Numerical Investigation of Hot Air Recirculation in an Air-Cooled Steam Condenser Under Ambient Conditions

2011 ◽  
Author(s):  
Weifeng He ◽  
Yiping Dai ◽  
Qingzhong Ma ◽  
Danmei Xie
Keyword(s):  
Wind Speed ◽  
Power Plant ◽  
Ambient Air ◽  
Finned Tube ◽  
Ambient Conditions ◽  
Navier Stokes Equation ◽  
Wind Speeds ◽  
Low Wind Speed ◽  
Hot Air ◽  
Air Flows

Air-cooled steam condensers (ACSCs) have been extensively utilized to reject heat in modern power plant. Hot air recirculation, which implies that the heated air from the exchangers is again drawn back into the axial fans influence the performance of the ACSC. Hot air recirculation under different wind speeds and directions is numerically simulated in an ACSC of a 2×600MW air-cooled power plant with the commercial Computational Fluid Dynamics (CFD) code, FLUENT, and the performance of the ACSC is investigated. Fan boundary is applied to simulate the fan characteristics when the ambient air flows through the rotor and the source term is added to the Navier-Stokes equation to simulate the pressure loss when the air flows through the exchangers. Phase transition is involved in the simulation because the turbine exhaust condensates in the finned tube exchangers while the ambient air flows outside. As a result, user define function based on the actual steam property is applied to simulate the heat transfer course between the exhaust and the ambient air. Two different mechanisms of hot air are simulated: one is based on wind speed and the other is based on wind direction. The simulation result shows that when the wind blows in the front of the ACSC, the hot air from the heat exchanger flow out free at low wind speed while it flows into the fan in the A-frame, and reverse irrigation occurs. Recirculation rate reaches its peak value at α = 135° under the obstacle effect of the turbine and boiler houses. The hot air recirculation under ambient conditions is systematically studied in the paper, and the research results provide the reference for the design and operation of the power plant.

Pressure Forecast of an Air-Cooled Steam Condenser under Wind Speeds

2011 ◽  
Vol 383-390 ◽  
pp. 6187-6193
Author(s):  
Wei Feng He ◽  
Yi Ping Dai
Keyword(s):  
Heat Transfer ◽  
Wind Speed ◽  
Power Plant ◽  
Heat Transfer Rate ◽  
Water Conservation ◽  
Transfer Rate ◽  
North China ◽  
Ambient Air ◽  
Wind Speeds ◽  
Turbine Exhaust

Direct air-cooled power plant is popularized in north China because of the water conservation. Different from the water-cooled condenser, the ambient air absorbs the latent heat that turbine exhaust in the heat exchangers releases. In this paper, the numerical model of a 2×600MW power plant is prepared to simulate the performance of the air–cooled steam condenser under different wind speeds. Heat transferring with phase change is very complicated so that User Define Function(UDF) is applied to calculate the heat transfer rate in the air-cooled condenser. The fan flow rate will drop obviously during the increasing of the wind speed. As a result, the heat transfer rate between the steam and the ambient air also decreases and the pressure of the condenser rises. Finally, the stable condenser pressures under different wind speeds are predicted. The result shows that the air-cooled condenser is very sensitive to the wind speed.

Numerical Investigation and Performance Optimization of an Air-Cooled Steam Condenser Cell Under Ambient Conditions

2011 ◽  
Author(s):  
Weifeng He ◽  
Yiping Dai ◽  
Qingzhong Ma
Keyword(s):  
Flow Field ◽  
Performance Optimization ◽  
Ambient Air ◽  
Absolute Pressure ◽  
High Wind ◽  
Ambient Conditions ◽  
Wind Speeds ◽  
Hot Air ◽  
Porous Media Model ◽  
And Performance

Air-cooled steam condensers (ACSCs) are so sensitive to the unpredictable ambient conditions that it is quite necessary to find the mechanism how the ambient conditions get into reaction and reasonable measurements can be employed to improve the performance. The numerical model of an ACSC cell is established in the paper. The influence of the ambient conditions on the performance of the ACSC cell is investigated, and the final stable back pressure (absolute pressure) the ACSC cell operates at is forecasted. Finally, wind wall is equipped to change the flow field around the ACSC cell and the performance is optimized. Aerodynamic characteristic of the ACSC cell is simulated by employing the FAN boundary and porous media model in FLUENT. User Define Function (UDF) based on the actual steam property is loaded to simulate the condensation of the steam in the exchangers. The flow field around the ACSC cell varies with the different wind speeds and directions. As a result, the fan volumetric effectiveness and the exchanger performance both decrease under high wind speed and adverse wind direction. Wind temperature gets into reaction mainly because it changes the cold side temperature of the exchangers. Under high wind temperature, the reduced temperature difference decreases the heat transfer rate between the exhaust steam and the ambient air. The equipped wind wall successfully reduces the hot air recirculation (HAR) although the fan performance is also affected due to the gathering effect between the wind wall and heat exchangers, and the performance of the ACSC cell is significantly improved under the dual effects.

scholarly journals Optimization of a Small Wind Power Plant for Annual Wind Speed Distribution

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1587
Author(s):  
Krzysztof Wrobel ◽  
Krzysztof Tomczewski ◽  
Artur Sliwinski ◽  
Andrzej Tomczewski
Keyword(s):  
Wind Speed ◽  
Power Plant ◽  
Wind Power ◽  
Power Plants ◽  
Control Method ◽  
Wind Power Plant ◽  
Switched Reluctance ◽  
Wind Speeds ◽  
Wind Speed Distribution ◽  
And Control

This article presents a method to adjust the elements of a small wind power plant to the wind speed characterized by the highest annual level of energy. Tests were carried out on the basis of annual wind distributions at three locations. The standard range of wind speeds was reduced to that resulting from the annual wind speed distributions in these locations. The construction of the generators and the method of their excitation were adapted to the characteristics of the turbines. The results obtained for the designed power plants were compared with those obtained for a power plant with a commercial turbine adapted to a wind speed of 10 mps. The generator structure and control method were optimized using a genetic algorithm in the MATLAB program (Mathworks, Natick, MA, USA); magnetostatic calculations were carried out using the FEMM program; the simulations were conducted using a proprietary simulation program. The simulation results were verified by measurement for a switched reluctance machine of the same voltage, power, and design. Finally, the yields of the designed generators in various locations were determined.

scholarly journals Design and Contruction of Vertical Axis Wind Turbine Triple-Stage Savonius Type as the Alternative Wind Power Plant

KnE Energy ◽  
2015 ◽  
Vol 2 (2) ◽  
pp. 172
Author(s):  
Tedy Harsanto ◽  
Haryo Dwi Prananto ◽  
Esmar Budi ◽  
Hadi Nasbey
Keyword(s):  
Wind Speed ◽  
Power Plant ◽  
Wind Turbine ◽  
Wind Power ◽  
Output Power ◽  
Vertical Axis ◽  
Wind Power Plant ◽  
Vertical Axis Wind Turbine ◽  
Low Wind Speed ◽  
Simple Materials

<p>A vertical axis wind turbine triple-stage savonius type has been created by using simple materials to generate electricity for the alternative wind power plant. The objective of this research is to design a simple wind turbine which can operate with low wind speed. The turbine was designed by making three savonius rotors and then varied the structure of angle on the three rotors, 0˚, 90˚ and 120˚. The dimension of the three rotors are created equal with each rotor diameter 35 cm and each rotor height 19 cm. The turbine was tested by using blower as the wind sources. Through the measurements obtained the comparisons of output power, rotation of turbine, and the level of efficiency generated by the three variations. The result showed that the turbine with angle of 120˚ operate most optimally because it is able to produce the highest output power and highest rotation of turbine which is 0.346 Watt and 222.7 RPM. </p><p><strong>Keywords</strong>: Output power; savonius turbine; triple-stage; the structure of angle</p>

scholarly journals Strategies for Enhancing the Low Wind Speed Performance of H-Darrieus Wind Turbine—Part 1

2019 ◽  
Vol 1 (1) ◽  
pp. 185-204 ◽  
Author(s):  
Palanisamy Mohan Kumar ◽  
Krishnamoorthi Sivalingam ◽  
Teik-Cheng Lim ◽  
Seeram Ramakrishna ◽  
He Wei
Keyword(s):  
Wind Speed ◽  
Poor Performance ◽  
Vertical Axis ◽  
Speed Ratio ◽  
Wind Speeds ◽  
Low Wind Speed ◽  
Viable Solution ◽  
Speed Performance ◽  
Low Wind Speeds ◽  
Starting Characteristics

Small wind turbines are key devices for micro generation in particular, with a notable contribution to the global wind energy sector. Darrieus turbines, despite being highly efficient among various types of vertical axis turbines, received much less attention due to their starting characteristics and poor performance in low wind speeds. Radically different concepts are proposed as a potential solution to enhance the performance of Darrieus turbine in the weak wind flows, all along the course of Darrieus turbine development. This paper presents a comprehensive review of proposed concepts with the focus set on the low wind speed performance and critically assessing their applicability based on economics, reliability, complexity, and commercialization aspects. The study is first of its kind to consolidate and compare various approaches studied on the Darrieus turbine with the objective of increasing performance at low wind. Most of the evaluated solutions demonstrate better performance only in the limited tip speed ratio, though they improve the low wind speed performance. Several recommendations have been developed based on the evaluated concepts, and we concluded that further critical research is required for a viable solution in making the Darrieus turbine a low speed device.

scholarly journals The Transition from Downward to Upward Air–Sea Momentum Flux in Swell-Dominated Light Wind Conditions

2018 ◽  
Vol 75 (8) ◽  
pp. 2579-2588 ◽  
Author(s):  
Ulf Högström ◽  
Erik Sahlée ◽  
Ann-Sofi Smedman ◽  
Anna Rutgersson ◽  
Erik Nilsson ◽  
...  
Keyword(s):  
Wind Speed ◽  
Momentum Flux ◽  
Water Surface ◽  
Sea Waves ◽  
Progressive Wave ◽  
Wind Speeds ◽  
Low Wind Speed ◽  
Light Wind ◽  
Wind Sea ◽  
Almost All

Abstract Fifteen hours of consecutive swell data from the experiment Flux, État de la Mer, et Télédétection en Condition de Fetch Variable (FETCH) in the Mediterranean show a distinct upward momentum flux. The characteristics are shown to vary systematically with wind speed. A hysteresis effect is found for wave energy of the wind-sea waves when represented as a function of wind speed, displaying higher energy during decaying winds compared to increasing winds. For the FETCH measurements, the upward momentum transfer regime is found to begin for wind speeds lower than about U = 4 m s−1. For the lowest observed wind speeds U &lt; 2.4 m s−1, the water surface appears to be close to dynamically smooth. In this range almost all the upward momentum flux is accomplished by the peak in the cospectrum between the vertical and horizontal components of the wind velocity. It is demonstrated that this contribution in turn is linearly related to the swell significant wave height Hsd in the range 0.6 &lt; Hsd &lt; 1.4 m. For Hsd &lt; 0.6 m, the contribution is zero in the present dataset but may depend on the swell magnitude in other situations. It is speculated that the observed upward momentum flux in the smooth regime, which is so strongly related to the cospectral peak at the dominant swell frequency, might be caused by the recirculation mechanism found by Wen and Mobbs in their numerical simulation of laminar flow of a nonlinear progressive wave at low wind speed.

scholarly journals Optimization of Straight-bladed Darrieus type vertical axis wind blade for low wind speed

2020 ◽  
Vol 211 ◽  
pp. 02008
Author(s):  
Christian M. Mortel ◽  
Nicanor L. Serrano ◽  
John Gabriel G. Decena
Keyword(s):  
Wind Speed ◽  
Optimal Design ◽  
Vertical Axis ◽  
Vertical Axis Wind Turbine ◽  
Navier Stokes Equation ◽  
Blade Height ◽  
3D Simulations ◽  
Low Wind Speed ◽  
Design Values ◽  
Blade Geometry

Straight-bladed Darrieus blade is a type of vertical axis wind turbine that requires low wind speed to operate but is considered less efficient due to conventional blade geometry. To increase its performance by means of dynamic torque, the study used a statistical method, central composite design, through DesignExpert software. The computational fluid dynamics (CFD) through SolidWorks Reynolds-Averaged Navier Stokes Equation (RANS) k – epsilon turbulence model was used to simulate the Design of Experiments. The study was composed of two phases, namely 2D and 3D simulations. The 2D simulation studied the effect of varying the camber, camber location, and thickness to the dynamic torque, while the 3D simulation varied the blade height, rotor radius, and materials. The camber’s optimal conditions, camber location, and thickness in 2D simulations are 4.75%, 45%, and 15.50% of the chord, respectively. These optimal design values could reach the dynamic torque equivalent to 60.6571 Newton-meter. Meanwhile, the blade height and rotor radius of the 3D simulations have optimal design values of 4.41 meters and 4.75 meters, respectively. These optimal values could increase the dynamic torque to 2310.01 Newton-meter. The dynamic torque of the optimal design obtained a 133% significant increase compared to the conventional blade. Thus, the research has proven the increase in the Darrieus Wind turbine’s performance by varying its blade geometry.

Effect of Swell on Wind Stress for Light to Moderate Winds

2020 ◽  
Vol 77 (11) ◽  
pp. 3759-3768
Author(s):  
Charles L. Vincent ◽  
Hans C. Graber ◽  
Clarence O. Collins
Keyword(s):  
Wind Speed ◽  
Gulf Of Mexico ◽  
Inflection Point ◽  
Friction Velocity ◽  
Flow Transition ◽  
Wind Speeds ◽  
Impact Stress ◽  
Low Wind Speed ◽  
Wind Sea ◽  
Low Wind Speeds

AbstractBuoy observations from a 1999 Gulf of Mexico field program (GOM99) are used to investigate the relationships among friction velocity u*, wind speed U, and amount of swell present. A U–u*sea parameterization is developed for the case of pure wind sea (denoted by u*sea), which is linear in U over the range of available winds (2–16 m s−1). The curve shows no sign of an inflection point near 7–8 m s−1 as suggested in a 2012 paper by Andreas et al. on the basis of a transition from smooth to rough flow. When observations containing more than minimal swell energy are included, a different U–u* equation for U < 8 m s−1 is found, which would intersect the pure wind-sea curve about 7–8 m s−1. These two relationships yield a bilinear curve similar to Andreas et al. with an apparent inflection near 7–8 m s−1. The absence of the inflection in the GOM99 experiment pure wind-sea curve and the similarity of the GOM99 swell-dominated low wind speed to Andreas et al.’s low wind speed relationship suggest that the inflection may be due to the effect of swell and not a flow transition. Swell heights in the range of only 25–50 cm may be sufficient to impact stress at low wind speeds.

Impact of wind speeds on turbulent transport of carbon dioxide (CO2) fluxes at a tropical location in Ile - Ife, southwest Nigeria

2020 ◽  
Author(s):  
Theodora Bello ◽  
Adewale Ajao ◽  
Oluwagbemiga Jegede
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Land Surface ◽  
Stable Boundary Layer ◽  
Turbulent Transport ◽  
Strong Wind ◽  
Stable Boundary ◽  
Wind Speeds ◽  
Low Wind Speed ◽  
Tropical Area

&lt;p&gt;The study investigates impact of wind speeds on the turbulent transport of CO&lt;sub&gt;2 &lt;/sub&gt;fluxes for a land-surface atmosphere interface in a low-wind tropical area between May 28&lt;sup&gt;th&lt;/sup&gt; and June 14&lt;sup&gt;th&lt;/sup&gt;, 2010; and May 24&lt;sup&gt;th&lt;/sup&gt; and June 15&lt;sup&gt;th&lt;/sup&gt;, 2015. Eddy covariance technique was used to acquire turbulent mass fluxes of CO&lt;sub&gt;2&lt;/sub&gt; and wind speed at the study site located inside the main campus of Obafemi Awolowo University, Ile &amp;#8211; Ife, Nigeria. The results showed high levels of CO&lt;sub&gt;2 &lt;/sub&gt;fluxes at nighttime attributed to stable boundary layer conditions and low wind speed. Large transport and distribution of CO&lt;sub&gt;2 &lt;/sub&gt;fluxes were observed in the early mornings due to strong wind speeds recorded at the study location. In addition, negative CO&lt;sub&gt;2 &lt;/sub&gt;fluxes were observed during the daytime attributed to prominent convective and photosynthetic activities. The study concludes there was an inverse relationship between turbulent transport of CO&lt;sub&gt;2 &lt;/sub&gt;fluxes and wind speed for daytime period while nighttime CO&lt;sub&gt;2&lt;/sub&gt; fluxes showed no significant correlation.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Keywords&lt;/strong&gt;: CO&lt;sub&gt;2 &lt;/sub&gt;fluxes, Wind speed, Turbulent transport, Low-wind tropical area, Stable boundary layer&lt;/p&gt;

scholarly journals 1980–2010 Variability in U.K. Surface Wind Climate

2013 ◽  
Vol 26 (4) ◽  
pp. 1172-1191 ◽  
Author(s):  
Nick Earl ◽  
Steve Dorling ◽  
Richard Hewston ◽  
Roland von Glasow
Keyword(s):  
Wind Speed ◽  
Decadal Variability ◽  
Surface Wind ◽  
Rayleigh Distribution ◽  
Daily Maximum ◽  
International Studies ◽  
Atlantic Sector ◽  
Wind Speeds ◽  
Low Wind Speed ◽  
Wind Climate

Abstract The climate of the northeast Atlantic region comprises substantial decadal variability in storminess. It also exhibits strong inter- and intra-annual variability in extreme high and low wind speed episodes. Here the authors quantify and discuss causes of the variability seen in the U.K. wind climate over the recent period 1980–2010. Variations in U.K. hourly mean (HM) wind speeds, in daily maximum gust speeds and in associated wind direction measurements, made at standard 10-m height and recorded across a network of 40 stations, are considered. The Weibull distribution is shown to generally provide a good fit to the hourly wind data, albeit with the shape parameter k spatially varying from 1.4 to 2.1, highlighting that the commonly assumed k = 2 Rayleigh distribution is not universal. It is found that the 10th and 50th percentile HM wind speeds have declined significantly over this specific period, while still incorporating a peak in the early 1990s. The authors' analyses place the particularly “low wind” year of 2010 into longer-term context and their findings are compared with other recent international studies. Wind variability is also quantified and discussed in terms of variations in the exceedance of key wind speed thresholds of relevance to the insurance and wind energy industries. Associated interannual variability in energy density and potential wind power output of the order of ±20% around the mean is revealed. While 40% of network average winds are in the southwest quadrant, 51% of energy in the wind is associated with this sector. The findings are discussed in the context of current existing challenges to improve predictability in the Euro-Atlantic sector over all time scales.

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