arXiv subjects

Shalabh C. Maroo

Publications and source records attributed to Shalabh C. Maroo.

8 recordsLinked to original sources

arXiv2022

Molecular Dynamics Simulation of Bubble Nucleation in Hydrophilic Nanochannels by Surface Heating

Bubble nucleation in liquid confined in nanochannel is studied using molecular dynamics simulations and compared against nucleation in the liquid over smooth (i.e. without confinement). Nucleation is achieved by heating part of a surface to high temperatures using a surface-to-liquid heating algorithm implemented in LAMMPS. The surface hydrophilicity of nanochannels is increased to understand its effect on nucleation behavior. Liquid structuring is found to play a significant role in altering thermodynamic properties of density and pressure in the nanochannels, which in turn changes the enthalpy of vaporization. Increased surface hydrophilicity in nanochannels results in the delay of bubble formation as more energy is required for nucleation. Thus, bubble nucleation in hydrophilic nanochannels can dissipate higher heat fluxes and can potentially be used towards the thermal management of hot spots in power electronics.

physics.flu-dyn↗

arXiv2021

Disjoining Pressure Driven Transpiration of Water in a Simulated Tree

We present an investigation of transpiration of water in a 100 m tall tree using continuum simulations. Disjoining pressure is found to induce absolute negative pressures as high as -23.5 atm at the liquid-vapor meniscus during evaporation, thus presenting a sufficient stand-alone explanation of the transpiration mechanism. In this work, we begin by first developing an expression of disjoining pressure in a water film as a function of distance from the surface from prior experimental findings. The expression is then implemented in a commercial computational fluid dynamics solver and the disjoining pressure effect on water wicking in nanochannels of height varying from 59 nm to 1 micron is simulated. The simulation results are in excellent agreement with experimental data, thus demonstrating and validating that near-surface molecular interactions can be integrated in continuum numerical simulations through the disjoining pressure term. Following the implementation, we simulate the transpiration process of passive water transport over a height of 100 m by using a domain comprising of nanopore connected to a tube with a ground-based water tank, thus mimicking the stomata-xylem-soil pathway in trees. By varying the evaporation rate from liquid-vapor interface in the nanopore, effects on naturally-created pressure difference and liquid flow velocity are estimated. Further, kinetic theory analysis is performed to study the combined effect of absolute negative liquid-film pressure and accommodation coefficient on the maximum mass flux feasible during transpiration. Continuum simulations coupled with kinetic theory reiterate the existence of an upper limit to height of trees. The numerical model developed here is adept to be employed to design and advance several other nanofluidics-based natural and engineering systems.

physics.flu-dyn↗

arXiv2021

Disjoining Pressure of Water in Nanochannels

Experiments of water wicking in 1D silicon-dioxide nanochannels of heights 59 nm, 87 nm, 124 nm and 1015 nm are used to estimate the disjoining pressure of water which was found to be as high as ~1.5 MPa while exponentially decreasing with increasing channel height. Such a relation resulting from curve fitting of experimentally-derived data was implemented and validated in computational fluid dynamics. This methodology integrates experimental nanoscale physics into continuum simulations thus enabling the numerical study of various phenomena where disjoining pressure plays an important role.

physics.flu-dyn↗

arXiv2021

Implementation of Near-Surface Disjoining Pressure Effect in Continuum Simulations

An expression of disjoining pressure in a water film, as a function of distance from the surface, is developed from prior experimental findings. The expression is implemented in commercial computational fluid dynamics solver and disjoining pressure effect on water wicking in nanochannels of height varying from 59 nm to 1 micron is simulated. The simulation results are in excellent agreement with experimental data, thus demonstrating and validating that near-surface molecular interactions can be integrated in continuum numerical simulations through the disjoining pressure term. Such an implementation can be used to design and advance nanofluidics-based engineering systems.

physics.flu-dyn↗

arXiv2021

Thermal Management of Photovoltaics using Porous Nanochannels

The photoelectric conversion efficiency of a solar cell is dependent on its temperature. When the solar radiation is incident on the photovoltaics (PV) panel, a large portion of it is absorbed by the underlying material which increases its internal energy leading to the generation of heat. An overheated PV panel results in a decline in its performance which calls for an efficient cooling mechanism that can offer an optimum output of the electrical power. In the present numerical work, thermal management with a porous nanochannels device capable to dissipate high heat flux is employed to regulate the temperature of a commercial PV panel by integrating the device on the back face of the panel. The spatial and temporal variation of the PV surface temperature is obtained by solving the energy balance equation numerically. By evaluating the steady-state PV surface temperature with and without thermal management, the extent of cooling and the resulting enhancement in the electrical power output is studied in detail. The nanochannels device is found to reduce the PV surface temperature significantly with an average cooling of 31.5 oC. Additionally, the enhancement in the electrical power output by ~33% and the reduction in the response time to 1/8th highlight the potential of using porous nanochannels as a thermal management device. Furthermore, the numerical method is used to develop a universal curve which can predict the extent of PV cooling for any generic thermal management device.

physics.app-ph↗

arXiv2021

Nano-Confinement Effects on Liquid Pressure

In this work, molecular dynamics simulations are performed to estimate the equilibrium pressure of liquid confined in nanopores. The simulations show that the pressure is highly sensitive to the pore size and can significantly change from absolute positive to negative values for a very small (0.1 nm) change in pore size. The contribution from the solid-liquid interaction always dominates the pressure in the first liquid layer adjacent to the surface and the sensitiveness of pressure on the pore size is due to the atom distribution in the liquid layers. A surface influence number S is introduced to quantitatively characterize the degree of the confinement. The S number decreases with increasing pore size based on a power law function at constant system temperature. In nanopores with large S number, the pore liquid pressure is found to be independent of bulk liquid pressure while the pore pressure increases with bulk pressure in nanopores with small S number.

cond-mat.soft↗

arXiv2020

Droplet Evaporation on Porous Nanochannels for High Heat Flux Dissipation

Droplet wicking and evaporation in porous nanochannels is experimentally studied on a heated surface at temperatures ranging from 35oC to 90oC. The fabricated geometry consists of cross-connected nanochannels of height 728 nm with micropores of diameter 2 um present at every channel intersection; the pores allow water from a droplet placed on the top surface to wick into the channels. Droplet volume is also varied and a total of 16 experimental cases are conducted. Wicking characteristics such as wicked distance, capillary pressure, viscous resistance and propagation coefficient are obtained at the high surface temperatures. Evaporation flux from the nanochannels/micropores is estimated from the droplet experiments, but is also independently confirmed via a new set of experiments where water is continuously fed to the sample through a microtube such that it matches the evaporation rate. Heat flux as high as ~294 W/cm2 is achieved from channels and pores. The experimental findings are applied to evaluate the use of porous nanochannels geometry in spray cooling application, and is found to be capable of dissipating high heat fluxes upto ~77 W/cm2 at temperatures below nucleation, thus highlighting the thermal management potential of the fabricated geometry.

physics.app-ph↗

arXiv2015

A new algorithm for contact angle estimation in molecular dynamics simulations

It is important to study contact angle of a liquid on a solid surface to understand its wetting properties, capillarity and surface interaction energy. While performing transient molecular dynamics (MD) simulations it requires calculating the time evolution of contact angle. This is a tedious effort to do manually or with image processing algorithms. In this work we propose a new algorithm to estimate contact angle from MD simulations directly and in a computationally efficient way. This algorithm segregates the droplet molecules from the vapor molecules using Mahalanobis distance (MND) technique. Then the density is smeared onto a 2D grid using 4th order B-spline interpolation function. The vapor liquid interface data is estimated from the grid using density filtering. With the interface data a circle is fitted using Landau method. The equation of this circle is solved for obtaining the contact angle. This procedure is repeated by rotating the droplet about the vertical axis. We have applied this algorithm to a number of studies (different potentials and thermostat methods) which involves the MD simulation of water.

cond-mat.soft↗