Isothermal Region Research Articles

Anomalous intensification of vortex heat transfer in the case of separated air flow over an inclined groove in a hot isothermal region of a flat plate

Anomalous heat transfer intensification in turbulent separated air flow over a long groove of moderate depth made in a plate inclined at an angle of 45°to the freestream is revealed both experimentally and numerically. The region under investigation includes a rectangle heated to 100°C by saturated water vapor. The Reynolds number varied from 103to 3×104. Using the gradient heatmetry the twofold increase, as compared with the case of a flat plate, of the heat transfer coefficient on the groove bottom is established at the Reynolds number Re = 3×104. The relative Nusselt number in different regions of the groove is determined both in the physical experiment and in the RANS calculations with the application of multiblock computational technologies and the SST model in the VP2/3 software package. The results are in good agreement in the turbulent flow regime at Re = (5, 10, and 30) ×103.

An integrated sample-to-answer graphene microchip for ultrafast detection of multiple microorganisms

The integrated detection of nucleic acids is a molecular biological technology integrating the entire process of nucleic acid detection into a “sample-to-answer” system, which is widely used in microbial identification and disease diagnosis. Although the integrated detection of nucleic acids has the advantages of fully-enclosed system and simple operation, it still faces challenges like dependence on bulky equipment, complex design, and long detection time. To address these challenges, we have proposed and fabricated an integrated graphene microchip for ultra-fast detection of multiple microorganisms. This microchip is composed of two main regions: the electrolysis-extraction region and the isothermal amplification-detection region. In the electrolysis-extraction region, the microchip was equipped with the micron-structured graphene interdigital electrode and a regular battery for power supply, and the nucleic acids of H. pylori were extracted only in 1.0 s by electrolysis. Then in the isothermal amplification-detection region, the nucleic acids of H. pylori were detected in less than 9 min at a concentration of 10 CFU/µL. As a result, the detection time of the whole process were controlled in merely 9 min. In addition, this integrated graphene microchip has three parallel channels for simultaneous detection of oral microorganisms, e.g., C. albicans, S. aureus and H. pylori. These characteristics make our integrated graphene microchip promising to contribute to the development in integrated technology of nucleic acid detection and be widely used at various medical structures or on-site environments such as home testing.

A traction coefficient formula for EHL point contacts operating in the linear isothermal region

Many mechanical systems including rolling/sliding parts, require traction data across a spectrum of operating conditions to predict their motion effectively. Numerous studies have examined the thermal effects and shear-thinning concerning the traction curve, but only a few have focused on the traction coefficient in the linear isothermal regime for low SRR. In this work, we investigate traction coefficient characteristics of EHL point contacts in the linear isothermal regime, over a wide range of operational conditions. To this end, we conduct numerical simulations utilizing a fully-coupled finite element-based model, resulting in a prediction formula for the traction coefficient slope. With this formula, the traction coefficient slope could be predicted for the operating conditions considered.

In-situ Raman spectroscopic study of conformational reorganization during heat treatment for high-density polyethylene solid

We investigated in-situ conformational reorganization in a quenched high-density polyethylene solid during heat treatments at various temperatures using in-situ Raman spectroscopic technique. The heat-treatment cycle included three steps: heating from room temperature, maintaining at a fixed sub-melting temperature (tempering), and cooling to room temperature. The heating process caused a conformational transformation from orthorhombic crystalline trans conformers to non-crystalline long trans segments outside the crystalline lattice, which were then amorphized. During the tempering or isothermal duration region, the amorphized long trans segments were steadily subjected to crystalline rearrangement. Finally, the cooling process modified the long trans component (including the amorphized component) into crystalline trans conformers. Overall, a single heat-treatment cycle increased the crystallinity through reorganization of non-crystalline long-trans segments without changing the interfacial content where the original amorphous content remained the same.

On the numerical treatment of heat sources in laser beam welding processes

AbstractLaser beam welding is a contact free fusion technique which has gained importance during the last years due to rising need for automatization in industrial processes. However, a well‐known problem is the formation of solidification cracks in the rear region of the melting pool. In order to investigate the formation of solidification cracks which is highly dependent on the chemical composition, the welding speed, weld beam intensity and the resulting temperature gradient in the material, the modeling of the laser beam as a heat source plays a prominent role. In order to investigate heat sources in laser beam welding, this contribution compares two methods, the Goldak model and a second model that mimics the region of the melt pool with the idea of an isothermal region. Suitable boundary value problems to show the differences of the methods are demonstrated.

A traction coefficient formula for EHL line contacts operating in the linear isothermal region

Many mechanical products including rolling/sliding parts are used with various lubricants and operating conditions. Increasing the efficiency and reliability of products requires an essential understanding of the traction characteristics of the rolling/sliding parts. Many researchers have investigated the traction characteristics of rolling/sliding EHL contacts considering shear-thinning, thermal effects, and roller compliance. There are, however, only a few papers concerning the modeling of traction characteristics in the linear isothermal region at low slide-to-roll ratios. We propose a prediction formula for the dimensionless traction coefficient for EHL line contacts in the linear isothermal region. The formula was obtained by numerical simulations using a fully-coupled finite-element EHL line contact solver, and it is applicable for the piezoviscous rigid/elastic, and the isoviscous rigid/elastic regimes.

What Determines Above-Anvil Cirrus Plume Infrared Temperature?

Abstract Above-anvil cirrus plumes (AACPs) in midlatitude convection are important indicators of severe storms and stratospheric hydration events. Recent studies of AACPs have shown large variability in their characteristics, although many of the causes remain unknown. Notably, some AACPs appear equally as cold (or colder) than the broader storm top when compared to the more frequently observed warm AACP feature in infrared satellite imagery. To confidently identify the presence of an AACP, trained experts utilize infrared imagery to support the primary source of AACP identification, visible imagery. Thus, nighttime AACPs are often left unidentified due to unavailable visible imagery, especially for cold AACPs. In this study, 89 warm and 89 cold AACPs from 1-min GOES-16 satellite imagery coupled with ground-based radar observations and reanalysis data are comparatively evaluated to answer the following research questions: 1) Why do some AACPs exhibit a warm feature in infrared imagery while others do not, and 2) what observable storm and environment differences exist between warm and cold AACPs? It is found that cold AACPs tend to occur in tropical environments, which feature higher, cold-point tropopauses. Conversely, warm AACPs tend to occur in midlatitude environments, with lower tropopauses accompanied by an isothermal region (or tropopause inversion layer) in the lower stratosphere. Similar storm characteristics are found for warm and cold AACP events, implying that infrared temperature variability is driven by environmental differences. Together, these results suggest that cold AACPs are predominantly tropospheric phenomena, while warm AACPs reside in the lower stratosphere. Significance Statement The purpose of this study is to determine why some storms with a specific cloud-top feature exhibit a broad warm spot in infrared satellite imagery while others appear cold. This is important because storms with this specific cloud-top feature, whether warm or cold, produce much more severe weather than most other storms. These cloud-top features are also potentially indicative of increased water vapor in the stratosphere, which results in warming of Earth’s climate. Our results help us better understand storms that are frequently severe and suggest that the storms with cold features are less important to understanding stratospheric water vapor and climate change.

Thermal Biometric Features for Drunk Person Identification Using Multi-Frame Imagery

In this work, multi-frame thermal imagery of the face of a person is employed for drunk identification. Regions with almost constant temperature on the face of sober and drunk persons are thoroughly examined for their capability to discriminate intoxication. Novel image processing approaches as well as feature extraction techniques are developed to support the drunk identification procedure. These techniques constitute novel ideas in the theory of image analysis and algorithm development. Nonlinear anisotropic diffusion is employed for a light smoothing on the images before feature extraction. Feature vector extraction is based on morphological operations performed on the isothermal regions on the face. The classifier chosen to verify the drunk person discrimination capabilities of the procedure is a Support Vector Machine (SVM). Obviously, the isothermal regions on the face change their shape and size with alcohol consumption. Consequently, intoxication identification can be carried out based only on the thermal signatures of the drunk person, while the signature of the corresponding sober person is not needed. A sample of 41 participants who drank in a controlled alcohol consumption procedure was employed for creating the database, which contains 4100 thermal images. The proposed method for intoxication identification achieves a success rate of over 86% and constitutes a fast non-invasive test that can replace existing breathalyzer check up.

Thermoelastic damping suppression method of micro-beam resonators with basically constant resonant frequency

High-Q micro-beam resonators have been widely applied in communication fields such as narrowband filters, but thermoelastic damping restricts the further improvement of quality factor. Traditional method such as overall size optimization used for thermoelastic quality factor (Q TED) improvement will cause the resonant frequency of the resonator change greatly, which will not be allowed in narrowband filters. In this article, three slots are introduced into a beam resonator to greatly reduce the thermoelastic damping by rationally arranging the length ratio of the central slot and the side slot, while the resonant frequency is basically kept unchanged. The feasibility is verified by parametric finite element simulation method. The results indicate that without changing the overall size of the micro-beam resonator, the resonant frequency remains unchanged and the Q TED of the resonator can be doubled over twice both in the isothermal region and adiabatic region by placing side slots of 10% and a central slot of 30%. The proposed thermoelastic damping suppression method shows potential applicability for MEMS resonators in high-order mode of vibration.

Predicting the potential distribution of a near-extinct avian predator on the Arabian Peninsula: implications for its conservation management.

Species distribution models (SDMs) generate predicted distribution maps which can be used as effective tools for conservation purposes. The persistence of isolated populations at the margin of a large distributional area depends on local threats which may differ from those faced by the main population. Environmental predictors can indicate suitable areas for these species and, indirectly, evaluate the impact on peripheral populations due to fragmentation and isolation. The Lanner Falcon (Falco biarmicus) is an Afro-tropical and Mediterranean polytypic species considered critically endangered (CR) in Arabian Peninsula by IUCN, but a lack of published information about its distribution persists. Here, we model the distribution of the Lanner Falcon in the Arabian Peninsula using nest-site data and map its core area and their habitat suitability using a robust algorithm with good prediction accuracy even at low sample sizes (MaxEnt). The predictive map suggests a potential distribution of the Lanner Falcons that runs from north to south along the eastern coast of the Red Sea. The Terrain Roughness Index contributed the most to the breeding range model predictions (57.6%), followed by isothermality (Bio3, 15.3%). The model suggests a tendency by Lanner Falcons to occupy areas with a low terrain complexity according to their behavioural patterns and breeding strategies. In addition, this falcon is highly sensitive to climate occupying high isothermal regions in order to avoid extreme heating events. Overall, predictive models indicate a narrow range of suitable environmental conditions for breeding as well restricted favourable areas during dispersal and migration. Thus, these small and fragmented populations are more likely prone to anthropogenic factors and must be buffered against them.

Atmospheric Characterization of Hot Jupiter CoRoT-1 b Using the Wide Field Camera 3 on the Hubble Space Telescope

Exoplanet CoRoT-1 b is intriguing because we predict it to be a transitional planet between hot Jupiters (equilibrium temperatures ∼1500 K) and ultrahot Jupiters (equilibrium temperatures >2000 K). In 2012, observations of CoRoT-1 b included one primary transit and three secondary eclipses with the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) combined with the G141 grism (1.1–1.7 μm) in stare mode. We aimed to further investigate CoRoT-1 b through its secondary eclipses, producing spectrophotometric light curves corrected for charge trapping, also known as the ramp effect in time-series observations with the WFC3. We found that, when correcting for the ramp effect and using the typically discarded first orbit, we are better capable of constraining and optimizing the emission and transmission spectra. We did a grid retrieval in this transitional temperature regime and found the spectra for CoRoT-1 b to be featureless and to agree with an inverted temperature–pressure (T–P) profile. We note, however, that the contribution function for the WFC3 indicates pressures probed near 10−3 to 100 bar, which correspond to a nearly isothermal region in our T–P profile, thereby indicating that the inversion at high altitude is model-dependent. Despite no distinct features, the analysis done on CoRoT-1 b paves the way to high-precision results with stare mode spectroscopy. As a new generation of observations from the James Webb Space Telescope (JWST) approaches, CoRoT-1 b might be an interesting follow-up target because the time-series spectroscopic modes of JWST’s NIRSpec, MIRI, and NIRCam instruments will be analogous to HST’s stare mode.

Composite Aerogel Comprised of Sodium Alginate and Bentonite via Supercritical CO2 Drying: An Efficient Adsorbent for Lysozyme.

To meet the demand for the separation of specific substances, the construction of porous composite aerogels with a high specific surface area and a strong adsorption capacity is still a challenge. Herein, a sodium alginate/bentonite composite aerogel was efficiently prepared through supercritical fluid drying. The aerogel’s volume shrank less during supercritical drying, maintaining its original three-dimensional mesh structure. The resulting aerogel had a large specific surface area (445 m2/g), a low density (0.059 g/cm3), and a large pore volume (3.617 cm3/g). Due to the fixation and intercalation effects, bentonite was uniformly dispersed in the sodium alginate matrixes. The adsorption of lysozyme by the composite aerogel was evaluated, and the results showed that the optimal adsorption pH was 8 when the pH of the phosphoric acid buffer solution was between pH = 5 and 8.5. The time for adsorption to reach equilibrium was 8 h. The adsorption capacity increased with the increase in bentonite content, and when the initial concentration of lysozyme was from 0.2 to 1.2 g/L, the adsorption capacity first increased and then stabilized, and the maximum adsorption amount was 697 mg/g. The adsorption behavior was simulated in the isothermal region, and the linear correlation coefficient of Langmuir isothermal adsorption fitting was found to be 0.997. Thus, this composite aerogel with strong adsorption capacity can be used as a good alternative to enzymatic adsorbents or immobilized materials.

Thermal energy performance due to convection process of nanofluid in a porous medium due to split lid motion in a right triangular enclosure

Abstract In the current phenomena, a study is carried out for the convection process of nanofluid within the porous media enclosed in a triangular permeable cavity. The heat generation effect within the nanofluid is developed when the two heat sources are applied through the split lids. To analyse the behaviour of nanofluids and steam lines, we have considered an elliptic (cold, adiabatic, and heated)-shaped obstacle that is placed inside the cavity. Mathematical modelling is carried out through continuity, momentum equation, and energy equations in the form of a system of non-linear partial differential equations. These equations are produced after incorporating the relations of viscosity, density, shapes of nanoparticle, and thermal conductivity for nanofluids Constraints are adjusted according to the forced convection due to the upper moving wall of the cavity. Four different cases of the upper double lid-driven wall are considered. All the emerging parameters, namely Reynolds number $( {25 \le {\rm{Re}} \le 750} ),$ heat generation $( { - {{10}^4} \le Q \le 40} ),\ $ nanoparticle volume fraction $\ ( {0 \le \phi \le 0.2} )$, and Darcy number ${10^{ - 5}} \le Da \le {10^{ - 3}}$, are analysed through variation of velocities, temperature profile, isotherms, and streamlines. Various cases at the surface of the inner elliptical obstacle provide significant contributions in the variation of heat transfer rate and velocity profiles. Nanoparticles provide a considerable increase in the heat transfer rate. The Darcy number shows the substantial variation in the formation of the isothermal region. An increase in heat generation parameter Q provides an improvement in temperature distribution inside the cavity and it also caused the formation of a single isothermal region around the heated obstacle.

Numerical investigations of heat transfer and skin effect characteristics within rods located in a 48-rod Siemens reactor heated by AC

Abstract In the polysilicon reduction furnace, all the energy is supplied by the heat generation on silicon rods which are heated up by the passage of electric current. The alternating current (AC) produces the alternating magnetic field, and the oscillating magnetic field induces the corresponding eddy current in the conductor, which causes the phenomenon of skin effect. In the present paper, the coupling model of thermal and electromagnetic field for the silicon rods has been developed by coupling Joule heating equation controlled by frequency and heat dissipation (radiation, convection and reaction energy). Comparing the calculated results with the industrial data, it is found that the average relative errors of the current intensities of the inner, middle and outer ring silicon rods are 7.55%, 5.55% and 7.43%, respectively, indicating that the model calculation results are accurate and can be used to accurately analyze the thermoelectric behavior of the silicon rods. Based on the Joule heating process of silicon rods in a 48-rod polysilicon reduction furnace, the influences of AC frequency on temperature and current density profile within rod arranged in different rings have been studied. The interesting results show that the high frequency current sources can generate an even temperature profile and an isothermal region inside the rod can be obtained when the RF increases to 10. Therefore, utilizing the high frequency current sources can decrease the temperature gradient within silicon rod effectively, which provides a method for producing larger diameter silicon rod. Furthermore, the voltage-current curves of low frequency (50 Hz) and high frequency (10 kHz and 50 kHz) can be predicted by the present Joule heating model, at the same time, a hybrid heating process of low frequency and high frequency is proposed.

Counter-flow for stabilization of microfluidic thermal reactors: Experimental and numerical study

This work presents a novel counter-flow design for stabilizing microfluidic thermal reactors. In such devices, the substrate material is held in an unchanging thermal state while any combination of isothermal and gradient regions may be enacted on the surface region, all of which are stable in time. When such a state is achieved, precise control of the temporal temperature of the moving liquid is possible. The aim of this work is to establish a linear thermal gradient within the microfluidic reactor under a no-flow condition and to maintain the temperature profile for a broad range of flow conditions. Experimental results show that counter-flow will have a powerful stabilizing effect: isothermal regions remain isothermal, and gradient regions linearize. Distortions due to both external and internal convection/advection are reduced by several orders of magnitude. Counter-flow and direct-flow glass composite devices with different interlayer materials (silicon, quartz, and glass) were fabricated to investigate the role of interlayer thermal conductivity. The best performance was achieved for a counter-flow case with silicon interlayer for which a wide and stable linear thermal gradient (1 K/mm) was established, enabling ramp rates of up to 143 K/s. 3-D numerical models are used to predict the in-channel fluid temperature, its relation with the device surface temperature, and to evaluate the performance of the devices under other heating configurations.

Influence of the Seasonal Thermocline on the Vertical Distribution of Larval Fish Assemblages Associated with Atlantic Bluefin Tuna Spawning Grounds

Temperature is often an important variable influencing the vertical position of fish larvae in the water column. The same species may show different vertical distributions in areas with a strong near-surface seasonal thermocline compared to isothermal near-surface regions. In areas with a strong surface thermocline, tuna larvae show a significant preference for the near-surface warmer layers. Little is known regarding larval tuna vertical distribution in isothermal waters and on the vertical distribution of the associated larval fish assemblages. We conducted vertical stratified sampling using the same methodology and fishing device (MOCNESS) in the two major spawning areas of Atlantic bluefin tuna (BFT): western Mediterranean Sea (MED), characterized by a surface thermocline, and the Gulf of Mexico (GOM) which lacks thermal stratification. Tuna larvae occupied the upper 30 m in both areas, but the average larval depth distribution was consistently deeper in the GOM. In the MED, vertical distribution of larval fish assemblages was explained by temperature, and species such as BFT, Thunnus alalunga, and Ceratoscopelus maderensis, among others, coexist above the thermocline and are separated from species such as Cyclothone braueri and Hygophum spp. (found below the thermocline). In the GOM, the environmental correlates of the vertical distribution of the larvae were salinity and fluorescence. Mesopelagic taxa such as Ceratoscopelus spp. and Cyclothone spp., among others, had a shallower average distribution than Lampanyctus spp., Hygophum spp., and Myctophum spp.

Quality Factor Extraction and Enhancement Across Temperature in Ring Resonators

This work demonstrates that thin slots strategically placed in MEMS ring resonators are able to enhance the quality factor (Q) of the device operated in a wineglass mode in the isothermal region. The devices are optimized using COMSOL for an increased Q through increased slot size, using the Zener curve as a comparative baseline. These parts are fabricated and encapsulated in an ultra-clean environment, and tested in various temperature and pressure conditions to directly measure changes in anchor, gas, and thermoelastic dissipation across temperature. [2020-0156]

Numerical Analysis of Stress and Temperature Fields in a Composite Stratum Based on a New Method of Shield Construction for Safety and Environmental Protection.

Safety and environmental protection are key issues in shield construction. Due to wear, the cutter of a shield machine must be changed after a period of excavation. In order to realize the tool change operation of a shield machine at atmospheric pressure, a method of cutter head freezing of the shield machine is described in this paper. The finite element simulation method is used to analyze the construction of a shield machine with a frozen cutter head in a composite stratum. For a composite stratum with uneven hard and soft layers in a ratio of 1:1, the stress and temperature fields are analyzed, and the stress change around the hob is recorded. Through numerical simulation, the change of the temperature field around the shield machine is determined in real time. As time goes on, the temperature around the shield machine decreases, and the frozen range expands. When the temperature field in a specific point reaches a critical value, the temperature at that point will remain constant, and the stress field around the cutter head will also tend to become stable. The isothermal region of the soil presents an annular distribution, and the final temperature tends to be stable and gradually increase as the distance from the frozen cutter head increases. The final temperature of the monitoring area reaches a stable value corresponding to −26.5 °C, the axial depth of the frozen wall is more than 2.5 m, the minimum frozen radius is 3.2 m, the stress distribution around the cutter head is unbalanced, the maximum stress is measured in the hard rock layer, and the stress around the cutter head at the hob level indicates that tool change is necessary. Compared with the traditional method, the construction method of a frozen cutter head is more effective and more environmentally friendly. Further research will allow a broad application of this method in shield excavation in a composite stratum.

Probing CO and N2 Snow Surfaces in Protoplanetary Disks with N2H+ Emission

Abstract Snowlines of major volatiles regulate the gas and solid C/N/O ratios in the planet-forming midplanes of protoplanetary disks. Snow surfaces are the 2D extensions of snowlines in the outer disk regions, where radiative heating results in an increasing temperature with disk height. CO and N2 are two of the most abundant carriers of C, N, and O. N2H+ can be used to probe the snow surfaces of both molecules, because it is destroyed by CO and formed from N2. Here we present Atacama Large Millimeter/submillimeter Array (ALMA) observations of N2H+ at ∼0.″2–0.″4 resolution in the disks around LkCa 15, GM Aur, DM Tau, V4046 Sgr, AS 209, and IM Lup. We find two distinctive emission morphologies: N2H+ is either present in a bright, narrow ring surrounded by extended tenuous emission, or in a broad ring. These emission patterns can be explained by two different kinds of vertical temperature structures. Bright, narrow N2H+ rings are expected in disks with a thick Vertically Isothermal Region above the Midplane (VIRaM) layer (LkCa 15, GM Aur, DM Tau) where the N2H+ emission peaks between the CO and N2 snowlines. Broad N2H+ rings come from disks with a thin VIRaM layer (V4046 Sgr, AS 209, IM Lup). We use a simple model to extract the first sets of CO and N2 snowline pairs and corresponding freeze-out temperatures toward the disks with a thick VIRaM layer. The results reveal a range of N2 and CO snowline radii toward stars of similar spectral type, demonstrating the need for empirically determined snowlines in disks.

Effects of the Isothermal Region in Protoplanetary Disks and the Protostar Irradiation on the Disk Instability Model for Giant Planet Formation

Abstract We construct an analytical model of gravitationally unstable protoplanetary disks consisting of three regions: the inner region where the internal dissipation dominates the heating, the intermediate region where the central protostar irradiation dominates, and the outer region where background irradiation dominates. We use this analytical model and an evolutionary numerical model of protoplanetary disks to calculate the cooling time and find out the location of the isothermal region. We investigate the effects of the isothermal region on the disk instability model for giant planet formation. We find that the fragmentation region found in previous studies is contained in the isothermal region of a disk. In this case, the cooling time criterion is not applicable for fragmentation. Therefore, the constraint on the disk instability model caused by the cooling time criterion should be relieved. The viability of the disk instability model is improved. When the isothermal region is considered, the inner boundary of the fragmentation region is extended inward to ∼20 au. We also show that if the contribution of the protostar irradiation to the disk surface temperature can be included in the cooling rate, the fragmentation region defined by the cooling time criterion can be extended inward to ∼26 au. We find that a disk tends to be isothermal in the region where the cooling time criterion is satisfied. We also find that at the later stage of disk instability, the inner boundary of the fragmentation region is determined by the inner boundary of the gravitationally unstable region.