Hot Layer Research Articles

Sunspot Bright Points

We used the flux calibrated images through the Broad Band Filter Imager and Stokes Polarimeter data obtained with the Solar Optical Telescope onboard the Hinode spacecraft to study the properties of bright points in and around the sunspots. The well isolated bright points were selected and classified as umbral dot, peripheral umbral dot, penumbral grains and G-band bright point depending on their location. Most of the bright points are smaller than about 150 km. The larger points are mostly associated with the penumbral features. The bright points are not uniformly distributed over the umbra but preferentially located around the penumbral boundary and in the fast decaying parts of umbra. The color temperature of the bright points, derived using the continuum irradiance, are in the range of 4600 K to 6600 K with cooler ones located in the umbra. The temperature increases as a function of distance from the center to outside. The G-band, CN-band and CaII H flux of the bright points as a function of their blue band brightness increase continuously in a nonlinear fashion unlike their red and green counterpart. This is consistent with a model in which the localized heating of the flux tube deplete the molecular concentration resulting the reduced opacity which leads to the exposition of deeper and hotter layers. The scatter in CaII H irradiance is higher compared to the G-band and CN-band irradiance. The light curve of the bright points show that the enhanced brightness at these locations last for about 15 to 60 minutes with the least contrast for the points out side the spot. The umbral dots near the penumbral boundary are associated with elongated filamentary structures.

Suppression of thermal stratification in gravity driven water pool of an advanced reactor using shrouds

Advanced and innovative reactor systems are considering the use of large pools as heat sink for various safety functions like decay heat removal or containment cooling. These designs generally have heat exchangers immersed in the pool. For enhanced safety and reliability, preferred heat transfer mode is considered to be passive so that heat sink availability is maintained even in failure of power supply and active components. However, heat transfer by natural convection in large pools poses a problem of thermal stratification. As a result of natural convection, hot layers of water may accumulate over the relatively cold one and in turn inhibit the natural convection itself. Not only the heat transfer performance may get deteriorated but some structural parts of the pool like concrete wall may be subjected to high temperature which is not desirable. In this paper, a new concept of employing shrouds around the heat source is proposed. These shrouds provide multiple natural circulation loops around the heat source, thereby facilitating mixing of hot and cold fluid, which eliminate stratification. The concept has been applied to the Gravity Driven Water Pool (GDWP) of Advance Heavy Water Reactor (AHWR) in which Isolation Condensers (ICs) tubes are submerged for decay heat removal of AHWR using ICS and thermal stratification phenomenon was predicted without and with ICS. Results indicate that the shrouds have application in elimination of thermal stratification in GDWP.

Parylene C coated microelectrodes for scanning electrochemical microscopy

Herein, we present a simple microelectrode preparation methodology consisting in coating a platinum wire or a carbon fiber with a thin insulating Parylene C film (e.g. 1–10μm), to produce SECM probes with a small and constant probe RG (i.e. ratio between the radius of the insulating sheath and the radius of the active electrode area). After exposition of a fresh active electrode area by blade cutting, a disc shaped electrode is obtained thanks to a protective hot mounting wax layer that avoids Parylene C coating deformation and is easily removed with acetone. Stiffness and straightness of the probe can be tuned by modifying the Parylene C coating thickness and the length of the carbon fiber or platinum wire. This simple electrode preparation method is highly reproducible (c.a.>90%). The prepared Parylene C coated microelectrodes were characterized by optical microscopy, cyclic voltammetry, scanning electrochemical microscopy (SECM) approach curves and finally applied to SECM imaging of Pt band structures in contact-less and contact mode.

Mantle dynamics in super-Earths: Post-perovskite rheology and self-regulation of viscosity

The discovery of extra-solar “super-Earth” planets with sizes up to twice that of Earth has prompted interest in their possible lithosphere and mantle dynamics and evolution. Simple scalings suggest that super-Earths are more likely than an equivalent Earth-sized planet to be undergoing plate tectonics. Generally, viscosity and thermal conductivity increase with pressure while thermal expansivity decreases, resulting in lower convective vigour in the deep mantle, which, if extralopated to the largest super-Earths might, according to conventional thinking, result in no convection in their deep mantles due to the very low effective Rayleigh number. Here we evaluate this. First, as the mantle of a super-Earth is made mostly of post-perovskite we here extend the density functional theory (DFT) calculations of post-perovskite activation enthalpy of to a pressure of 1TPa, for both slowest diffusion (upper-bound rheology) and fastest diffusion (lower-bound rheology) directions. Along a 1600K adiabat the upper-bound rheology would lead to a post-perovskite layer of a very high (∼1030Pas) but relatively uniform viscosity, whereas the lower-bound rheology leads to a post-perovskite viscosity increase of ∼7 orders of magnitude with depth; in both cases the deep mantle viscosity would be too high for convection. Second, we use these DFT-calculated values in statistically steady-state numerical simulations of mantle convection and lithosphere dynamics of planets with up to ten Earth masses. The models assume a compressible mantle including depth-dependence of material properties and plastic yielding induced plate-like lithospheric behaviour. Results confirm the likelihood of plate tectonics for planets with Earth-like surface conditions (temperature and water) and show a self-regulation of deep mantle temperature. The deep mantle is not adiabatic; instead feedback between internal heating, temperature and viscosity regulates the temperature such that the viscosity has the value needed to facilitate convective loss of the radiogenic heat, which results in a very hot perovskite layer for the upper-bound rheology, a super-adiabatic perovskite layer for the lower-bound rheology, and an azimuthally-averaged viscosity of no more than 1026Pas. Convection in large super-Earths is characterised by large upwellings (even with zero basal heating) and small, time-dependent downwellings, which for large super-Earths merge into broad downwellings. In the context of planetary evolution, if, as is likely, a super-Earth was extremely hot/molten after its formation, it is thus likely that even after billions of years its deep interior is still extremely hot and possibly substantially molten with a “super basal magma ocean” – a larger version of the proposal of Labrosse et al. (Labrosse, S., Hernlund, J.W., Coltice, N. [2007]. Nature 450, 866–869), although this depends on presently unknown melt–solid density contrast and solidus.

Flexible Pavement Performance in relation to In Situ Mechanistic and Volumetric Properties Using LTPP Data

This research study focuses on the actual performance of the flexible pavements and its relationship with the in-situ mechanistic and volumetric properties. The data required for the study were obtained using the Long Term Pavement Performance database. Approximately, 116 flexible pavement sections throughout United States were analyzed and discussed. The results indicated that the temperature has a significant affect on the backcalculated modulus of the hot mix asphalt layer. However, no strong relationship was observed between the hot mix asphalt backcalculated modulus and in situ air voids. It was found that fatigue life was a function of tensile strain at the bottom of hot mix asphalt layer, peak surface deflection, hot mix asphalt air voids and maximum specific gravity, and ambient air temperature. Similar relationships between the rut life, mechanistic and volumetric properties were established for wet-freeze and wet-no-freeze climatic zones. The sensitivity analysis revealed that the rut performance in wet-no-freeze sections is mainly affected by higher base and roadbed compressive stresses and strains. On the other hand, the performances in wet-freeze sections are highly depended on roadbed compressive strain and modulus ratio of subbase to roadbed.

Ammonium oxidization at room temperature and plasmonic photocatalytic enhancement

Abstract In an alkaline condition, ammonium can be efficiently reduced with hydroxide ion using a spinning disk reactor at room temperature. To some extent, illumination can boost the processing efficiency by warming water. A homogeneous 8 nm crystallized platinum thin film deposited on a B270-glass substrate by plasma-enhanced atomic layer deposition absorbs light from 350 nm to 2500 nm. The absorbed light transforms plasmonic resonance energy on the platinum thin film and forms a high temperature hot layer. The plasmonic heating effect, or plasmonic photocatalytic reaction, enhances the activity of the Pt thin film for the oxidation of NH4+.

Radiological performance of hot water layer system in open pool type reactor

The paper presents the calculated dose rate carried out by using MicroShield code to show the importance of hot water layer system (HWL) in 22MW open pool type reactor from the radiation protection safety point of view. The paper presents the dose rate profiles over the pool surface in normal and abnormal operations of HWL system. The results show that, in case of losing the hot water layer effect, the radiation dose rate profiles over the pool surface will increase from values lower than the worker permissible dose limits to values very higher than the permissible dose limits.

An effective layer pattern optimization model for multi-stream plate-fin heat exchanger using genetic algorithm

For multi-stream plate-fin heat exchangers (MPFHEs), a crucial factor affecting performance is the layer pattern used to distribute hot and cold streams. However, for the design of MPFHE layer pattern, so far it still remains at semi-qualitative, empirical or trial-and-error stage, lacking efficient approaches to obtain the optimum. In this paper, an effective layer pattern optimization model using genetic algorithm (GA) is developed in detail. It includes the chromosome of binary string that represents hot and cold layers alternatively arranged, the dual fitness functions that act on chromosome individuals alternatively, the constraint that requires the spacing layers between hot and cold streams to be no less than 1 and no greater than 2, the selection of optimization tool and the corresponding setting of GA parameters. When used to optimize the layer pattern of actual MPFHE, this model exhibits well. The average thermal efficiency of exchanger reaches up to 98% of that obtained under the ideal common wall temperature assumption. Furthermore, the study of this paper make it clear the association of previous classical deviation from ideal of layer pattern zigzag curve with MPFHE thermal performance, which is not a strict monotonic decreasing relation as people thought to be, but a multiple vs. multiple relation.

Air pumping action of a plume in a room fire

Air pumping effect of a fire plume to give higher intake rate through vertical openings in a post-flashover room fire will be discussed in this paper. The thermal balance equation was set up with known fire phenomena in a room. The hydrostatic model was applied to study the air intake rate through vertical openings. An equation relating heat release rate to room air temperature rise with empirical constants was then justified by reported experimental data on post-flashover room fire. The heat release rate was measured by the oxygen consumption method in that experiment. The predicted heat release rate from the empirical equation reported in the literature was observed to be proportional to the room air temperature rise as derived from hydrostatics. However, the proportionality constant is lower than the experimental value. A possible explanation is due to neglecting another fire phenomenon on air pumping action of the fire plume in a real room fire. Higher pressure differences across the door would give higher airflow rates across an opening. This would supply more air to give higher heat release rate as observed in the experiment. In this paper, the pressure due to air pumping of the fire plume is taken as a proportion of the hydrostatic pressure due to temperature differences between the upper hot layer and lower cool layer. Comparing the measured heat release rate with the estimated heat release rate due only to hydrostatics will give the air pumping action. The possible increase in heat release rate in a post-flashover fire can then be estimated accordingly.

Design and installation of a hot water layer system at the Tehran research reactor

A hot water layer system (HWLS) is a novel system for reducing radioactivity under research reactor containment. This system is particularly useful in pool-type research reactors or other light water reactors with an open pool surface. The main purpose of a HWLS is to provide more protection for operators and reactor personnel against undesired doses due to the radio- activity of the primary loop. This radioactivity originates mainly from the induced radioactivity contained within the cooling water or probable minute leaks of fuel elements. More importantly, the bothersome radioactivity is progressively proportional to reactor power and, thus, the HWLS is a partial solution for mitigating such problems when power upgrading is planned. Following a series of tests and checks for different parameters, a HWLS has been built and put into operation at the Tehran research reactor in 2009. It underwent a series of comprehensive tests for a period of 6 months. Within this time-frame, it was realized that the HWLS could provide a better protection for reactor personnel against prevailing radiation under containment. The system is especially suitable in cases of abnormality, e. g. the spread of fission products due to fuel failure, because it prevents the mixing of pollutants developed deep in the pool with the upper layer and thus mitigates widespread leakage of radioactivity.

Study on Flashover in an Open Kitchen Fire by Nonlinear Dynamics

There are concerns on open kitchen fires in small flats of tall residential buildings. Flashover should be avoided in providing fire safety. It is believed that flashover of a compartment fire is a nonlinear physical process. In this article, nonlinear dynamics was used to study flashover in an example open kitchen fire. The mathematical model developed earlier by taking the fire compartment as a thermal system with a hot and layer and a cool air layer was taken as the simulation tool. The two-layer zone model was simplified by taking the smoke layer thickness at a constant value. The compartment fire was then studied with only one variable on the hot smoke layer temperature. The model was programmed in symbolic mathematics software. The single variable on smoke or hot air temperature is then analyzed for system stability. An example open kitchen was selected to illustrate the concept. Control parameters for flashover to occur have been identified for providing fire safety to open kitchens.

An investigation into the use of asphalt layers to control stress and strain levels in railway track foundations

A hot mixed asphalt layer can be inserted between the ballast and subgrade layers in the foundations of rail tracks to improve the stress and strain distributions in these layers and also reduce track vibrations and level of damage in the track’s superstructure. These phenomena depend on various parameters such as the manner of operation of the railway and the mechanical characteristics of the foundations. This study is devoted to the derivation of analytical equations that describe the tensile strain on the asphalt layer and compression stress in the subgrade layer in terms of these parameters. A series of numerical analyses have been performed using the KENTRACK simulation code in which the railway axle load, asphalt thickness, ballast modulus and California bearing ratio of the subgrade were varied. The obtained values of the maximum tensile strain in the asphalt and compression stress on the subgrade were analysed using a least squares method in order to extract correlation equations that consider the maximum tensile strain in the asphalt layer and compression stress on the subgrade layer in terms of the varied parameters. A comparison of the obtained simulation results with measured data reported in the literature shows a good agreement between the results.

ON THE NATURE OF THE HOT COMPONENT IN THE SYMBIOTIC, SUPERSOFT X-RAY BINARY AG DRACONIS

AG Dra is a symbiotic variable consisting of a metal poor, yellow giant mass donor under-filling its Roche lobe, and a hot accreting white dwarf, possibly surrounded by an optically thick, bright accretion disk which could be present from wind accretion. We constructed NLTE synthetic spectral models for white dwarf spectra and optically thick accretion disk spectra to model a FUSE spectrum of AG Dra, obtained when the hot component is viewed in front of the yellow giant. The spectrum has been de-reddened (E(B-V) = 0.05) and the model fitting carried out, with the distance regarded as a free parameter, but required to be larger than the Hipparcos lower limit of 1 kpc. We find that the best-fitting model is a bare accreting white dwarf with Mwd = 0.4 Msun, Teff = 80,000K and a model-derived distance of 1543 pc. Higher temperatures are ruled out due to excess flux at the shortest wavelengths while a lower temperature decreases the distance below 1 kpc. Any accretion disk which might be present is a only a minor contributor to the FUV flux. This raises the possibility that the soft X-rays originate from a very hot boundary layer between a putative accretion disk and the accreting star.

Numerical Simulation of Smoke Exhausts Function of Roof Vent in Compartment Fires

The influence of roof vent area and fire source area on smoke exhaust function of roof vent is provided in this paper. Numerical simulation results show that the temperature of hot smoke layer increases with the increases of heat release rate and decreases as the roof vent area increases. For the evaluation criterion with temperature difference, with the increase in roof vent area and fire source area, the smoke exhausts function of roof vent was enhanced. But for the evaluation criterion with efficiency of smoke exhaust, the smoke exhaust efficiency increases as the roof vent area increase and decreases with the increases of fire source area.

Constraints on the formation of the Martian crustal dichotomy from remnant crustal magnetism

The Martian crustal dichotomy characterizing the topographic difference between the northern and southern hemispheres is one of the most important features on Mars. However, the formation mechanism for the dichotomy remains controversial with two competing proposals: exogenic (e.g., a giant impact) and endogenic (e.g., degree-1 mantle convection) mechanisms. Another important observation is the Martian crustal remnant magnetism, which shows a much stronger field in the southern hemisphere than in the northern hemisphere and also magnetic lineations. In this study, we examine how exogenic and endogenic mechanisms for the crustal dichotomy are constrained by the crustal remnant magnetism. Assuming that the dichotomy is caused by a giant impact in the northern hemisphere, we estimate that the average thickness of ejecta in the southern hemisphere is 20–25km. While such a giant impact may cause crustal demagnetization in the northern hemisphere, we suggest that the impact could also demagnetize the southern hemisphere via ejecta thermal blanketing, impact demagnetization, and heat transfer from the hot layer of ejecta, thus posing a challenge for the giant impact model. We explore how the pattern of magnetic lineations relates to endogenic theories of dichotomy formation, specifically crustal production via degree-1 mantle convection. We observe that the pattern of lineations roughly corresponds to concentric circles about a single pole, and determine the pole for the concentric circles at 76.5° E and 84.5° S, which nearly overlaps with the centroid of the thickened crust in the southern hemisphere. We suggest that the crustal magnetization pattern, magnetic lineations, and crustal dichotomy (i.e., thickened crust in the highlands) can be explained by a simple endogenic process; one-plume convection causes melting and crustal production above the plume in the southern hemisphere, and strong crustal magnetization and magnetic lineations are formed in the southern hemisphere as crustal production fronts spread radially out from the plume center and as the newly created crust cools in the presence of a dynamo with polarity reversals.

Vibration Induced by Rail Traffic: Evaluation of Attenuation Properties in a Bituminous Sub-ballast Layer

The attenuation properties of a Hot-Mix Asphalt track bed containing crumb rubber (particle size 2-5mm) are evaluated. A large number of vibration measurements have been carried out in a test section of a railway interconnection (Turin-Milan HS Railway) where two solutions of 12cm of sub-ballast layer have been realized (with and without rubber). The vibrations were measured using a set of piezoelectric accelerometers positioned at various distances from the track to measure their generation and propagation. The results show that the new hot mix asphalt layer can influence the train vibration transmission.

Theoretical Analysis and Experimental Study on Whirling Flames in Enclosure Fires

Whirling flames are not commonly observed in enclosure fires, but some special hazards will be induced for their characteristics once they occur. Employing the theories of vorticity transport and fire dynamics, the formation mechanism of whirling flames in enclosure fires has been analyzed, and the factor expression governing the formation of whirling flames occurring in single rooms with ceiling and lower openings, which are familiar to us in industrial buildings, has been deduced. Using a small-scale firebox with a lower door and a ceiling opening, the experiments of whirling flames in enclosure fires were carried out. Based on the experimental results, the characteristics of whirling flames in enclosure fires were studied, and the basic parameters of fires with and without whirling flame were compared. Combining the results of the theoretical analysis and experimental study, the formation criterion of swirling flames in enclosure fires were derived. Furthermore the reasons that whirling flames cause increases in some parameters, such as hot gas layer temperatures and floor radiant heat flux, were analyzed.

On the scaling of heat transfer for mixed heating convection in a spherical shell

Planetary mantles and solid shells of icy satellites potentially undergoing natural convection are subjected to a mixed heating configuration including basal (from thermal exchanges with a subjacent, possibly liquid, layer) and internal (from radioactive decay or tidal dissipation) sources. In the quasi-static approximation, the average cooling/heating of the layer is also considered as an instantaneous internal heat source to model transient evolutions. In a previous study (Choblet and Parmentier, 2009), we have proposed simple scaling relationships to describe heat transfer for an isoviscous fluid in such a mixed heating configuration in the case of a Cartesian geometry. Here, we extend this analysis to the case of a spherical shell. A framework based on a temperature scale associated with the global surface heat flux is introduced. This enables a simple description of the cold boundary layer, independent of the heating configuration and of the relative radius of the inner boundary of the shell. When free-slip mechanical boundaries are prescribed, numerical experiments present a significant departure from the prediction (up to ≃30%). We show that this is caused by the impact of hot plumes on the cold boundary layer when a large amount of basal heating is prescribed. The results of no-slip calculations are well predicted by the scaling which thus could be applied to planetary mantles where convection occurs beneath a rigid lithosphere. The lower hot boundary layer is included in our analysis through the ratio of the temperature differences across both boundary layers: the simple scaling indicates that this ratio is independent of the Rayleigh number, and varies only with the amount of basal heating and with the curvature of the layer. This is shown to be valid in the no-slip case. In the free-slip case, a departure from this scaling is observed in the calculations but for the range of values corresponding to planetary bodies, the agreement is good. We conduct transient numerical experiments and show that the quasi-static approximation is valid in the configuration investigated here. Implications for more complex planetary set-ups are discussed.

Numerical Simulation of Temperature Profile in a Compartment Fire with a Roof Opening

Fifteen numerical simulations are presented in this article to investigate the influence of roof opening size and fire source size on gas temperature profiles in a compartment. The fire source size has a significant impact on the temperature hot smoke layer. The temperature of hot smoke layer increases as the increase of fire source size. The roof opening has cooling function to gas temperature in the compartment especially for large roof opening. The temperatures of hot smoke layer decrease with the roof opening size increase in all cases.

Wall Smoke Deposition from a Hot Smoke Layer

Smoke deposition from a hot smoke layer onto wall surfaces was studied in a hood apparatus using polymethylmethacrylate, polypropylene, and gasoline as fuels. Based upon prior analysis by Butler and Mulholland, the smoke deposition was expected to be dominated by thermophoresis. The deposited smoke samples were collected on glass filter paper attached to the hood wall and the mass per unit area of smoke deposited was measured gravimetrically. Measurements were made of quantities required for the prediction of thermophoretic smoke deposition. The smoke deposition measured in the experimental program was well predicted by the thermophoretic smoke deposition equation. The thermophoretic smoke deposition equation was found to be suitable for predicting smoke deposition onto wall surfaces exposed to fire environments.