scholarly journals Numerical Study the Effect of Blade Number on Archimedes Screw Turbine Utilized in Pico-Hydro in Horizontal Position

2021 ◽  
Vol 10 (2) ◽  
pp. 71
Author(s):  
Fajar Anggara
Keyword(s):  
Energy Balance ◽  
Flow Rate ◽  
Pressure Loss ◽  
Numerical Study ◽  
Horizontal Position ◽  
Energy Extraction ◽  
Blade Number ◽  
Small Flow ◽  
High Torque ◽  
Velocity Contour

Application of Archimedes Screw Turbine (AST) on pico-hydro has been very popular due to its capability to has a high torque with small flow rate and environmentally friendly to biotic of vicinity. This study uses CFD to investigate AST performance when the number of blades is varied. Independency of mesh is conducted to find an efficient number of mesh and it is obtained at 80 thousand mesh. Variation A, B and C respectively has 4,6, and 9 blades varied to analyze the correspondence with torque, pressure loss and velocity contour. The results show that with a higher number of blades would make higher torque. This is because energy extraction from water would be more efficient at higher number blade. However, the side back at such number would arise such as the higher-pressure loss. This is corresponding to energy balance where a high delta pressure is proportional with a generated energy turbine. 

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.

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 Numerical Study of the Air Ingress Accident of the HTR-PM and Possible Mitigation Measures

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Wei Xu ◽  
Han Zhang ◽  
Heng Xie ◽  
Lei Shi ◽  
Jun Sun
Keyword(s):  
Flow Rate ◽  
Numerical Study ◽  
Reactor Core ◽  
Mitigation Measures ◽  
Injection Velocity ◽  
Primary Circuit ◽  
Small Flow Rate ◽  
Small Flow ◽  
Hypothetical Accident ◽  
Air Ingress

The double-ended guillotine break (DEGB) of the horizontal coaxial gas duct of a high-temperature gas-cooled reactor is an extremely hypothetical accident, which could cause the air to enter into the primary circuit and react with graphite in the reactor core. The performance of the HTR-PM plant under this extremely hypothetical accident has been studied by the system code TINTE in this work. The results show that the maximum fuel temperature will not reach the temperature design limitation, and the graphite oxidation will not cause unacceptable consequences even under some conservative assumptions. Moreover, nitrogen and helium injected from the fuel charging tube were studied as the possible mitigation measures to further alleviate the consequences of this air ingress accident. The preliminary results show that only the flow rate of nitrogen injected reaches a certain value, which can effectively alleviate the consequences, while for helium injection, both high and small flow rate can prevent or cut off the natural circulation and alleviate the consequences. The reason is that helium is much lighter than nitrogen, and the density difference between the coolant channel and the reactor core is small when helium is injected. Considering the injection velocity, the total usage amount, and the start time of gas injection, helium injected with a small flow rate is suggested.

An Experimental and Numerical Study of Heat Transfer and Pressure Loss in a Rectangular Channel With V-Shaped Ribs

2006 ◽  
Author(s):  
Michael Maurer ◽  
Jens von Wolfersdorf ◽  
Michael Gritsch
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
High Reynolds Numbers ◽  
High Reynolds

An experimental and numerical study was conducted to determine the thermal performance of V-shaped ribs in a rectangular channel with an aspect ratio of 2:1. Local heat transfer coefficients were measured using the steady state thermochromic liquid crystal technique. Periodic pressure losses were obtained with pressure taps along the smooth channel sidewall. Reynolds numbers from 95,000 to 500,000 were investigated with V-shaped ribs located on one side or on both sides of the test channel. The rib height-to-hydraulic diameter ratios (e/Dh) were 0.0625 and 0.02, and the rib pitch-to-height ratio (P/e) was 10. In addition, all test cases were investigated numerically. The commercial software FLUENT™ was used with a two-layer k-ε turbulence model. Numerically and experimentally obtained data were compared. It was determined that the heat transfer enhancement based on the heat transfer of a smooth wall levels off for Reynolds numbers over 200,000. The introduction of a second ribbed sidewall slightly increased the heat transfer enhancement whereas the pressure penalty was approximately doubled. Diminishing the rib height at high Reynolds numbers had the disadvantage of a slightly decreased heat transfer enhancement, but benefits in a significantly reduced pressure loss. At high Reynolds numbers small-scale ribs in a one-sided ribbed channel were shown to have the best thermal performance.

scholarly journals A Numerical Study of Sub-Millisecond Integrated Mix-and-Inject Microfluidic Devices for Sample Delivery at Synchrotron and XFELs

2021 ◽  
Vol 11 (8) ◽  
pp. 3404
Author(s):  
Majid Hejazian ◽  
Eugeniu Balaur ◽  
Brian Abbey
Keyword(s):  
Molecular Dynamics ◽  
Flow Rate ◽  
Numerical Study ◽  
Three Dimensional ◽  
Microfluidic Devices ◽  
Liquid Jets ◽  
Mixing Efficiency ◽  
X Ray Diffraction ◽  
Cross Sectional ◽  
Time Required

Microfluidic devices which integrate both rapid mixing and liquid jetting for sample delivery are an emerging solution for studying molecular dynamics via X-ray diffraction. Here we use finite element modelling to investigate the efficiency and time-resolution achievable using microfluidic mixers within the parameter range required for producing stable liquid jets. Three-dimensional simulations, validated by experimental data, are used to determine the velocity and concentration distribution within these devices. The results show that by adopting a serpentine geometry, it is possible to induce chaotic mixing, which effectively reduces the time required to achieve a homogeneous mixture for sample delivery. Further, we investigate the effect of flow rate and the mixer microchannel size on the mixing efficiency and minimum time required for complete mixing of the two solutions whilst maintaining a stable jet. In general, we find that the smaller the cross-sectional area of the mixer microchannel, the shorter the time needed to achieve homogeneous mixing for a given flow rate. The results of these simulations will form the basis for optimised designs enabling the study of molecular dynamics occurring on millisecond timescales using integrated mix-and-inject microfluidic devices.

scholarly journals Research on a Piezoelectric Pump with Flexible Valves

2021 ◽  
Vol 11 (7) ◽  
pp. 2909
Author(s):  
Weiqing Huang ◽  
Liyi Lai ◽  
Zhenlin Chen ◽  
Xiaosheng Chen ◽  
Zhi Huang ◽  
...  
Keyword(s):  
Flow Rate ◽  
Fluid Transport ◽  
Smooth Transition ◽  
Driving Voltage ◽  
Piezoelectric Pump ◽  
Venous Valve ◽  
Output Pressure ◽  
Small Flow ◽  
Working Principle ◽  
Opening And Closing

Imitating the structure of the venous valve and its characteristics of passive opening and closing with changes in heart pressure, a piezoelectric pump with flexible valves (PPFV) was designed. Firstly, the structure and the working principle of the PPFV were introduced. Then, the flexible valve, the main functional component of the pump, was analyzed theoretically. Finally, an experimental prototype was manufactured and its performance was tested. The research proves that the PPFV can achieve a smooth transition between valved and valveless by only changing the driving signal of the piezoelectric (PZT) vibrator. The results demonstrate that when the driving voltage is 100 V and the frequency is 25 Hz, the experimental flow rate of the PPFV is about 119.61 mL/min, and the output pressure is about 6.16 kPa. This kind of pump can realize the reciprocal conversion of a large flow rate, high output pressure, and a small flow rate, low output pressure under the electronic control signal. Therefore, it can be utilized for fluid transport and pressure transmission at both the macro-level and the micro-level, which belongs to the macro–micro combined component.

scholarly journals Model of thermal buoyancy in cavity-ventilated roof constructions

2021 ◽  
pp. 174425912098418
Author(s):  
Toivo Säwén ◽  
Martina Stockhaus ◽  
Carl-Eric Hagentoft ◽  
Nora Schjøth Bunkholt ◽  
Paula Wahlgren
Keyword(s):  
Analytical Model ◽  
Flow Rate ◽  
Numerical Study ◽  
Air Flow ◽  
Wind Pressure ◽  
Air Flow Rate ◽  
Test Set ◽  
Air Cavity ◽  
Thermal Buoyancy ◽  
The Impact

Timber roof constructions are commonly ventilated through an air cavity beneath the roof sheathing in order to remove heat and moisture from the construction. The driving forces for this ventilation are wind pressure and thermal buoyancy. The wind driven ventilation has been studied extensively, while models for predicting buoyant flow are less developed. In the present study, a novel analytical model is presented to predict the air flow caused by thermal buoyancy in a ventilated roof construction. The model provides means to calculate the cavity Rayleigh number for the roof construction, which is then correlated with the air flow rate. The model predictions are compared to the results of an experimental and a numerical study examining the effect of different cavity designs and inclinations on the air flow rate in a ventilated roof subjected to varying heat loads. Over 80 different test set-ups, the analytical model was found to replicate both experimental and numerical results within an acceptable margin. The effect of an increased total roof height, air cavity height and solar heat load for a given construction is an increased air flow rate through the air cavity. On average, the analytical model predicts a 3% higher air flow rate than found in the numerical study, and a 20% lower air flow rate than found in the experimental study, for comparable test set-ups. The model provided can be used to predict the air flow rate in cavities of varying design, and to quantify the impact of suggested roof design changes. The result can be used as a basis for estimating the moisture safety of a roof construction.

scholarly journals Numerical Study of Thermal-Hydraulic Performance of a New Spiral Z-Type PCHE for Supercritical CO2 Brayton Cycle

Energies ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4417
Author(s):  
Tingting Xu ◽  
Hongxia Zhao ◽  
Miao Wang ◽  
Jianhui Qi
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Pressure Loss ◽  
Numerical Study ◽  
Hydraulic Performance ◽  
Optimal Structure ◽  
Original Structure ◽  
Brayton Cycle ◽  
Compact Structure ◽  
Spiral Angle

Printed circuit heat exchangers (PCHEs) have the characteristics of high temperature and high pressure resistance, as well as compact structure, so they are widely used in the supercritical carbon dioxide (S-CO2) Brayton cycle. In order to fully study the heat transfer process of the Z-type PCHE, a numerical model of traditional Z-type PCHE was established and the accuracy of the model was verified. On this basis, a new type of spiral PCHE (S-ZPCHE) is proposed in this paper. The segmental design method was used to compare the pressure changes under 5 different spiral angles, and it was found that increasing the spiral angle θ of the spiral structure will reduce the pressure drop of the fluid. The effects of different spiral angles on the thermal-hydraulic performance of S-ZPCHE were compared. The results show that the pressure loss of fluid is greatly reduced, while the heat transfer performance is slightly reduced, and it was concluded that the spiral angle of 20° is optimal. The local fluid flow states of the original structure and the optimal structure were compared to analyze the reason for the pressure drop reduction effect of the optimal structure. Finally, the performance of the optimal structure was analyzed under variable working conditions. The results show that the effect of reducing pressure loss of the new S-ZPCHE is more obvious in the low Reynolds number region.

Numerical Characterization of Hot Gas Ingestion Through Turbine Rim Seals

2016 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini ◽  
Carl M. Sangan ◽  
James A. Scobie ◽  
Gary D. Lock
Keyword(s):  
Flow Rate ◽  
Numerical Study ◽  
Axial Flow ◽  
Radial Clearance ◽  
Buffering Effect ◽  
Hot Gas ◽  
Numerical Predictions ◽  
Wide Range ◽  
Thermal Buffering

This paper deals with a numerical study aimed at the characterization of hot gas ingestion through turbine rim seals. The numerical campaign focused on an experimental facility which models ingress through the rim seal into the upstream wheel-space of an axial-turbine stage. Single-clearance arrangements were considered in the form of axial- and radial-seal gap configurations. With the radial-seal clearance configuration, CFD steady-state solutions were able to predict the system sealing effectiveness over a wide range of coolant mass flow rates reasonably well. The greater insight of flow field provided by the computations illustrates the thermal buffering effect when ingress occurs: for a given sealing flow rate, the effectiveness on the rotor was significantly higher than that on the stator due to the axial flow of hot gases from stator to rotor caused by pumping effects. The predicted effectiveness on the rotor was compared with a theoretical model for the thermal buffering effect showing good agreement. When the axial-seal clearance arrangement is considered, the agreement between CFD and experiments worsens; the variation of sealing effectiveness with coolant flow rate calculated by means of the simulations display a distinct kink. It was found that the “kink phenomenon” can be ascribed to an over-estimation of the egress spoiling effects due to turbulence modelling limitations. Despite some weaknesses in the numerical predictions, the paper shows that CFD can be used to characterize the sealing performance of axial- and radial-clearance turbine rim seals.

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