Thermally-driven nanoscale pump by molecular dynamics simulation

Minsub Han 대한기계학회 2008 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.22 No.1

The feasibility of a device is studied that drives a fluid in nanoscale channel using a phenomenon called thermal transpiration, where the fluid is set in motion by a temperature gradient in the fluid-solid interface. Four different types of systems are considered using the Molecular Dynamics Simulation. They differ mainly in channel configuration and the way the gradient is applied. The simulation results show that the design of the device has major technical obstacles. One is a difficulty in imposing a sufficiently-large temperature gradient in the small scale. In this case, the feature like thermal-contact-resistance at the interface needs to be included in design considerations. The second is a limited flowdevelopment under an increased viscous drag in the narrow channel. One of the considered systems proves to be effective in a pumping operation. The system is based on a unit that repeats itself periodically in the system. The unit is composed of two regions: one that drives a fluid by thermophoretic force and the other that guides the fluid smoothly with little thermophoretic force. The latter region is made of a thermally-insulating, weakly-interacting solid.

Mass exchange at liquid-solid interface: a molecular simulation scheme applied to evaporation phenomena

Minsub Han 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.9

A numerical technique is presented that enables mass exchange at the liquid– solid interface region in a molecular simulation. Particles can be inserted and deleted in the solid region where interaction between the fluid and solid atoms is temporarily inactivated during the process. A simple momentum-increase scheme drives the inserted particles against the unfavorable free energy. The technique is efficient and stable for insertion of particles into dense and inhomogeneous regions. The thin film and sessile-drop evaporation phenomena are then investigated using the proposed technique that allows steady-state simulations. The evaporation coefficients for the nanoscale thin film and contact line were accurately and reliably measured. The evaporation coefficient near the contact line shows a discrepancy compared to that far from the contact line.

Thermophoresis in Dense Gases: a Study by Born-Green- Yvon Equation

Han Minsub The Korean Society of Mechanical Engineers 2005 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.19 No.4

Thermophoresis in dense gases is studied by using a multi-scale approach and Born- Yvon­Green (BYG) equation. The problem of a particle movement in an ambient dense gas under temperature gradient is divided into inter and outer ones. The pressure gradient in the inner region is obtained from the solutions of BYG equation. The velocity profile is derived from the conservation equations and calculated using the pressure gradient, which provides the particle velocity in the outer problem. It is shown that the temperature gradient applied to the quiescent ambient gas induces some pressure gradient and thus flow tangential to the particle surface in the interfacial region. The mechanism that induces the flow may be the dominant source of the thermophretic particle movement in dense gases. It is also shown that the particle velocity has a nonlinear relationship with the applied temperature gradient and decreases with increasing temperature.

Thermophoresis in Dense Gases : a Study by Born-Green-Yvon Equation

Minsub Han 대한기계학회 2005 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.19 No.4

Thermophoresis in dense gases is studied by using a multi-scale approach and Born-Yvon- Green (BYG) equation. The problem of a particle movement in an ambient dense gas under temperature gradient is divided into inter and outer ones. The pressure gradient in the inner region is obtained from the solutions of BYG equation. The velocity profile is derived from the conservation equations and calculated using the pressure gradient, which provides the particle velocity in the outer problem. It is shown that the temperature gradient applied to the quiescent ambient gas induces some pressure gradient and thus flow tangential to the particle surface in the interfacial region. The mechanism that induces the flow may be the dominant source of the thermophretic particle movement in dense gases. It is also shown that the particle velocity has a nonlinear relationship with the applied temperature gradient and decreases with increasing temperature.

Development of Water-Cooled Heat Sink for High-Power IGBT Inverter

Minsub Han,Su-Dong Lee,Chanook Hong,Chun-Suk Yang,Kyung-Seo Kim 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-

We present the development of a water-cooled heat sink that provides reliable thermal performance for high-power IGBT inverter. The development process comprises three stages. In the concept design, the thermal performances of two design proposals are considered. The thermal system of each design is particularly analyzed using the compact model. In the detailed design stage, specific dimensions of the heat sink are determined considering the design options under given external restrictions and the results from three-dimensional heat transfer analysis. The prototype of the resultant design is made and tested on the rig for final confirmation. We emphasize the relevant use of the thermal analysis on each stage and also discuss various practical issues involved.

고체 면에 흡착된 박막에서의 분리압력 특성에 관한 연구

한민섭(Minsub Han) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.2

The disjoining pressure is an important physical property in modeling the small-scale transport phenomena on thin film. It is a very useful definition in characterizing the non-continuum effects that are not negligible in heat and mass transport of the film thinner than submicro-scales. We present the calculated values of disjoining pressure of He, Kr and Xe thin films absorbed on graphite substrate using Molecular Dynamics Simulation (MD). The disjoining pressure is accurately calculated in the resolution of a molecular scale of the film thickness. The characteristics of the pressure are discussed regarding the molecular nature of the fluid system such as molecular diameter and intermolecular interaction parameters. The MD results are also compared with those based on the continuum approximation of the slab-like density profile and the results on other novel gases in the previous study. The discrepancies of the continuum model with MD results are shown in all three configurations and discussed in the view point of molecular features.

다상 유체 시스템의 다중 스케일 시뮬레이션 기법에 관한 연구

한민섭(Minsub Han) 대한기계학회 2010 大韓機械學會論文集B Vol.34 No.6

다상 유체 시스템에 적용할 수 있는 다중스케일 입자 시뮬레이션 기법을 개발하였다. 거시 모델과 미시모델이 만나는 경계영역에서 세가지로 구별되는 기능을 수행하도록 하였다. 먼저, 기상과 액상을 분리하여 연결하기 위해 벽을 설정하였다. 또 경계영역을 근처에서 경계의 위치를 측정하고 이것에 벽의 각도와 위치가 연동하여 접촉각 값을 미시모델에서 거시모델로 전달하게 하였다. 마지막으로, 입자의 삽입과 제거를 통해 경계영역의 질량과 온도를 거시적 조건에 맞추도록 하였다. 이 알고리즘들을 적용한 완전습윤과 부분습윤 시스템들은 좋은 결합 결과를 보였다. A multiscale particle simulation technique that can be applied to a multiphase fluid system has been developed. In the boundary region where the macroscopic- and microscopic-scale models overlap each other, three distinctive features are introduced in the simulation. First, a wall is set up between the gas and liquid phases to separate them and match the phases respectively to the macroscopic conditions stably. Secondly, the interfacial profile is obtained near the matching region and the wall translates and rotates to accommodate the change in the liquid-vapor interfacial position in the molecular model. The contact angle thus obtained can be sent to the macroscopic model. Finally, a state of mass and temperature in the region is maintained by inserting and deleting the particles. Good matching results are observed in the cases of the complete and partial wetting fluid systems.

계면 열전달 특성에 대한 분자동력학 시뮬레이션 연구

한민섭(Minsub Han) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.4

분자동역학 전산모사를 이용한 박막의 불안정성 및 나노 구조물 형성에 관한 연구

한민섭(Minsub Han),이준식(Joon Sik Lee),박승호(Seungho Park),최영기(Young Ki Choi) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11

It has recently been shown that the instability of thin film of a nanoscale can be used in the processes of<br/> building nano-size structures, which have potential practical importance in nanotechnology. Molecular<br/> dynamics simulation is conducted to probe the thin fluid film of a nano-size and its dynamic behavior during<br/> destabilization and structure formation. Non-continuum characteristics are shown in the properties like<br/> pressure tensor, viscosity, and thermal conductivity. The thermocapillary force induces a slow growth of long<br/> waves in the scale considered. A long-range interaction with the solid wall induces vertical structures, whose<br/> formation time and space between neighbors are proportional to the strength of the interaction.

분자동력학 시뮬레이션을 이용한 나노채널 대류에서의 열류 분포에 대한 연구

한민섭(Minsub Han),이준식(Joon Sik Lee),박승호(Seungho Park) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5

We study the convective heat transport phenomenon of liquid in a nanoscale straight channel by performing the nonequilibrium molecular dynamics simulation (NEMD). Fundamental heat transfer phenomenon distinctive in a nanoscale is reported by Han and Lee [Phys. Rev. E 70, 061205 (2004)]. It is the significant heat transfer in the upstream direction even in the absence of temperature gradient in the direction. A planar Poiseuille flow is considered in the simulation, where liquid argon in a straight channel of Pt atoms is driven by a gravity-like body force with periodic boundary conditions applied in the tangential directions to the surfaces. The heat transfer is induced by the active role of intermolecular force and plane peculiar velocity. It becomes significant when the velocity gradient is sizable in the range of the intermolecular force. The generalized Fourier's law in the literature is compared with NEMD results.