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Flow and Heat or Mass Transfer in the Chemical Process...
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Flow and Heat or Mass Transfer in the Chemical Process Industry

A special issue of Fluids (ISSN 2311-5521).

Deadline for manuscript submissions: closed (15 December 2017) | Viewed by 85888

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Prof. Dr. Dimitrios V. Papavassiliou

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Guest Editor
School of Chemical, Biological, and Materials Engineering, The University of Oklahoma, Norman, OK 73019, USA
Interests: hemodynamics; nanofluidics; computational transport; turbulent transport; flow and transport in porous media
Special Issues, Collections and Topics in MDPI journals
Dr. Quoc T. Nguyen

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Guest Editor
School of Chemical, Biologicl, and Materials Engineering, The University of Oklahoma, Norman, OK 73019, USA
Interests: turbulent transport; hemodynamis; numerical fluid mechanics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Flow through process equipment in a chemical or manufacturing plant (e.g., heat exchangers, reactors, catalyst regeneration units, separation units, pumps, pipes, smoke stacks, etc.) is usually coupled with heat and/or mass transfer. Rigorous investigation of this coupling of momentum, heat, and mass transfer is not only important for the practice of designing process equipment, but is also important for improving our overall theoretical understanding of transfer phenomena. While generalizations and empiricisms, like the concept of the heat transfer coefficient or the widely used Reynolds analogy in turbulence, or the use of empirical transfer equations for flow in separation towers and reactors packed with porous media, have served practical needs in prior decades, such empiricisms can now be revised or altogether replaced by bringing modern experimental and computational tools to bear in understanding the interplay between flow and transfer. The patterns of flow play a critical role in enhancing the transfer of heat and mass. Typical examples are the coherent flow structures in turbulent boundary layers, which are responsible for turbulent transfer and mixing in a heat exchanger and for dispersion from a smoke stack, and the flow patterns that are a function of the configuration of a porous medium and are responsible for transfer in a fixed bed reactor or a fluid bed regenerator unit. The goal of this special issue is to be a forum for recent developments in theory, state-of-the-art experiments and computations on the interactions between flow and transfer in single and multi-phase flow, and from small scales to large scales, which can be important for the design of equipment in a chemical processing plant.

Prof. Dr. Dimitrios V. Papavassiliou
Dr. Quoc T. Nguyen
Guest Editors

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Keywords

  • convective transfer
  • turbulent dispersion
  • transfer in porous media
  • transfer in multi-phase flow
  • passive scalar transfer
  • mixing
  • heat transfer in nanofluids
  • large eddy simulation modeling for heat transfer
  • thermal lattice Boltzman simulations
  • computational modeling of heat and fluid flow

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Published Papers (15 papers)

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Editorial

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3 pages, 159 KiB  
Editorial
Flow and Heat or Mass Transfer in the Chemical Process Industry
by Dimitrios V. Papavassiliou and Quoc Nguyen
Fluids 2018, 3(3), 61; https://doi.org/10.3390/fluids3030061 - 28 Aug 2018
Cited by 1 | Viewed by 2878
Abstract
n/a Full article
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)

Research

Jump to: Editorial

16 pages, 10707 KiB  
Article
Quality Measures of Mixing in Turbulent Flow and Effects of Molecular Diffusivity
by Quoc Nguyen and Dimitrios V. Papavassiliou
Fluids 2018, 3(3), 53; https://doi.org/10.3390/fluids3030053 - 30 Jul 2018
Cited by 2 | Viewed by 4994
Abstract
Results from numerical simulations of the mixing of two puffs of scalars released in a turbulent flow channel are used to introduce a measure of mixing quality, and to investigate the effectiveness of turbulent mixing as a function of the location of the [...] Read more.
Results from numerical simulations of the mixing of two puffs of scalars released in a turbulent flow channel are used to introduce a measure of mixing quality, and to investigate the effectiveness of turbulent mixing as a function of the location of the puff release and the molecular diffusivity of the puffs. The puffs are released from instantaneous line sources in the flow field with Schmidt numbers that range from 0.7 to 2400. The line sources are located at different distances from the channel wall, starting from the wall itself, the viscous wall layer, the logarithmic layer, and the channel center. The mixing effectiveness is quantified by following the trajectories of individual particles with a Lagrangian approach and carefully counting the number of particles from both puffs that arrive at different locations in the flow field as a function of time. A new measure, the mixing quality index Ø, is defined as the product of the normalized fraction of particles from the two puffs at a flow location. The mixing quality index can take values from 0, corresponding to no mixing, to 0.25, corresponding to full mixing. The mixing quality in the flow is found to depend on the Schmidt number of the puffs when the two puffs are released in the viscous wall region, while the Schmidt number is not important for the mixing of puffs released outside the logarithmic region. Full article
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)
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20 pages, 818 KiB  
Article
Evaluation of Interfacial Heat Transfer Models for Flashing Flow with Two-Fluid CFD
by Yixiang Liao and Dirk Lucas
Fluids 2018, 3(2), 38; https://doi.org/10.3390/fluids3020038 - 1 Jun 2018
Cited by 25 | Viewed by 5902
Abstract
The complexity of flashing flows is increased vastly by the interphase heat transfer as well as its coupling with mass and momentum transfers. A reliable heat transfer coefficient is the key in the modelling of such kinds of flows with the two-fluid model. [...] Read more.
The complexity of flashing flows is increased vastly by the interphase heat transfer as well as its coupling with mass and momentum transfers. A reliable heat transfer coefficient is the key in the modelling of such kinds of flows with the two-fluid model. An extensive literature survey on computational modelling of flashing flows has been given in previous work. The present work is aimed at giving a brief review on available theories and correlations for the estimation of interphase heat transfer coefficient, and evaluating them quantitatively based on computational fluid dynamics simulations of bubble growth in superheated liquid. The comparison of predictions for bubble growth rate obtained by using different correlations with the experimental as well as direct numerical simulation data reveals that the performance of the correlations is dependent on the Jakob number and Reynolds number. No generally applicable correlations are available. Both conduction and convection are important in cases of bubble rising and translating in stagnant liquid at high Jakob numbers. The correlations combining the analytical solution for heat diffusion and the theoretical relation for potential flow give the best agreement. Full article
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)
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18 pages, 5696 KiB  
Article
Thermal Fluid Analysis of Cold Plasma Methane Reformer
by Sarvenaz Sobhansarbandi, Lizon Maharjan, Babak Fahimi and Fatemeh Hassanipour
Fluids 2018, 3(2), 31; https://doi.org/10.3390/fluids3020031 - 1 May 2018
Cited by 2 | Viewed by 6303
Abstract
One of the most important methods of methane utilization is the conversion to synthesis gas (syngas). However, conventional ways of reforming methane usually require very high temperature, therefore non-thermal (non-equilibrium) plasma methane reforming is an attractive alternative. In this study, a novel plasma [...] Read more.
One of the most important methods of methane utilization is the conversion to synthesis gas (syngas). However, conventional ways of reforming methane usually require very high temperature, therefore non-thermal (non-equilibrium) plasma methane reforming is an attractive alternative. In this study, a novel plasma based reformer named 3D Gliding Arc Vortex Reformer (3D-GAVR) was investigated for partial oxidation of methane to produce syngas. The tangential input creates a vortex in the plasma zone and an expanded plasma presides within the entire area between the two electrodes. Using this method, the experimental results show that hydrogen can be produced for as low as $ 4.45 per kg with flow rates of around 1 L per minute. The maximum methane conversion percentage which is achieved by this technology is up to 62.38%. In addition, a computational fluid dynamics (CFD) modeling is conducted for a cold plasma reformer chamber named reverse vortex flow gliding arc reactor (RVF-GA) to investigate the effects of geometry and configuration on the reformer performance. In this modified reformer, an axial air input port is added to the top of the reaction vessel while the premixed reactants can enter the cylindrical reaction zone through tangential jets. The CFD results show that a reverse vortex flow (RVF) scheme can be created which has an outer swirling rotation along with a low pressure area at its center with some component of axial flow. The reversed vortex flow utilizes the uniform temperature and heat flux distribution inside the cylinder, and enhances the gas mixtures leading to expedition of the chemical reaction and the rate of hydrogen production. Full article
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)
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14 pages, 5739 KiB  
Article
Time-Dependent Shear Stress Distributions during Extended Flow Perfusion Culture of Bone Tissue Engineered Constructs
by Cortes Williams, Olufemi E. Kadri, Roman S. Voronov and Vassilios I. Sikavitsas
Fluids 2018, 3(2), 25; https://doi.org/10.3390/fluids3020025 - 3 Apr 2018
Cited by 14 | Viewed by 5353
Abstract
Flow perfusion bioreactors have been extensively investigated as a promising culture method for bone tissue engineering, due to improved nutrient delivery and shear force-mediated osteoblastic differentiation. However, a major drawback impeding the transition to clinically-relevant tissue regeneration is the inability to non-destructively monitor [...] Read more.
Flow perfusion bioreactors have been extensively investigated as a promising culture method for bone tissue engineering, due to improved nutrient delivery and shear force-mediated osteoblastic differentiation. However, a major drawback impeding the transition to clinically-relevant tissue regeneration is the inability to non-destructively monitor constructs during culture. To alleviate this shortcoming, we investigated the distribution of fluid shear forces in scaffolds cultured in flow perfusion bioreactors using computational fluid dynamic techniques, analyzed the effects of scaffold architecture on the shear forces and monitored tissue mineralization throughout the culture period using microcomputed tomography. For this study, we dynamically seeded one million adult rat mesenchymal stem cells (MSCs) on 85% porous poly(l-lactic acid) (PLLA) polymeric spunbonded scaffolds. After taking intermittent samples over 16 days, the constructs were imaged and reconstructed using microcomputed tomography. Fluid dynamic simulations were performed using a custom in-house lattice Boltzmann program. By taking samples at different time points during culture, we are able to monitor the mineralization and resulting changes in flow-induced shear distributions in the porous scaffolds as the constructs mature into bone tissue engineered constructs, which has not been investigated previously in the literature. From the work conducted in this study, we proved that the average shear stress per construct consistently increases as a function of culture time, resulting in an increase at Day 16 of 113%. Full article
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)
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10 pages, 2109 KiB  
Article
On the Bias in the Danckwerts’ Plot Method for the Determination of the Gas–Liquid Mass-Transfer Coefficient and Interfacial Area
by German E. Cortes Garcia, Kevin M. P. Van Eeten, Michiel M. De Beer, Jaap C. Schouten and John Van der Schaaf
Fluids 2018, 3(1), 18; https://doi.org/10.3390/fluids3010018 - 20 Feb 2018
Cited by 7 | Viewed by 5283
Abstract
The Danckwerts’ plot method is a commonly used graphical technique to independently determine the interfacial area and mass-transfer coefficient in gas–liquid contactors. The method was derived in 1963 when computational capabilities were limited and intensified process equipment did not exist. A numerical analysis [...] Read more.
The Danckwerts’ plot method is a commonly used graphical technique to independently determine the interfacial area and mass-transfer coefficient in gas–liquid contactors. The method was derived in 1963 when computational capabilities were limited and intensified process equipment did not exist. A numerical analysis of the underlying assumptions of the method in this paper has shown a bias in the technique, especially for situations where mass-transfer rates are intensified, or where there is limited liquid holdup in the bulk compared to the film layers. In fact, systematic errors of up to 50% in the interfacial area, and as high as 90% in the mass-transfer coefficients, can be expected for modern, intensified gas–liquid contactors, even within the commonly accepted validity limits of a pseudo-first-order reaction and Hatta numbers in the range of 0.3 < Ha < 3. Given the current computational capabilities and the intensified mass-transfer rates in modern gas–liquid contactors, it is therefore imperative that the equations for reaction and diffusion in the liquid films are numerically solved and subsequently used to fit the interfacial area and mass-transfer coefficient to experimental data, which would traditionally be used in the graphical Danckwerts’ method. Full article
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)
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11 pages, 5515 KiB  
Article
Coherent Vortical Structures and Their Relation to Hot/Cold Spots in a Thermal Turbulent Channel Flow
by Suranga Dharmarathne, Venkatesh Pulletikurthi and Luciano Castillo
Fluids 2018, 3(1), 14; https://doi.org/10.3390/fluids3010014 - 8 Feb 2018
Cited by 5 | Viewed by 4338
Abstract
Direct numerical simulations of a turbulent channel flow with a passive scalar at R e τ = 394 with blowing perturbations is carried out. The blowing is imposed through five spanwise jets located near the upstream end of the channel. Behind the blowing [...] Read more.
Direct numerical simulations of a turbulent channel flow with a passive scalar at R e τ = 394 with blowing perturbations is carried out. The blowing is imposed through five spanwise jets located near the upstream end of the channel. Behind the blowing jets (about 1 D , where D is the jet diameter), we observe regions of reversed flow responsible for the high temperature region at the wall: hot spots that contribute to further heating of the wall. In between the jets, low pressure regions accelerate the flow, creating long, thin, streaky structures. These structures contribute to the high temperature region near the wall. At the far downstream of the jet (about 3 D ), flow instabilities (high shear) created by the blowing generate coherent vortical structures. These structures move hot fluid near the wall to the outer region of the channel; thereby, these are responsible for cooling of the wall. Thus, for engineering applications where cooling of the wall is necessary, it is critical to promote the generation of coherent structures near the wall. Full article
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)
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17 pages, 3214 KiB  
Article
Characterization of Bubble Size Distributions within a Bubble Column
by Shahrouz Mohagheghian and Brian R. Elbing
Fluids 2018, 3(1), 13; https://doi.org/10.3390/fluids3010013 - 7 Feb 2018
Cited by 29 | Viewed by 10960
Abstract
The current study experimentally examines bubble size distribution (BSD) within a bubble column and the associated characteristic length scales. Air was injected into a column of water via a single injection tube. The column diameter (63–102 mm), injection tube diameter (0.8–1.6 mm) and [...] Read more.
The current study experimentally examines bubble size distribution (BSD) within a bubble column and the associated characteristic length scales. Air was injected into a column of water via a single injection tube. The column diameter (63–102 mm), injection tube diameter (0.8–1.6 mm) and superficial gas velocity (1.4–55 mm/s) were varied. Large samples (up to 54,000 bubbles) of bubble sizes measured via 2D imaging were used to produce probability density functions (PDFs). The PDFs were used to identify an alternative length scale termed the most frequent bubble size (dmf) and defined as the peak in the PDF. This length scale as well as the traditional Sauter mean diameter were used to assess the sensitivity of the BSD to gas injection rate, injector tube diameter, injection tube angle and column diameter. The dmf was relatively insensitive to most variation, which indicates these bubbles are produced by the turbulent wakes. In addition, the current work examines higher order statistics (standard deviation, skewness and kurtosis) and notes that there is evidence in support of using these statistics to quantify the influence of specific parameters on the flow-field as well as a potential indicator of regime transitions. Full article
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)
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20 pages, 8416 KiB  
Article
Fluid Dynamics and Mass Transfer in Spacer-Filled Membrane Channels: Effect of Uniform Channel-Gap Reduction Due to Fouling
by Chrysafenia P. Koutsou, Anastasios J. Karabelas and Margaritis Kostoglou
Fluids 2018, 3(1), 12; https://doi.org/10.3390/fluids3010012 - 2 Feb 2018
Cited by 16 | Viewed by 4220
Abstract
The time-varying flow field in spacer-filled channels of spiral-wound membrane (SWM) modules is mainly due to the development of fouling layers on the membranes that modify the channel geometry. The present study is part of an approach to tackling this extremely difficult dynamic [...] Read more.
The time-varying flow field in spacer-filled channels of spiral-wound membrane (SWM) modules is mainly due to the development of fouling layers on the membranes that modify the channel geometry. The present study is part of an approach to tackling this extremely difficult dynamic problem at a small spatial scale, by uncoupling the fluid dynamics and mass transfer from the fouling-layer growth process. Therefore, fluid dynamics and mass transfer are studied for a spacer-filled channel whose geometry is altered by a uniform deposit thickness h. For this purpose, 3D direct numerical simulations are performed employing the “unit cell” approach with periodic boundary conditions. Specific thickness values are considered in the range 2.5–10% of the spacer-filament diameter D as well as other conditions of practical significance. The qualitative characteristics of the altered flow field are found to be very similar to those of the reference geometry with no gap reduction. For a given flow rate, the pressure drop, time-average wall-shear stresses and mass-transfer coefficients significantly increase with increasing thickness h due to reduced channel-gap, as expected. Correlations are obtained, applicable at the “unit cell” scale, of the friction factor f and Sherwood number Sh, which exhibit similar functional dependence of f and Sh on the Reynolds and Schmidt numbers as in the reference no-fouling case. In these correlations the effect of channel-gap reduction is incorporated, permitting predictions in the studied range of fouling-layer thickness (h/D) = 0–0.10. The usefulness of the new results and correlations is discussed in the context of ongoing research toward improved modeling and dynamic simulation of SWM-module operation. Full article
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)
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11 pages, 4109 KiB  
Article
Design of a Novel μ-Mixer
by Athanasios G. Kanaris and Aikaterini A. Mouza
Fluids 2018, 3(1), 10; https://doi.org/10.3390/fluids3010010 - 28 Jan 2018
Cited by 7 | Viewed by 4598
Abstract
In this work, the efficiency of a new μ-mixer design is investigated. As in this type of devices the Reynolds number is low, mixing is diffusion dominated and it can be enhanced by creating secondary flows. In this study, we propose the [...] Read more.
In this work, the efficiency of a new μ-mixer design is investigated. As in this type of devices the Reynolds number is low, mixing is diffusion dominated and it can be enhanced by creating secondary flows. In this study, we propose the introduction of helical inserts into a straight tube to create swirling flow. The influence of the insert’s geometrical parameters (pitch and length of the propeller blades) and of the Reynolds number on the mixing efficiency and on the pressure drop are numerically investigated. The mixing efficiency of the device is assessed by calculating a number—i.e., the index of mixing efficiency—that quantifies the uniformity of concentration at the outlet of the device. The influence of the design parameters on the mixing efficiency is assessed by performing a series of ‘computational’ experiments, in which the values of the parameter are selected using design of experiments (DOE) methodology. Finally using the numerical data, appropriate design equations are formulated, which, for given values of the design parameters, can estimate with reasonable accuracy both the mixing efficiency and the pressure drop of the proposed mixing device. Full article
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)
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16 pages, 23689 KiB  
Article
Experimental Analysis of a Bubble Wake Influenced by a Vortex Street
by Sophie Rüttinger, Marko Hoffmann and Michael Schlüter
Fluids 2018, 3(1), 8; https://doi.org/10.3390/fluids3010008 - 20 Jan 2018
Cited by 5 | Viewed by 4720
Abstract
Bubble column reactors are ubiquitous in engineering processes. They are used in waste water treatment, as well as in the chemical, pharmaceutical, biological and food industry. Mass transfer and mixing, as well as biochemical or chemical reactions in such reactors are determined by [...] Read more.
Bubble column reactors are ubiquitous in engineering processes. They are used in waste water treatment, as well as in the chemical, pharmaceutical, biological and food industry. Mass transfer and mixing, as well as biochemical or chemical reactions in such reactors are determined by the hydrodynamics of the bubbly flow. The hydrodynamics of bubbly flows is dominated by bubble wake interactions. Despite the fact that bubble wakes have been investigated intensively in the past, there is still a lack of knowledge about how mass transfer from bubbles is influenced by bubble wake interactions in detail. The scientific scope of this work is to answer the question how bubble wakes are influenced by external flow structures like a vortex street behind a cylinder. For this purpose, the flow field in the vicinity of a single bubble is investigated systematically with high spatial and temporal resolution. High-speed Particle Image Velocimetry (PIV) measurements are conducted monitoring the flow structure in the equatorial plane of the single bubble. It is shown that the root mean square (RMS) velocity profiles downstream the bubble are influenced significantly by the interaction of vortices. In the presence of a vortex street, the deceleration of the fluid behind the bubble is compensated earlier than in the absence of a vortex street. This happens due to momentum transfer by cross-mixing. Both effects indicate that the interaction of vortices enhances the cross-mixing close to the bubble. Time series of instantaneous velocity fields show the formation of an inner shear layer and coupled vortices. In conclusion, this study shows in detail how the bubble wake is influenced by a vortex street and gives deep insights into possible effects on mixing and mass transfer in bubbly flows. Full article
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)
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0 pages, 769 KiB  
Article
RETRACTED: Dual Solutions in a Boundary Layer Flow of a Power Law Fluid over a Moving Permeable Flat Plate with Thermal Radiation, Viscous Dissipation and Heat Generation/Absorption
by Aftab Ahmed, Javed I. Siddique and Muhammad Sagheer
Fluids 2018, 3(1), 6; https://doi.org/10.3390/fluids3010006 - 9 Jan 2018
Cited by 14 | Viewed by 5923 | Retraction
Abstract
The aim of the present study is to investigate the combined effects of the thermal radiation, viscous dissipation, suction/injection and internal heat generation/absorption on the boundary layer flow of a non-Newtonian power law fluid over a semi infinite permeable flat plate moving in [...] Read more.
The aim of the present study is to investigate the combined effects of the thermal radiation, viscous dissipation, suction/injection and internal heat generation/absorption on the boundary layer flow of a non-Newtonian power law fluid over a semi infinite permeable flat plate moving in parallel or reversely to a free stream. The resulting system of partial differential equations (PDEs) is first transformed into a system of coupled nonlinear ordinary differential equations (ODEs) which are then solved numerically by using the shooting technique. It is found that the dual solutions exist when the flat plate and the free stream move in the opposite directions. Dimensionless boundary layer velocity and temperature distributions are plotted and discussed for various values of the emerging physical parameters. Finally, the tables of the relevant boundary derivatives are presented for some values of the governing physical parameters. Full article
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)
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5193 KiB  
Article
Computational Modelling for Efficient Transdentinal Drug Delivery
by Agathoklis D. Passos, Dimitris Tziafas, Aikaterini A. Mouza and Spiros V. Paras
Fluids 2018, 3(1), 4; https://doi.org/10.3390/fluids3010004 - 27 Dec 2017
Cited by 3 | Viewed by 4778
Abstract
This work deals with the numerical investigation of the delivery of potential therapeutic agents through dentinal discs (i.e., a cylindrical segment of the dentinal tissue) towards the dentin–pulp junction. The aim is to assess the main key features (i.e., molecular size, initial concentration, [...] Read more.
This work deals with the numerical investigation of the delivery of potential therapeutic agents through dentinal discs (i.e., a cylindrical segment of the dentinal tissue) towards the dentin–pulp junction. The aim is to assess the main key features (i.e., molecular size, initial concentration, consumption rate, disc porosity and thickness) that affect the delivery of therapeutic substances to the dental pulp and consequently to define the necessary quantitative and qualitative issues related to a specific agent before its potential application in clinical practice. The computational fluid dynamics (CFD) code used for the numerical study is validated with relevant experimental data obtained using micro Laser Induced Fluorescence (μ-LIF) a non-intrusive optical measuring technique. As the phenomenon is diffusion dominated and strongly dependent on the molecular size, the time needed for the concentration of released molecules to attain a required value can be controlled by their initial concentration. Finally, a model is proposed which, given the maximum acceptable time for the drug concentration to attain a required value at the pulpal side of the tissue along with the aforementioned key design parameters, is able to estimate the initial concentration to be imposed and vice versa. Full article
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)
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1423 KiB  
Communication
Thermal Jacket Design Using Cellulose Aerogels for Heat Insulation Application of Water Bottles
by Hai M. Duong, Ziyang Colin Xie, Koh Hong Wei, Ng Gek Nian, Kenneth Tan, Hong Jie Lim, An Hua Li, Ka-Shing Chung and Wen Zhen Lim
Fluids 2017, 2(4), 64; https://doi.org/10.3390/fluids2040064 - 23 Nov 2017
Cited by 13 | Viewed by 7925
Abstract
Thermal jacket design using eco-friendly cellulose fibers from recycled paper waste is developed in this report. Neoprene as an outmost layer, cellulose aerogels in the middle and Nylon as an innermost layer can form the best sandwiched laminate using the zigzag stitching method [...] Read more.
Thermal jacket design using eco-friendly cellulose fibers from recycled paper waste is developed in this report. Neoprene as an outmost layer, cellulose aerogels in the middle and Nylon as an innermost layer can form the best sandwiched laminate using the zigzag stitching method for thermal jacket development. The temperature of the ice slurry inside the water bottle covered with the designed thermal jackets remains at 0.1 °C even after 4 h, which is the average duration of an outfield exercise. Interestingly, the insulation performance of the designed thermal jackets is much better than the commercial insulated water bottles like FLOE bottles and is very competition to that of vacuum flasks for a same period of 4 h and ambient conditions. Full article
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)
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4940 KiB  
Article
Computational Fluid Dynamics Simulations of Gas-Phase Radial Dispersion in Fixed Beds with Wall Effects
by Anthony G. Dixon and Nicholas J. Medeiros
Fluids 2017, 2(4), 56; https://doi.org/10.3390/fluids2040056 - 21 Oct 2017
Cited by 16 | Viewed by 5812
Abstract
The effective medium approach to radial fixed bed dispersion models, in which radial dispersion of mass is superimposed on axial plug flow, is based on a constant effective dispersion coefficient, DT. For packed beds of a small tube-to-particle diameter ratio (N), [...] Read more.
The effective medium approach to radial fixed bed dispersion models, in which radial dispersion of mass is superimposed on axial plug flow, is based on a constant effective dispersion coefficient, DT. For packed beds of a small tube-to-particle diameter ratio (N), the experimentally-observed decrease in this parameter near the tube wall is accounted for by a lumped resistance located at the tube wall, the wall mass transfer coefficient km. This work presents validated computational fluid dynamics (CFD) simulations to obtain detailed radial velocity and concentration profiles for eight different computer-generated packed tubes of spheres in the range 5.04 ≤ N ≤ 9.3 and over a range of flow rates 87 ≤ Re ≤ 870 where Re is based on superficial velocity and the particle diameter dp. Initial runs with pure air gave axial velocity profiles vz(r) averaged over the length of the packing. Then, simulations with the tube wall coated with methane yielded radial concentration profiles. A model with only DT could not describe the radial concentration profiles. The two-parameter model with DT and km agreed better with the bed-center concentration profiles, but not with the sharp decreases in concentration close to the tube wall. A three-parameter model based on classical two-layer mixing length theory, with a wall-function for the decrease in transverse radial convective transport in the near-wall region, showed greatly improved ability to reproduce the near-wall concentration profiles. Full article
(This article belongs to the Special Issue Flow and Heat or Mass Transfer in the Chemical Process Industry)
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