scholarly journals Numerical Investigation of the Effects of Steam Mole Fraction and the Inlet Velocity of Reforming Reactants on an Industrial-Scale Steam Methane Reformer

Energies ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 2082
Author(s):  
Chun-Lang Yeh
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Mole Fraction ◽  
Production Control ◽  
Industrial Scale ◽  
Hydrogen Yield ◽  
Tube Surface ◽  
Inlet Velocity ◽  
Steam Methane ◽  
Wall Shear

Steam methane reforming (SMR) is the most common commercial method of industrial hydrogen production. Control of the catalyst tube temperature is a fundamental demand of the reformer design because the tube temperature must be maintained within a range that the catalysts have high activity and the tube has minor damage. In this paper, the transport and chemical reaction in an industrial-scale steam methane reformer are simulated using computational fluid dynamics (CFD). Two factors influencing the reformer temperature, hydrogen yield and stress distribution are discussed: (1) the mole fraction of steam (YH2O) and (2) the inlet velocity of the reforming reactants. The purpose of this paper is to get a better understanding of the flow and thermal development in a reformer and thus, to make it possible to improve the performance and lifetime of a steam reformer. It is found that the lowest temperature at the reforming tube surface occurs when YH2O is 0.5. Hydrogen yield has the highest value when YH2O is 0.5. The wall shear stress at the reforming tube surface is higher at a higher YH2O. The surface temperature of a reforming tube increases with the inlet velocity of the reforming reactants. Finally, the wall shear stress at the reforming tube surface increases with the inlet velocity of the reforming reactants.

scholarly journals The influence of inlet velocity profile on predicted flow in type B aortic dissection

2020 ◽  
Author(s):  
Chlöe Harriet Armour ◽  
Baolei Guo ◽  
Selene Pirola ◽  
Simone Saitta ◽  
Yifan Liu ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Aortic Dissection ◽  
Patient Specific ◽  
Type B ◽  
Flow Waveform ◽  
Type B Aortic Dissection ◽  
Specific Data ◽  
Inlet Velocity ◽  
Wall Shear

Abstract In order for computational fluid dynamics to provide quantitative parameters to aid in the clinical assessment of type B aortic dissection, the results must accurately mimic the hemodynamic environment within the aorta. The choice of inlet velocity profile (IVP) therefore is crucial; however, idealised profiles are often adopted, and the effect of IVP on hemodynamics in a dissected aorta is unclear. This study examined two scenarios with respect to the influence of IVP—using (a) patient-specific data in the form of a three-directional (3D), through-plane (TP) or flat IVP; and (b) non-patient-specific flow waveform. The results obtained from nine simulations using patient-specific data showed that all forms of IVP were able to reproduce global flow patterns as observed with 4D flow magnetic resonance imaging. Differences in maximum velocity and time-averaged wall shear stress near the primary entry tear were up to 3% and 6%, respectively, while pressure differences across the true and false lumen differed by up to 6%. More notable variations were found in regions of low wall shear stress when the primary entry tear was close to the left subclavian artery. The results obtained with non-patient-specific waveforms were markedly different. Throughout the aorta, a 25% reduction in stroke volume resulted in up to 28% and 35% reduction in velocity and wall shear stress, respectively, while the shape of flow waveform had a profound influence on the predicted pressure. The results of this study suggest that 3D, TP and flat IVPs all yield reasonably similar velocity and time-averaged wall shear stress results, but TP IVPs should be used where possible for better prediction of pressure. In the absence of patient-specific velocity data, effort should be made to acquire patient’s stroke volume and adjust the applied IVP accordingly.

Efficiency of tube bundle cleaning by low-frequency flow pulsations with solid particles

Vestnik IGEU ◽  
2020 ◽  
pp. 14-25
Author(s):  
A.D. Lipagina ◽  
A.I. Khaibullina ◽  
A.A. Sinyavin ◽  
V.K. Il’in
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Heat Exchangers ◽  
Erosion Rate ◽  
Tube Bundle ◽  
Low Frequency ◽  
Solid Particles ◽  
Tube Surface ◽  
Flow Pulsations ◽  
Wall Shear

Scale buildup on the tube surface in the intertubular space of the shell-and-tube heat exchangers reduce their efficiency. The topical issue is the search for clean-in-place methods. The tube bundle cleaning by low-frequency nonsymmetrical pulsations is understudied. The aim of the paper is numerical analysis of the influence of pulsations on the key cleaning factors (wall shear stress, erosion rate). For the numerical experiment the symmetrical element of a staggered tube bundle with a crossflow of turbine oil (T22) (Re = 100; Pr = 273) and the quartz sand as a cleaning agent is used. The model of incompressible fluid flow comprises the system of Navier-Stokes and continuity equations, the turbulent model Spallart-Allmaras. The motion of solid particles is calculated by the discrete element method, and the erosion rate is calculated by the Campos-Amezcua method. In unsteady conditions with time step 0,001 sec, numerical simulations are performed in Ansys Fluent. Pulsations are generated on entry boundary condition. To estimate the flow pulsation efficiency, the wall shear stresses on the central tube of bundle and erosion rates are compared under the same average rate in steady and nonsteady flow. It is found that asymmetrical flow pulsations (duty cycle 0,25) increase of wall shear stress in all the modes under consideration (amplitude 25 ≤ A/d ≤ 35, frequency 0,3125 ≤ f ≤ 0,5 Гц), but an increase in erosion rate takes place only at maximal frequency. The amplitude variation displaces the localization of the reinforcing effect of flow pulsations on the tube surface. However, it is found that flow pulsations increase the wall shear stress and erosion rate in the front and rear sides of the tubes that are most susceptible to scale buildup. The conducted analysis confirms the significant influence of asymmetrical pulsations on cleaning factors and the perspective of their application for intensification of tube bundle cleaning. The detected effects can be the base to develop new technologies of cleaning intertubular space of heat exchangers.

Correction: Development of a Two-Dimensional Wall Shear Stress Sensor for Wind Tunnel Applications

2019 ◽  
Author(s):  
Brett Freidkes ◽  
David A. Mills ◽  
Casey Keane ◽  
Lawrence S. Ukeiley ◽  
Mark Sheplak
Keyword(s):  
Shear Stress ◽  
Wind Tunnel ◽  
Wall Shear Stress ◽  
Two Dimensional ◽  
Stress Sensor ◽  
Shear Stress Sensor ◽  
Wall Shear

Basic study on estimation method of wall shear stress in common carotid artery using blood flow imaging

2020 ◽  
Vol 59 (SK) ◽  
pp. SKKE16 ◽  
Author(s):  
Ryo Nagaoka ◽  
Kazuma Ishikawa ◽  
Michiya Mozumi ◽  
Magnus Cinthio ◽  
Hideyuki Hasegawa
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Carotid Artery ◽  
Wall Shear Stress ◽  
Common Carotid Artery ◽  
Estimation Method ◽  
Flow Imaging ◽  
Basic Study ◽  
Blood Flow Imaging ◽  
Wall Shear

scholarly journals The Effect of Wall Shear Stress on Two Phase Fluctuating Flow of Dusty Fluids by Using Light Hill Technique

Water ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1587
Author(s):  
Dolat Khan ◽  
Ata ur Rahman ◽  
Gohar Ali ◽  
Poom Kumam ◽  
Attapol Kaewkhao ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Base Fluid ◽  
Perturbation Technique ◽  
Fluid Velocity ◽  
Dust Particles ◽  
Stress Effect ◽  
Parallel Plates ◽  
Dusty Fluid ◽  
Wall Shear

Due to the importance of wall shear stress effect and dust fluid in daily life fluid problems. This paper aims to discover the influence of wall shear stress on dust fluids of fluctuating flow. The flow is considered between two parallel plates that are non-conducting. Due to the transformation of heat, the fluid flow is generated. We consider every dust particle having spherical uniformly disperse in the base fluid. The perturb solution is obtained by applying the Poincare-Lighthill perturbation technique (PLPT). The fluid velocity and shear stress are discussed for the different parameters like Grashof number, magnetic parameter, radiation parameter, and dusty fluid parameter. Graphical results for fluid and dust particles are plotted through Mathcad-15. The behavior of base fluid and dusty fluid is matching for different embedded parameters.

scholarly journals Numerical modeling in arterial hemodynamics incorporating fluid-structure interaction and microcirculation

2021 ◽  
Vol 18 (1) ◽  
Author(s):  
Fan He ◽  
Lu Hua ◽  
Tingting Guo
Keyword(s):  
Numerical Modeling ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Fluid Structure Interaction ◽  
Rigid Wall ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Arterial Hemodynamics ◽  
Wall Compliance ◽  
Wall Shear

Abstract Background The effects of arterial wall compliance on blood flow have been revealed using fluid-structure interaction in last decades. However, microcirculation is not considered in previous researches. In fact, microcirculation plays a key role in regulating blood flow. Therefore, it is very necessary to involve microcirculation in arterial hemodynamics. Objective The main purpose of the present study is to investigate how wall compliance affects the flow characteristics and to establish the comparisons of these flow variables with rigid wall when microcirculation is considered. Methods We present numerical modeling in arterial hemodynamics incorporating fluid-structure interaction and microcirculation. A novel outlet boundary condition is employed to prescribe microcirculation in an idealised model. Results The novel finding in this work is that wall compliance under the consideration of microcirculation leads to the increase of wall shear stress in contrast to rigid wall, contrary to the traditional result that wall compliance makes wall shear stress decrease when a constant or time dependent pressure is specified at an outlet. Conclusions This work provides the valuable study of hemodynamics under physiological and realistic boundary conditions and proves that wall compliance may have a positive impact on wall shear stress based on this model. This methodology in this paper could be used in real model simulations.

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