The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Necar Merah - One of the best experts on this subject based on the ideXlab platform.
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3-D finite element analysis of roller-expanded heat exchanger tubes in over-enlarged tubesheet holes
Applied Petrochemical Research, 2012Co-Authors: Necar Merah, A. Al-aboodi, A. N. Shuaib, Y. Al-nassarAbstract:Repeated de-stubbing and re-tubing of heat exchangers in petrochemical plants during their useful lifetime may result in over-enlarged tubesheet holes with overtolerances that exceed those prescribed by Tubular Exchanger Manufacturing Association (TEMA) standards ( 1988 ). Roller expansion of tubes in these over-enlarged holes may result in tube thinning and weakening of the joint due to a decrease of Interfacial Pressure between the tube and tubesheet. In the present work, a 3-D finite element (FE) model of a tube-tubesheet joint was used to determine displacement and stress distributions along the axial direction of roller expanded tube-tubesheet joint and to evaluate the combined effects of large initial clearance and strain hardening of tube material on Interfacial Pressure and tube deformation. The results obtained from the present model are compared to those of axisymmetric FE analysis and to the experimental results. Both axisymmetric and 3-D models are found to yield comparable trends showing that for elastic perfectly plastic tube material the residual contact Pressure remains constant well above the prescribed TEMA maximum overtolerance values. In addition, both models show that for strain hardening tube materials the Interfacial Pressure increases with increasing clearance. An appreciable difference is observed at high overtolerances where the 3-D model predicts cut-off clearances (clearance at which the Interfacial Pressure starts to drastically drop) which are about 30% lower than those predicted by the axisymmetric models. The tube inner surface deformation and pull out forces estimated from 3-D results compares very well with those obtained from the experimental tests.
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Combined Effects of Tube Projection, Initial Tube-Tubesheet Clearance, and Tube Material Strain Hardening on Rolled Joint Strength
Journal of Pressure Vessel Technology-transactions of The Asme, 2009Co-Authors: Necar Merah, A. N. Shuaib, Y. Al-nassar, Abdulaziz S. Alaboodi, S. S. Al-aniziAbstract:The tube-to-tubesheet joint strength is measured in terms of Interfacial Pressure between the tube’s outer surface and tubesheet bore. The strength of a rolled joint is influenced by several design parameters, including the type of tube and tubesheet materials, initial tube projection, and the initial radial clearance between the tube and tubesheet, among other factors. This paper uses finite element analysis (FEA) to evaluate the effect of several parameters on the strength of rolled joints having large overtolerances, a situation that applies to used equipment. An axisymmetric finite element model based on the sleeve diameter and rigid tube expanding roller concepts was used to analyze the effects of tube projection, initial tube-tubesheet clearance, and tube material strain-hardening property on the deformation behavior of the rolled tube and on the strength of the tube-tubesheet joint. The FEA results show that for zero tube projection (flush) the initial clearance effect is dependent on the strain-hardening capability of the tube material. For low strain-hardening tube material the Interfacial Pressure remains constant well above the Tubular Exchanger Manufacturer’s Association maximum overtolerance. A drastic reduction in joint strength is observed at high values of radial clearances. The cut-off clearance (clearance at which the Interfacial Pressure starts to drop) is found to vary linearly with the tube material hardening level, and the contact stress increases slightly for moderate strain-hardening tube materials but shows lower cut-off clearance levels. Furthermore, with flush tubes the maximum contact Pressure occurs close to the secondary face (at the end of rolling) while for joints with initial tube projection the contact Pressure shows two maxima occurring near the primary and the secondary faces. This is attributed to the presence of two elbows in tube deformation near the primary and secondary faces. The average Interfacial Pressure increased with increasing projection length for all clearances. Tube material strain hardening enhances the Interfacial Pressure in a similar fashion for all initial tube projection lengths considered in the analysis.
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modeling the effects of initial tube tubesheet clearance wall reduction and material strain hardening on rolled joint strength
Journal of Pressure Vessel Technology-transactions of The Asme, 2008Co-Authors: Abdulaziz S. Alaboodi, Necar Merah, A. N. Shuaib, Y Alnassar, S S AlaniziAbstract:between the tube’s outer surface and tubesheet hole surfaces. The joint integrity is affected by several design parameters, including the type of tube and tubesheet materials, the level of expansion, and the initial radial clearance between the tube and tubesheet. In the present work, an axisymmetric finite element model based on the sleeve diameter and rigid roller concepts is developed. The model has been used to evaluate the combined effects of clearance, wall reduction level, and strain hardening of tube and tubesheet materials on the Interfacial Pressure between tube and tubesheet. The finite element results show that the initial clearance effect is dependent on the strain hardening capability of the tube material. For low strain hardening tube materials, the Interfacial Pressure remains almost constant well above the Tubular Exchanger Manufacturing Association maximum radial over tolerance of 0.0254 mm 0.001 in.. These results are validated by the experimental data developed during the research program. As expected, a drastic reduction in joint strength is observed at high values of radial clearances. The cutoff clearance (clearance at which the Interfacial Pressure starts to drop) is found to vary linearly with tube material hardening level. The residual Pressure is found to increase slightly for moderate strain hardening tube materials but shows lower cutoff clearances. Wall reductions ranging from 1% to 12% were utilized in calculating the contact Pressure as a function of radial clearance. The results show that for low strain hardening materials the optimum value of residual contact stress is obtained for the industry recommended value of 5%. Finally, because of the absence of plastic deformation in the ligament, the level of tubesheet material strain hardening does not have any noticeable effect on the joint strength. DOI: 10.1115/1.2967809
Y. Al-nassar - One of the best experts on this subject based on the ideXlab platform.
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3-D finite element analysis of roller-expanded heat exchanger tubes in over-enlarged tubesheet holes
Applied Petrochemical Research, 2012Co-Authors: Necar Merah, A. Al-aboodi, A. N. Shuaib, Y. Al-nassarAbstract:Repeated de-stubbing and re-tubing of heat exchangers in petrochemical plants during their useful lifetime may result in over-enlarged tubesheet holes with overtolerances that exceed those prescribed by Tubular Exchanger Manufacturing Association (TEMA) standards ( 1988 ). Roller expansion of tubes in these over-enlarged holes may result in tube thinning and weakening of the joint due to a decrease of Interfacial Pressure between the tube and tubesheet. In the present work, a 3-D finite element (FE) model of a tube-tubesheet joint was used to determine displacement and stress distributions along the axial direction of roller expanded tube-tubesheet joint and to evaluate the combined effects of large initial clearance and strain hardening of tube material on Interfacial Pressure and tube deformation. The results obtained from the present model are compared to those of axisymmetric FE analysis and to the experimental results. Both axisymmetric and 3-D models are found to yield comparable trends showing that for elastic perfectly plastic tube material the residual contact Pressure remains constant well above the prescribed TEMA maximum overtolerance values. In addition, both models show that for strain hardening tube materials the Interfacial Pressure increases with increasing clearance. An appreciable difference is observed at high overtolerances where the 3-D model predicts cut-off clearances (clearance at which the Interfacial Pressure starts to drastically drop) which are about 30% lower than those predicted by the axisymmetric models. The tube inner surface deformation and pull out forces estimated from 3-D results compares very well with those obtained from the experimental tests.
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Combined Effects of Tube Projection, Initial Tube-Tubesheet Clearance, and Tube Material Strain Hardening on Rolled Joint Strength
Journal of Pressure Vessel Technology-transactions of The Asme, 2009Co-Authors: Necar Merah, A. N. Shuaib, Y. Al-nassar, Abdulaziz S. Alaboodi, S. S. Al-aniziAbstract:The tube-to-tubesheet joint strength is measured in terms of Interfacial Pressure between the tube’s outer surface and tubesheet bore. The strength of a rolled joint is influenced by several design parameters, including the type of tube and tubesheet materials, initial tube projection, and the initial radial clearance between the tube and tubesheet, among other factors. This paper uses finite element analysis (FEA) to evaluate the effect of several parameters on the strength of rolled joints having large overtolerances, a situation that applies to used equipment. An axisymmetric finite element model based on the sleeve diameter and rigid tube expanding roller concepts was used to analyze the effects of tube projection, initial tube-tubesheet clearance, and tube material strain-hardening property on the deformation behavior of the rolled tube and on the strength of the tube-tubesheet joint. The FEA results show that for zero tube projection (flush) the initial clearance effect is dependent on the strain-hardening capability of the tube material. For low strain-hardening tube material the Interfacial Pressure remains constant well above the Tubular Exchanger Manufacturer’s Association maximum overtolerance. A drastic reduction in joint strength is observed at high values of radial clearances. The cut-off clearance (clearance at which the Interfacial Pressure starts to drop) is found to vary linearly with the tube material hardening level, and the contact stress increases slightly for moderate strain-hardening tube materials but shows lower cut-off clearance levels. Furthermore, with flush tubes the maximum contact Pressure occurs close to the secondary face (at the end of rolling) while for joints with initial tube projection the contact Pressure shows two maxima occurring near the primary and the secondary faces. This is attributed to the presence of two elbows in tube deformation near the primary and secondary faces. The average Interfacial Pressure increased with increasing projection length for all clearances. Tube material strain hardening enhances the Interfacial Pressure in a similar fashion for all initial tube projection lengths considered in the analysis.
A. N. Shuaib - One of the best experts on this subject based on the ideXlab platform.
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3-D finite element analysis of roller-expanded heat exchanger tubes in over-enlarged tubesheet holes
Applied Petrochemical Research, 2012Co-Authors: Necar Merah, A. Al-aboodi, A. N. Shuaib, Y. Al-nassarAbstract:Repeated de-stubbing and re-tubing of heat exchangers in petrochemical plants during their useful lifetime may result in over-enlarged tubesheet holes with overtolerances that exceed those prescribed by Tubular Exchanger Manufacturing Association (TEMA) standards ( 1988 ). Roller expansion of tubes in these over-enlarged holes may result in tube thinning and weakening of the joint due to a decrease of Interfacial Pressure between the tube and tubesheet. In the present work, a 3-D finite element (FE) model of a tube-tubesheet joint was used to determine displacement and stress distributions along the axial direction of roller expanded tube-tubesheet joint and to evaluate the combined effects of large initial clearance and strain hardening of tube material on Interfacial Pressure and tube deformation. The results obtained from the present model are compared to those of axisymmetric FE analysis and to the experimental results. Both axisymmetric and 3-D models are found to yield comparable trends showing that for elastic perfectly plastic tube material the residual contact Pressure remains constant well above the prescribed TEMA maximum overtolerance values. In addition, both models show that for strain hardening tube materials the Interfacial Pressure increases with increasing clearance. An appreciable difference is observed at high overtolerances where the 3-D model predicts cut-off clearances (clearance at which the Interfacial Pressure starts to drastically drop) which are about 30% lower than those predicted by the axisymmetric models. The tube inner surface deformation and pull out forces estimated from 3-D results compares very well with those obtained from the experimental tests.
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Combined Effects of Tube Projection, Initial Tube-Tubesheet Clearance, and Tube Material Strain Hardening on Rolled Joint Strength
Journal of Pressure Vessel Technology-transactions of The Asme, 2009Co-Authors: Necar Merah, A. N. Shuaib, Y. Al-nassar, Abdulaziz S. Alaboodi, S. S. Al-aniziAbstract:The tube-to-tubesheet joint strength is measured in terms of Interfacial Pressure between the tube’s outer surface and tubesheet bore. The strength of a rolled joint is influenced by several design parameters, including the type of tube and tubesheet materials, initial tube projection, and the initial radial clearance between the tube and tubesheet, among other factors. This paper uses finite element analysis (FEA) to evaluate the effect of several parameters on the strength of rolled joints having large overtolerances, a situation that applies to used equipment. An axisymmetric finite element model based on the sleeve diameter and rigid tube expanding roller concepts was used to analyze the effects of tube projection, initial tube-tubesheet clearance, and tube material strain-hardening property on the deformation behavior of the rolled tube and on the strength of the tube-tubesheet joint. The FEA results show that for zero tube projection (flush) the initial clearance effect is dependent on the strain-hardening capability of the tube material. For low strain-hardening tube material the Interfacial Pressure remains constant well above the Tubular Exchanger Manufacturer’s Association maximum overtolerance. A drastic reduction in joint strength is observed at high values of radial clearances. The cut-off clearance (clearance at which the Interfacial Pressure starts to drop) is found to vary linearly with the tube material hardening level, and the contact stress increases slightly for moderate strain-hardening tube materials but shows lower cut-off clearance levels. Furthermore, with flush tubes the maximum contact Pressure occurs close to the secondary face (at the end of rolling) while for joints with initial tube projection the contact Pressure shows two maxima occurring near the primary and the secondary faces. This is attributed to the presence of two elbows in tube deformation near the primary and secondary faces. The average Interfacial Pressure increased with increasing projection length for all clearances. Tube material strain hardening enhances the Interfacial Pressure in a similar fashion for all initial tube projection lengths considered in the analysis.
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modeling the effects of initial tube tubesheet clearance wall reduction and material strain hardening on rolled joint strength
Journal of Pressure Vessel Technology-transactions of The Asme, 2008Co-Authors: Abdulaziz S. Alaboodi, Necar Merah, A. N. Shuaib, Y Alnassar, S S AlaniziAbstract:between the tube’s outer surface and tubesheet hole surfaces. The joint integrity is affected by several design parameters, including the type of tube and tubesheet materials, the level of expansion, and the initial radial clearance between the tube and tubesheet. In the present work, an axisymmetric finite element model based on the sleeve diameter and rigid roller concepts is developed. The model has been used to evaluate the combined effects of clearance, wall reduction level, and strain hardening of tube and tubesheet materials on the Interfacial Pressure between tube and tubesheet. The finite element results show that the initial clearance effect is dependent on the strain hardening capability of the tube material. For low strain hardening tube materials, the Interfacial Pressure remains almost constant well above the Tubular Exchanger Manufacturing Association maximum radial over tolerance of 0.0254 mm 0.001 in.. These results are validated by the experimental data developed during the research program. As expected, a drastic reduction in joint strength is observed at high values of radial clearances. The cutoff clearance (clearance at which the Interfacial Pressure starts to drop) is found to vary linearly with tube material hardening level. The residual Pressure is found to increase slightly for moderate strain hardening tube materials but shows lower cutoff clearances. Wall reductions ranging from 1% to 12% were utilized in calculating the contact Pressure as a function of radial clearance. The results show that for low strain hardening materials the optimum value of residual contact stress is obtained for the industry recommended value of 5%. Finally, because of the absence of plastic deformation in the ligament, the level of tubesheet material strain hardening does not have any noticeable effect on the joint strength. DOI: 10.1115/1.2967809
Moon-sun Chung - One of the best experts on this subject based on the ideXlab platform.
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An Advanced Semi-Implicit Method for Two-Phase Flow Calculation
2010 14th International Heat Transfer Conference Volume 1, 2010Co-Authors: Sung-jae Yi, Moon-sun ChungAbstract:Introducing the Interfacial Pressure jump terms based on the surface tension into the momentum equations of two-phase two-fluid model, the system of governing equations is turned mathematically into the hyperbolic system. The eigenvalues of the equation system become always real representing the void wave and the Pressure wave propagation speeds as shown in the present authors’ reference: Numerical Heat Transfer —Part B, vol. 40, pp. 83–97. To solve the Interfacial Pressure jump terms with void fraction gradients implicitly, the conventional semi-implicit method should be modified as an intermediate iteration method for void fraction at fractional time step. Owing to this modified numerical scheme with surface tension effect, the advanced semi-implicit method (ASIM) then becomes stable without conventional additive terms. As a consequence, including the Interfacial Pressure jump terms with the advanced semi-implicit method, the numerical solutions of typical two-phase problems can be more stable and sound than those calculated exclusively by using any other terms like virtual mass, or artificial viscosity.Copyright © 2010 by ASME
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A modified semi-implicit method for a hyperbolic two-fluid model
Applied Numerical Mathematics, 2009Co-Authors: Moon-sun ChungAbstract:By introducing the Interfacial Pressure jump terms based on a surface tension into the momentum equations of a two-phase two-fluid model, the mathematical property of the governing equations is changed to a hyperbolic type. Then the eigenvalues of the equation system always become always real values representing the void wave and the Pressure wave propagation speeds as shown in the present author's former article: Numerical Heat Transfer - Part B (40) (2001) 83-97. To solve the Interfacial Pressure jump terms with void fraction gradients implicitly, the conventional semi-implicit method should be modified by inserting an intermediate calculation process for a void fraction at a fractional time step. This modified semi-implicit method then becomes stable without conventional additive terms. Consequently, by including the Interfacial Pressure jump terms with the modified semi-implicit method, the numerical calculations of the void discontinuity propagation and water faucet problems can become more stable and sound than those calculated by using virtual mass terms.
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Characteristic development of hyperbolic two-dimensional two-fluid model for gas–liquid flows with surface tension
Applied Mathematical Modelling, 2007Co-Authors: Moon-sun ChungAbstract:Abstract A new hyperbolic, two-dimensional two-fluid model is developed to properly solve two-phase gas–liquid flows. Adopting the Interfacial Pressure jump terms in the momentum equations, the numerical stability is confirmed owing to the improvement in the mathematical property of the equation system. The derivation of the Interfacial Pressure jump terms is based on the infinitesimal surface-tension effect incorporated in the Pressure difference at the gas–liquid interface. Through the characteristic analysis on the equation system, the eight eigenvalues are obtained analytically and they are proved real values representing phasic convective velocities and phasic sound speeds. Furthermore, the characteristic sound speeds are comparable with the earlier experimental data in excellent agreements. In addition, the eigenvectors are obtained analytically and they are shown to be linearly independent. Consequently, the governing equation system is mathematically hyperbolic with reasonable characteristic speeds by which the upwind numerical method avails. Advantage and possibility of the present model are discussed in some detail.
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On the Wave Dispersion Relevant to the Virtual Mass Terms in the Two-Phase Two-Fluid Model
Numerical Heat Transfer Part A-applications, 2001Co-Authors: Moon-sun ChungAbstract:Interfacial Pressure jump terms are introduced in the momentum equations of the two-fluid two-phase flow while at the same time we keep the conventional virtual mass force as a nonobjective formulation. The Pressure discontinuity across a thin interface due to the surface tension is compactly represented by a function of the fluid bulk moduli. The governing equations with the Interfacial Pressure jump terms produced a hyperbolic equation system having real eigenvalues for the bubbly flow, regardless of whether the virtual mass terms are added or not. The mixture sound speed for the two-phase flow evaluated using the combined Interfacial Pressure jump and conventional virtual mass terms has shown increasing dispersion of the small-amplitude waves when the virtual mass coefficient is larger. When the virtual mass terms are added to account for the accelerating flow, care should be exercised therefore not to introduce nonphysical wave dispersion.
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Effect of Interfacial Pressure jump and virtual mass terms on sound wave propagation in the two-phase flow
Journal of Sound and Vibration, 2001Co-Authors: Moon-sun Chung, Keun Sick ChangAbstract:Virtual mass terms as an Interfacial force, taking account of relative acceleration of the bubbles in the liquid phase, have been generally accepted in the two-phase flow models since they conditionally stabilize the numerical scheme. Despite the convincing physical reasoning associated with the bubble flow dynamics, it can be shown that the virtual mass terms unfortunately cause non-physical dispersion in the sound wave propagation. By introducing in the momentum equations new Interfacial Pressure jump terms based on the surface tension and represented by a function of the fluid bulk moduli, the governing equation system becomes strictly hyperbolic in the present paper with real eigenvalues, regardless of inclusion of the virtual mass terms. It is remarkable that the eigenvalues give realistic speeds of sound when the objective virtual mass terms are reduced more and more until they vanish. On the occasion that the virtual mass terms have to be kept with the Interfacial Pressure jump terms in the wave-dominant two-phase flow problems, we recommend that the non-physical wave dispersion due to the virtual mass terms should be appropriately controlled.
V. B. Fainerman - One of the best experts on this subject based on the ideXlab platform.
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Dilational visco-elasticity of BLG adsorption layers at the solution/tetradecane interface – Effect of pH and ionic strength A Physicochemical and engineering aspects
Colloids and Surfaces, 2020Co-Authors: G. Gochev, V. Ulaganathan, Jürgen Krägel, Eugene V. Aksenenko, V. B. Fainerman, Reinhard MillerAbstract:Drop profile analysis tensiometry is applied to measure the dilational visco-elasticity of BLG at the buffered aqueous solution/tetradecane (W/TD) interface using oscillating drops of TD immersed in W at frequencies between 0.01–0.2Hz. The buffered solutions were investigated at pH 3, pH 5 (isoelectric point) and pH 7 at different buffer concentrations (1mM, 10mM and 100mM). The real part of the complex visco-elasticity shows a maximum when plotted as a function of the Interfacial Pressure Π. In contrast to the water/air surface (W/A) where we observe maximum elasticity values between 15 and 20mN/m, at the W/TD interface these maximum values are up to 65–70mM/m, which is in parallel with the much higher Interfacial Pressure values at the W/TD interface when compared to the W/A surface.
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Dilational visco-elasticity of BLG adsorption layers at the solution/tetradecane interface – Effect of pH and ionic strength
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2017Co-Authors: G. Gochev, V. Ulaganathan, Jürgen Krägel, Eugene V. Aksenenko, V. B. Fainerman, Reinhard MillerAbstract:Abstract Drop profile analysis tensiometry is applied to measure the dilational visco-elasticity of BLG at the buffered aqueous solution/tetradecane (W/TD) interface using oscillating drops of TD immersed in W at frequencies between 0.01–0.2 Hz. The buffered solutions were investigated at pH 3, pH 5 (isoelectric point) and pH 7 at different buffer concentrations (1 mM, 10 mM and 100 mM). The real part of the complex visco-elasticity shows a maximum when plotted as a function of the Interfacial Pressure Π. In contrast to the water/air surface (W/A) where we observe maximum elasticity values between 15 and 20 mN/m, at the W/TD interface these maximum values are up to 65–70 mM/m, which is in parallel with the much higher Interfacial Pressure values at the W/TD interface when compared to the W/A surface.
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thermodynamics Interfacial Pressure isotherms and dilational rheology of mixed protein surfactant adsorption layers
Advances in Colloid and Interface Science, 2016Co-Authors: V. B. Fainerman, E V Aksenenko, J Kragel, R MillerAbstract:Abstract Proteins and their mixtures with surfactants are widely used in many applications. The knowledge of their solution bulk behavior and its impact on the properties of Interfacial layers made great progress in the recent years. Different mechanisms apply to the formation process of protein/surfactant complexes for ionic and non-ionic surfactants, which are governed mainly by electrostatic and hydrophobic interactions. The surface activity of these complexes is often remarkably different from that of the individual protein and has to be considered in respective theoretical models. At very low protein concentration, small amounts of added surfactants can change the surface activity of proteins remarkably, even though no strongly Interfacial active complexes are observed. Also small added amounts of non-ionic surfactants change the surface activity of proteins in the range of small bulk concentrations or surface coverages. The modeling of the equilibrium adsorption behavior of proteins and their mixtures with surfactants has reached a rather high level. These models are suitable also to describe the high frequency limits of the dilational viscoelasticity of the Interfacial layers. Depending on the nature of the protein/surfactant interactions and the changes in the Interfacial layer composition rather complex dilational viscoelasticities can be observed and described by the available models. The differences in the Interfacial behavior, often observed in literature for studies using different experimental methods, are at least partially explained by a depletion of proteins, surfactants and their complexes in the range of low concentrations. A correction of these depletion effects typically provides good agreement between the data obtained with different methods, such as drop and bubble profile tensiometry.