Influence Of Phase Change Research Articles

Study on the hydro-thermal-salt-mechanical coupling characteristics of sulfate saline soil under freeze-thaw cycles

The theoretical and experimental studies have been carried out on the water and salt migration and deformation characteristics of sulfate saline soil during freeze-thaw cycles. Based on the theory of unsaturated soil mechanics and the thermoelastic continuum and considering the influence of phase change within the pore on thermodynamic and hydrodynamic parameters, the multi-physical fields coupled model of hydro-thermal-salt-mechanical in unsaturated sulfate saline soil has been established. The variation processes of the temperature field, water field, salt field, and stress field of the soil during freeze-thaw cycles were analyzed, and the validity of the theoretical model was verified by indoor experiments. The results show that there are significant attenuation and hysteresis effects when heat is transferred in the soil during freeze-thaw cycles. The water content of migration in the soil increases with the height of the soil column, while the increment of migration water content decreases with the number of freeze-thaw cycles. The formation and dissolution of salt crystals from top to bottom and the sudden increase in the salt crystallization rate are mainly caused by variations in the solubility of the salt solutions due to temperature changes. The formation and dissolution of ice and salt crystals in the soil induce expansion and contraction, and the freeze-thaw cycle conditions have a significant effect on the expansion and residual deformation of the soil.

Experimental and computational investigation of heat transfer during quenching of semi-solid aluminum plates under hot cracking condition

The present work attempts to study the cooling characteristics of 7050 aluminium alloy under semi-solid conditions during the jet impingement quenching. An aluminium plate heated to 485℃ (10% liquid fraction) is prone to hot cracks, causing large fluctuations in the temperature data. The 2-D direct heat transfer problem is formulated with the finite element technique, and moving boundary conditions are applied to simulate the quenching process. The heat flux is estimated from the boiling curve parameters (Qmax, TDNB, TLeid) by matching the simulated and experimental temperature data. The cracks are incorporated as the interface elements in the finite element domain along with the phase change model to simulatethe heat transfer phenomena. The influence of phase change and hot cracks on heat transfer is studied in detail with static and dynamic cracking conditions. The parity plot reveals that experimental and simulation results are in good agreement for uncracked plates, with an error range of ± 3% and R2 = 0.9987. Phase change incorporation improves the simulation results for cracked plates, reducing the error range from ± 10% (without phase change) to ± 5% (with phase change) along with R2 values of 0.9929 and 0.9863, respectively. The Boiling curve parameters for the cracked plate are found to be Qmax: 7.2 MW/m2, TDNB: 190℃, and TLeid: 450℃. Further, the findings show that the crack originates in the impingement zone of the quenched side of the plate.

Transient multiphase CO2 release from high‐pressure tanks: Influence of phase changes, viscous heating, and Joule–Thomson effect

AbstractIn this study, CO2 free expansion from high‐pressure tanks is studied in a transient state while considering the influence of different phenomena—that is, viscous heating, phase transition (solid/liquid/vapour phase), and the Joule–Thomson effect—in an initially supersonic flow. This investigation is performed using computational fluid dynamics (CFD) techniques, comparing the obtained results with some experimental data of the literature with a maximum discrepancy of around 8.5%. In particular, for the first time from the literature, it is observed that, according to the velocity evolution at the outlet, the discharge process is conveniently divided into three here‐defined stages: (1) shocking flow, where pressure abruptly decreases with time and flow becomes supersonic, this leading to the condensation of part of CO2; (2) transition flow, characterized by a sort of constant pressure time trend; and (3) flashing flow, where pressure decreases less abruptly following an asymptotic pattern up to the atmospheric one and flow becomes subsonic. Furthermore, non‐equilibrium condensation occurring in the tank, tube, and outlet is observed, finding that the minimum temperature reached by the fluid is around 235 K (−38°C). As well, the non‐equilibrium condensation is taken into account in order to give an indication of the amount of liquid CO2 leaving the outlet in the form of high‐speed jet, which can be a serious danger for personnel and surrounding installations. Moreover, we observe an important effect of viscous heating in the early‐stage expansion for a relatively short time range, within which the temperature in the tube experiences an abrupt increase of around 210 K (from 170 to 380 K). The same effect in the external room creates a convection flow, pushing CO2 towards the top. The results of the present work can be used for health, safety, and environment (HSE) management purposes and for a more precise process design related to CO2 storage and sequestration.

MODIFICATION OF THE STRUCTURALLY THE PHASE STATE OF ALUMINUM ALLOY AS A RESULT OF RADIATION THERMAL TREATMENT

The effect of relativistic electron beams on the change in the structure of the 2014 aluminum alloy was studied. The mechanical characteristics (hardness, ultimate strength, conditional yield stress) of the samples were measured before and after irradiation. The influence of phase changes on these mechanical characteristics was investigated. The possibility of cleaning the surface of alloy 2014 using electron beams was studied. The identification of phase inclusions in the aluminum alloy was carried out. The changes in the number of phases that occurred as a result of irradiation with relativistic electron beams were determined.

Theoretical study of steady-state characteristics of natural circulation system

In this paper, the conservation equations of mass, momentum and energy are established for the natural circulation system. A complete set of constitutive models for solving the steady-state thermal hydraulic parameters are obtained including heat conduction, condenser, pipe, pressurizer, system flow and other auxiliary modules. For calculating natural circulation systems with different structures conveniently, the modular modeling method is adopted. By comparing with the data of different experiments, it proves that modular modeling is universal for systems with different structures, and the correctness of the process of model establishment and model solution is also proved. It is found that the mass flow would increase with the increase of heat flux and the decrease of inlet subcooling of test section. The influence of phase change on the mass flow depended on the structural characteristics of the system. The appearance of two-phase not only increases the driving force of natural circulation system, but also increases the flow resistance. When the increase of driving force is dominant, the appearance of two-phase will further increase the mass flow. Otherwise, the two-phase flow will hinder the increase of mass flow and may even cause its decrease. For the structural design of natural circulation system, the introduction of large form resistance should be avoided as far as possible so as to avoid the establishment of natural circulation process hindered by two-phase flow. The steady-state model of natural circulation system established in this paper has laid a good foundation for the following transient studies and is of great significance.

Parameter identification of nonlinear system via a dynamic frequency approach and its energy harvester application

A dynamic frequency-based parameter identification approach is applied for the nonlinear system with periodic responses. Starting from the energy equation, the presented method uses a dynamic frequency to precisely obtain the analytical limit cycle expression of nonlinear system and utilizes it as the mathematic foundation for parameter identification. Distinguished from the time-domain approaches, the strategy of using limit cycle to describe the system response is unaffected by the influence of phase change. The analytical expression is fitted with the value sets from phase coordinates measured in periodic oscillation of the nonlinear systems, and the unknown parameters are identified with the interior-reflective Newton method. Then the performance of this identification methodology is verified by an oscillator with nonlinear stiffness and damping. Besides, numerical simulations under noisy environment also verify the efficiency and robustness of the identification procedure. Finally, we apply this parameter identification method to the modeling of a large-amplitude energy harvester, to improve the accuracy of mechanical modeling. Not surprisingly, good agreement is achieved between the experimental data and identified parameters. It also verifies that the proposed approach is less time-consuming and more accuracy in identification procedure.

Investigation of a double-PCM-based thermoelectric energy-harvesting device using temperature fluctuations in an ambient environment

Energy-harvesting devices, consisting of thermoelectric modules and phase change materials (PCMs), can extract energy from the ambient environment for the self-power supply of many small electronic devices such as wireless sensors. However, due to the distinct temperature ranges of various seasons in different places, these devices’ power generation performance may be seriously impaired. In this paper, a new double-PCM-based thermoelectric energy-harvesting device based on temperature fluctuations in the ambient environment is proposed to improve device performance. A double-PCM-based device has been built and tested in an environment with a large temperature range (0–40°C) for three days. Experimental results show that the average output power of the double-PCM-based thermoelectric energy-harvesting device under matched load resistance outperforms that of the single-PCM device by 35.8%. A one-dimensional unsteady heat transfer model is established to describe the temperature variation of PCMs. The influence of phase change is considered through variations in PCMs’ specific heat capacity. This work demonstrates that the proposed double-PCM-based thermoelectric energy-harvesting device performs better over a large temperature range and is more suitable for small electronic devices operating at different times and in different places.

On the Influence of Phase Change in Highly Loaded Frictional Contacts

Highly loaded lubricated contacts may present a friction plateau on which the friction force becomes independent from the sliding velocity. Although this phenomenon has been known for a long time, its physical origin remains poorly known. The present paper aims at giving further insight on the physical mechanisms triggering the friction plateau. The study specifically focuses on the influence of pressure on the physical state of the lubricant. An uncoupled experimental approach (rheology, tribology, spectrometry) has been conducted on a model lubricant. The lubricant behavior has been probed both at rest by Brillouin light scattering spectroscopy and dynamically under stationary conditions in a lubricated contact. The first experimental approach led to evidence a transition pressure associated with the lubricant glass transition, which has then been correlated to the lubricant macroscopic response in friction. We show that the onset of the plateau behavior occurs for Hertzian pressures close to the glass transition pressure, corresponding to a very small fraction of lubricant in a “nominal glassy state” within the contact.

Dissociative influence of H2O vapour/spray on lean blowoff and NOx reduction for heavily carbonaceous syngas swirling flames

Recent studies have described and evidenced the enhancement of fundamental combustion parameters such as laminar flame speed due to the catalytic influence of H2O with heavily carbonaceous syngas mixtures. In this study, the potential benefits of these subtle changes in water loading and hence reaction pathways are explored in terms of delayed lean blowoff, and primary emission reduction in a premixed turbulent swirling flame (Ø = 0.6–0.8), scaled for practical relevance. Chemical kinetic models initially confirm that H2O has a substantial impact on the employed fuel behaviour; increasing flame speed by up to 60% across an experimental range representative of fluctuation in atmospheric humidity (∼1.8 mol%). OH* chemiluminescence and OH planar laser induced fluorescence (PLIF) were employed to analyse the changes in heat release structure resulting from the experimental addition of H2O vapour to the combustor. Equivalent concentrations of liquid H2O were introduced into the central recirculation zone of the premixed flame as an atomised spray, to investigate the influence of phase changes on the catalytic effect. Near the lean stability limit, H2O addition compresses heat release to shorten the elongated flame structure. Whereas with a stable and well-defined flame structure, the addition triggers a change in axial heat release location, causing the flame front to retract upstream toward the burner outlet. Higher quantities of two-phase flow were combined to explore the possibility of employing the spray as a stabilising mechanism, effectively dampening the observed influence of humidity. The chemical enhancement induced by the controlled supply was shown to reduce the lean blowoff stability limit, enabling an increase in additional air flow of almost 10%. However, the catalytic effect of H2O diminishes with excessive supply and thermal quenching prevails. There is a compound benefit of NOx reduction from the use of H2O as a flame stabiliser with the practically-relevant syngas: First NOx production decreases due to thermal effect of H2O addition, with potential for further reduction from the change in lean stability limit; leanest experimental concentrations reduced by up to a factor of four with two-phase flow at the highest rates of supply. Hence, the catalytic effect of H2O on reaction pathways and reaction rate predicted and observed in the laminar environment, is shown to translate into practical benefits in the challenging environment of turbulent, swirl-stabilised flames.

Influence of phase change on self-pressurization in cryogenic tanks under microgravity

Future operations of many fluid, thermal and power systems and their ability to store, transfer, and manage a variety of single or multiphase fluids in reduced gravity environment are of great importance. For many of these systems, cryogenic conditions will play an important role. Cryogenic vaporization, caused by heat leakage into the tank from the surrounding environment, is one of the main causes of mass loss and leads to self-pressurization of the storage tanks. Available publications on self-pressurization and stratification of cryogenic tanks mainly focus on the convection and surface evaporation influences. Because large superheats increase the likelihood of evaporation in the liquid, the evaporation and its effect on vapor pressure under microgravity is studied numerically in this paper. The effects of reduced gravity, contact angle of the vapor bubble, and surface tension are investigated. The computations are carried out by using the CFD software package, Ansys Fluent, and an in-house developed code to calculate the source term associated with the phase change. A coupled level set and the volume-of-fluid method (CLSVOF) are used to solve a single set of conservation equations for the whole domain and the interface between the two phases is tracked or captured. A heat and mass transfer model is implemented into the Fluent code for solving problems involving evaporation or condensation. Results show that small tiny vapor regions caused by the evaporation process change the pressure rise. Vortices are observed due to the vapor dynamics.

Numerical studies of the effects of phase transitions on Venusian mantle convection

This paper presents a study on the effects of phase transitions on the mantle convection of Venus in a three-dimensional (3D) spherical shell domain. Our model includes strong depth- and temperature-dependent viscosity and exothermic phase change from olivine to spinel as well as endothermic phase change from spinel to perovskite. From extensive numerical simulations of the effects of Rayleigh number (Ra), and the Clapeyron slopes and depths of phase changes, we found the following: (1) The endothermic phase change prevents mass flow through the interface. Increasing the absolute value of the Clapeyron slopes decreases radial mass flux and normalized radial mass flux at the endothermic phase boundary, and decreases the number of mantle plumes. In other words, mass flow through the phase boundary decreases. The inhibition influence of phase changes increases, as do convective wavelengths. (2) Increasing Ra also increases the convective wavelength and decreases the number of mantle plumes, but it has less influence on the mass exchange. As Ra increases, the convective vigor increases along with the radial mass flux and the mass flow through the phase boundary; however, the normalized mass flux through the phase boundary varies little with Ra, which is different from the conclusion that increasing Ra will greatly increase the inhibition of mass flow through the phase boundary based on two-dimensional (2D) modeling. (3) Increasing the depth of endothermic phase change will slightly decrease the number of mantle plumes, but has little effect on the mass flow through the phase boundary. Consistent with previous studies, our results show that the phase change from spinel to perovskite could inhibit the mass flow through the phase boundary, but they also show that the buildup of hot materials under the endothermic phase boundary in the 3D model could not be so large as to cause strong episodic overturns of mantle materials, which is quite different from previous 2D studies. Our results suggest that it is difficult for phase changes to cause significant magmatism on Venus; in other words, phase changes may not be the primary cause of catastrophic resurfacing on Venus.

Representing moisture fluxes and phase changes in glacier debris cover using a reservoir approach

Abstract. Due to the complexity of treating moisture in supraglacial debris, surface energy balance models to date have neglected moisture infiltration and phase changes in the debris layer. The latent heat flux (QL) is also often excluded due to the uncertainty in determining the surface vapour pressure. To quantify the importance of moisture on the surface energy and climatic mass balance (CMB) of debris-covered glaciers, we developed a simple reservoir parameterization for the debris ice and water content, as well as an estimation of the latent heat flux. The parameterization was incorporated into a CMB model adapted for debris-covered glaciers. We present the results of two point simulations, using both our new "moist" and the conventional "dry" approaches, on the Miage Glacier, Italy, during summer 2008 and fall 2011. The former year coincides with available in situ glaciological and meteorological measurements, including the first eddy-covariance measurements of the turbulent fluxes over supraglacial debris, while the latter contains two refreeze events that permit evaluation of the influence of phase changes. The simulations demonstrate a clear influence of moisture on the glacier energy and mass-balance dynamics. When water and ice are considered, heat transmission to the underlying glacier ice is lower, as the effective thermal diffusivity of the saturated debris layers is reduced by increases in both the density and the specific heat capacity of the layers. In combination with surface heat extraction by QL, subdebris ice melt is reduced by 3.1% in 2008 and by 7.0% in 2011 when moisture effects are included. However, the influence of the parameterization on the total accumulated mass balance varies seasonally. In summer 2008, mass loss due to surface vapour fluxes more than compensates for the reduction in ice melt, such that the total ablation increases by 4.0%. Conversely, in fall 2011, the modulation of basal debris temperature by debris ice results in a decrease in total ablation of 2.1%. Although the parameterization is a simplified representation of the moist physics of glacier debris, it is a novel attempt at including moisture in a numerical model of debris-covered glaciers and one that opens up additional avenues for future research.

Thermal conductivity measurements of a phase change material slurry under the influence of phase change

Phase change material slurry is widely used in such applications as thermal energy storage and thermal management. Thermal conductivity of phase change material slurry is one of the most important thermo-physical properties that are necessary for system design and performance evaluation. In the present study, thermal conductivity of a phase change material slurry, tetra-n-butylammonium bromide (TBAB) clathrate hydrate slurry (CHS), is experimentally measured by using transient hot-wire method. The theoretical model of thermal conductivity measurement of phase change material slurry under the influence of phase change is proposed and numerically analyzed to obtain real thermal conductivity. It is found that phase change significantly affects the measurement of thermal conductivity in that the real thermal conductivity is smaller than that obtained directly from the experiments because phase change enhances heat transfer during the measurement. The smaller the solid fraction of TBAB CHS, the larger the influence of phase change on thermal conductivity is. Such effect is apparently ubiquitous, which should also be taken into consideration in thermal conductivity measurement of other phase change material slurries.

Theoretical investigation on the magnetocaloric effect in amorphous systems, application to: Gd80Au20 and Gd70Ni30

The temperature dependence of the magnetocaloric effect in Gd80Au20 and Gd70Ni30 amorphous alloys were investigated, using the Handrich-Kobe model with a modified Brillouin function that takes an additional exchange fluctuation term. The exchange fluctuation parameters were determined to give better fits to magnetic entropy changes and adiabatic temperature changes. The magnetic entropy changes of 2.20 Jmol−1K−1 and 1.50 Jmol−1K−1 and the refrigerant capacity values of 135 Jmol−1 (ΔB=5 T) and 146 Jmol−1 (ΔB=7 T) are obtained for Gd80Au20 and Gd70Ni30, respectively. In addition, the influence of phase changes between crystalline and amorphous states on the isothermal entropy change was investigated.

The Thermo-Hydro Coupled Model of Low-Temperature Rock In Consideration of Phase Change

Considering the influence of phase change and temperature variation on the physical and mechanical properties of low-temperature rock in cold regions, the mathematical model for the Thermo-Hydro(TH) coupled problem is proposed based on the theory of convective heat transfer for porous medium. In this model, the influence of moisture migration on heat conduction in rock is taken into account, as well as the influence of temperature gradient on the seepage. The involved parameters are determined according to the related equations given in this paper. Then the finite element model of a gas transmission pipeline in cold region is established using the proposed mathematical model. By selecting suitable boundary conditions, initial conditions and heat computation parameters, the freezing problem of low-temperature rock surrounding the pipeline is analyzed. The calculated values of the temperature field and the measured data are basically consistent, which indicates that the proposed TH coupling model for rock in cold regions is reasonable and reliable.

Effect of fast neutron fluence on the creep anisotropy of Zr–2.5Nb tubes

The in-reactor behaviour of internally pressurised capsules of Zr–2.5Nb tubes is analysed in detail to separate the stress dependent component of deformation (creep). It is found by a rigorous statistical analysis that the creep rate varies with fast neutron fluence. At 555 K the axial creep rate increases while the transverse creep rate decreases with fluence. At 588 K the creep rate in both the axial and transverse directions increases with fluence. It is also shown that the creep anisotropy ratio R, i.e., the ratio of axial to transverse creep rate for a pressurised tube, varies with fluence, stress and irradiation temperature. These findings are discussed in terms of the irradiation-induced evolution in microstructure. The possible impact of the evolution of the dislocation substructure is discussed with reference to a self-consistent polycrystalline model that takes into account the crystallographic texture and the grain interaction strains present in zirconium alloys. The lower temperature creep behaviour is consistent with an increase with fast fluence of the single crystal creep compliance related to prismatic dislocation climb and glide, or a decrease in the single crystal creep compliances relating to basal and pyramidal slip. The creep behaviour at the higher irradiation temperature is more complicated, and there may be an influence of phase changes as well as dislocation structure. It appears that all three eigenvalues describing the single crystal creep behaviour depend on fast fluence.

Influence of Phase Change in Intergranular Oxides to Thermal Conductivity of AlN Sintered by Millimeter-Wave Heating

Influence of Phase Change in Intergranular Oxides to Thermal Conductivity of AlN Sintered by Millimeter-Wave Heating

Opposed-flow flame spread over polymeric materials: influence of phase change

A numerical model for flame spread over polymeric surfaces is constructed. The dependence of the flame spread rate on phase change and thermal properties is investigated by varying three non-dimensional parameters, St, k̄ l , and C̄ Pl . Quantitative comparisons indicate that the numerical model provides excellent agreement to an analytical formula in the cases of variable latent heat of the phase change, variable liquid thermal capacity, and variable thermal conductivity. However, the deRis formula yields a constant spread rate higher than the numerical result and is independent of phase change. Qualitatively, with the increase of St, or with the decrease of k̄ l or C̄ Pl , the flame spread rate increases. In addition, k̄ l is the strongest determinant of the influence of the thickness of the liquid region. The mechanisms of flame spread at the steady state are interpreted by applying an energy balance principle for the control volume upstream of the flame leading edge. It is found that a ratio between the total heat applied to the condensed material upstream of the flame leading edge and the spread rate reveals the physical mechanisms that control the preheating of the condensed material to the ignition temperature. The dependence of flame structure on St, k̄ l , and C̄ Pl is studied. It is found that with the increase of St or k̄ l , or with the decrease of C̄ Pl , the size of the flame increases. These results indicate that flame size dependence follows the magnitude of the spread rate when the properties of the condensed material are variable.

The influence of phase changes on debris-cloud interactions with protected structures

The physical state of the debris cloud generated by the interaction of a projectile with a thin target depends on the energy balance associated with the impact event. At impact velocities well above the sound speeds of the materials involved, the cloud is expected to consist of material in solid, liquid, and vapor phases. A series of numerical calculations using the multi-dimensional finite-difference hydrocode CTH has been used to evaluate the effect of phase changes ( i.e., different vapor fractions) on these clouds, and on their subsequent interaction with backwall structures. In the calculations, higher concentrations of vapor are achieved either by (1) increasing the initial temperature of both the projectile and the thin shield while keeping the impact velocity constant, or (2) by actually increasing the impact velocity. The nature of the debris cloud and its subsequent loading on the protected structure depend on both its thermal and physical state. This interaction can cause rupture, spallation, or simply bulging of the backwall. These computational results are discussed and compared with new experimental observations obtained at an impact velocity of ∼ 10 km/s. In the experiment, the debris cloud was generated by the impact of a plate-shaped titanium projectile with a thin titanium shield.

Influence of phase change within a 90-year-old Sequoia sempervirens on its in vitro organogenic capacity and protein patterns

Shoot-tips collected from stump shoots at the base of a 90-year-old Sequoia sempervirens and from the crown of the same donor tree were compared in respect of their organogenic performance in in vitro conditions. The cultures derived from stump shoots appeared to be much more responsive in terms of growth increment and adventitious rooting capacity — rooting rate, root length, average number of neoformed roots and root score — than cultures derived from the crown, although considerable variation was observed in all the organogenic criteria examined. The persisting topophysical differences in potential for in vitro organogenic and associated morphological traits characteristic of phase change were found to be connected with quantitative modifications of protein content. Thus, 23 membrane-associated proteins with molecular weights ranging from 22 to 58 kDa appeared to be synthesized in greater abundance in the culture originating from the stump shoots.