Thermal Equilibrium Temperature Research Articles

Transient Thermal Analysis Model of Damaged Bearing Considering Thermo-Solid Coupling Effect.

As one of the important parameters of bearing operation, temperature is a key metric to diagnose the state of service of a bearing. However, there are still some shortcomings in the study of the temperature variation law for damaged bearings. In this paper, according to the structural characteristics of bearings, the influence law of thermal-solid coupling effect on bearing structure is considered, and a novel transient temperature analysis model of damaged bearings is established. First, a quasi-static analysis of the bearing is performed to obtain the variation laws of the key parameters of the bearing under thermal expansion. Then, the load variation law of the bearing under the condition of damage is discussed, and the heat generation and heat transfer of the damaged bearing during operation are studied. Based on the thermal grid method, a transient temperature analysis model of the damaged bearing is developed. Finally, the model is tested experimentally and the influence of the rotate speed and load on the bearing temperature variation is analyzed. The results show that the established model can effectively predict the temperature variation and thermal equilibrium temperature of damaged bearings.

Halloysite-based aerogels by bidirectional freezing with mechanical properties, thermal insulation and flame retardancy

Halloysite (Hal) is a natural nanotubular clay mineral with the characteristics of low price and easy availability. The aerogels prepared by Hal are low thermal conductivities, good thermal stabilities and low flammability, which have great application prospects in the field of thermal insulation with flame retardancy. However, they typically suffer from inferior mechanical property and difficulty of mechanically resilient or flexible. Herein, aerogels with anisotropic mechanical properties were prepared by bidirectionally freezing aqueous suspensions of Hal with a small proportion of chitosan (CS). The directionally aligned porous structure gave the aerogels prominent strength in the direction of lamellar orientation, and superelasticity in the vertical direction. The Hal-based aerogels showed good performance in the combination of thermal insulation and flame retardancy. The thermal equilibrium temperatures of Hal/CS aerogels at 50 °C and 100 °C are 27.5 °C and 35.2 °C, respectively. They also remained unscathed after 180 s of burning in a candle flame. The present study provided a versatile method for design and fabrication aerogels for high-performance thermal insulation materials and had significance in the high-value utilization of Hal mineral resources.

New wellbore temperature control design for preventing failure and poor performance of logging tools in high pressure – high temperature wells

Failure and poor performance of logging tools in high pressure-high temperature wells; the associated technical consequences and the resultant high cost of logging operations are recurrent problems in the oil & gas industry worldwide. The aforesaid prompted this work to invent the “New Wellbore Temperature Control Design” for protection of logging tools against high bottom-hole temperatures. It hinges on the novel concept of thermal drainage radius and the temperature-drop effect of chilled oil-based mud to reduce bottom-hole temperature prior to logging. The methods applied include laboratory testing, mathematical modeling and design. The novel concept of “thermal drainage radius” quantified the radial extent of temperature-drop effect in the formation, away from the wellbore. Novel mathematical models were also invented. Laboratory results showed that the formation temperature-drop from bottom-hole temperature to thermal equilibrium temperature increased with bottom-hole temperature per chilled oil-based mud. The temperature-drop duration and temperature-rise duration increased with bottom-hole temperature per chilled oil-based mud. The temperature-rise duration increased with decrease in the temperature of the chilled oil-based mud per bottom-hole temperature. Job design results showed that when placed in the zone of interest in the wellbore the heat energy absorbed increased with quantity of the chilled oil based mud but the temperature rise duration decreased with increasing heat transfer rate from the formation and vice versa. Furthermore, results revealed that the higher the thermal conductivity of the formation, the longer the thermal drainage radius and vice versa. The logging operation should commence after placement of the chilled oil-based mud in the zone of interest (no circulation of the chilled oil-based mud) and be completed before the end of the temperature-rise duration. Oil-based mud is cheap and available in every country unlike the expensive vacuum flasks and thermal insulating jackets currently used for protecting logging tools against high temperature. The new wellbore temperature control design has global applicability.

Metal-Dielectric Thin Film Structure Metamaterial for Obtaining High Equilibrium Temperature Under Direct Solar Optical Radiation

Metal-dielectric thin film structure metamaterials can be designed to absorb solar light radiation over a wide spectral band. By using Kirchhoff's law, metal-dielectric thin film metamaterials are investigated for obtaining high equilibrium temperatures under direct solar light radiation at normal incidence. It is found that among all metal-dielectric thin film structures, the dielectric layer on metal (DLM) surface structure is the optimal structure for producing the highest thermal equilibrium temperature under direct solar optical radiation.

Numerical Analysis and Optimization of Heat Dissipation of Mechanical Automation Equipment Based on Thermal Model

If the internal heat of mechanical automation equipment exceeds or does not reach the thermal equilibrium temperature range, it will adversely affect the operational reliability, environmental protection and production efficiency of the equipment. To tackle the problem, there has been some research on the internal heat dissipation of mechanical automation equipment, but mostly of the existing studies have simply aimed to change the parameters of the cooling system, and little has been done on the loading process and implementation details of the thermal model. Therefore, this paper provides numerical analysis and optimization of the space heat dissipation of mechanical automation equipment based on a thermal model. First, the heat dissipation mechanism of mechanical automation equipment was elaborated in detail, and the structure of the cooling system for mechanical automation equipment was given. Then, a spatial thermal model of mechanical automation equipment was established, and the heat dissipation design process of mechanical automation equipment was given. After that, the differences between the natural convection heat dissipation in large space and that in confined space inside mechanical automation equipment were explored. The experimental results verified the effectiveness of the numerical simulation model proposed in this paper.

Evaluation of Surfactants on Graphene Dispersion and Thermal Performance for Heat Dissipation Coating.

With the development of thin and high-power electronic devices, heat dissipation has become an important and urgent issue in thermal management. In this study, a water-based epoxy was used as a polymer matrix to prepare heat dissipation coatings utilizing low volatile organic compounds, which were environmentally friendly and had a high heat-dissipating performance. Graphene flakes, multi-walled carbon nanotubes and aluminum oxide particles were used as fillers for preparing the heat dissipation coating. The graphene flakes and multi-walled carbon nanotubes were dispersed in a water-based epoxy by adding sodium dihexyl sulfosuccinate and poly (dimethyldiallylammonium chloride). These two surfactants were combined as a dispersant to improve the dispersibility of the carbon nanomaterials in the water-based epoxy. The synergistic effect of the well-dispersed fillers improved the heat-dissipating performance. The experimental results show that the infrared emissivity of the heat dissipation film was 0.96 after filling 30 wt% aluminum oxide particles, 2 wt% graphene flakes and 2 wt% multi-walled carbon nanotubes into a water-based epoxy. The heat dissipation film reduced the thermal equilibrium temperature of the bare copper panel by 17.8 °C under a heating power of 10 W. The film was applied in a heat dissipation test on a 15 W LED bulb, and the thermal equilibrium temperature was reduced by 21.3 °C. The results demonstrate that the carbon nanomaterial-based heat dissipation coating with a water-based epoxy could significantly reduce the thermal equilibrium temperature, giving a high potential for the application of thermal management.

A Note on Holevo Quantity of SU(2)-invariant States

The Holevo quantity and the SU(2)-invariant states have particular importance in quantum information processing. We calculate analytically the Holevo quantity for bipartite systems composed of spin-j and spin-\(\frac {1}{2}\) subsystems with SU(2) symmetry, when the projective measurements are performed on the spin-\(\frac {1}{2}\) subsystem. The relations among the Holevo quantity, the maximal values of the Holevo quantity and the states are analyzed in detail. In particular, we show that the Holevo quantity increases in the parameter region F < Fd and decreases in region F > Fd when j increases, where F is function of temperature in thermal equilibrium and Fd = j/(2j + 1), and the maximum value of the Holevo quantity is attained at F = 1 for all j. Moreover, when the dimension of system increases, the maximal value of the Holevo quantity decreases.

Quantum simulation of interacting fermions

Fermions are basic building blocks in the standard model. Interactions among these elementary particles determine how they assemble and consequently form various states of matter in our nature. Simulating fermionic degrees of freedom is also a central problem in condensed matter physics and quantum chemistry, which is crucial to understanding high-temperature superconductivity, quantum magnetism and molecular structure and functionality. However, simulating interacting fermions by classical computing generically face the minus sign problem, encountering the exponential computation complexity. Ultracold atoms provide an ideal experimental platform for quantum simulation of interacting fermions. This highly-controllable system enables the realizing of nontrivial fermionic models, by which the physical properties of the models can be obtained by measurements in experiment. This deepens our understanding of related physical mechanisms and helps determine the key parameters. In recent years, there have been versatile experimental studies on quantum ground state physics, finite temperature thermal equilibrium, and quantum many-body dynamics, in fermionic quantum simulation systems. Quantum simulation offers an access to the physical problems that are intractable on the classical computer, including studying macroscopic quantum phenomena and microscopic physical mechanisms, which demonstrates the quantum advantages of controllable quantum systems. This paper briefly introduces the model of interacting fermions describing the quantum states of matter in such a system. Then we discuss various states of matter, which can arise in interacting fermionic quantum systems, including Cooper pair superfluids and density-wave orders. These exotic quantum states play important roles in describing high-temperature superconductivity and quantum magnetism, but their simulations on the classical computers have exponentially computational cost. Related researches on quantum simulation of interacting fermions in determining the phase diagrams and equation of states reflect the quantum advantage of such systems.

Investigation of the Evolution of Be, Ni, Mo, and W Dust Grains in Fusion Plasma

In this work, evolution of dust grains from different materials used in fusion energy installations was studied and a model was constructed that describes the generation of dust. The model accounts for the thermochemical, electrical, and other properties of the materials of the fusion reactor wall. It was shown that the dominant process that leads to the decrease in dust grain mass is the thermal evaporation, which is determined by the saturated vapor pressure at thermal equilibrium temperature. Estimates of the lifetime of dust grains from different materials were obtained depending on plasma parameters. The findings of this work can be useful for estimates of the length of penetration of dust grains into the reactor. The difference in the dynamics of particles from light and heavy elements was shown. Out of the four elements under study (Be, Ni, Mo, and W), nickel grains demonstrate the highest penetrating ability due to their long lifetime and moderate weight.

Interpretable Machine Learning for the Thermodynamic Phases in 2D XY Model

We study the interpretable machine learning of thermodynamic phases in the two-dimensional classical XY model. We find that the neural network can accurately classify the different phases. We utilize the anchor algorithm to explain the mechanism of classification during the machine learning. The prediction based on the anchor is very close to that according to the raw spin configurations. With the help of linearity measurement, we find that the neural network shows strong nonlinearity when classifies the low temperature phase and strong linearity when classifies the high temperature thermal equilibrium phase, which means that the machine has strong adaptability to the thermodynamic fluctuation. The interpretable machine learning can be applied to other classical or quantum many-body systems.

Heat Transfer and Temperature Characteristics of a Working Digital Camera.

Digital cameras represented by industrial cameras are widely used as image acquisition sensors in the field of image-based mechanics measurement, and their thermal effect inevitably induces thermal-induced errors of the mechanics measurement. To deeply understand the errors, the research for digital camera’s thermal effect is necessary. This study systematically investigated the heat transfer processes and temperature characteristics of a working digital camera. Concretely, based on the temperature distribution of a typical working digital camera, the heat transfer of the working digital camera was investigated, and a model describing the temperature variation and distribution was presented and verified experimentally. With this model, the thermal equilibrium time and thermal equilibrium temperature of the camera system were calculated. Then, the influences of thermal parameters of digital camera and environmental temperature on the temperature characteristics of working digital camera were simulated and experimentally investigated. The theory analysis and experimental results demonstrate that the presented model can accurately describe the temperature characteristics and further calculate the thermal equilibrium state of working digital camera, all of which contribute to guiding mechanics measurement and thermal design based on such camera sensors.

Migration and phase change study of leaking molten salt in tank foundation material

Molten salt is widely used as a heat transfer and thermal storage medium in concentrated solar power plants. This paper mainly focuses on the migration and phase change characteristics of molten salt leaking from a high-temperature storage tank to the thermal-steady porous foundation materials. The effects of the different conditions, including material structure, leakage pore size, operating temperature and leaking molten salt mass, are investigated via the self-designed experimental system that models the actual leaking process. Results show that the molten salt migrates rapidly in the porous foundation material during the leaking process and begins to solidify on the bottom, hindering molten salt from further flowing down. After molten salt leakage, the thermal equilibrium temperature of foundation material increases. It is found that the molten salt migration depth distinctly decreases with the smaller porosity of the porous material. When the leakage pore size diminishes or the operating temperature increases, the migration depth obviously increases, while the migration diameter decreases. Nevertheless, within a certain range, the leaking molten salt mass has some effect on the migration diameter but has little effect on the migration depth. These results provide quantitative references for the pollution control and disposition of molten salt leakage accidents.

SpitzerSpace Telescope observations of bilobate comet 8P/Tuttle

Context.Comet 8P/Tuttle is a nearly isotropic comet whose physical properties are poorly known and might be different from those of ecliptic comets owing to their different origin. Two independent observations have shown that 8P/Tuttle has a bilobate nucleus.Aims.Our goal is to determine the physical properties of the nucleus (size, shape, thermal inertia, and albedo) and coma (water and dust) of 8P/Tuttle.Methods.We observed the inner coma of 8P/Tuttle with the infrared spectrograph and the infrared camera of theSpitzerSpace Telescope. We obtained one spectrum (5–40μm) on 2 November 2007 and a set of 19 images at 24μm on 22–23 June 2008 sampling the rotational period of the nucleus. The data were interpreted using thermal models for the nucleus and the dust coma, and we considered two possible shape models of the nucleus derived fromHubbleSpace Telescope visible and Arecibo radar observations.Results.We favor a model for the nucleus shape that is composed of two contact spheres with respective radii of 2.7 ± 0.1 km and 1.1 ± 0.1 km and a pole orientation with RA = 285 ± 12° and Dec = +20 ± 5°. The thermal inertia of the nucleus lies in the range 0–100 J K−1m−2s−1∕2and theR-band geometric albedo is 0.042 ± 0.008. The water production rate amounts to 1.1 ± 0.2 × 1028molecules s−1at 1.6 AU from the Sun pre-perihelion, which corresponds to an active fraction of ≈9%. At the same distance, theɛfρquantity amounts to 310 ± 34 cm, and it reaches 325 ± 36 cm at 2.2 AU post-perihelion. The dust grain temperature is estimated to be 258 ± 10 K, which is 37 K higher than the thermal equilibrium temperature at 1.6 AU. This indicates that the dust grains that contribute to the thermal infrared flux have a typical size of ≈10μm. The dust spectrum exhibits broad emission around 10μm (1.5σconfidence level) and 18μm (5σconfidence level) that we attribute to amorphous pyroxene.

Quantum-Memory-Assisted Entropic Uncertainty in Two-Qubit Heisenberg XX Spin Chain Model

We have studied the quantum-memory-assisted entropic uncertainty relation (QMA-EUR) in two-qubit Heisenberg XX spin chain model with Dzyaloshinskii-Moriya (DM) interaction and external magnetic field. It shows that the DM interaction |Dz| and the spin interaction |J| can efficiently suppress the entropic uncertainty of Pauli observables (σx and σz), even make the entropic uncertainty close to zero. The external magnetic field that acts on the two spin sites along z-direction leads to two different effects on entropic uncertainty under the different thermal equilibrium temperature. Furthermore, the dynamic features of entropic uncertainty with DM interactions and spin interactions under intrinsic decoherence condition are investigated. We find that when the Werner state acts as initial state, the larger purity parameter can yield smaller value of entropic uncertainty at the initial evolution time. And the entropic uncertainty of the XX model with DM interaction in z-direction is independent of external magnetic field ${\mathscr{B}}$. We also verified the entropic uncertainty is anti-correlated with the quantum discord of the spin chain system in full evolution time. Meanwhile, DM interactions and the spin interactions can make the evolutions of entropic uncertainty and its lower bound oscillate with evolution time, and the increasing of strengthen of DM interactions and spin interactions can lead to an increasing of oscillation frequency, and the variations of amplitudes are different for these two kinds of interactions. Especially, when the strength of spin interaction is larger, the trends of entropic uncertainty and its lower bound can be changed from oscillation to smoothness, which can be regarded as there is no DM interaction.

Enhanced Photothermal Conversion by Hot-Electron Effect in Ultrablack Carbon Aerogel for Solar Steam Generation.

Ecofriendly, highly effective, and low-cost solar steam generation has great potential in the applications of power generation, seawater desalination, and industry wastewater treatment. Solar steam generation requires an evaporator that has strong light absorption over a wide-frequency band (200-3000 nm), high photothermal conversion efficiency, and good thermal insulation to avoid excessive heat loss. Herein, foam-strengthened ultrablack carbon aerogels (CAs) with micropores, mesopores, and macropores were prepared using freeze drying. The small-size conductor effect in ultrablack CAs could increase the surface electron concentration, leading to the increase of light absorption and ultimately enhancing photothermal conversion efficiency. Consequently, under 1 sun illumination, dried CA-5 exhibited a fast temperature rise rate and the highest thermal equilibrium temperature of 87.6 °C among CAs, the equilibrium temperature is 20.8 °C higher than that of the foam. Besides, CA-5 exhibited a high water evaporation rate of 1.29 kg m-2 h-1 under only 1 sun illumination. To further increase the hot-electron effect, CO2 activation was implemented. The highest water evaporation rate among activated CAs (ACAs) was 1.37 kg m-2 h-1, which is about 2.85 times higher than that of pure water. The highest water evaporation efficiency was 87.51%, which is better than most of the previously reported evaporation efficiencies. Besides the hot-electron enhancement effect, ACAs with thermal insulation, mechanical strength, and thermal stability show great potential for producing fresh water from seawater, industrial wastewater, and even concentrated acidic or alkaline solutions.

Adiabatic Thermal Radiation Pumps for Thermal Photonics.

We control the direction and magnitude of thermal radiation, between two bodies at equal temperature (in thermal equilibrium), by invoking the concept of adiabatic pumping. Specifically, within a resonant near-field electromagnetic heat transfer framework, we utilize an instantaneous scattering matrix approach to unveil the critical role of wave interference in radiative heat transfer. We find that appropriately designed adiabatic pumping cycling near diabolic singularities can dramatically enhance the efficiency of the directional energy transfer. We confirm our results using a realistic electronic circuit setup.

Modeling and Control of A High Speed On/Off Valve Actuator

Accurate electromagnetic force control in a high speed on/off valve actuator (HSVA) can improve the performance of a vehicle braking system, and an accurate theoretical model is the key to smoothly controlling the high speed on/off valve. Therefore, a nonlinear model of an HSVA is proposed in this paper. Three subsystems are modeled as a spring/mass/damper system, a nonlinear resistor/inductor system and a multiwall heat transfer system, respectively. Then, a sliding-model controller combined with a sliding-model observer is designed to adjust the electromagnetic force for an accurate HSVA state control, taking the effect of the coil heating into account. The feasibility of the three submodels and the sliding-model controller are verified by comparing the simulation results with the experimental results obtained on a test bench. Our study shows that the three subsystems are coupled to one another through resistance, displacement, and temperature. When the excitation voltage exceeds 9 V, the coil temperature can reach more than 150 degrees Celsius within 300 s, and the electromagnetic force decreases by approximately 30 %. However, by applying the above control strategy, the electromagnetic force can also be stable, fluctuating within 5 % even if the temperature of the coil rises to the thermal equilibrium temperature.

Quantifying methane vibrational and rotational temperature with Raman scattering

This work describes the theoretical basis and implementation of the measurement of vibrational (Tvib) and rotational (Trot) temperatures in CH4 by fitting spontaneous Raman scattering spectra in the Pentad region. This method could be applied for thermal equilibrium temperature measurements applications, e.g. in combustion, or vibrational-rotational non-equilibrium applications, such as in plasma chemistry.The method of calculating these temperatures is validated against known temperature thermal equilibrium spectra up to 860 K from published data, giving an estimated relative error of 10%. This demonstrates that both the calculated stick spectrum and the algorithm to determine Tvib and Trot for CH4 is robust to 860 K, but we expect it is valid to 1500 K. Additionally, a number of non-equilibrium spectra generated with a pulsed microwave plasma are fitted to find Tvib and Trot, further demonstrating the applicability of this method in fitting non-equilibrium spectra.

Excellent Temperature-Control Based on Reversible Thermochromic Materials for Light-Driven Phase Change Materials System

Light-driven phase change materials (PCMs) have received significant attention due to their capacity to convert visible light into thermal energy, storing it as latent heat. However, continuous photo-thermal conversion can cause the PCMs to reach high thermal equilibrium temperatures after phase transition. In our study, a novel light-driven phase change material system with temperature-control properties was constructed using a thermochromic compound. Thermochromic phase change materials (TC-PCMs) were prepared by introducing 2-anilino-6-dibutylamino-3-methylfluoran (ODB-2) and bisphenol A (BPA) into 1-hexadecanol (1-HD) in various proportions. Photo-thermal conversion performance was investigated with solar radiation (low power of 0.09 W/cm2) and a xenon lamp (at a high power of 0.14 W/cm2). The TC-PCMs showed a low equilibrium temperature due to variations in absorbance. Specifically, the temperature of TC-PCM180 (ODB-2, bisphenol A and 1-HD ratio 1:2:180) could stabilize at 54 °C approximately. TC-PCMs exhibited reversibility and repeatability after 20 irradiation and cooling cycles.

On the effective spectral emissivity of clear skies and the radiative cooling potential of selectively designed materials

Thermophotonic devices are optically designed to be spectrally selective in order to reject heat to outer space through atmospheric windows of low thermal absorption. The determination of thermal equilibrium temperatures for thermophotonic devices requires the knowledge of the effective spectral emissivity of the sky. In this work, individual contributions of participating gases and aerosols to the spectral values of the sky emissivity are analyzed in the entire infrared spectrum as well as in seven distinct bands for which water vapor either dominates or is virtually transparent to infrared radiation. We also propose high-fidelity correlations for the effective sky emissivity as functions of the normalized ambient partial pressure of water vapor (pw) for both broadband and for the seven spectral bands. The correlations are derived using a combination of ground experimental data, high resolution spectral data for the main atmospheric constituents and spectral models to reconstruct the spectral distribution of infrared thermal radiation from the atmosphere to the ground. These results enable direct calculation of the equilibrium temperature and cooling efficiency of radiative cooling devices in terms of meteorological conditions observed at the surface level. For hot and dry conditions, the passive radiative coolers have a cooling potential of 150.8 W m−2 while for humid conditions, the coolers are mostly ineffective.