scholarly journals Influence of the position and energy of local rapid heating of the supersonic gas flow on the position of the separation point on the surface of airfoil

2021 ◽  
Vol 2100 (1) ◽  
pp. 012004
Author(s):  
A S Saveliev
Keyword(s):  
Energy Release ◽  
Energy Input ◽  
Gas Flow ◽  
Rapid Heating ◽  
Local Heat ◽  
Initial Position ◽  
Separation Point ◽  
Variable Position ◽  
Gas Heating ◽  
Before And After

Abstract Using numerical simulation, the study of the process of rapid local energy release in supersonic flow in a two-dimensional unsteady case and the process of separation point shift by a gas-dynamic perturbation caused by the energy input into the flow were carried out. The flow around the airfoil was modeled as laminar, and local heat release as a instantaneous isochoric process without changing the gas density. The value of energy input and the place of gas heating on the surface of the airfoil were varied. The cases of initiation of energy input at a certain distance before and after the initial position of the separation point, as well as immediately before the separation point, were considered. During obtained flow patterns processing, the displacement of the separation point position downstream, the time of this displacement, the position and size of the separation region with reattachment and the lifetime of this flow zone were determined. The obtained data can help to choose a strategy for initiating energy input in a repetitively pulsed regime, as well as in a regime of a variable position of energy release on the surface of a body, streamlined by compressible gas flow.

scholarly journals Strategies to Reduce Porosity in Al-Mg WAAM Parts and Their Impact on Mechanical Properties

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 524
Author(s):  
Maider Arana ◽  
Eneko Ukar ◽  
Iker Rodriguez ◽  
Amaia Iturrioz ◽  
Pedro Alvarez
Keyword(s):  
Mechanical Properties ◽  
Gas Flow ◽  
Bottom Layer ◽  
Local Heat ◽  
High Porosity ◽  
Shielding Gas ◽  
Heat Accumulation ◽  
High Mechanical Property ◽  
Building Conditions ◽  
Static Tensile

With the advent of disruptive additive manufacturing (AM), there is an increasing interest and demand of high mechanical property aluminium parts built directly by these technologies. This has led to the need for continuous improvement of AM technologies and processes to obtain the best properties in aluminium samples and develop new alloys. This study has demonstrated that porosity can be reduced below 0.035% in area in Al-Mg samples manufactured by CMT-based WAAM with commercial filler metal wires by selecting the correct shielding gas, gas flow rate, and deposition strategy (hatching or circling). Three phase Ar+O2+N2O mixtures (Stargold®) are favourable when the hatching deposition strategy is applied leading to wall thickness around 6 mm. The application of circling strategy (torch movement with overlapped circles along the welding direction) enables the even build-up of layers with slightly thicker thickness (8 mm). In this case, Ar shielding gas can effectively reduce porosity if proper flow is provided through the torch. Reduced gas flows (lower than 30 Lmin) enhance porosity, especially in long tracks (longer than 90 mm) due to local heat accumulation. Surprisingly, rather high porosity levels (up to 2.86 area %) obtained in the worst conditions, had a reduced impact on the static tensile test mechanical properties, and yield stress over 110 MPa, tensile strength over 270 MPa, and elongation larger than 27% were achieved either for Ar circling, Ar hatching, or Stargold® hatching building conditions. In all cases anisotropy was lower than 11%, and this was reduced to 9% for the most appropriate shielding conditions. Current results show that due to the selected layer height and deposition parameters there was a complete re-melting of the previous layer and a thermal treatment on the prior bottom layer that refined the grain size removing the original dendritic and elongated structure. Under these conditions, the minimum reported anisotropy levels can be achieved.

Probing boron thermite energy release at rapid heating rates

2021 ◽  
Vol 231 ◽  
pp. 111491
Author(s):  
Jennifer L. Gottfried ◽  
Elliot R. Wainwright ◽  
Sidi Huang ◽  
Yue Jiang ◽  
Xiaolin Zheng
Keyword(s):  
Energy Release ◽  
Rapid Heating ◽  
Heating Rates

Effects of Rib Arrangements on Pressure Drop and Heat Transfer in a Rib-Roughened Channel With a Sharp 180 deg Turn

1997 ◽  
Vol 119 (3) ◽  
pp. 610-616 ◽  
Author(s):  
S. Mochizuki ◽  
A. Murata ◽  
M. Fukunaga
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Secondary Flow ◽  
Flow Direction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Diameter Ratio ◽  
Equivalent Diameter ◽  
Before And After ◽  
Rib Roughened

The objective of this study was to investigate, through experiments, the combined effects of a sharp 180 deg turn and rib patterns on the pressure drop performance and distributions of the local heat transfer coefficient in an entire two-pass rib-roughened channel with a 180 deg turn. The rib pitch-to-equivalent diameter ratio P/de was 1.0, the rib-height-to-equivalent diameter ratio e/de was 0.09, and the rib angle relative to the main flow direction was varied from 30 ∼ 90 deg with an interval of 15 deg. Experiments were conducted for Reynolds numbers in the range 4000 ∼ 30,000. It was disclosed that, due to the interactions between the bend-induced secondary flow and the rib-induced secondary flow, the combination of rib patterns in the channel before and after the turn causes considerable differences in the pressure drop and heat transfer performance of the entire channel.

scholarly journals Influence of Laser Energy Input and Shielding Gas Flow on Evaporation Fume during Laser Powder Bed Fusion of Zn Metal

Materials ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2677
Author(s):  
Yu Qin ◽  
Jinge Liu ◽  
Yanzhe Chen ◽  
Peng Wen ◽  
Yufeng Zheng ◽  
...  
Keyword(s):  
Energy Input ◽  
Gas Flow ◽  
Evaporation Rate ◽  
Laser Energy ◽  
Circulation System ◽  
Powder Bed Fusion ◽  
Shielding Gas ◽  
Laser Powder Bed Fusion ◽  
Conservation Of Energy ◽  
Powder Bed

Laser powder bed fusion (LPBF) of Zn-based metals exhibits prominent advantages to produce customized biodegradable implants. However, massive evaporation occurs during laser melting of Zn so that it becomes a critical issue to modulate laser energy input and gas shielding conditions to eliminate the negative effect of evaporation fume during the LPBF process. In this research, two numerical models were established to simulate the interaction between the scanning laser and Zn metal as well as the interaction between the shielding gas flow and the evaporation fume, respectively. The first model predicted the evaporation rate under different laser energy input by taking the effect of evaporation on the conservation of energy, momentum, and mass into consideration. With the evaporation rate as the input, the second model predicted the elimination effect of evaporation fume under different conditions of shielding gas flow by taking the effect of the gas circulation system including geometrical design and flow rate. In the case involving an adequate laser energy input and an optimized shielding gas flow, the evaporation fume was efficiently removed from the processing chamber during the LPBF process. Furthermore, the influence of evaporation on surface quality densification was discussed by comparing LPBF of pure Zn and a Titanium alloy. The established numerical analysis not only helps to find the adequate laser energy input and the optimized shielding gas flow for the LPBF of Zn based metal, but is also beneficial to understand the influence of evaporation on the LPBF process.

Energy in the 1980s - Future trends in utilization of coal energy conversion

1974 ◽  
Vol 276 (1261) ◽  
pp. 527-539 ◽  
Keyword(s):  
Electricity Generation ◽  
Energy Input ◽  
Large Scale ◽  
Fossil Fuels ◽  
Energy Systems ◽  
Local Heat ◽  
Future Trends ◽  
Feed Stock ◽  
Environmental Considerations ◽  
Potential Reserve

World reserves of fossil fuels are sufficient for many decades of increasing usage. During the next few decades at least, fossil fuels will be much the most important energy source. These fuels should be exploited in a complementary manner. Coal represents much the largest potential reserve, followed probably by hydrocarbons less easily utilized than those commonly being exploited now. Techniques exist for the conversion of coal into coke and carbons, electricity, gas and substitute oil-feed stock. Improvements in these processes are possible but their large-scale introduction depends on economics. Where coal burning can meet a requirement (local heat or steam, or electricity generation) fluidized combustion can be the most efficient process; better integration with mining techniques are possible and environmental considerations are favourable. Fluidized combustion would be a high priority unit in a ‘ Coalplex ’ which could have electricity, gas and oil as possible products. The best mix could depend on the value ascribed to the products and this in turn invokes consideration of the overall economics of energy storage, transport and demand flexibility. Looking farther ahead, coal will certainly remain a vital chemical component for various proposed energy systems and will also probably be able to compete as the energy input into conversion schemes. The technology of coal utilization may also have applications for other fossil fuels.

Precise Control of Carbon Nanotube Synthesis of a Single Chirality

2007 ◽  
Author(s):  
David R. Huitink ◽  
Debjyoti Banerjee ◽  
Saion K. Sinha
Keyword(s):  
Gas Flow ◽  
Chemical Vapor ◽  
Synthesis Conditions ◽  
Precise Control ◽  
Catalyst Composition ◽  
Cvd Synthesis ◽  
Before And After ◽  
Characterization Studies ◽  
Uniform Diameter ◽  
Carbon Nanotube Synthesis

This work demonstrates precise control over the synthesis conditions and location during CNT formation, such that single chirality tubes are obtainable. This technique obviates two significant hurdles that prevent the exploitation of CNTs in micro- and nano-devices. Microelectronic applications require precise location and chirality of synthesized CNTs. Conventional CVD synthesis techniques typically yield mixtures of CNTs (semi-conducting and metallic types) that grow at random locations. Dip Pen Nanolithography (DPN) techniques were used to deposit the catalysts at precisely defined locations and to pattern the catalysts on a substrate with specific sizes as well as to control the catalyst composition. After deposition of catalysts, a low temperature Chemical Vapor Deposition (CVD) process was used to synthesize CNT. Various known catalysts were deposited. Characterization studies before and after CVD synthesis of CNT showed that the CNT were of a single chirality as well as uniform diameter (with a very narrow range of variability). The results indicate that the chirality of the synthesized CNT can be controlled by changing the synthesis conditions (e.g., size of the catalyst patterns, composition of the catalysts, temperature of CVD, gas flow rates, etc.).

Improving Semi-Dry Scrubber Performance Through Gas Flow Modeling

2005 ◽  
Author(s):  
Nikita Gorsky ◽  
C. F. Peter Bowen
Keyword(s):  
Velocity Distribution ◽  
Residence Time ◽  
Flue Gas ◽  
Gas Flow ◽  
Waste To Energy ◽  
Distribution Data ◽  
Outlet Temperature ◽  
Flow Modeling ◽  
Before And After ◽  
Distribution Testing

Poor flue gas flow distribution in the semi-dry scrubbers used in Waste-to-Energy facilities can cause reduced residence time for lime slurry spray droplet evaporation and subsequent “wet carryover” resulting in solids deposits on the scrubber vessel walls and ductwork and also baghouse bag blinding. In addition to promoting corrosion, the removal of deposits during boiler outages is very labor intensive. This paper identifies how gas flow modeling conducted in conjunction with Nels Consulting Services, Inc. on several different types of scrubbers at Covanta Energy’s Waste-to-Energy facilities resulted in modifications which increased the actual flue gas residence time, considerably reduced the solids deposits (scale) and associated maintenance costs, and in some cases reduced the pressure drop across the scrubbers and baghouses. The data presented includes typical model study velocity distribution data (before and after the modifications), vessel sketches, and photographs. Associated work included in-field scrubber outlet duct temperature and velocity distribution testing. The results of the in-field scrubber outlet temperature distribution testing, done both before and after the scrubber modifications, confirmed the improvements numerically by showing reduced flue gas temperature variation in the scrubber outlet duct.

scholarly journals Nonstationary gas-dynamics and local heat transfer in the output channel of the turbocharger compressor

2019 ◽  
Vol 196 ◽  
pp. 00007 ◽  
Author(s):  
Leonid Plotnikov ◽  
Nikita Grigor'ev ◽  
Nikolaj Kochev
Keyword(s):  
Heat Transfer ◽  
Gas Dynamics ◽  
Gas Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Measuring System ◽  
Rotor Speed ◽  
Outlet Channel ◽  
Thermomechanical Characteristics ◽  
Channel Configuration

Thermomechanical characteristics of the gas flow at the turbocharger compressor outlet largely determine the quality of the intake process in piston engines with boost. The article presents the results of an experimental study of gas-dynamics and heat transfer of gas flows after compression in a turbocharger centrifugal compressor. A brief description of the experimental setup, the configuration of pipes under investigation, the measuring system and the experimental features are given. The studies were carried out on a free compressor, i.e. without considering the piston part. Different conditions in the compressor outlet channel were created by installing special nozzles with different hydraulic resistances. It has been established that the local heat transfer increases from 23 to 46 % with an increase in the turbocharger rotor speed, depending on the outlet channel configuration. It should be noted that an increase in rotor speed is also accompanied by an increase in air flow through the channel. The increase in flow rate was from 10 to 42 %.

Annular Liquid Film Flow Under Local Heating in Microchannel

2005 ◽  
Author(s):  
Elizaveta Ya. Gatapova ◽  
Vladimir V. Kuznetsov ◽  
Oleg A. Kabov ◽  
Jean-Claude Legros
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Biot Number ◽  
Gas Flow ◽  
Film Flow ◽  
Local Heating ◽  
Local Heat Transfer ◽  
Flow Region ◽  
Local Heat ◽  
Liquid Film Flow

In our previous investigations the formation of liquid bump of locally heated laminar liquid film with co-current gas flow was obtained [1,2]. The evaporation of liquid was left out of account. Heat transfer to the gas phase was approximately specified by a constant Biot number [2,3]. The aim of this work is an investigation of the evaporation effect, the hydrodynamics and the heat transfer of liquid film flow in a channel 0.2–1 mm height. The 2-D model of locally heated liquid film moving under gravity and the action of co-current gas flow with low viscosity in a channel are considered. The channel can be inclined at an angle with respect to horizon. It is supposed that the height of the channel is much less than its width. Surface tension is assumed to depend on temperature. The velocity profiles for gas and liquid regions are found from problem of joint motion of isothermal non-deformable liquid film and gas flow. Using the findings the joint solution of heat transfer and diffusion problem with corresponding boundary condition is calculated. Having the temperature field in the whole of liquid and gas flow region we find a local heat transfer coefficient on the gas-liquid interface and Biot number as a function of flow parameters and spatial variables.

The Thermocapillary Convection in Locally Heated Laminar Liquid Film Flow Caused by a Co-Current Gas Flow in Narrow Channel

2003 ◽  
Author(s):  
E. Y. Gatapova ◽  
Y. V. Lyulin ◽  
I. V. Marchuk ◽  
O. A. Kabov ◽  
J.-C. Legros
Keyword(s):  
Free Surface ◽  
Analytical Solution ◽  
Liquid Film ◽  
Gas Flow ◽  
Surface Deformation ◽  
Plane Channel ◽  
Film Surface ◽  
Local Heat ◽  
Narrow Channel ◽  
Liquid Film Flow

A two-dimensional model of a steady laminar flow of liquid film and co-current gas flow in a plane channel is considered. It is supposed that the height of a channel is much less than its width. There is a local heat source on the bottom wall of the channel. An analytical solution for the temperature distribution problem in locally heated liquid film is obtained, when the velocity profile is linear. An analytical solution of the linearized equation for thermocapillary film surface deformation is found. A liquid bump caused by the thermocapillary effect in the region where thermal boundary layer reaches the film surface is obtained. Damped oscillations of the free surface may exist before the bump. This is obtained according to the solution of the problem in an inclined channel. It depends on the forces balance in the film. The defining criterion is found for this effect. The oscillations of free surface do not exist for horizontally located channel.

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