An efficient heat-based model for solid-liquid-gas phase transition and dynamic interaction

Effect of metal foam on improving solid–liquid phase change in a multi-channel thermal storage tank

International audience

Physically-based modeling: past, present, and future

Ice clouds have a significant impact on the thermodynamic structure of their environment due to diabatic effects such as latent heat release in phase transitions. On the other hand, the ice clouds themselves are crucially affected by the local dynamics e.g. due to atmospheric gravity waves generated by frontal systems or the flow over a mountain. The interaction of the relevant dynamical processes and ice cloud microphysics on different length and time scales is not yet well understood. We investigate the influence of atmospheric gravity waves on ice cloud microphysics using a Lagrangian approach.The ice cloud properties are modelled by an ODE system where the variables are number and mass concentration as well as the supersaturation of water vapour over ice, while the vertical updraft is externally driving the system. The dynamical effects due to gravity waves are described by a Taylor-Goldstein type equation, which is then used to calculate trajectories of air parcels. We investigate the ice cloud microphysical properties along such trajectories. In this framework, we are able to run many simulations and thus study the setting for several different initial and environmental conditions.While the ice cloud system can be regarded as a non-linear oscillator for constant vertical motion, more complex behaviour emerges in the case of the non-constant updraft along trajectories. Due to the non-linearity of the ice cloud model and the overall complexity of the equations of the coupled systems, the feasibility of analytical calculations is limited and the investigation of the coupled system is largely based on numerical approaches.

Dynamics of molecules and phase transitions in the crystals of pure and binary mixtures of n-paraffins

A study is made of the problem of the flow and heat transfer of a fluid formed by the phase transition (melting or sublimation) when the end of a rod touches a heated surface. Problems of this kind arise, in particular, when a heated surface is cooled by means of the heats of the phase transitions of materials with an energy content. A solution is obtained to a simplified system of heat and mass transfer equations obtained by estimating the order of magnitude of the various terms in the Navier-Stokes equations in a manner similar to that in [1–3]. The parameters that govern the process are identified, and an approximate analytic solution is found for the quasi-stationary case. The analytic solution is compared with a numerical solution obtained iteratively.

Consecutive charging and discharging of a PCM-based plate heat exchanger with zigzag configuration

We present a seminumerical simulation method called SIRFEM, which enables the efficient prediction of high-frequency transducer outputs. In particular, this is important for acoustic microscopy where the specimen under investigation is immersed in a coupling fluid. Conventional finite-element (FE) simulations for such applications would consume too much computational power due to the required spatial and temporal discretization, especially for the coupling fluid between ultrasonic transducer and specimen. However, FE simulations are in most cases essential to consider the mode conversion at and inside the solid specimen as well as the wave propagation in its interior. SIRFEM reduces the computational effort of pure FE simulations by treating only the solid specimen and a small part of the fluid layer with FE. The propagation in the coupling fluid from transducer to specimen and back is processed by the so-called spatial impulse response (SIR). Through this hybrid approach, the number of elements as well as the number of time steps for the FE simulation can be reduced significantly, as it is presented for an axis-symmetric setup. Three B-mode images of a plane 2-D setup-computed at a transducer center frequency of 20MHz-show that SIRFEM is, furthermore, able to predict reflections at inner structures as well as multiple reflections between those structures and the specimen's surface. For the purpose of a pure 2-D setup, the SIR of a curved-line transducer is derived and compared to the response function of a cylindrically focused aperture of negligible extend in the third spatial dimension.

At the Karlsruhe Light Ion Facility (KALIF) high-power proton beams with power densities up to ∼ 1 TW/cm2 are generated depositing up to 40 kJ of ion energy in a focal spot of 6∼8-mm diameter. With peak proton energies of ∼ 1.7 MeV, specific power densities of up to 200 TW/g and energy densities of several MJ/g can be realized. This is a regime in which experiments providing information on the equation of state (EOS), dynamics of the beam interaction with condensed targets, and properties of solids and plasma at high-energy densities are of particular interest. In the present paper we report on shock-wave experiments using solid targets and high-resolution laser-Doppler velocimetry. The empirical data provided are used to verify code simulations and the used EOS-data in these calculations, to investigate the beam-target interaction, and to perform series of shock-wave measurements of properties of different materials. The ∼40-ns FWHM proton beam can be used to generate, by material ablation or impact of ablatively accelerated flyers, intense shock waves, permitting the investigation of shock compressibility, dynamic failure of solids under nanosecond load duration, phase transitions, and viscosity at strain rates up to ∼108 s-1. Recently an improved line-imaging velocimeter was set up to measure the spatial velocity variation with a maximum resolution of < 10 μm, opening the possibility to address new issues like growth of instabilities or local dynamics of the spall fracture.

Improving the ability to model, manage and communicate the impact of uncertainty in complex interacting systems is becoming increasingly important. This is particularly important for defence as the nature of warfare is rapidly changing due to the incursion of novel defence technologies. The dominant attribute of modern warfare is its network-centric characteristic, which can be both an enabling and a limiting factor. Network-centric warfare refers to a potentially large number of entities or assets with varying capabilities for autonomous decision making whose coordinated fighting power is enabled through information exchange within a constrained system structure that can be described in terms of interacting networks. Such networks are known to be able to exhibit complex behaviours such as rapid phase transitions, oscillations, chaos, disturbance rejection, and adaptation. Understanding the potential for complex behaviours associated with particular military operations is essential to establish appropriate simulation and data collection processes that inform decisions about force design and asset acquisition. To explore these concepts in an unclassified manner, this project developed a bushfire emergency response simulator as a surrogate for similar Defence problems. This paper describes our multi-agent simulation design which is intended to capture key dynamic characteristics of emergency response operations including individual fire response asset behaviours and team hierarchies in perception and decision making. This new bushfire emergency response simulator includes assets to be protected, command and control assets, fixed and mobile sensing assets, and assets within the response team with perception, decision, action and communication capabilities and with different capabilities to move and fight the fire. A new cellular automata type bushfire model with dynamical cell interactions considering fuel and wind is introduced, that enables simulation of a greater range of fire behaviours with higher fidelity, than simple cellular automata models.This is the second in a series of papers describing bushfire emergency response simulation as a surrogate for Defence problems to explore the quantification of uncertainty in modelling, simulation and analysis of complex systems. This paper describes in further detail the bushfire emergency response simulator which was applied to uncertainty quantification in Bruggemann et al. (2019).

Constraining the transport of mass in the Earth’s mantle over a broad range of timescales is a key step in order to understand the mantle convection and its dynamic interactions with tectonic plates and core flows. Mapped with high accuracy all over the globe from GRACE and GRACE Follow-On satellite missions, the temporal variations of the gravity field can provide unique information on potential rapid mass redistributions within the Earth’s deep interior, even if their separation with the signals from the Earth’s fluid enveloppe is challenging. In the present study, we focus on the base of the mantle and the boundary with the core (CMB). Applying dedicated methods of space-time patterns recognition in the gravity field, we identify a rapid, anomalous north-south oriented gravity signal at large spatial scales across the Eastern Atlantic ocean in January 2007, which evolves over months to years. We show that this signal likely originates, at least partly, from the solid Earth ; it appears concomittant, both spatially and temporally, with the 2007 geomagnetic jerk. We hypothesize that it may be induced by vertical displacements of the perovskite to post-perovskite phase transition, caused by moving thermal anomalies near the base of the African Large Low Shear Velocity Province. This may result in the creation of a decimetric dynamic CMB topography over a timespan of a few years. To assess a potential link with the 2007 geomagnetic jerk, we finally investigate the impact of these changes in core-mantle boundary topography on the flow and the geomagnetic field in a thin layer at the top of the core. These results stress the interest of satellite gravimetry for providing novel insights into the dynamical interactions between the mantle and the core.

Numerical study on the dynamic process of reciprocating liquid hydrogen pumps for hydrogen refueling stations

CONVECTIVE SYSTEMS: THE USE OF AIR IN THERMOSYPHONIC FLOW IN SOLAR THERMAL SYSTEMS - A NEW WAY TOWARDS COST-EFFICIENT APPLIANCES -

Phase transition and decomposition temperatures, heat capacities and viscosities of pyridinium ionic liquids

There is growing interest in heat pumps based on materials that show thermal changes when phase transitions are driven by changes of electric, magnetic or stress field. Importantly, regeneration permits sinks and loads to be thermally separated by many times the changes of temperature that can arise in the materials themselves. However, performance and parameterization are compromised by net heat transfer between caloric working bodies and heat transfer fluids. Here we show that this net transfer can be avoided-resulting in true, balanced regeneration-if one varies the applied electric field while an electrocaloric (EC) working body dumps heat on traversing a passive fluid regenerator. Our EC working body is represented by bulk PbSc0.5Ta0.5O3 (PST) near its first-order ferroelectric phase transition, where we record directly measured adiabatic temperature changes of up to 2.2 K. Indirectly measured adiabatic temperature changes of similar magnitude were identified, unlike normal, from adiabatic measurements of polarization, at nearby starting temperatures, without assuming a constant heat capacity. The resulting high-resolution field-temperature-entropy maps of our material, and a small clamped companion sample, were used to construct cooling cycles that assume the use of an ideal passive regenerator in order to span $\leq$20 K. These cooling cycles possess well defined coefficients of performance that are bounded by well defined Carnot limits, resulting in large ($>$50%) well defined efficiencies that are not unduly compromised by a small field hysteresis. Our approach permits the limiting performance of any caloric material in a passive regenerator to be established, optimized and compared; provides a recipe for true regeneration in prototype cooling devices; and could be extended to balance active regeneration.