Dynamics Simulation Of Heat Transfer Research Articles

Computational fluid dynamics simulation of heat transfer from densely packed gold nanoparticles to isotropic media

Computational fluid dynamics simulation of heat transfer from densely packed gold nanoparticles to isotropic media

Molecular dynamics simulation of heat transfer through solid-liquid interface in ionic-liquid-based supercapacitors

In this article, molecular dynamics simulations were performed to investigate the heat transfer through the electrode-electrolyte interfaces of supercapacitors based on ionic liquids. The factors of thermal conductivity of interfaces between the graphene electrode and ionic liquids were analyzed. Simulation results show that when the electrode is charged, stable electrical double layers form at the electrode, and the change of EDL structure increases the molecular volume ratio, thus improving the interfacial heat transfer. At the negatively charged electrode, the extra adsorption peak makes the heat transfer stronger than that at the positively charged electrode. The interfacial thermal conductivity of the double layer at electrodes with the nanoscale roughness is lower than that of the smooth one. This is because there are fewer carbon atoms involved in heat transfer at the rough surface, which reduces the contacting area and thus weakens the heat transfer at the interface.

Molecular Dynamics Simulation of Heat Transfer and Stresses in Thin Films Caused by a Short Laser Pulse

Molecular Dynamics Simulation of Heat Transfer and Stresses in Thin Films Caused by a Short Laser Pulse

Molecular dynamics study of effect of wettability on rapid boiling over copper nanoparticle in water pool

Many special phenomena occur during rapid boiling of a liquid when it is largely superheated near the thermodynamic critical temperature which is much higher than the saturation temperature. However, although there are many experimental work reported the observation of rapid ejection near the surface region of the materials, they are limited in either length or time scales due to the limitation of classical macroscopic theory. In this work, molecular dynamics simulation of heat transfer from nanoparticle to a surrounding liquid pool is carried out to study the effect of solid-liquid interfacial wettability on the boiling phenomena of water around the nanoparticle. The interactions among copper atoms are described by the embedded atom method (EAM) potentials, and the TIP4P water model is used to describe water atoms. The results show that the interfacial thermal conductance is influenced by the interfacial wettability. Increasing the wettability between the particle and the fluid reduces the interfacial resistance. The nucleation of bubbles and formation of vapor occur more quickly for increased solid-liquid interfacial wettability. The results might change due to the uncertainties of the potential functions, therefore further investigation is worthwhile to study rapid boiling of water on nanoparticles using different water models.

Molecular Dynamics Simulation of Heat Transfer at Contact Interface of Hot Forming Die

During metal hot forming process, the billet and the die interact by contact under high temperature, high pressure and severe sliding. In this paper, an atomistic approach is utilized to study the behaviour of heat transfer at the contact interface of hot forming die and the material. Based on non-equilibrium molecular dynamics and phonon scattering theory, the phonon heat transfer process at the billet/die rough interface at nano-scale is analysed. The effects of interfacial lattice defect concentration and average interfacial temperature on the phonon heat transfer coefficient are examined. It is found that when the lattice defect concentration increases the phonon mismatch at the interface deteriorates and the interfacial thermal resistance increases, which leads to a sharp decrease in phonon heat transfer coefficient. A higher temperature of the contact body and a higher average interface temperature lead to a higher probability of inelastic scattering of phonons at the interface. Moreover, the high frequency phonons at high temperature might be decomposed into two or more low frequency phonons during the energy transmission, which increases the propagation of phonon at the interface; thus the phonon heat transfer coefficient increases accordingly.

Dynamic Simulation of Heat Transfer through External Building Constructions

Dynamic Simulation of Heat Transfer through External Building Constructions

Heat transfer around copper nanoparticle with high superheat in water pool: A molecular dynamics simulation

Rapid boiling of a liquid occurs when it is highly superheated near the thermodynamic critical temperature that is much higher than the saturation temperature. Many experimental investigation have been conducted to observe the rapid ejection phenomenon near the heated surface. However, these study were limited by either length or time scale because of the limitation of classical macroscopic theory. In this work, a molecular dynamics simulation of heat transfer from a nanoparticle to its surrounding liquid pool was carried out to study the effect of nanoparticle diameter on the heat transfer of water around it. The interactions among copper atoms were described by the Embedded Atom Method (EAM) potentials, and the TIP4P water model was used to model the water atoms. The results show that the temperature of water increases more quickly for nanoparticle with larger diameter, the heat flux increases apparently when the nanoparticle diameter increases, and the interfacial thermal resistance is relatively larger for bigger nanoparticle due to the vibrational mismatch present at the interface.

Computational fluid dynamics simulation of heat transfer and fluid flow characteristics in a vortex tube by considering the various parameters

In this paper, the effects of number of inlets, tube length and diameter of cold outlet on temperature, flow rates passing through the vortex tube are investigated. The results including temperature of cold outlet and flow rates passing through the vortex tube are discussed. The effect of length, number of inlets, ranging from 1 to 5 inlets and the effect of cold outlet on the results are investigated. According to obtained results, we conclude that the passing flow rate from a cold outlet is increased as its diameter increase and by increasing the length of the vortex tube, the passing mass flow rates from the cold and hot cross-sections slightly increased and slightly increased, respectively. Also, the temperatures at both outlets decreased as the number of inlets increased, while increases were observed as the radius of cold outlet increased and the temperature of exiting gas is considerably higher than hot and cold outlets compared to the case where more number of inlets with reduced diameters is used. As shown, for L/D=15 and as the radius of cold outlet is increased, the fraction of mass flow rate is decreased from 0.8 to 0.7 and then 0.6, from 0.65 to 0.58 and then 0.52, and from 0.42 to 0.32 and then 0.24 for n=1, 3 and 5.

Modelling Natural Ventilation in Double Skin Facade

The assessment of the energy performance of buildings with Double Skin Facades (DSF) requires proper dynamic simulation tools, based on models capable of predicting heat and mass transfer in the DSF under variable boundary conditions, at the price of a reasonable computational effort.Many DSF simplified models have been developed and implemented in building simulation tools, but the validation of these tools is still an open issue, especially for the prediction of the mass flow rate in naturally ventilated DSF. The CFD modelling activity presented in this work aims at investigating the reliability of the assumptions and hypotheses employed in the simplified model, which was specifically developed for the dynamic simulation of heat transfer in buildings.Both the CFD and simplified models have been tested and evaluated on an experimental case study, using the database provided by a research program developed under IEA ECBCS Annex 43/SHC Task 34, reporting the results of a measurement campaign conducted on an a transparent naturally ventilated DSF tested in Denmark, in an experimental facility called “the Cube”.

Molecular Dynamics Simulation of Heat Transfer during Quenching in CNT Nanofluids

Abstract Nanofluids exhibit superior thermal properties to conventional fluid and particle-fluid suspensions and show a great potential as quenching media for quench hardening of steel components. The heat transfer mechanism in nanofluid is very complex and unclear. In this paper, molecular dynamics (MD) simulation method is used to theoretically study the heat transfer from a metal surface at different temperatures to a water-based nanofluid with functionalized carbon nanotubes (FCNTs). To model the quenching process, an initial temperature jump between the nanofluid and an iron slab is employed, and non-equilibrium molecular dynamics (NEMD) simulations are performed. The MD results reveal the heat transfer process in the initial stage of quenching and at the first moment of contact of a liquid nanofluid with a hot metal surface. The thermodynamics and transport properties of the nanofluid and the heat transfer characteristics are discussed with the atomistic details of the interactions of the FCNT with the iron atoms and the water molecules.

Molecule Dynamics Simulation of Heat Transfer Between Argon Flow and Parallel Copper Plates

Molecular dynamics (MD) simulation aiming to investigate heat transfer between argon fluid flow and two parallel copper plates in the nanoscale is carried out by simultaneously control momentum and temperature of the simulation box. The top copper wall is kept at a constant velocity by adding an external force according to the velocity difference between on-the-fly and desired velocities. At the same time the top wall holds a higher temperature while the bottom wall is considered as physically stationary and has a lower temperature. A sample region is used in order to measure the heat flux flowing across the simulation box, and thus the heat transfer coefficient between the fluid and wall can be estimated through its definition. It is found that the heat transfer coefficient between argon fluid flow and copper plate in this scenario is lower but still in the same order magnitude in comparison with the one predicted based on the hypothesis in other reported work.

Development of EEM based silicon–water and silica–water wall potentials for non-reactive molecular dynamics simulations

Molecular dynamics simulations of heat transfer in gases are computationally expensive when the wall molecules are explicitly modeled. To save computational time, an implicit boundary function is often used. Steele's potential has been used in studies of fluid–solid interface for a long time. In this work, the conceptual idea of Steele's potential was extended in order to simulate water–silicon and water–silica interfaces. A new wall potential model is developed by using the electronegativity-equalization method (EEM), a ReaxFF empirical force field and a non-reactive molecular dynamics package PumMa. Contact angle simulations were performed in order to validate the wall potential model. Contact angle simulations with the resulting tabulated wall potentials gave a silicon–water contact angle of 129°, a quartz–water contact angle of 0°, and a cristobalite–water contact angle of 40°, which are in reasonable agreement with experimental values.

Molecular Dynamics Simulation of Heat Transfer from a Gold Nanoparticle to a Water Pool

Heat transfer from nanoparticles to a surrounding liquid pool is an essential process for many applications. This work investigates the heat transfer process upon a continuous wave laser heating to a gold nanoparticle (GNP) in a water pool through molecular dynamics (MD) simulations based on realistic potentials. The interactions among gold atoms are described by the embedded atom method (EAM) potentials, both the rigid and flexible TIP3P water models are examined, and a modified Lennard-Jones potential is used for the interaction between the GNP and water. The results show that the interfacial thermal conductance is influenced by the selection of different water models and the interfacial wettability. The interfacial thermal conductance is smaller but increases slightly with the increase of heat flux for the flexible water model, while it keeps almost constant for the rigid model. Increasing the wettability between the particle and the fluid reduces the interfacial resistance. The rise of the interfacial...

3D dynamic simulation of heat transfer and melt flow in an inductively heated crystallization furnace for mc-silicon with PID temperature control

A heat transfer model of a semi-industrial induction furnace has been build, using a 3D finite element model in order to analyze the entire process cycle, based on the heating, melting, solidification and cooling phases of a multi-crystalline square ingot. In the modeling of the entire process, heat transfer phenomena such as radiation and conduction in the furnace have been taken into account. A PID (Proportional Integral Differential) control algorithm has been implemented into the model for adjusting the power input in the heaters, so that the heater temperature is kept at prescribed time-varying values. The furnace model and the PID control algorithm are validated by temperature measurements from a crystallization experiment. Subsequently the validated model was used to investigate the melt flow field and its impact on the solid–liquid interface shape.

Molecular dynamics simulation of heat transfer through a water layer between two platinum slabs

Heat transfer through micro channels is being investigated due to its importance in micro channel cooling applications. Molecular dynamics simulation is regarded as a potential tool for studying such microscopic phenomena in detail. However, the applicability of molecular dynamics method is limited due to scarcely known inter atomic interactions involved in complex fluids. In this study we use an empirical force field (ReaxFF), which is parameterized using accurate quantum chemical simulation results for water, to simulate heat transfer phenomena through a layer of water confined between two platinum slabs. The model for water seems to reproduce the macroscopic properties such as density, radial distribution function and diffusivity quite well. The heat transfer phenomena through a channel filled with water, which is confined by two platinum (100) surfaces are studied using ReaxFF. The model accurately predicts the formation of surface mono-layer. The heat transfer analysis shows temperature jumps near the walls which are creating significant heat transfer resistances. A low bulk density in the channel creates a multi-phase region with vapor transport in the region.

Computational Fluid Dynamics Modeling of a Self-Recuperative Burner and Development of a Simplified Equivalent Radiative Model

The solution for dynamic modeling of reheating furnaces requires a burner model, which is simultaneously accurate and fast. Based on the fact that radiative heat transfer is the most dominant heat transfer mode in high-temperature processes, the present study develops a simplified flame representation model that can be used for dynamic simulation of heat transfer in reheating furnaces. The first part of the paper investigates, experimentally and computationally, gas combustion in an industrial burner. Experiments aim at establishing an experimental database of the burner characteristics. This database is compared with numerical simulations in order to establish a numerical model for the burner. The numerical burner model was solved using a commercial computational fluid dynamics (CFD) software (FLUENT 6.3.26). A selection of results is presented, highlighting the usefulness of CFD as a modeling tool for industrial scale burners. In the second part of the paper, a new approach called the “emissive volume approach” is established. This approach consists of replacing the burner flame by a number of emissive volumes that replicates the radiative effect of the flame. Comparisons with CFD results show a difference smaller than 1% is achieved with the emissive volume approach, while computational time is divided by 40.

Molecular dynamics simulation of heat transfer with effects of fluid–lattice interactions

The nonequilibrium molecular dynamics simulation is employed to investigate the thermal properties of fluid confined in different FCC nanochannels. The results show that fluid in different lattice channels appears diverse wetting characteristics at low temperature. Based on wall parameters, a ratio is defined to describe the fluid–lattice interaction. Wall attraction, number of absorbed particles and thermal conductivity are increased as the increase of this ratio as well as the location of particles get closer to the wall. Thermal resistance exists along with the fluid–wall interface and loses the dominant of heat transport as the system temperature gets raised. At the same time, the thermal conductivity of nanoscale experiences unconventional increase. The fluid thermal properties are influenced both by wall–fluid interaction and temperature.

A molecular dynamics boundary condition for heat exchange between walls and a fluid

In molecular dynamics simulations of heat transfer in micro channels, a lot of computation time is used when the wall molecules are explicitly simulated. To save computation time, implicit boundary conditions, such as the Maxwell conditions, can be used. With these boundary conditions, heat transfer is still a problem. In this work, we derive a new boundary condition based on a vibrating potential wall. The heat-transfer properties of the new boundary condition are shown to be comparable with those of the explicit wall. The computation time needed for the implicit boundary condition is very small compared with that needed for the explicit simulation.

Computational fluid dynamics simulations of heat transfer between the dense‐phase of a high‐temperature fluidized bed and an immersed surface

AbstractThe transient process of heat transfer between a high‐temperature emulsion packet and the wall of an immersed surface is simulated using computational fluid dynamics (CFD). From these simulations, the total heat transfer coefficient and its radiant contribution due to the emulsion (dense) phase are evaluated. The results are compared with experimental data (Ozkaynak et al., “An experimental investigation of radiant heat transfer in high temperature fluidized beds,” in Fluidization IV, 1983:371–378) and with predicted values from the generalized heterogeneous model (GHM), (Mazza et al., “Evaluation of overall heat transfer rates between bubbling fluidized beds and immersed surfaces,” Chem Eng Commun., 1997;162:125–149). The CFD simulations are in good agreement with both, experimental data and theoretical GHM predictions and provide a reliable way to quantify the studied heat transfer process. Also, the GHM is validated as a practical tool to this end. © 2011 American Institute of Chemical Engineers AIChE J, 58: 412–426, 2012

Model non-equilibrium molecular dynamics simulations of heat transfer from a hot gold surface to an alkylthiolate self-assembled monolayer

Model non-equilibrium molecular dynamics (MD) simulations are presented of heat transfer from a hot Au {111} substrate to an alkylthiolate self-assembled monolayer (H-SAM) to assist in obtaining an atomic-level understanding of experiments by Wang et al. (Z. Wang, J. A. Carter, A. Lagutchev, Y. K. Koh, N.-H. Seong, D. G. Cahill, and D. D. Dlott, Science, 2007, 317, 787). Different models are considered to determine how they affect the heat transfer dynamics. They include temperature equilibrated (TE) and temperature gradient (TG) thermostat models for the Au(s) surface, and soft and stiff S/Au(s) models for bonding of the S-atoms to the Au(s) surface. A detailed analysis of the non-equilibrium heat transfer at the heterogeneous interface is presented. There is a short time temperature gradient within the top layers of the Au(s) surface. The S-atoms heat rapidly, much faster than do the C-atoms in the alkylthiolate chains. A high thermal conductivity in the H-SAM, perpendicular to the interface, results in nearly identical temperatures for the CH(2) and CH(3) groups versus time. Thermal-induced disorder is analyzed for the Au(s) substrate, the S/Au(s) interface and the H-SAM. Before heat transfer occurs from the hot Au(s) substrate to the H-SAM, there is disorder at the S/Au(s) interface and within the alkylthiolate chains arising from heat-induced disorder near the surface of hot Au(s). The short-time rapid heating of the S-atoms enhances this disorder. The increasing disorder of H-SAM chains with time results from both disorder at the Au/S interface and heat transfer to the H-SAM chains.