Nano Heat Pipe: Nonequilibrium Molecular Dynamics Simulation

2016 ◽  
Author(s):  
Mohammad Moulod ◽  
Gisuk Hwang
Keyword(s):  
Molecular Dynamics ◽  
Heat Flux ◽  
Heat Pipe ◽  
Thermal Management ◽  
Operating Conditions ◽  
Dynamics Simulation ◽  
Nonequilibrium Molecular Dynamics ◽  
Management Systems ◽  
Working Fluid ◽  
Maximum Heat

A heat pipe has been known as a thermal superconductor utilizing a liquid-vapor phase change, and it has drawn significant attentions for advanced thermal management systems. However, a challenge is the size limitation, i.e., the heat pipe cannot be smaller than the evaporator/condenser wick structures, typically an order of micron, and a new operating mechanism is required to meet the needs for the nanoscale thermal management systems. In this study, we design the nanoscale heat pipe employing the gas-filled nanostructure, while transferring heat via ballistic fluid-particle motions with a possible returning working fluid via surface diffusions along the nanostructure. The enhanced heat flux for the nano heat pipe is demonstrated using the nonequilibrium molecular dynamics simulations (NEMDS) for the argon gas confined by the 20 nm-long Pt nanogap with a post wall with the temperature difference between the hot and cold surfaces of 20 K. The predicted results show that the maximum heat flux through the gas-filled nanostructure (heat pipe) nearly doubles that of the nanogap without the post wall at 100 < T < 140 K. The optimal operating conditions/material selections are discussed. The results for the nanogap agree with those obtained from the kinetic theory, and provide insights into the design of advanced thermal management systems.

Adsorption-Controlled Thermal Diode: Nonequilibrium Molecular Dynamics Simulation

2016 ◽  
Author(s):  
Tadeh Avanessian ◽  
Gisuk Hwang
Keyword(s):  
Heat Transfer ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Thermal Management ◽  
Accommodation Coefficient ◽  
Dynamics Simulation ◽  
Nonequilibrium Molecular Dynamics ◽  
Management Systems ◽  
Thermal Switches ◽  
Ar Gas

A thermal diode is a system controlling the heat transfer preferentially in one direction. This serves as a basic building block to design advanced thermal management systems in energy saving applications and to provide implications to design new application such as thermal computers. The development of the thermal diode has been of great interest as electrical diodes have similarly made significant impacts on modern industries. Numerous studies have demonstrated thermal diode mechanisms using non-linear heat transfer mechanisms, but the main challenges in current systems are poor steady-state performance, slow transient response, and/or extremely difficult manufacturing for the viable solutions. In this study, an adsorption-based thermal diode is examined for a fast and efficient thermal diode mechanism as a completely new class, using a gas-filled, heterogeneous nanogap with asymmetric surface interactions in Knudsen regime. Ar gas atoms confined in Pt-based solid surfaces are selected to predict the degree of rectification, R ∼ 10, using non-equilibrium molecular dynamics simulation with the nanogap size of Lz = 20 nm and ΔT = 20 K for various average plate temperatures, 80 < T < 130 K. Different surface energies for the thermal diode is studied and a maximum degree of rectification, Rmax ∼ 10, is found at T = 80 K which results from the significant adsorption-controlled thermal accommodation coefficient (TAC). The obtained results provide insights into the design of advanced thermal management systems including thermal switches and thermal computing systems.

Effect of Fluid Loading on the Performance of Wicked Heat Pipes

Volume 3 ◽  
2004 ◽  
Author(s):  
R. Kempers ◽  
A. Robinson ◽  
C. Ching ◽  
D. Ewing
Keyword(s):  
Heat Flux ◽  
Heat Pipe ◽  
Heat Transport ◽  
Heat Pipes ◽  
Working Fluid ◽  
Fluid Loading ◽  
Maximum Heat ◽  
Horizontal Orientation ◽  
Maximum Heat Flux ◽  
Dry Out

A study was performed to experimentally characterize the effect of fluid loading on the heat transport performance of wicked heat pipes. In particular, experiments were performed to characterize the performance of heat pipes with insufficient fluid to saturate the wick and excess fluid for a variety of orientations. It was found that excess working fluid in the heat pipe increased the thermal resistance of the heat pipe, but increased maximum heat flux through the pipe in a horizontal orientation. The thermal performance of the heat pipe was reduced when the amount of working fluid was less than required to saturate the wick, but the maximum heat flux through the heat pipe was significantly reduced at all orientations. It was also found in this case the performance of this heat pipe deteriorated once dry-out occurred.

Thermal Conductivity of Graphene on Nanostructure Size from Nonequilibrium Molecular Dynamics Simulations

2020 ◽  
Vol 17 (4) ◽  
pp. 1566-1570
Author(s):  
Xianqi Wei ◽  
Zelin Li ◽  
Junchen Lu ◽  
Shunlong Xu ◽  
Yuancheng Zhu ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Thermal Management ◽  
Strong Dependence ◽  
Thermal Conductance ◽  
Mean Free Path ◽  
Dynamics Simulation ◽  
Nonequilibrium Molecular Dynamics ◽  
Edge Type ◽  
Dynamics Simulations

Thermal transport of graphene occupies a unique place in thermal management of electronic devices, especially for nanosize devices with high-density integration and high dissipated power. The structure of graphene on nanometer scale changes its thermal conductance. Here, the thermal characters of graphene have been researched by nonequilibrium molecular dynamics simulation (NEMDS) at room temperature. Special attention is focused on the edge type (zigzag or armchair) and nanostructure size dependence of conductivity for heat. The consequences suggest that the thermal conductivity of zigzag edge has been higher than that of armchair, which is because of the higher phonon group velocities. Furthermore, thermal conductivity shows a rising tendency, when the model is calculated from length of 21.84 nm to 43.78 nm. The result indicates that the thermal property performs a strong dependence on nanostructure size which is less than phonon mean free path (775 nm). Our research highlights the significance of structure attribute relationships together with providing useful guideline in calculations for nanosize devices thermal management.

A Heat Plate Leading Edge for Hypersonic Vehicles

2008 ◽  
Author(s):  
Scott D. Kasen ◽  
Doug T. Queheillalt ◽  
Craig A. Steeves ◽  
Anthony G. Evans ◽  
Haydn N. G. Wadley
Keyword(s):  
Heat Flux ◽  
Low Temperature ◽  
Heat Pipe ◽  
Thermal Management ◽  
Leading Edge ◽  
Maximum Temperature ◽  
Working Fluid ◽  
Hypersonic Vehicles ◽  
Vapor Flow ◽  
Leading Edges

The intense thermal flux at the leading edges of hypersonic vehicles (traveling at Mach 5 and greater) requires creative thermal management strategies to prevent damage to leading edge components. Carbon fiber composites and/or ablative coatings have been widely utilized to mitigate the effects of the impinging heat flux. This paper focuses on an alternative, metallic leading edge heat pipe concept which combines efficient structural load support and thermal management. The passive concept is based on high thermal conductance heat pipes which redistribute the high heat flux at the leading edge stagnation point through the evaporation, vapor flow, and condensation of a working fluid to a location far from the heat source. Structural efficiency is provided by a sandwich construction using an open-cell core that also allows for vapor flow. A low temperature proof-of-concept copper–water system has been investigated by experimentation. Measuring of the axial temperature profile indicates effective spreading of thermal energy, a lowering of the maximum temperature and reduced overall thermal gradient compared to a non-heat pipe leading edge. A simple transient analytical model based on lumped thermal capacitance theory is compared with the experimental results. The low-temperature prototype shows potential for higher temperature metallic leading edges that can withstand the hypersonic thermo-mechanical environment.

Flat Heat Pipe Cooling Devices for Mobile Computers

2003 ◽  
Author(s):  
Yaxiong Wang ◽  
G. P. Peterson
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Thermal Management ◽  
High Efficiency ◽  
Junction Temperature ◽  
Working Fluid ◽  
Closed Chamber ◽  
Maximum Heat ◽  
Micro Heat Pipe ◽  
Mobile Computers

The rapid increases in package density in the high-performance microprocessors utilized in laptop, notebook and other mobile computers has resulted in power-densities that are challenging the existing thermal management technologies. In order to accomodate these challenges within the existing space and volume constraints, a novel, flat, micro heat pipe (MHP) cooling device has been conceptualized, designed, and evaluated analytically. The novel device consists of a flat micro heat pipe heat spreader, fabricated by sintering copper mesh and wires between two thin copper sheets to form a closed chamber. High-efficiency folded fins are then bonded to the condenser to produce a device that is capable of dissipating the high heat loads and reducing the thermal resistance typically present in these packages. Because of its high latent heat and surface tension, water was used as the working fluid. A number of different designs with different CPU mounting positions and fin sets were examined theoretically in an effort to optimize the initial design. The effects of the physical properties of the mesh, wire diameter, and effective thermal conductivity of the capillary structure were then evaluated and optimized. This process resulted in a design optimized on thermal performance, that is an excellent candidate for the thermal management of laptop and/or notebook computers. At a junction temperature of 85 °C, the maximum heat transport capacity and corresponding thermal resistance of an optimized MHP heat sink, 25.4 man wide and 152.4 mm long, were 33 W and 0.80 W/°C, respectively, for an environmental temperature of 45 °C.

Experimental and Numerical Simulation for Thermal Investigation of Oscillating Heat Pipe Using VOF Model

2020 ◽  
Vol 38 (1A) ◽  
pp. 88-104
Author(s):  
Anwar S. Barrak ◽  
Ahmed A. M. Saleh ◽  
Zainab H. Naji
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Heat Input ◽  
Cfd Simulation ◽  
Working Fluid ◽  
Maximum Deviation ◽  
Inlet Temperature ◽  
Maximum Heat ◽  
Oscillating Heat Pipe ◽  
Vof Model

This study is investigated the thermal performance of seven turns of the oscillating heat pipe (OHP) by an experimental investigation and CFD simulation. The OHP is designed and made from a copper tube with an inner diameter 3.5 mm and thickness 0.6 mm and the condenser, evaporator, and adiabatic lengths are 300, 300, and 210 mm respectively.  Water is used as a working fluid with a filling ratio of 50% of the total volume. The evaporator part is heated by hot air (35, 40, 45, and 50) oC with various face velocity (0.5, 1, and 1.5) m/s. The condenser section is cold by air at temperature 15 oC. The CFD simulation is done by using the volume of fluid (VOF) method to model two-phase flow by conjugating a user-defined function code (UDF) to the FLUENT code. Results showed that the maximum heat input is 107.75 W while the minimum heat is 13.75 W at air inlet temperature 35 oC with air velocity 0.5m/s. The thermal resistance decreased with increasing of heat input. The results were recorded minimum thermal resistance 0.2312 oC/W at 107.75 W and maximum thermal resistance 1.036 oC/W at 13.75W. In addition, the effective thermal conductivity increased due to increasing heat input.  The numerical results showed a good agreement with experimental results with a maximum deviation of 15%.

Dynamical Behavior and Flow Mechanism of Fluid in Nanochannel by Molecular Dynamics Simulation

2009 ◽  
Author(s):  
Juanfang Liu ◽  
Chao Liu ◽  
Qin Li
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Dynamical Behavior ◽  
Velocity Profiles ◽  
The Other ◽  
Dynamics Simulation ◽  
Nonequilibrium Molecular Dynamics ◽  
Interfacial Region ◽  
Flow Mechanism ◽  
Bulk Fluid

The flow properties and dynamical behavior of fluid in a nanochannel were investigated by nonequilibrium molecular dynamics simulation. First of all, the locale distribution of molecules in the channel is found to be strongly inhomogeneous compared to the bulk fluid. In the vicinity of the wall, portion of the fluid molecules are absorbed on the surface of wall due to the strong interaction of the atoms between the wall and liquid, so that the fluid density in the contact region would be much larger than one of the bulk fluid. But in the other region, the local density value approaches one of the bulk fluids with the increasing distance from the wall. This oscillatory behavior of density resulted in different motion behavior of molecules in the different region of nanochannel. The molecular behavior in the interfacial region is remarkably different from those of fluid atoms in the center of channel and wall atoms, which posses both the motion properties of bulk liquids and a solid atom. At the molecular level, macroscopic continuum hypothesis failed, that is, the results predicted by the Navier-Stoke equations deviate from the simulation data adopted by molecular dynamics simulation. In the paper, the velocity profiles for the channels with different width were plotted, which demonstrated that the time-averaged velocity profiles was not quadratic when the channel width was less than 10 molecular diameters. But on the other cases, the velocity profiles will agree well with the analytical solution based on the NS theory. The molecular dynamics simulation method can withdraw the important microscopical information from the simulation process, which benefit to analyze the flow mechanism at such length scale channel.

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