Flow Characteristics in a Channel With Corona Wind Generator

2010 ◽  
Author(s):  
J. Zhang ◽  
F. C. Lai
Keyword(s):  
Volume Flow Rate ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Square Channel ◽  
Wind Generator ◽  
Numerical Predictions ◽  
Wide Range ◽  
Flow Transport ◽  
Corona Wind

Electrohydrodynamically induced flows have shown great potential for many engineering applications. Previous studies have revealed that a corona wind generator can be used to enhance flow transport in a channel. In this study, a corona wind generator with emitting wire electrodes flush mounted on the channel walls is considered for a wide range of operating conditions. Specifically, three configurations of the generator (with 4, 12, and 28 pins of emitting electrodes) are evaluated for their effectiveness in delivering the air flow. To investigate the flow characteristics inside a square channel, three-dimensional governing equations for electric and flow fields are numerically solved. The corona current is first measured experimentally and used in the numerical calculations. Numerical predictions on the velocity profile of corona-induced air flows as well as the volume flow rate delivered have been successfully verified by experimental results.

Enhanced Forced Convection in a Square Channel With Two-Stage Corona Wind Generator

2012 ◽  
Author(s):  
A. K. M. Monayem H. Mazumder ◽  
F. C. Lai
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Thermal Management ◽  
Forced Convection ◽  
Two Stage ◽  
Maximum Enhancement ◽  
Square Channel ◽  
Wind Generator ◽  
Wide Range ◽  
Corona Wind

In this study, enhancement in forced convection inside a square channel by a two-stage electrohydrodynamic (EHD) gas pump has been examined by numerical simulations. The EHD gas pump with 28 emitting electrodes in each stage has been evaluated for a wide range of operating voltages starting from the corona threshold voltage up to 28 kV for further improvement in its performance over that of a single-stage. To achieve the maximum enhancement in heat transfer, the emitting electrodes of the corona wind generator are flush mounted on the channel walls so that the corona wind produced directly perturbs the boundary layer. The results show that EHD technique has a great potential for applications in thermal management.

Optimized Chaotic Heat Exchanger Configurations for Process Industry: A Numerical Study

2013 ◽  
Author(s):  
Akram Ghanem ◽  
Thierry Lemenand ◽  
Dominique Della Valle ◽  
Hassan Peerhossaini
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Numerical Study ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Process Intensification ◽  
Point Of View ◽  
Square Duct ◽  
Square Channel ◽  
Duct Geometry

A numerical investigation of chaotic laminar flow and heat transfer in isothermal-wall square-channel configurations is presented. The computations, based on a finite-volume method with the SIMPLEC algorithm, are conducted in terms of Péclet numbers ranging from 7 to 7×105. The geometries, based on the split-and-recombine (SAR) principle, are first proposed for micromixing purposes, and are then optimized and scaled up to three-dimensional minichannels with 3-mm sides that are capable of handling industrial fluid manipulation processes. The aim is to assess the feasibility of this mass- and heat-transfer technique for out-of-laboratory commercial applications and to compare different configurations from a process intensification point of view. The effects of the geometry on heat transfer and flow characteristics are examined. Results show that the flux recombination phenomenon mimicking the baker’s transform in the SAR-1 and SAR-2 configurations produces chaotic structures and promotes mass transfer. This phenomenon also accounts for higher convective heat transfer exemplified by increased values of the Nusselt number compared to the chaotic continuous-flow configuration and the baseline plain square-duct geometry. Energy expenditures are explored and the overall heat transfer enhancement factor for equal pumping power is calculated. The SAR-2 configuration reveals superior heat-transfer characteristics, enhancing the global gain by up to 17-fold over the plain duct heat exchanger.

scholarly journals Improvement of Pump Performance at Off-Design Conditions

1985 ◽  
Author(s):  
J. Paulon ◽  
C. Fradin ◽  
J. Poulain
Keyword(s):  
Experimental Study ◽  
Flow Field ◽  
Mass Flow ◽  
Flow Characteristic ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Pump Performance ◽  
Wide Range ◽  
Mass Flows ◽  
Design Value

Industrial pumps are generally used in a wide range of operating conditions from almost zero mass flow to mass flows larger than the design value. It has been often noted that the head-mass flow characteristic, at constant speed, presents a negative bump as the mass flow is somewhat smaller than the design mass flows. Flow and mechanical instabilities appear, which are unsafe for the facility. An experimental study has been undertaken in order to analyze and if possible to palliate these difficulties. A detailed flow analyzis has shown strong three dimensional effects and flow separations. From this better knowledge of the flow field, a particular device was designed and a strong attenuation of the negative bump was obtained.

Experimental and Numerical Study for Improved Understanding of Mixed-Convection Type of Flows in Turbine Casing Cavities During Shut-Down Regimes

2021 ◽  
Author(s):  
Oguzhan Murat ◽  
Budimir Rosic ◽  
Koichi Tanimoto ◽  
Ryo Egami
Keyword(s):  
Natural Convection ◽  
Flow Field ◽  
Mixed Convection ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Scale Model ◽  
Unsteady Temperature ◽  
Numerical Predictions ◽  
Wide Range ◽  
Turbine Casing

Abstract Due to increase in the power generation from renewable sources, steam and gas turbines will be required to adapt for more flexible operations with frequent start-ups and shut-downs to provide load levelling capacity. During shut-down regimes, mixed convection takes place with natural convection dominance depending on the operating conditions in turbine cavities. Buoyant flows inside the turbine that are responsible for non-uniform cooling leading to thermal stresses and compromise clearances directly limits the operational flexibility. Computational fluid dynamics (CFD) tools are required to predict the flow field during these regimes since direct measurements are extremely difficult to conduct due to the harsh operating conditions. Natural convection with the presence of cross-flow -mixed convection has not been extensively studied to provide detailed measurements. Since the literature lacks of research on such flows with real engine representative operating conditions for CFD validation, the confidence in numerical predictions is rather inadequate. This paper presents a novel experimental facility that has been designed and commissioned to perform very accurate unsteady temperature and flow field measurements in a simplified turbine casing geometry. The facility is capable of reproducing a wide range of Richardson, Grashof and Reynolds numbers which are representative of engine realistic operating conditions. In addition, high fidelity, wall resolved LES with dynamic Smagorinsky subgrid scale model has been performed. The flow field as well as heat transfer characteristics have been accurately captured with LES. Lastly, inadequacy of RANS for mixed type of flows has been highlighted.

PIV Measurements in Diffuser of the Radial Pump

2015 ◽  
Author(s):  
Sung Yong Jung ◽  
Young Uk Min ◽  
Kyung Lok Lee
Keyword(s):  
High Speed ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Internal Flows ◽  
Piv Measurements ◽  
Image Velocimetry ◽  
Acquisition Device ◽  
Field Information ◽  
Radial Pump

The performance characteristics of the radial pump commonly used as a multistage (8 or 10 stage) pump have been investigated experimentally. Due to the complex three-dimensional geometries, the hydraulic performance of multistage pumps is closely related to the internal flows in diffuser and return vanes. In order to investigate the flow characteristics in these regions by Particle Image Velocimetry (PIV) technique, a transparent pump is designed. A 532 nm continuous laser and a high-speed camera are used as a light source and an image acquisition device, respectively. The velocity field information in a diffuser of the radial pump is successfully obtained by two-dimensional PIV measurements at various operating conditions.

Application of an Improved Streamline Curvature Approach to a Modern, Two-Stage Transonic Fan: Comparison With Data and CFD

2002 ◽  
Author(s):  
Keith M. Boyer ◽  
Walter F. O’Brien
Keyword(s):  
Three Dimensional ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Model Parameters ◽  
Two Stage ◽  
Streamline Curvature ◽  
Wide Range ◽  
Improved Model ◽  
Transonic Fan ◽  
Streamline Curvature Method

A streamline curvature method with improvements to key loss models is applied to a two-stage, low aspect ratio, transonic fan with design tip relative Mach number of approximately 1.65. Central to the improvements is the incorporation of a physics-based shock model. The attempt here is to capture the effects of key flow phenomena relative to the off-design performance of the fan. A quantitative analysis regarding solution sensitivities to model parameters that influence the key phenomena over a wide range of operating conditions is presented. Predictions are compared to performance determined from overall and interstage measurements, as well as from a three-dimensional, steady, Reynolds-averaged Navier-Stokes method applied across the first rotor. Overall and spanwise comparisons demonstrate that the improved model gives reasonable performance trending and generally accurate results. The method can be used to provide boundary conditions to higher-order solvers, or implemented within novel approaches using the streamline curvature method to explore complex engine-inlet integration issues, such as time-variant distortion.

scholarly journals Numerical Investigation of Liquid–Liquid Mixing in Modified T Mixer with 3D Obstacles

2021 ◽  
pp. 25-32
Author(s):  
Md. Readul Mahmud
Keyword(s):  
Numerical Investigation ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Channel Length ◽  
Navier Stokes ◽  
Mixing Efficiency ◽  
Mixing Performance ◽  
Wide Range

The fluids inside passive micromixers are laminar in nature and mixing depends primarily on diffusion. Hence mixing efficiency is generally low, and requires a long channel length and longtime compare to active mixers. Various designs of complex channel structures with/without obstacles and three-dimensional geometries have been investigated in the past to obtain an efficient mixing in passive mixers. This work presents a design of a modified T mixer. To enhance the mixing performance, circular and hexagonal obstacles are introduced inside the modified T mixer. Numerical investigation on mixing and flow characteristics in microchannels is carried out using the computational fluid dynamics (CFD) software ANSYS 15. Mixing in the channels has been analyzed by using Navier–Stokes equations with water-water for a wide range of the Reynolds numbers from 1 to 500. The results show that the modified T mixer with circular obstacles has far better mixing performance than the modified T mixer without obstacles. The reason is that fluids' path length becomes longer due to the presence of obstacles which gives fluids more time to diffuse. For all cases, the modified T mixer with circular obstacle yields the best mixing efficiency (more than 60%) at all examined Reynolds numbers. It is also clear that efficiency increase with axial length. Efficiency can be simply improved by adding extra mixing units to provide adequate mixing. The value of the pressure drop is the lowest for the modified T mixer because there is no obstacle inside the channel. Modified T mixer and modified T mixer with circular obstacle have the lowest and highest mixing cost, respectively. Therefore, the current design of modified T with circular obstacles can act as an effective and simple passive mixing device for various micromixing applications.

scholarly journals Comparative analysis of air and water flows in simplified hydraulic turbine models

2022 ◽  
Vol 2150 (1) ◽  
pp. 012001
Author(s):  
S G Skripkin ◽  
D A Suslov ◽  
I V Litvinov ◽  
E U Gorelikov ◽  
M A Tsoy ◽  
...  
Keyword(s):  
Comparative Analysis ◽  
Pressure Pulsation ◽  
Swirling Flow ◽  
Flow Characteristics ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
Precessing Vortex Core ◽  
Wide Range ◽  
Turbine Runner ◽  
The Fourier Transform

Abstract This article presents a comparative analysis of flow characteristics behind a hydraulic turbine runner in air and water. Swirling flow with a precessing vortex core (PVC) was investigated using a laser Doppler anemometer and pressure pulsation sensors. The experiments were conducted on aerodynamic and hydrodynamic test rigs over a wide range of hydraulic turbine operating conditions. Part-load modes of hydraulic turbine operation were investigated using the Fourier transform of pressure pulsations obtained from acoustic sensors. The features of the swirling flow were shown for the range of operating conditions from deep partl-load to overload.

Development of LP Blade Module for High Back Pressure-Aerodynamic Design

2017 ◽  
Author(s):  
Ambrish ◽  
Nand Kumar Singh
Keyword(s):  
Steam Turbine ◽  
Power Plants ◽  
Volume Flow Rate ◽  
Back Pressure ◽  
Operating Conditions ◽  
Total Efficiency ◽  
Aerodynamic Design ◽  
Streamline Curvature ◽  
Pressure Application ◽  
Wide Range

In steam turbine power plants, the appropriate design of the last stage blades is critical in determining the plant efficiency and reliability. The development of LP module for desert applications is finding applications for a number of industrial steam turbine operating with air cooled condensers. The conventional LP Module for water cooled condenser operates at low back pressure (Pexit = 0.09 bar) and are generally not suitable for high back pressure application. This paper focuses on the aerodynamic design & optimization of last stages of LP blade module for high back pressure application and validation through 3D CFD. The guide and moving blade are designed with seven equally-spaced profiles section from hub to shroud through Axstream S/w. The profile and incidence losses are minimized for the design and off-design conditions. Aeromechanical design of LP blade module consisting of 2 stages for 0.2 bar back pressure, 1.1 bar inlet static pressure and a mass flow of 61.2 kg/s is carried out. An optimization process through a streamline curvature code and design optimization software using Optimus is established and flow path contours is optimized thoroughly, a total to total efficiency of 81.4% is achieved for the rated condition. The off-design performance is investigated for a wide range of operating conditions, especially at low volume flow rate of steam condition.

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