NUMERICAL STUDY OF MICROCONVECTIVE WATER-FLOW CHARACTERISTICS WITH VARIATIONS IN PROPERTIES

A numerical program is developed to solve two-dimensional continnum-based governing differential equations for liquid flow in axisymmetric circular microchannel geometry. The effects of variable thermal properties in single-phase laminar forced convection with constant wall heat flux boundary conditions are studied. The numerical analysis of fully developed flow behavior investigates the effect of rho(T), mu(T), and k(T) on convection and friction characteristics in isolation and in combination. For the case of heated water, mu(T) variation and k(T) variation increases the Nusselt number due to the following effects: (1) nonnegligible radial convection causes flattening of the axial velocity profile, (2) reduction in wall temperature and axial bulk mean fluid temperature causes significant axial conduction along the flow. The effect of.(T) and mu(T) variation on friction is indirect as follows: the viscosity gradient and shear stress at the wall reduce along the flow; therefore, the Poiseuille number deviates from constant properties solution (Po = 64). The investigations also showed that pressure drop significantly differs at the microscale compared to the macroscale

Numerical Investigation on Laminar Microconvective Liquid Flow With Entrance Effect and Graetz Problem due to Variation in Thermal Properties

This work deals with the analysis of forced convection in single-phase laminar flow of liquid through microsized circular geometry with a diameter of 100 x 10(-6) m. The problem with hydrodynamically and thermally developing flow in the entrance region with no-slip, no-temperature jump and constant wall heat flux boundary condition is numerically studied. Two-dimensional (with axisymmetry) simulation is carried out to understand the effect of fluid property variations on flow development and heat transfer. Pure continuum-based governing equations are solved to predict the significance of momentum and energy transport due to temperature-dependent viscosity and thermal conductivity variation, respectively. The radial inward flow is induced due to temperature-dependent density variation that sharpens the axial velocity profile. The investigation also analyzes the change in Nusselt number with locations in the channel for Graetz problem with uniform heating condition. The flattening of axial velocity profile, radial temperature profile, and inward radial flow influences the heat flow characteristics. The investigations in computational domain show that Nusselt number in thermal entrance region deviates from constant properties solution due to scaling effects

Numerical study of compressible convective heat transfer with variations in all fluid properties

The effects of property variations in single-phase laminar forced micro-convection with constant wall heat flux boundary condition are investigated in this work. The fully-developed flow through micro-sized circular (axisymmetric) geometry is numerically studied using two-dimensional continuum-based conservation equations. The non-dimensional governing equations show significance of momentum transport in radial direction due to mu(T) variation and energy transport by fluid conduction due to k(T) variation. For the case of heated air, variation in C(p)(T) and k(T) causes increase in Nu. This is owing to: (i) reduction in T(w) (T(w)-T(m)), and (delta T/delta r)(w) and (ii) change in delta T(m)/delta z results in axial conduction along the flow. The effects of rho(p,T) and mu(T) variation on convective-flow are indirect and lead to: (i) induce radial velocity which alters u(r) profile significantly and (ii) change in (delta u/delta r)(w) along the flow. It is proposed that the deviation in convection with C(p)(T), k(T) variation is significant through temperature field than rho(p,T), mu(T) variation on velocity field. It is noted that Nu due to variation in properties differ from invariant properties (Nu = 48/11) for low subsonic flow. (C) 2009 Elsevier Masson SAS.