Heat transfer coefficients from Newtonian and non-Newtonian fluids flowing in laminar regime in a helical coil

Abstract

A B S T R A C TThis study aimed to carry out experimental work to obtain, for Newtonian and non-Newtonian fluids, heat transfer coefficients, at constant wall temperature as boundary condition, in fully developed laminar flow inside a helical coil. The Newtonian fluids studied were aqueous solutions of glycerol, 25%, 36%, 43%, 59% and 78% (w/w) and the non-Newtonian fluids aqueous solutions of carboxymethylcellulose (CMC), a polymer, with concentrations 0.1%, 0.2%, 0.3%, 0.4% and 0.6% (w/w) and aqueous solutions of xanthan gum (XG), another polymer, with concentrations 0.1% and 0.2% (w/w). According to the rheological study performed, the polymer solutions had shear thinning behavior and different values of elasticity. The heli-cal coil used has internal diameter, curvature ratio, length and pitch, respectively: 0.004575 m, 0.0263, 5.0 m and 11.34 mm. The Nusselt numbers for the CMC solutions are, on average, slightly higher than those for Newtonian fluids, for identical Prandtl and generalized Dean numbers. As outcome, the viscous component of the shear thinning polymer tends to potentiate the mixing effect of the Dean cells. The Nusselt numbers of the XG solutions are significant lower than those of the Newtonian solutions, for identical Prandtl and generalized Dean numbers. Therefore, the elastic component of the polymer tends to diminish the mixing effect of the Dean cells. A global correlation, for Nusselt number as a function of Péclet, generalized Dean and Weissenberg numbers for all Newtonian and non-Newtonian solutions studied, is presented.K e y w o r d s

Design of Heat Transfer Surfaces in Agitated Vessels

“…Moreover, it is an equipment that has low cost and it is easy to build [21]. The increase on the heat transfer through this kind of surface has two disadvantages: the need for baffles to avoid the formation of vortexes and the difficulty of maintenance and cleaning when submitted to fouling fluids.…”

Determination of the Effective Radial Thermal Diffusivity for Evaluating Enhanced Heat Transfer in Tubes Under Non-Newtonian Laminar Flow

“…Mixing in laminar flow can also be induced by high relative wall roughness, mechanical vibration or the presence of fittings or curves. Since the mathematical modeling of these systems can be rather complex (Bergles and Joshi, 1983;Pimenta and Campos, 2013), the use of the straight tube model derived in this section with an "effective radial thermal diffusivity" (α eff ≥ α) is suggested. The augmentation of the heat transfer due to mixing in laminar flow could be modeled as a higher thermal diffusivity acting in the radial direction.…”

“…In the case of coiled tubes or corrugated tubes under laminar flow, the development of secondary flows improves fluid mixing and, consequently, heat transfer. However, the mathematical modeling of these cases is more complex and studies often rely on empirical correlations (Barba et al, 2002;Vicente et al, 2004;Naphon, 2007;Pimenta and Campos, 2013;Pawar and Sunnapwar, 2013).…”

HCharacterization of Pressure Drops and Heat Transfer of Non-Newtonian Power-Law Fluid Flow Flowing in Chaotic Geometry

“…Since the work realized by Dean [3] and [4] where he initiated theoretical studies of viscous flow, the curved pipes are widely studied numerically and experimentally. The Dean vortexes formed in these ducts have a significant effect on the pressure loss and heat transfer of non-Newtonian fluids flow [5][6][7][8]. The second alternative method is to create chaotic trajectories [9] while keeping the laminar flow that ensures the efficient stretching and folding of material lines.…”