Analysis Of Flow And Heat Transfer Affected By Electrical Double Layer In Micro-channels

Significant improvements have been observed in microchannel applications and pressure-driven flows with developments in micro-technology.Micro-scale mechani-cal equipment generates high energy levels and therefore high temperatures are ob-served in these devices.Microchannel structures are used to reduce the elevated temperatures,where liquids with high conduction properties are used.In some cases,nano-particles are injected into the fluid in order to increase its conductivity.Flow properties of these fluids are affected by many factors due to small channel radius.One of these factors is the electrical effects from the formation of electrical double layer(EDL)within the channel.Although a wide range of research can be found on the subjects of microchannel flow,nanofluid flow and porous media,literature gaps exist in the context of flow behavior in the presence of electro-osmotic effects within these flows,such as EDL.This study therefore considers some pressure-driven microchannel flow cases with electrical effects from an EDL.This work aims to investigate electrical effects from an electrical double layer in various scenarios of micro-radius channel flow.In this context,four problems of microchannel flow in the presence of electro-kinetic effects from an electrical double layer are considered,where fluid flow and heat transfer analyses are performed with and without nanoparticles.These four problems are:an analysis of mixed convection in a vertical channel in the presence of electrical double layer;two-layer nanofluid flow in a microchannel with electro-osmotic effects by means of Buongiorno's model;entropy analysis of a nanofluid flow through a micro-radius pipe with electro-osmotic effects;and finally,an unsteady laminar flow of pulsating nature in a saturated porous microchannel is considered with EDL effects.Each problem is formulated through a set of governing equations,which primar-ily consists of the Poisson-Boltzmann equation for electrostatic potential,momentum equation for fluid flow,energy equation for heat transfer and Buongiorno's model(where applicable)for nano-particle volume fraction,depending on the physical as-sumptions of the system.Simplified through appropriate similarity transformations,the consequent system is solved through the homotopy analysis method for the first three problems,while the final problem is solved through a substitution approach.Highly accurate HAM solutions are validated through the maximum total average squared error.Different physical aspect,of the flow have been considered,such as the Nusselt number,the skin friction coefficient and the total entropy.The result,s show that electro-osmotic effects from EDL are higher when the electro-osmotic parameter has lower values.These effects seem to decrease and even-tually vanish as the electro-osmotic parameter increases to significantly higher values.However,these effects are negligible in the presence of an external electric field.Ad-ditionally7 heat transfer and skin friction coefficient in the flow are highly dependent on the electro-osmotic parameter,Grashof number and Hartman number(and Darcy number in case of channels with porous medium).Furthermore,the flow behavior is highly dependent on the thermophoresis diffusion and viscosity.Therefore,total entropy of the system changes with change in the Hartman number,the Brinkman number,the electro-osmotic parameter and the thermophoretic parameter.In the case of unsteady pulsating flow,the flow also depends on the angular velocity.This work therefore presents a base to study further effects of electrical double layer on micro-scale flows.