EHD Flow Research Papers - Academia.edu (original) (raw)

2024

This paper refers to a long-term research, begun more than ten years ago, about heat transfer in reduced gravity and/or in the presence of an electric field and summarises the main results and the main conclusion achieved so far. After a somehow detailed analysis of the impact of heat transfer on modern society and of the motivation of low gravity research on this subject, the authors describe their own research work on the effects of gravitational and electric forces on single-phase convection and pool boiling. This research has the twofold aim to investigate on the basic mechanism of natural convective heat transfer, and to identify technological devices to made it possible also in the lack of buoyancy. It has been experimentally shown that the application of an external electric field enhances any kind of convective heat transfer around a heated wire: the enhancement can be modulated by varying the value of the applied voltage. Critical heat flux is enhanced as well. In reduced gravity, heat transfer performance is generally degraded to a various extent: the application of a sufficiently intense electric field restores the same value of heat transfer coefficient and critical heat flux measured in normal gravity conditions, thus demonstrating the progressive overwhelming of the electrical force on the buoyancy one.

2024

An experimental facility was set up and operated in parabolic flight to investigate pool boiling in FC-72 on a 0.2-mm heated wire in the presence of an electric field and in microgravity. The electric field was generated by imposing up to 10 kV dc to a cylindrical “squirrel cage’’ surrounding the heater. The flow field (bubble size and velocity) was dramatically altered by the variation of the gravity acceleration. The electric field proved to be effective in reducing bubble coalescence. However, such changes of pattern were not reflected in an appreciable variation of boiling performance, i.e. of the heat transfer coefficient, both in the presence or in the absence of electric field. A significant improvement in critical heat flux (CHF) due to electric field, already encountered in normal gravity, took also place in microg. Thus the electric field proved to be useful in increasing the operational margins of boiling equipment versus CHF and in preventing the formation of big chunks ...

2024, Proceedings of the 2014 International Conference on Physics and its Applications

The aim of this research is study of Electrohydrodynamic (EHD) flow by discharge corona generator with electrodes configuration of Pin-Dual Ring Concentric. We measured the velocity of EHD flow with electrodes configuration of Pin-Dual Ring Concentric and compare the result to Pin-Single Ring electrodes. The pin needle was made by stainless steel with a length of 50 mm and a tip diameter of 0.01 mm. The dual ring electrodes constructed by two metal material connected to each other with diameter of 24 mm and width of 16 mm. The thickness of rings is 2 mm and 3 mm, respectively. Single ring electrode has diameter, width and thickness of 24 mm , 2 mm and 3 mm, respectively. The EHD was generated by using a DC high voltage of 10 kV. The Pin act as an active electrode of corona discharge and concentric rings dual / single ring electrodes act as ions collector and passive electrodes. The velocity of EHD flow was measured by a Hot-Wire Anemometer. We found that the velocity of EHD flow with electrodes configuration of pin-dual ring concentric electrodes is larger than pin-single ring electrode. The velocity of EHD flow for two cases of electrodes configuration were saturated at the certain spacing of inter-electrodes distance. The maximum velocity of the of EHD flow using electrodes configuration of pin-dual rings concentric was 0,6 m/s at a distance of inter-electrodes distance 6 mm and a voltage of 3,2 kV.

2024

The paper deals with heat transfer experiments in single and two-phase convection from a thin platinum wire mainly focused on studying the influence of external force fields, namely gravity and electric forces, on these processes. In particular the application of an electric field is studied in microgravity (parabolic flights and sounding rockets) with the twofold aim of • gaining a better understanding of the action of the electric field in the absence of the masking effect of gravity; • finding a method of improving fluid motion and heat transfer in microg to develop an effective fluid management and heat exchange technologies appropriate for space applications. The results obtained with two different cooling fluids (Freon 113 and Vertrel XF by Du Pont) are presented herein. A review of the main results obtained so far for pool boiling and critical heat flux is presented together with some preliminary findings on single phase convection, both on earth and in reduced gravity. Then ...

2024

2024, Journal of Electrostatics

Electrohydrodynamic (EHD) air blowers are receiving increasing attention as a thermal management cooling solution to overcome the restrictions of traditional rotary cooling systems used in small-scale consumer electronics. In this work, the performance and flow pattern characteristics of miniature EHD air blowers are evaluated for practical convective heat transfer applications, based on device size, operating voltage and power, and generated flow rate. For a range of blower heights up to 10 mm, two-dimensional (2D) and three-dimensional (3D) numerical models of a wire-to-plane EHD channel configuration are developed and validated against previous experimental data. Investigation of the influence of blower sidewalls, based on width parameter, on flow characteristics reveals that the 2D simulations for short and wide blower domains are valid to predict the generated flow rates effectively compared to that obtained by the means of 3D simulations. An optimized combined EHD blower is developed as a flow-controlled cooling system in thermal management applications, which minimizes the required operating voltages for specified flow rates. Comparisons against commercial rotary blowers demonstrate that the miniature EHD blowers are more competitive as cooling solutions for compact applications and extended heated surfaces based on transduction efficiency, blower size, flow production of uniform velocity profile, and power consumption.

2024, IEEE Transactions on Plasma Science

As the demand for advanced microelectronic devices of small form factor and high power density has increased, the capability of the miniaturized mechanical solutions for effective cooling has become critical. Electrohydrodynamic (EHD) air blowers have great potential as alternative cooling solutions over the traditional mechanical systems to meet the thermal management requirements with flexible design and considerable flow production for effective heat removal. In the present work, a numerical analysis and optimization of wire-toplane EHD air blowers are performed based on 2D developed models validated against previous data. For a range of blower heights from 2 to 10 mm, the location and length of the collecting plane located at the blower walls apart from the emitter wire electrode are investigated and optimized based on pumping efficiency using ranges of fixed operating powers and voltages. Simple relations for each optimization method are presented to determine the optimal blower configuration. Results of flow rate and static pressure obtained by each optimized blower show good agreement with those predicted by EHD scaling laws previously presented.

2024, IEEE Transactions on Plasma Science

2024, Applied Thermal Engineering

Electrohydrodynamic (EHD) air blowers are uniquely positioned to overcome the limitations of miniaturized mechanical fans in small-scale and consumer electronic devices. A novel cooling system design using optimized EHD blowers integrated with a plate-fin heat sink is presented and proposed for thin consumer electronics such as laptop applications. A three-dimensional (3D) numerical model is developed and validated to solve the coupled equations of EHD flow and conjugate heat transfer and predict the cooling performance of the integrated EHD system. For a range of heat sink heights from 6 to 12 mm, a parametric study is performed to investigate the influence of geometric parameters and operating conditions on the thermal performance of the EHD systems based on heat sink thermal resistance and the highest operating temperature. Numerical results demonstrate that the proposed EHD cooling system is able to provide effective cooling performance and maintain the temperature within the safe and typical operating range. Under a range of thermal design power (TDP) up to 30 W, trends of predicted operating temperatures show that the developed EHD cooling systems have great potential to compete with mechanical blowers in low-profile laptops with higher TDP, lower device height and reduced installation volume compared to a selected list of current standard laptops available commercially.

2024, RSC Adv.

A nanoslit-concentration-chip (NC-chip) integrated microbead assay system was fabricated to overcome the assay limits of the conventional microbead-based protein assay. The proposed assay system was composed of a microbead-trapping-chip (MT-chip) and a NC-chip as a protein-capturing device and a quantitative and sensitive protein detection device, respectively. Microbeads trapped in the MT-chip formed a three-dimensional microbead packed column leading to efficient protein capturing. The NCchip was used to trap and concentrate nanoparticle (NP) probes that were specifically captured in the microbead bed of the MT-chip. Furthermore, the nanoslit-patterned membrane of the NC-chip enabled both signal enhancement and quantification of the amount of the trapped NPs. The NC-chip integrated microbead assay system was successfully applied to a protein assay. The sensitivity and reliability of streptavidin detection by HPQ motif containing peptide ligands were compared to those of other reported assay systems. This novel protein assay system could be applied to various microbead-based bioassays, and integration of the NC-chip could further improve their sensitivity and reliability.

2024, Experimental Thermal and Fluid Science

An experimental investigation to clarify the bubble flow and the effects of rising bubbles on boiling heat transfer in tube bundle was conducted by using nitrogen bubble simulation. The experimental results showed that the rising bubbles from the different parts of the lower tube surface have different flow characteristics and only a part of rising bubbles can impact and slide over the test tube and form a microlayer between a sliding bubble and boiling surface. The effects of sliding bubbles on enhancing heat transfer were evaluated at different heat fluxes.

2023, Energy Conversion and Management

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 2 m and collector radius of 3 m. The results show that, the collector inlet of 6 cm, the chimney height of 3 m, and the chimney diameter of 10 cm 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.

2023, Energy Conversion and Management

The effect of the electrohydrodynamic system with various electrode layouts on a solar chimney pilot is investigated experimentally. A pilot setup was constructed which consisted of a chimney with 3 m height and 3 m collector diameter. The purpose of this research was to enhance the solar chimney performance with the electrohydrodynamic system for the parallel, radial, and symmetric layouts. By using of corona wind, the outlet fluid temperature is increased, and the outlet absorber is decreased. For the three layouts, the most growth in the outlet fluid temperature is 14°C, which is observed in the parallel layout. Also, in the parallel array, the most outlet absorber temperature drop is 7°C. The results show that parallel layout with six electrodes and 3 cm spacing between the electrodes has the best performance. Also, various hours of the day are studied and the best time for turning on the electrohydrodynamic system is 1:00 p.m. The electrohydrodynamic system makes an increase in the fluid velocity from 1.7 to 2.3 m s À1 , and this growth improves the performance about 28%.

2023, Renewable and Sustainable Energy Reviews

Nowadays, referring to the increasing rate of environmental pollution and limitation on fossil fuel resources, the use of sustainable energies seems to be inevitable and an absolute necessity for the world. Renewable energies are known as the best alternative for solving the energy shortage and CO 2 emission problems. Among the renewable sources, solar energy plays a significant role in aspects of accessibility of resource and diversity of energy conversion means. Solar chimney is a power plant that uses solar radiation to produce electricity by the created wind at the entrance of chimney. A solar chimney pilot power plant with 3 m collector diameter and 2 m chimney height was designed and constructed in University of Tehran, Iran. The temperature distributions and air velocity were measured and evaluated. The temperature difference between the chimney inlet and ambient reached to 26.3 1C. The output data for different collector inlet heights were obtained and the report shows that reducing the inlet size has a positive effect on the solar chimney power production performance. The air inversion at the latter of the chimney was not observed and it was found that this phenomenon directly associated with the geometry. The maximum air velocity of 1.3 m/s was recorded inside the chimney, while the collector entrance velocity was around zero.

2023, Energy Conversion and Management

2023, Engineered Science

Advanced thermal management for future electronics have promoted the development and investigation of two-phase heat transfer devices (i.e., micro heat pipes, vapor chambers, capillary pumped loops etc.). The electrohydrodynamics (EHD) pumping is an attractive solution to insufficient liquid supply and dryout occurrence in wicks of such devices. In this study, the wicking performance of rectangular microgrooves is characterized and evaluated by axial maximum capillary wetting length at steady state and dynamic rise rate at transient state during rate-of-rise experiments. Two planar electrodes are used to generate electric field. The maximum axial capillary wetting length under EHD effects at steady state is experimentally conducted and theoretical analyzed, and the predicted results agree well with the experimental data. The dynamic wicking characteristics with considering the electric field are investigated at transient state, and the empirical correlations are obtained according to the fitting experimental data as ℎ 2~t curve at initial stage, and ℎ~− curve at long-term stage. EHD pumping mechanism is also analyzed. EHD effects can decrease the wall temperature of microgrooves. There exists an optimal electric voltage to obtain the highest economic efficiency and wicking performance in this study.

2023, Drying Technology

In this study, hot air combined with EHD drying is examined as an improved method for drying mushroom slices. The effects of three levels of voltage (17, 19, and 21 kV) and electrode gap (5, 6, and 7 cm) on the drying kinetics, time, effective water diffusion coefficient, and energy consumption of the EHD, pure hot air (provided within a chamber), and hot air combined with EHD drying systems were investigated. ANOVA showed that there were significant differences between EHD treatments and control (pure hot-air-drying treatment) for all of the investigated responses. Voltage and electrode gap factors had significant effects on all investigated responses. The results confirmed that the combination of EHD and hot air can significantly reduce the drying period, resulting in a greater effective water diffusion coefficient and drying rate and reduced energy consumption. As such, this technique offers a promising solution to the considerable energy consumption of the drying industry.

2023, Energy

In this study, the convective drying rate of a porous body driven by Electrohydrodynamics (EHD) was numerically investigated. Two different types of collecting electrode were compared: wall plate collector and segmented plate collector. Firstly, wall plate collector was examined and compared with non-EHD case. The numerical results showed that the moisture removal in the wall plate collector was 5 times higher than the non-EHD case. Secondly, the wall plate collector was replaced with a segmented plate collector. Different arrangements, as well as the various vertical distances between the emitter and the collectors, were examined to find a higher mass transfer. The numerical results showed that moisture removal in the segmented collector in the most appropriate conditions was about 3 times greater than the wall plate collector case. Finally, to gain a more general conclusion, the specific energy consumption (SEC) and pressure loss of all cases were evaluated. The results indicated that the pressure loss has increased greatly by using the EHD-induced flow. Moreover, it was depicted that for the wall plate collector the SEC reached to 8.2 watt-hr/kg when it decreased to orders of 10-2 watt-hr/kg for the segmented collector cases.

2023, Journal of Electrostatics

Using turbulent models for electrohydrodynamic (EHD) induced flow modeling in hydraulically laminar flow ranges has been always questionable. This study is concerned with EHD cases in natural convection heat transfer within an enclosure. Here, the micropolar model was engaged and became the main motivation of the current study as an alternative approach for the fluid dynamic behavior. The numerical investigations were performed to study the effect of the various key parameters: the applied voltage, Rayleigh number, and the gap size of the electrodes. The main challenge of using the micropolar model is the evaluation of the adequate material parameter (κ ω /μ); all the presented numerical investigations conducted to find the proper material parameter for various flow conditions. All cases were carried out for a two-dimensional approach with a non-uniform structured grid, which is used by a finite volume algorithm to solve the EHD natural convection governing equations. Comparing the results of the micropolar approach with those obtained from the turbulent standard k-ε model reveals that the micropolar model can be an appropriate candidate to simulate the EHD natural convection flow instead of fully turbulent models. The results depicted that by increasing Rayleigh number and the applied voltage, the discrepancy between the results of the micropolar and the standard k-ε model increases.

2023, Solar Energy

The present paper investigates the effect of geometrical parameters by using energy and exergy analysis and hydrophobic surfaces as an innovative method were proposed to enhance the performance of Solar Chimney Power Plant (SCPP). Furthermore, the best radiation model for SCPP simulation was represented. Hereupon, firstly large-scale SCPP using reverse fan model was validated based on Manzanares constructed power plant. For reducing the computational cost, nine different small scale 3-D models defined respect to prior experimental study under Tehran-Iran meteorological condition. The first and second laws of thermodynamics were studied, and an optimization was done for representing the best functional diameter, height and turbine pressure jump by the means of improvability rate and clarified optimization factor. Results show that the optimal state of chimney can be defined in relation to a certain condition; hence, the geometrical parameters under investigation should simultaneously be evaluated in system designs. Furthermore, applying the slip condition on walls to simulate hydrophobic surfaces was attempted to reduce shear stress on walls which led to roughly 11% performance enhancement. Consequently, Discrete Ordinates (DO) radiation model could be trusted based on its more factual outcomes with referred to prior experimental results of Heat flux method.

2023, Energies

Solar chimney power plants (SCPPs) are encouraging sustainable energy sources due to their low cost, abundance, low maintenance, and eco-friendliness. However, despite significant efforts to optimize SCPP design, their efficiency and power generation capabilities remain limited. Researchers have explored modifications in plant geometry and hybridization to improve efficiency. Despite extensive work in this area, commercialization of SCPPs has not yet been achieved. Most of the research is numerical and may differ from real-world practical use. The number of experimental studies is also relatively small. To facilitate commercialization, further investigation with practical and feasible dimensions is required. This comprehensive review paper aims to provide an in-depth analysis of experimental approaches and advancements in the field of SCPPs. The paper begins with an introduction, highlighting the background, significance, and objectives of the review. It provides an overview of the ...

2023, Fluid Dynamics & Materials Processing

A study is conducted to optimize the geometry of a solar chimney equipped with a horizontal absorber in order to improve its performances in relation to the provision of ventilation. The problem is tackled through numerical solution of the governing equations for mass, momentum and energy in their complete three-dimensional and unsteady formulation. The numerical framework also includes a turbulence model (k-ε) and a radiant heat transfer (DO) model. Moreover, a Multi-Objective Genetic Algorithm (MOGA) is employed to derive the optimal configuration of the considered solar chimney. It is shown that an air velocity of 0.2 m/s can be obtained. This value is the minimum allowed air velocity according to the ASHRAE' s (American Society of Heating, Refrigerating and AirConditioning Engineers) adaptive comfort approach. KEYWORDS Natural ventilation; adaptative comfort; solar chimney; fluent; MOGA Nomenclature Greek letters Units absorptivity dissipation rate Reynolds stress tensor turbulence kinetic energy Density (Kg/m 3) Stepan's coefficient (W/m 2 /K 4) turbulent Prandtl numbers for k turbulent Prandtl numbers for e Thermal Expansion Coefficient (1/K) This work is licensed under a Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

2023, Food and Bioproducts Processing

In this paper, drying of button mushroom (Agaricus bisporus) slices with an innovative drying technique of hot air combined with Electrohydrodynamic (EHD) drying process was investigated at three electrode gaps (5, 6, and 7 cm) and voltage levels (17, 19, and 21 kV). The effects of different hot air combined with EHD drying treatments on the temperature of the mushroom slices, drying time, final color and protein denaturation features including enthalpy (H), onset temperature (T o), peak transition temperature (T p), conclusion temperature (T c), and temperature range (T c-T o) of endothermic peaks were systematically evaluated. In addition, water state changes in DSC cooling thermograms of dried mushroom slices were investigated. The results obtained by differential scanning calorimetry showed that the H values in the DSC traces of the EHD-dried mushroom slices were reduced with a decrease in the electrode gap and an increase in the voltage. Specifically, among voltages of 21, 17, and 19 kV, a voltage of 21 kV resulted in the lowest H and T c-T o values and the highest T p and T o values. This result indicated that voltage had a significant effect on these responses. Similarly, the DSC results showed a considerable effect of high electric field intensity on H, T c-T o and T p responses related to protein denaturation in comparison to low electric field intensity.

2023

As the demand for energy increases, it will be more and more necessary for Turkey to diversify its energy sources by investing in renewable energy technologies. In this study, we have presented an updated review of solar chimney power plants, including most analytical, experimental, and numerical simulation studies. We have also analyzed the effect of environmental factors on the performance of a large/small scale prototype of a solar chimney with a thermal storage system for different meteorological data. We have considered five regions of Turkey corresponding to different weather conditions (Adana, Antalya, Burdur, Isparta, and Izmir). The small-scale prototype's theoretical results were compared with the solar chimney prototype's experimental data acquired at the Suleyman Demirel University. Good agreement is observed between theoretical and experimental results. The obtained results showed that the global horizontal irradiance, the temperature, the relative humidity, and...

2023

2023, Journal of Al-Azhar University Engineering Sector

In the current study, potential improvements in both flow field and heat transfer characteristics of a prototype solar chimney for power generation through passive flow control approaches have been numerically examined. The numerical modeling was conducted for three different schemes to enhance the velocity magnitude at the entrance of the chimney. The first scheme is concerned with the effect of the number of turbulent generators on the maximum flow speed obtained while the second scheme deals with the effect of throat area at the entrance of the chimney. The last scheme is related to investigating the effect of making round edges having different radii at the entrance of the chimney.

2023, IET Renewable Power Generation

Although solar chimney power plant (SCPP) has a promising potential to convert the solar energy to electric power, greater efforts are needed to ensure its successful commercialisation on a large scale. The main obstacles with regard to the large-scale applications of SCPP are its efficiency, bulk size and dependency on solar irradiation. A comprehensive study on the integration of the Internet-of-Things (IoT) as a novel technique to monitor and hence improve its performance is presented. A small-scale SCPP is designed and constructed specifically for this purpose in Aswan, Egypt. The instantaneous performance parameters (temperature, solar intensity, wind speed, open circuit voltage, power etc.) were measured and further processed using IoT. The results show that IoT has a promising potential to enhance the performance of the system by providing a complete picture of the whole measurements. This is considered as a step forward for enhancing the technologies which will ensure the success of large-scale SCPP in the real world.

2023, Brazilian Journal of Physics

The aim of this work is to analyze the characteristics of the corona discharge in blade-to-plane electrode configuration. An experimental investigation has been carried out on the geometric parameters that govern the formation of both positive and negative corona discharges, such as the inter-electrode distance, the blade-to-blade spacing, and the number of the discharging blades. The current-voltage characteristics, the breakdown voltage, and the Warburg current distribution were measured. The assisted corona discharge is an example of a blade electrode discharge that can be used to reduce the operating voltage of a conventional corona discharge. The current-voltage characteristics of both positive and negative corona discharges in a blade-to-plane electrode configuration are of the Townsend's law form. The general formula proposed by Meng et al. can also be applied in this system. It has been shown that the breakdown voltage and the corona conductance are strongly affected by the inter-electrode distance. To obtain a maximum current, the blade electrodes should be distant from each other by a value of 2a≥h. To obtain a constant value of current, the blade electrodes should be separated by a value of 2a>>h, confirming the Cooperman's law. The current density distribution is satisfied; an exponent of 5.0 is taken for positive polarity and an exponent of 4.8 for negative polarity.

2023, International Journal of Thermal Sciences

Presently, limited studies are available in understanding the ionic wind's behaviour under restricted or extreme environmental conditions. Thus, this study aims to investigate ionic wind characteristics and its convective heat transfer enhancement under the influence of varying air pressures. Here, an ionic wind generated from a cone to mesh configuration was used. Results showed that the discharge current (which translates to power consumption) and velocity of the ionic wind behaved in opposing manners at pressures above and below atmospheric pressure. Increasing the pressure above the atmospheric pressure led to a decrease in velocity for both positive and negative ionic wind, while the wind velocity was relatively constant at air pressures below atmospheric pressure. On the other hand, the power consumption was also seen to be consistent for positive ionic wind, while the negative ionic wind showed a power consumption decline with increasing air pressure. The highest power consumption was observed for the negative ionic wind at the lowest air pressure. Further investigations on the convective heat transfer showed a maximum achievable enhancement of 17% over natural convection for both positive and negative ionic wind. The optimum performance, which is defined as the heat transfer enhancement ratio over power consumption of the ionic wind, was found to be at just beneath the atmospheric pressure at 0.9 bar for both positive and negative ionic wind, with the positive ionic wind superseding the efficiency of negative ionic wind by 17%.

2023, IET Renewable Power Generation

2023, European Journal of Electrical Engineering

In this article, a numerical study was conducted to analyze the effect of electro-convection and electro-thermo-convection in a solar chimney geometry subjected to the simultaneous action of an electric field and a thermal gradient (in the case of electro-thermo-convection). The full set of equations is solved using the finite element software COMSOL Multiphysics. The effects of thermal and electric Rayleigh numbers on charge density distribution, fluid flow and temperature distribution are analyzed. Also the impact of different chimney collector widths is studied in order to determine the optimum width allowing achieving the maximum fluid velocity. It was shown that using a smaller chimney collector width is more convenient in order to increase the fluid flow velocity. In addition, an evaluation of the heat transfer enhancement was made by observing the evolution of heat flow at the exit of the chimney tower as a function of both, the electric and thermal Rayleigh numbers. It was found that the heat transfer enhancement reaches more than 90 % when thermal Rayleigh rises from 5000 to 20000. Finally, the effect of Prandtl number was investigated.

2023, Energy Conversion and Management

A solar chimney power plant (SCPP) is a renewable-energy power plant that transforms solar energy into electricity. The SCPP consists of three essential elements-solar air collector, chimney tower, and wind turbine(s). The present work is aimed at optimizing the geometry of the major components of the SCPP using a computational fluid dynamics (CFD) software ANSYS-CFX to study and improve the flow characteristics inside the SCPP. The overall chimney height and the collector diameter of the SCPP were kept constant at 10 m and 8 m respectively. The collector inlet opening was varied from 0.05 m to 0.2 m. The collector outlet diameter was also varied from 0.6 m to 1 m. These modified collectors were tested with chimneys of different divergence angles (0°-3°) and also different chimney inlet openings of 0.6 m to 1 m. The diameter of the chimney was also varied from 0.25 m to 0.3 m. Based on the CFX computational results, the best configuration was achieved using the chimney with a divergence angle of 2°a nd chimney diameter of 0.25 m together with the collector opening of 0.05 m and collector outlet diameter of 1 m. The temperature inside the collector is higher for the lower opening resulting in a higher flow rate and power.

2023, Fluid Dynamics & Materials Processing

2023, Global Journal of Pure and Applied Sciences

The study of thermal and ventilation parameters, obtained in a transient, laminar solar chimney of reduced dimensions, (1 < m <3) m with a square collector (side = 2m) is presented. Experimental measurements has been made to determine the temperature of the absorber and the fluid in the collector, it is shown that at the entrance of the chimney, the temperature of the absorber decreases slightly while that of the fluid is maintained at a maximum level. Temperature differences were observed up to 32°C between the atmosphere and the fluid in April. A temperature variation at the absorber depending on the stack height is presented. Temperature measurements in the chimney, at various heights depending on the axial coordinate, show a variable temperature profile. It is, from these, shown that, in the selected interval of stack height, the average speeds of output increase linearly as a function of stack height. For a chimney of 3m in height and 20cm in diameter, a maximum speed of approximately 0.7 ms-1 was observed. The lack of appropriate equipment handicaps the velocity measurement at the chimney entrance. Thus, the results of simulations with the computer code COMSOL 5.1 has confirmed temperature values measured at the chimney entrance and after this, velocity values are determined.

2023, IEEE Transactions on Dielectrics and Electrical Insulation

Although it has been found that the insulating characteristics of thermal induced twophase flow changes with pressure and heat power, its breakdown mechanism has not been clarified so far. In order to obtain actual working conditions of two-phase flow state of fluorocarbon, a special apparatus with self-heating electrodes has been manufactured to study AC breakdown voltage (BDV) under different pressure, electrode gap distance and heating density. The experimental data outline that the variation of breakdown voltage vs. heat density is an elongated "Z" shaped curve: Breakdown voltage maintains the liquid value in the Invariant Interval, and drops sharply in the Converting Interval, finally reduces to gas value and maintains in the Maintaining Interval. It is pointed out that the steep converting of BDV is closely related to the change of flow pattern and bubble generation on heating electrode surface. And the threshold of converting point is highly consistent with the peak of electrode surface overheating T, therefore it can be used as an excellent signal to detect the BDV converting. An electric field model is established based on bubble thermodynamics to explain the discharge mechanism of "vapor lock" effect, offering a theoretical minimum limit of BDV value in the thermal induced two-phase flow, which provides a useful guide to design the insulation subjected to various high voltages.

2023, Renewable Energy

The tilted solar chimney (TSC) system has been introduced as one of the novel solar thermal approaches, whose performance in the presence of ambient crosswinds (ACW) is still somewhat unclear. The present research offers an in-depth experimental and numerical investigation of a TSC operating at a range of ambient wind velocities. Besides ACW investigations, numerical simulations examine the influence of solar radiation and chimney tilt angle (measured from the vertical line) on the fluid flow and thermal performance of the system. Results suggest that the ACW has an adverse effect on power performance at relatively low crosswind speeds. It is found that tilted solar chimney in windy conditions at a range of tilt angles between 10 o-20 o has better flow performance compared with the fixed chimney arrangement. Dimensional analysis is carried out to establish the dimensionless parameters for predicting the system power output in a large-scale prototype with 200m chimney height. The results indicated that at 15 o chimney tilt angle, the power output increases between 5% to 20% depending on the ACW velocities compared to the vertical chimney at the same crosswind speeds. The present research would be valuable for evaluating the power capacity of similar full-scale facilities.

2022, Journal of Food Engineering

In this study, the application of high voltage electrostatic field (HVEF) is examined to improve the still air thawing of frozen tuna fish cubes. The experimental tuna cubes (2 Â 4 Â 4 cm 3) were thawed under HVEF subjected to three different voltages from the corona wind onset voltage to breakdown voltage with electrode gaps of 3, 4.5, and 6 cm. The still air thawing without HVEF was applied in a controlled incubator at 20 C. Thawing time and energy consumption of still air method with/without HVEF were determined. The results showed that thawing with HVEF significantly improves thawing time and energy consumption. In addition, results indicated that increasing voltage or decreasing electrode gap provide such advantages as lower thawing time and total specific energy consumption (SEC total) in the still air method. This is while increasing applied voltage and decreasing electrode gap significantly decreases SEF total but increases SEC EF in the HVEF system.

2022, Progress In Electromagnetics Research M

This paper presents the results of Boundary Element Method (BEM) numerical procedures of voltages distribution between transmission lines in order to investigate the theoretical corona discharges. The algorithm of the voltage distributions are coded in Mathematica studying size of the system under controlling Neumann and Dirichlet boundary conditions. Conducting experimental work at a high voltage (HV) is potentially very dangerous. Therefore, simulation is a vital research approach, and computer modeling offers significant advantages to estimate optimal calculation over established system to prevent dangerous voltage and not to exceed the corona voltage. In this paper, the BEM results are verified with Finite Element Methods (FEM) which is coded in Mathematica too.

2022, Lecture Notes in Electrical Engineering

The electric field distribution in an air gap between a wire-cylinder electrode configuration, has been studied by implementing Finite Element Analysis. The electrodes were assumed to be surrounded by air at normal conditions, while high dc voltage has been applied across them, with positive polarity at the wire. Numerical analysis on the maximum electric field intensity along the wire-cylinder gap axis, as well as on the potential distribution in the air surrounding the electrodes has been carried out, considering different geometrical characteristics of the electrodes. The applied mesh parameters were optimized, in terms of accuracy and processing power. The maximum field intensity was mainly associated with the wire radius r and the electrode gap length d. The cylindrical electrode radius R had a limited impact on the maximum electric field intensity but, on the other hand, it had a strong effect in the distribution of the electric field lines. Finally, a formula for the estimation of the maximum electric field intensity is proposed.

2022

The electric field distribution in a wire-cylinder electrode arrangement in air, under high voltage dc application, has been studied by implementing the Finite Element Analysis (FEA). The applied mesh parameters have been optimized in terms of accuracy and processing power. Numerical analysis has been carried out on the field intensity, along the wire-cylinder gap axis, considering different geometrical characteristics of the electrodes, which play an important role in the spatial distribution of the electric field. The maximum field intensity was mainly associated to the wire-cylinder radii ratio, while the distance between the electrodes strongly affected the distribution along the axis of the gap. On the other hand, the potential distribution was almost independent of the gap length.

2022, Lecture Notes in Electrical Engineering

2022, Renewable Energy

Wind energy characteristics include lack of "stability and predictability". Solar updraft tower, also known as solar chimney SC, is a device in which wind is locally generated by the thermal effects of a solar collector which covers an area surrounding the chimney. In this work computational fluid dynamics, is applied to model the heat and transport relations in the collector and chimney area. The geometry, mesh layout and the existing analytical models are verified for consistency against the experimental data of Manzanares plant in Spain. As one of the geometrical parameters such as collector diameter is changed, an optimization process occurs, leading to a decision on the best matching size for the other dimensions. The process checks the output against the optimized profiles of temperature, velocity and pressure. Based on studying 180 cases in 15 groups for collector size against chimney height and diameter and another 130 cases in 12 groups for collector height, a table and graphs of matching dimensions are obtained. As a consequence of this work, it is possible now to make a more accurate decision on consistent dimensions for a solar chimney plant.

2022, Drying Technology

2022

In this study, the heat transfer enhancement on semicircular ribs established on the floor of rectangular duct is investigated. These ribs were used as heat sources and cooling of them has been achieved with electrohydrodynamic (EHD) active method by experimental procedure. The flow was 3-D, steady, viscous and incompressible with regimes of both laminar and turbulent (500 ≤ ReDh ≤ 4500). The hydrodynamics and heat transfer behavior of the air-flow was studied by EHD active method with application of corona wind. The aim of this work is application of EHD active method for convective heat transfer enhancement. In this method, two arrangements of wire electrodes have been achieved. The results show that in same Reynolds numbers and voltages of wire electrodes, the heat transfer enhancement was increase in Arrangement 1 than Arrangement 2.

2022, Renewable Energy and Environmental Sustainability

The simplicity of solar chimney power plant (SCPP) makes it very attractive for power generation. This paper investigates the technical feasibility of using a locally-produced plastic film (Low-Density Poly-Ethylene “LDPE”) as a solar chimney power plant collector cover. The idea is to combine a very low-cost material with a simple technical solution. As LDPE is subject to deterioration, the effect of aging on the initial properties of the used material is analyzed. Natural aging was privileged over the accelerated one by exposing the studied film, for a time duration of 3 years, to environmental constraints similar to the local conditions where the SCPP collectors are installed. Various experimental tests were carried out to show the decrease of mechanical resistance and to confirm the structural degradation. Results showed that after an exposure time of 3 years, a decrease of more than 50% of the failure stress is recorded. The spectroscopic analysis confirmed the progressive degr...

2022

Applying corona wind as a novel technique can lead to a great level of heat and mass transfer

2022

This paper presents computational fluid dynamics (CFD) simulation of the solar chimney power plant to analyze to analyze buoyancy-nature of heated air by har- nessing solar energy. ANSYS Fluent a fi nite volume code has been used for axisym- metric model of the solar chimney power plant (SCPP) prototype in Manzanares, Spain considering updraft tower. A standard k- turbulence model and Boussinesq approximation for buoyancy driven flow is considered. Small pressure difference because of natural draft inside the chimney during day time has been observed due to solar radiation. The numerical results obtained for average velocity and temper- ature at chimney inlet are validated with the experimental results of the prototype. It has been observed that both the velocity and temperature of air inside the SCPP increases signifi cantly with the increment in solar radiation. Increase in the chimney height and collector radius also increases the power output of the plant. The effect of chimney...

2022, Lecture Notes in Electrical Engineering

2022, ICAST 2021: Advances of Science and Technology pp 391–412 - SpringerLink

The Solar chimney power plant is a naturally driven power generating system. In this research, a solar chimney power plant is studied by developing an experimental model for a maximum power output of 32 W. The performance of large-scale electricity generation from the plant is predicted by analyzing different geometrical configurations. CFD model is used to study flow characteristics of air temperature inside the collector. Then, for 30 kW power output, the selected optimized dimensions are: chimney height, collector diameter, chimney diameter, and collector height are estimated to be 15 m, 15 m, 0.2 m, and 0.2 m respectively. For a fixed chimney diameter and collector height, an increase in height of the chimney raises the power output until it reaches the designed optimum height, an increase in chimney height beyond the optimum value will result in an energy loss due to a lower total pressure difference caused by frictional pressure rise. The experimental model developed is scaled down to a chimney height of 3m and collector diameter of 2m with a maximum
power output of 32 W. In the experiment, the characteristics of the temperature inside the collector are studied by varying the height of the collector above the ground. The temperature difference between collector exit and collector inlet from the comparison of experimental and simulated models is in good agreement. It was found that the implementation of a solar chimney power plant is technically feasible for the generation of electrical energy up to the desired potential by adjusting chimney height and collector diameter.