scholarly journals Study of Flow Characteristics of Gas Mixtures in a Rectangular Knudsen Pump

Micromachines ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 79 ◽  
Author(s):  
Zhijun Zhang ◽  
Xiaowei Wang ◽  
Lili Zhao ◽  
Shiwei Zhang ◽  
Fan Zhao
Keyword(s):  
Flow Characteristics ◽  
Direct Simulation Monte Carlo ◽  
Gas Mixtures ◽  
Thermal Creep ◽  
Temperature Fields ◽  
Thermally Induced ◽  
Creep Effect ◽  
Molecular Masses ◽  
Induced Flow ◽  
Knudsen Pump

A Knudsen pump operates under the thermal transpiration effect or the thermal edge effect on the micro-scale. Due to the uneven temperature distribution of the walls in the channel axis direction or the constant temperature of the tips on the walls, directional thermally-induced flow is generated. In this paper the Direct Simulation Monte Carlo (DSMC) method is applied for N2–O2 gas mixtures in the ratios of 4:1, 1:1, and 1:4 with different Knudsen numbers in a classic rectangular Knudsen pump to study the flow characteristics of the gas mixtures in the pump. The results show that the changing in the gas physical properties does not affect the distribution of the velocity field, temperature fields, or other fields in the Knudsen pump. The thermal creep effect is related to the molecular mass of the gas. Even in N2 and O2 gas mixtures with similar molecular masses, N2 can be also found to have a stronger thermal creep effect. Moreover, the lighter molecular weight gas (N2) can effectively promote the motion of the heavier gas (O2).

Thermally Induced Flow in a Rotating Annulus Filled With a Compressible Fluid

1988 ◽  
Vol 110 (2) ◽  
pp. 134-139 ◽  
Author(s):  
M. A. Ortega ◽  
J. T. Sielawa
Keyword(s):  
Flow Field ◽  
Inner Core ◽  
Temperature Fields ◽  
Bottom Plate ◽  
Rossby Number ◽  
Thermally Induced ◽  
Coaxial Cylinders ◽  
Induced Flow ◽  
Velocity And Temperature Fields ◽  
Induced Velocity

The thermally induced flow field, in a rapidly rotating container consisting of a pair of coaxial cylinders bounded on the top and bottom by horizontal end plates, is considered. The top plate is heated and the bottom plate is cooled, both by small amounts, so that the thermal Rossby number is small, and the cylinders are supposed to be conductive. The induced velocity and temperature fields are determined by subdivision of the flow field; the equation for the central part, the inner core, is solved numerically as well as analytically.

scholarly journals Numerical Investigation into the Flow Characteristics of Gas Mixtures in Knudsen Pump with Variable Soft Sphere Model

Micromachines ◽  
2020 ◽  
Vol 11 (9) ◽  
pp. 784
Author(s):  
Chunlin Du ◽  
Xiaowei Wang ◽  
Feng Han ◽  
Xiaoyu Ren ◽  
Zhijun Zhang
Keyword(s):  
Flow Pattern ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Gas Flow ◽  
Molecular Diffusion ◽  
Flow Characteristics ◽  
Gas Mixtures ◽  
Soft Sphere ◽  
Knudsen Pump

In Knudsen pumps with geometric configuration of rectangle, gas flows are induced by temperature gradients along channel walls. In this paper, the direct simulation Monte Carlo (DSMC) method is used to investigate numerically the flow characteristics of H2–N2 mixtures in the Knudsen pump. The variable soft sphere (VSS) model is applied to depict molecular diffusion in the gas mixtures, and the results obtained are compared with those calculated from a variable hard sphere (VHS) model. It is demonstrated that pressure is crucial to affecting the variation of gas flow pattern, but the gas concentration in H2–N2 mixtures and the collision model do not change the flow pattern significantly. On the other hand, the velocity of H2 is larger than that of N2. The velocities of H2 and N2 increase if the concentration of H2 rises in the gas mixtures. The results of velocity and mass flow rate obtained from VSS and VHS models are different. Finally, a linear relation between the decrease of mass flow rate and the increase of H2 concentration is proposed to predict the mass flow rate in H2–N2 mixtures.

Testing Long-Term Predictions from Hydro-Geochemical Models

1993 ◽  
Vol 333 ◽  
Author(s):  
William E. Glassley ◽  
Carol J. Bruton ◽  
William L. Bourcier
Keyword(s):  
Yucca Mountain ◽  
Taupo Volcanic Zone ◽  
Ambient Conditions ◽  
Volcanic Zone ◽  
Site Specific ◽  
Thermally Induced ◽  
Induced Flow ◽  
Geochemical Models ◽  
Kinetics And Thermodynamic

ABSTRACTThermally induced flow of liquid water and water vapor at the potential repository site at Yucca Mountain, Nevada, will extend hundreds of meters away from the repository edge. The resultant transfer of heat and mass will sufficiently perturb the ambient conditions such that a variety of mineralogical and chemical reactions will occur that may modify hydrological properties. The consequences of this “coupling” of geochemical and hydrological processes will vary through time, and will occur to different degrees in four regimes (T < Tboiling; T = Tboiling; T > T boiling; cooling) that will develop within the repository block. The dominant processes in the regimes differ, and reflect the local balance between: 1) kinetics and equilibrium; 2) dissolution and precipitation; 3) evaporation and boiling; and 4) fluid flow in matrix and fractures. Simulations were conducted of the evolution of these regimes, using laboratory derived kinetics and thermodynamic data, and site specific mineralogical and hydrological properties. These simulations identify regions where chemical and mineralogical equilibrium is likely to be achieved, and where net changes in hydrological properties will be concentrated. Tests of the results of these simulations have been initiated using field data from the Taupo Volcanic Zone, New Zealand. A preliminary series of calculations suggest that relative changes in porosity of as much as ± 20% to 30% may be possible for rocks with an initial porosity of 10%.

Numerical Study on Flow Characteristics in High Multi-Stage Pressure Reducing Valve

2017 ◽  
Author(s):  
Fu-qiang Chen ◽  
Zhi-xin Gao ◽  
Jin-yuan Qian ◽  
Zhi-jiang Jin
Keyword(s):  
Energy Consumption ◽  
Numerical Study ◽  
Research Work ◽  
Flow Characteristics ◽  
Temperature Fields ◽  
Turbulent Dissipation ◽  
Technological Support ◽  
Multi Stage ◽  
Valve Opening ◽  
Pressure Reducing Valve

In this paper, a new high multi-stage pressure reducing valve (HMSPRV) is proposed. The main advantages include reducing noise and vibration, reducing energy consumption and dealing with complex conditions. As a new high pressure reducing valve, its flow characteristics need to be investigated. For that the valve opening has a great effect on steam flow, pressure reduction and energy consumption, thus different valve openings are taken as the research points to investigate the flow characteristics. The analysis is conducted from four aspects: pressure, velocity, temperature fields and energy consumption. The results show that valve opening has a great effect on flow characteristics. No matter for pressure, velocity or temperature field, the changing gradient mainly reflects at those throttling components for all valve openings. For energy consumption, in the study of turbulent dissipation rate, it can be found that the larger of valve opening, the larger of energy consumption. It can be concluded that the new high multi-stage pressure reducing valve works well under complex conditions. This study can provide technological support for achieving pressure regulation, and benefit the further research work on energy saving and multi-stage design of pressure reducing devices.

Thermally Induced Instability of Laminated Beams and Plates

1996 ◽  
Vol 63 (4) ◽  
pp. 884-890 ◽  
Author(s):  
A. Tylikowski ◽  
R. B. Hetnarski
Keyword(s):  
Stochastic Stability ◽  
Direct Method ◽  
Wide Band ◽  
Temperature Fields ◽  
Time And Space ◽  
Thermally Induced ◽  
Stability Problems ◽  
Linear Elastic ◽  
Liapunov Direct Method ◽  
Short Time

A theoretical investigation of dynamic stability for linear elastic structures due to non-uniform, time and space-dependent stochastic temperature fields is presented. The study is based on the reformulation of stochastic stability problems as a stability of Itoˆ type equations in some appropriate Hilbert space and is adopted for stability problems of structures with time and space-dependent stochastic coefficients. Uniform stochastic stability criteria of the structure equilibrium are derived using the Liapunov direct method. The energy-like functional and the generalized ltoˆ lemma are used to derive the sufficient stability conditions of the equilibrium state. A symmetrically laminated crossply plate subjected to the wide-band Gaussian temperature distribution and a laminated beam subjected to local short-time heatings are analysed in detail.

scholarly journals Geometrical form assessment of a CFD based breathing thermal manikins, designed by simplified polygonal shapes

2019 ◽  
Vol 85 ◽  
pp. 02002
Author(s):  
Martin Ivanov ◽  
Sergey Mijorski
Keyword(s):  
Flow Characteristics ◽  
Temperature Fields ◽  
Geometrical Shape ◽  
Thermal Plume ◽  
Flow Acceleration ◽  
Geometrical Shapes ◽  
Geometrical Form ◽  
The Difference ◽  
High Degree ◽  
Positive Effect

The presented paper focuses on a CFD based analyses of the complexity in the geometrical shape of the breathing thermal manikins, associated with their main functionalities. Both impacts of the external manikin’s form were studied – over the velocity and over the temperature fields in the thermal plume zone above the head. Three different geometrical shapes are analysed – a physiologically identified (called Humanoid Manikin) and two other shapes, designed to match the overall 95th percentile of the anthropometric size of the standard person (called Polygonal Manikins). The first model represents a comprehensive multifaceted figure of a manikin with high degree of physiological identity with a female human being. The second and third one, are simplified, but still with anatomically realistic component forms, accurately representing the anthropometric size of a standard person. The difference between them is in the presence of additional flow optimization collars in the third model. The numerical results demonstrate the clear impact of the manikins’ geometrical characteristics over the simulated breathing and convective flows. The optimization with the proposed collars had a positive effect over the resulted flow acceleration at top head and chest zones. However, the improvement of the flow characteristics was observed for two of the simulated three breathing phases and further shape optimization is required.

scholarly journals Evolution of Late Wintertime Thermally Driven Local Flows and Temperature Fields over Far-Western Nepal

2016 ◽  
Vol 21 (1) ◽  
pp. 35-47
Author(s):  
Ram P. Regmi ◽  
Sangeeta Maharjan
Keyword(s):  
Thermal Environment ◽  
Flow Characteristics ◽  
Temperature Fields ◽  
Valley Wind ◽  
Plain Area ◽  
Slope Winds ◽  
Thermally Driven ◽  
Slope Wind ◽  
Wrf Modeling ◽  
Southern Plain

Atmospheric processes over the Himalayan complex terrain are yet to be studied extensively. Only a few significant researches are reported from this region and the Far-Western Region (FWR) of Nepal still remains untouched. Thus, the present study was conceived to understand the meteorological flow characteristics and thermal environment over the region and associated areas during the late wintertime with the application of the state-of-the-art-of Weather Research and Forecasting (WRF) Modeling System. The study revealed that the northern mountainous region developed strong down slope wind during the night and morning times, which sweeps out the southern plain area of Nepal and may reach just beyond the border. The wind over the plain was very shallow whose depth was just about 100 m. The down slope winds over the southern slope of the Daijee and Nandhaur mountain ranges were significantly enhanced by the subsidence of the southerly wind that prevails above 1 km height above the mean sea level. Close to the noon time a very gentle southerly valley wind from the southern plain replaced the nighttime down slope. Very shallow but strong surface inversion builds up over the plain that breaks up in the late morning. The depth of the mixed layer and the valley wind may reach up to 1km in the afternoon. The thermal environment over the FWR of Nepal was fairly hot that may remain around 35°C in the afternoon around the Mahendranagar area whereas the temperature during the nighttime may go as low as 23°C. The study revealed that, contrary to the general perception, temperature over plain areas of Nepal was significantly higher than further southern areas belonging to India. The meteorological flow fields over the FWR of Nepal executed diurnal periodicity with little day-to-day variation during the late wintertime.Journal of Institute of Science and TechnologyVolume 21, Issue 1, August 2016, page: 35-47

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