Journal articles on the topic 'Transient non-isothermal mode'
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1
Krause, Maike, Katharina Sessler, Anna Kaziales, Richard Grahl, Sabrina Noettger, Holger Barth, and Herbert Schmidt. "Variants of Escherichia coli Subtilase Cytotoxin Subunits Show Differences in Complex Formation In Vitro." Toxins 11, no. 12 (December 3, 2019): 703. http://dx.doi.org/10.3390/toxins11120703.
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The subtilase cytotoxin (SubAB) of Shiga toxin-producing Escherichia coli (STEC) is a member of the AB5 toxin family. In the current study, we analyzed the formation of active homo- and hetero-complexes of SubAB variants in vitro to characterize the mode of assembly of the subunits. Recombinant SubA1-His, SubB1-His, SubA2-2-His, and SubB2-2-His subunits, and His-tag-free SubA2-2 were separately expressed, purified, and biochemically characterized by circular dichroism (CD) spectroscopy, size-exclusion chromatography (SEC), and analytical ultracentrifugation (aUC). To confirm their biological activity, cytotoxicity assays were performed with HeLa cells. The formation of AB5 complexes was investigated with aUC and isothermal titration calorimetry (ITC). Binding of SubAB2-2-His to HeLa cells was characterized with flow cytometry (FACS). Cytotoxicity experiments revealed that the analyzed recombinant subtilase subunits were biochemically functional and capable of intoxicating HeLa cells. Inhibition of cytotoxicity by Brefeldin A demonstrated that the cleavage is specific. All His-tagged subunits, as well as the non-tagged SubA2-2 subunit, showed the expected secondary structural compositions and oligomerization. Whereas SubAB1-His complexes could be reconstituted in solution, and revealed a Kd value of 3.9 ± 0.8 μmol/L in the lower micromolar range, only transient interactions were observed for the subunits of SubAB2-2-His in solution, which did not result in any binding constant when analyzed with ITC. Additional studies on the binding characteristics of SubAB2-2-His on HeLa cells revealed that the formation of transient complexes improved binding to the target cells. Conclusively, we hypothesize that SubAB variants exhibit different characteristics in their binding behavior to their target cells.
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Patisson, Fabrice, Magda Galant François, and Denis Ablitzer. "A non-isothermal, non-equimolar transient kinetic model for gas-solid reactions." Chemical Engineering Science 53, no. 4 (February 1998): 697–708. http://dx.doi.org/10.1016/s0009-2509(97)00333-3.
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Shah, A. A., G. S. Kim, P. C. Sui, and D. Harvey. "Transient non-isothermal model of a polymer electrolyte fuel cell." Journal of Power Sources 163, no. 2 (January 2007): 793–806. http://dx.doi.org/10.1016/j.jpowsour.2006.09.022.
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Ziabicki, Andrzej, Beata Misztal-Faraj, and Leszek Jarecki. "Kinetic model of non-isothermal crystal nucleation with transient and athermal effects." Journal of Materials Science 51, no. 19 (June 28, 2016): 8935–52. http://dx.doi.org/10.1007/s10853-016-0145-8.
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Gonçalves, Willer P., Danmer M. Quinones, Abelardo B. Barreto, and Marcio S. Carvalho. "Petroleum reservoir parameters estimation using non-isothermal transient model and optimization methods." Journal of Petroleum Science and Engineering 212 (May 2022): 110269. http://dx.doi.org/10.1016/j.petrol.2022.110269.
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Bharath, S., B. C. Nakra, and K. N. Gupta. "Mathematical Model of a Railway Pneumatic Brake System With Varying Cylinder Capacity Effects." Journal of Dynamic Systems, Measurement, and Control 112, no. 3 (September 1, 1990): 456–62. http://dx.doi.org/10.1115/1.2896164.
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Governing equations for the analysis of pressure transient are derived from the principle of conservation of mass and momentum for a pneumatic brake system, which consists of a train pipe connected to a number of linear actuators (brake cylinders with piston displacement). The governing one-dimensional non-linear partial differential equations for the train pipe, non-linear ordinary differential equations for the brake cylinders, and second-order differential equation of motion for piston displacement are solved to determine the pressure transients in the brake system for a step change in pressure at the inlet. The governing equations are nondimensionalized and reduced to a set of ordinary nonlinear differential difference equations and integrated by standard numerical methods. The flow is considered isothermal, and the friction effects for turbulent and laminar flow are evaluated by quasi-steady state approximation. The auxiliary reservoir volume effect is also included. The results are compared with the experimental data obtained on a brake test rig.
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Poudyal, Hari, Suma R. Das, and Abhilash J. Chandy. "NON-ISOTHERMAL EFFECTS IN PARTIALLY FILLED RUBBER MIXING SIMULATIONS OF MANUFACTURING PROCESSES." Rubber Chemistry and Technology 92, no. 1 (January 1, 2019): 152–67. http://dx.doi.org/10.5254/rct.19.82590.
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ABSTRACT A finite volume technique is used to analyze the isothermal and non-isothermal flow behavior for the rubber mixing process in a two-dimensional, partially filled (75%) internal mixer, which consists of two counterrotating rotors rotating at 20 rpm. In order to capture the interface between air and rubber, an Eulerian multiphase model called volume of fluid (VOF) has been employed here. The transient flow behavior was accomplished by a sliding mesh technique, and the highly viscous, non-Newtonian properties of the rubber have been characterized using the Bird–Carreau model. Most of the previous computational fluid dynamic (CFD)-based investigations of rubber mixing assumed isothermal flow, and consequently negligible viscous heat generation, temperature rise, and viscosity drop associated with heat generation. Hence, a non-isothermal simulation is carried out, and results are compared with those of an equivalent isothermal simulation. In addition, dispersive and distributive mixing characteristics are assessed using statistics calculated from particle tracks generated by a set of massless and neutral particles that have been injected in the simulation. For this purpose, quantities such as the cumulative distribution of maximum shear stress, length of stretch, and cluster distribution index are calculated and compared between isothermal and non-isothermal conditions. Results showed a significant difference between the isothermal and non-isothermal simulations, thus making the isothermal assumption critical. Also, the non-isothermal simulation predicted better mixing during the entire mixing cycle.
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Chu, Dandan, Xin Li, and Shu Zhang. "A non-isothermal transient model for a metal-free quinone–bromide flow battery." Electrochimica Acta 190 (February 2016): 434–45. http://dx.doi.org/10.1016/j.electacta.2015.12.128.
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Shabaniverki, Soheila, and Siamak Serajzadeh. "The kinetics of isothermal and non-isothermal recovery within cold-rolled aluminum alloy." Multidiscipline Modeling in Materials and Structures 11, no. 1 (June 8, 2015): 88–101. http://dx.doi.org/10.1108/mmms-12-2013-0072.
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Purpose – The purpose of this paper is to study the kinetics of static recovery in cold-rolled aluminum alloy under different heating rates. Design/methodology/approach – Deformation modeling was first performed to assess the distributions of plastic strain and stress within the deformed alloy. In the next stage, thermal analysis and the rate equation of static recovery were employed to determine the progress of static recovery under non-isothermal conditions. Accordingly, a thermal finite element analysis and the Runge-Kutta method were utilized to handle the transient heat conduction and the progress of static recovery. Finally, low temperature annealing heat treatments were conducted to verify the model predictions. Accordingly, the tensile tests were conducted to measure the yield stresses of cold-rolled plates subjected to the subsequent annealing treatment at different temperatures and durations. Findings – The results indicate that the employed algorithm can be used as an appropriate predictive tool for designing a low temperature heat treatment schedule to achieve the desired yield stress. Originality/value – The kinetics of non-isothermal recovery and resulting yield stress are well predicted under practical annealing conditions.
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Chen, Xing Long, Bin Jia, Yan Yin, and Qing Du. "Numerical Simulation of Transient Response of Inlet Relative Humidity for High Temperature PEM Fuel Cells with Material Properties." Advanced Materials Research 625 (December 2012): 226–29. http://dx.doi.org/10.4028/www.scientific.net/amr.625.226.
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High temperature proton exchange membrane fuel cells (HT-PEMFCs) have been drawing much attention due to their easy water management and other advantages. A three-dimensional non-isothermal transient model of HT-PEMFCs with phosphoric acid doped polybenzimidazole (PBI) membrane is developed in this study. The inlet relative humidity (RH) is considered for the membrane conductivity in the model. The effect of inlet RH on the transient response of the cell is discussed and the results show that the increase of inlet RH had positive effect on cell performance but negative effect on transient response.
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Yang, Jian, Yue Zhang, Mingxin Gao, and Hua Song. "Effects of non-isothermal oxidation on transient conjugate heat transfer of the cryo-supersonic air-quenching." Thermal Science, no. 00 (2021): 147. http://dx.doi.org/10.2298/tsci201111147y.
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In this paper, the effects of non-isothermal oxidation on transient conjugate heat transfer of the cryo-supersonic air-quenching are investigated based on a double-layered oxidation kinetics model, while a unified conjugate heat transfer formula is developed to synthetically consider the near-wall turbulence, non-isothermal oxidation, and surface radiation. The comparison between numerical and experimental results are also presented to check the validity of the developed model. The results indicate that the film growth has some degree of inhibition to the conjugate heat transfer, in particular, the stagnation temperature increases linearly by about 5 K per 100 ?m increase in film thickness, and the effective conjugate heat transfer coefficient in the stagnation region decreases linearly by about 55 Wm-2K-1 per 100 ?m increase in film thickness. Moreover, the oxide film would have little impact on transient conjugate heat transfer when the near-wall velocity is higher due to the effect of viscous dissipation.
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Wang, Xiaoyu, Xing Jin, Yonggao Yin, Xing Shi, and Xin Zhou. "A transient heat and moisture transfer model for building materials based on phase change criterion under isothermal and non-isothermal conditions." Energy 224 (June 2021): 120112. http://dx.doi.org/10.1016/j.energy.2021.120112.
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Subani, Norazlina, and Norsarahaida Amin. "The effect of mass ratio on the flow characteristics of hydrogen-natural gas mixture using reduced order modelling." Malaysian Journal of Fundamental and Applied Sciences 13, no. 4-1 (December 5, 2017): 381–89. http://dx.doi.org/10.11113/mjfas.v13n4-1.801.
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This work focuses on the development of a mathematical model as a viable alternative to pinpoint locations of gas leaks in a pipeline. The transient non-isothermal flow of hydrogen-natural gas mixture is considered because hydrogen is often transported in the same pipeline as natural gas to reduce the transportation cost. The mathematical model developed took into consideration the effect of the mass ratio of gas mixture. The gas mixture was assumed to be homogeneous and the transient pressure wave was created by the sudden or instantaneous closure of a downstream shut-off valve to ensure the attainment of minimum pressure at the downstream end within a short time. The governing equations were numerically solved using the reduced order modelling (ROM) technique, which had not been previously applied on non-isothermal models involving gas mixtures. Numerical results observed that the mass ratio of hydrogen to natural gas should not be more than 0.5 to ensure that leakage does not occur before the estimated leak position. An increase in the mass ratio leads to an increase in the pressure and celerity wave, while the leak location and the amount of leak discharge decrease.
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Esparza-Isunza, Tristán, and Felipe López-Isunza. "Modeling the Transient VOC (toluene) Oxidation in a Packed-Bed Catalytic Reactor." International Journal of Chemical Reactor Engineering 14, no. 6 (December 1, 2016): 1177–85. http://dx.doi.org/10.1515/ijcre-2016-0026.
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Abstract A model is developed to study the transient behavior of a non-isothermal, non-adiabatic packed-bed reactor during VOC (toluene) oxidation with air on a mixed-oxide catalyst via Mars-van Krevelen kinetic scheme. The aim is to find a safe reactor design and operating conditions for VOC elimination, which has been collected in a battery of adsorption units from dilute VOC streams. Once each adsorption column is saturated, a non-isothermal desorption takes place, and the gas stream exiting the sequence of VOC desorption columns feeds continuously the catalytic reactor for VOC elimination. The reactor model describes a 2D two-phase system interacting through the gas-solid interphase, including convection and axial and radial dispersions of mass and heat. The simulations show that the gas flow velocity, and reactor and particle diameters, are key parameters to achieve a safe design, and that traveling reaction fronts in the packed-bed exist when a series of reversible stepwise changes are performed in the concentration and temperature at the feed, as a result of the transient balance between heat generation and heat elimination along the packed-bed. When comparing the perturbation in VOC concentration at the feed versus those in temperature, a large parametric sensitivity is observed for the latter case without the presence of multiple steady states. Due to the uncertainty in the values of the effective heat transport parameters, transient responses of different magnitude are observed for the same operating conditions when using heat transport parameter of different magnitude.
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Chang, L., M. N. Webster, and A. Jackson. "On the Pressure Rippling and Roughness Deformation in Elastohydrodynamic Lubrication of Rough Surfaces." Journal of Tribology 115, no. 3 (July 1, 1993): 439–44. http://dx.doi.org/10.1115/1.2921656.
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The objective of this paper is to conduct a qualitative analysis on the effects of lubricant shear thinning, lubricant shear heating and the roughness-induced transients on the pressure rippling and roughness deformation that occurs under elastohydrodynamic lubrication (EHL) conditions. To facilitate the analysis, the numerical solutions to an example problem of EHL line contact between a perfectly smooth surface and a sinusoidal rough surface are presented. This micro-EHL problem is first solved using the conventional model of a Newtonian lubricant and a stationary rough surface under isothermal conditions. It is then solved by including the non-Newtonian effects, the roughness-induced transients and the thermal effects in sequence, so that the changes in the results brought about by each of these elements can be clearly observed and then analyzed. The analysis, which is not limited to the model problem solved in this paper, suggests that misleading results of large pressure rippling and flattened surface roughness are obtained using the Newtonian lubricant models under steady-state, isothermal conditions. Much less micro-deformation of the surface roughness is actually produced because the magnitude of the pressure ripples is greatly limited by either the lubricant non-Newtonian shear thinning and shear heating or the roughness-induced transients.
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Xia, Ming. "Thermo-mechanical coupling particle simulation of three-dimensional large-scale non-isothermal problems." Engineering Computations 34, no. 5 (July 3, 2017): 1551–71. http://dx.doi.org/10.1108/ec-04-2016-0135.
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Purpose The main purpose of this paper is to present a comprehensive upscale theory of the thermo-mechanical coupling particle simulation for three-dimensional (3D) large-scale non-isothermal problems, so that a small 3D length-scale particle model can exactly reproduce the same mechanical and thermal results with that of a large 3D length-scale one. Design/methodology/approach The objective is achieved by following the scaling methodology proposed by Feng and Owen (2014). Findings After four basic physical quantities and their similarity-ratios are chosen, the derived quantities and its similarity-ratios can be derived from its dimensions. As the proposed comprehensive 3D upscale theory contains five similarity criteria, it reveals the intrinsic relationship between the particle-simulation solution obtained from a small 3D length-scale (e.g. a laboratory length-scale) model and that obtained from a large 3D length-scale (e.g. a geological length-scale) one. The scale invariance of the 3D interaction law in the thermo-mechanical coupled particle model is examined. The proposed 3D upscale theory is tested through two typical examples. Finally, a practical application example of 3D transient heat flow in a solid with constant heat flux is given to illustrate the performance of the proposed 3D upscale theory in the thermo-mechanical coupling particle simulation of 3D large-scale non-isothermal problems. Both the benchmark tests and application example are provided to demonstrate the correctness and usefulness of the proposed 3D upscale theory for simulating 3D non-isothermal problems using the particle simulation method. Originality/value The paper provides some important theoretical guidance to modeling 3D large-scale non-isothermal problems at both the engineering length-scale (i.e. the meter-scale) and the geological length-scale (i.e. the kilometer-scale) using the particle simulation method directly.
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Adewumi, Michael A., E. S. Eltohami, and A. Solaja. "Possible Detection of Multiple Blockages Using Transients." Journal of Energy Resources Technology 125, no. 2 (June 1, 2003): 154–59. http://dx.doi.org/10.1115/1.1525002.
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This work explores the possibility of utilizing the interaction between a pressure pulse propagating in a pipe with the blockages therein, as a means of blockage detection and characterization. Whereas an earlier work focused on a single blockage, the present work attempts to extend the strategy to multiple blockages. A one-dimensional isothermal non-compositional single-phase Eulerian model was used to describe the propagation of a pressure pulse through a pipe with multiple blockages. Pressure variations at the inlet caused by reflections of the propagating transient are monitored and analyzed. This analysis is used to make deductions about the internal configuration of the pipe. The results demonstrate that the technique is feasible and that accurate characterization of multiple blockages is possible.
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Slimani, Zakaria, Abdelkrim Trabelsi, Joseph Virgone, and Roberto Zanetti Freire. "Study of the Hygrothermal Behavior of Wood Fiber Insulation Subjected to Non-Isothermal Loading." Applied Sciences 9, no. 11 (June 9, 2019): 2359. http://dx.doi.org/10.3390/app9112359.
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Building envelopes are constantly subjected to temperature and moisture gradients. This loading induces a complex response, particularly for highly hygroscopic insulating materials. Latent effects can no longer be neglected for these materials in which heat and moisture transfers are strongly coupled. The purpose of this article is to analyze the behavior of a wood fiber insulation subjected to non-isothermal loading under a vapor concentration gradient. An experimental setup and a mathematical model of hygrothermal transfer were developed to analyze the behavior of the wall. The mathematical model describes the main physical phenomena involved, notably water vapor adsorption and the dependence of thermophysical properties in state variables. The experimental setup developed allows studying a wall under controlled conditions. The temperature and relative humidity profiles within the wall were measured. The evolution of the profiles with time suggests that the adsorption of the water vapor occurs together with the redistribution of liquid water within the envelope. The comparison of the experimental results with the numerical model shows good agreement although the prediction can be improved during the transient phase. The comparisons of these results with a purely diffusive thermal transfer model show the limits of the latter and permit quantifying the latent effects on the total heat transfer.
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Nikas, George K. "Fatigue Life and Traction Modeling of Continuously Variable Transmissions." Journal of Tribology 124, no. 4 (September 24, 2002): 689–98. http://dx.doi.org/10.1115/1.1491976.
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A model was developed to study the elastohydrodynamics and contact mechanics of toroidal Continuously Variable Transmission (CVT) type contacts. The aim is to predict the fatigue life, traction and efficiency of such contacts with the intention of making optimizations based on design criteria and constraints. A generalized Reynolds equation was developed for isothermal, transient lubrication of elliptical rough contacts with mixed rolling, two-dimensional sliding, and spinning conditions, incorporating any non-Newtonian model, roughness asperity isothermal elastoplastic interactions, and a three-dimensional subsurface stress analysis. The output is in the form of film thickness and traction maps, including contact efficiency, three-dimensional stress fields, and, finally, the predicted fatigue lives of CVT contacts, based on the Ioannides-Harris life model. A parametric study reveals the effect of surface roughness, lubricant bulk temperature, contact ellipticity ratio, slide-roll ratio, and contact load on the fatigue life, traction and contact efficiency of CVTs, and allows for design optimizations based on a compromise between life, traction and efficiency.
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Li, Xianglin, and Amir Faghri. "Optimization of the Cathode Structure of Lithium-Air Batteries Based on a Two-Dimensional, Transient, Non-Isothermal Model." Journal of The Electrochemical Society 159, no. 10 (2012): A1747—A1754. http://dx.doi.org/10.1149/2.043210jes.
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Zhang, Yue, Jian Yang, Ming-Xin Gao, and Hua Sono. "Heat transfer analysis of the forced air quenching with non-isothermal and non-uniform oxidation." PLOS ONE 16, no. 6 (June 17, 2021): e0253240. http://dx.doi.org/10.1371/journal.pone.0253240.
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In this paper, the heat transfer characteristics of the forced air quenching with non-isothermal and non-uniform oxidation are investigated. By introducing the variations of interfacial temperature and oxygen partial pressure, a three-layered non-isothermal high-temperature oxidation kinetic model is developed, in which a discrete-time modeling method is employed to solve the problem of integration of the transient terms, and a special interfacial grid treatment is used for considering the growth of each oxide layer and updating of the thermal properties. Moreover, a parameter identification method using the multi-objective genetic algorithm is proposed for the inverse solution of the oxidation parabolic parameters based on the measured scale thicknesses in oxidation experiment. A case study of the forced air quenching of a Q235 disk is presented to validate the availability of the developed formulas. Then the interfacial heat transfer characteristics are analyzed, while the numerical solutions with and without oxidation are both performed for in-depth comparison. Results indicate that the active quenching region is mainly centralized in the vicinity of stagnation region. The radial variation regularity of the temperature difference across the total oxide layer is mainly determined by the thermal conductivity and the scale thickness. The existence of the oxide scale actually produces a certain thermal resistance during the quenching process and the effects of the oxide scale increases with the radial coordinate due to the interfacial temperature distribution. The results obtained can provide theoretical derivation for precise control of the internal phase transformation during the forced air quenching process.
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Meng, Hua. "Numerical investigation of transient responses of a PEM fuel cell using a two-phase non-isothermal mixed-domain model." Journal of Power Sources 171, no. 2 (September 2007): 738–46. http://dx.doi.org/10.1016/j.jpowsour.2007.06.029.
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Xu, Zhengming, Xianzhi Song, Gensheng Li, Kan Wu, Zhaoyu Pang, and Zhaopeng Zhu. "Development of a transient non-isothermal two-phase flow model for gas kick simulation in HTHP deep well drilling." Applied Thermal Engineering 141 (August 2018): 1055–69. http://dx.doi.org/10.1016/j.applthermaleng.2018.06.058.
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Osiadacz, Andrzej. "Assessing Hydrate Formation in Natural Gas Pipelines Under Transient Operation / Ocena zjawiska tworzenia się hydratów w warunkach nieustalonego przepływu gazu w gazociągach." Archives of Mining Sciences 58, no. 1 (March 1, 2013): 131–44. http://dx.doi.org/10.2478/amsc-2013-0009.
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This work presents a transient, non-isothermal compressible gas flow model that is combined with a hydrate phase equilibrium model. It enables, to determine whether hydrates could form under existing operating conditions in natural gas pipelines. In particular, to determine the time and location at which the natural gas enters the hydrate formation region. The gas flow is described by a set of partial differential equations resulting from the conservation of mass, momentum, and energy. Real gas effects are determined by the predictive Soave-Redlich-Kwong group contribution method. By means of statistical mechanics, the hydrate model is formulated combined with classical thermodynamics of phase equilibria for systems that contain water and both hydrate forming and non-hydrate forming gases as function of pressure, temperature, and gas composition. To demonstrate the applicability a case study is conducted.
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Górecki, Paweł, Krzysztof Górecki, and Janusz Zarębski. "Accurate Circuit-Level Modelling of IGBTs with Thermal Phenomena Taken into Account." Energies 14, no. 9 (April 22, 2021): 2372. http://dx.doi.org/10.3390/en14092372.
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This paper proposes a new compact electrothermal model of the Insulated Gate Bipolar Transistors (IGBT) dedicated for SPICE (Simulation Program with Integrated Circuit Emphasis). This model makes it possible to compute the non-isothermal DC characteristics of the considered transistor and the waveforms of terminal voltages and currents of the investigated device and its internal temperature at transients. This model takes into account the nonlinearity of thermal phenomena in this device. The form of the formulated model is described and the problem of estimating its parameter values is discussed. The correctness of the proposed model was verified experimentally both at DC operation and at transients. The obtained results are compared to the results of computations performed with the use of the classical literature model. A very good agreement between the results of measurements and computations performed with the new model is obtained at different cooling conditions and in a wide range of changes of parameters characterising the electrical excitation of the tested device.
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Hanna, Farah, Guilhem Michel Roux, Olivier Asserin, Jean Christophe Brachet, and René Billardon. "Modelling of the Non-Isothermal Austenite Formation Kinetics of a X10CrMoVNb9-1 Martensitic Steel." Solid State Phenomena 172-174 (June 2011): 815–20. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.815.
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This work is part of a collaborative study between CEA-Saclay and LMT-Cachan on the numerical simulation of multi-pass GTA-Welding of thick specimens made of X10CrMoVNb9-1 (ASTM 387 or “T91”) steel. This material is considered as a candidate for some components of future Very High Temperature nuclear Reactors. Some parts of these components should be manufactured by assembling thick components (typically 200 mm) using narrow groove multi-pass GTA-Welding process. This welding process generates complex thermo-mechanical cycles in the HAZ (Heat Affected Zone) inducing complex microstructural transformations and residual stresses which should affect the integrity of the vessels behaviour. In a previous study, G.-M. Roux [1] developed a first version of a Thermo-Metallurgical-Mechanical "TMM" model for the X10CrMoVNb9-1 martensitic steel. This model was validated regarding residual stresses on simple mono-pass spot-welding tests. In this paper, focus is made on the modelling of the complex austenitisation process of the tempered martensitic steel as induced by the multi-pass process. Three different approaches are presented, viz. a model first proposed by Brachet et al., second a new model based on JMA approach and last, the simple differential Leblond model that is implemented in various finite element codes. These models are identified from standard dilatometry tests performed over a large range of heating rates, viz. [0.1°C/s, 100°C/s]. Finally, the response of these models, and therefore, their predicting capabilities, are compared to the experimental response of the material for different transients that have been designed to be representative of the temperature history in different points of a multi-pass welding HAZ.
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Shi, Yan, Fu Gang Wang, Guan Hong Feng, Hai Long Tian, and Hong Wu Lei. "Numerical Simulation and Parameter Analysis on Low-Temperature Geothermal System in Homogeneous Porous Medium." Applied Mechanics and Materials 409-410 (September 2013): 578–83. http://dx.doi.org/10.4028/www.scientific.net/amm.409-410.578.
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According to the mass and energy conservation principle of simulation program TOUGH2 used for non-isothermal multi-phase fluid and heat flow in porous and fractured media, the heat transport mathematical model of low-temperature shallow geothermal system is set up in homogeneous porous medium. The fundamental scientific issues on heat transfer characteristics and distribution of transient temperature field of heat exchange wells in summer is discussed in this paper. In addition, the significance and correlation between the changes of hydrogeology parameters and temperature field of the soil is analyzed. So as to the practical application of geothermal energy development can be guided by the achievements of the research.
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Narahari, Marneni, Suresh Kumar Raju Soorapuraju, Rajashekhar Pendyala, and Ioan Pop. "Transient two-dimensional natural convection flow of a nanofluid past an isothermal vertical plate using Buongiorno’s model." International Journal of Numerical Methods for Heat & Fluid Flow 27, no. 1 (January 3, 2017): 23–47. http://dx.doi.org/10.1108/hff-09-2015-0394.
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Purpose The purpose of this paper is to present a numerical investigation of the transient two-dimensional natural convective boundary-layer flow of a nanofluid past an isothermal vertical plate by incorporating the effects of Brownian motion and thermophoresis in the mathematical model. Design/methodology/approach The problem is formulated using the Oberbeck–Boussinesq and the standard boundary-layer approximations. The governing coupled non-linear partial differential equations for conservation of mass, momentum, thermal energy and nanoparticle volume fraction have been solved by using an efficient implicit finite-difference scheme of the Crank–Nicolson type, which is stable and convergent. Numerical computations are performed and the results for velocity, temperature and nanoparticle volume fraction are presented in graphs at different values of system parameters such as Brownian motion parameter, thermophoresis parameter, buoyancy ratio parameter, Prandtl number, Lewis number and dimensionless time. The results for local and average skin-friction and Nusselt number are also presented graphically and discussed thoroughly. Findings It is found that the velocity, temperature and nanoparticle volume fraction profiles enhance with respect to time and attain steady-state values as time progresses. The local Nusselt number is found to decrease with increasing thermophoresis parameter, while it increases slightly with increasing Brownian motion parameter. To validate the present numerical results, the steady-state local Nusselt number results for the limiting case of a regular fluid have been compared with the existing well-known results at different Prandtl numbers, and the results are found to be in an excellent agreement. Research limitations/implications The present analysis is limited to the transient laminar natural convection flow of a nanofluid past an isothermal semi-infinite vertical plate in the absence of viscous dissipation and thermal radiation. The unsteady natural convection flow of a nanofluid will be investigated for various physical conditions in a future work. Practical implications Unsteady flow devices offer potential performance improvements as compared with their steady-state counterparts, and the flow fields in the unsteady flow devices are typically transient in nature. The present study provides very useful information for heat transfer engineers to understand the heat transfer enhancement with the nanofluid flows. The present results have immediate relevance in cooling technologies. Originality/value The present research work is relatively original and illustrates the transient nature of the natural convective nanofluid boundary-layer flow in the presence of Brownian motion and thermophoresis.
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Wulandari, R., S. Permana, and Suprijadi. "Basic analysis on heat transfer phenomena in natural circulation for liquid sodium." Journal of Physics: Conference Series 2072, no. 1 (November 1, 2021): 012012. http://dx.doi.org/10.1088/1742-6596/2072/1/012012.
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Abstract Natural convention, the heat transfer on fluid due to density differences that can be caused by differences in fluid temperature. One example application of natural convection is cooling system, such as nuclear reactor cooling system. The purpose of this study is to analysis the basic characteristic heat transfer of sodium liquid in the natural circulation system for steady state analysis and transient characteristic with Finite Element Method. The selected module is the Non-Isothermal FLow (NITF) module. This module is a combination of three basic equations, namely the continuity equation, the Navier-Stokes equation, and the dynamic equation of heat transfer in fluid. The simulation model measures 1.5 x 2 (m) with sodium liquid (Na) as a fluid.
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Arouca, Fábio de Oliveira, and João Jorge Ribeiro Damasceno. "The Use of High Energies Radiations to Characterise Solid-Liquid Systems." Materials Science Forum 498-499 (November 2005): 49–54. http://dx.doi.org/10.4028/www.scientific.net/msf.498-499.49.
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The behavior of an isothermal and non-reaction solid-liquid system can be model using a mathematical model based on the Mixtures’ Theory of Continuum Mechanics. The knowledge of the constitutive equations of this phenomenon, as pressure on the solids and medium permeability, is very important in the design and performance evaluation of the continuous thickeners or filters. In this work the batch sedimentation phenomena of a kaolin aqueous suspensions was investigated. The technique consists on measuring of the gamma rays attenuation when they cross the physical media as a function of the local concentration at several vertical positions in a reservoir. Using the experimental data and local concentration as a function of the attenuation curve, it is possible to determine the constitutive equations. The results were satisfactory, allowing simulations of this phenomenon for steady and transient regimes in future papers.
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Hosseini, S. M. Amin, Martin Schäkel, Ismet Baran, Henning Janssen, Martin van Drongelen, and Remko Akkerman. "Non-uniform crystallinity and temperature distribution during adjacent laser-assisted tape winding process of carbon/PA12 pipes." International Journal of Advanced Manufacturing Technology 111, no. 11-12 (November 7, 2020): 3063–82. http://dx.doi.org/10.1007/s00170-020-06215-8.
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AbstractThe non-uniform temperature and crystallinity distributions present in carbon fiber–reinforced PA12 composite pipes, produced via laser-assisted tape winding (LATW), are investigated in this paper. The width of the laser source is usually larger than the substrate width which causes multiple heating and cooling of some regions of the (neighboring) substrate and hence temperature and crystallinity gradients during the adjacent hoop winding. A kinematic-optical-thermal (KOT) model coupled with a non-isothermal crystallinity model is developed to capture the transient temperature and crystallinity distributions for growing substrate thickness and width. The predicted temperature trends are validated with thermocouple and thermal camera measurements. The substrate temperature varies in the width direction up to 52%. This will lead to extra polymer remelting and possible degradation. The maximum variation of the crystallinity degree across the width is found to be 270% which shows agreement with the trend of the measured crystallinity degree. It is found that a more realistic description of the melting behavior of the matrix is needed to obtain a more accurate prediction of the crystallinity distribution.
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Su, Li Zheng, Le Hua Qi, Ji Ming Zhou, Yu Shan Wang, and Fang Yang. "Numerical Simulation of Heat and Mass Transfer of the Infiltration in Liquid Infiltration Extrusion Process." Materials Science Forum 532-533 (December 2006): 953–56. http://dx.doi.org/10.4028/www.scientific.net/msf.532-533.953.
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The pressure infiltration process of porous preforms by molten metals was investigated numerically in this paper. The finite element model of heat and mass transfer of the infiltration in liquid infiltration extrusion process was founded by the introduction of a new continuum model of fluid in porous medium and a distribution resistance concept. The proposed model can describe the transient flow behavior of semisolid materials qualitatively. Numerical simulations were developed in particular for non-isothermal infiltrations which take into account the thermal aspects (the mould, the fibres and the metal are initially preheated at different temperatures). The temperature distribution, infiltration front and infiltration depth in the infiltration area were gained by the simulation of ANSYS／FLOTRAN code. It is shown that the fiber volume fraction and initial temperature have a strong effect on the infiltration process. The simulation results of axisymmetric infiltration have a good agreement with their experimental ones. In addition, the infiltration time was predicted to get the effective infiltration depth based on the simulation results.
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Saha, Chayan Kumer, Qianying Yi, David Janke, Sabrina Hempel, Barbara Amon, and Thomas Amon. "Opening Size Effects on Airflow Pattern and Airflow Rate of a Naturally Ventilated Dairy Building—A CFD Study." Applied Sciences 10, no. 17 (September 1, 2020): 6054. http://dx.doi.org/10.3390/app10176054.
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Airflow inside naturally ventilated dairy (NVD) buildings is highly variable and difficult to understand due to the lack of precious measuring techniques with the existing methods. Computational fluid dynamics (CFD) was applied to investigate the effect of different seasonal opening combinations of an NVD building on airflow patterns and airflow rate inside the NVD building as an alternative to full scale and scale model experiments. ANSYS 2019R2 was used for creating model geometry, meshing, and simulation. Eight ventilation opening combinations and 10 different reference air velocities were used for the series of simulation. The data measured in a large boundary layer wind tunnel using a 1:100 scale model of the NVD building was used for CFD model validation. The results show that CFD using standard k-ε turbulence model was capable of simulating airflow in and outside of the NVD building. Airflow patterns were different for different opening scenarios at the same external wind speed, which may affect cow comfort and gaseous emissions. Guiding inlet air by controlling openings may ensure animal comfort and minimize emissions. Non-isothermal and transient simulations of NVD buildings should be carried out for better understanding of airflow patterns.
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Che Sidik, Nor Azwadi, A. S. Ahmad Sofianuddin, and K. Y. Ahmat Rajab. "Transient Removal of Contaminants in Cavity of Mixed Convection in a Channel by Constrained Interpolated Profile Method." Applied Mechanics and Materials 554 (June 2014): 312–16. http://dx.doi.org/10.4028/www.scientific.net/amm.554.312.
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Research in contaminated fluid flow becomes an interest in fluid dynamic research recently. In pipeline involving mix solution, residues can accumulate and deposit usually trapped inside the pipeline. This problem was studied by model it as a cavity channel flow with small particles inside the cavity enhanced by mixed convection. Constrained interpolated profile (CIP) was used to solve advection part of momentum equation while non-advection was solved by using finite difference for fluid part. Passive particles were located inside a square cavity in a channel represent contaminant in the cavity. Bottom wall of the cavity was heated to create mixed convection effect in the removal process and represent by various Grashof number. Validation study was done with experimental study at isothermal condition and show good comparison to present study. Higher removal process was observed at higher Grashof number. In the beginning of removal process, the contaminants were removed faster but after some period, the removal rate began to slow down and steady stated was achieved. At steady state, there will be no more removal of particle and it will remain circulate in the cavity.
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Dickinson, Edmund J. F., and Graham Smith. "Modelling the Proton-Conductive Membrane in Practical Polymer Electrolyte Membrane Fuel Cell (PEMFC) Simulation: A Review." Membranes 10, no. 11 (October 28, 2020): 310. http://dx.doi.org/10.3390/membranes10110310.
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Theoretical models used to describe the proton-conductive membrane in polymer electrolyte membrane fuel cells (PEMFCs) are reviewed, within the specific context of practical, physicochemical simulations of PEMFC device-scale performance and macroscopically observable behaviour. Reported models and their parameterisation (especially for Nafion 1100 materials) are compiled into a single source with consistent notation. Detailed attention is given to the Springer–Zawodzinski–Gottesfeld, Weber–Newman, and “binary friction model” methods of coupling proton transport with water uptake and diffusive water transport; alongside, data are compiled for the corresponding parameterisation of proton conductivity, water sorption isotherm, water diffusion coefficient, and electroosmotic drag coefficient. Subsequent sections address the formulation and parameterisation of models incorporating interfacial transport resistances, hydraulic transport of water, swelling and mechanical properties, transient and non-isothermal phenomena, and transport of dilute gases and other contaminants. Lastly, a section is dedicated to the formulation of models predicting the rate of membrane degradation and its influence on PEMFC behaviour.
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Dinu, C., D. E. Beasley, and R. S. Figliola. "Frequency Response Characteristics of an Active Heat Flux Gage." Journal of Heat Transfer 120, no. 3 (August 1, 1998): 577–82. http://dx.doi.org/10.1115/1.2824314.
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The transient response and frequency response of a constant-temperature platinum film gage are computationally modeled for application to heat flux measurement. The probe consists of a thin platinum film (sensor) deposited on a Pyrex substrate, and coated with aluminum oxide. The probe is exposed to a convective environment, and the power required to maintain the sensor at a constant temperature is a direct indication of the local, instantaneous heat transfer rate. In application, the probe is mounted in a heated, high thermal conductivity material, creating an isothermal heat transfer surface. A two-dimensional numerical model was developed to represent the sensor, the Pyrex substrate and the coating. Ideally, the probe would be operated with the platinum at identically the same temperature as the isothermal surface. In the present study, the effects of non-ideal operating conditions, resulting in differences between the sensor and surface temperature, are examined. Frequency response characteristics are presented in a nondimensional form. The results of this modeling effort clearly indicate the importance of precise control over the sensor temperature in employing the present method for heat flux measurement. With the sensor temperature equal to the isothermal surface temperature, the probe calibration is insensitive to the heat transfer rate over a wide range of heat transfer coefficients. However, a 0.5°C difference between the sensor and surface temperatures yields a change in the calibration of approximately 20 percent over a range of heat transfer coefficient of 500 W/m2K. At an input frequency of 10 Hz and an average heat transfer coefficient of 175 W/m2K, amplitude errors increase from 3 percent to 35 percent as the temperature difference changes from zero to 1°C. These results are useful guide to calibration, operation, and data reduction in active heat flux measurement.
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Spina, Roberto, Marcel Spekowius, and Christian Hopmann. "Analysis of Polymer Crystallization with a Multiscale Modeling Approach." Key Engineering Materials 611-612 (May 2014): 928–36. http://dx.doi.org/10.4028/www.scientific.net/kem.611-612.928.
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The main objective of the presented work is to describe the crystallization kinetics of semi-crystalline thermoplastics with a multiscale model implemented into the COMSOL software and the in-house developed code SphäroSim. The filling and cooling simulations, implemented by using the computational fluid dynamics (CFD) and heat transfer (HT) modules of COMSOL, require the simultaneous solution of non-Newtonian multi-phase flow (polymer/air) and thermal fields in non-isothermal condition and transient regime. The simulation results are collected, converted into the OpenSource file format VTK (Visualization Toolkit) and transferred to the SphäroSim code after a matching operation with the COMSOL mesh. The SphäroSim code uses COMSOL results as input data to compute crystallization kinetics, using the COMSOL data as boundary conditions in the microstructure simulation. This allows the time resolved calculation of the crystallization process and a prediction of the final microstructure in the part which can be used in further simulations such as a structural analysis. The analytical parameters needed to connect crystallization kinetics with molecular material properties and applying the analytical scheme to the numerical simulation during filling and cooling in an injection moulding process are identified.
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Gault, R. I., D. J. Thornhill, and R. Fleck. "Alternative method to evaluate discharge coefficients. Part 1: Feasibility study." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 221, no. 12 (December 1, 2007): 1653–63. http://dx.doi.org/10.1243/09544062jmes725.
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The purpose of the current paper is to demonstrate the feasibility of a new technique whereby mass flowrates, and hence discharge coefficients can be estimated for a range of pipe discontinuities such as poppet valves, throttles, cylinder ports, and orifices. The requirement to directly measure the mass flowrates using a standard conventional steady flow apparatus has been eliminated. As such, flow characteristics were examined during the transient charging or inflow of air, from atmosphere, through a sharp-edged orifice into a partially evacuated cylinder of known volume. In particular, the current study focused on measuring the transient mass flowrates, pressures, and temperatures of air during an inflow test. Comparison between measured gas pressures and temperatures were made with predicted values from an adiabatic and non-adiabatic zero-dimensional inflow model. Mass flowrates calculated from measured cylinder gas pressure data, without heat transfer correction, were shown to be approximately 20 per cent lower, across the full pressure ratio range, than those measured using the mass flow meter. Iterative trial and error techniques were employed to determine the constant and time varying convective heat transfer coefficients needed to correlate the cumulative mass during inflow with the total mass of air, from initial and final cylinder conditions. Heating the cylinder wall to ensure isothermal conditions resulted in an improved correlation between the measured and estimated mass flowrates.
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Degiovanni, A., and B. Remy. "An alternative to heat transfer coefficient: A relevant model of heat transfer between a developed fluid flow and a non-isothermal wall in the transient regime." International Journal of Thermal Sciences 102 (April 2016): 62–77. http://dx.doi.org/10.1016/j.ijthermalsci.2015.10.036.
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Limrungruengrat, Sitthichai, Arisara Chaikittiratana, Tonkid Chantrasmi, Sacharuck Pornpeerakeat, and Utid Suripa. "Effects of Rubber and Mould Temperatures on the Solid Tire Curing Process." Key Engineering Materials 856 (August 2020): 323–30. http://dx.doi.org/10.4028/www.scientific.net/kem.856.323.
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Vulcanization or curing process is a very important process in producing useful rubber products. The quality, performance as well as manufacturing cost of a rubber product are largely affected by the curing process. The curing process takes place when heat is transferred to the rubber compounds inside a heated mould. Curing of a thick article, such as a solid tire, often occurs under transient non-isothermal conditions. The temperature distribution in the rubber significantly affects the cure level distribution throughout the part, especially in a large rubber component. Therefore the ability to predict the distribution of cure level in a rubber part during curing is of great importance for improving the process efficiency and the quality of the final product. In this work, simulations of the curing process of a solid tire, consisting of three layers of different rubber compounds, were performed and the cure level distribution results were evaluated. The simulations are carried out using the commercial finite element software ABAQUS with the cure kinetics model for rubber implemented through the user subroutine UMATHT. The effects of the mold temperature and initial temperature of the solid tire on the cure level distribution and cure time were investigated.
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Egorov, K. S., and L. V. Stepanova. "Heat Exchange and Friction Analysis in Noble Gas Mixtures for Closed Gas Turbines." Herald of the Bauman Moscow State Technical University. Series Mechanical Engineering, no. 4 (139) (December 2021): 4–18. http://dx.doi.org/10.18698/0236-3941-2021-4-4-18.
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The types of heat exchange surfaces used in closed gas turbines for space applications and their conversion version (ground application) as autonomous long-resource power plants of low power (less than 10 kW) are considered. The data of the works currently known in Russia and abroad on the developed turbulent flow in the tube when using gas mixtures with abnormally low Prandtl numbers (0.2) have been analyzed. Recommendations on the application of the analytical relations of Kays, Petukhov and Popov for the calculation of the Nusselt number in pipes are given. The influence of non-isothermal flow and initial pipe section on friction as well as the working body Prandtl number on heat exchange and friction for highly compact plate and fin heat exchange surfaces with staggered arrangement of ribs are analyzed. It is revealed that the relations obtained for the air model are inapplicable for working bodies with Prandtl numbers different from the air Prandtl number. The necessity of further experimental and analytical investigations of heat exchange and friction in tubes under transient flow regime and in highly compact finned surfaces with staggered ribs is confirmed
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Saavedra, J., G. Paniagua, and S. Lavagnoli. "On the transient response of the turbulent boundary layer inception in compressible flows." Journal of Fluid Mechanics 850 (July 12, 2018): 1117–41. http://dx.doi.org/10.1017/jfm.2018.502.
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The behavioural characteristics of thermal boundary layer inception dictate the efficiency of heat exchangers and the operational limits of fluid machinery. The specific time required by the thermal boundary layer to be established is vital to optimize flow control strategies, as well as the thermal management of systems exposed to ephemeral phenomena, typically on the millisecond scale. This paper presents the time characterization of the momentum and thermal boundary layer development in transient turbulent compressible air flows. We present a new framework to perform such estimations based on detailed unsteady Reynolds averaged Navier–Stokes simulations that may be extended to higher fidelity simulations. First of all, the aerodynamic boundary layer initiation is described using adiabatic simulations. Additional numerical calculations were then performed by setting the isothermal wall condition to evaluate the additional time required by the thermal boundary layer to establish after the aerodynamic boundary layer reaches its steady state. Finally, full conjugate simulations were executed to compute the warm up effect of the solid during the blowdown of a hot fluid over a colder metallic test model. The transient performance of the turbulent thermal and momentum boundary layers is quantified through numerical simulations of air blowdown over a flat plate for different mainstream flow conditions. The effects of Reynolds number, free stream velocity, transient duration, test article length and free stream temperature were independently assessed, to then define a mathematical expression of the momentum boundary layer settlement. This paper presents a novel numerical correlation of the additional time required by the thermal boundary layer to be stablished after the settlement of the momentum boundary layer. The time scales of the aerodynamic and thermal boundary layers are presented as a function of relevant non-dimensional numbers, as well as the description of the response of the near wall flow to sudden free stream changes. The characterization of the boundary layer mechanisms discussed in this paper contribute to the establishment of an evidence-based foundation for advances in the field of flow control.
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Das, Suma R., Pashupati Dhakal, Hari Poudyal, and Abhilash J. Chandy. "ASSESSMENT OF THE EFFECT OF SPEED RATIOS IN NUMERICAL SIMULATIONS OF HIGHLY VISCOUS RUBBER MIXING IN A PARTIALLY FILLED CHAMBER." Rubber Chemistry and Technology 89, no. 3 (September 1, 2016): 371–91. http://dx.doi.org/10.5254/rct.16.83778.
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ABSTRACT Three-dimensional, transient, isothermal, and incompressible computational fluid dynamics (CFD) simulations are carried out for rubber mixing with two counter-rotating rotors in a partially filled chamber in order to assess the effect of different speed ratios. The three different speed ratios that are investigated include 1.0, 1.125, and 1.5. In addition to the solution of the incompressible continuity and momentum equations, a Eulerian multiphase model is employed to simulate two phases, rubber and air, and the volume of fluid (VOF) technique is used to calculate the free surface flow between the phases. The Bird–Carreau model is used to characterize the non-Newtonian highly viscous rubber. Massless particles are injected in the simulations to obtain data required for statistical calculations related to dispersive and distributive mixing characteristics. Specifically, joint probability density functions of mixing index and shear rate, and cumulative distribution functions of maximum shear stress are calculated to assess dispersive mixing, while distributive mixing capabilities are evaluated using various quantities such as cluster distribution index, axial distribution, interchamber particle transfer, and segregation scale. Results showed the speed ratio 1.125 to be consistently superior to 1.5 and 1.0, in terms of both dispersive and distributive mixing performance. The large speed difference between the rotors in the case of 1.5 caused it to perform the worst.
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Dumych, Tetiana, Clarisse Bridot, Sébastien Gouin, Marc Lensink, Solomiya Paryzhak, Sabine Szunerits, Ralf Blossey, Rostyslav Bilyy, Julie Bouckaert, and Eva-Maria Krammer. "A Novel Integrated Way for Deciphering the Glycan Code for the FimH Lectin." Molecules 23, no. 11 (October 28, 2018): 2794. http://dx.doi.org/10.3390/molecules23112794.
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The fimbrial lectin FimH from uro- and enteropathogenic Escherichia coli binds with nanomolar affinity to oligomannose glycans exposing Manα1,3Man dimannosides at their non-reducing end, but only with micromolar affinities to Manα1,2Man dimannosides. These two dimannoses play a significantly distinct role in infection by E. coli. Manα1,2Man has been described early on as shielding the (Manα1,3Man) glycan that is more relevant to strong bacterial adhesion and invasion. We quantified the binding of the two dimannoses (Manα1,2Man and Manα1,3Man to FimH using ELLSA and isothermal microcalorimetry and calculated probabilities of binding modes using molecular dynamics simulations. Our experimentally and computationally determined binding energies confirm a higher affinity of FimH towards the dimannose Manα1,3Man. Manα1,2Man displays a much lower binding enthalpy combined with a high entropic gain. Most remarkably, our molecular dynamics simulations indicate that Manα1,2Man cannot easily take its major conformer from water into the FimH binding site and that FimH is interacting with two very different conformers of Manα1,2Man that occupy 42% and 28% respectively of conformational space. The finding that Manα1,2Man binding to FimH is unstable agrees with the earlier suggestion that E. coli may use the Manα1,2Man epitope for transient tethering along cell surfaces in order to enhance dispersion of the infection.
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Toffolon-Masclet, Caroline, Clara Desgranges, Carolina Corvalan-Moya, and Jean Christophe Brachet. "Simulation of the β→α(O) Phase Transformation due to Oxygen Diffusion during High Temperature Oxidation of Zirconium Alloys." Solid State Phenomena 172-174 (June 2011): 652–57. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.652.
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The EKINOX numerical code, formerly developed to simulate high temperature oxidation of Ni alloys, has been recently adapted to solve out the issue of high temperature oxidation of Zirconium alloys. This numerical code is a one dimensional model that simulates the growth of an oxide layer using a specific algorithm for moving boundaries problem. In order to simulate the oxygen diffusion inside Zr alloys, an adaptation of the EKINOX code was necessary. It consisted in adding, first, a non-null oxygen equilibrium concentration in the substrate and second, a new interface in order to simulate the β/α(O) phase transformation due to oxygen diffusion. In this study, EKINOX has also been coupled with the thermodynamic database for zirconium alloys ZIRCOBASE (thermocalc formalism) in order to obtain accurate concentrations values in each phases (considering local equilibrium at each interface). The present paper illustrates the simulation ability of the code by comparing experimental and calculated oxygen diffusion profiles corresponding to different cases, from isothermal oxidations at high temperature (900 < T < 1250°C) to the study of dissolution kinetics of a pre-transient oxide layer under a neutral environment. The influence of pre-hydriding from a few hundreds up to thousands weight-ppm is also derived from the calculations.
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Imponenti, Luca, Kevin J. Albrecht, and Gregory S. Jackson. "Rapid Redox Cycle Stability of Doped CaMnO3 Particles for High-Temperature Thermochemical Energy Storage." ECS Meeting Abstracts MA2018-01, no. 32 (April 13, 2018): 1963. http://dx.doi.org/10.1149/ma2018-01/32/1963.
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A-site doped Ca1-xSrxMnO3-δ and B-site doped CaCryMn1-yO3-δ have been studied for high specific thermochemical energy storage (TCES) in concentrating solar power and other high-temperature applications. With low levels of doping (5 and 10%) for both compositions, these perovskites have demonstrated significant reduction in high temperatures at O2 partial pressures P O2 ≈10-4 bar with as much as 450 kJ/kg of chemical energy can be stored (for Ca0.95Sr0.05MnO3-δ) at 900 ºC on top of sensible energy in a TCES system [1]. The viability of such high specific TCES in these perovskites depends on their rates of energy accommodation during heating cycles and their phase and morphological stability during rapid reduction and reoxidation for energy capture and release respectively. In this study, Ca1-xSrxMnO3-δ and CaCryMn1-yO3-δ were studied for reduction at temperatures up to 1000 ºC and tested in extended redox cycling to explore their stability for energy storage and release at such high-temperatures where the materials undergo expansion/compression and phase transitions during these cycles. The results as highlighted below suggest that these materials have significant promise for high-temperature large-scale TCES. Ca1-xSrxMnO3-δ (x = 0.05 and 0.10) and CaCryMn1-yO3-δ (y = 0.05 and 0.10) were synthesized as particles with solid-state-reactive sintering [1] and cycled as particles (diameter range of 250-425 μm) between air P O2 (≈ 0.17 bar) and P O2 ≈10-4 bar both in isothermal experiments up to 1000 ºC and in long-term cycling experiments between 500 and 900 ºC to simulate TCES system operation. Over these conditions, the doped CaMnO3-δ perovskites undergo significant reduction (δ > 0.2 at 1000 ºC) at phase transitions (orthorhombic to cubic to tetragonal perovskite phase), reduction, and associated lattice expansion as observed in hot-stage XRD for similar composition [1]. The isothermal redox cycling tests in conjunction with thermodynamics derived from TGA/DSC measurements as reported elsewhere [2,3] provided a basis for fitting thermodynamically consistent surface reaction rates [4,5] and bulk ionic transport properties to measured transient evolution in oxygen non-stoichiometry δ which went as high as 0.3 for Ca0.95Sr0.05MnO3-δ at 1000 ºC. These experiments are illustrated with ten-cycle averaged plots in Figure 1 with data for Ca0.9Sr0.1MnO3-δ compared to packed bed models [4] used to fit surface kinetic and bulk transport rate expressions. Figure 1 also shows the chemical energy incorporated into the perovskite with increasing δ during reduction based on thermodynamics derived from fitting equilibrium δ over a range of T and P O2. The packed bed results and model fits show fast rates of reoxidation relative to reduction. The rapid reoxidation i.e., oxygen incorporation rates are limited by the inlet flow supply for a substantial fraction of the experiments. The high-degree of reduction and the rapid rates of reoxidation and associated phase transitions raise questions about the stability of these materials in non-isothermal redox cycling for high-temperature TCES system applications. The selected perovskite materials were thus cycled for over 1000 times under non-isothermal conditions to simulate TCES system operation. The long-term cycling for all four doped CaMnO3-δ perovskites occurred with heating from a fully oxidized state at 500 ºC to a reduced state at 900 ºC in P O2 ≈10-4 bar followed by subsequent reoxidation and cooling in air back to 500 ºC. Figure 2 shows the transient evolution of δ during reduction and heating, averaged over successive 100 cycles for all four materials. An initial induction period of increasing maximum δ is followed by a stable period of redox cycling in spite of the rapid reoxidation. Only CaCr0.05Mn0.95O3-δ shows evidence of a significant loss in maximum δ, and this composition showed the slowest to undergo phase transitions in DTA experiments. Ex situ X-ray diffraction shown in Figure 3 of the particles before and after the long-term non-isothermal redox testing show that the particles maintain their dominant perovskite phase with evidence of small fractions of a secondary spinel phase. The stability of these cyclic tests particular for the Ca1-xSrxMnO3-δ reveal the promise of these materials as a media for effective TCES in a range of high-temperature energy storage applications. Reference [1] E.I. Leonidova, I.A. Leonidov, M.V. Patrakeev, V.L. Kozhevnikov, Journal of Solid State Electrochemistry, 15 (2011) 1071-1075. [2] L. Imponenti, K.J. Albrecht, R.J. Braun, G.S. Jackson, ECS Transactions, 72 (2016) 11-22. [3] L. Imponenti, K.J. Albrecht, J.W. Wands, M.D. Sanders, G.S. Jackson, Solar Energy, 151 (2017) 1-13. [4] K.J. Albrecht, "Multiscale Modeling and Experimental Interpretation of Perovskite Oxide Materials in Thermochemical Energy Storage and Conversion in Applications for Concentrating Solar Power", Ph.D. Dissertation, Colorado School of Mines, 2016. [5] R. Merkle, J. Maier, Angewandte Chemie-International Edition, 47 (2008) 3874-3894. Figure 1
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Miroshnichenko, Igor, Mikhail Sheremet, and Ali J. Chamkha. "Turbulent natural convection combined with surface thermal radiation in a square cavity with local heater." International Journal of Numerical Methods for Heat & Fluid Flow 28, no. 7 (July 2, 2018): 1698–715. http://dx.doi.org/10.1108/hff-03-2018-0089.
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Purpose The purpose of this paper is to conduct a numerical analysis of transient turbulent natural convection combined with surface thermal radiation in a square cavity with a local heater. Design/methodology/approach The domain of interest includes the air-filled cavity with cold vertical walls, adiabatic horizontal walls and isothermal heater located on the bottom cavity wall. It is assumed in the analysis that the thermophysical properties of the fluid are independent of temperature and the flow is turbulent. Surface thermal radiation is considered for more accurate analysis of the complex heat transfer inside the cavity. The governing equations have been discretized using the finite difference method with the non-uniform grid on the basis of the special algebraic transformation. Turbulence was modeled using the k–ε model. Simulations have been carried out for different values of the Rayleigh number, surface emissivity and location of the heater. Findings It has been found that the presence of surface radiation leads to both an increase in the average total Nusselt number and intensive cooling of such type of system. A significant intensification of convective flow was also observed owing to an increase in the Rayleigh number. It should be noted that a displacement of the heater from central part of the bottom wall leads to significant modification of the thermal plume and flow pattern inside the cavity. Originality/value An efficient numerical technique has been developed to solve this problem. The originality of this work is to analyze unsteady turbulent natural convection combined with surface thermal radiation in a square air-filled cavity in the presence of a local isothermal heater. The results would benefit scientists and engineers to become familiar with the analysis of turbulent convective–radiative heat transfer in enclosures with local heaters, and the way to predict the heat transfer rate in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors and electronics.
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Papon, Easir Arafat, Anwarul Haque, and Muhammad Ali Rob Sharif. "Numerical study for the improvement of bead spreading architecture with modified nozzle geometries in additive manufacturing of polymers." Rapid Prototyping Journal 27, no. 3 (February 4, 2021): 518–29. http://dx.doi.org/10.1108/rpj-05-2019-0142.
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Purpose This paper aims to develop a numerical model of bead spreading architecture of a viscous polymer in fused filament fabrication (FFF) process with different nozzle geometry. This paper also focuses on the manufacturing feasibility of the nozzles and 3D printing of the molten beads using the developed nozzles. Design/methodology/approach The flow of a highly viscous polymer from a nozzle, the melt expansion in free space and the deposition of the melt on a moving platform are captured using the FLUENT volume of fluid (VOF) method based computational fluid dynamics code. The free surface motion of the material is captured in VOF, which is governed by the hydrodynamics of the two-phase flow. The phases involved in the numerical model are liquid polymer and air. A laminar, non-Newtonian and non-isothermal flow is assumed. Under such assumptions, the spreading characteristic of the polymer is simulated with different nozzle-exit geometries. The governing equations are solved on a regular stationary grid following a transient algorithm, where the boundary between the polymer and the air is tracked by piecewise linear interface construction (PLIC) to reconstruct the free surface. The prototype nozzles were also manufactured, and the deposition of the molten beads on a flatbed was performed using a commercial 3D printer. The deposited bead cross-sections were examined through optical microscopic examination, and the cross-sectional profiles were compared with those obtained in the numerical simulations. Findings The numerical model successfully predicted the spreading characteristics and the cross-sectional shape of the extruded bead. The cross-sectional shape of the bead varied from elliptical (with circular nozzle) to trapezoidal (with square and star nozzles) where the top and bottom surfaces are significantly flattened (which is desirable to reduce the void spaces in the cross-section). The numerical model yielded a good approximation of the bead cross-section, capturing most of the geometric features of the bead with a reasonable qualitative agreement compared to the experiment. The quantitative comparison of the cross-sectional profiles against experimental observation also indicated a favorable agreement. The significant improvement observed in the bead cross-section with the square and star nozzles is the flattening of the surfaces. Originality/value The developed numerical algorithm attempts to address the fundamental challenge of voids and bonding in the FFF process. It presents a new approach to increase the inter-bead bonding and reduce the inter-bead voids in 3D printing of polymers by modifying the bead cross-sectional shape through the modification of nozzle exit-geometry. The change in bead cross-sectional shape from elliptical (circular) to trapezoidal (square and star) cross-section is supposed to increase the contact surface area and inter-bead bonding while in contact with adjacent beads.
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Kelton, Kenneth F. "The Importance of Transient Nucleation and Non-Equilibrium Viscosity for Glass Formation." MRS Proceedings 57 (1985). http://dx.doi.org/10.1557/proc-57-255.
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AbstractThe process of nucleation and growth in glasses and undercooled liquids is modeled by directly simulating the evolution of the molecular cluster distribution under both isothermal and non-isothermal conditions. Results of that simulation for the nucleation rate during the quench, and for the number of nuclei produced and the volume fraction transformed at the end of the quench are presented. The following three points are discussed: (1) The importance of transient, or non-steady state, nucleation rates on glass formation is assessed by considering three model glass forming systems: lithium disilicate, a relatively good glass former, and two metallic glasses, (Au85Cu15)77Si9Gd14 and Au81Si19. (2) Using experimentally determined values for the steady state nucleation rates and growth velocities for Pd40Ni40P20, it is demonstrated that, in agreement with recent experimental results, this alloy may be cycled at rates on the order of 1 K/sec between the melting and glass transition temperatures without crystallization. Transient effects are shown to be unimportant under these conditions in this system. (3) The effect on glass formation of a non-equilibrium viscosity during the quench due to configurational freezing is evaluated by assuming a phenomenological model for the changing viscosity.
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Chimanpure, A. S., A. Kahraman, and D. Talbot. "A Transient Mixed Elastohydrodynamic Lubrication Model for Helical Gear Contacts." Journal of Tribology 143, no. 6 (October 27, 2020). http://dx.doi.org/10.1115/1.4048499.
Full textAbstract:
Abstract In this study, a non-Newtonian, transient, isothermal, mixed elastohydrodynamic lubrication (EHL) model is proposed for helical gear contacts. The model accounts for nonelliptical contacts subject to spatially varying sliding and rolling velocity fields that are not aligned with any principal axis of the contact region, which is the case for helical gear contacts. The time-varying changes pertaining to key contact parameters and relative motion of roughness profiles on mating tooth surfaces are captured simultaneously to follow the contact from the root to the tip of a tooth while accounting for the transient effect due to relative motions of the roughness profiles. Actual tooth load distributions, contact kinematics, and compliances of helical gear contacts are provided to this model by an existing helical gear load distribution model. Measured three-dimensional roughness profiles covering the entire meshing zone are incorporated in the analyses to investigate its impact on the EHL conditions as well as mechanical power loss. Results of a parametric sensitivity study are presented to demonstrate the influence of operating conditions and surface roughness on the EHL behavior and the resultant gear mesh mechanical power loss of an example helical gear pair. The accuracy of the proposed mixed-EHL model is assessed by comparing the mechanical power loss predictions to available experimental results.