Chimney Model Research Articles

Experimental and Theoretical Investigation of Performance of a Solar Chimney Model, Part I: Experimental Investigation

This paper presents the experimental data that was collected from small pilot solar chimney. The experimental data together with ambient conditions are used to evaluate the performance and study the behavior of the solar chimney; this data will be used for comparison with theoretical models in another paper [part II). The solar chimney prototype was designed and constructed at the Subrata Faculty of Engineering-Libya. The data were collected over several days of June 2011. The solar chimney system contains two main components; the solar collector and the solar chimney. The solar collector root‘ has a circular area of126 m3, the solar chimney is a PVC tube with internal diameter of 0.2 m and the total height of chimney is 9.3 m. The measurements include the intensity of solar radiation inside/outside the collector, temperature and velocity of air at the entrance of the chimney, temperature and speed of wind outside the collector, temperature of the ground inside collector al1d temperature measurements of air at speci?c points at different levels throughout the collector. Solar irradiance was found to affect the chimney temperature and subsequently affects chimney air velocity. The experimental results showed that temperature differences of (30 - 45°C) were recorded between the ambient temperature and that of air inside the chimney in the middle of the day, where the highest air temperature of 73.4°C was recorded at the entrance of the solar chimney. The maximum air velocity of 3.6 m/s was recorded inside the solar chimney at noon on 9 June. Wind speed outside the collector had a small effect on the speed of the air inside the chimney and tends to change slightly, hence, can neglect influence of wind speed on the performance of the system. Also the experimental results indicate that such type of system can trap a suf?cient amount of solar radiation, which elevates the air temperature to a suf?cient value able to generate enough air ?ow to operate a wind turbine to produce electricity; this means the solar chimney system for electricity production can work in the north-western part of Libya in the summer time at least.

Modified solar chimney configuration with a heat exchanger: Experiment and CFD simulation

The performance of a modified solar chimney is studied numerically and experimentally. In this solar chimney, the classical solar collector array is replaced by a heat exchanger located in the middle section of the chimney. The natural convection inside is simulated by the commercial Computational Fluid Dynamics (CFD) code COMSOL. This software is used first to perform an optimization of the power output and to determine the optimal dimensions of the chimney prototype. From the parameters obtained numerically, a two-meter high chimney model is built to measure temperature profiles and power output of the chimney. The comparison between numerical and experimental results shows a difference lower than 6.2% for the power generated. Our prototype achieves a higher power density in comparison with other reported prototypes based on conventional solar chimney concept of similar height.

Simplified multimode control of seismic response of high-rise chimneys using distributed tuned mass inerter systems (TMIS)

The industrial chimney is one of the important components used in industrial processes. The tuned mass damper was introduced in previous studies to improve its reliability for resisting earthquakes. However, a large additional mass is generally required for applying a tuned mass damper in a chimney, which may be inappropriate owing to the additional moment action. In this study, the tuned mass inerter system (TMIS) is adopted as an ungrounded lightweight passive control device for the seismic response mitigation of high-rise chimneys. The ungrounded TMIS consists of a tuned mass element and a parallel-connected tuning spring and inerter subsystem. Considering that the influence of high modes on the responses of a high-rise chimney may not be neglected, distributed TMISs (d-TMISs) are proposed for installation on the chimney for multimode control of seismic response. A strategy to optimize d-TMISs for multimode control of high-rise chimneys is developed. A typical numerical chimney model is established to illustrate the proposed optimal design method. Time history analysis and comparative studies are conducted to verify the optimal multimode control design and the lightweight effect of d-TMISs compared to the traditional tuned mass dampers. The results show that by applying the proposed optimization in d-TMISs, the performance objectives can be achieved and the chimney’s responses involving the high-order modes can be reduced as anticipated. The required weight of d-TMISs is less than that for tuned mass dampers under an identical performance objective. It is observed that the proposed optimal multimode control method is effective and that d-TMISs can achieve the lightweight effect.

Hyperchaos and synchronization in two element nonlinear chimney model

The two element chimney model with nonlinearity is studied with the aim of modeling the swaying of trees at high wind speeds. We found solutions for various parameters and also the Lyapunov spectrum numerically. The system is chaotic for a wide range of parameters. We also observed hyperchaos in a subregion of this parameter space. We noticed that the hyperchaos was suppressed when the largest Lyapunov exponent crossed a threshold value. Synchronization between the lower and the upper segments was also studied and, for some parameters, phase synchronization is observed. We also observed transition to antisynchronization and also toggling between the two as the parameters are varied.

Particle Image Velocimetry (PIV) experiment of the buoyant flow field of a thermal chimney model designed for geothermal power plants

ABSTRACT To enhance the air-cooling process in geothermal power plants for economical utilization of the exhaust steam from expansion, a natural-draft thermal chimney design was proposed and studied here in this paper. In view of the necessity of accurate velocity field measurements which would provide further insight into the physics behind the evolving plumes above heated horizontal cylinders, Particle Image Velocimetry (PIV) was employed to experimentally investigate the buoyant flow in the thermal chimney system. Two configurations have been tested to understand the flow induced by the horizontally heated cylinders inside the thermal chimney. Firstly, flow field above a single row of cylinders was tested while they were isothermally heated to simulate of an air-cooled condenser. After that, a second row of cylindrical heaters (air-heater) was added above the first row to enhance the buoyant flow, aiming at enhancing the air side flow of the air-cooled condenser. Flow characteristics and velocity enhancement were studied for both configurations. The results show that significant flow unsteadiness occur near the cylindrical heaters because of the non-steady crossing flows between adjacent cylinders, and the unsteadiness attenuates in the downstream. The effects of cylinder row distance, surface temperature as well as downstream distance on the flow field were then analyzed. Flow velocity is increased by the air-heater as the buoyancy force is enhanced, proving the idea of flow enhancement of the thermal chimney configuration. It is also observed that the velocity fluctuation, turbulent kinetic energy and vorticity change significantly after adding the second row of heaters. The present study provides further insight into natural convection flow theory of heated cylinders for a Rayleigh number range of 1.3E4 to 2.2E4, which is fundamental for the flow enhancement designing of the proposed natural-convection-driven cooling system.

A CFD based approach for determining the optimum inclination angle of a roof-top solar chimney for building ventilation

A CFD based procedure is described to identify the optimum inclination angle of a small-scale roof-top solar chimney for maximum ventilation performance. The absorber wall of the chimney under consideration is 500-mm long and the air gap width is 40 mm. Firstly, CFD simulations are performed on a two-dimensional solar chimney model with inclination angles varying from 30° to 90° relative to the horizontal plane under different heat fluxes. Subsequently, a mathematical procedure using the CFD data to estimate the ventilation performance of the solar chimney at different inclination angles under real climate conditions is described. The procedure accounts for the effect of the inclination angle on receivable solar irradiance and is applied to three Australian cities, corresponding to three different latitudes. It is found that the optimum inclination angle varies from 45° to 60°, depending on the latitude and season of operation.

Modeling Frequency‐Independent Q Viscoacoustic Wave Propagation in Heterogeneous Media

AbstractQuantifying the attenuation of seismic waves propagating in the Earth interior is critical to study the subsurface structure. Previous studies have proposed fractional anelastic wave equations to model the frequency‐independent Q seismic wave propagation. Such wave equations involve fractional derivatives that pose computational challenges for the numerical schemes in terms of accuracy and efficiency when dealing with heterogeneous Earth media. To tackle these challenges, here we derive a new viscoacoustic wave equation, where the power terms of the fractional Laplacian operators are spatially independent, thus accurate and efficient methods (e.g., the Fourier pseudospectral method) can be adopted. Our derivation enables the resultant equation to capture both amplitude and phase signatures of the anelastic wave propagation by matching the complex wave numbers for all the frequencies of interest. We verify the derivation by comparing the dispersion curves of both the attenuation factor and the phase velocity produced by the new wave equation with their theoretical values as well as the Pierre Shale in situ measurements. Following that, we use a synthetic attenuating gas chimney model to demonstrate the attenuation effects on seismic waveforms and then construct the Q‐compensated reverse time migration to undo these effects for seismic image enhancement. Finally, we find that our forward modeling results can characterize the spatiotemporal attenuation effects revealed in the Frio‐II CO2 injection time‐lapse seismic monitoring data. We expect this proposed equation to be useful to quantify the attenuation in seismic data to push the resolution limits of seismic imaging and inversion.

Lotus seedpod-inspired hydrogels as an all-in-one platform for culture and delivery of stem cell spheroids

3D culture of stem cells can improve therapeutic effects. However, there is limited research on how to deliver cultured stem cell spheroids to the desired target. Here, we developed lotus seedpod-inspired hydrogel (LoSH) containing microwells for culture and delivery of stem cell spheroids. Human adipose-derived stem cells (hADSCs) inside the square microwells (200 or 400 μm in width with various depths) spontaneously formed spheroids with high viability (94.08 ± 1.56%), and fibronectins conjugated to the hydrogel successfully gripped the spheroids, similar to the funiculus gripping seeds in the lotus seedpod. The spheroids slightly bound to the LoSH surface at 37 °C were detached by the expansion of LoSH at lower temperature of 4 °C. After spheroid formation, LoSH was placed on the target substrate upside-down, expanded at 4 °C for 10 min, and removed from the target. As a result, the spheroids within the microwell were successfully transferred to the target substrate with high transfer efficiency (93.78 ± 2.30%). A delivery of spheroids from LoSH to full-thickness murine skin wound with chimney model showed significant enhancement of the number of SMA-positive vessels at day 21 compared to the group received the same number of spheroids by injection. Together, our findings demonstrate LoSH as a one-step platform that can culture and deliver spheroids to a large target area, which will be useful for various biomedical applications.

Thermo-hydrodynamic behavior of an innovative solar chimney

Production of electricity through solar systems is a viable alternative, especially for deserted regions where access to electricity is difficult. Solar chimney power plant (SCPP) is one of the promising concepts in renewable energy technology that needs performance enhancement. The objective of this research is to investigate a novel concept, which consists of a horizontal solar chimney power plant with an adapted collector entrance, named sloped collector entrance SCPP (SCESCPP). The effect of the collector entrance shape (slope, sloping distance) is investigated. For each sloping distance, eleven values for the slope are examined. Thus, a numerical investigation is carried out using a 2D axisymmetric chimney model. The model was first validated using experimental results. The influence on air thermo-hydrodynamic behavior of this system is comprehensively studied to enhance the understanding and deepen the analysis in order to improve the performance of the SCPP. The results indicate that the new collector entrance design influences the system performance in a significant manner. It is shown that the best performing configuration (sloping distance of 0.8 and slope of 9.1°) produces an available power reaching 16.36% more than that for zero slope collector roof at same conditions. Moreover, it is found that the optimal slope depends on sloping distance and remains almost the same for different Rayleigh numbers.

Chaotic Properties of Single Element Nonlinear Chimney Model: Effect of Directionality

We generalize the chimney model by introducing nonlinear restoring and gravitational forces for the purpose of modeling swaying of trees at high wind speeds. We have derived the general equations governing the system using Lagrangian formulation. We studied the simplest case of a single element in more detail. The governing equation we arrive at for this case has not been studied so far. We study the chaotic properties of this simple building block and also the effect of directionality in the wind on the chaotic properties. We also consider the special case of two elements.

Influence of canopy condensate film on the performance of solar chimney power plant

Presence of dust and/or condensate film affects the transmissivity of solar radiation through the transparent canopy/cover of solar collectors. This paper presents experimental investigation results of water vapor film condensate on the upper and lower surfaces of the canopy and how it affects solar chimney performance. The experimental measurements were carried out utilizing the solar chimney model, which has a collector of 7.0 m diameter and chimney of 6.5 m height above the collector. After 10 days of measurements and observation, radiation transmittance was considerably reduced from 7:30 a.m. until 10:30 a.m. due to the presence of condensate. Consequently, collector and solar chimney performance were influenced. A 9%–10% variation in solar radiation transmittance was found between dry and wet canopy. The condensate film required 2.0–3.0 h to evaporate. During the evaporation time (7:30 a.m. to 10:30 a.m.), the increase in the collector air temperature under wet canopy was 3.0 °C–5.0 °C less compared with that under dry canopy. Solar radiation from the sun until 10:30 a.m. was absorbed by the condensate film to evaporate. A delay was observed in the energy conversion processes from solar to thermal to kinetic, thereby delaying power generation. The presence of water condensate film reduced the hydrothermal performance of the solar chimney by two ways: by reducing the transmittance of solar radiation and by absorbing solar radiation from the water vapor particles to evaporate. An auxiliary heat source that supplies heat before sunrise is necessary to evaporate the condensate film and allow the solar chimney to operate early.

Wind-induced responses of a tall chimney by aeroelastic wind tunnel test using a continuous model

This study aims to investigate wind-induced responses of a 300 m high chimney by using wind tunnel tests on an aeroelastic model. Due to the fact that it is unrealistic to simulate wind flow with a high Reynolds number as high as 1 × 108 for a chimney model in a wind tunnel, roughness paper strips were attached to the model surface to artificially achieve effective high Reynolds number flow in the full-scale condition. An optimal thickness of the roughness paper strips was determined via a series of pressure measurement tests on a rigid model of the chimney. To examine wind-induced responses of the chimney, a continuous aeroelastic chimney model was manufactured with the DEVCON plastic steel liquid. After roughening the aeroelastic model by the paper strips with the optimal thickness, a series of wind tunnel tests were conducted on the model to directly acquire the structural responses, for three different oncoming wind flow conditions. Results show that the response of the roughened model is much smaller than that for the model without roughness element, indicating that ignoring the Reynolds number effect will overestimate the response. The across-wind acceleration response of the chimney is more considerable than that in the along-wind direction, when the reduced wind velocity Vr is larger than 4. In addition, the across-wind acceleration response is usually larger in the more turbulent wind flow, although the lock-in phenomenon is more evident in uniform flow.

Estimate the Ventilation Effect from Wire Mesh Screen Assisted Solar Chimney

In 1750s European houses, chimneys are used to remove smoke and dust particle from the fire place to the ambient. At present the applications of chimneys are extended for house ventilation, which is known as solar chimney assisted ventilation system. In this paper, the effect of wire mesh screen on chimney assisted ventilation system is studied and presented. Natural draft chimney integrated with solar heating system that is known as solar chimney, can be used for building ventilation. Number of research works had been conducted on different types of solar chimney to enhance the building ventilation performance. In this study a solar chimney model is designed and modified with wire mesh screens. An electric heating system is installed in the models to replace the solar absorber in the solar chimney. The airflow rates and the exit air temperatures are also measured and compared for normal chimney and modified chimneys under different heat loads. The performances of the chimneys are evaluated to determine the effects of wire mesh screen on the solar chimney. Experimental results indicated the solar chimney model with 0.64 mm × 0.64 mm pore size wire mesh screen at the exit is able to enhance velocity and the exit air temperature are about 54% and 41%, respectively. It has been concluded that the wire mesh screen has significant effect of model solar chimney and is able to enhance the performance.

Experimental and Numerical Study of Collector Geometry Effect on Solar Chimney Performance

There have been many advances in the solar chimney power plant since 1930 and the first pilot work was built in Spain (Manzanares) that produced 50 KW. The solar chimney power plant is considered of a clean power generation that needs to be investigated to enhance the performance by studying the effect of changing the area of passage of air to enhance the velocity towards the chimney to maximize design velocity. In this experimental and numerical study, the reduction area of solar collector was investigated. The reduction area that mean changing the height of glass cover from the absorbing plate (h1=3.8cm, h2=2.6cm and h3=1.28cm). The numerical study was performed using ANSYS Fluent software package (version 14.0) to solve governing equations. The aim of this work was to study the effect of change the height of reduction area to the design velocity (velocity move the blade of turbine at inlet in the chimney). The results showed that the third height (h3=1.28cm) gives the best result because when decreasing the height between the glass cover and absorbing plate, the area between them decreased and the design velocity increased then the efficiency of solar chimney model was increased.

Mixing of hot and cold fluid inside a square chimney model for a pool type research reactor – An experimental study

Mixing of hot and cold fluid inside a scaled down model of chimney structure for a pool type nuclear research reactor was studied experimentally. Chimney structures are often used in pool type reactors to prevent mixing of radioactive water from reactor core and reactor pool water. This helps in reducing radiation field at the reactor pool top so that the pool top area can be accessible during reactor operation. During normal operation, chimney top opening serves as the inlet for the cold fluid from the reactor pool and the chimney bottom opening serves as the inlet for the hot fluid from core outlet. The chimney structure considered in the present work has two arms which act as the outlets for the mixed flow of core outlet water and pool water. These arms are connected to the pump suctions of two independent recirculation loops of the primary coolant system. Depending on the reactor operation with one loop or two loops, outlet flow from the chimney structure to the pump suction will take place either through single arm or through both the arms. To study the difference in mixing behaviour for one-loop operation and two-loop operation, experimental investigations were carried out inside a 2/9th scaled down model of the chimney structure of a pool type research reactor being developed at BARC. The bypass flow was varied from 0 to 15% of the core flow. Flow visualization of the mixing zone was carried out using dye injection and vortex spread height was observed. Fluid temperatures were measured in the mixing region and temperature profile was obtained. It was observed that increase in bypass flow reduces vortex spread height and pool temperature front height. Larger mixing zone and higher temperature front height were found for one-loop operation than that for two-loop operation. It was observed that minimum bypass flow should be 10% of the core flow in case of one-loop operation and minimum chimney height should be six times the hydraulic diameter of chimney.

Adaptive stabilization forQ-compensated reverse time migration

Reverse time migration (RTM) for attenuating media should take amplitude compensation and phase correction into consideration. However, attenuation compensation during seismic propagation suffers from numerical instability because of the boosted high-frequency ambient noise. We have developed a novel adaptive stabilization method for [Formula: see text]-compensated RTM ([Formula: see text]-RTM), which exhibits superior properties of time variance and [Formula: see text] dependence over conventional low-pass filtering-based method. We derive the stabilization operator by first analytically deriving [Formula: see text]-space Green’s functions for a constant-[Formula: see text] wave equation with decoupled fractional Laplacians and its compensated equation. The time propagator of Green’s function for the viscoacoustic wave equation decreases exponentially, whereas that of the compensated equation is exponentially divergent at a high wavenumber, and it is not stable after the wave is extrapolated for a long time. Therefore, the Green’s functions theoretically explain how the numerical instability existing in [Formula: see text]-RTM arises and shed light on how to overcome this problem pertinently. The stabilization factor required in the proposed method can be explicitly identified by the specified gain limit according to an empirical formula. The [Formula: see text]-RTM results for noise-free data using low-pass filtering and adaptive stabilization are compared over a simple five-layer model and the BP gas chimney model to verify the superiority of the proposed approach in terms of fidelity and stability. The [Formula: see text]-RTM result for noisy data from the BP gas chimney model further demonstrates that our method enjoys a better antinoise performance and helps significantly to enhance the resolution of seismic images.

Analysis of Solar Chimneys in Different Climate Zones - Case of Social Housing in Ecuador

The aim of this research is to simulate the performance of a solar chimney located in different macro-zones in Ecuador. The proposed solar chimney model was simulated using a python script in order to predict the temperature distribution and the mass flow over time. The results obtained were firstly compared with experimental data for dry-warm climate. Then, the model was evaluated and tested in real weather conditions: dry-warm, moist-warm and rainy-cold. In addition, the assumed chimney dimensions were chosen according to the literature for the studied conditions. In spite of evaluating the best nightly ventilation, different chimney wall materials were tested: solid brick, common brick and reinforced concrete. The results showed that concrete in a dry-warm climate, a metallic layer on the gap with solid brick in a moist–warm climate and reinforced concrete in a rainy cold climate used for the absorbent wall improve the thermal inertia of the social housing.

Experimentally Identify the Effective Plume Chimney over a Natural Draft Chimney Model

The demands of energy are in increasing order due to rapid industrialization and urbanization. The researchers and scientists are working hard to improve the performance of the industry so that the energy consumption can be reduced significantly. Industries like power plant, timber processing plant, oil refinery, etc. performance mainly depend on the cooling tower chimney’s performance, either natural draft or forced draft. Chimney is used to create sufficient draft, so that air can flow through it. Cold inflow or flow reversal at chimney exit is one of the main identified problems that may alter the overall plant performance. The presence Effective Plume Chimney (EPC) is an indication of cold inflow free operation of natural draft chimney. Different mathematical model equations are used to estimate the EPC height over the heat exchanger or hot surface. In this paper, it is aim to identify the EPC experimentally. In order to do that, horizontal temperature profiling is done at the exit of the chimneys of face area 0.56m2, 1.00m2 and 2.25m2. A wire mesh screen is installed at chimneys exit to ensure cold inflow chimney operation. It is found that EPC exists in all modified chimney models and the heights of EPC varied from 1 cm to 9 cm. The mathematical models indicate that the estimated heights of EPC varied from 1 cm to 2.3 cm. Smoke test is also conducted to ensure the existence of EPC and cold inflow free option of chimney. Smoke test results confirmed the presence of EPC and cold inflow free operation of chimney. The performance of the cold inflow free chimney is increased by 50% to 90% than normal chimney.

Experimental and Theoretical Investigation of Performance of a Solar Chimney Model Part II: Model Development and Validation

A mathematical model based on the momentum, continuity, and energy balance equations was developed to simulate the behavior of the airflow inside the solar chimney system. The model can estimate the power output and performance of solar chimney systems. The developed mathematical model is validated by the experimental data that were collected from a small pilot solar chimney; (the experiment was presented in part I(. Good agreement was obtained between the experimental results and that from the mathematical model. The model can be used to analyze the solar chimney systems and to determine the effect of geometricalparameters such as chimney height and collector diameter on the power output and the efficiency of the system.

New Insights into the Petroleum Potential of the onshore Otway Basin, Victoria Australia

A seismic attribute study was conducted over a subset of data located in the onshore area of the Otway Basin, Victoria. Attributes were developed from the original legacy processed seismic data including energy and frequency attributes. With investigation and analysis it was possible to identify an amplitude anomaly with multiple stacked attribute anomalies directly related to reservoir levels with observed hydrocarbon shows from legacy well data close to the structure. This study combined with a new independent evaluation of the exploration potential revealing thickening and extension of an excellent reservoir and indications of trapped hydrocarbons that have previously gone unnoticed on data acquired in the 1980’s. Evaluation of the well data identified a thick sequence of stacked sandstones representing a facies change of the lower Eumeralla Fm. Identification of anomalous energy and frequency and combined with a neural network chimney model that demonstrates a gas cloud overlying the reservoir interval; presents a clear target for further evaluation. Seismic mapping identified potential closure from a coarse 2D seismic grid. The nearby Greenslopes-1 well, located in a highly structured zone, represents high risk leak potential from migrated hydrocarbons and was drilled in a zone of low seal potential. This well however, provides an excellent test of the good quality reservoir potential at the level of the interpreted anomalous energy and frequency attributes. Deterministic volumetrics of the prospect assuming a 70% recovery factor estimate recoverable gas volumes of 108 BCF. If a 10 barrel/MMCF ratio is assumed for condensate then the estimated recoverable condensate volume is estimated at 1.08 MMBBL. The overlying gas cloud potentially indicates significant liquids enrichment and it is likely the reservoir contains a fully saturated hydrocarbon charge. Due to the current moratorium for onshore oil and gas drilling in Victoria the target will undergo further evaluation to assess the oil potential.