Thematische Bibliographien / Phase change hysteresis

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Auswahl der wissenschaftlichen Literatur zum Thema „Phase change hysteresis“

Autor: Grafiati

Veröffentlicht am 28. Juni 2021

Zuletzt aktualisiert am 1. Februar 2022

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Zeitschriftenartikel zum Thema "Phase change hysteresis"

Meyers, Jeremy P. „Hysteresis and Phase Change in Electrochemical Materials“. ECS Transactions 16, Nr. 13 (18.12.2019): 167–73. http://dx.doi.org/10.1149/1.2987768.

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Aiki, T., E. Minchev und T. Okazaki. „Mathematical models for phase change problems with hysteresis effect“. Nonlinear Analysis: Theory, Methods & Applications 63, Nr. 5-7 (November 2005): e1185-e1198. http://dx.doi.org/10.1016/j.na.2005.03.089.

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Zastawna-Rumin, Anna, Tomasz Kisilewicz und Umberto Berardi. „Novel Simulation Algorithm for Modeling the Hysteresis of Phase Change Materials“. Energies 13, Nr. 5 (05.03.2020): 1200. http://dx.doi.org/10.3390/en13051200.

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Latent heat thermal energy storage (LHTES) using phase change materials (PCM) is one of the most promising ways for thermal energy storage (TES), especially in lightweight buildings. However, accurate control of the phase transition of PCM is not easy to predict. For example, neglecting the hysteresis or the effect of the speed of phase change processes reduces the accuracy of simulations of TES. In this paper, the authors propose a new software module for EnergyPlus™ that aims to simulate the hysteresis of PCMs during the phase change. The new module is tested by comparing simulation results with experimental tests done in a climatic chamber. A strong consistency between experimental and simulation results was obtained, while a discrepancy error of less than 1% was obtained. Moreover, in real conditions, as a result of quick temperature changes, only a partial phase transformation of the material is often observed. The new model also allows the consideration of the case with partial phase changes of the PCM. Finally, the simulation algorithm presented in this article aims to represent a better way to model LHTES with PCM.

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Hu, Yue, Rui Guo, Per Kvols Heiselberg und Hicham Johra. „Modeling PCM Phase Change Temperature and Hysteresis in Ventilation Cooling and Heating Applications“. Energies 13, Nr. 23 (06.12.2020): 6455. http://dx.doi.org/10.3390/en13236455.

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Applying phase change material (PCM) for latent heat storage in sustainable building systems has gained increasing attention. However, the nonlinear thermal properties of the material and the hysteresis between the two-phase change processes make the modelling of PCM challenging. Moreover, the influences of the PCM phase transition and hysteresis on the building thermal and energy performance have not been fully understood. This paper reviews the most commonly used modelling methods for PCM from the literature and discusses their advantages and disadvantages. A case study is carried out to examine the accuracy of those models in building simulation tools, including four methods to model the melting and freezing process of a PCM heat exchanger. These results are compared to experimental data of the heat transfer process in a PCM heat exchanger. That showed that the four modelling methods are all accurate for representing the thermal behavior of the PCM heat exchanger. The model with the DSC Cp method with hysteresis performs the best at predicting the heat transfer process in PCM in this case. The impacts of PCM phase change temperature and hysteresis on the building energy-saving potential and thermal comfort are analyzed in another case study, based on one modelling method from the first case study. The building in question is a three-room apartment with PCM-enhanced ventilated windows in Denmark. The study showed that the PCM hysteresis has a larger influence on the building energy consumption than the phase change temperature for both summer night cooling applications and for winter energy storage. However, it does not have a strong impact on the yearly total energy usage. For both summer and winter transition seasons, the PCM hysteresis has a larger influence on the predicted percentage of dissatisfied (PPD) than the phase change temperature, but not a strong impact on the transition season average PPD. It is therefore advised to choose the PCM hysteresis according to whether it is for a summer night cooling or a winter solar energy storage application, as this has a significant impact on the system’s overall efficiency.

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Frame, James D., Nicolas G. Green und Xu Fang. „Modified Maxwell Garnett model for hysteresis in phase change materials“. Optical Materials Express 8, Nr. 7 (28.06.2018): 1988. http://dx.doi.org/10.1364/ome.8.001988.

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Szilard, D., W. J. M. Kort-Kamp, F. S. S. Rosa, F. A. Pinheiro und C. Farina. „Hysteresis in the spontaneous emission induced by VO2 phase change“. Journal of the Optical Society of America B 36, Nr. 4 (07.03.2019): C46. http://dx.doi.org/10.1364/josab.36.000c46.

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Green, Nicolas G., und Xu Fang. „A Modified Maxwell Garnett Model: Hysteresis in phase change materials“. Journal of Physics: Conference Series 1322 (Oktober 2019): 012038. http://dx.doi.org/10.1088/1742-6596/1322/1/012038.

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Serikawa, Mao, Kensaku Mabuchi, Makoto Satoh, Yoshinobu Nozue, Yoshihiko Hayashi und Masahiro Yokoyama. „Measurement of full-scale phase change material products considering hysteresis“. Applied Thermal Engineering 192 (Juni 2021): 116895. http://dx.doi.org/10.1016/j.applthermaleng.2021.116895.

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Abrahams, S. C., J. Ravez, H. Ritter und J. Ihringer. „Structure–property correlation over five phases and four transitions in Pb5Al3F19“. Acta Crystallographica Section B Structural Science 59, Nr. 5 (25.09.2003): 557–74. http://dx.doi.org/10.1107/s0108768103011509.

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The calorimetric and dielectric properties of Pb5Al3F19 in the five phases stable under ambient pressure are correlated with structure for fuller characterization of each phase. The first-order transition between ferroelectric phase V and antiferroelectric phase IV at T V,IV = 260 (5) K exhibits a thermal hysteresis of 135 (5) K on heating, with a maximum atomic displacement Δ(xyz)max = 1.21 (6) Å; the transition from phase IV to ferroelastic phase III at 315 (5) K is also first order but with a thermal hysteresis of 10 (5) K and Δ(xyz)max = 0.92 (7) Å; that from phase III to paraelastic phase II at 360 (5) K is second order without hysteresis and has Δ(xyz)max = 0.69 (4) Å; and the transition from phase II to paraelectric phase I at 670 (5) K is second or higher order, with Δ(xyz)max = 0.7 (4) Å. The measured entropy change ΔS at T V,IV agrees well with ΔS as derived from the increased configurational energy by Stirling's approximation. For all other phase transitions, 0.5 ≥ ΔS > 0 J mol−1 K−1 is consistent with an entropy change caused primarily by the changes in the vibrational energy. The structure of phase III is determined both by group theoretical/normal mode analysis and by consideration of the structures of phases II, IV and V reported previously; refinement is by simultaneous Rietveld analysis of the X-ray and neutron diffraction powder profiles. The structure of prototypic phase I is predicted on the basis of the atomic arrangement in phases II, III, IV and V. The introduction of 3d electrons into the Pb5Al3F19 lattice disturbs the structural equilibrium, the addition of 0.04% Cr3+ causing significant changes in atomic positions and increasing T IV,III by ∼15 K. Substitution of Al3+ by 20% or more Cr3+ eliminates the potential minima that otherwise stabilize phases IV, III and II.

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Li, Yan Shan, Shu Jun Wang, Hong Yan Liu, Wan Gang Zheng, Huan Qing Ma und Fan Bin Meng. „Recent Advances in Form-Stable Phase Change Materials of Polyethylene Glycol“. Advanced Materials Research 850-851 (Dezember 2013): 164–68. http://dx.doi.org/10.4028/www.scientific.net/amr.850-851.164.

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The polyethylene glycol is a kind of phase change energy storage material with small thermal hysteresis effect, the phase change enthalpy and phase transition temperature varies with its different molecular weight. This article summarizes polyethylene glycol as research progress of phase change energy storage material, which mainly discusses the preparation methods and outlook about form-stable phase change materials.

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Dissertationen zum Thema "Phase change hysteresis"

Petrášová, Anna. „Počítačové modelování teplotní hystereze při změně skupenství“. Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-445463.

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This thesis deals with computer modeling of temperature hysteresis during phase change, namely complete and partial phase change. There is performed a review of methods for modeling temperature hysteresis based on the enthalpy method and the effective heat capacity method. In the case of complete phase change, there are several methods that use the effective heat capacity method, as well as the heat source method, which, on the contrary, is a certain analogy of the enthalpy method. The following are works dealing with modelling of partial phase change, the most interesting of which is due to the validation method of static hysteresis and the method designed by Bony and Citherlet. The second part of this thesis deals with the hysteresis behavior of the material with phase change, which is organic paraffin RT 27. The input data obtained by differential scanning calorimetry was converted to the dependence of the enthalpy on temperature. These curves was represented by piecewise linear function. In the case of partial phase transformations, a modeling method based on the methods proposed by Bonym and Citherlet was designed. An one-dimensional model enabling thermal simulation of the material was implemented in the MATLAB software environment. The results obtained with this simulation are finally compared with a model that does not consider thermal hysteresis.

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Andersson, Martin. „Phase Phenomena in Polymer Networks : Empirical Studies on the Influence of Hydrophobicity, Charge Density and Crosslinks on Macroion-Induced Phase Transitions in Polyelectrolyte Gels“. Doctoral thesis, Uppsala universitet, Institutionen för farmaci, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-145381.

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The thesis concerns polyelectrolyte gels in contact with oppositely charged proteins and surfactant micelles, and includes of four papers (I-IV). In paper I confocal Raman spectroscopy was introduced as a method to trace micelles and investigate the structure of gel-surfactant complexes, in phase separated gel spheres. In paper II, the binding of surfactants to microspheres (~50-100 µm) was investigated by means of a micromanipulator-assisted microscopy method. The two surfactants were found to display qualitative difference respect to degree of swelling, surfactant distribution in the gels, and the difference is discussed in terms of absence/presence of hydrophobic attraction to the polyelectrolyte gel network. Kinetics of volume change in gels were analyzed. Aggregation numbers of micelles in polystyrenesulfonate (PSS) solutions, obtained from fluorescence quenching measurements, are presented. In paper III, phase behaviour, protein assembly and diffusion, was studied in PSS gel microspheres. Interpretation of results was aided by measurements of osmotic swelling of individual gel networks, and by combining the results with studies of protein diffusion in macroscopic (cm-sized) gel spheres. Complexes formed were further analyzed with small angle x-ray spectroscopy. In paper IV phase behaviour of mixed ionic/nonionic surfactant micelles is investigated in cm-sized gel spheres. The coexistence of three phases, the formation of dense shells in the bulk of the gels and other phenomena are described for the first time, and the results are presented along with discussion on the charge-density of spherical micelles and of network induced hysteresis effects in gels. The composition and microstructure of phases are investigated by confocal Raman spectroscopy and small-angle x-ray scattering respectively. The results are interpreted with aid of highly detailed theoretical model calculations.

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Chung, Feng-Ju, und 鍾奉儒. „Microencapsulated Yolk Shell Metal and Alloy Phase Change Materials with Lower Thermal Hysteresis as Higher Thermal Absorber for Thermal Energy Storage“. Thesis, 2018. http://ndltd.ncl.edu.tw/handle/n67y59.

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Hsu, Ting-Heng, und 許廷亨. „Thermal Hysteresis Study on Phase Changed Core-Shell Micro particles“. Thesis, 2017. http://ndltd.ncl.edu.tw/handle/skz6j9.

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Bücher zum Thema "Phase change hysteresis"

Sheppard, Charles R. C., Simon K. Davy, Graham M. Pilling und Nicholas A. J. Graham. Consequences to reefs of changing environmental stress. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198787341.003.0009.

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A stable state in a healthy reef is a dynamic equilibrium which is maintained by interactions between different trophic groups and by a balance between growth and erosion, which is caused by weather and eroding species. If the stable, coral-dominated state is perturbed beyond a critical point, the system undergoes a phase shift and switches to an alternative state, perhaps one dominated by macroalgae; this alternative state itself is then relatively stable. A hysteresis effect means that removal of the stresses that caused the switch in the first place may not be sufficient to reverse the condition back to that of a healthy reef. Changes to structural species, particularly the main architectural species, are particularly difficult to reverse, as are changes which encourage bioeroding species. Trophic balances are lost and results include loss of productivity and a loss of wave-breaking effects, which in turn causes shoreline erosion and further loss of productivity.

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Buchteile zum Thema "Phase change hysteresis"

Promislow, Keith S. „Phase Change and Hysteresis in PEMFCs“. In Topics in Applied Physics, 253–95. New York, NY: Springer New York, 2009. http://dx.doi.org/10.1007/978-0-387-78691-9_8.

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Hilpert, Martin. „On Uniqueness for Evolution Problems with Hysteresis“. In Mathematical Models for Phase Change Problems, 377–88. Basel: Birkhäuser Basel, 1989. http://dx.doi.org/10.1007/978-3-0348-9148-6_19.

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Skoko, Željko, und Stanko Popović. „Microstructure of Al-Cu, Al-Zn, Al-Ag-Zn, and Al-Zn-Mg Alloys“. In Encyclopedia of Aluminum and Its Alloys. Boca Raton: CRC Press, 2019. http://dx.doi.org/10.1201/9781351045636-140000172.

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The precipitation phenomena and their connection with the microstructure of several Al alloys (Al-Cu, Al-Zn, Al-Ag-Zn, Al-Zn-Mg) are described with respect to the concentration and applied thermal treatment. The alloys were rapidly quenched or slowly cooled from a temperature higher than the solid solution temperature to room temperature. Both quenched-aged and slowly cooled alloys were heated from room temperature to the solid solution state and cooled back to room temperature, and their microstructure and precipitation phenomena were followed in situ by X-ray powder diffraction, e.g., anisotropy of thermal expansion, phase transitions, thermal hysteresis in phase transitions, change of precipitate shape, partial or complete dissolution of precipitates in the matrix, and formation of solid solution. It has been shown that the microstructure strongly depends on the previous thermal history of the alloys.

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„Nonlinear Transient Analysis“. In Structural Dynamics and Static Nonlinear Analysis From Theory to Application, 264–84. IGI Global, 2021. http://dx.doi.org/10.4018/978-1-7998-4399-3.ch010.

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In this chapter, the author begin by presenting the main causes of non-linearity, which are geometric and material source, change in boundary condition. The last presented source is pretensions. Then they go to the physical understanding of non-linear behavior by presenting the different phases of hysteresis curve sequence of a reinforced concrete structure. In this chapter, readers pass over various numerical formulation, which allow them to deal with non-linearity, namely Lagrange and Euler formulation, total Lagrangian formulation, Piola-Kirchhoff 2, and corotational formulation. Some examples are exposed at the end of the chapter.

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Koch, Christof. „Phase Space Analysis of Neuronal Excitability“. In Biophysics of Computation. Oxford University Press, 1998. http://dx.doi.org/10.1093/oso/9780195104912.003.0013.

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The previous chapter provided a detailed description of the currents underlying the generation and propagation of action potentials in the squid giant axon. The Hodgkin-Huxley (1952d) model captures these events in terms of the dynamical behavior of four variables: the membrane potential and three state variables determining the state of the fast sodium and the delayed potassium conductances. This quantitative, conductance-based formalism reproduces the physiological data remarkably well and has been extremely fertile in terms of providing a mathematical framework for modeling neuronal excitability throughout the animal kingdom (for the current state of the art, see McKenna, Davis, and Zornetzer, 1992; Bower and Beeman, 1998; Koch and Segev, 1998). Collectively, these models express the complex dynamical behaviors observed experimentally, including pulse generation and threshold behavior, adaptation, bursting, bistability, plateau potentials, hysteresis, and many more. However, these models are difficult to construct and require detailed knowledge of the kinetics of the individual ionic currents. The large number of associated activation and inactivation functions and other parameters usually obscures the contributions of particular features (e.g., the activation range of the sodium activation particle) toward the observed dynamic phenomena. Even after many years of experience in recording from neurons or modeling them, it is a dicey business predicting the effect that varying one parameter, say, the amplitude of the calcium-dependent slow potassium current (Chap. 9), has on the overall behavior of the model. This precludes the development of insight and intuition, since the numerical complexity of these models prevents one from understanding which important features in the model are responsible for a particular phenomenon and which are irrelevant. Qualitative models of neuronal excitability, capturing some of the topological aspects of neuronal dynamics but at a much reduced complexity, can be very helpful in this regard, since they highlight the crucial features responsible for a particular behavior. By topological aspects we mean those properties that remain unchanged in spite of quantitative changes in the underlying system. These typically include the existence of stable solutions and their basins of attraction, limit cycles, bistability, and the existence of strange attractors.

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Konferenzberichte zum Thema "Phase change hysteresis"

Charvat, Pavel, Martin Zalesak und Lubomir Klimes. „The Influence of the Phase Change Temperature Range and the Phase Change Hysteresis of a PCM on the Performance of an Air-PCM Heat Storage Unit“. In ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-10438.

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Abstract The influence of the phase change temperature range and the hysteresis of the enthalpy-temperature relationship h(T) of PCMs on the performance of thermal energy storage (TES) systems is rarely quantified. In the present study, the quantification is done by the comparison of the amounts of heat stored in (and discharged from) the air-PCM heat exchanger (TES unit) operating between constant air temperatures. All simulations were conducted for the same mean phase change temperature of the PCM (30 °C). The inlet air temperature of the air-PCM HEX was 40 °C during the heat charging period and 20 °C during the heat discharge period. The maximum considered phase change temperature range of the PCM was 10 °C. The maximum phase transition hysteresis, in the study defined as the temperature difference between the melting and solidification peaks, was 4 °C. The results indicate that in case of the PCMs with a wide phase change temperature range and a significant hysteresis of the h(T) curves, the influence of these properties cannot be neglected in the simulation studies in order to achieve accurate results.

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Zhang, Jun, Emmanuelle Merced, Nelson Sepúlveda und Xiaobo Tan. „Modeling of Non-Monotonic Hysteresis Behavior in VO2-Coated Microactuators“. In ASME 2012 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/smasis2012-7940.

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Vanadium dioxide (VO2) undergoes a thermally induced solid-to-solid phase transition. A VO2-coated silicon cantilever demonstrates large change in its bending curvature across its phase transition. Due to phase transition and thermal expansion effects, the curvature – temperature hysteresis in VO2 actuators comes with a non-monotonic hysteretic behavior, introducing new challenges in its modeling. Motivated by the underlying physics, in this paper we present a novel model that combines a monotonic Preisach hysteresis operator with a linear operator. A constrained least square scheme is proposed to estimate the model parameters. For comparison purposes, we also consider a Preisach operator with a signed weighting function, and a hybrid model consisting of a monotonic Preisach operator for the curvature within the transition and linear operators outside the transition. Experimental results confirm the effectiveness of the proposed model.

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Orejon, Daniel, Yota Maeda, Fengyong Lv, Peng Zhang und Yasuyuki Takata. „Effect of Microstructures on Superhydrophobic and Slippery Lubricant-Infused Porous Surfaces During Condensation Phase-Change“. In ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/icnmm2018-7640.

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Superhydrophobic surfaces (SHSs) and slippery lubricant-infused porous surfaces (SLIPSs) are receiving increasing attention for their excellent anti-icing, anti-fogging, self-cleaning and condensation heat transfer properties. The ability of such surfaces to passively shed and repel water is mainly due to the low-adhesion between the liquid and the solid surface, i.e., low contact angle hysteresis, when compared to hydrophilic or to hydrophobic surfaces. In this work we investigated the effect of surface structure on the condensation performance on SHSs and SLIPSs. Three different SHSs with structures varying from the micro- to the nano-scale were fabricated following easy and scalable etching and oxidation growth procedures. The condensation performance on such surfaces was evaluated by optical microscopy in a temperature and humidity controlled environmental chamber. On SHSs important differences on the size and on the number of the coalescing droplets required for the jump to ensue were found when varying the surface structure underneath the condensing droplets. A surface energy analysis is proposed to account for the suppression of the droplet-jumping performance in the presence of microstructures. On other hand, by impregnating the same SHSs with a low surface tension oil, i.e., SLIPSs, the adhesion between the condensate and the SLIPSs can be further reduced. On SLIPSs slight differences on the droplet density over time and shedding performance upon the inclusion of microstructures were observed. Droplets were found to shed faster and with smaller diameters on SLIPSs in the presence of microstructures when compared to solely nanostructured SLIPSs. We conclude that on SHSs the droplet-jumping performance of micrometer droplets is deteriorated in the presence of microstructures with the consequent decrease in the heat transfer performance, whereas on SLIPSs the droplet self-removal is actually improved in the presence of microstructures.

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Chen, Ce, JinFu Yang, ChaoQun Nie, Ying Cui, DaRen Yu, ShengBo Yang, Kun Yang und ZhongGuang Fu. „Research on Circumferential Fluid Pressure Distribution and Whirl Stability of Rotor-Bearing System“. In ASME Turbo Expo 2008: Power for Land, Sea, and Air. ASMEDC, 2008. http://dx.doi.org/10.1115/gt2008-50882.

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This paper presents a theoretical analysis of the mechanism of oil whirl, oil whip, and hysteresis in oil whip. A qualitative analysis of the interrelation between whirl frequency, natural frequency, and eccentricity ratio versus speed was conducted using the rotor-bearing load balance equation. By analyzing the interrelation among whirl speed, eccentricity ratio versus speed, rotating speed, oil supply pressure and bearing load, and observing the oil-film load circumferential fluid pressure distribution in the three phases of oil-film load attenuation, instability transition, and oil-film load instability, it was found that in the whirl instability transition phase, the amplitude of rotor whirl speed exceeds half the value of rotor rotation speed, which causes the pressure change in the oil convergent wedge to change from positive to negative, and the pressure change in the divergent wedge to change from negative to positive, and the change in oil-film pressure distribution causes the instability of oil whirl; These changes in oil film pressure distribution are the indicator of oil whirl instability. An experimental study on the whirl instability in a pump supported on fluid film bearings is also presented in this paper to validate the theoretical approach.

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Hong, Jie, Baolong Liu, Dayi Zhang und Yanhong Ma. „Shape Memory Effect and Hysteresis Behavior of Shape Memory Alloy Metal Rubber“. In ASME Turbo Expo 2012: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/gt2012-69244.

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The present work focuses on the shaping craft of shape memory alloy metal rubber (SMAMR) and its temperature dependent mechanical properties. Heat treatment process was conducted to form a stable SMAMR sample beyond the general procedure of metal rubber (MR) in order to resist the shape memory effect (SME). The influence of the heat treatment procedure on the mechanical properties was tested. The quasi-static experimental investigations were carried out to obtain the storage modulus and energy loss factor varying with the structural parameter, strain amplitude, and material temperature. It is found from the experiment results that the SMAMR sample which underwent the heat treatment was able to remember its original moulding shape and recover from the overloading plastic deformation when heated above the phase transition temperature. For comparison, another sample without the heat treatment was heated to the same temperature after the plastic deformation, but the final shape deviated from the original one. It is also confirmed that the heat treatment procedure obviously increased the storage modulus and loss factor of SMAMR. Just like the variety elastic modulus of shape memory alloy (SMA), the storage modulus of SMAMR increased obviously while the material was heated above the phase transformation temperature due to the elastic modulus change of SMA wire. The quasi-static experiments showed a hysteretic property of the stress–strain curve in a certain temperature. But the hysteretic curve was temperature and structural parameter dependent. It is concluded that the heat treatment process is necessary to obtain a stable SMAMR during the phase transformation. The varying storage modulus and superior loss factor performances of SMAMR make itself a kind of attractive functional material which will be available in the active suppression of vibration. For example, it can be fabricated to a rotor bearing with changeable stiffness and damping, which is of practical significance in the active control of synchronous vibration of rotors crossing resonance condition.

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Cao, Yunqi, David Torres, Tongyu Wang und Nelson Sepúlveda. „Influence of VO2 Thin Film Coatings on the Performance of Integrated MEMS Bridges and Cantilevers“. In ASME 2016 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/smasis2016-9217.

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Vanadium oxide (VO2) shows a solid-solid phase transition at around 68 °C where its mechanical and electrical properties start to change dramatically. During the phase transition, the large compressive stress generated by the VO2 thin film coating could induce a significant frequency shift in the bimorph structures such as clamped-clamped (C-C) beams and clamed-free (C-F) beams. However, for regions outside the phase transition, the stress produced by the thermal expansion coefficient difference between VO2 and the cantilever or bridge structural material dominates the frequency shift. Therefore, the two ends of the frequency hysteresis curve exhibits a pattern or behavior that can be different than the one shown during the phase transition. It was observed that opposite trends have been found before and after the phase transition region. This phenomena can be explained by the two competing mechanisms present in VO2-based MEMS: frequency shift due to thermal coefficient difference between VO2 and silicon dioxide (SiO2) (the materials in the bimorph), and the frequency change induced by the phase transition of VO2.

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Iso, Yoshiyuki, und Xi Chen. „Numerical Simulation of Gas-Liquid Two-Phase Flows on Wetted Walls“. In ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-31249.

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Gas-liquid two-phase flows on the wall like liquid film flows, which are the so-called wetted wall flows, are observed in many industrial processes such as absorption, desorption, distillation and others. For the optimum design of packed columns widely used in those kind of processes, the accurate predictions of the details on the wetted wall flow behavior in packing elements are important, especially in order to enhance the mass transfer between the gas and liquid and to prevent flooding and channeling of the liquid flow. The present study focused on the effects of the change of liquid flow rate and the wall surface texture treatments on the characteristics of wetted wall flows which have the drastic flow transition between the film flow and rivulet flow. In this paper, the three-dimensional gas-liquid two-phase flow simulation by using the volume of fluid (VOF) model is applied into wetted wall flows. Firstly, as one of new interesting findings in this paper, present results showed that the hysteresis of the flow transition between the film flow and rivulet flow arose against the increasing or decreasing stages of the liquid flow rate. It was supposed that this transition phenomenon depends on the history of flow pattern as the change of curvature of interphase surface which leads to the surface tension. Additionally, the applicability and accuracy of the present numerical simulation were validated by using the existing experimental and theoretical studies with smooth wall surface. Secondary, referring to the texture geometry used in an industrial packing element, the present simulations showed that surface texture treatments added on the wall can improve the prevention of liquid channeling and can increase the wetted area.

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Iso, Yoshiyuki, und Xi Chen. „Gas-Liquid Two-Phase Flow Simulation of Wetted Wall Flows in Packed Columns“. In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-40494.

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Gas-liquid two-phase interfacial flows on the wall like liquid film flows, which are the so-called wetted wall flows, are observed in many industrial processes such as absorption, desorption, and distillation. For the optimum design of packed columns widely used in those kind of processes, the accurate predictions of the details on the small scale behavior of wetted wall flows in packing elements are very important, especially in order to enhance the mass transfer between the gas and liquid and to prevent flooding and channeling of the liquid flow. The present study focuses on the effects of the change of liquid flow rate and the wall surface texture treatments on the characteristics of wetted wall flows which have the drastic flow transition between the film flow and rivulet flow. In this paper, the three-dimensional gas-liquid two-phase flow simulation by using the volume of fluid (VOF) model is applied into wetted wall flows. Firstly, present results showed that the hysteresis of the flow transition between the film flow and rivulet flow arose against the increasing or decreasing stages of the liquid flow rate. It was supposed that this transition phenomenon depends primarily on the history of flow pattern as the change of curvature of interphase surface which leads to the surface tension. Additionally, the applicability and accuracy of the present numerical simulation were validated by using the existing experimental and theoretical studies. Secondary, referring to the texture geometry used in an industrial packing element, the present simulations showed that surface texture treatments added on the wall can improve the prevention of liquid channeling and can increase the wetted area.

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Folley, Matt, und Trevor Whittaker. „The Effect of Plenum Chamber Volume and Air Turbine Hysteresis on the Optimal Performance of Oscillating Water Columns“. In ASME 2005 24th International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2005. http://dx.doi.org/10.1115/omae2005-67070.

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It is well known that air compressibility is likely to influence the performance of oscillating water columns (OWC’s) and this has previously been modelled and estimated using linear aero-hydrodynamic lump-mass models. In addition, the optimum performance of specific OWC’s has been determined, with the effect of air compressibility included within the optimisation. This paper extends this work to determine the optimum performance of any OWC, defined by its hydrodynamic coefficients and serves as a reminder to experimentalists of the importance of considering air compressibility in their models. Moreover, the optimisation is analytical and so produces explicit expressions for maximum power capture, optimum damping, etc. The results indicate that for the majority of OWC’s the maximum power capture decreases with increasing plenum chamber volume, accompanied by a reduction in the optimum turbine damping and an increase in optimum water column motion. However, the results also show that air compressibility will increase maximum power capture for OWC’s when the incident wave period is shorter than the natural period of the water column. To date, air turbine hysteresis has been studied as a purely aerodynamic phenomenon and its effect on the optimum hydrodynamic performance of OWC’s has not been investigated. This paper uses a linearised phase shift to model an approximation of turbine hysteresis that shows that turbine hysteresis will have a small but significant influence on hydrodynamic performance, where the magnitude of influence is similar to the effect of subtle blade profile and blade sweep angle modifications on aerodynamic performance. The results indicate that hysteresis should be considered in turbine design, especially if a turbine modification improves aerodynamic performance whilst reducing hydrodynamic performance due to a change in the turbine hysteresis.

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Chen, Chuan-Hua, Qingjun Cai und Chung-Lung Chen. „Evaporation and Condensation on Two-Tier Superhydrophobic Surfaces“. In ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer. ASMEDC, 2008. http://dx.doi.org/10.1115/mnht2008-52355.

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Superhydrophobic surfaces exhibit large contact angle and small hysteresis which promote liquid transport and enhance heat transfer. Here, liquid-vapor phase change behavior is reported on superhydrophobic surfaces with short carbon nanotubes deposited on micromachined posts, a two-tier texture mimicking the surface structure of lotus leaves. Compared to one-tier microtexture which energetically favors the Wenzel state, the two-tier texture with nanoscale roughness favors the Cassie state, the desired superhydrophobic state. During droplet evaporation, the two-tier texture delays the transition from Cassie to Wenzel state. Using two-tier texture with hexadeconethiol coating, continuous dropwise condensation was demonstrated for the first time on engineered superhydrophobic surfaces.

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Berichte der Organisationen zum Thema "Phase change hysteresis"

Bos, R. J., T. N. Dey und J. C. Boettger. Influence of the hysteretic phase change in granite on seismic and hydrodynamic coupling of nuclear explosions. Office of Scientific and Technical Information (OSTI), Dezember 1994. http://dx.doi.org/10.2172/10118226.

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