Chimney Heights Research Articles

The effects of geometric factors on power generation performance in solar chimney power plants

This research aims to create an admissible source for specifying the relation between the plant's output power and specified geometrical parameters unique to each simulated chimney dimension. In the current study, the solar chimney output power has been studied considering 49 solar chimneys, including different collector diameters, chimney heights, and chimney diameters. The study employs the Ansys-CFX to simulate the numerical model for the unsteady k-ε turbulent flow for a vast number of geometries. The obtained results indicate that the velocity as the main factor in generating the output power has significantly improved by elevating the collector radius. The output power increased up to 50 % by elevating the collector radius and around 30 % by enhancing the chimney heights which cause an increase in airflow, temperature differentials. Moreover, increasing the chimney height has generally ascended the power plant system. Among all geometrical parameters, chimney radius had the least impact on solar chimney performance. The results indicate that the best ratio between collector radius and chimney height is 6 %–10 % to achieve the optimized output power. Our findings were verified with the available experimental setups.

Do strength of zirconia-abutment-interfaces depend on cement, zirconia type and titanium abutment dimensions?

ObjectivesPart 1 of this study investigates the influence of zirconia types, chimney heights, and gingival heights on the strength of the zirconia-abutment-interface. Part 2 extends the analysis to include adhesive brands and macro-retentions. MethodsIn Part 1, the study utilized three zirconia types (700 MPa, 1000 MPa, 1200 MPa) to fabricate 234 screw-retained zirconia crowns with varying chimney heights (3.5 mm, 4.1 mm, 5 mm) and gingival heights (0.65 mm, 1.2 mm, 3 mm) of the titanium abutments. All adherend surfaces underwent sandblasting with aluminum oxide before cementation with a specific resin cement. In Part 2, the investigation of 240 screw-retained zirconia crowns focused on a single zirconia type (1000 MPa) with chimney heights of 3.5 mm and 5 mm and a gingival height of 0.65 mm of the titanium abutments, cemented with three different resin cements. All adherent surfaces underwent sandblasting with aluminum oxide before cementation, whereas 120 out of 240 abutments received additional macro retentions. Storage in water at 37 °C for 24 h preceded the tensile test. ResultsThe study revealed a substantial impact of chimney height and zirconia type on the bond strength of the zirconia-abutment-interface. Neither adhesive brands nor macro retentions significantly impacted the bond strength. Fracture incidence was significantly influenced by gingival height and zirconia type in part 1, whereas in part 2 smaller chimney heights correlated with a higher fracture incidence. SignificanceThis study contributes insights into the complex interplay of factors influencing the zirconia-abutment-interface. The results provide a foundation for refining clinical approaches, emphasizing the importance of chimney height and zirconia type in achieving successful anterior gap implant restorations.

Experimental evaluation of the performance and power output enhancement of a divergent solar chimney power plant by increasing the chimney height

Solar energy is an attractive renewable energy option for countries located in the tropical region. Harvesting this energy using simple yet innovative technologies such as solar chimney power plants (SCPP) will help the developing countries in meeting their sustainable development goals. In an SCPP, air is heated under a greenhouse collector and the hot air is passed to a chimney, where it drives a turbine while rising up. Research efforts have been directed in the past at improving the performance and power output of an SCPP by varying its geometric parameters. The chimney height of a previously optimized solar chimney power plant, having a divergent chimney, was increased from 4 to 6 m and then to 8 m in this first experimental work of this kind. The temperature variations inside the collector, along the chimney height, the velocity at the turbine section, the power available and the output power of an air turbine, estimated by applying mechanical load, are compared for the three chimney heights. The temperature rise of the air inside the collector was the highest for the 4 m tall SCPP and reduced as the chimney height was increased to 6 and 8 m due to the lower time of stay of air in the collector for greater chimney heights. Along the height of the divergent chimney, the temperature dropped with the maximum drop occurring for the 8 m tall SCPP indicating a lower enthalpy loss at the chimney exit. The air velocity at the turbine section was found to increase with chimney height for given solar insolation/time of the day due to the higher driving force which is the buoyancy effect produced by the hot air. The maximum turbine output power for the 8 m tall SCPP increased by 252% compared to the 4 m tall SCPP indicating that significant improvement in the power output can be achieved by increasing the height of a divergent chimney SCPP. An average power of about 40 kW will be available for a chimney height of 100 m which will be extremely beneficial for the sustainable development of small islands.

Modeling and Optimal Design of a Desalination System Integrated Between a Glass-Covered Solar Collection Water Chamber and a Heat Dissipating Chimney

Abstract Solar thermal energy is trapped in a glass-covered water chamber/basin to provide the heat for evaporation of brackish water in a novel desalination system. To harvest clean water, a chimney is integrated with the water basin, which draws air into the chamber to be humidified by the vapor and then being ventilated via buoyance force. Uniquely, thermal conductive metal sheet is recommended to make the chimney, which allows the vapor in the humid air condenses easily when flowing up. The condensate at the inner wall of the chimney flows down to be collected as clean water. Mathematical modeling and numerical computation have been carried out to delineate the coupling of the buoyance-force-driven flow with the heat and mass transfer of air and water in the solar collection chamber and the condensation of vapor in the heat-dissipating chimney. The objective of the simulation and optimization of the system is to find the best match of the dimensions of the water chamber with a chimney to maximize the production of clean water and energy efficiency. The model has been used to simulation several cases (of water from 40 °C to 50 °C) with available experimental data from the authors’ previous work, and the agreement was satisfactory. The optimization studies found that there is a maximum air flowrate corresponding to a critical chimney height due to the requirement that the chimney is designated to dissipate heat as much as possible to condense water vapor. With the chimney height greater than the critical height, the airflow rate will have a slight decrease. Nevertheless, higher than a critical height is still needed for a chimney to condense more moisture. Optimized chamber diameters at different chimney heights are provided for reference of optimal system designs.

Optimization of emission chimney heights for uranium enrichment facility based on individual dose

The individual dose caused by airborne effluents varies with the height of the chimney. In order to reduce the individual dose caused by uranium enrichment facilities, the height of the chimney is optimized, and considering the impact of radioactive effluents within 5 km of the site, the Cairdos program is used to simulate and predict the long-term atmospheric diffusion factors and individual dose distribution.The results showed that 234U had a greater impact on individual dose contribution, and the long-term dispersion factor and the maximum individualdose appeared in the southeast-east (ESE) direction. The individual dose caused by 10 m, 30 m and 60 m chimneys was 6.78, 3.41 and 1.60 times that of the 80 m chimney, respectively. Therefore, increasing the height of the chimney can effectively reduce the individual dose. The peak value of the individual dose caused by the 150 m and 200 m chimneys was 0.39 and 0.32 times that of the 80 m chimney, respectively. Therefore, When the chimney height is higher than 80m, the extra high chimney can reduce the individual dose, but the decrease of the individual dose is significantly less than the increase of chimney height.

Clinical, Technical, and Radiologic Outcomes of 182 Implant-Supported Zirconia Single Crowns Using Titanium-Base Abutments: A Retrospective Study.

To evaluate the biologic, technical, and radiographic outcomes of CAD/CAM-milled bilayer and monolithic zirconia crowns using implants and Ti-base abutments with up to 5 years of follow-up. A total of 182 implant-supported "screw-mentable" (hybrid screw/cement retention) single crowns were evaluated in 118 patients. Ti-base abutments were selected according to the chimney (3.5 or 5 mm) and gingival (1, 2, or 3 mm) heights in the virtual model. Zirconia crowns were designed using CAD/CAM software and then milled from partially stabilized zirconia blocks. After all crowns were cemented onto Ti-base abutments, they were clinically screwed onto the implants. Both implants and crowns were followed up for up to 5 years, and their clinical, technical, and radiologic results were recorded. A total of 118 patients (86 women and 32 men) who received 182 implant-supported screw-mentable crowns were included in this study. The mean follow-up period was 32 ± 18 months (range: 24 to 60 months) for all implants and crowns. No implant was lost during the follow-up period, yielding a cumulative implant survival rate of 100%. Two technical complications were observed in two bruxer patients, yielding a cumulative restoration survival rate of 98.9%. The marginal bone loss was 0.7 ± 0.5 mm from the baseline radiograph to the radiograph taken at the final recall visit. No implants were diagnosed with peri-implantitis. The outcomes of this study suggest that Ti-base abutments are a feasible and affordable alternative to CAD/CAM abutments and that they can successfully support single zirconia crowns.

Performance Evaluation of a Biomass Cook Stove with Variation of Chimney Height and Air Intake System

Biomass cook stove is one of the conventional methodsof cooking in rural households and industries. Typical stove designs presume inefficient combustion processes along with harmful emissions. Subsequently a more efficient design of biomass cook stove has been a foremost research interest for scientists during the last decades. The study focused on enhancing thecombustion process altering the key parameters of a biomass cook stove i.e. height of the chimney and the air intake port opening. From the study, it is found that height of the chimney and the air intake port opening is very influential on the performance characteristics of the biomass cook stove. For estimating the comprehensive performance of the improved biomass stove water boiling test (WBT) was carried outfor varied chimney heights (95 cm, 80 cm, 65 cm & 50 cm) &varied air intake port opening (40%, 60%, 80% & 100 %). At chimney height of 80 cm & fully air intake port opening, optimum thermal efficiency has been found to be 33.76%, 33.79%, respectively. The highest concentration of CO was identified around 23 ppm during the 40% opening of the air intake port and it minimized to 9 ppm as the air intake port opened fully. Both the values for CO2/CO and indoor air quality were within acceptable limits.

Natural convection compound heat transfer enhancement by discrete rings and the chimney effect in a vertical cylinder

Natural convection is an indispensable heat transfer process considered in the design of advanced autonomous nuclear reactors. The renaissance of inherently safe micro nuclear reactors calls for increased post shut down heat rejection rates by passive means. This study numerically investigated heat transfer enhancement in a heated cylinder by discrete rings and the chimney effect. Five equally spaced rings of varying thicknesses and heights were fitted in the heated channel to effect enhancement by flow interruption. The chimney effect was studied by appending adiabatic chimney extensions of different heights, giving rise to extension ratios of 1.5, 1.6, 1.65, and 1.75. Compound enhancement was achieved by attaching chimney extensions to a ringed channel. Nusselt number ratios, mass flow rates, temperature, and velocity profiles were presented. The results showed that compound heat transfer enhancement could increase Nusselt numbers by between 44 and 54% and lower temperatures by over 30% depending on the chimney height. Furthermore, very short chimney heights would be required in the compound setup in comparison to the tall chimneys in the chimney-only cases, for the same target heat transfer rates. The resulting compactness could greatly influence the design of very small reactors and contribute to improvements of other air-cooled passive systems.

Optimization of Emission Chimney Heights for Uranium Enrichment Facility Based on Public Dose

Optimization of Emission Chimney Heights for Uranium Enrichment Facility Based on Public Dose

Innovative Low-Cost Naturally Ventilated Maize Seed Storage System

A 22-m3 residential room was converted to a seed storage facility by retrofitting a solar collector on the roof. Three different chimney sizes of diameter and height of 200 mm x 3.6 m, 200 mm x 4.8 m, 300 mm x 3.6 m, and 300 mm x 4.8 m were investigated to determine the best size of the chimney to be used for ventilation in a storage facility. The parameters measured were the air velocity in the chimney duct, as well as the air temperature and relative humidity at the inlet, centre, and outlet of the storage facility. The diameter of the chimney had a significant effect (P<0.05) on the ventilation rate achieved in the storage facility. Significant differences were found between the different chimney diameters and heights (P≤0.05). The 300 mm diameter chimneys were able to extract hot air from the roof solar collector; however, the 200 mm diameter failed. The modified naturally-ventilated seed storage room was able to reduce the relative humidity from 69.7% to a safe relative humidity of 37.9%, while at the same time the temperature increased from 23.3℃ to 35℃ in the 300 mm x 4.8 m chimney.

Numerical analysis of the performance of a hybrid solar chimney system with an integrated external thermal source

In this study, a three-dimensional hybrid solar chimney with an integrated external thermal source is developed to complements the solar energy for uninterruptible power generation using flue gas channels as a supply source in the collector. The hybrid system is examined numerically using ANSYS Fluent software including a solar air collector with a diameter of 6 m, a 6.65-meter-long chimney, and four thermal channels. The timetable is set for different hours, namely for two modes, i.e. without flue gas during daytime (1st Case), with flue gas during daytime (Case 2-A), and with flue gas during night (Case 2-B). Moreover, the turbine effect in different day hours and with different heat sources during night are applied. The numerical method is validated by comparing its results with previous works based on different chimney heights. The present results show that the hybrid approach increases system performance significantly. Simulation is done in thermal channel with 0.0015 kg/s in chimney temperature of 116 °C. The results indicate that mass flow rate and power increased by 7.63% and 11.48%, respectively, compared to the mode with no flue gas. This study proved that the proposed method can eliminate the night defect and allow the operation of solar chimney power plants at night.

The bassoon tonehole lattice: Links between the open and closed holes and the radiated sound spectrum.

The acoustics of the bassoon has been the subject of relatively few studies compared with other woodwind instruments. One reason for this may lie in its complicated resonator geometry, which includes irregularly spaced toneholes with chimney heights ranging from 3 to 31 mm. The current article evaluates the effect of the open and closed tonehole lattice (THL) on the acoustic response of the bassoon resonator. It is shown that this response can be divided into three distinct frequency bands that are determined by the open and closed THL: below 500 Hz, 500-2200 Hz, and above 2200 Hz. The first is caused by the stopband of the open THL, where the low frequency effective length of the instrument is determined by the location of the first open tonehole. The second is due to the passband of the open THL, such that the modes are proportional to the total length of the resonator. The third is due to the closed THL, where part of the acoustical power is trapped within the resonator. It is proposed that these three frequency bands impact the radiated spectrum by introducing a formant in the vicinity of 500 Hz and suppressing radiation above 2200 Hz for most first register fingerings.

Cross-boundary transport and source apportionment for PM2.5 in a typical industrial city in the Hebei Province, China: A modeling study

Cross-boundary transport of air pollution is a difficult issue in pollution control for the North China Plain. In this study, an industrial district (Shahe City) with a large glass manufacturing sector was investigated to clarify the relative contribution of fine particulate matter (PM2.5) to the city's high levels of pollution. The Nest Air Quality Prediction Model System (NAQPMS), paired with Weather Research and Forecasting (WRF), was adopted and applied with a spatial resolution of 5 km. During the study period, the mean mass concentrations of PM2.5, SO2, and NO2 were observed to be 132.0, 76.1, and 55.5 μg/m3, respectively. The model reproduced the variations in pollutant concentrations in Shahe at an acceptable level. The simulation of online source-tagging revealed that pollutants emitted within a 50-km radius of downtown Shahe contributed 63.4% of the city's total PM2.5 concentration. This contribution increased to 73.9±21.2% when unfavorable meteorological conditions (high relative humidity, weak wind, and low planetary boundary layer height) were present; such conditions are more frequently associated with severe pollution (PM2.5 ≥ 250 μg/m3). The contribution from Shahe was 52.3±21.6%. The source apportionment results showed that industry (47%), transportation (10%), power (17%), and residential (26%) sectors were the most important sources of PM2.5 in Shahe. The glass factories (where chimney stack heights were normally < 70 m) in Shahe contributed 32.1% of the total PM2.5 concentration in Shahe. With an increase in PM2.5 concentration, the emissions from glass factories accumulated vertically and narrowed horizontally. At times when pollution levels were severe, the horizontally influenced area mainly covered Shahe. Furthermore, sensitivity tests indicated that reducing emissions by 20%, 40%, and 60% could lead to a decrease in the mass concentration of PM2.5 of of 12.0%, 23.8%, and 35.5%, respectively.

Analysis of tall chimney with piled raft foundation under wind load using ANSYS

Chimneys are the principal structures in any industry that emits pollutants to higher parts of the atmosphere. The geometrical traits of the chimney are so unique that it has slender dimensions and tapering geometry and therefore the analysis and design of chimney and other forms of tower structures should be carried out individually. Nowadays chimney heights have gone up from 100 m to more than 400 m according to the purpose that it serves. These tall chimneys are very sensitive to wind loads. Wind load is one of the most important parameters that affect the response of tall building’s chimneys. When tall chimneys are subjected to wind load, it may undergo lateral deflection. It also leads to the development of radial and tangential moments along with base moments. The dynamic wind effects on chimneys by analytical procedures are intricate and take a great amount of time. To analyze and further improve the response of chimneys, analysis using commercial finite element (FE) software ANSYS is carried out. Chimney with and without providing stiffeners is analyzed using ANSYS and the lateral deflection and bending moment found from the chimney models are compared. This method is more economical and time-saving.

Chimney Height, a Determining Factor in the Dispersion of Pollutants and Their Concentration

This work proposes a way of modelling two-dimensional complex meshes using elliptic equations, which the computational grid coincides with the problem geometry, making computational processing more suitable. A multiblock technique was used in order to achieve a better representation of the problem domain. In this way, numerical simulations of the movement and dispersion of pollutant emissions in the atmosphere are presented in the generated domains, using the Navier-Stokes pollutant transport equations. The curvilinear coordinates and the finite difference method are used for the discretization. The model was verified in two tests. In the first test, three cases were proposed, with geometries containing a chimney followed by an obstacle, using different chimney heights, and the obstacle height was fixed. The test aims to verify the vortices appearance, in the blocks, to obtain agreement with as presented in the literature. In the second test, the geometry is described by a chimney and an obstacle that represents one of the mountains in the valley. The performed tests made possible to verify that the height of the chimney can be considered a determining factor to describe the dispersion of pollutants, as well as their concentration in the proximity of industrial areas.

Woodwind instrument design optimization based on impedance characteristics with geometric constraints.

Computational optimization algorithms coupled with acoustic models of wind instruments provide instrument makers with an opportunity to explore new designs. Specifically, they enable the automatic discovery of geometries exhibiting desired resonance characteristics. In this paper, the design optimization of woodwind instruments with complex geometrical features (e.g., non-cylindrical bore profile and side holes with various radii and chimney heights) is investigated. Optimal geometric designs are searched so that their acoustic input impedance has peaks with specific target frequencies and amplitudes. However, woodwind instruments exhibit complex input impedance whose features, such as resonances, might have non-smooth evolution with respect to design variables, thus hampering gradient-based optimization. For this reason, this paper introduces new formulations of the impedance characteristics (resonance frequencies and amplitudes) using a regularized unwrapped angle of the reflection function. The approach is applied to an illustrative instrument subjected to geometric constraints similar to the ones encountered by manufacturers (a key-less pentatonic clarinet with two-registers). Three optimization problems are considered, demonstrating a strategy to simultaneously adjust several impedance characteristics on all fingerings.

Performance Assessment of Solar Chimneys: Part I – Impact of Chimney Height on Power Output

Solar chimney is a truly sustainable and green energy technology, which is a potential alternative to carbon-based energy economy. The working principle of solar chimneys is based on the buoyant nature of air to turn a turbine that produces electrical power. Solar chimneys are highly in the centre of interest among all solar energy applications since they enable both day and night time operation owing to greenhouse and chimney effects. A typical solar chimney consists of three main parts as chimney, collector and turbine. When the in-situ applications of solar chimneys are gone through, it can be easily asserted that the driving force in electricity generation comes from the chimney effect as a consequence of the notable pressure differences between the inlet and outlet of the chimneys. In most cases, the greenhouse effects on power output are considered auxiliary only due to non-optimised geometric properties for the air medium beneath the collector. Within the scope of this CFD research, the impacts of chimney height on power output of a typical solar chimney are evaluated. A commercial and reliable CFD software ANSYS FLUENT is considered for the numerical analyses. For different chimney heights, the average velocity at the inlet of chimney in which the turbine is placed is determined by applying k-e turbulence model, continuity, momentum and energy equations for a 2D model. The results reveal that there is an exponential relationship between the pressure difference and the average air velocity and the solar chimney is found to be practical after a certain value of chimney height. For a chimney and collector diameter of 10 and 1000 m, respectively, the average velocity at the inlet of chimney is calculated to be 25.17 m/s for a chimney height of 100 m, whereas it is 18.06 m/s for the height of 50 m. The findings are of vital importance in terms of feasibility studies on solar chimneys since they give a clear understanding about the influence of chimney height on the electrical power output of any solar chimney power plant.

Impact of rooftop stack configuration on 2D street canyon air quality

We experimentally investigated the impact of rooftop stack position on the pollutant entrapment within 2D street canyon configurations. Analyses were performed in a water channel loop system by using the image analysis techniques: FTV (Feature Tracking Velocimetry) and LIF (Light Induced Fluorescein) respectively for measuring velocity and concentration. The set-up consists in an array of 20 identical buildings with aspect ratio equal to one (ARB = B/H, where H is the height of the eaves and B is the building width), mimicking an idealized 2D urban canopy. They were equally spaced with a unitary canyon aspect ratio (defined as ARC = W/H; where W is the distance between buildings facades), and varied in shape by using flat and gable roofs with pitch α = 45°, with different chimney positions and heights, for a total number of 9 investigated configurations. Results demonstrate that the presence of gable roof significantly varies the flow in the shear layer, which, in combination with different chimney position and height, lead to not trivial effects on pollutants dispersion.

Numerical modelling of a passive scalar transport from thermal power plants to air environment

The number of thermal power plants is growing due to the industry development and the growth of energy consumption. This leads to an increase in harmful emissions in the atmosphere. There is a necessity to control the emission concentration level in the areas of power plants location. The aim of this work was to study the level of pollution concentration at different distances from the source. The mathematical model and the numerical algorithm were verified by solving test problems and comparing them with the experimental data and numerical results of other authors. Furthermore, the pollution distribution in three-dimensional case was investigated in a real physical scale. CO2 was considered as polluting gas. As a real example, the Ekibastuz SDPP-1 coal-fired thermal power plant was simulated. The remarkable feature of this thermal power plant is that the pollution emits from two chimneys of different heights (330 and 300 m). The results showed that due to the difference between chimney heights (30 m), the pollution concentration from the higher chimney dropped far away from source, than from the lower one (2160 and 1970 m, respectively). Obviously, building higher chimneys helps to reduce the harmful impact of emissions on the environment. Also, it can be used to control the emissions level at already existing power plants.

Effect of chimney height and collector roof angle on flow parameters of solar updraft tower (SUT) plant

Solar updraft tower (SUT) is a viable option to produce electrical energy from solar energy. Extensive studies needed to estimate the flow parameters and analyse this set-up. A 3D numerical model is developed to analyse the flow parameters such as pressure, temperature and velocity of SUT plant. Effect of geometrical parameters such as chimney height and collector roof angle is studied numerically in this work. The diameter of absorber plate and chimney as 3.5 m and 0.6 m and the collector roof angle, chimney height and inlet gap as 30o, 6 m and 0.1 m, respectively, are selected for numerical simulation. A parametric study is performed for varying chimney heights from 3 to 8 m and collector roof angle 20o–35o with an increment of 5o each case. The airflow inside the SUT is turbulent, renormalization group (RNG) k-e model is selected, and (discrete ordinates) DO model is incorporated for evaluation of radiation effect inside the domain. From the simulation results, it is concluded that when collector roof angle is increased, air velocity is increased and also air temperature is slightly dropped. It is found that there is 31% velocity enhancement when the chimney height is increased from 3 to 8 m.