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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 ρ(T), μ(T), and k(T) on convection and friction characteristics in isolation and in combination. For the case of heated water, μ(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 ρ(T) and μ(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.