It is highly desirable to understand the fluid flow and the heat transfer characteristics of buoyancy-induced micropump and microheat exchanger in microfluidic and thermal systems. In this study, we analytically investigate the fully developed natural convection in an open-ended vertical parallel-plate microchannel with asymmetric wall temperature distributions. Both of the velocity slip and the temperature jump conditions are considered because they have countereffects both on the volume flow rate and the heat transfer rate. Results reveal that in most of the natural convection situations, the volume flow rate at microscale is higher than that at macroscale, while the heat transfer rate is lower. It is, therefore, concluded that the temperature jump condition induced by the effects of rarefaction and fluid-wall interaction plays an important role in slip-flow natural convection.
Thermal creep occurs in anisothermal gas microflow. It is highly desirable to understand the creep effect on the flow and heat transfer characteristics for developing natural convective microflow. In this study, we investigate the steady developing natural convective flow in an open-ended vertical parallel-plate microchannel with asymmetric wall temperature distributions. The boundary-layer equations subject to the boundary conditions with respect to dynamic pressure at the channel entry as well as higher-order jump temperature and slip velocity with thermal creep along the channel surface are employed. The mathematical model and the numerical code are validated through available macroscale work. Numerical solutions of high-order slip coefficient, slip/jump, velocity, pressure, temperature, flow rate, flow drag and heat transfer rate are presented for air at the standard reference state with complete accommodation. It is found that thermal creep has significant effect on the high-order slip effect and the flow and thermal fields. The creep effect is to increase the flow rate; moreover, valuable reduced flow drag and enhanced heat transfer are obtained.
Thermal creep occurs in gas microflow with wall heat fluxes. In this study, we investigate the creep effect on the steady natural convection in an open-ended vertical parallel-plate microchannel with asymmetric wall heat fluxes. The fully developed solutions for the velocity, pressure, temperature, flow rate, flow drag and heat transfer rate are derived analytically and presented for air at the standard reference state with complete accommodation. It is found that thermal creep has a significant effect. The effect is to unify the velocity and pressure and to elevate the temperature. Moreover, it tends to enhance the flow rate and heat transfer rate and to reduce the maximum gas temperature and flow drag. Its logarithm can be magnified by the decrease in the channel length and the increase in the Knudsen number.
Anisothermal flow prevails in a heated microchannel. It is desirable to understand the influence of temperature-dependent physical properties on the flow and heat transfer characteristics for natural convective gas microflow. In this study, formulas for the shear viscosity, thermal conductivity, constant-pressure specific heat, density, and molecular mean free path are proposed in power-law form and validated through experimental data. Natural convective gas flow with variable physical properties in a long open-ended vertical parallel-plate microchannel with asymmetric wall temperature distributions is further investigated. The full Navier–Stokes equations and energy equation combined with the first-order slip∕jump boundary conditions are employed. Analysis process shows that the compressibility and viscous dissipation terms in balance equations are negligible. Numerical solutions are presented for air at the standard reference state with complete accommodation. It is found that the effect of variable properties should be considered for hotter-wall temperatures greater than 306.88K. The effect is to advance the velocity slip and temperature jump as well as the velocity symmetry and temperature nonlinearity. Moreover, it tends to reduce the mass flow rate and the local heat transfer rate excluding on the cooler-wall surface where the temperature-jump effect prevails over the temperature-nonlinearity effect. Increasing the cooler-wall temperature magnifies the effect on flow behavior but minifies that on thermal behavior.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.