Induced Density Changes Research Articles

Elastic limit and charging times of compressible microencapsulated phase change materials

Thermo-mechanical models of encapsulated phase change materials have been proposed throughout the literature. Heat transfer rates can be enhanced through the encapsulation of a phase change material. The improvement of heat transfer rates, constitutes a challenge that seeks to meet the energy demand in high temperature and cold energy storage applications. Thermo-mechanical models proposed in the literature, have been applied to estimate the effects of encapsulating shells on the dynamics of the phase transition and on the energy storage capacity of phase change materials. Modeling of the phase change dynamics allows to determine melting or solidification times, that constitute a key parameter in energy storage applications. Previous thermo-mechanical models constitute an attempt to understand the thermal kinetics of microencapsulated phase change materials. The mathematical models have been consistently neglecting density variations induced by the inner pressure within the encapsulating shell. In this work, a thermo-mechanical model that couples the pressure induced density changes with the elastic properties of the shell, is proposed. The effects of density changes are incorporated in the proposed model, through the compressibility of the liquid and solid phases. Three compressibility regimes are defined and significant differences in the melting dynamics between these regimes, are found. To the authors knowledge, the models found in the literature only describe the thermal kinetics of incompressible phase change materials. In this work, we consider a silicon carbide shell with a large Young’s modulus as the encapsulating material. We found that melting rates and thermal kinetics is considerably slower in phase change materials with compressible phases. The examples discussed in this work, show that melting times can be twice as long for materials with compressible phases than melting times when incompressible phases are assumed. Additionally, we found that the encapsulating shell always reaches the elastic limit at low melting fractions by assuming incompressible phases. However, when compressible phases are incorporated, a threshold thickness for which the encapsulating material will never reach the elastic limit, is found. Finally, we found that the appearance of steady states in phase change materials with incompressible phases, can reduce the thermal energy density at typical heating temperatures by as much as 30%.

Thermo-elastic model for the prediction of thermodynamic properties of high temperature phase change materials under confinement: Isobaric and isochoric regimes

Thermal energy storage through encapsulation of phase change materials is critical for the efficient usage of renewable energy. In this paper, a model is proposed to include thermal and pressure induced density changes in a confined phase change material. To the best of the authors’ knowledge, the local energy balance at the interface and the total mass balance that couple thermal and pressure induced density changes during melting of confined phase change materials are proposed for the first time. The proposed model is solved for a KNO3 salt and several values of the elastic constant in order to probe the phase transition in the whole pressure domain. The behavior of the thermodynamic variables is investigated for other kinds of salts used in high temperature thermal energy storage applications and in the high pressure regime. In all the examples shown, and when the phase change process takes place close to the isochoric regime, the effects of temperature dependent densities are found to be enhanced by pressure induced density changes. However, close to the isobaric regime, the effects of temperature dependent densities are almost negligible. Finally, the thermal energy stored during the melting process is obtained. Close to the isochoric regime, and depending on the types of boundary conditions, the sensible heat stored is found to be enhanced by thermal expansion, while the latent heat absorbed is significantly reduced.

Making a Simple A+B→C Reaction Oscillate by Coupling to Hydrodynamic Effect.

We present a new mechanism through which chemical oscillations and waves can be induced in batch conditions with a simple A+B→C reaction in the absence of any nonlinear chemical feedback or external trigger. Two reactants A and B, initially separated in space, react upon diffusive contact and the product actively fuels insitu convective Marangoni flows by locally increasing the surface tension at the mixing interface. These flows combine in turn with the reaction-diffusion dynamics, inducing damped spatiotemporal oscillations of the chemical concentrations and the velocity field. By means of numerical simulations, we single out the detailed mechanism and minimal conditions for the onset of this periodic behavior. We show how the antagonistic coupling with buoyancy convection, due to concurrent chemically induced density changes, can control the oscillation properties, sustaining or suppressing this phenomenon depending on the relative strength of buoyancy- and surface-tension-driven forces. The oscillatory instability is characterized in the relevant parametric space spanned by the reactor height, the Marangoni (Ma_{i}) and the Rayleigh (Ra_{i}) numbers of the ith chemical species, the latter ruling the surface tension and buoyancy contributions to convection, respectively.

SU‐E‐T‐527: Is CTV‐Based Robust Optimized IMPT in Non‐Small‐Cell Lung Cancer Robust Against Respiratory Motion?

Purpose:To determine which proton planning technique on average‐CT is more vulnerable to respiratory motion induced density changes and interplay effect among (a) IMPT of CTV‐based minimax robust optimization with 5mm set‐up error considered, (b, c) IMPT/SFUD of 5mm‐expanded PTV optimization.Methods:Three planning techniques were optimized in Raystation with a prescription of 60/25 (Gy/fractions) and almost the same OAR constraints/objectives for each of 10 NSCLC patients. 4D dose without/with interplay effect was recalculated on eight 4D‐CT phases and accumulated after deforming the dose of each phase to a reference (exhalation phase). The change of D98% of each CTV caused by density changes and interplay was determined. In addition, evaluation of the DVH information vector (D99%, D98%, D95%, Dave, D50%, D2%, D1%) which compares the whole DVH by η score = (cosine similarity × Pearson correlation coefficient − 0.9) × 1000 quantified the degree of DVH change: score below 100 indicates changed DVH.Results:Three 3D plans of each technique satisfied our clinical goals. D98% shift mean±SD (Gy) due to density changes was largest in (c): −0.78±1.1 while (a): −0.11±0.65 and (b): − 0.59±0.93. Also the shift due to interplay effect most was (c): −.54±0.70 whereas (a): −0.25±0.93 and (b): −0.12±0.13. Moreover lowest η score caused by density change was also (c): 69, while (a) and (b) kept around 90. η score also indicated less effect of interplay than density changes. Note that generally the changed DVH were still acceptable clinically. Paired T‐tests showed a significantly smaller density change effect in (a) (p<0.05) than in (b) or (c) and no significant difference in interplay effect.Conclusion:CTV‐based robust optimized IMPT was more robust against respiratory motion induced density changes than PTV‐based IMPT and SFUD. The interplay effect was smaller than the effect of density changes and similar among the three techniques.The JSPS Core‐to‐Core Program (No. 23003), Japan Society for the Promotion of Science Grant‐in‐Aid for Scientific Research (No. 23390300), Grant‐in‐Aid for Young Scientists (B) (No. 21791194) and Grant‐in‐Aid for Cancer Research (H22‐3rd Term Cancer Control‐General‐043)

Detection of a novel mechanism of acousto-optic modulation of incoherent light.

A novel form of acoustic modulation of light from an incoherent source has been detected in water as well as in turbid media. We demonstrate that patterns of modulated light intensity appear to propagate as the optical shadow of the density variations caused by ultrasound within an illuminated ultrasonic focal zone. This pattern differs from previous reports of acousto-optical interactions that produce diffraction effects that rely on phase shifts and changes in light directions caused by the acoustic modulation. Moreover, previous studies of acousto-optic interactions have mainly reported the effects of sound on coherent light sources via photon tagging, and/or the production of diffraction phenomena from phase effects that give rise to discrete sidebands. We aimed to assess whether the effects of ultrasound modulation of the intensity of light from an incoherent light source could be detected directly, and how the acoustically modulated (AOM) light signal depended on experimental parameters. Our observations suggest that ultrasound at moderate intensities can induce sufficiently large density variations within a uniform medium to cause measurable modulation of the intensity of an incoherent light source by absorption. Light passing through a region of high intensity ultrasound then produces a pattern that is the projection of the density variations within the region of their interaction. The patterns exhibit distinct maxima and minima that are observed at locations much different from those predicted by Raman-Nath, Bragg, or other diffraction theory. The observed patterns scaled appropriately with the geometrical magnification and sound wavelength. We conclude that these observed patterns are simple projections of the ultrasound induced density changes which cause spatial and temporal variations of the optical absorption within the illuminated sound field. These effects potentially provide a novel method for visualizing sound fields and may assist the interpretation of other hybrid imaging methods.

Reproducibility of target coverage in stereotactic spot scanning proton lung irradiation under high frequency jet ventilation

PurposeTo investigate scanned-beam proton dose distribution reproducibility in the lung under high frequency jet ventilation (HFJV). Materials and methodsFor 11 patients (12 lesions), treated with single-fraction photon stereotactic radiosurgery under HFJV, scanned-beam proton plans were prepared with the TRiP98 treatment planning system using 2, 3–4 and 5–7 beams. The planning objective was to deliver at least 95% of the prescription of 33Gy (RBE) to 98% of the PTV. Plans were subsequently recomputed on localization CT scans. Additionally, for selected cases, the effects of range uncertainties were investigated. ResultsMedian GTV V98% was 98.7% in the original 2-field plans and 93.7% in their recomputation (p=0.039). The respective values were 99.0% and 98.0% (p=0.039) for the 3–4-field plans and 100.0% and 99.6% (p=0.125) for the 5–7-field plans. CT calibration uncertainties of ±3.5% led to a GTV V98% reduction below 1.5 percentual points in most cases and reaching 3 percentual points for 2-field plans with beam undershoot. ConclusionsThrough jet ventilation, reproducible tumor fixation for proton radiotherapy of lung lesions is achievable, ensuring excellent target coverage in most cases. In few cases, non-optimal patient setup reproducibility induced density changes across beam entrance channels, leading to dosimetric deterioration between planning and delivery.

Femtosecond laser induced density changes in GeO_2 and SiO_2 glasses: fictive temperature effect [Invited

Density changes of GeO2 and SiO2 glasses subjected to irradiation by tightly focused femtosecond pulses are observed by Raman scattering. It is shown that densification caused by the void formation in GeO2 glass is very similar to the changes under hydrostatic pressure. In contrast, the experimental observations in SiO2 glass could be explained by pressure effect or by the fictive temperature anomaly, i. e., a resultant smaller specific volume of the glass (a denser phase) at a high thermal quenching rate. Density changes of GeO2 and SiO2 glasses are opposite upon close-to-equilibrium heating; this gives new insights into the mechanisms of densification under highly non-equilibrium conditions: fs-laser induced micro-explosions, heating and void formation. The pressure and temperature effects of glass modification by ultra-short laser pulses are discussed considering applications in optical memory, waveguiding, and formation of micro-optical elements.

A nonsteady‐state firn‐densification model for the percolation zone of a glacier

A simple steady status firm‐densification model is modified to account for short‐term time variations of accumulation rate and surface temperature. The temporal surface‐elevation‐ and mass changes at two sites in the percolation zone of an ice sheet in response to various climate histories are determined. It is shown that a straight‐forward translation of observed short‐term ice sheet surface‐elevation variations into mass changes may be completely misleading, particularly for the percolation zone of the ice sheet, where temperature driven variations of melting/refreezing rates have a strong impact on near surface density. In the lower percolation zone, the mass change associated with a temperature anomaly in respect to the mean climate may for example amount to as little as 10 percent of the observed, simultaneous surface elevation change. Moreover, significant surface elevation change may occur even in periods of constant surface climate, and consequently unchanged mass balance, as a delayed response to previous changes of the local surface climate. Forcing the model with cyclic temperature variations mimicking fluctuations of West Greenland instrumental temperature records during the past hundred years, shows that surface elevation may increase by as much as 1 m in 5 years in periods with no mass change at all. In the lower percolation zone, temperature induced density changes rather than fluctuations of accumulation rate are the dominant cause of short‐term surface elevation changes in contrast to the situation in the higher percolation zone, where short‐term surface‐elevation change is dominated by fluctuations of accumulation rate.

Self-similarity of Rayleigh–Taylor mixing rates

We establish a renormalized self-similar scaling law for fluid mixing in the deeply compressible regime. Compressibility introduces a new length scale into the mixing but our time dependent analysis of the density contrast largely removes the effects of this length scale, so that self-similarity is maintained. Dynamically induced density changes lead to a dynamic Atwood number to measure density contrasts. We improve previous density renormalizations to allow a unified treatment of mass diffusion and compressible density stratification in a range of weakly to strongly compressible three-dimensional multimode Rayleigh–Taylor simulations. Some of these simulations use front tracking to prevent numerical interfacial mass diffusion, while the others are untracked and diffusive. Using the dynamic Atwood number A(t) as opposed to the customary t=0 Atwood number A=A(t=0) to define growth rate constants, approximate universality of the mixing rate constant αb is obtained at low compressibility. Furthermore, earlier results giving consistent simulation, experiment and theory for nearly incompressible mixing, are now extended to show renormalized self-similar scaling with increases in the mixing rates for simulations of highly compressible mixing. The renormalized (i.e., dynamic Atwood number corrected) mixing rates of the diffusive and nondiffusive simulations agree, and show very similar compressibility dependence, with self-similar mixing rates tripling as compressibility becomes strong.

The influence of starting state on neutron induced density changes observed in Nb-1Zr and Mo-41Re at high exposures

Both Nb-1Zr and Mo-41Re were irradiated in FFTF at five temperatures between 420 and 730°C, reaching maximum exposure levels of 58 to 111 dpa, depending on the irradiation temperature. Each alloy was irradiated in two starting conditions, cold-worked and aged or annealed and aged. The neutron-induced swelling behavior in response to starting condition was quite different for the two alloys and appeared to reflect a strong role of precipitation in each. While transmutation does not play a major role in the response of Nb-1Zr, it plays a significant role in the behavior of Mo-41Re, which becomes a heavily-precipitated Mo-Re-Os-Tc-Ru alloy. This strong response may preclude the use of Mo-Re alloys for fusion application.

A Model for Predicting Diurnal Height Variations of Quasi-Constant-Density Tetroons

Abstract A model has been developed for predicting diurnal height changes of quasi-constant-density Mylar tetroons resulting from the complex interaction between thermally induced density changes of the tetroon and height-dependent ambient diurnal density changes in the lower 600 m of the atmosphere. The effects of solar and nocturnal radiation on tetroon altitude are included in the model. These cyclic height variations would be additive to the effects of mechanical and thermal vertical air currents acting on the tetroon. The magnitudes of the height variations for flights at <300 m above ground are so large that they should be considered in flight planning to prevent premature grounding of the tetroons. A diurnal surface temperature range of 13°C (24°F) and the condition that air and tetroon temperature are always equal, gives a predicted diurnal height change of ∼250 m for tetroons deployed for flight at 300 m above the surface. By applying 8°C maximum superheating by day and 7°C supercooling by night,...

Nonlinear optics in radiatively cooled vapors

We consider the use of a radiatively cooled resonant vapor as a media for 3rd order nonlinear optics processes. The 3rd order nonlinear refractive index coefficient due to both steady state saturation of the atomic polarizability and electrostrictive induced density changes are computed for a radiatively cooled vapor with sodium as an example. For pump detuning on the order of the natural linewidth the electrostrictive and saturation induced nonlinear refractive index coefficients are comparable and several orders of magnitude greater than the highest values yet reported. At pump detunings larger than the natural linewidth the electrostrictive mechanism is shown to dominate in the steady state.

Shock induced density changes in metastable BCC phases

Shock induced density changes in metastable BCC phases

Frequency Factors for Annealing Fast-Neutron Induced Density Changes in Vitreous Silica

Isothermal and step-annealing data were obtained and show that the frequency factor is ∼1014/sec for processes having activation energies beyond the peak of the distribution but some orders of magnitude lower and possibly dispersed for the portions of the distribution at activation energies less than the peak.