Cold Layer Research Articles

Experimental investigation on the thermal performance of double-layer PCM radiant floor system containing two types of inorganic composite PCMs

Double-layer radiant floor systems that consist of two inorganic phase change layers placed at different positions, were first explored for regulating the indoor thermal comfort in winter and summer climates. Specifically, two hydrated salts having different melting points were respectively compounded with expanded graphite to obtain enhanced thermal conductivity. In the floor systems, Na2HPO4•12H2O-based composite (31.3 °C) and CaCl2•6H2O-based composite (20.2 °C) were used for the heat storage layer and the cold storage layer, respectively. It is found, in the winter climate, the room equipped with a radiant floor system consisting of an upper heat storage layer and a lower cold storage layer, realizes a thermal comfort duration of 2.2 times that of the reference room containing pebbles in the floor. Significantly, the radiant floor system constructed by just exchanging the positions of the two layers endows the room with a thermal comfort duration of 8.1 h in the summer climate, which is 1.7 times that of the reference room. Moreover, appropriately enhancing the thermal conductivity of the composites can promote energy savings by reducing the operating time of the active system. It is estimated that the double-layer radiant floor systems can save economic costs by shifting the peak load.

Mycobiont contribution to tundra plant acquisition of permafrost-derived nitrogen.

As Arctic soils warm, thawed permafrost releases nitrogen (N) that could stimulate plant productivity and thus offset soil carbon losses from tundra ecosystems. Although mycorrhizal fungi could facilitate plant access to permafrost-derived N, their exploration capacity beyond host plant root systems into deep, cold active layer soils adjacent to the permafrost table is unknown. We characterized root-associated fungi (RAF) that colonized ericoid (ERM) and ectomycorrhizal (ECM) shrub roots and occurred below the maximum rooting depth in permafrost thaw-front soil in tussock and shrub tundra communities. We explored the relationships between root and thaw front fungal composition and plant uptake of a 15 N tracer applied at the permafrost boundary. We show that ERM and ECM shrubs associate with RAF at the thaw front providing evidence for potential mycelial connectivity between roots and the permafrost boundary. Among shrubs and tundra communities, RAF connectivity to the thaw boundary was ubiquitous. The occurrence of particular RAF in both roots and thaw front soil was positively correlated with 15 N recovered in shrub biomass Taxon-specific RAF associations could be a mechanism for the vertical redistribution of deep, permafrost-derived nutrients, which may alleviate N limitation and stimulate productivity in warming tundra.

A felületelőkészítés hatása a felületi réteg maradó feszültségi állapotára hidegalakító szerszámacélokon

In order to increase the wear resistance and service life of tool steels, we often use ceramic coatings. The performance of these coatings is determined not only by their properties, but also significantly by the characteristics of the surface- and near-surface layer, including their residual stress state. In this paper we investigated the residual stresses developing during grinding, polishing and glass bead blusting in the surface layer of an X153CrMoV12 high-alloy cold forming tool steel, that is intended to be coated by mono- and multilayer superhard DLC coatings. It has been found that each surface treat ment process can result in extremely different stress states, with predominantly tensile stresses after grinding, typically low compressive stresses after polishing, and compressive residual stresses one order of magnitude higher than for polishing as a result of glass bead blasting. Based on the literature, we found that these residual stresses can be greatly modified by changing the processing conditions and technological parameters, emphasizing that in addition to the residual stresses, several other influencing factors must be taken into account when designing the surface quality of the substrate under the ceramic coatings.

2-T algorithm for temperature estimation in a non-uniform zone by line-of-site diode laser absorption spectroscopy

A new two-temperature (2-T) algorithm for an estimation of the temperatures in a non-uniform hot zone by absorption spectrometry with tunable diode lasers (TDLAS) is demonstrated in experiments with the Wolfhard–Parker burner. A laminar premixed flame of the burner has a planar structure with zones of relatively constant temperature and zones with pronounced temperature gradients. The temperature was evaluated by fitting the experimental absorption spectra of a H2O molecule by the linear combination of two single temperature spectra simulated using spectroscopic databases. The radiation of the two diode lasers generating in 7185 cm−1 and 7444 cm−1 spectral ranges crossed the flame in the direction along the slots at different heights above the burner. Temperature profiles of the flame obtained by fitting the line-of-sight TDLAS experimental spectra using a 2-T algorithm are compared with the local temperatures measured by coherent anti-Stokes Raman spectroscopy (CARS). The maximum and minimum temperatures estimated by the TDLAS and CARS coincide well if the line-of-sight optical path of the probing diode laser beam consists of a dominantly hot or dominantly cold layer.

Temperature dependence of indentation behavior of Ti-6Al-4V alloy for bio medical applications

Numerical analysis of spherical indentation was carried out to study temperature dependence (300-673K) of elasto-plastic deformation behavior of Ti-6Al-4V alloy. Flow stress and strain hardening exponent ‘n’ were determined from load versus indenter penetration depth profiles generated through FE model using Dao’s reverse analysis approach. The upward flow around the residual impression as a function of average strain, which describes the strain hardening behaviour of the alloys was also investigated. The simulated values of CF have been used to predict high strain-rate plastic flow behavior considering indentation data. It was observed that there is a good correlation between data from simulation and experimental results in the literature. The FE model developed in the current investigation can be used for simulating the flow behavior of Ti-6Al-4V alloy. The temperature dependent CF value in the fully plastic regime from the current study is approximately 2.69 against experimentally evaluated value of 2.95. Meyer’s hardness is generally high due to the presence of cold layer resulting from grinding and polishing of the test specimen. Absence of such effects in simulation of spherical indentation resulted in reduced value of CF.

Melting heat transfer of a non-Newtonian phase change material in a cylindrical vertical-cavity partially filled porous media

Purpose This paper aims to investigate melting heat transfer of a non-Newtonian phase change material (PCM) in a cylindrical enclosure-space between two tubes using a deformed mesh method. Design/methodology/approach Metal foam porous layers support the inner and outer walls of the enclosure. The porous layers and clear space of the enclosure are filled with PCM. The natural convection effects during the phase change are taken into account, and the governing equations for the molten region and solid region of the enclosure are introduced. The governing equations are transformed into non-dimensional form and then solved using finite element method. The results are compared with the literary works and found in good agreement. The non-Newtonian effects on the phase change heat transfer and melting front are studied. Findings The results show that the increase of non-Newtonian effects (the decrease of the power-law index) enhances the heat melting process in the cavity at the moderate times of phase change heat transfer. The temperature gradients in porous metal foam over the hot wall are small, and hence, the porous layer notably increases the melting rate. When the melting front reaches the cold porous layer, strong non-linear behaviors of the melting front can be observed. Originality/value The phase change heat transfer of non-Newtonian fluid in a cylindrical enclosure partially filled with metal foams is addressed for the first time.

Gas temperature and boundary layer thickness measurements of an inert mixture using filtered broadband natural species emission (Part I)

A new experimental methodology to simultaneously measure gas temperature and boundary layer thickness was developed and explained for the first time in this work. The new methodology is based on the line-of-sight broadband filtered natural infrared emission of species and it solves one of the main challenges of using the broadband spectroscopy to measure gas temperatures: quantification of the absorption of the core gas infrared emission due to the cold boundary layer on the optical access of combustion systems. To evaluate and validate the new methodology, it was applied to measure the gas temperature and boundary layer thickness of a mixture of methane, carbon dioxide, and nitrogen using Rapid Compression Machine RCM). High-speed infrared cameras with two filters at wavelength ranges of 3.329 to 3.629 μm and 4.069 to 4.445 μm were used to measure the filtered natural emission of methane and carbon dioxide during the post-compression period. Measured gas temperatures at two conditions were compared with the modeled temperature calculated using the isentropic compression equation. Excellent agreement, within 1%, was reached between modeled and measured gas temperatures.

ФОРМИРОВАНИЕ ХОЛОДНОГО ПРОМЕЖУТОЧНОГО СЛОЯ В ШЕЛЬФОВО-СКЛОНОВОЙ ЗОНЕ СЕВЕРО-ВОСТОЧНОЙ ЧАСТИ ЧЕРНОГО МОРЯ

The paper presents an overview of the existing hypotheses about the formation areas and the distribution mechanisms of the cold intermediate layer (CIL) in the Black Sea. The testing of the statistical hypothesis about the relationship of the CIL parameters in the shelf-slope zone of the Black Sea Northeastern part with the temperature of the atmosphere surface layer in the central part of the eastern cyclonic gyre is performed. The obtained high values of the correlation coefficients (~0.98) confirmed the dependence of the CIL parameters during its formation period from the air temperature over the Northeastern part of the Black Sea. One of the concepts of the “convective-advective” hypothesis by Ovchinnikov and Popov (1987) about approximately 2 months time shift between the processes of cold air masses invasion into the water area of the Black Sea and the developed CIL waters appearance in the coastal zone of the Gelendzhik area is also confirmed.

СЕЗОННАЯ ИЗМЕНЧИВОСТЬ ГИДРОЛОГИЧЕСКИХ ХАРАКТЕРИСТИК НА СЕВЕРО-ВОСТОЧНОМ ШЕЛЬФЕ О. САХАЛИН

The long-term mean temperature and salinity distributions on 5 standard oceanological sections on the northeast shelf of Sakhalin were analyzed for 4 months of the navigation period (July-October) including a radical restructuring of hydrological conditions in the transition from summer to autumn. The data of soundings performed during the pollock ichthyoplankton surveys were used to study oceanological conditions in June. The low salinity water formed by the Amur River runoff are shown to appear on the northeastern shelf in the first half of June after the heavy ice breaking in the southern Sakhalin Bay. Low salinity water and ice are pushed off toward the deep sea under the influence of the southern winds typical for a warm season, and an oceanological front is formed near the 52°N. This front prevents the low-salinity water from flowing southward until the second half of September, when changes into a winter monsoon with the prevailing northerly winds take place. This promotes destruction of hydrological front and deepening of the cold intermediate water layer. The waters with the 4–6°C temperature and salinity of about 31 psu occur at the shelf edge along the northeastern Sakhalin coast. A powerful stream with the relatively warm low salinity water is being formed along the shore that reaches the southeastern part of Sakhalin and northern coasts of Hokkaido Island.

Numerical study of combustion of the diesel fuel sprayed with a steam jet in a prospective burner device

A prospective laboratory-scale burner device that employs a concept of liquid fuel spraying in the high-speed superheated steam jet is considered. The presented work is devoted to numerical study of aerothermochemical processes occurring in this novel-design burner during the combustion of diesel fuel sprayed with axial jet of water steam. The mathematical model is based on Euler-Lagrange approach for two-phase turbulent reacting flow description applied in 2D axisymmetric steady-state formulation. The vaporized diesel fuel combustion is described via EDC model with chemical kinetics mechanism for n-heptane (30 species, 66 reactions). The two-step soot model is also used, as well as NOx prediction at post-processing stage. The fields of velocity, temperature, heat fluxes, gas species and disperse phase concentrations, including soot and NOx, have been obtained from numerical simulation for a typical operational mode with diesel supply rate of 1.2 kg/hour and water steam flowrate of 0.8 kg/hour. Analysis of these flowfield data has allowed to reveal the two-layer coaxial structure of reacting flow (consisting of relatively cold near-axis jet layer and the coaxial layer formed by the hot recirculation zone) inside the burner.

Scaling of heat transfer in stagnant lid convection for the outer shell of icy moons: Influence of rheology

The persistence of subsurface oceans in icy moons primarily depends on the efficiency of heat transfer through the outer ice shell. Scaling laws for heat transfer have already been determined by previous studies. These consider however a simplified rheology assuming a single creep mechanism, often using a linearized version of the temperature-dependent viscosity law (called Frank-Kamenetskii approximation). In the present study, we test the influence of ice rheology on the efficiency of heat transfer by considering a more realistic composite viscosity law, including diffusion creep, grain boundary sliding, basal slip and dislocation creep. We performed a large number of numerical simulations of thermal convection in the stagnant lid regime using a 2-D spherical annulus geometry with different rheology assumptions. Our results show that the dynamics of the ice shell is mainly controlled by the dominant creep mechanism in the rheological sublayer (the unstable lower portion of the cold boundary layer beneath the stagnant lid), which is mostly determined by grain size. For grain sizes lower than 3 mm, diffusion creep is the dominant creep mechanism in the rheological sublayer, while a combination of grain boundary sliding and basal sliding prevails for coarser grains. We derive new simple scaling relationships for the heat transfer suitable for the specific case of thin ice shells that account for the activation energy of the dominant creep mechanisms, thus allowing for a more accurate quantification of the temperature profile in the ice shell and cooling rate of the internal oceans.

Multilayered Kelvin–Helmholtz Instability in the Solar Corona

Abstract The Kelvin–Helmholtz (KH) instability is commonly found in many astrophysical, laboratory, and space plasmas. It could mix plasma components of different properties and convert dynamic fluid energy from large-scale structure to smaller ones. In this study, we combined the ground-based New Vacuum Solar Telescope (NVST) and the Solar Dynamic Observatories/Atmospheric Imaging Assembly (AIA) to observe the plasma dynamics associated with active region 12673 on 2017 September 9. In this multitemperature view, we identified three adjacent layers of plasma flowing at different speeds, and detected KH instabilities at their interfaces. We could unambiguously track a typical KH vortex and measure its motion. We found that the speed of this vortex suddenly tripled at a certain stage. This acceleration was synchronized with the enhancements in emission measure and average intensity of the 193 Å data. We interpret this as evidence that KH instability triggers plasma heating. The intriguing feature in this event is that the KH instability observed in the NVST channel was nearly complementary to that in the AIA 193 Å. Such a multithermal energy exchange process is easily overlooked in previous studies, as the cold plasma component is usually not visible in the extreme-ultraviolet channels that are only sensitive to high-temperature plasma emissions. Our finding indicates that embedded cold layers could interact with hot plasma as invisible matters. We speculate that this process could occur at a variety of length scales and could contribute to plasma heating.

BERING SEA: 2018 AS THE EXTREME LOW-ICE AND WARM YEA

Phenomenon of anomalous oceanographic conditions in the Bering Sea in 2018 is considered, with heightened air and water temperature and very low ice cover, as well as its consequences for the water structure, circulation, and chemical properties. These extreme conditions were formed on the background of warming tendency observed in the Bering Sea since 2014, but they were exceptional even relative to this background: deflections of some parameters from their normal values exceeded the standard deviations more than twice (> 2s). The main reason for such conditions was the southern winds prevalence over the entire Sea in winter, in opposite to usual regime when the southern winds blew over its southeastern part only; another factor was strengthened advection of the oceanic waters, still abnormally warm after the period of extreme warming in the North-East Pacific in 2014–2016. As the result, the ice cover in winter and spring was more than twice lower the normal values, the air and water temperatures through the year were above their normal values in 15 and 5 degrees Celsius, respectively. The winter convection was weakened that caused deepening of the cold subsurface layer core and prevented forming of the cold near-bottom water masses on the shelf that was usual for the Bering Sea. Under this considerable redistribution of the water density coupled with unusual wind regime, the water circulation changed, in particular in the northern Bering Sea where the Navarin Current were weakened or even absent and the northward water transport was realized through the eastern shelf delivering to the northern shelf and Bering Strait the coastal waters from Alaska instead of the deep-water basins waters, as usually. Strong advection of the oceanic waters through the Aleutian Straits promoted growth of nutrients concentrations and lowering of oxygen content in the intermediate layer of the Bering Sea. These extreme oceanographic conditions in the Bering Sea in 2018 were statistical outliers, atypical even for recent period of warming, but such conditions would be expected frequently if the warming will continue. Thus, phenomenon of the year 2018 could be useful for understanding and prediction of the oceanographic regime reconstruction in the nearest future.

Destruction of the Lava Dome of an Underwater Volcano

The stress state and destruction of the lava dome of the underwater volcano exposed to temperature gradients and external pressure from hot magma melt and the cold water layer are investigated. Methods of the linear elasticity theory and statistical strength theory are used for mathematical modeling of the behavior of lava domes. It has been revealed in the course of evaluation calculations that the role of temperature gradients in the lava dome destruction process is as important as that of an external pressure. It is established that the lava dome is destroyed layer by layer, and the time of this destruction is determined in this paper.

A comparison of gas stream cooling and plunge cooling of macromolecular crystals.

Cryocooling for macromolecular crystallography is usually performed via plunging the crystal into a liquid cryogen or placing the crystal in a cold gas stream. These two approaches are compared here for the case of nitro-gen cooling. The results show that gas stream cooling, which typically cools the crystal more slowly, yields lower mosaicity and, in some cases, a stronger anomalous signal relative to rapid plunge cooling. During plunging, moving the crystal slowly through the cold gas layer above the liquid surface can produce mosaicity similar to gas stream cooling. Annealing plunge cooled crystals by warming and recooling in the gas stream allows the mosaicity and anomalous signal to recover. For tetragonal thermolysin, the observed effects are less pronounced when the cryosolvent has smaller thermal contraction, under which conditions the protein structures from plunge cooled and gas stream cooled crystals are very similar. Finally, this work also demonstrates that the resolution dependence of the reflecting range is correlated with the cooling method, suggesting it may be a useful tool for discerning whether crystals are cooled too rapidly. The results support previous studies suggesting that slower cooling methods are less deleterious to crystal order, as long as ice formation is prevented and dehydration is limited.

L1495 revisited: a ppmap view of a star-forming filament

ABSTRACT We have analysed the Herschel and SCUBA-2 dust continuum observations of the main filament in the Taurus L1495 star-forming region, using the Bayesian fitting procedure ppmap. (i) If we construct an average profile along the whole length of the filament, it has FWHM $\simeq 0.087\pm 0.003\, {\rm pc};\,\,$ but the closeness to previous estimates is coincidental. (ii) If we analyse small local sections of the filament, the column-density profile approximates well to the form predicted for hydrostatic equilibrium of an isothermal cylinder. (iii) The ability of ppmap to distinguish dust emitting at different temperatures, and thereby to discriminate between the warm outer layers of the filament and the cold inner layers near the spine, leads to a significant reduction in the surface-density, $\varSigma$, and hence in the line-density, μ. If we adopt the canonical value for the critical line-density at a gas-kinetic temperature of $10\, {\rm K}$, $\mu _{{\rm CRIT}}\simeq 16\, {\rm M_{\odot }\, pc^{-1}}$, the filament is on average trans-critical, with ${\bar{\mu }}\sim \mu _{{\rm CRIT}};\,\,$ local sections where μ > μCRIT tend to lie close to prestellar cores. (iv) The ability of ppmap to distinguish different types of dust, i.e. dust characterized by different values of the emissivity index, β, reveals that the dust in the filament has a lower emissivity index, β ≲ 1.5, than the dust outside the filament, β ≳ 1.7, implying that the physical conditions in the filament have effected a change in the properties of the dust.

Subglacial water pressure and ice-speed variations at Johnsons Glacier, Livingston Island, Antarctic Peninsula

ABSTRACTTo study subglacial hydrological condition and its influence on the glacier dynamics, we drilled Johnsons Glacier on Livingston Island in the Antarctic Peninsula region. Subglacial water pressure was recorded in boreholes at two locations over 2 years, accompanied by high-frequency ice-speed measurements during two summer melt seasons. Water pressure showed two different regimes, namely high frequency and large amplitude variations during the melt season (January–April) and small fluctuations near the overburden pressure the rest of the year. Speed-up events were observed several times in each summer measurement period. Ice motion during these events substantially contributed to total glacier motion, for example, fast ice flow over 1 week accounted for ~70% of the total displacement over a 25-day long measurement period. We did not find a clear relationship between subglacial water pressure and ice speed. This was probably because subglacial hydraulic conditions were spatially inhomogeneous and thus our borehole data did not always represent a large-scale subglacial condition. Ice temperature measurements in the boreholes confirmed the existence of a cold ice layer near the glacier surface. Our data provide a basis to better understand the dynamic and hydrological conditions of relatively unstudied glaciers in the Antarctic Peninsula region.

A multivariate statistical approach of X-ray fluorescence characterization of a large collection of reverse glass paintings

We present an X-ray fluorescence spectroscopy (XRF) study combined with a multivariate approach that allow to detect compositional differences and similarities among the glass supports of a large set of reverse glass paintings belonging to the collection of the Mistretta museum. Reverse painting on glass is an old decorative technique used since the Roman time consisting in applying a cold paint layer on the reverse side of a glass support. The collection shows a large spreading of provenience and dating of the items. In consideration of the current classification solely based on stylistic criteria, we applied a multivariate analysis on the XRF measurements data set to find a more objective classification criterion based on the elemental composition of the glass support. Results showed that glass supports can be divided into different typologies on the basis of their different elemental composition. Assignment of these typologies to the current assignment to a given geographical area or a given period is not straightforward, due to reuse or original erroneous attribution.

Low‐Level and Surface Wind Jets Near Sea Ice Edge in the Beaufort Sea in Late Autumn

AbstractLow‐level wind jets (LLJs) and strong surface winds are frequently observed near the sea ice edge in the presence of strong thermal contrast between open water and sea ice. Two LLJ cases near the sea ice edge in the Beaufort Sea are examined using dropsonde observations made from Seasonal Ice Zone Reconnaissance Survey flights. Ensembles of Polar Weather Research and Forecast simulations with and without sea ice demonstrate the contribution of the surface thermal contrast to the boundary layer structure, the LLJ, and surface ice edge jets. Because the surface temperature contrast only influences the lower most hundreds of meters in the atmospheric boundary layer, its contribution to the temperature gradient and wind speed at the level of the LLJ is limited. The sea ice does strengthen the LLJ by extending the LLJ northward over sea ice and increasing the maximum LLJ wind speeds by up to 13% and as much as 29% further north at a lower altitude. However, the primary reason for the observed strong winds in these two cases are the synoptic interactions between anticyclones and approaching cyclones. The effect of the surface thermal contrast on surface winds is controlled by a separate mechanism. The cold and stable boundary layer over sea ice prevents the momentum transport from the LLJ to the surface. This leads to weaker surface winds over sea ice and confines the strong surface winds close to the sea ice edge. This mechanism contributes to the frequent occurrence of the surface “ice edge jets.”

Stratification Has Strengthened in the Baltic Sea – An Analysis of 35 Years of Observational Data

Stratification of the water column, consisting of the three layers (upper, intermediate, and deep layer), is an important factor for the functioning of the brackish Baltic Sea. In the present work, changes in the vertical structure of temperature and salinity, as well as heat content, salt mass and stratification conditions were estimated on the basis of in-situ and remote sensing data in 1982-2016. The seasonal thermocline and the halocline have strengthened in most of the sea by a rate of 0.33 – 0.39 kg m-3 and 0.70 – 0.88 kg m-3, respectively, during 35 years. The upper layer has warmed by 0.03 – 0.06 °C year-1 and sub-halocline deep layer 0.04 – 0.06 °C year-1 in most of the sea. The total warming trend in the whole Baltic has been 1.07 °C for 35 years, being approximately twice higher compared to the upper 100 m in the Atlantic Ocean. Average upper layer warming of the sea from May to September has been 0.07 – 0.08 °C year-1 while in winter, trends were mostly statistically not significant. More rapid warming during summers has occurred in shallower, closed-end areas of gulfs. Possible reasons for high warming there might be shallow depths and limited water exchange, stronger stratification, and/or higher turbidity. Sea surface temperature trends estimated by in-situ and satellite data agree well. Trends of freshening (-0.005 to -0.014 g kg-1 year-1) of the upper layer and increasing salinity (0.02 to 0.04 g kg-1 year-1) in the sub-halocline deep layer were detected. Increased salinity in the deep layer is likely caused by the increased lateral import of saltier water from the North Sea. Changes in the upper layer salinity might not be related to the accumulated river runoff only, but decadal changes of vertical salt flux might also contribute. The vertically distinct changes cancel each other and no significant trend in the mean salinity of the Baltic Sea was detected. No remarkable changes have occurred in the cold intermediate layer. In conclusion, different dominating processes have caused distinct long-term trends in the three layers of the Baltic Sea.