Volume 4: Heat and Mass Transfer Under Extreme Conditions; Environmental Heat Transfer; Computational Heat Transfer; Visualization of Heat Transfer; Heat Transfer Education and Future Directions in Heat Transfer; Nuclear Energy, 2013
By utilizing molecular dynamics (MD) simulations, we study the interfacial thermal conductance at... more By utilizing molecular dynamics (MD) simulations, we study the interfacial thermal conductance at the interface of graphene and paraffin. In doing so, we conduct non-equilibrium heat source and sink simulations on systems of parallel and perpendicular configurations in which the heat flow is parallel and perpendicular to the surface of graphene, respectively. For the perpendicular configuration, graphene with different number of layers are considered. The results show that the interfacial thermal conductance decreases with the number of layers and converges to a value which is equal to the obtained conductance by using the parallel configuration. We also study the conductance for the solid phase paraffin. The results indicate that solid paraffin-graphene interfaces have higher conductance values with respect to the corresponding liquid phase systems.
We have studied the mechanisms of heat transfer in a porous crystal-gas mixture system, motivated... more We have studied the mechanisms of heat transfer in a porous crystal-gas mixture system, motivated by the not insignificant challenge of quickly dissipating heat generated in metal-organic frameworks (MOFs) due to gas adsorption. Our study reveals that the thermal conductance of the system (crystal and gas) is dominated by lattice thermal conductivity in the crystal, and that conductance is reduced as the concentration of gas in the pores increases. This mechanism was observed from classical molecular simulations of a monatomic gas in an idealized porous crystal structure. We show that the decreased conductivity associated with increased gas concentration is due to phonon scattering in the crystal due to interactions with gas molecules. Calculations of scattering rates for two phonon modes reveal that scattering of the lowest frequency mode scales linearly with gas density. This result suggests that the probability of a phonon-gas collision is simply proportional to the number of gas...
ABSTRACT A review of studies focused on enhancing the thermal conductivity of phase change materi... more ABSTRACT A review of studies focused on enhancing the thermal conductivity of phase change materials (PCM) for thermal energy storage upon introduction of nanostructures is presented. These emerging materials have only been studied since 2005 and represent a clear departure from previous/existing practices of utilizing fixed, stationary high-conductivity inserts/structures into PCM. Carbon-based nanostructures (nanofibers, nanoplatelets and graphene flakes), carbon nanotubes, both metallic (Ag, Al, C/Cu and Cu) and metal oxide (Al2O3, CuO, MgO and TiO2) nanoparticles and silver nanowires have been explored as the materials of the thermal conductivity promoters. Emphasis of the work so far has been placed on the dependence of the enhanced thermal conductivity on mass fraction of the nanostructures and temperature for both liquid and solid phases, however issues related to modifications of the degree of supercooling, melting temperature, viscosity, heat of fusion, etc. are also reported. In general, carbon-based nanostructures and carbon nanotubes exhibit far greater enhancement of thermal conductivity in comparison to metallic/metal oxide nanoparticles due to the high aspect-ratio of these nanofillers. Utilizing a figure of merit for the observed thermal conductivity enhancement, the majority of 340+ measured data points in both liquid and solid phases are summarized.
Molecular dynamics simulations have been utilized to study thermal conductivity of liquid and sol... more Molecular dynamics simulations have been utilized to study thermal conductivity of liquid and solid mixtures of paraffin and carbon-based high aspect-ratio nano-additives, i.e. carbon nanotubes and graphene. In agreement with existing experimental data, we observe high enhancement in thermal conductivity through adding these graphitic nano-additives into paraffin, particularly in the solid phase. We demonstrate that this significant improvement is mainly achieved by the enhancement in thermal conductivity of the matrix itself. This is caused by carbon nanotubes and graphene promoting ordering of the matrix molecules which consequently leads to improvement of its thermal conductivity.
Characteristics of thermal conductivity in classical water models J. Chem. Phys. 138, 064505 (201... more Characteristics of thermal conductivity in classical water models J. Chem. Phys. 138, 064505 (2013) Thermoelectric properties of molten Bi2Te3, CuI, and AgI Appl. Phys. Lett. 102, 033903 (2013) Water droplets on a hydrophobic insulator surface under high voltages: A thermal perspective Appl. Phys. Lett. 101, 131602 (2012) Equilibrium molecular dynamics determination of thermal conductivity for multi-component systems J. Appl. Phys. 112, 054310 (2012) Nonequilibrium molecular dynamics simulations of the thermal conductivity of water: A systematic investigation of the SPC/E and TIP4P/2005 models J. Chem. Phys. 137, 074503 Additional information on J. Appl. Phys.
International Journal of Heat and Mass Transfer, 2013
Molecular dynamics simulations were utilized to investigate the relationship between the structur... more Molecular dynamics simulations were utilized to investigate the relationship between the structure of paraffins in solid and liquid states and its thermal conductivity. We observe that upon crystallization, a nanocrystalline paraffin structure develops and the value of thermal conductivity doubles, in agreement with experimental data. The introduction of carbon nanotubes or graphene layers leads to liquid ordering and associated thermal conductivity enhancement. More prominently, carbon nanofillers provide a template for directed crystallization and lead to even greater thermal conductivity increases. Our results indicate that introducing carbon nanotubes and graphene into long-chain paraffins leads to a considerable enhancement in thermal conductivity, not only due to the presence of a conductive filler, but also due to the filler-induced alignment of paraffin molecules.
Volume 4: Heat and Mass Transfer Under Extreme Conditions; Environmental Heat Transfer; Computational Heat Transfer; Visualization of Heat Transfer; Heat Transfer Education and Future Directions in Heat Transfer; Nuclear Energy, 2013
By utilizing molecular dynamics (MD) simulations, we study the interfacial thermal conductance at... more By utilizing molecular dynamics (MD) simulations, we study the interfacial thermal conductance at the interface of graphene and paraffin. In doing so, we conduct non-equilibrium heat source and sink simulations on systems of parallel and perpendicular configurations in which the heat flow is parallel and perpendicular to the surface of graphene, respectively. For the perpendicular configuration, graphene with different number of layers are considered. The results show that the interfacial thermal conductance decreases with the number of layers and converges to a value which is equal to the obtained conductance by using the parallel configuration. We also study the conductance for the solid phase paraffin. The results indicate that solid paraffin-graphene interfaces have higher conductance values with respect to the corresponding liquid phase systems.
We have studied the mechanisms of heat transfer in a porous crystal-gas mixture system, motivated... more We have studied the mechanisms of heat transfer in a porous crystal-gas mixture system, motivated by the not insignificant challenge of quickly dissipating heat generated in metal-organic frameworks (MOFs) due to gas adsorption. Our study reveals that the thermal conductance of the system (crystal and gas) is dominated by lattice thermal conductivity in the crystal, and that conductance is reduced as the concentration of gas in the pores increases. This mechanism was observed from classical molecular simulations of a monatomic gas in an idealized porous crystal structure. We show that the decreased conductivity associated with increased gas concentration is due to phonon scattering in the crystal due to interactions with gas molecules. Calculations of scattering rates for two phonon modes reveal that scattering of the lowest frequency mode scales linearly with gas density. This result suggests that the probability of a phonon-gas collision is simply proportional to the number of gas...
ABSTRACT A review of studies focused on enhancing the thermal conductivity of phase change materi... more ABSTRACT A review of studies focused on enhancing the thermal conductivity of phase change materials (PCM) for thermal energy storage upon introduction of nanostructures is presented. These emerging materials have only been studied since 2005 and represent a clear departure from previous/existing practices of utilizing fixed, stationary high-conductivity inserts/structures into PCM. Carbon-based nanostructures (nanofibers, nanoplatelets and graphene flakes), carbon nanotubes, both metallic (Ag, Al, C/Cu and Cu) and metal oxide (Al2O3, CuO, MgO and TiO2) nanoparticles and silver nanowires have been explored as the materials of the thermal conductivity promoters. Emphasis of the work so far has been placed on the dependence of the enhanced thermal conductivity on mass fraction of the nanostructures and temperature for both liquid and solid phases, however issues related to modifications of the degree of supercooling, melting temperature, viscosity, heat of fusion, etc. are also reported. In general, carbon-based nanostructures and carbon nanotubes exhibit far greater enhancement of thermal conductivity in comparison to metallic/metal oxide nanoparticles due to the high aspect-ratio of these nanofillers. Utilizing a figure of merit for the observed thermal conductivity enhancement, the majority of 340+ measured data points in both liquid and solid phases are summarized.
Molecular dynamics simulations have been utilized to study thermal conductivity of liquid and sol... more Molecular dynamics simulations have been utilized to study thermal conductivity of liquid and solid mixtures of paraffin and carbon-based high aspect-ratio nano-additives, i.e. carbon nanotubes and graphene. In agreement with existing experimental data, we observe high enhancement in thermal conductivity through adding these graphitic nano-additives into paraffin, particularly in the solid phase. We demonstrate that this significant improvement is mainly achieved by the enhancement in thermal conductivity of the matrix itself. This is caused by carbon nanotubes and graphene promoting ordering of the matrix molecules which consequently leads to improvement of its thermal conductivity.
Characteristics of thermal conductivity in classical water models J. Chem. Phys. 138, 064505 (201... more Characteristics of thermal conductivity in classical water models J. Chem. Phys. 138, 064505 (2013) Thermoelectric properties of molten Bi2Te3, CuI, and AgI Appl. Phys. Lett. 102, 033903 (2013) Water droplets on a hydrophobic insulator surface under high voltages: A thermal perspective Appl. Phys. Lett. 101, 131602 (2012) Equilibrium molecular dynamics determination of thermal conductivity for multi-component systems J. Appl. Phys. 112, 054310 (2012) Nonequilibrium molecular dynamics simulations of the thermal conductivity of water: A systematic investigation of the SPC/E and TIP4P/2005 models J. Chem. Phys. 137, 074503 Additional information on J. Appl. Phys.
International Journal of Heat and Mass Transfer, 2013
Molecular dynamics simulations were utilized to investigate the relationship between the structur... more Molecular dynamics simulations were utilized to investigate the relationship between the structure of paraffins in solid and liquid states and its thermal conductivity. We observe that upon crystallization, a nanocrystalline paraffin structure develops and the value of thermal conductivity doubles, in agreement with experimental data. The introduction of carbon nanotubes or graphene layers leads to liquid ordering and associated thermal conductivity enhancement. More prominently, carbon nanofillers provide a template for directed crystallization and lead to even greater thermal conductivity increases. Our results indicate that introducing carbon nanotubes and graphene into long-chain paraffins leads to a considerable enhancement in thermal conductivity, not only due to the presence of a conductive filler, but also due to the filler-induced alignment of paraffin molecules.
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Papers by Hasan Babaei