Theoretical and DSMC Study on Heat Conduction of Gas in Nanoscale Pores

2016 ◽  
Author(s):  
Chuan-Yong Zhu ◽  
Zeng-Yao Li
Keyword(s):  
Heat Conduction ◽  
Numerical Study ◽  
Direct Simulation Monte Carlo ◽  
Mean Free Path ◽  
Local Heat ◽  
Temperature Jumps ◽  
Thermal Conductivity Model ◽  
Local Heat Flux ◽  
Side Walls ◽  
Simulation Monte Carlo

This article presents a theoretical and numerical study on the heat conduction of gas confined in a nanoscale cube. An effective thermal conductivity model of confined gas using a modified mean free path is proposed for the heat conduction in transition regime inside a closure. Excellent agreement of the present model with the results from our simulations by the method of direct simulation Monte Carlo (DSMC) has been achieved for different boundary conditions of side walls. The temperature jumps and the reduction of local heat flux near the side walls are observed from the DSMC results.

Theoretical and DSMC Studies on Heat Conduction of Gas Confined in a Cuboid Nanopore

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Chuan-Yong Zhu ◽  
Zeng-Yao Li ◽  
Wen-Quan Tao
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Effective Thermal Conductivity ◽  
Numerical Study ◽  
Direct Simulation Monte Carlo ◽  
Mean Free Path ◽  
Confined Space ◽  
Temperature Jumps ◽  
Side Walls ◽  
The Impact

This paper presents a theoretical and numerical study on the heat conduction of gas confined in a cuboid nanopore, in which there exists a temperature difference between the top and bottom walls and the side walls are adiabatic. A modified gas mean free path in confined space is proposed by considering the impact of collisions between molecules and solid surfaces, with which an effective thermal conductivity model of gas in the transition regime is derived. A direct simulation Monte Carlo (DSMC) study on the heat conduction of argon and helium in a cuboid nanopore is carried out to validate the present model. The influences of the Knudsen number and the treatments of boundary conditions on the heat conduction and effective thermal conductivity of gas in nanopores are studied. The temperature jumps and the reduction of heat flux near side walls are analyzed.

Parallel Particle Simulation of the Near-Continuum Hypersonic Flows Over Compression Ramps

2003 ◽  
Vol 125 (1) ◽  
pp. 181-188 ◽  
Author(s):  
J.-S. Wu ◽  
K.-C. Tseng
Keyword(s):  
Flow Field ◽  
Direct Simulation Monte Carlo ◽  
Adaptive Mesh ◽  
Mean Free Path ◽  
Particle Simulation ◽  
Computational Time ◽  
Local Mean ◽  
Simulation Monte Carlo ◽  
Compression Ramp ◽  
Compression Ramps

This paper describes the analysis of the near-continuum hypersonic flow over a compression ramp using the two-dimensional parallel direct simulation Monte Carlo (DSMC) method. Unstructured and triangular solution-based adaptive mesh depending on the local mean free path is used to improve the resolution of solution for the flow field with highly varying properties. In addition, a freestream parameter is defined to help reduced the cell numbers in the freestream area, resulting in appreciable decrease of the computational time (20–30%) without sacrificing the accuracy of the solution. The two-step multilevel graph partition technique is used for physical domain decomposition, employing estimated particle number distribution in each cell as the graph vertex weight. 32 IBM-SP2 processors are used throughout the study unless otherwise specified. The Effect of the outflow vacuum boundary condition, compression ramp angle, freestream condition, and length of the ramp to the flow field are investigated. Computational results are compared with previous numerical results whenever available.

DSMC Simulations of Squeeze Film Between a Micro Beam Undergoing Large Amplitude Oscillations and a Substrate

2012 ◽  
Author(s):  
Nadim A. Diab ◽  
Issam A. Lakkis
Keyword(s):  
Rarefied Gas ◽  
Numerical Study ◽  
Direct Simulation Monte Carlo ◽  
Squeeze Film ◽  
Rf Switch ◽  
Dsmc Method ◽  
Flow Parameters ◽  
Fluid Behavior ◽  
Simulation Monte Carlo ◽  
The Impact

This paper investigates the behavior of a gas film in a micro RF switch. A Two-dimensional numerical study of the flow field is performed as the micro-beam oscillates harmonically between its equilibrium position and the fixed substrate underneath. Unlike previous work in literature, the beam undergoes large displacements throughout the film gap thickness and the behavior of the gas film along with its impact on the moving RF switch (force exerted by gas on the beam’s front and back faces) are discussed. Since the gas film thickness is of the order of few microns (i.e. 0.01<Kn<1), the rarefied gas exists in the non-continuum regime and, as such, the Direct Simulation Monte Carlo (DSMC) method is used to simulate the fluid behavior. The impact of the squeeze film on the beam is investigated over a range of frequencies, velocity amplitudes, and for different film gases, corresponding to ranges of dimensionless flow parameters such as the Reynolds (Re), Strouhal (St) and Mach (Ma) numbers on the gas film behavior.

Numerical analysis of local heat flux and thin-slab solidification in a CSP funnel-type mold with electromagnetic braking

2020 ◽  
Vol 117 (6) ◽  
pp. 602
Author(s):  
Heping Liu ◽  
Jianjun Zhang ◽  
Hongbiao Tao ◽  
Hui Zhang
Keyword(s):  
Heat Flux ◽  
Casting Speed ◽  
Shell Growth ◽  
Local Heat ◽  
Operating Conditions ◽  
Thin Slab ◽  
Wide Face ◽  
Slab Width ◽  
Steel Grades ◽  
Local Heat Flux

In this article, based on the actual monitored temperature data from mold copper plate with a dense thermocouple layout and the measured magnetic flux density values in a CSP thin-slab mold, the local heat flux and thin-slab solidification features in the funnel-type mold with electromagnetic braking are analyzed. The differences of local heat flux, fluid flow and solidified shell growth features between two steel grades of Q235B with carbon content of 0.19%C and DC01 of 0.03%C under varying operation conditions are discussed. The results show the maximum transverse local heat flux is near the meniscus region of over 0.3 m away from the center of the wide face, which corresponds to the upper flow circulation and the large turbulent kinetic energy in a CSP funnel-type mold. The increased slab width and low casting speed can reduce the fluctuation of the transverse local heat flux near the meniscus. There is a decreased transverse local heat flux in the center of the wide face after the solidified shell is pulled through the transition zone from the funnel-curve to the parallel-cure zone. In order to achieve similar metallurgical effects, the braking strength should increase with the increase of casting speed and slab width. Using the strong EMBr field in a lower casting speed might reverse the desired effects. There exist some differences of solidified shell thinning features for different steel grades in the range of the funnel opening region under the measured operating conditions, which may affect the optimization of the casting process in a CSP caster.

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