Latent Heat Effects Research Articles

Accounting for moist processes in a sub‐grid orographic drag scheme

AbstractA method for estimating the effective moist stability within a sub‐grid orographic drag scheme is described. It accounts for latent heat effects during low‐level saturated sub‐grid orographic ascent, with the lifting condensation level determining how much of the assumed sub‐grid ascents are saturated. The scheme has been verified for two cases with moist south to southwesterly low‐level flow impinging on mountain ranges of the USA and India, within both low‐resolution global simulations and high‐resolution limited‐area model simulations with degraded orography. It produces significant improvements to the model wind fields in both regions. In particular, the amount of low‐level orographic blocking predicted by the orographic drag scheme is reduced, particularly at low resolution, as are the associated large negative near‐surface wind biases over the mountains. Precipitation is shifted slightly downstream. A suite of 24 five‐day global NWP forecasts at N320 resolution was used to demonstrate that these results are robust, and that similar effects are seen over a number of mountain ranges. Over India, the convection scheme is very active in the global simulations, and has a larger effect on the winds at all levels than the orographic drag scheme. However the two schemes interact. Reducing the sub‐grid low‐level orographic blocking drag resulted in a reduction in the convergence occurring as the westerly flow decelerates towards the mountains. This decreased the amount of convection occurring over the sea upstream and along the coast, reducing the associated negative low‐level wind bias there, as well as reducing the negative wind biases over land.

Martensitic microstructure evolution in austenitic steel: A thermomechanical polycrystalline phase field study

We have performed coupled thermomechanical phase field simulations of martensitic transformation in single-crystalline and polycrystalline 301-stainless steel by coupling Ginzburg–Landau equation to the mechanical equilibrium and non-stationary heat conduction equations. Simulations accounted for elastic anisotropy, under different thermal and mechanical BCs, i.e., clamped, embedded, and near-open, as well as adiabatic and isothermal with and without latent heat effects. To the best of authors’ knowledge, no such simulations are reported in literature on polycrystalline materials which provides the effects of various thermomechanical BCs incorporating latent heat. We have utilized a multivariant single embryo as an initial condition in both systems to mitigate the lack of nucleation criteria at the mesoscale; without any initial constraint, the model can select the martensitic transformation path and final microstructure. Simulations showed excellent capabilities in predicting influence of such thermomechanical BCs on martensitic microstructural formation including autocatalytic transformation process in polycrystalline steel and its evolution. Martensitic microstructure in a single-crystalline, and b polycrystalline steel, in deformed configuration (deformation scale factor is $$1\times$$ ) for near-open, embedded, and clamped boundary conditions (from left to right). Dataset edges in blue show initial undeformed configuration

Calorimetric study of the giant magnetocaloric effect in (MnNiSi)0.56(FeNiGe)0.44

${(\mathrm{MnNiSi})}_{0.56}{(\mathrm{FeNiGe})}_{0.44}$ belongs to a new family of alloys, similar to MnAs, showing a magnetostructural first-order transition near room temperature with large latent heat and magnetocaloric effect (MCE). From isothermal magnetization, remarkable values of the entropy change have been reported, such as $|\mathrm{\ensuremath{\Delta}}{S}_{T}|=11.5$ J/kg K at 290 K for the small field change of 1 T, or $|\mathrm{\ensuremath{\Delta}}{S}_{T}|=70.1$ J/kg K for 5 T on a slightly different composition. Strangely, this last value almost doubles that obtained from the Clausius-Clapeyron equation. Therefore, a very detailed set of calorimetric determinations have been made including heat capacity by adiabatic and differential scanning calorimetry (DSC), and direct measurement of the heat absorbed on isothermal demagnetization for several magnetothermal histories of the sample. We found high values of $|\mathrm{\ensuremath{\Delta}}{S}_{T}|=45.7$ J/kg K at 289.4 K for a field change of 7 T, for a sample previously cooled to a low temperature and then heated under magnetic field to the target temperature. This value is high but very far from previously reported data, which happened to be nonphysical but obtained from a very frequently used, but incorrect, experimental protocol to determine $\mathrm{\ensuremath{\Delta}}{S}_{T}$ from magnetization, via the Maxwell relation. The spurious contribution has been analyzed and computed, explaining the nonphysical reported values. The strong thermal and magnetic hysteresis of 8.4 K and 8.3 T, respectively, make this alloy useless for magnetic refrigeration, but the results encourage searching for other derivatives with lower hysteresis which could have even higher $|\mathrm{\ensuremath{\Delta}}{S}_{T}|$.

Investigating solution effects injury of human T lymphocytes and its prevention during interrupted slow cooling

Cooling rate is a critical parameter affecting the success of cell cryopreservation. Fast cooling can result in intracellular ice formation (IIF), while slow cooling can bring solution effects injury, both are detrimental to the cells. Whilst most of the studies have investigated how IIF affects cells, solution effects injury has received little attention. Here, we studied the solution effects injury of human T lymphocytes by cryomicroscopy and tested the osmoprotective ability of some frequently used cryoprotective agents (CPAs) such as dimethyl sulfoxide (DMSO), glycerol, trehalose, urea and l-proline. We further investigated the relationship between cell volume, latent heat and solution effects cell injury. We found that solution effects injury during interrupted slow cooling was caused by high concentration of the extracellular solution rather than eutectic formation and solutes precipitation. DMSO, glycerol and trehalose can protect cells from solution effects injury, while l-proline and urea cannot under the same condition. The cell volume and latent heat are not crucial for causing solution effects injury in cells. This work confirms that high osmotic pressure, rather than eutectic formation, leads to cell injury. It also suggests that cell volume and latent heat may not be a key factor for explaining solution effects injury and its prevention in the cryopreservation of human T lymphocytes.

Hysteresis, latent heat and cycling effects on the magnetocaloric response of (NiMnSi)0.66(Fe2Ge)0.34 alloy

In this work, we further analyze the promising magnetocaloric (NiMnSi)0.66(Fe2Ge)0.34 alloy, which presents isothermal entropy change values as large as 29 J kg−1 K−1 for 2 T at room temperature. It undergoes a magnetostructural transition accompanied by large thermal/magnetic hysteresis, which remains up to high magnetic fields (corroborated by the elaboration of an experimental magnetic phase diagram). We illustrate that this huge hysteretic behavior (i.e. different responses when magnetizing or demagnetizing) can lead to erroneous interpretation of the order of the phase transition by applying the conventional Banerjee's criterion or the recently developed field dependence analysis of the magnetocaloric effect. Additionally, the cyclability of the response is characterized, showing that after several measurements the magnetocaloric response is significantly reduced (by ≈ 40%) due to sample breaking. These dependences together with the large latent heat of the transition (15.0 kJ kg−1) lead to relatively small values of the adiabatic temperature change for powdered samples at moderate field changes, reaching around 0.6 K for 1.75 T by direct measurement methods.

Dynamics of the spatiotemporal morphology of Mei-yu fronts: an initial survey

Mei-yu fronts are often accompanied with prominent diabatic heating due to the development of frontal clouds and rain bands. The direct effect and relative importance of diabatic heating on the spatiotemporal morphology of Mei-yu fronts however remain unclear. Here a new frontogenesis function is derived to isolate the effect of diabatic heating and this function is then applied to the latest high resolution reanalysis product ERA5 to conduct an initial survey of dynamic and thermodynamic processes driving the intensity and structure evolutions of three typical Mei-yu fronts. It is found that the direct effect of latent heating (moisture depletion) is always frontogenetical (frontolytical) in the pre-frontal and frontal zone throughout the lifecycle of the front with latent heating (moisture depletion) in general dominates the front intensification (dissipation). Tilting is another critical process that turns the vertical gradient of equivalent potential temperature into horizontal gradient leading to frontogenesis during the front development stage, and, after the release of convective instability ahead of the front, flattens the front surface leading to frontolysis during the front decaying stage. Therefore titling maintains consistently positive contributions to the evolution of a Mei-yu front and its importance depends highly on the convective intensity near the front. The deformation effect appears frontogenetical but carries a much smaller weight compared to diabatic heating, moisture depletion and tilting. The structure evolutions of the three Mei-yu fronts studied here exhibit two distinct patterns: “bending and breaking”, and “moving and rotating”. Both patterns are dominated by the front propagation (i.e., frontogenesis through air parcels), further highlighting the critical roles played by diabatic heating, moisture depletion and titling in determining the spatiotemporal characteristics of Mei-yu fronts. As these three processes are all closely tied to updrafts, clouds and precipitation near the fronts, improved representations of clouds and convection are needed to accurately depict their feedbacks to frontal evolutions and ultimately achieve better predictions of heavy rainfall and floods associated with Mei-yu fronts.

Sensitivity analysis of thermophysical properties on PCM selection under steady and fluctuating heat sources: A comparative study

Previous studies on phase change material (PCM) selection for latent thermal energy storage (LTES) mainly focused on steady heat source conditions without considering the effects of thermal fluctuation of real heat sources, and how fluctuating heat sources will affect the charging performance of LTES and material selection is still unclear. This study aims to compare the difference in material selection for a shell-and-tube LTES under steady and fluctuating heat sources, which comprehensively considers the effects of PCM thermophysical properties including the melting temperature, density, specific heat capacity, thermal conductivity and latent heat, as well as their interaction effects. By taking heat storage capacity and charging rate as objectives, orthogonal experiment design and stepwise regression analysis have been conducted to specify the significant factors among these parameters under steady and fluctuating heat source conditions. To further investigate the difference in the ranking of candidate PCMs under two conditions, fourteen pre-screened PCMs are ranked under steady and fluctuating heat sources. The results show that the order of prominent factors for heat storage capacity is ρ·Cp, followed by ρ·L under both conditions. However, when considering the charging rate, temperature fluctuation will weaken the effect of melting temperature, and strengthen the effect of specific heat capacity and latent heat. The order of prominent factors for charging rate is λ·Cp and Cp·L under fluctuating heat source. According to the ranking results, LiNO3-NaNO2 within the melting temperature of 100–200 °C has an excellent comprehensive charging performance under both conditions.

Traveling wave solutions of a free boundary problem with latent heat effect

We study a free boundary problem of two competing species with latent heat effect. We establish the existence and uniqueness of the traveling wave solution and derive upper and lower bounds for the wave speed. Especially our results show that the latent heat retards propagation of the waves.

A thermo-hydro-mechanical finite-element model with freezing processes in saturated soils

Freezing and thawing of soil are dynamic thermo-hydro-mechanical (THM) interacting coupled processes and have attracted more and more attention due to their potentially severe consequences in geotechnical engineering. In this paper, a fully coupled thermo-hydro-mechanical freezing (THM-F) model is established for advanced system design and scenario analysis. The model is derived within the framework of the theory of porous media and solved numerically using the finite-element method. Particularly, the derivation of theoretical aspects pertaining to the governing equations, including in particular the thermo-mechanical decomposition treatment of the solid phase, is presented in detail. Verification examples are provided from purely freezing, THM and THM-F perspectives. Attention is paid to the heat and mass transfer, thermodynamic relations and the formation of frost heave. The migration of pore fluid from the unfrozen zone to the freezing area and the blockage of pore space by ice lenses within the porous media are studied. The model is able to capture various coupled physical phenomena during freezing – for example, the latent heat effect, groundwater flow alterations and mechanical deformation.

Preparation and Performance of Microencapsulated Phase Change Material with Paraffin Core and SiO2 Shell for High Latent Heat and Low Heat Loss by Sol–Gel Method

Microencapsulated phase change materials (MicroPCM) were prepared via sol–gel method using paraffin as heat storage core and silica as inorganic shell. The morphology feature, chemical structure, thermal properties and thermal stability of MicroPCM were characterized by the field emission scanning electron microscope (FE-SEM), Fourier transform infrared spectroscopy (FTIR), the differential scanning calorimeter (DSC), simultaneous thermal analyzer (STA) and the thermal conductivity meter. The results indicated that MicroPCM were spherical in shape with the shell thickness in the range from 236[Formula: see text]nm to 303[Formula: see text]nm. The stirring speed and TEOS dosage were key factor on the latent heat and supercool effect of MicroPCM. The maximum latent heat of MicroPCM was 240.2[Formula: see text][Formula: see text] with the heat loss of only 0.2[Formula: see text][Formula: see text] in phase transformation when it was prepared at the stirring speed of 400[Formula: see text]r/min and TEOS dosage of 20[Formula: see text]ml. MicroPCM was a promising material for thermal energy storage (TES).

A thermal fluid dynamics framework applied to multi-component substrates experiencing fusion and vaporisation state transitions

The fluid dynamics of multi-component alloy systems subjected to high energy density sources of heat largely determines the local composition, microstructure, and material properties. In this work a multi-component thermal fluid dynamics framework is presented for the prediction of alloy system development due to melting, vaporisation, condensation and solidification phenomena. A volume dilation term is introduced into the continuity equation to account for the density jump between liquid and vapour species, conserving mass through vaporisation and condensation state changes. Mass diffusion, surface tension, the temperature dependence of surface tension, buoyancy terms and latent heat effects are incorporated. The framework is applied to describe binary vapour collapse into a heterogeneous binary liquid, and a high energy density power beam joining application; where a rigorous mathematical description of preferential element evaporation is presented.

An Asymmetric Elasto-Plastic Phase-Field Model for Shape Memory Effect, Pseudoelasticity and Thermomechanical Training in Polycrystalline Shape Memory Alloys

We propose an elasto-plastic phase-field model (PFM) to conduct the first microscopic computational study of shape memory effect (SME), pseudoelasticity, stress assisted two-way memory effect (SATWME), and thermomechanical training of CuAlBe shape memory alloy (SMA). This non-isothermal PFM model considers the effects of temperature dependent properties, latent heat, grain boundaries, and asymmetric transformation and plasticity. PFM simulations demonstrate the capacity of our model to capture the thermomechanical and purely mechanical shape recovery in the SMA. When considering transforming grain boundaries, grain refinement generates a higher transformation stress, a steeper transformation hardening, and smaller hysteresis loops for both SME and pseudoelasticity. The results also point out slightly higher transformation stress when geometrical grain boundaries are used. The simulations of SATWME highlight an augmentation of the residual martensite as the hold stress increases, which is consistent with experimental observations. This is the first PFM that can mimic the thermal training within several SATWME cycles, showing an asymptotic increase of plastic strain and the related retained transformation strain until the fourth cycle, and their stabilization thereafter. The activation of plasticity occurs always after initiation of phase transformation. Although plasticity results in more stress relaxation, it deteriorates the shape recovery for both SME and pseudoelasticity by hindering the reverse transformation. Comparison between tension and compression demonstrates the capacity of this PFM to account for, for the first time, the nonsymmetrical transformation and plastic responses of SMAs.

Effects of microencapsulated phase change materials on the thermal behavior of multilayer thermal protective clothing

Microencapsulated phase change materials (MPCMs) are increasingly seen as an adequate tool for heat management. The addition of a MPCM layer into a typical firefighters’ protective clothing can be used to mitigate burn injuries, increasing the time to second degree burns. A numerical approach is introduced to simulate the heat transfer in multilayer fabrics with MPCM. An overview of temperature field and total heat flux distribution for the multilayer fabric system with and without the MPCM is presented. Additionally, the effects of MPCM mass fraction, latent heat, specific heat and thickness are investigated to assess the thermal protective performance. The results demonstrate that the addition of a MPCM layer into the multilayer fabric assembly can be used to decrease the temperature obtained at the comfort liner boundary. Effect of heat intensity and radiation distance between the fabric system and heating source is also analyzed and discussed. The findings obtained in this study can provide some useful information on the beneficial design of clothing containing MPCMs.

Comparative experimental investigation on the effects of heavy alcohols- safflower biodiesel blends on combustion, performance and emissions in a power generator diesel engine

The experimental works carried out in this article evaluates the potential of using heavy alcohol and safflower biodiesel as the blended fuel mixtures without making any modifications in the tests diesel engine. For this purpose, volumetrically 20% of Propanol, Pentanol, Butanol, and Octanol were blended with safflower biodiesel fuel and they were named as PR20, PE20, BU20, and OC20, respectively. The performance, combustion, and emission data were found out at the same conditions of constant engine speed and various loads and compared with pure biodiesel (B100) and diesel fuel(ULSD). In the experiments, a four-cylinder, water-cooled diesel engine that was loaded by an electrical power generator was used for the tests. The addition of alcohol causes an increase in fuel consumption due to a decrease in lower thermal performance. The use of heavy alcohols in diesel engine in specific quantities by mixing with biodiesel significantly increases engine brake thermal efficiency. Negative effects of low cetane number and high latent heat of vaporization that may decrease ignition delay and decrease cylinder pressure while increase peak heat release was considered to be compensated by the better mixing properties and atomization of alcohol blended biodiesel thus eventually improve the combustion. Alcohol addition to biodiesel fuel can be accepted as a useful application to increase brake thermal efficiency and reduce nitrogen oxide (NOx), carbon monoxide (CO), and hydrocarbon (HC) emissions by reducing the density and viscosity.

Twenty years of European mountain permafrost dynamics—the PACE legacy

This paper reviews and analyses the past 20 years of change and variability of European mountain permafrost in response to climate change based on time series of ground temperatures along a south–north transect of deep boreholes from Sierra Nevada in Spain (37°N) to Svalbard (78°N), established between 1998 and 2000 during the EU-funded PACE (Permafrost and Climate in Europe) project. In Sierra Nevada (at the Veleta Peak), no permafrost is encountered. All other boreholes are drilled in permafrost. Results show that permafrost warmed at all sites down to depths of 50 m or more. The warming at a 20 m depth varied between 1.5 °C on Svalbard and 0.4 °C in the Alps. Warming rates tend to be less pronounced in the warm permafrost boreholes, which is partly due to latent heat effects at more ice-rich sites with ground temperatures close to 0 °C. At most sites, the air temperature at 2 m height showed a smaller increase than the near-ground-surface temperature, leading to an increase of surface offsets (SOs). The active layer thickness (ALT) increased at all sites between c. 10% and 200% with respect to the start of the study period, with the largest changes observed in the European Alps. Multi-temporal electrical resistivity tomography (ERT) carried out at six sites showed a decrease in electrical resistivity, independently supporting our conclusion of ground ice degradation and higher unfrozen water content.

The sensitivity of atmospheric blocking to upstream latent heating – numerical experiments

Abstract. Recent studies have pointed to an important role of latent heating during cloud formation for the dynamics of anticyclonic circulation anomalies such as atmospheric blocking. However, the effect of latent heating on blocking formation and maintenance has not yet been fully elucidated. To explicitly study this cause-and-effect relationship, we perform sensitivity simulations of five selected blocking events with the Integrated Forecast System (IFS) global weather prediction model in which we artificially eliminate latent heating in clouds upstream of the blocking anticyclones. This elimination has substantial effects on the upper-tropospheric circulation in all case studies, but there is also significant case-to-case variability: some blocking systems do not develop at all without upstream latent heating, while for others the amplitude, size, and lifetime of the blocking anticyclones are merely reduced. This strong influence of latent heating on the midlatitude flow is due to the injection of air masses with low potential vorticity (PV) into the upper troposphere in strongly ascending “warm conveyor belt” airstreams and the interaction of the associated divergent outflow with the upper-level PV structure. The important influence of diabatic heating demonstrated with these experiments suggests that the accurate representation of moist processes in ascending airstreams in weather prediction and climate models is crucial for blocking dynamics.

Different effects of latent heat in planetary boundary layer and cloud microphysical processes on Typhoon Sarika (2016)

Three simulation experiments were conducted on Typhoon (TC) “Sarika” (2016) using the WRF model, different effects of the latent heat in planetary boundary layer and cloud microphysical process on the TC were investigated. The control experiment well simulated the changes in TC track and intensity. The latent heat in planetary boundary layer or cloud microphysics process can affect the TC track and moving speed. Latent heat affects the TC strength by affecting the TC structure. Compared with the CTL experiment, both the NBL experiment and the NMP experiment show weakening in dynamics and thermodynamics characteristics of TC. Without the effect of latent heat, the TC cannot develop upwards and thus weakens in its intensity and reduces in precipitation; this weakening effect appears to be more obvious in the case of closing the latent heat in planetary boundary layer. The latent heat in planetary boundary layer mainly influences the generation and development of TC during the beginning stage, whereas the latent heat in cloud microphysical process is conducive to the strengthen and maintenance of TC in the mature stage. The latent heat energy of the cloud microphysical process in the TC core region is an order of magnitude larger than the surface enthalpy. But the latent heat release of cloud microphysical processes is not the most critical factor for TC enhancement, while the energy transfer of boundary layer processes is more important.

Parametric influence study of cryogenic hydrogen dispersion on theoretical aspect

In this paper, we proposed a theoretical model to study the dispersion of hydrogen. The model given a correlation between the concentration and temperature for cryogenic gases. The model based on adiabatic mixing hypothesis and neglected exterior heat sources, and thought the gas mixture was always at quasi-steady state. Real-gas law was adopted, and thermal physical properties of the gases are obtained from NIST REFPROP database. The concentration curve approximately appears a decreasing straight line, and turns on dew point and ice point, since heat released from water vapor phase change. Compared with liquid hydrogen and liquid natural gas spill experimental data, the model obtained well agreement solutions.Effects of three typical weather conditions (atmospheric temperature, relative humidity and barometric pressure) on hydrogen dispersion were quantitatively studied. It is confirmed that the dispersion is excited in summer, and is depressed in winter and transition seasons with increased ambient temperature. With increased ambient temperature, the effect of increased enthalpy reduction of the dry air components and the effect of the water latent heat are respectively dominate in the 268.15–293.15 K and 293.15–308.15 K ranges. Compared to ambient temperature and barometric pressure, relative humidity has the strongest positive effect on hydrogen dispersion, and the slight dampening effect of barometric pressure could be neglected.

Performance Evaluation of the Louver-type Double-skin Facade System using PCM Film for Cooling Energy Reduction

Purpose: There are problems with the construction method for liquid-type phase change materials (PCMs), and with the load generated in the melting process. The PCM film is thus used as a solution for enhancing stability and workability, reducing indoor cooling energy and PCM film installability. In this study, film applicability is considered; we propose a louver-type double skin system using PCM film, evaluate its performance in comparison with existing liquid-type PCMs, and confirm the installability of PCM film and the cooling energy reduction effect. Method: A total of four types of experimental bodies were manufactured for comparative analysis of thermal performance and temperature change. The experimental period was 4 days a week, the actual data measurement was performed every 12 h during the night and daytime, the results were compared and analyzed graphically, and the possibility of installing a louver-type double-hull system using PCM film was verified. The cooling energy reduction effect was also confirmed. Result: Although the liquid-type PCM had the best performance, its practical use in building materials was evaluated based on workability and stability. On the other hand, the performance of the PCM film was 11.66% lower than that of the liquid PCM, which was determined to be high. There will be need for further work on deriving the melting temperature using an appropriate PCM film, and controlling the sensible and latent heat effects to satisfy both the cooling and the heating effects.

Multiphysics Simulation of Nucleation and Grain Growth in Selective Laser Melting of Alloys

Abstract Selective laser melting (SLM) builds parts by selectively melting metallic powders layer by layer with a high-energy laser beam. It has a variety of applications in aerospace, medical device, and other low-volume manufacturing. Nevertheless, the lack of fundamental understanding of the process-structure-property relationship for better quality control inhibits wider applications of SLM. Recently, a mesoscale simulation approach, called phase field and thermal lattice Boltzmann method (PF-TLBM), was developed to simulate microstructure evolution of alloys in SLM melt pool with simultaneous consideration of solute transport, heat transfer, phase transition, and latent heat effect. In this paper, a nucleation model is introduced in the PF-TLBM framework to simulate heterogeneous nucleation at the boundary of the melt pool in SLM. A new method is also developed to estimate the thermal flux out of the SLM melt pool model given a constant cooling rate. The effects of latent heat and cooling rate on dendritic morphology and solute distribution are studied. The simulation results of AlSi10Mg alloy suggest that the inclusion of latent heat is necessary because it reveals the details of the formation of secondary arms, reduces the overestimation of microsegregation, and provides more accurate kinetics of dendritic growth.