Pressure-Driven Gas Flows in Long Rectangular Microchannels With Uniform Heat Flux Boundary Conditions

2010 ◽  
Author(s):  
Zhanyu Sun ◽  
Yogesh Jaluria
Keyword(s):  
Heat Flux ◽  
Boundary Conditions ◽  
Viscous Dissipation ◽  
Knudsen Number ◽  
Uniform Heat Flux ◽  
Pressure Work ◽  
Uniform Heat ◽  
Compressibility Effects ◽  
Rarefaction Effects ◽  
Pressure Driven

This paper focuses on the numerical simulation of pressure-driven gas flow in long microchannels, with uniform heat flux wall boundary conditions. The flow is assumed to be two-dimensional and the momentum and energy equations are solved, considering variable properties, rarefaction effects, including velocity slip, thermal creep and temperature jump, compressibility effects and viscous dissipation. A combined serial-parallel algorithm is employed to simulate the flow in long microchannels. The numerical solution is found to be much more involved than that for the isothermal boundary conditions and the convergence of the scheme to be much slower, as expected. The numerical results are also quite different and, in some cases, quite unexpected. The thermal and hydraulic characteristics are carefully examined and analyzed. It is found that a nonlinear temperature profile arises along the microchannel due to the combined effects of pressure work and viscous dissipation. Similarly, compressibility effects lead to a nonlinear centerline pressure profile. The ratio of pressure work to viscous dissipation is investigated as a function of the Knudsen number and is found to increase with the Knudsen number. The rarefaction effects are found to increase the Nusselt number near the outlet and to decrease it near the inlet. An increase in the inlet/outlet pressure ratio is seen to significantly enhance microchannel cooling.

Numerical Investigation on Viscous Dissipation Effect in Forced Convection in Rectangular Microchannels With Nanofluids

2016 ◽  
Author(s):  
Bernardo Buonomo ◽  
Luca Cirillo ◽  
Davide Ercole ◽  
Oronzio Manca ◽  
Sergio Nardini
Keyword(s):  
Heat Flux ◽  
Numerical Investigation ◽  
Forced Convection ◽  
Viscous Dissipation ◽  
Convection Flow ◽  
Uniform Heat Flux ◽  
Inlet Section ◽  
Transfer Coefficients ◽  
Rectangular Microchannel ◽  
Uniform Heat

In this paper a numerical investigation on laminar forced convection flow of a water-Al2O3 nanofluid in a rectangular microchannel, taking into account the viscous dissipation, is accomplished. A constant and uniform heat flux on the external surfaces has been applied and a single-phase model approach has been employed. The analysis has been performed in steady state regime for particle size in nanofluids equal to 38 nm. The CFD commercial code Ansys-Fluent has been employed in order to solve the 3-D numerical model. The geometrical configuration under consideration consists in a duct with a rectangular shaped crossing area. A steady laminar incompressible flow with viscous dissipation and different nanoparticle volume fractions has been considered. The base fluid is water and nanoparticles are made up of alumina (Al2O3). Thermo-physical properties of the nanofluid are considered constant with temperature. The length the edge and height of the duct are 0.030 m, 1.7 × 10−7 and 1.1 × 10−7 m, respectively. A constant and uniform heat flux q on the top wall is applied, the others are adiabatic and at the inlet section uniform temperature and velocity profiles are assumed. The results showed the increase of the convective heat transfer coefficients, in particular, for high concentration of nanoparticles and for increasing values of Reynolds number. However, the disadvantages are represented by the growth of the wall shear stress and the required pumping power, observed in particular, at high particle concentrations.

Two-phase investigation of water-Al2O3 nanofluid in a micro concentric annulus under non-uniform heat flux boundary conditions

2019 ◽  
Vol 30 (4) ◽  
pp. 1795-1814 ◽  
Author(s):  
Davood Toghraie ◽  
Ramin Mashayekhi ◽  
Hossein Arasteh ◽  
Salman Sheykhi ◽  
Mohammadreza Niknejadi ◽  
...  
Keyword(s):  
Heat Flux ◽  
Reynolds Number ◽  
Boundary Conditions ◽  
Surface Area ◽  
Uniform Heat Flux ◽  
Two Phase ◽  
Content Type ◽  
Concentric Annulus ◽  
Uniform Heat ◽  
Flux Boundary Conditions

Purpose This is a 3D numerical study of convective heat transfer through a micro concentric annulus governing non-uniform heat flux boundary conditions employing water-Al2O3 nanofluid. The nanofluid is modeled using two-phase mixture model, as it has a good agreement to experimental results. Design/methodology/approach Half of the inner pipe surface area of the annulus section of a double pipe heat exchanger is exposed to a constant heat flux which two models are considered to divide the exposing surface area to smaller ones considering the fact that in all cases half of the inner pipe surface area has to be exposed to the heat flux: in model (A), the exposing surface area is divided radially to two parts (A1), four parts (A2) and eight parts (A3) by covering the whole length of the annulus and in model (B) the exposing surface area is divided axially to two parts (B1), four parts (B2) and eight parts (B3) by covering half of the annulus radially. Findings The results reveal that model (B) leads to higher Nusselt numbers compared to model (A); however, at Reynolds number 10, model (A3) exceeds model (B3). The average Nusselt number is increased up to 142 and 83 per cent at models (A3) with Reynolds number 10 and model (B3) with Reynolds number 1000, respectively. Originality/value This paper is a two-phase investigation of water-Al2O3 nanofluid in a micro concentric annulus under non-uniform heat flux boundary conditions.

Sign in / Sign up

Export Citation Format

Share Document