STUDY OF FLOW AERODYNAMICS IN A CHANNEL WITH DUMBBELL-SHAPED DIMPLES

2016 ◽  
Vol 6 (1) ◽  
pp. 15-20
Author(s):  
Ivan Dmitrievich FEDOTENKOV ◽  
Anna Aleksandrovna TSYNAEVA
Keyword(s):  
Flow Rate ◽  
Heat Exchangers ◽  
Gas Flow ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Aerodynamic Resistance ◽  
Smooth Wall ◽  
Heat Transmission ◽  
Flow Rates ◽  
Small Flow

The paper deals with the study of aerodynamic resistance in a channel with dumbbell-shaped dimples on the surface and with smooth walls. It has been found that the hydraulic resistance of a channel with dumbbell-shaped dimples is higher than of a smooth one. The surface of the channel of the proposed design is also higher. It can be used for the intensification of heat transmission in recuperative heat exchangers of ventilation systems. The numerical study of the flow in a rectangular channel with one-sided arrangement of dimples of proposed geometry has been carried out. It has been determined that the use of such dimples at small flow rates near the inlet (1-0.5 m/s) will increase the rate of gas flow near the surface with dimples in comparison with a smooth wall to 20 %. When the flow rate near the inlet is 16.5 m/s, the areas with lower rates appear near the dimples.

scholarly journals Net-exergetic, hydraulic and thermal optimization of coaxial heat exchangers using fixed flow conditions instead of fixed flow rates

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Tobias Blanke ◽  
Markus Hagenkamp ◽  
Bernd Döring ◽  
Joachim Göttsche ◽  
Vitali Reger ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Exchangers ◽  
Circular Ring ◽  
Flow Conditions ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Pipe Radius

AbstractPrevious studies optimized the dimensions of coaxial heat exchangers using constant mass flow rates as a boundary condition. They show a thermal optimal circular ring width of nearly zero. Hydraulically optimal is an inner to outer pipe radius ratio of 0.65 for turbulent and 0.68 for laminar flow types. In contrast, in this study, flow conditions in the circular ring are kept constant (a set of fixed Reynolds numbers) during optimization. This approach ensures fixed flow conditions and prevents inappropriately high or low mass flow rates. The optimization is carried out for three objectives: Maximum energy gain, minimum hydraulic effort and eventually optimum net-exergy balance. The optimization changes the inner pipe radius and mass flow rate but not the Reynolds number of the circular ring. The thermal calculations base on Hellström’s borehole resistance and the hydraulic optimization on individually calculated linear loss of head coefficients. Increasing the inner pipe radius results in decreased hydraulic losses in the inner pipe but increased losses in the circular ring. The net-exergy difference is a key performance indicator and combines thermal and hydraulic calculations. It is the difference between thermal exergy flux and hydraulic effort. The Reynolds number in the circular ring is instead of the mass flow rate constant during all optimizations. The result from a thermal perspective is an optimal width of the circular ring of nearly zero. The hydraulically optimal inner pipe radius is 54% of the outer pipe radius for laminar flow and 60% for turbulent flow scenarios. Net-exergetic optimization shows a predominant influence of hydraulic losses, especially for small temperature gains. The exact result depends on the earth’s thermal properties and the flow type. Conclusively, coaxial geothermal probes’ design should focus on the hydraulic optimum and take the thermal optimum as a secondary criterion due to the dominating hydraulics.

Optimization of Inlet Ring Groove Arrangement for Suppression of Unstable Flow in a Centrifugal Impeller

2005 ◽  
Author(s):  
Masahiro Ishida ◽  
Daisaku Sakaguchi ◽  
Hironobu Ueki
Keyword(s):  
Flow Rate ◽  
The Other ◽  
Centrifugal Impeller ◽  
Shape Parameters ◽  
Unstable Flow ◽  
Ring Groove ◽  
Flow Rates ◽  
Small Flow ◽  
Specific Speed ◽  
Large Flow

An optimization of the inlet ring groove arrangement has been pursued in the present study for obtaining better impeller characteristics and a wider operation range at both small and large flow rates in a high specific speed type centrifugal impeller with inducer. The effects of the shape parameters with respect to the inlet ring groove on the impeller characteristic and the flow incidence were analyzed mainly based on numerical simulations, but also compared to the experimental results. At small flow rates, a significant improvement in the impeller characteristic is achieved due to reduction in the excessive-positive flow incidence by optimizing both location and width of the rear groove near the inducer tip throat. On the other hand, the impeller characteristic is improved at large flow rates by implementing the corner radius at the rear groove edge and by placing another front ring groove in the suction pipe. As a result, by the optimized configuration of the front and rear ring grooves, the unstable flow range of the test impeller can be reduced by about 50% without deterioration of the impeller characteristic even at the 125% flow rate.

scholarly journals Numerical Simulation of Secondary Flow in Gas Turbine Disc Cavities, Including Conjugate Heat Transfer

1996 ◽  
Author(s):  
Y.-H. Ho ◽  
M. M. Athavale ◽  
J. M. Forry ◽  
R. C. Hendricks ◽  
B. M. Steinetz
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Conjugate Heat Transfer ◽  
Gas Flow ◽  
Numerical Study ◽  
Labyrinth Seal ◽  
Temperature Fields ◽  
Heat Transfer Analysis ◽  
Flow Rates ◽  
Turbine Disc

A numerical study of the flow and heat transfer in secondary flow elements of the entire inner portion of the turbine section of the Allison T-56/501D engine is presented. The flow simulation included the interstage cavities, rim seals and associated main path flows, while the energy equation also included the solid parts of the turbine disc, rotor supports, and stator supports. Solutions of the energy equations in these problems usually face the difficulty in specifications of wall thermal boundary conditions. By solving the entire turbine section this difficulty is thus removed, and realistic thermal conditions are realized on all internal walls. The simulation was performed using SCISEAL, an advanced 2D/3D CFD code for predictions of fluid flows and forces in turbomachinery seals and secondary flow elements. The mass flow rates and gas temperatures at various seal locations were compared with the design data from Allison. Computed gas flow rates and temperatures in the rim and labyrinth seal show a fair 10 good comparison with the design calculations. The conjugate heat transfer analysis indicates temperature gradients in the stationary intercavity walls, as well as the rotating turbine discs. The thermal strains in the stationary wall may lead to altered interstage labyrinth seal clearances and affect the disc cavity flows. The temperature, fields in the turbine discs also may lead to distortions that can alter the rim seal clearances. Such details of the flow and temperature fields are important in designs of the turbine sections to account for possible thermal distortions and their effects on the performance. The simulation shows that the present day CFD codes can provide the means to understand the complex flow field and thereby aid the design process.

scholarly journals Influence of Pressure on Gas/Liquid Interfacial Area in a Tray Column

2020 ◽  
Vol 10 (13) ◽  
pp. 4617
Author(s):  
Adel Almoslh ◽  
Falah Alobaid ◽  
Christian Heinze ◽  
Bernd Epple
Keyword(s):  
Flow Rate ◽  
Gas Flow ◽  
Volumetric Flow Rate ◽  
Interfacial Area ◽  
Gas Flow Rate ◽  
Test Rig ◽  
Flow Rates ◽  
Waste Gas ◽  
Simulated Waste ◽  
Series Of Experiments

The influence of pressure on the gas/liquid interfacial area is investigated in the pressure range of 0.2–0.3 MPa by using a tray column test rig. A simulated waste gas, which consisted of 30% CO2 and 70% air, was used in this study. Distilled water was employed as an absorbent. The temperature of the inlet water was 19 °C. The inlet volumetric flow rate of water was 0.17 m3/h. Two series of experiments were performed; the first series was performed at inlet gas flow rate 15 Nm3/h, whereas the second series was at 20 Nm3/h of inlet gas flow rate. The results showed that the gas/liquid interfacial area decreases when the total pressure is increased. The effect of pressure on the gas/liquid interfacial area at high inlet volumetric gas flow rates is more significant than at low inlet volumetric gas flow rates. The authors studied the effect of decreasing the interfacial area on the performance of a tray column for CO2 capture.

Effect of Inner Cavity’s Gas Flow Rate on the Extrusion Forming of Plastic Micro-Pipe

2020 ◽  
Vol 842 ◽  
pp. 279-284
Author(s):  
Zhong Ren ◽  
Xing Yuan Huang
Keyword(s):  
Finite Element ◽  
Normal Stress ◽  
Flow Rate ◽  
Gas Flow ◽  
Normal Stress Difference ◽  
Stress Difference ◽  
Gas Flow Rate ◽  
Flow Rates ◽  
First Normal Stress Difference ◽  
Extrusion Forming

During the manufacture of plastic micro-pipe, a certain volume of gas should be properly injected into the inner cavity to overcome the collapse and adhesion problems. In this work, the extrusion forming of plastic micro-tube under the role of inner cavity’s gas were numerically studied. At the same time, the effect of inner cavity’s gas flow rate on the extrusion deformation of plastic micro-pipe was also numerically investigated by using the finite element method. A kind of 2D two-phase fluid geometric model and finite element mesh were established and some reasonable boundary conditions and material parameters were imposed. Under a fixed volume flow rate of melt, different flow rates of inner cavity gas were imposed on the inlet of inner cavity’s gas. The extrusion deformation profile and deformation ratio of plastic micro-pipe under different flow rates of gas were all obtained. To ascertain the mechanisms of effect of inner cavity’s gas flow rate on the extrusion deformation of plastic micro-tube, the flow velocities, pressure, shear rate, normal stress, and the first normal stress difference of melt all obtained and analyzed. Numerical results show that with the increase of inner cavity’s gas flow rate, the radial velocity, axial velocity, pressure, shear rate, normal stress, and the first normal stress difference of melt all increase, which makes the extrusion deformation become more and more serious. In practice, reasonable controlling of the inner cavity’s gas flow rate is very important. In the other hand, it can adjust the size of extruded plastic micro-pipe.

Behavior of Secondary Flow in a Low Solidity Tandem Cascade Diffuser

2012 ◽  
Author(s):  
Daisaku Sakaguchi ◽  
Hironobu Ueki ◽  
Masahiro Ishida ◽  
Hiroshi Hayami
Keyword(s):  
Secondary Flow ◽  
Flow Rate ◽  
Flow Separation ◽  
Lift Coefficient ◽  
Pressure Recovery ◽  
Suction Surface ◽  
Flow Rates ◽  
Blade Loading ◽  
Small Flow Rate ◽  
Small Flow

Low solidity circular cascade diffuser abbreviated by LSD was proposed by Senoo et al. showing a high blade loading or a high lift coefficient without stall even under small flow rate conditions. These high performances were achieved by that the flow separation on the suction surface of the LSD blade was successfully suppressed by the secondary flow formed along the side walls. The higher performance of the LSD was achieved in both pressure recovery and operating range by adopting the tandem cascade because the front blade of the tandem cascade was designed suitably for small flow rates while the rear blade of the tandem cascade was designed suitably for large flow rates. In order to clarify the reason why the tandem cascade could achieve a high pressure recovery in a wide range of flow rate, the flow in the LSD with the tandem cascade is analyzed numerically in the present study by using the commercial CFD code of ANSYS-CFX 13.0. The behavior of the secondary flow is compared between the cases with the single cascade and the tandem one. It is found that the high blade loading of the front blade is achieved at the small flow rate by formation of the favorable secondary flow which suppresses the flow separation on suction surface of the front blade, and the flow separation on pressure surface of the front blade appeared at the design flow rate can be suppressed by the accelerated flow in the gap between the trailing edge of the front blade and the leading edge of the rear blade, resulting in the positive lift coefficient in spite of a large negative angle of attack.

scholarly journals Numerical Investigation of Mixing Characteristic for CH4/Air in Rotating Detonation Combustor

2020 ◽  
Vol 10 (4) ◽  
pp. 1298
Author(s):  
Shan Jin ◽  
Qingyang Meng ◽  
Zhiming Li ◽  
Ningbo Zhao ◽  
Hongtao Zheng ◽  
...  
Keyword(s):  
Mass Flow ◽  
Flow Rate ◽  
Pressure Loss ◽  
Equivalence Ratio ◽  
Numerical Study ◽  
Ignition Energy ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Critical Ignition ◽  
Rotating Detonation

The mixing process of fuel and oxidizer is a very critical factor affecting the real operating performance of non-premixed rotating detonation combustor. In this paper, a two-dimensional numerical study is carried out to investigate the flow and mixing characteristics of CH4/air in combustor with different injection structures. On this basis, the effect of CH4/air mixing on the critical ignition energy for forming detonation is theoretically analyzed in detail. The numerical results indicate that injection strategies of CH4 and air can obviously affect the flow filed characteristic, pressure loss, mixing uniformity and local equivalence ratio in combustor, which further affect the critical ignition energy for forming detonation. In the study for three different mass flow rates (the mass flow rates of air are 12.01 kg/s,8.58 kg/s and 1.72 kg/s, respectively), when air is radially injected into combustor (fuel/air are injected perpendicular to each other), although the mixing quality of CH4 and air is improved, the total pressure loss is also increased. In addition, the comparative analysis also shows that the increase of mass flow rate of CH4/air can decrease the difference of the critical ignition energy for forming detonation at a constant total equivalence ratio. The ignition energy decreases with the decrease of the total flow rate and then increases gradually.

Effects of Gas Flow Rate and Catalyst Loading on Polymer Electrolyte Membrane (PEM) Fuel Cell Performance and Degradation

2010 ◽  
Author(s):  
A. Chukwujekwu Okafor ◽  
Hector-Martins Mogbo
Keyword(s):  
Fuel Cell ◽  
Flow Rate ◽  
Gas Flow ◽  
Open Circuit Voltage ◽  
Polymer Electrolyte Membrane ◽  
Open Circuit ◽  
Catalyst Loading ◽  
Gas Flow Rate ◽  
Flow Rates ◽  
Electrolyte Membrane

In this paper, the effects of gas flow rates, and catalyst loading on polymer electrolyte membrane fuel cell (PEMFC) performance was investigated using a 50cm2 active area fuel cell fixture with serpentine flow field channels machined into poco graphite blocks. Membrane Electrode Assemblies (MEAs) with catalyst and gas flow rates at two levels each (0.5mg/cm2, 1mg/cm2; 0.3L/min, 0.5L/min respectively) were tested at 60°C without humidification. The cell performance was analyzed by taking AC Impedance, TAFEL plot, open circuit voltage, and area specific resistance measurements. It was observed that MEAs with lower gas flow rate had lesser cell resistance compared to MEAs with a higher gas flow rate. TAFEL plot shows the highest exchange current density value of −2.05 mAcm2 for MEA with 0.5mg/cm2 catalyst loading operated at reactant gas flow rate of 0.3L/min signifying it had the least activation loss and fastest reaction rate. Open circuit voltage curve shows a higher output voltage and lesser voltage decay rate for MEAs tested at higher gas flow rates.

High-Accuracy Wet-Gas Multiphase Well Testing and Production Metering

SPE Journal ◽  
2006 ◽  
Vol 11 (02) ◽  
pp. 199-205 ◽  
Author(s):  
David I. Atkinson ◽  
Oyvind Reksten ◽  
Gerald Smith ◽  
Helge Moe
Keyword(s):  
Flow Rate ◽  
Liquid Flow ◽  
Gas Flow ◽  
Volume Fraction ◽  
Well Testing ◽  
Gas Flow Rate ◽  
Flow Rates ◽  
Wet Gas ◽  
New Interpretation ◽  
Interpretation Model

Summary Dedicated wet-gas flowmeters are now commercially available for the measurement of gas and liquid flow rates and offer a more compact measurement solution than does the traditional separator approach. The interpretation models of traditional multiphase flowmeters emphasize the liquid rate measurements and have been used to well test and meter mostly liquid-rich flow streams. These models were not developed for the measurement of gas flow rates, particularly those of wet gas. A new interpretation is described that allows a traditional multiphase flowmeter to operate in a dual mode either as a multiphase meter or as a wet-gas meter in 90 to 100% gas. The new interpretation model was developed for a commercially available multiphase flowmeter consisting of a venturi and a dual-energy composition meter. This combination results in excellent predictions of the gas flow rate; the liquid rate prediction is made with acceptable accuracy and no additional measurements. The wet gas and low-liquid-volume-fraction interpretation model is described together with the multiphase flowmeter. Examples of applying this model to data collected on flow loops are presented, with comparison to reference flow rates. The data from the Sintef and NEL flow loops show an error (including the reference meter error) in the gas flow rate, better than ± 2% reading (95% confidence interval), at line conditions; the absolute error (including the reference meter error) in the measured total liquid flow rate at line conditions was better than ± 2 m3/h (< ± 300 B/D: 95% confidence interval). This new interpretation model offers a significant advance in the metering of wet-gas multiphase flows and yields the possibility of high accuracies to meet the needs of gas-well testing and production allocation applications without the use of separators. Introduction There has been considerable focus in recent years on the development of new flow-measurement techniques for application to surface well testing and flow-measurement allocation in multiphase conditions without separating the phases. This has resulted in new technology from the industry for both gas and oil production. Today, there are wet-gas flowmeters, dedicated to the metering of wet-gas flows, and multiphase meters, for the metering of multiphase liquid flows. The common approach to wet-gas measurement relates gas and liquid flows to a "pseudo-gas flow rate" calculated from the standard single-phase equations. This addresses the need for gas measurement in the presence of liquids and can be applied to a limit of liquid flow [or gas volume fraction, (GVF)], though the accuracy of this approach decreases with decreasing GVF. The accurate determination of liquid rates by wet-gas meters is restricted in range. The application and performance of multiphase meters has been well documented through technical papers and industry forums, and after several years of development is maturing (Scheers 2004). Some multiphase measurement techniques can perform better, and the meters provide a more compact solution, than the traditional separation approach. It is not surprising that the use of multiphase flowmeters has grown significantly, the worldwide number doubling in little over a 2-year period (Mehdizadeh et al. 2002). Multiphase-flowmeter interpretation emphasizes the liquid rate measurement, and the application of multiphase flowmeters has been predominantly for liquid-rich flow stream allocation and well testing.

Effect of Powder Flow Rate and Gas Flow Rate on the Evolving Properties of Deposited Ti6Al4V/Cu Composites

2014 ◽  
Vol 1016 ◽  
pp. 177-182 ◽  
Author(s):  
Mutiu F. Erinosho ◽  
Esther Titilayo Akinlabi ◽  
Sisa Pityana
Keyword(s):  
Flow Rate ◽  
Gas Flow ◽  
Pure Copper ◽  
Metal Deposition ◽  
Powder Flow ◽  
Laser Metal Deposition ◽  
Gas Flow Rate ◽  
Flow Rates ◽  
Powder Flow Rate ◽  
Hardness Values

—Pure copper was deposited with Ti6Al4V alloy via laser metal deposition (LMD) process to produce Ti6Al4V/Cu composites. This paper reports the effect of powder flow rate (PFR) and gas flow rate (GFR) of laser metal deposited Ti6Al4V/Cu composites. The deposited samples were characterised through the evolving microstructure and microhardness. It was observed that the PFR and GFR have an influence on the percentage of porosity present in the samples. The higher the flow rates of the powder and the gas, the higher the degree of porosity and vice versa. The widmanstettan structures were observed to be finer as the flow rate reduces which in turn causes a decrease in the hardness values of the deposited composites. The hardness values varied between HV381.3 ± 60 and HV447.3 ± 49.

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