Thermal Quantities Research Articles

Preliminary Experiments While Designing a Cold Crucible for Metal Melting

This article deals with issues arising during the design and production of a cold crucible (CC) for melting metals and alloys using electromagnetic induction. The article deals particularly with the results from tests and numerical simulations for designing the CC. The heat fluxes from different metals and their alloys to two different CCs and one calorimeter were measured during the tests. The required magnetohydrodynamic effects on the melted load were verified, and related (independent) electrical and thermal quantities were measured. The dependent electric parameters (R, L, Z) were measured on the inductor and on the primary side of the high frequency transformer. The experiments were numerically simulated first, and the experimental and simulated results were then compared. The final part of the article contains the final design of the CC. The final CC was tested for the transfer of energy from the inductor into a load placed inside the CC and the required magnetohydrodynamic effects on the melted load inside the CC were partly verified too.

Phenomenological Mean-Field Theory of Metamagnetism in Heavy Fermions

Metamagnetism observed in some heavy fermion compounds is an intriguing phenomena. To understand this phenomena, we explore the phenomenological mean-field theory for heavy fermion systems without microscopic mechanism. We write an extension of the Landau-like free energy density with the Bragg-Williams entropy. By minimising this free energy density with respect to the sub-lattice magnetizations, we can obtain thermal equilibrium quantities. As examples, the magnetic behaviors of CeRu2Si2(the metamagnetism with crossover) and CeTiGe (the first order metamagnetism) are explained qualitatively, where the scaling hypothesis is used to consult with experimental data under the constant pressure condition.

Thermoelastic Vibration of Temperature-Dependent Nanobeams Due to Rectified Sine Wave Heating—A State Space Approach

In this study, the second type of Green and Naghdi's thermoelasticity theory is applied to present the vibration of a nanobeam subjected to rectified sine wave heating based upon the nonlocal thermoelasticity theory. Both Young's modulus and thermal conductivity are considered to be linear functions of the temperature. The Laplace transform domain is adopted to solve the governing partial differential equations using the state space approach. Numerical computations are carried out using the inverse of Laplace transforms. The effects of nonlocal parameter and angular frequency on the thermal vibration quantities are discussed. The results of all quantities are illustrated graphically and investigated.

Simple Formulas to Predict Center and Mean Temperatures and Total Heat Transfer in Regular Configurations With Surface Temperature Under Small- and Large-Time Conditions

Simple formulas for the prediction of three important thermal quantities, the center temperature, the mean temperature, and the total heat transfer in regular configurations (large plane wall, long cylinder, and sphere) cooled/heated with prescribed uniform surface temperature during “small time,” are addressed in the present paper. Two immediate engineering applications deal with quenching of metals and sterilization of canned food. The simple formulas emanate from the truncated one term series of the supplementary infinite series at small time. The small time subregion has been traditionally characterized in the heat conduction literature by the dimensionless time or Fourier number τ< 0.24 in the large plane wall, τ< 0.21 in the long cylinder, and τ< 0.19 in the sphere. Excellent agreement between the obtained simple formulas and the traditional solutions (namely the exact, analytical infinite series for “all time”) are attained for the center temperature, mean temperature, and total heat transfer in the large plane wall, long cylinder, and sphere.

Structural, elastic, anisotropic and thermodynamic properties of the caged intermetallics RETi2Al20 (RE= La, Ce, Gd and Ho): A first-principles study

First principles method were used to explore the structural stability, mechanical properties, anisotropic properties and thermodynamic properties of RETi2Al20 (RE = La, Ce, Gd and Ho) intermetallics. The calculated formation enthalpy and phonon frequencies indicate that RETi2Al20 intermetallics are satisfied with the structural stability. The elastic constants Cijs and elastic moduli (B, G, E) confirm that RETi2Al20 intermetallics possess the better elastic properties than pure Al. The values of B/G demonstrate that RETi2Al20 intermetallics are all brittle materials. The anisotropy in elastic constants, Young's modulus and acoustic velocities indicate that RETi2Al20 intermetallics are anisotropic and the degree of anisotropy of four compounds are larger than that of pure Al. Importantly, the calculated thermal quantities demonstrate that these RETi2Al20 intermetallics possess the better thermo-physical properties at high temperature.

Testing the performance of a prototype thermal energy storage tank working with organic phase change material for space heating application conditions

A prototype Latent Heat Thermal Energy Storage (LHTES) unit has been designed, constructed, and experimentally analysed for its thermal storage performance under different operational conditions considering heating application and exploiting solar and geothermal energy. The system consists of a rectangular tank filled with Phase Change Material (PCM) and a finned tube staggered Heat Exchanger (HE) while water is used as Heat Transfer Fluid (HTF). Different HTF inlet temperatures and flow rates were tested to find out their effects on LHTES performance. Thermal quantities such as HTF outlet temperature, heat transfer rate, stored energy, were evaluated as a function of the conditions studied. Two commercial organic PCMs were tested A44 and A46. Results indicate that A44 is more efficient during the charging period, taking into account the two energy sources, solar and heat pump. During the discharging process, it exhibits higher storage capacity than A46. Concluding, the developed methodology can be applied to study different PCMs and building applications.

The Problem of Identifying Possible Signals of Extra-Terrestrial Civilizations in the Framework of the Information-Based Method

Aims: The purpose of this work is to formulate the requirements for future methods of searching for extra-terrestrial civilizations by use of the concepts of information theory and the theoretically grounded method. Methodology: To realize it, the number of dimensionless criteria contained in the International System of Units (SI) has been calculated. This value, without additional assumptions, allows us to present a formula for calculating the comparative uncertainty of the model of any physical phenomenon. Based on these formulas, the magnitude of the inevitable threshold of misunderstanding of two civilizations in the universe is determined. Results: New theoretical recommendations for choosing the most effective methods to search the techno signatures of extra-terrestrial civilizations are formulated. Conclusion: Using the calculated amount of information embedded in the model, we showed that the most promising methods for finding potential residents in the Universe should combine frequency radiation with thermal or electromagnetic quantities.

Contribution of open-air concrete slabs to the heat stress on working mano

The objective of this work was to evaluate the heat stress on workers of the construction industry on open-air concrete slabs in the city of Campinas, São Paulo, Brazil. Brazilian NR-15 provides a method for evaluating the heat stress to which a person is exposed using the WBGT (wet bulb globe temperature) index, prescribing rest pauses according to the type of activity. The methodology included measurements of environmental thermal variables and atmospheric quantities, followed by the calculation of the WBGT index. Data was collected at 12 different locations from August/2017 to March/2018, covering three diferent seasons. Results show that moderate and heavy activities on concrete slabs require pauses in every month, except in August.

First-principles investigations on structural stability, mechanical, and thermodynamic properties of LaT2Al20 (T = Ti, V, Cr, Nb, and Ta) intermetallic cage compounds** Project supported by the Program for Ph. D Start-up Fund of Liaoning Province of China (Grant No. 201601161).

First principles calculations were used to explore the structural stability, mechanical properties, and thermodynamic properties of LaT2Al20 (T = Ti, V, Cr, Nb, and Ta) intermetallics. The calculated formation enthalpy and phonon frequencies indicate that LaT2Al20 intermetallics exhibit the structural stability. The elastic moduli (B, G, E, and Hv) indicate that these intermetallics possess the better elastic properties than pure Al. The values of Poisson’s ratio v and B/G demonstrate that LaT2Al20 intermetallics are all brittle materials. The anisotropy of elasticity and Young’s modulus (three- and two-dimensional figures) indicate that LaT2Al20 compounds are anisotropic. Importantly, the calculated thermal quantities demonstrate that LaT2Al20 intermetallics possess the better thermal physical properties than pure Al at high temperatures.

First-principles investigation of the mechanical, anisotropic and thermodynamic properties of RET2Al20 (RE=La, Ce, Gd, T=Ti, V) intermetallics

First principles calculations were used to explore the mechanical properties, anisotropic properties and thermodynamic properties of RET2Al20 (RE = La, Ce, Gd, T = Ti, V) intermetallics. The elastic constants Cijs and elastic moduli (B, G, E) confirm that RET2Al20 intermetallics possess the better elastic properties than pure Al. The values of Poisson's ratio v and B/G demonstrate that RET2Al20 intermetallics are all brittle materials. The anisotropy in elastic constants and Young's modulus indicates that RET2Al20 compounds are anisotropic materials. The phonon calculations indicate that RET2Al20 intermetallics exhibit the dynamical stability. Importantly, the calculated thermal quantities demonstrate that RET2Al20 intermetallics possess the better thermodynamic properties than pure Al at high temperature.

Plain correlation asymptotes to predict the center and mean temperatures and total heat transfer in simple solid objects with uniform surface temperature at limiting small-time conditions

Within the platform of unsteady, one-dimensional heat conduction in simple solid objects (large plate, long cylinder and sphere) cooled/heated with uniform surface temperature, the three important thermal quantities that need to be quantified are: the center temperature, the mean temperature and the total heat transfer. One objective of the study is the accurate determination of new dimensionless critical times for the mean and center temperatures that describe the large time sub-domain using a symbolic algebra software. Another objective of the study is to use regression analysis to construct plain correlation asymptotes for the center temperature, the mean temperature and the total heat transfer in the small time sub-domain using as input data the exact, analytical temperature distributions for the plate, cylinder and sphere expressed by infinite series for all time. Excellent agreement for the center temperature, mean temperature and total heat transfer are achieved in the small time sub-domain using the two different computational procedures.

MULTI® - rope-less elevator demonstrator at test tower Rottweil

Background: The world’s first linear motor driven passenger elevator system MULTI® started test operation at test tower Rottweil, Germany. A full scale showcase has been installed, the commissioning is finished and extensive testing activities are performed. The new test tower in Rottweil provides the perfect test and certification environment to get this ground-breaking product onto the market.
 The propulsion of the cars is based on an ironless long-stator linear motor with distributed active drive, motor and sensor elements. This technology allows cars to move individually in the same elevator shaft without any ropes. The same type of linear motor will also be used to exchange cars horizontally from one shaft to another. Herewith a movement of the cars in a loop or any vertical and horizontal travel path can be realized. The testing procedures to characterize the operation of the MULTI® include measurements of electrical, mechanical and thermal quantities.
 Smart energy management feeds power of descending cars for rising cars. To overcome the high power demand for acceleration cars, an energy buffering system is installed.
 Aim: This paper focuses on the power and energy management of the MULTI® demonstrator. The benefit of intelligent buffering strategy is depicted.
 Methods: Full scale prototype, numerical simulation, testing and measurement. 
 Results: This paper presents first measurement results of the MULTI® demonstrator mainly focusing on the power and energy characteristics of the propulsion system.
 Conclusion: Using an energy buffering system, the peak input power of the MULTI® can be reduced to 50% of the peak power level without energy buffer. The power from downward moving cars is recuperated and used for upward driving cars, balanced by the energy buffer without stressing the grid.

Experimental validation of a looped-tube thermoacoustic engine with a stub for tuning acoustic conditions

Thermoacoustic engines with a looped-tube structure and multiple thermoacoustic stages are able to efficiently utilize low-grade heat. If additional measures to counteract acoustic reflections are taken, similar results can be achieved by using only one single stage. The implementation of a stub, which is a compliant duct closed on one side and T-branched to the engine’s loop on the other side, allows a precise tuning of acoustic conditions. By only changing position and length of the stub, phase difference and normalized impedance in the regenerator can be adjusted over a wide range. The method is experimentally validated by this paper. A test-rig is introduced that works with argon at atmospheric pressure. Measurements of thermal and acoustic conditions were conducted for several configurations of the stub. Afterwards, results are used to adjust a numerical DeltaEC-model. The proposed procedure employs simple and reasonable correction parameters. They take minor acoustic losses, non-linear effects and geometrical errors into account. Eventually, the simulated acoustic field is in very good agreement with experimental results. The stub’s acoustic tuning capability is verified. Further, the results show a large mismatch of thermal quantities. Gedeon streaming is expected to be responsible. It is later eliminated by use of a jet pump with a novel design. Hence, a major discrepancy is still observable being related to other effects of thermoacoustic streaming. Eventually, impacts of the jet pump to the acoustic field on system level are analyzed.

Transient behaviors of mixed convection in a square enclosure with an inner impulsively rotating circular cylinder

This work numerically investigated the unsteady mixed convective heat transfer between a square enclosure and an inner concentric circular cylinder maintained at different temperatures. The cylinder undergoes a transition of motion whose physics is significant for engineering applications such as cooling of rotating shaft and lubricating of journal bearing. It keeps stationary at first and steady-state natural convective flow is achieved, then impulsively rotates at a constant angular velocity and the flow arrives at a new final steady-state. Although the mixed convective heat transfer for rotating cylinder configurations are analyzed in a number of works, the transient behaviors of the thermal and flow characteristics from the onset of cylinder rotation to the final steady-state are not investigated, which restrains the thorough understandings on the relevant flow physics and mechanisms. The present work performs the first numerical investigation on the targeted physical problem. The objective is to explore the transient characteristics of the mixed convective heat transfer, and to identify the effects of cylinder rotation and rotation speed (tangential velocity at cylinder surface, V0) on the flow and heat transfer behaviors. The results are presented and analyzed by the temporal variations and spatial distributions of the thermal field, mean heat transfer rate, local heat transfer rate and velocity/temperature in certain regions where the flow is significantly affected. Our numerical results for the first time identify two flow regimes depending on the tangential velocity: mixed buoyancy-shear stress dominated flow for V0 ≤ 1.0 where the effect of natural convection is pronounced and the flow is driven by both buoyancy and shear stress from the cylinder surface, and shear stress dominated flow for V0 ≥ 2.0 where the flow is almost entirely driven by rotating cylinder and heat transfer is realized by conduction. The transient behaviors of the thermal and flow quantities are characterized and categorized based on the two regimes.

First-principles prediction of the physical properties of ThM2Al20 (M= Ti, V, Cr) intermetallics

First principles calculations were used to explore the structural stability, elastic properties, ductile or brittle behavior, anisotropy, dynamical stability and thermodynamic properties of pure Al and ThM2Al20 intermetallics. The calculated formation enthalpy and phonon frequencies confirm that ThM2Al20 intermetallics are satisfied with the structural stability. The elastic constants Cijs, elastic moduli (B, G, E) and hardness (Hv) indicate these intermetallics possess the higher hardness and better resistance against the deformation than pure Al. The values of Poisson's ratio and B/G demonstrate that ThM2Al20 intermetallics are all brittle materials. The anisotropic constants and anisotropy of Young's modulus indicate that ThM2Al20 intermetallics exhibit anisotropic properties. Importantly, the calculated thermal quantities demonstrate that ThM2Al20 intermetallics possess the better thermal physics properties than pure Al at high temperature.

Thermal and magnetic correlation in apparent strain down to 1,53 K and up to 6 T on strain gauges

In recent years the exceptional development of cryogenic technology in connection with applications in the fields of superconductivity, research concerning particle acceleration, thermonuclear fusion and in the spatial sector, has clearly shown the necessity of characterizing materials and transducers suitable to operate in the range from room temperature to that of super-liquid helium (4,2 K). Besides fulfilling its institutional tasks of the realization and maintenance of the primary standards of thermal and mechanical quantities, the Istituto di Metrologia “G. Colonnetti” (IMGC-CNR), now Istituto Nazionale di Ricerca Metrologica (INRIM) carries out also work concerning the metrological characterization of sensors and transducers. In particular was undertaken a work for the characterization of stress/strain sensors to be used at cryogenic temperature and in high magnetic fields.The present paper describes the IMGC facilities for strain gauge characterization from room temperature down to 1.53 K. Apparent Strain and Gauge Factors (K) are given from 293 K to 4.2 K and for high magnetic fields (from 0 T to 6 T).

A moving thermal dielectric crack in piezoelectric ceramics with a shearing force applied on its surface

• A dynamic, thermal dielectric crack model is proposed for piezoelectric materials. • Explicit expressions for the thermal, electric and elastic quantities are given. • The electric displacement inside the opening crack is determined. • Thermal stress intensity factor is presented for real or complex eigenvalues. • Influence of the crack moving velocity is shown. This article conducts an exact analysis of a thermal dielectric crack moving in piezoelectric materials. Self-generating thermal and electric loadings by the crack interior are exerted on the crack surfaces as well as various external loadings including a shearing force. Fundamental solutions of the thermal and electro-elastic coupling fields are given by determining a temperature function and a harmonic function with eigenvalues properties due to material properties considered. Analytical expressions are obtained benefiting evaluation of key parameters. Numerical analysis is done and some interesting observations are found. There is a critical crack velocity within and beyond which the electric loading exerts different influences on the thermal flux of crack interior and the thermal stress intensity factor.

Utilization of heat quantity to model thermal errors of machine tool spindle

Thermal error modeling of the spindle plays an important role in predicting thermal deformation and improving machining precision. Even though the modeling method using temperature as the input variable is widely applied, it is less effective due to severe loss of thermal information and pseudo-hysteresis between temperature and thermal deformation. This paper presents a novel modeling method considering heat quantity as the input variable with theoretical analysis and experimental validation. Firstly, the change of thermal state of a metal part being heated is discussed to reveal the essence of the relationship between heat, thermal deformation and temperature, and the theoretical basis of the modeling method proposed in this paper is elaborated. Subsequently, the relationship between thermal deformation and heat quantity is further studied through modeling the thermal deformations of stretching bar and bending beam using heat quantity as the independent variable, and the stretching model is verified based on finite element method. Then, the thermal error models of the spindle are developed with the heat elastic mechanics theory and the lumped heat capacity method. In succession, the parameter identification of thermal error models is carried out experimentally using the least square method. The average fitting accuracy of these models is up to 91.3%, which verifies the good accuracy and robustness of the models. In addition, these models are of good prediction capability. The proposed modeling method deepens the research of thermal errors and will help to promote the application of relevant research results in the actual production.

Nanoscale polysilicon in sensors of physical values at cryogenic temperatures

Studies of polysilicon in a wide range of concentrations from 2.4 × 1018 to 1.7 × 1020 in temperature range 1.6–300 K and high magnetic fields up to 14Т were carried out in order to predict the characteristics of a material suitable for the creation of microelectronic sensors of physical values based on SemOI-structures. One of the advantages of SemOI-structures is the ability to receive layers with difference in resistivity in a wide range: several orders of magnitude. As it is determined by studies at low temperatures the transfer of charge carriers in polysilicon occurs due to hopping on localized impurities. There have also been found combined mechanisms of current flow at low temperatures, which, depending on the observation temperature, are evident in the transition from the Mott law to the percolation mechanism of Shklovskii-Efros. Those effects can be used to create elements of sensor technology. Sensors of thermal quantities for cryogenic temperatures were developed with TCR = − 9% × K−1 in the range of 4.2–50 K and mechanical quantities for cryogenic temperatures were developed for ultra-sensitivity with coefficient of gauge-factor K = 15500 in the range of 4.2–50 K. Investigation in wide range of cryogenic temperatures was conducted with the purpose of optimizing the geometry of the sensor membrane (its thickness and surface area) in order to obtain optimal stresses and deformations in the membrane. This process is essential for the sensor to be able to provide a sufficient amount of the output signal while maintaining the strength of the membrane and the sensor structure as a whole.

SIMULASI KENYAMANAN TERMAL MODEL REKOMENDASI TAMAN AIR BERARSITEKTUR TRADISIONAL BALI PADA TAMAN KOTA I GUSTI NGURAH MADE AGUNG DI DENPASAR

People will always try to condition his environment to achieve thermal comfort for his body. To conditioning the external environment is strongly influenced by climatic conditions. In other words, the comfort that humans feel in the outer space is depend on the thermal conditions of the environment. The object of outer space in this research is the built environment with the shape of Taman Kota I Gusti Ngurah Agung in Denpasar City. City Park as the object of research so far only judged from its function as a convenient recreational facility for the city community, both from the visual comfort and the thermal comfort. To answer the needs of thermal comfort in the city park, the focus of this research is the conditioning of the outer space elements with the concept of Balinese Traditional Architecture to improve the thermal comfort of the esksisting conditions. The purpose of this research is to produce thermal comfort optimization of city park through recommendation of arrangement model with the concept of Water Garden of Traditional Architecture of Bali. It takes thermal condition visualization using Envi-MET 3.1 software to see thermal enhancement improvement in the research object recommendation model. The result of this research is mapping of the increase of thermal comfort quantity distribution at the condition of urban park recommendation model. From the mapping of the thermal conditions, it is known that the thermal comfort level of the urban park recommendation model is higher. This result can then be followed up as a recommendation model of Taman Kota I Gusti Ngurah Made Agung with the concept of Water Garden of Traditional Architecture of Bali and the future can be applied in other cities with similar characteristics.