducted. In this new system, the solar tower was installed at the exit of the solar chimney. The results of the theoretical study showed that, the new system generates more power compared with the conventional system. It was found that the maximum power extracted from the new system was about two times that obtained from the conventional system at the same height, for the specified range studied in this work. In addition, it was found that the new system has higher overall efficiency and generates higher speeds of air at the chimney inlet. This increase in both maximum power and air speed at the chimney inlet from the new system is enhanced with the rise in solar irradiance, radius of collector, and ratio of solar tower height to solar chimney height. Moreover, the results indicated that there is a certain ratio between solar tower length and width at which the maximum extracted mechanical power reached a maximum value for the specified parameters of solar irradiance, collector radius, height of chimney, and height of solar tower.

Transient Thermal Efficiency of Natural Hybrid Dryer System on Chimney Height Variation of Exhaust Moist Air

In developing countries, the sun and biomass are very important as the alternative and renewable energy sources that is very necessary the effort for utilizing them maximally. This study has developed a natural hybrid dryer system utilizing the heat energy was generated from the biomass stove and the solar collector. This dryer system has been tested on the chimney height variation of exhaust moist air, namely: 2m, 4m, and 6m. For assessment of thermal efficiency, several variables of experimental data was collected consist of: several point of air flow temperatures, the ambient temperature, air flow velocities, mass of material which was dried, and solar radiation. Further, the efficiency of solar collector, the efficiency of biomass stove, the efficiency of drying chamber, and the total efficiency of system against the time as the purpose of this study. The result showed that with increased of chimney height of exhaust moist air caused the increase of air mass flow rate, and further caused the increase of heat transfer rate in the biomass stove and solar collector against the time. It caused the increased of transient thermal efficiency of biomass stove and solar collector against the time and it was influencing the increase of evaporation rate. Thus, the drying speed was increasing and with chimney height of 6m was the fastest with the drying time was 7 hours, while 7.5 hours and 8 hours were for height of 4m and 2m respectively. With increased of chimney height of exhaust moist air caused the efficiency of the drying chamber was decreasing and the total efficiency of system was increasing slightly, each was decreasing against the time due to decreasing of mass.

Heat transfer effects of chimney height, diameter, and Prandtl number

This study investigates the heat transfer enhancement of a chimney system, both experimentally and numerically, by varying the height and diameter of the chimney, and the Prandtl number of the working fluid. Mass transfer experiments are carried out using a sulfuric acid and copper sulfate electroplating system based on analogy concepts. Numerical simulations are executed using FLUENT 6.3. Natural convection experiments and numerical calculations performed without a chimney showed good agreement with the Le Fevre correlation for natural convection on a vertical plate. As the chimney height is increased, the heat transfer rates are enhanced for all Prandtl numbers, but the enhancement rates decrease as the Prandtl number increases. An optimal chimney diameter is found that maximizes the heat transfer. An increase in heat input or heated length results in an additional enhancement of the heat transfer, increasing the buoyancy force. Numerical results provide visualizations of the temperature and velocity fields in the chimneys, showing their interactions and flow regimes.

Transient flows in displacement ventilation enhanced by solar chimney and fan

Theoretical analysis was carried out to develop an unsteady-state model for displacement ventilation in buildings with solar chimneys and fans. The influence of solar radiation intensity and the height of the solar chimney on the interface height, reduced gravity and natural ventilation rate was analyzed, as well as the mechanical ventilation rate and the area ratio of the openings. It was found that the interface height and airflow rate increased significantly with solar radiation intensity and the height of the solar chimney for a relatively smaller time scale ratio, but reduced gravity increased significantly for a larger time scale ratio. When the mechanical force assisted the thermal force, the increasing mechanical ventilation rate and area ratio increased the interface height and total ventilation rate, but decreased the natural ventilation rate in hybrid ventilation.