Dynamic Heat Transport Research Articles

Dynamic photon heat transport through a Majorana fermion modulated circular mesoscopic Josephson device adjusted by ac magnetic flux

The photonic heat current and conductance of circular mesoscopic Josephson junction device coupled with Majorana fermions under the application of ac magnetic flux have been investigated. This system is equivalent to the situation that the Josephson junction is biased by the dc voltage V and an ac voltage with frequency Ω0. The dc voltage induce the Josephson current with oscillation frequency ω=2eVħ. The time-dependent Landauer-like formula and linear dc photonic heat conductance formula are derived. The application of Majorana fermions suppresses the amplitude, and splits the resonant peaks of heat current. The heat conductance is suppressed with increasing the coupling constants of Majorana fermions. With the coupling of Majorana fermions, the magnitude of heat conductance is enhanced with the increase of ω/Ω0, and it is suppressed due to increasing the magnitude of applied ac flux. The photon-pumping heat current has been evaluated at thermal equilibrium state, to show the suppression and splitting effects resulting from Majorana fermions.

Water vapor transmission parameters of the Kežmarok sandstone

Dynamic complex heat and water transport in building constructions can be calculated using modern simulation software such as Wufi, Delphin, Math, Comsol Multiphysics and other. This software is suitable for the evaluation of the thermal and hygric processes in constructions of historical buildings. Because it includes many important factors such as dynamic boundary conditions, solar radiation, driven rain, ground water, diffusion and others. The heat and water transport parameters of historical materials are needed for simulation of coupled heat and water transport in building materials. The Kežmarok sandstone was chosen for analysis. One of the important material parameters for evaluation of complex heat and water transport in building constructions are water vapor transmission parameters. Vapor transport can be described as water vapor diffusion resistance factor, water vapor diffusion coefficient and diffusion equivalent air layer thickness. The dry cup and wet cup method were used to determine the water vapor transmission parameters of Kežmarok sandstone.

Dynamic stabilization and heat transport characteristics of monolayer SnSe at finite temperature: A study by phonon quasiparticle approach

The structural stability of monolayer SnSe at finite temperature is investigated by the phonon quasiparticle approach that combines first-principles molecular dynamics and lattice dynamics. At 300 K, we witness the dynamic stability of monolayer Pmmn SnSe that is originated from the Cmcm bulk phase. The pair correlation and atomic displacement distribution functions of Sn and Se atoms confirm the lattice stability at high temperature. The hardening of Raman activated ${\mathrm{A}}_{g}^{2}$ and ${\mathrm{B}}_{2g}$ modes at the $\mathrm{\ensuremath{\Gamma}}(0,0,0)$ point and normal modes at the boundary $M(0,\frac{1}{2},\frac{1}{2})$ point of the Brillouin zone is observed with giant frequency shifts, revealing the heavy anharmonicity in monolayer SnSe. The calculated anharmonic phonon dispersions and density of states show significant temperature dependence and some medium-frequency phonon modes adopt giant frequency shifts. Due to the lattice anharmonicity, the predicted lattice thermal conductivity within the framework of a phonon gas model is very low for monolayer SnSe, close to the value of the bulk phase along the out-of-plane direction. As temperature increases, the characteristic of covalent bonds between Sn and Se atoms in plane and the normal direction of monolayer SnSe becomes isotropic. This results in a high degeneracy of the electronic band structure, beneficial to the electronic transport properties. A thermoelectric $ZT$ of $\ensuremath{\sim}0.52$ for $n$ doping is predicted at 300 K, hinting that the monolayer SnSe is a fairly good thermoelectric material suitable for application at room temperature.

Moisture Dry-Out Capability of Steel-Faced Mineral Wool Insulated Sandwich Panels

Moisture dry-out from steel-faced insulated sandwich panels has previously received little attention from researchers. This paper reports the results from laboratory tests and dynamic heat, air, and moisture transport simulations of the moisture dry-out capabilities of a steel-faced sandwich panel with a mineral wool core. Three test walls (TWs) with dimensions of 1.2 m × 0.4 m × 0.23 m were put above water containers to examine the moisture transport through the TWs. A calibrated simulation model was used to investigate the hygrothermal regime of a sandwich panel wall enclosure with different initial moisture contents and panel joint tightening tapes. The moisture dry-out capacity of the studied sandwich panels is limited (up to 2 g/day through a 30-mm-wide and 3-m-long vertical joint without tapes). When the vertical joint was covered with a vapour-permeable tape, the moisture dry-out was reduced to 1 g/day and when the joint was covered with a vapour-retarding tape, the dry-out was negligible. A very small amount of rain would be enough to raise the moisture content to water vapour saturation levels inside the sandwich wall, had the rain ingressed the enclosure. The calculated time of wetness (TOW) on the internal surface of the outer steel sheet stayed indefinitely at about 5500 h/year when vapour-retarding tapes were used and the initial relative humidity (RH) was over 80%. TOW stabilised to about 2000 h/year when a vapour-permeable tape was used regardless of the initial humidity inside the panel. A vapour-permeable tape allowed moisture dry-out but also vapour diffusion from the outside environment. To minimise the risk of moisture damage, avoiding moisture ingress during construction time or due to accidents is necessary. Additionally, a knowledge-based method is recommended to manage moisture safety during the construction process.

System efficiency of pvt collector-driven heat pumps

Abstract The use of standard heat pump (HP) systems offers an efficient option to replace conventional heating systems (e.g. oil and gas boilers) for space heating and domestic hot water. Due to the higher noise emissions and the lower overall energy efficiency of air-to-water heat pumps, the use of ground-coupled heat pump systems is increasingly in demand. The cost-efficient dimensioning of horizontal ground heat exchanger (HGHE) systems, considering possible solar waste heat potentials to improve regeneration behaviour, is particularly challenging. The reason for this is the complex system and control engineering optimisation possibilities resulting from the dynamic heat transport behaviour of the horizontal ground heat exchanger. Essential influencing variables such as the water content of the soil due to the groundwater level, rainwater infiltration and surface evaporation can only be described with massive effort using the model equations of the unsaturated zones. However, these variables are necessary to obtain a better fundamental understanding of the usable storage potential of solar-coupled systems and to be able to derive targeted optimisations at the system level. Therefore, the waste heat utilisation potential of PVT collectors for the regeneration of heat pump coupled horizontal ground heat exchanger systems are analysed employing simulations. For this purpose, a PVT-collector model and a HGHE model based on a single-family were developed and validated by experimental investigations. Based on this, a system simulation model consisting of the components PVT-collector, heat pump, heat delivery system, HGHE and the corresponding control units were built using TRNSYS. With the help of the simulation model, parameter studies were carried out, and the main factors influencing the overall energy efficiency (COP) of the system and the seasonal performance factors (SPF) were identified. Furthermore, the solar waste heat utilisation potential of the PVT collectors was analysed to increase the efficiency of the heat pump system.

Dynamic photon heat transport through a mesoscopic Josephson device biased by dc and ac voltages

Photon heat transport through a mesoscopic Josephson junction (MJJ) device under the perturbation of dc and ac voltages has been investigated, where the MJJ device is coupled to photon reservoirs, and the Caldeira–Leggett circuit theory has been used. The photon heat current and differential heat conductance have been evaluated to show the dynamic behaviors governed by the applied fields. The dc voltage V induces time t oscillating supercurrent with frequency ω=2eV∕ħ. The ac voltage Ṽcos(Ω0t) generates a series of supercurrent branches relating to the ac voltage frequency Ω0 and its magnitude Ṽ. The photon heat current is determined by the superposition of different heat current branches induced by the dc and ac fields. The frequencies ω and Ω0 relating to dc and ac fields play important role in controlling the photon heat current and conductance. The detailed magnitude and oscillation structure are strongly dependent on the frequency ratio ω∕Ω0, and the scaled magnitude of ac field Λ=2eṼħΩ0. Resonant heat current appears when ω and Ω0 possess commensurate relations, where the superposition of heat current branches displays coherent interference. As ω and Ω0 possess incommensurate relations, heat current is much smaller, and it fluctuates fiercely compared with the commensurate cases. Beat-like resonance emerges by tuning the frequencies ω and Ω0 at some definite values of Coulomb energy.

A conceptual model of oceanic heat transport in the Snowball Earth scenario

Abstract. Geologic evidence suggests that the Earth may have been completely covered in ice in the distant past, a state known as Snowball Earth. This is still the subject of controversy, and has been the focus of modeling work from low-dimensional models up to state-of-the-art general circulation models. In our present global climate, the ocean plays a large role in redistributing heat from the equatorial regions to high latitudes, and as an important part of the global heat budget, its role in the initiation a Snowball Earth, and the subsequent climate, is of great interest. To better understand the role of oceanic heat transport in the initiation of Snowball Earth, and the resulting global ice covered climate state, the goal of this inquiry is twofold: we wish to propose the least complex model that can capture the Snowball Earth scenario as well as the present-day climate with partial ice cover, and we want to determine the relative importance of oceanic heat transport. To do this, we develop a simple model, incorporating thermohaline dynamics from traditional box ocean models, a radiative balance from energy balance models, and the more contemporary "sea glacier" model to account for viscous flow effects of extremely thick sea ice. The resulting model, consisting of dynamic ocean and ice components, is able to reproduce both Snowball Earth and present-day conditions through reasonable changes in forcing parameters. We find that including or neglecting oceanic heat transport may lead to vastly different global climate states, and also that the parameterization of under-ice heat transfer in the ice–ocean coupling plays a key role in the resulting global climate state, demonstrating the regulatory effect of dynamic ocean heat transport.

Dynamic Heat and Moisture Transport Modeling of Industrial Floors on Different Climates

In this paper a conjugated heat and moisture transport investigation of industrial floors is presented. We have analyzed 2D general segments of wall and foundation connections in three different climatic conditions: Budapest (Hungary), Lisbon (Portugal) and Espoo (Finland). We also modeled the component with horizontal or vertical edge insulations with various thicknesses and lengths, and two different soil compositions under the floors. The design of the floor and wall components was performed according to the current standards. We examined 126 combination of the segment and the results shows difference both in relative humidity across the components and heat losses through the internal faces. In conclusion, the simulations and results can improve the energy efficient design of industrial buildings across Europe.

Global Climate Impacts of Fixing the Southern Ocean Shortwave Radiation Bias in the Community Earth System Model (CESM)

Abstract A large, long-standing, and pervasive climate model bias is excessive absorbed shortwave radiation (ASR) over the midlatitude oceans, especially the Southern Ocean. This study investigates both the underlying mechanisms for and climate impacts of this bias within the Community Earth System Model, version 1, with the Community Atmosphere Model, version 5 [CESM1(CAM5)]. Excessive Southern Ocean ASR in CESM1(CAM5) results in part because low-level clouds contain insufficient amounts of supercooled liquid. In a present-day atmosphere-only run, an observationally motivated modification to the shallow convection detrainment increases supercooled cloud liquid, brightens low-level clouds, and substantially reduces the Southern Ocean ASR bias. Tuning to maintain global energy balance enables reduction of a compensating tropical ASR bias. In the resulting preindustrial fully coupled run with a brighter Southern Ocean and dimmer tropics, the Southern Ocean cools and the tropics warm. As a result of the enhanced meridional temperature gradient, poleward heat transport increases in both hemispheres (especially the Southern Hemisphere), and the Southern Hemisphere atmospheric jet strengthens. Because northward cross-equatorial heat transport reductions occur primarily in the ocean (80%), not the atmosphere (20%), a proposed atmospheric teleconnection linking Southern Ocean ASR bias reduction and cooling with northward shifts in tropical precipitation has little impact. In summary, observationally motivated supercooled liquid water increases in shallow convective clouds enable large reductions in long-standing climate model shortwave radiation biases. Of relevance to both model bias reduction and climate dynamics, quantifying the influence of Southern Ocean cooling on tropical precipitation requires a model with dynamic ocean heat transport.

Dynamic Heat Transfer through the External Wall of a Timber Structure

The article compares results of temperature and heat flux measurements in the external wall of a real timber structure with results obtained by numerical modeling using the finite element method in the ANSYS software. The measured temperature values are compared with results obtained from numerical simulation of dynamic heat transport using non-stationary boundary conditions. In the article there is evaluated a suitability of theoretical numerical calculations for a thermal field and heat flux prediction in a building structure.

Nondestructive detection of cracks near the surface of wooden boards by dynamic heat dissipation

A method to detect cracks near the surface of wooden boards has been developed where the change in surface temperature of the wood sample is monitored using an infrared camera following momentary heating by a flash. Cylindrical holes simulating cracks were drilled into the wood samples, and blackbody paint was painted onto the surface of the samples to assist flash absorption. This method uses the dynamic heat transport process from the blackbody paint to the surface of the wood sample to the cracks over a short timescale. The theoretical foundations of the observation method were outlined, and the technique was verified in experiments with samples of Cercidiphyllum japonicum, Western red cedar, Japanese cedar, Balsa, and medium-density fiberboard. The developed technique is able to detect the presence of holes located near the surface of some samples. However, this method could not detect the presence of holes in Balsa nor holes located deeper than 1 mm from the surface of the sample. A theoretical analysis of these phenomena was provided to help interpreting them.

Experimental and Numerical Analysis of Thermal and Hygrometric Characteristics of Building Structures Employing Recycled Plastic Aggregates and Geopolymer Concrete

The correct estimation of building energy consumptions is assuming an always increasing importance, and a detailed reproduction of building structures, with all the single components involved, is necessary to achieve this aim. In addition, the current ecological development tries to limit the use of natural raw materials as building components, in favor of alternative (waste) materials, which ensure significant advantages from the economic, energetic and environmental point of views. In this work, dynamic heat and vapor transport in a typical three-dimensional (3D) building structure, involving different types of environmental-friendly concrete mixtures, have been simulated by using finite elements. In particular, the authors propose to substitute part of the aggregates with plastic waste and to use a fly ash based geopolymeric binder for the production of low conductivity concrete, to be employed in eco-efficient buildings. Concrete produced with natural limestone aggregates has been considered as the reference benchmark. The whole characterization of the different types of concrete tested in the present work has been obtained through laboratory experiments. The structure taken into account in the simulations is a 3D thermal bridge, typical of building envelopes. The thermal and hygrometric transient behavior of this structure, employing plastic waste in different percentages and geopolymer concrete, has been analyzed by the authors.

Dynamic thermoelectric and heat transport in mesoscopic capacitors

We discuss the low-frequency response of charge and heat transport to oscillatory voltage and temperature shifts in mesoscopic capacitors. We obtain within scattering theory generic expressions for the quantum admittances up to second order in the ac frequencies in terms of electric, thermoelectric and heat capacitances and relaxation resistances. Remarkably, we find that the thermocurrent can lead or lag the applied temperature depending on the gate voltage applied to a quantum $RC$ circuit. Furthermore, the relaxation resistance for cross terms becomes nonuniversal as opposed to the purely electric or thermal cases.

Nondestructive analysis of uneven paint coatings by dynamic heat conduction following flash heating

A method of assessing uneven paint coatings is described, wherein a painted surface is rapidly heated by a light flash and the subsequent surface temperature changes are monitored using thermography. This method exploits the differences in dynamic heat transport caused by variations in paint thickness, using thermographic observation to track differences in temperature related to thickness. During trials with intentionally uneven test specimens spray coated with blackbody paint or red, blue, and green acrylic lacquers, we determined that surfaces with thinner paint coatings exhibited lower temperatures. Based on our findings, this article also discusses the theoretical basis of the detection method. While this technique can detect uneven painting, it is difficult to determine a quantitative relationship between temperature variations in the coated surfaces and paint thickness, since the relationship is dependent not only on the particular substrate and paint, but also on the optical reflectance of the paint. We consider that the proposed method is currently capable of detecting uneven paint coatings with variations in thickness of approximately 20 μm, although improvements in detection resolution are possible. Although detection sensitivity is somewhat low, this technique allows rapid analysis of coatings to assess evenness through visual examination.

Phonon-magnon interaction in low dimensional quantum magnets observed by dynamic heat transport measurements.

Thirty-five years ago, Sanders and Walton [Phys. Rev. B 15, 1489 (1977)] proposed a method to measure the phonon-magnon interaction in antiferromagnets through thermal transport which so far has not been verified experimentally. We show that a dynamical variant of this approach allows direct extraction of the phonon-magnon equilibration time, yielding 400 μs for the cuprate spin-ladder system Ca(9)La(5)Cu(24)O(41). The present work provides a general method to directly address the spin-phonon interaction by means of dynamical transport experiments.

An Investigation of the Initial Development of the Double-ITCZ Warm SST Biases in the CCSM

Abstract This paper investigates the initial development of the double ITCZ in the Community Climate System Model version 3 (CCSM3) in the central Pacific. Starting from a resting initial condition of the ocean in January, the model developed a warm bias of sea surface temperature (SST) in the central Pacific from 5°S to 10°S in the first three months. This initial bias is caused by excessive surface shortwave radiation that is also present in the stand-alone atmospheric model. The initial bias is further amplified by biases in both surface latent heat flux and horizontal heat transport in the upper ocean. These biases are caused by the responses of surface winds to SST bias and the thermocline structure to surface wind curls. This study also showed that the warming biases in surface solar radiation and latent heat fluxes are seasonally offset by cooling biases from reduced solar radiation after the austral summer due to cloud responses and in the austral fall due to enhanced evaporation when the maximum SST is closest to the equator. The warming biases from the dynamic heat transport by ocean currents however stay throughout all seasons once they are developed, which are eventually balanced by enhanced energy exchange and penetration of solar radiation below the mixed layer. It was also shown that the equatorial cold tongue develops after the warm biases in the south-central Pacific, and the overestimation of surface shortwave radiation recurs in the austral summer in each year. The results provide a case study on the physical processes leading to the development of the double ITCZ. Applicability of the results in other models is discussed.

Convection Parameterization, Tropical Pacific Double ITCZ, and Upper-Ocean Biases in the NCAR CCSM3. Part II: Coupled Feedback and the Role of Ocean Heat Transport

Abstract This study investigates the coupled atmosphere–ocean feedback and the role of ocean dynamic heat transport in the formation of double ITCZ over the tropical Pacific in the NCAR Community Climate System Model, version 3 (CCSM3) and its alleviation when a revised Zhang–McFarlane (ZM) convection scheme is used. A hierarchy of coupling strategy is employed for this purpose. A slab ocean model is coupled with the atmospheric component of the Community Atmosphere Model, version 3 (CAM3) to investigate the local feedback between the atmosphere and the ocean. It is shown that the net surface energy flux differences in the southern ITCZ region between the revised and original ZM scheme seen in the stand-alone CAM3 simulations can cool the SST by up to 1.5°C. However, the simulated SST distribution is very sensitive to the prescribed ocean heat transport required in the slab ocean model. To understand the role of ocean heat transport, the fully coupled CCSM3 model is used. The analysis of CCSM3 simulations shows that the altered ocean dynamic heat transport when the revised ZM scheme is used is largely responsible for the reduction of SST bias in the southern ITCZ region, although surface energy flux also helps to cool the SST in the first few months of the year in seasonal variation. The results, together with those from Part I, suggest that the unrealistic simulation of convection over the southern ITCZ region in the standard CCSM3 leads to the double-ITCZ bias through complex coupled interactions between atmospheric convection, surface winds, latent heat flux, cloud radiative forcing, SST, and upper-ocean circulations. The mitigation of the double-ITCZ bias using the revised ZM scheme is achieved by altering this chain of interactions.

Fourth-order algorithm for solving 2D transient heat and moisture transfer simulation through fabric

We discuss a better higher-order finite difference algorithm for solving dynamic heat and moisture transport equations of fabric. The algorithm is fourth-order accurate in spatial dimensions and second-order in time derivatives. We use central-difference operator for the second space derivatives in the 2D model. It is similar to that used in the standard second-order algorithms, such as the Crank–Nicolson algorithm. Numerical simulation results agree with the real case.

Modeling and solving building physics problems with FemLab

The commercially available software package FemLab is evaluated as solver for building physics problems based on partial differential equations (PDEs). The software is designed to simulate systems of coupled PDEs which may be 1D, 2D or 3D, non-linear and time dependent. An important feature of FemLab is that the user can focus on the model (PDE coefficients on the domain and boundary) and does not have to spend much time on solving and visualization. In this paper, 4 cases are considered. First, in order to illustrate how FemLab works, an example including the complete code for solving as well as the results are given for a simple 2D steady-state heat transfer problem. In the next 2 cases, the reliability is tested for two very different building physics problems: A 2D dynamic airflow problem, modeled using Navier–Stokes and buoyancy equations, and a 1D dynamic non-linear moisture transport in a porous material. These simulation results are validated and show a good agreement with measurements. In the last case, FemLab's capability of simulating 3D problems is shown by a dynamic combined heat and moisture transport problem. This example is a 3D extension of a given 2D problem from IEA Annex 24 (Final Report—Task 1). For all models the crucial part of the codes (geometry, PDEs and boundary specifications) are given. The FemLab software is written in the MatLab environment (The Mathworks, Inc. MatLab manual, Version 5.3, 1998) and therefore it is possible to use the visualization tools, toolboxes and all other programs written in MatLab. The evaluation illustrates the powerful and flexible nature of FemLab for solving scientific and engineering building physics problems.

Computer prediction of human thermoregulatory and temperature responses to a wide range of environmental conditions.

A mathematical model for predicting human thermal and regulatory responses in cold, cool, neutral, warm, and hot environments has been developed and validated. The multi-segmental passive system, which models the dynamic heat transport within the body and the heat exchange between body parts and the environment, is discussed elsewhere. This paper is concerned with the development of the active system, which simulates the regulatory responses of shivering, sweating, and peripheral vasomotion of unacclimatised subjects. Following a comprehensive literature review, 26 independent experiments were selected that were designed to provoke each of these responses in different circumstances. Regression analysis revealed that skin and head core temperature affect regulatory responses in a nonlinear fashion. A further signal, i.e. the rate of change of the mean skin temperature weighted by the skin temperature error signal, was identified as governing the dynamics of thermoregulatory processes in the cold. Verification and validation work was carried out using experimental data obtained from 90 exposures covering a range of steady and transient ambient temperatures between 5 degrees C and 50 degrees C and exercise intensities between 46 W/m2 and 600 W/m2. Good general agreement with measured data was obtained for regulatory responses, internal temperatures, and the mean and local skin temperatures of unacclimatised humans for the whole spectrum of climatic conditions and for different activity levels.