Browsing by Author "Murad, Sohail"

Now showing 1 - 5 of 5
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    Dynamics of Nanoscale Jet Formation And Impingement on Flat Surfaces
    Murad, Sohail; Puri, Ishwar K. (AIP Publishing, 2007-12-01)
    Molecular-dynamics simulations are used to investigate the formation of water nanojets. The fluid is forced through a nano-orifice to establish a nanojet, which then impinges on a flat surface. The simulations show that to produce jets in the 1 nm diameter range, the orifice surface must be hydrophobic, otherwise the nanojet kinetic energy/inertia may never be able to overcome the attractive forces of the surface to form a jet. In addition, for the nanojet to form a stable liquid film on the surface of impingement, the surface cannot be either hydrophobic or too hydrophilic. Finally the stability/formation of the nanojet is not sensitive to the orifice surface temperature. The same physical laws that govern flows at the micro- and macroscales adequately describe nanojet flows in the absence of strong interfacial forces.
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    A thermal logic device based on fluid-solid interfaces
    Murad, Sohail; Puri, Ishwar K. (AIP Publishing, 2013-05-01)
    Thermal rectification requires that thermal conductivity not be a separable function of position and temperature. Investigators have considered inhomogeneous solids to design thermal rectifiers but manipulations of solid lattices are energy intensive. We propose a thermal logic device based on asymmetric solid-fluid resistances that couples two fluid reservoirs separated by solid-fluid interfaces. It is the thermal analog of a three terminal transistor, the hot reservoir being the emitter, the cold reservoir the output, and smaller input reservoirs as the base. Changing the input temperature alters the transport factor and the flux gain as does the base current in a transistor. (C) 2013 AIP Publishing LLC.
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    Thermal rectification in a fluid reservoir
    Murad, Sohail; Puri, Ishwar K. (AIP Publishing, 2012-03-01)
    An organized nonuniform mass distribution in solids leads to a monotonically varying thermal conductivity in a nanomaterial so that the heat flux is directionally dependent. We investigate through molecular dynamics simulations if the influence of an organized mass distribution in a fluid also leads to thermal rectification. Heat transfer is monitored in a water reservoir placed between two (hot and cold) silicon walls. The distribution of the fluid in the reservoirs is organized by applying an external force to each water molecule in a specified direction, creating a density gradient. This external force is smaller than the intermolecular forces in water, in most cases by much more than an order of magnitude. The simulations reveal that mass graded fluid-containing nanosystems can be engineered to possess an asymmetric axial thermal conductance that leads to greater heat flow in the direction of decreasing mass density. The rectification improves as the thermal conductivity is enhanced by increasing the fluid density adjacent to a hot wall, since doing so decreases the interfacial resistance and increases the heat flux. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3696022]
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    Thermal transport across nanoscale solid-fluid interfaces
    Murad, Sohail; Puri, Ishwar K. (AIP Publishing, 2008-03-01)
    An explanation for the effective thermal resistance R(K) can be based on the impedance to the passage of thermal phonons across an interface. We conjecture that (1) increasing the fluid pressure, and (2) making an interface more hydrophilic should facilitate better acoustic matching and thus lower R(K). Our molecular dynamics simulations confirm this. Overall, R(K) decreases with increasing temperature and is inversely proportional to the heat flux.
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    Thermal transport through superlattice solid-solid interfaces
    Murad, Sohail; Puri, Ishwar K. (AIP Publishing, 2009-08-01)
    Using molecular dynamics, we consider the thermal resistances of superlattices consisting of varying numbers of distinct nanolayers of two different materials. These are placed between two water reservoirs at uniform hot and cold temperatures. The interfacial resistances produced between different solid layers can lead to significantly lower heat transfer for a specified temperature difference. Such a large reduction in thermal transport cannot be explained by the interfacial resistance alone. In addition to the interfacial resistance between two adjacent superlattice layers, the relatively wide thermal boundary layers that are produced adjacent to the interfaces introduces a supplementary resistance.