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

Abstract

-Enhanced heat transfer in tubes under laminar flow conditions can be found in coils or corrugated tubes or in the presence of high wall relative roughness, curves, pipe fittings or mechanical vibration. Modeling these cases can be complex because of the induced secondary flow. A modification of the Graetz problem for non-Newtonian power-law flow is proposed to take into account the augmented heat transfer by the introduction of an effective radial thermal diffusivity. The induced mixing was modeled as an increased radial heat transfer in a straight tube. Three experiments using a coiled tube and a tubular heat exchanger with high relative wall roughness are presented in order to show how this parameter can be obtained. Results were successfully correlated with Reynolds number. This approach can be useful for modeling laminar flow reactors (LFR) and tubular heat exchangers available in the chemical and food industries.

Modeling sterilization value and nutrient degradation in the thermal processing of liquid foods under diffusive laminar flow with associations of tubular heat exchangers

“…Based on the case study with: D efA = 10 −5 m 2 .s −1 and F heat1 = 15, Figure allows observing the influence of the diffusion parameters change. Methods for estimating the effective radial conductivity of heat are described by Morais and Gut () while method for determine effective radial diffusivities under laminar flow are presented by Dantas et al ().…”

“…Enhanced diffusion can occur due to corrugated tube wall, high relative wall roughness, mechanical vibration or presence of curves or coils (Bergles & Joshi, ). In the case of heat transfer, Morais and Gut () defined an enhancement factor for the radial diffusivity ( F h eat ) that multiplies the thermal conductivity of the fluid, and consequently the thermal diffusivity ( α = k / ρ. C p ).…”

“…Since the inner tube of the ViscoLine™ Monotube is corrugated, effective diffusion parameters were used for product flow: D efA = 10 −5 m 2 .s −1 (Dantas et al, ) F heat1 = 15 (Morais & Gut, ). The reference mass diffusion value for liquid–liquid systems is 10 −9 m 2 s −1 (Bird et al, ; Foster & Cussler, ).…”

“…Heat and mass diffusions can be enhanced in laminar flow with the use of coiled tubes or corrugated tubes. Moreover, mechanical vibration or high relative wall roughness can also induce mixing under laminar flow (Bergles & Joshi, ; Dantas, Pegoraro, & Gut, ; Morais & Gut, ).…”

Prediction of mass transfer parameters and thermodynamic properties using the refractance WindowTM technique for drying of Yam (Dioscorea Trifida) paste

“…Optimal control of the drying process is fundamental and requires complete information on the drying behavior of the materials, requiring an accurate model capable of predicting water removal rates and describing the drying performance of each product under certain conditions (Khatchatourian et al, 2013). Mathematical models are an effective tool in the development, design, and improvement of drying systems and analysis of mass transfer phenomena during the drying process (Silva et al, 2014;Morais & Gut, 2015;Zarein et al, 2015;Qiu et al, 2018). Dincer & Dost (1995) developed analytical models to characterize the mass transfer during drying of objects presenting regular geometry (plate, cylinder, and sphere) and based on the assumption that the effective moisture diffusivity during drying process remains constant.…”