Flow Inside Tubes Research Articles

Mass transfer of bilirubin and bovine serum albumin in hollow fiber membrane module of artificial liver

Understanding the mass transfer behaviors in hollow fiber membrane module of artificial liver is important for improving toxin removal efficiency. A three-dimensional numerical model was established to study the mass transfer of small molecule bilirubin and macromolecule bovine serum albumin (BSA) in the hollow fiber membrane module. Effects of tube-side flow rate, shell-side flow rate, and hollow fiber length on the mass transfer of bilirubin and BSA were discussed. The simulation results showed that the clearance of bilirubin was significantly affected by both convective and diffusive solute transport, while the clearance of macromolecule BSA was dominated by convective solute transport. The clearance rates of bilirubin and BSA increasd with the increase of tube-side flow rate and hollow fiber length. With the increase of shell-side flow rate, the clearance rate of bilirubin first rose rapidly, then slowly rose to an asymptotic value, while the clearance rate of BSA gradually decreased. The results can provide help for designing structures of hollow fiber membrane module and operation parameters of clinical treatment.

Numerical Simulation of Mass Transfer in Hollow Fiber Membrane Module for Membrane-Based Artificial Organs.

The mass transfer behavior in a hollow fiber membrane module of membrane-based artificial organs (such as artificial liver or artificial kidney) were studied by numerical simulation. A new computational fluid dynamics (CFD) method coupled with K-K equation and the tortuous capillary pore diffusion model (TCPDM) was proposed for the simulations. The urea clearance rate predicted by the use of the numerical model agrees well with the experimental data, which verifies the validity of our numerical model. The distributions of concentration, pressure, and velocity in the hollow fiber membrane module were obtained to analyze the mass transfer behaviors of bilirubin and bovine serum albumin (BSA), and the effects of tube-side flow rate, shell-side flow rate, and fiber tube length on the bilirubin or BSA clearance rate were studied. The results show that the solute transport mainly occurred in the near inlet regions in the hollow fiber membrane module. Increasing the tube-side flow rate and the fiber tube length can effectively enhance the solute clearance rate, while the shell-side flow rate has less influence on the BSA clearance. The clearance of macromolecule BSA is dominated by convective solute transport, while the clearance of small molecule bilirubin is significantly affected by both convective and diffusive solute transport.

The reactive Graetz problem for a first order homogeneous decomposition reaction, and the limit of moderately large reaction constants

The long term goal of the present study is to facilitate the inversion of experimental data on cluster evaporation in laminar flow inside tubes. This requires the determination of reactant and product fluxes as functions of three dimensionless governing parameters: the axial position x along the tube, the reaction rate coefficient K, and the ratio γ of product and reactant diffusivities. The reactant flux is first calculated by separation of variables, including the accurate determination of the first 35 eigenvalues for 13 discrete values of K in the range 0<K<500. This approach is far less efficient for the product flux because the eigenfunctions are not standard functions. A numerical solution is also implemented for the reactant and its product, though it can hardly cover the full range of the three relevant parameters. The most common experimental situation involves relatively large values of K, for which a three term asymptotic solution is developed in negative powers of K1/2, with errors of order K−2. These approximate results represent well the numerically calculated reactant fluxes for K > 10 in terms of two functions, H0(s) and H1(s), reported in tables. The product fluxes require two functions, I0(s,γ), I1(s,γ). These we compute for six values of γ, and report as simple analytical fits covering continuously the full physically relevant range 1<γ<1.5. The desired ability to analyze experimental data to yield kinetic information is therefore achieved without the need for additional numerical solutions to partial differential equations.

Experimental study on the heat transfer and pressure drop of oil-based nanofluids in laminar flow inside horizontal tubes

Experimental study on the heat transfer and pressure drop of oil-based nanofluids in laminar flow inside horizontal tubes

Numerical investigation of tubeside maldistribution in shell-and-tube heat exchangers

Shell-and-tube heat exchangers (STHE) are widely used in the process and energy industry. Maldistribution and the often resulting fouling in these STHE cause additional energy consumption and lower production throughput. Increased average wall shear stress, compared to that of the maldistributed case inside the tubes is expected to mitigate fouling. This can be achieved by a uniform distribution into the tubes. Field and laboratory data suggest that common crude oil fouling is profoundly mitigated above 10 Pa and is significantly reduced above a wall shear stress of 15 Pa [1]. Many STHE already have lower design shear stresses than those mentioned. Therefore, if maldistribution takes place, tubes with less flow velocity will have even more fouling. To investigate tubeside flow maldistribution, a parametric STHE model is studied with computational fluid dynamics (CFD). At first, a comparison between the standard k-ϵ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\epsilon$$\\end{document}-model and the new standard SST-model is performed to check if SST could provide improved simulation results. Afterward, a range of geometrical parameters will be investigated to find influencing quantities of maldistribution. The resulting velocity distributions are visualized and evaluated by using different statistical approaches. At least, a sensitivity analysis will be done to show how each parameter influences the tubeside flow distribution in STHE.

Analysis of Condensation Flow and Heat Transfer Characteristics Inside Spiral Tubes

Spiral wound tube heat exchanger (SWHE) was confirmed as the core equipment of natural gas liquefaction (LNG). However, there was rare experimental research on large-scale SWHE for LNG, and the theory of heat transfer is not perfect. To investigate the tube-side flow and heat transfer characteristics in spiral tubes, an experimental system was proposed. To ensure the accuracy of the experimental data, the heat transfer coefficients of liquid propane under different conditions were measured, and the data acquired through the experiment were compared with two classical heat transfer correlation (Dittus–Boelter and Geielinski) under the identical working conditions. The applicability of the existing correlation was analyzed using the experimental data, and a novel heat transfer correlation was developed. As indicated by the results, the deviation between the experimental system and the classical correlation under the identical working condition was lower than ±10%. Furthermore, the error comparison between the novel correlation prediction value and the experimental data was less than ±15%.

Effect of hydrophilic and hydrophobic metal foams on condensation characteristics of refrigerant flow inside annular tubes: Experimental study

Effect of hydrophilic and hydrophobic metal foams on condensation characteristics of refrigerant flow inside annular tubes: Experimental study

Entropy Generation Minimization for Boiling Flow Inside Evaporator Tube With R32 and R410A Refrigerants: A Comparison of Different Two-Phase Flow Models

AbstractThe objective of the present work is to find out the optimal mass flux of two common refrigerants, R32 and R410A, undergoing boiling in an evaporator tube based on the entropy generation minimization approach. An entropy generation model is developed for two-phase boiling flow based on the drift flux approach. The distinct terms for entropy generation due to heat transfer and pressure drop are developed. The optimal solutions of the present model under a practical range of parametric conditions are compared with that obtained from the existing homogeneous and separated flow-based model. Analysis reveals that increasing the evaporator diameter and heat flux increases the optimal mass flux at minimum entropy generation for both refrigerants. On the other hand, increasing the evaporator length decreases the optimal mass flux. It is observed that the optimal mass flux data for all parametric conditions deviate within 10–15% on the positive and negative sides for drift flux and homogeneous models, respectively, compared to separate flow model. The present analysis also reveals that the overall deviation of data of the drift flux model and homogeneous flow model indicates a standard deviation of 1.95–1.98%, respectively.

Peristaltic transport of Rabinowitsch nanofluid with moving microorganisms

The key objective of the current examination is to examine a symmetrically peristaltic movement of microorganisms in a Rabinowitsch fluid (RF). The Boussinesq approximation, buoyancy-driven flow, where the density with gravity force term is taken as a linear function of heat and concentrations, is kept in mind. The flow moves with thermophoretic particle deposition in a horizontal tube with peristalsis. The heat distribution and volume concentration are revealed by temperature radiation and chemical reaction characteristics. The originality of the existing study arises from the importance of realizing the benefits or the threats that nanoparticles, microbes, and bacteria cause in the flow inside peristaltic tubes. The results are an attempt to understand what factors perform additional advantages and or reduce damages. The controlling nonlinear partial differential equations (PDEs) are made simpler by employing the long wavelength (LWL) and low-Reynolds numeral (LRN) approximations. These equations are subjected to a set of non-dimensional transformations that result in a collection of nonlinear ordinary differential equations (ODEs). By employing the Homotopy perturbation method (HPM), the configuration of equational analytical solutions is examined. Analytical and graphical descriptions are provided for the distributions of axial speed, heat, microbes, and nanoparticles under the influence of these physical characteristics. The important findings of the current work may help to comprehend the properties of several variations in numerous biological situations. It is found that the microorganisms condensation decays with the rise of all the operational parameters. This means that the development of all these factors benefits in shrinking the existence of harmful microbes, viruses, and bacteria in the human body’s peristaltic tubes, especially in the digestive system, and large and small intestines.

New configuration gas-cooled fluidized bed membrane reactor to reduce the thermodynamic limitations of dimethyl ether production

In this study, a gas-cooled fluidized bed membrane reactor with a new configuration was investigated aiming to reduce thermodynamic limitations in DME production. In this configuration, two Pd-Ag and alumina-silica membranes were used simultaneously for the permeation of hydrogen into the reactor and to remove its containing water, respectively. The heat of the exothermic DME synthesis reactions is removed by heat transfer with sweep and hydrogen gaseous flows. The simulation of the fluidized bed membrane reactor shows that the presence of the membranes increases DME production and carbon monoxide (CO) conversion by about 30.6% and 28.3%, respectively. Enhanced DME production was observed by raising temperature, pressure, and shell and tube side flow rates. Space velocity and H2/CO ratio had an optimum point in DME production. The proposed model can be used for the design of an industrial catalytic membrane reactor for DME production from synthesis gas.

Multi-criterion optimization of a biologically-produced nanofluid flow inside tubes fitted with coaxial twisted tape based on first and second law viewpoints

The current study deals with a numerical simulation of heat transfer inside enhanced tubes having the coaxial double-twisted tape in the presence of an eco-friendly nanofluid containing graphene nanoplatelets (GNPs). The results unveil that when the particle concentration ( ϕ ) escalates, the thermal entropy generation rate ( S ̇ h ) tends to decline, whereas the heat transfer coefficient enhances. It was found that around 21.6% reduction in the S ̇ h is attained by a decrease of the twisted ratio ( ω ) from 3.5 to 2.5 at the concentration of 0.075% and Reynolds number of 10,000. Adding more GNPs to the water yields an increment in either the pressure drop or the frictional entropy generation. The findings refer to this issue that a multi-criterion optimization to find the best optimum state is required. A genetic algorithm-based optimization with the entropy generation rate, heat transfer, and pressure loss results in the optimum values at Re = 16,995.4, ϕ = 0.093%, and ω = 3.41. • Employing an eco-friendly nanofluid containing graphene nanosheets. • Second law analysis of a novel coaxial double twisted tape inside tubes. • Smaller twisted ratio causes further decrement in total entropy generation rate. • The higher Reynolds numbers weaken the positive effect of the nanofluid. • Multi-criterion optimization is done to determine the best optimum state.

Experimental and numerical study on tube-side flow and heat transfer characteristics of superheated vapor flow in catalyst-filled LH2 spiral wound heat exchanger

High energy consumption is considered to be one of the most persistent problems in liquid hydrogen (LH2) plants. The combination of heat exchanger and ortho-para (O–P) hydrogen conversion has attracted considerable attention as a cutting-edge technology to reduce energy consumption. The flow and heat transfer characteristics of O–P hydrogen conversion catalyst-filled spiral wound heat exchanger (SWHE) were investigated in this study in two steps. In the first step, pressure-drop experiments were performed in a tube filled with porous media. The results indicated that the pressure drop was overestimated when using Ergun's equation. Therefore, a new empirical pressure-drop correlation for a channel filled with O–P catalyst was formulated. Subsequently, a novel heat transfer model was established based on this correlation for further numerical simulations. The distributions of the temperature, pressure, and para hydrogen content in a catalyst-filled tube were determined. In addition, the influence of the flow rate on the heat exchange coefficient and outlet para hydrogen was clarified; it was found that, with an increase in the flow rate, the heat exchange coefficient increased, whereas the outlet para hydrogen content decreased. At a flow rate of 0.5 m3/h, the para hydrogen content increased by 44% after hydrogen flowed through the channel filled with the O–P catalyst. Furthermore, a prediction model for the para hydrogen content with a flow rate range of 0–1.5 m3/h was derived. This study provides promising theoretical evidence for the engineering application of SWHEs filled with O–P catalysts in large-scale hydrogen liquefaction units.

Experimental study and general correlation for frictional pressure drop of two-phase flow inside microfin tubes

The adiabatic pressure drop in a microfin tube with an outside diameter of 3.5 mm was experimentally studied herein. The experiments were conducted using R1234yf as a working fluid at saturation temperatures of 20 °C and 30 °C with varying mass velocities from 50 to 300 kg m−2s−1 and vapor qualities ranging from 0.1 to 0.9. The effects of experimental conditions were analyzed and discussed with present and previous data. A new two-phase flow frictional pressure drop correlation has been developed using the data with tube diameter of 2.5–9.52 mm, mass velocity of 50–1000 kg m−2s−1, and many kinds of refrigerants. The proposed correlation predicts the experimental data of other researchers with mean deviation of 17.6%.

Performance analysis of shell and helical tube heat exchanger using CuO/water and Al2O3/water nanofluids

PurposeA computational fluid dynamics based parametric analysis for shell and helical tube heat exchanger (SHTHE) using CuO/water and Al2O3/water nanofluids is the main purpose of the present work. The parameters having impact on the performance of a heat exchanger have been studied in depth. As the solid nanoparticle shows higher thermal conductivity compared to liquid particles, inclusion of this nanoparticle into the base fluid significantly enhances the thermal conductivity of the liquid. Incorporation of nanofluid in the heat exchanger can increase its performance.Design/methodology/approachThe simulation is performed in Solid-Works flow simulation, and the performance of SHTHE is observed by varying the pitch of helical tube from 0.013 to 0.018 m and coil diameter from 0.0813 to 0.116 m, keeping the other parameters constant. The tube side and shell side flow rate is kept as 2 LPM.FindingsThe results indicate that the effectiveness of the heat exchanger increases with the increase of pitch and coil diameter. The maximum effectiveness of 0.5022 for CuO/water and 0.4928 for Al2O3/water nanofluid is observed at a pitch of 0.018 m and the coil diameter of 0.116 m.Originality/valueIt is observed that CuO/water nanofluid shows better performance compared with Al2O3/water nanofluid. For a coil diameter of 0.116 m and pitch of 0.018 m, the SHTHE with CuO/water nanofluid shows 1.82% greater effectiveness compared to the effectiveness with Al2O3/water nanofluid.

Parameter Study of Geometrically Induced Flow Maldistribution in Shell and Tube Heat Exchangers

Abstract Shell and tube heat exchangers (STHEs) are the most common type of heat exchanger in preheat trains (PHT) of oil refineries and in chemical process plants. Most commercial design software tools for STHE assume uniform distribution over all tubes of a tube bundle. This leads to various challenges in the operation of the affected devices. Flow maldistribution reduces heat duty of STHE in many applications and supports fouling buildup in fluids that tend to particle, bio, and crystallization fouling (Verein Deutscher Ingenieure, ed., 2010, Heat Atlas, 2nd ed., VDI-Buch., Springer-Verlag). In this article, a fluid mechanics study about tube side flow distribution of crude oil and related hydrocarbons in two-pass PHT heat exchangers is described. It is shown that the amount of flow maldistribution varies significantly between the different STHE designs. Therefore, a parameter study was conducted to investigate reasons for maldistribution. For instance, the nozzles diameter, type, and orientation were identified as crucial parameters. In consequence, simple design suggestions for reducing tube side flow maldistribution are proposed.

New Approach to Obtain the Mean Heat Transfer Coefficients for Single-Phase Fluid Flow Inside Tubes by Simulating Evolution of Nusselt Equation (I)

New Approach to Obtain the Mean Heat Transfer Coefficients for Single-Phase Fluid Flow Inside Tubes by Simulating Evolution of Nusselt Equation (I)

Numerical simulation of the calcium hydroxide/calcium oxide system dehydration reaction in a shell-tube reactor

The Ca(OH)2/CaO system is a promising candidate for thermochemical energy storage because of its high energy density, low cost and negligible heat loss. Coupling mechanisms of multiple physiochemical processes still need further investigation and the system performance should be further improved. In this work, for the first time, a three-dimensional numerical model is developed to study the thermochemical energy storage process by Ca(OH)2 dehydration reaction in a shell-tube reactor. The turbulent heat transfer fluid flow in the shell side, and the steam flow, heat transfer and dehydration reaction in the tube side are comprehensively taken into account. Effects of operation conditions and reactor geometry parameters on the dehydration process are also investigated in detail. Five indicators are proposed to comprehensively evaluate the reactor performance, including reaction time, energy storage density, heat exchange power, heat exchange efficiency and energy storage efficiency. The results reveal that higher inlet temperature and inlet velocity of heat transfer fluid can enhance the heat transfer and accelerate the reaction. Lower porosity, although increases the energy storage density, leads to higher flow resistance and impedes the reaction. With deep understanding of the physiochemical processes, 16 more tubes are properly added in the by-pass flow region, leading to shorter reaction time and higher energy storage amount. The low values of heat exchange efficiency and energy storage efficiency reveal that the input heat cannot be efficiently transferred to the tube side. To improve the energy conversion performance of reactor, additional schemes are discussed including regenerative HTF, optimization of reactor geometry, increase of reactant thermal conductivity, reducing tube-side flow resistance and extending HTF residence time. The numerical model and simulation results in the present work could be helpful for optimizing the shell-tube Ca(OH)2/CaO reactor and improving the thermochemical energy storage performance.

Effect of Hydrophilic and Hydrophobic Metal Foams on Condensation Characteristics of Refrigerant Flow Inside Annular Tubes: An Experimental Study

Effect of Hydrophilic and Hydrophobic Metal Foams on Condensation Characteristics of Refrigerant Flow Inside Annular Tubes: An Experimental Study

Numerical investigation on turbulent flow and heat transfer characteristics of ferro-nanofluid flowing in dimpled tube under magnetic field effect

• This is the first study on dimpled tube under magnetic field effect. • Effects of dimple geometry and magnetic field on the thermal and hydrodynamic behaviour have been investigated. • The Nu enhances with increasing volume fraction of magnetic nanoparticle. • The highest PEC is obtained for Ha = 75, magnetic nanoparticle fraction of 2.5 vol% and dimpled tube with P 2 /d = 7.5. For the aim of increasing the heat transfer enhancement, a hybrid method in which active and passive heat recovery techniques have been used together. The usage of nanofluid, MHD and dimpled fins tube have not been utilized together so far. Regarding this issue, this study is the first numerical study to determine effect of usage of three effects together comprehensively. In this study, thermo-hydraulic performance of Fe 3 O 4 /H 2 O nanofluid (ferro-nanofluid) flow inside dimpled tube under magnetic field effect has been examined numerically. The main purpose of the study is to obtain numerical data for turbulent flow in the spherical dimpled tubes providing some aid to design a highly efficient thermal energy storage devices. Dimple geometry with nondimensional pitch ratio ( P/d = 3.75, 7.50 and 11.25 ), Hartmann number ( Ha = 75, 150, 225) and nanoparticle volume fraction ( φ = 0.5, 1.0 and 2.5 vol % ) are the parameters investigated in this study. The numerical analyses have been carried out Reynolds number ranging from 10,000 to 50,000 at a constant heat flux at 20 kW/m 2 . The simulations have been built up by Realizable k- ε turbulence model and single-phase approach. Also, “MagnetoHydroDynamic” ( MHD ) module has also been activated for defining magnetic field effect. The results showed that Nusselt number increases with increasing Reynolds number and decreasing pitch ratio. The dimple geometry type of P/d = 7.50 has been determined as the most efficient dimple geometry type. In the case of highest magnetic field intensity, the highest Nusselt number increment (72.48%) has been obtained for φ = 2.5 vol% compared to the base fluid of distilled water using as the working fluid for smooth tube. The highest PEC value was also obtained as 1.126 for the case of P/d = 7.5, φ = 2.5 vol% and Ha = 75. In addition, the effect of magnetic field intensity on velocity and temperature distributions has been presented with contour graphs.

Pressure oscillations with ultra-low frequency induced by vortical flow inside Francis turbine draft tubes

The present paper aims to reveal the flow mechanism for the pressure oscillations with ultra-low frequency captured by the model test of Francis turbine operated at part-load condition. The experimental results indicate that the precessing vortex rope (PVR) induces the dominant pressure oscillation in the draft tube, and its frequency i.e. fPVR is one-fifth of runner rotation frequency (15.12 Hz). To investigate the PVR evolution in the turbine, numerical simulations based on the MSST PANS (modified SST based partially-averaged Navier-Stokes) model have been conducted, and the DMD (dynamic mode decomposition) method has been applied to analyze the modes for unstable flow inside the draft tube. To make out the effect of draft tube structure on the PVR and pressure oscillation, the conventional elbow-type draft tube i.e. EDT, and the conical draft tube i.e. CDT are treated for comparison. Under non-cavitation operation, both experiment and simulation capture two pressure oscillation components with ultra-low frequencies near fPVR/3 and 2fPVR/3. The analysis based on internal flow and DMD method depicts that the pressure oscillations with ultra-low frequency occur due to the strong interaction between the PVR and the backflow in the draft tube, and the elbow structure promotes the interaction and the swirling flow in the draft tube. It is also noted that the cavitation remarkably changes the dynamic characteristics of the precessing vortex rope in the draft tube. Further, cavitation alleviates the interaction between the PVR and backflow at the rear part of the PVR and suppresses the pressure oscillations with ultra-low frequency in the draft tube. Finally, it is confirmed that DMD analysis is helpful to depict the modal of the flow field and make out the important flow structure at various operations in the draft tube.