CFD analysis Of printed circuit heat exchanger

Abstract

Printed Circuit compact heat exchangers that are increasingly being used for viscous media thermal processing applications have semicircular flow channels. But due to some manufacturing constraints, these become semi elliptical in nature. In practice, these channels have very small hydraulic diameters and relatively large (L/dh). Because of length scales and the viscous nature of the fluids being handled, the flows are generally laminar and both hydro dynamically and thermally fully developed. At first, fully developed laminar flow and heat transfer in straight circular smooth duct under constant heat flux has been studied using FLUENT and fanning friction factor, Nusselt no. and Colburn factor have been calculated to check the accuracy of the solution using this package. Then following the same procedure, fully developed laminar flow and heat transfer in three-dimensional, periodic straight duct as well as sinusoidal duct with semiellptic cross section with different aspect ratios are considered. Computational Fluid Dynamics (CFD) using FLUENT is used to investigate the effect of Reynolds number (50 ≤ Re ≤ 500), aspect ratio of semi elliptical cross-sections for straight duct and amplitude to wavelength ratio(A/L=0.3 & 0.5) for sinusoidal channel(with L/D=4.5) on heat transfer enhancement and pressure drop for steady, incompressible, constant property, air (Pr=0.7044) flows under the constant wall heat flux boundary conditions. Velocity, temperature fields, Fanning friction factor, Colburn factor, good ness factor are being studied. Due to the interruption of the boundary layers formed near the solid surface and replacement of the boundary layer with the fluid from the core, thus creating a new boundary layer with an increased temperature gradient, the overall heat transfer coefficient as well as the pressure drop penalty in case of sinusoidal ducts increase as compared to straight ducts. Finally correlations between the Fanning friction factor and Colburn factor with Reynolds number and geometrical parameters have been found out for the above geometries.