Measurement Of Thermal Properties Research Articles

Performance Evaluation of Current Leads for a 5 Tesla Electromagnetic Properties Measurement System

The development of the Electromagnetic Property Measurement System is underway at the Korea Basic Science Institute. The Electromagnetic Property Measurement System is used for electrical, thermal, and magnetic specimen property measurements in variable magnetic fields and temperatures with a low-temperature superconducting magnet. To activate low-temperature superconducting magnet that operates with liquid helium, we propose the use of vapor-cooled current leads. The low-temperature superconducting magnet is connected to the power supply at room temperature through a pair of current leads. Accordingly, heat inflows through the current leads and represents one of the major contributory factors of the entire heat inflow. Therefore, design optimization and evaluation of the current leads is necessary to minimize heat and liquid helium consumption. Vapor-cooled, and hybrid current leads were designed and fabricated, and testing in liquid helium cryostat was conducted. The low-temperature superconducting magnet was charged with electrical current up to the operating level, and the liquid helium boil-off rate was measured with respect to the supplied electrical current level. The performances of the two current leads were accessed based on the thermal load and boil-off rate of the liquid helium. The experimental and analyzed liquid helium boil-off rates associated with the current leads were in close agreement.

The Influence of In-Cavity Pressure on Heat Transfer and Porosity Formation During High-Pressure Die Casting of A380 Alloy

This paper is concerned with the measurement of thermal properties and in-cavity pressures in cold chamber high-pressure die casting. The influence of in-cavity pressure on the casting porosity, heat flux, and heat transfer coefficient has been investigated during die casting of an A380 alloy. The die was instrumented with heat transfer and pressure sensors to measure these values directly. Direct measurement of the in-cavity pressure was found to be more reliable than the metal pressure calculated from pressure measurements in the hydraulic system. Variations on the intensification pressure directly affect the in-cavity pressure. Changing the intensification pressure between 17 MPa and 90 MPa had little effect on the heat flux and heat transfer which likely reach saturation at a lower pressure during the rapid filling stages. Increases in intensification pressure reduced the level of porosity within the castings, being most effective up to a value of 67.4 MPa.

Advances in heat‐pulse methods: Measuring soil water evaporation with sensible heat balance

AbstractSoil water evaporation is an important process in hydrology, engineering, and agriculture. Few techniques are capable of measuring soil water evaporation in situ. An approach has been developed to measure in situ subsurface soil water evaporation using a soil sensible heat balance (SHB) with measurement data obtained from multi‐needle heat‐pulse sensors. Terms in the SHB (i.e., sensible heat flux and change in sensible heat storage) are calculated from heat‐pulse sensor derived soil temperature and thermal property (i.e., thermal conductivity and heat capacity) measurements for a thin soil layer with thickness corresponding to the sensor geometry. The quantity of latent heat required for soil water vaporization can be determined as the residual to the SHB (i.e., change in heat flux with depth minus change in sensible heat storage with time) for the soil layer. Dividing latent heat (per unit time) by heat of vaporization for water allows data to be converted to evaporation rate. Numerical analysis indicates that the SHB approach is most sensitive to the heat flux component of the SHB. Laboratory and field tests indicate that SHB results compare favorably with mass‐balance and micrometeorologic approaches for evaporation measurement, with SHB typically differing by <0.2 mm d−1 from the reference methods.

Thermo–time domain reflectometry method: Advances in monitoring in situ soil bulk density

AbstractSoil bulk density (ρb) is a critical parameter for describing soil structure and physical processes, yet traditional methods are unable to capture spatial and temporal changes in ρb. Recently the thermo–time domain reflectometry (thermo‐TDR) technique has been applied to determine in situ ρb on the basis of soil thermal property and water content measurements. Here, we present theory, instrumentation, procedures, and comments for monitoring in situ ρb with the thermo‐TDR sensor. We conclude that the thermo‐TDR sensor offers a useful tool for determining ρb continuously and nondestructively.

Thermal properties measurement and performance evaluation of water/ZnO nanofluid in a mini channel with offset fins

The present study experimentally and numerically investigated the heat transfer and flow behavior of ZnO/water nanofluid in a mini channel with offset fins with a 1.59mm hydraulic diameter. The thermal properties including density, viscosity and thermal conductivity with 0.75% and 1.5% volume concentration were measured and compared with correlations firstly. Then, the thermal and flow characteristics under different operational conditions were evaluated. Results indicate that the existing correlations can desirably predict the density and thermal conductivity but heavily underestimate the viscosity. The existence of offset fins eliminates the obvious transition zone from laminar flow to turbulent flow. Even though the Nusselt number of nanofluid can be improved by 7.9% and 10.5% averagely for concentrations of 0.75% and 1.5%, the friction factor is also significantly enlarged. The heat load shows negligible impact on the flow and heat transfer performance. For the thermal performance factor, its value is around 1 under different concentration and Reynolds number, which means that no benefit will be brought about by nanofluid considering both thermal and hydrodynamic performance. As the existing correlation fails to accurately predict the Nusselt number, a new correlation is put forward with a MARD of 1.7% for ZnO nanofluid flow in mini channel with offset fins. Numerically, the simulation results of single-phase, mixture and Eulerian model were compared with experimental ones. It is found that the single-phase model gives the best prediction of Nusselt number with a MARD of 8.64%. In addition, the mixture model has the smallest prediction derivation of friction factor with a MARD of 18.8%.

Extremely Rapid Self-Healable and Recyclable Supramolecular Materials through Planetary Ball Milling and Host-Guest Interactions.

The host-guest interaction as noncovalent bonds can make polymeric materials tough and flexible based on the reversibility property, which is a promising approach to extend the lifetime of polymeric materials. Supramolecular materials with cyclodextrin and adamantane are prepared by mixing host polymers and guest polymers by planetary ball milling. The toughness of the supramolecular materials prepared by ball milling is approximately 2 to 5 times higher than that of supramolecular materials prepared by casting, which is the conventional method. The materials maintain their mechanical properties during repeated ball milling treatments. They are also applicable as self-healable bulk materials and coatings, and they retain the transparency of the substrate. Moreover, fractured pieces of the materials can be re-adhered within 10 min. Dynamic mechanical analysis, thermal property measurements, small-angle X-ray scattering, and microscopy observations reveal these behaviors in detail. Scars formed on the coating disappear within a few seconds at 60°C. At the same time, the coating shows scratch resistance due to its good mechanical properties. The ball milling method mixes the host polymer and guest polymer at the nano level to achieve the self-healing and recycling properties.

Measurement and comparison of thermal conductivity of porous materials using box, dual-needle, and single-needle probe methods-A case study

Thermal conductivity controls heat transfer through materials, so accurate assessment of thermal conductivity is necessary when modeling the thermal behavior of a material. In this study, the thermal conductivities of a silty clay specimen, a sand specimen, and six types of mortar specimens with various mixing ratios of sand as an additive, were measured using box, dual-needle, and single-needle probes, with and without thermal grease, under saturated and oven-dried conditions. The results obtained with the needle probes were compared to those measured using the box probe, given the high accuracy of the box probe method. After applying thermal grease to single- and dual-needle probes, the thermal contact resistance decreased, resulting in increased thermal-conductivity values for soil and mortar specimens under saturated (wet) and oven-dried conditions. The thermal-conductivity values measured via the single-needle probe were as accurate as those measured by the box probe, whereas those measured using the dual-needle probe underestimated the material's thermal conductivity. Further research is required regarding thermal-conductivity measurements and the design of the tests and equipment used. The results of this study provide useful information for future studies of thermal-property measurements and probe development.

Thermal property measurements of metal injection moulded Inconel 625 and Inconel 718 using combined thermal analysis techniques

ABSTRACT The high-temperature thermal properties of powder metallurgy derived superalloys have not been reported in the literature. In this study, the coefficient of thermal expansion (CTE), specific heat and thermal diffusivity of metal injection moulded (MIM) Inconel 625 and Inconel 718 were measured. Measurements of wrought Nickel 200 were also made to verify the methods. These thermal property measurements were made in the range of room temperature to 1000–1200°C using dilatometry, differential scanning calorimetry and laser flash analysis. Thermal conductivity of all three materials was calculated using the measured diffusivity, specific heat and CTE. All the MIM results were compared to published data for the wrought form of these alloys and found to be in close agreement outside of phase transition regions.

Small amounts of poly(d-lactic acid) on the properties of poly(l-lactic acid)/microcrystalline cellulose/ poly(d-lactic acid) blends

Stereocomplexation is utilized to improve and control the mechanical and thermal properties of poly(lactic acid) (PLA) where enantiomeric polymers poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) form stereocomplexation. This research reports the effects of minor amounts of PDLA on the properties of PLLA/microcryslalline cellulose (MCC)/PDLA blends. Blends of PLLA/MCC/PDLA are prepared with constant percentage of MCC and different percentage of PLLA and PDLA by solution casting methods and are characterized by FTIR for the confirmation of blends compatibility, WAXS and SEM for the analysis of morphology, TGA and DTA for thermal properties measurement. Shifting of peaks of FTIR profiles observe in blends with and without PDLA due to hydrogen bonding which helps to have compatibility of blends component. XRD analysis show three new peaks after adding PDLA in PLLA/MCC blends confirm the formation of stereocomplex (SC) crystalline structure. TGA and DTG results indicate that PDLA can improve the heat resistivity of the PLLA/MCC blends by increasing its degradation temperature. DTA peaks profile also ensure the development of thermal properties. Image of SEM show the improvement of surface morphology.

Direct Measurement of Temperature Diffusivity of Nanocellulose-Doped Biodegradable Composite Films.

The thermal properties of novel nanomaterials play a significant role in determining the performance of the material in technological applications. Herein, direct measurement of the temperature diffusivity of nanocellulose-doped starch–polyurethane nanocomposite films was carried out by the micro-contact method. Polymer films containing up to 2 wt%. of nanocellulose were synthesised by a simple chemical process and are biodegradable. Films of a high optical transmittance (for a 200 m thick film), which were up to 44% crystalline, were characterised. Two different modalities of temperature diffusivity based on (1) a resistance change and (2) micro-thermocouple detected voltage modulation caused by the heat wave, were used for the polymer films with cross sections of ∼100 m thickness. Twice different in-plane and out-of-plane temperature diffusivities were directly determined with high fidelity: m/s and m/s. This work provides an example of a direct contact measurement of thermal properties of nanocellulose composite biodegradable polymer films. The thermal diffusivity, which is usually high in strongly interconnected networks and crystals, was investigated for the first time in this polymer nanocomposite.

Thermal conductivity of a Jurkat cell measured by a transient laser point heating method

To understand and quantify the thermal energy transfer in a biological cell, the measurement of thermal properties at a cellular level is emerging as great importance. We report herein a unique technique that utilizes a laser point heat source for temporal temperature rise in a micro-pipette thermal sensor; this technique characterizes heat conduction of a measured sample, the Jurkat cell, thus measuring the sample's thermal conductivity (TC). To this end, we incorporated the computational model in COMSOL to solve for the transient temperature and used the multi-parameter fitting of the experimental data using MATLAB. To address the influence of a Jurkat cell's chemical composition on TC, we compared three structural models for prediction of effective thermal conductivity in heterogeneous materials thereby determining the weight percentage of the Jurkat cell. When considering water and protein as the major constituents, we found that a combination of Maxwell-Euken and Effective Medium Theory modeling provides the closest approximation to published weight percent data and, therefore, is recommended for prediction of the cell composition. We validate the accuracy of the measurement technique, itself, by measuring polyethylene microspheres and observed 1% deviation from published data. The unique technique was determined to be mechanically non-invasive, capable of maintaining viable cells, and capable of measuring the thermal conductivity of a Jurkat cell, which was demonstrated to be 0.538 W/(m⋅K) ± 1%.

Measurement of thermal transport properties of selected superlattice and thin films using frequency-domain photothermal infrared radiometry

Thermal transport properties in multi-layered semiconductor samples are reported using modulated photothermal infrared radiometry (PTR). The cross-plane thermal conductivity and diffusivity of thin AlxGa(1-x)As layers and AlAs/GaAs superlattices were determined by fitting solutions of the heat equation for multi-layered systems to PTR data. The thermal conductivity of an AlxGa(1-x)As film with x = 0.5 was found to be lower than an AlxGa(1-x)As film with x = 0.33 which is expected as scattering from alloy disorder is maximized for x = 0.5. In addition, it was found that thermal conductivities of AlAs/GaAs superlattices decrease when the superlattice period is decreased for a constant total thickness which is expected since the number of AlAs/GaAs interfaces (which impede thermal transport) increases as the period decreases. The maximum PTR amplitude signal was found to occur when the diffusion length of the thermal wave is on other order of the thickness of the semiconductor layer. The accuracy and applicability of photothermal infrared radiometry to the study of semiconductor multilayer structures are further discussed in the paper.

A comparative study of chemical and physical properties of copper and copper alloys affected by acidic, alkaline and saline environments

Chemical and physical behavior including corrosion performance, thermal conductivity and visual color change of the copper-based alloys brass and bronze have been studied prior and after corrosion in acidic, alkaline and saline media. The concentrations of 0.5 M H2SO4, 0.5 M NaOH and 0.5 M NaCl were used in which copper and copper-alloy samples were immersed and left to corrode at room temperature for 28 days. The experiments were performed prior and after corrosion, using conventional gravimetric measurements accompanied with measurements of thermal conductivity, microstructure and optical properties. The color change of different samples was also studied through tristimulus color parameter (L*, a* and b*) values. It is concluded that the corrosion rate of copper and copper alloys is greater in acidic than in salt and alkaline media. This is due to the extent of disruption of the passive film formed on the surfaces. In the cases of alkaline and salt media, the passive films on the surface remain stable to a large extent. Small increase of thermal conductivity takes place due to formation of a very thin film of oxide and hydroxide bonded to the surface. The environment also affects the color of copper and copper alloys by chemical changes like oxidation and formation of different intermetallics on the surfaces. A microstructural study of experimental materials confirms that corrosion after 28 days results in formation of pores on the surfaces in acidic environment, and passive film that grows thicker on the surfaces in alkaline and saline environments. Aluminum oxide that is more stable than zinc oxide causes better anti-corrosion performance and minimal color variation of bronze compared to brass, especially in acidic environment.

High‐Resolution Measurement of Soil Thermal Properties and Moisture Content Using a Novel Heated Fiber Optics Approach

AbstractHydrological parameters are scale dependent. Efficient monitoring techniques capable of measuring hydrological parameters, such as soil moisture content (θ), over a wide range of spatial scales are essential for understanding the complexity of water and energy movement across the landscape. Techniques to measure θ over spatial scales in the range from centimeters to thousands of meters, however, are sorely lacking. Recent improvements in the distributed temperature sensing (DTS) technology supported the development of novel techniques to fill that gap. However, improvements in the accuracy and applicability of DTS techniques are still needed. This study investigates the possibility of improving the accuracy of the fiber optics dual‐probe heat‐pulse (FO‐DPHP) DTS technique by using a new design to maintain the spacing between the FO‐DPHP probes and by introducing a novel data interpretation approach. The accuracy of the novel FO‐DPHP design was tested at different θ in a sand column experiment. The FO‐DPHP measurements obtained using traditional and novel data interpretation approaches were compared against independent measurements from several calibrated soil water content (EC5) sensors. Monte‐Carlo analyses were also performed to assess the impact of DTS measurement errors on the accuracy achieved using the data interpretation approaches. The novel design and data interpretation approach allowed for accurate measurements of soil thermal properties and θ without the need to perform a hard‐to‐achieve soil‐specific calibration. Measured θ had mean errors and standard deviations <0.03 and <0.01 m3 m−3, respectively, for moisture conditions ranging from dry to near saturation. The standard deviation in the measured heat capacity was <0.01 MJ m−3 K−1.

Thermal transport, magnetism, and quantum oscillations in Weyl semimetal BaMnSb2

Topological semimetals host unique electronic phases with either Dirac or Weyl characteristic. One way to obtain the Weyl phase is to break the time-reversal symmetry by establishing magnetic ordering. We have investigated the electrical and magnetic properties of a magnetic Weyl semimetal candidate $\mathrm{BaMnS}{\mathrm{b}}_{2}$ under the application of magnetic field $(H)$ up to 35 T. We find that $\mathrm{BaMnS}{\mathrm{b}}_{2}$ undergoes three magnetic phase transitions with a ferromagnetic transition at ${T}_{\mathrm{C}}\ensuremath{\sim}690\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and two antiferromagnetic transitions at ${T}_{\mathrm{N}1}\ensuremath{\sim}286\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{N}2}\ensuremath{\sim}450\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. At low temperatures, both the Shubnikov-de Haas and de Haas-van Alphen oscillations are observed by applying H along the $c$ axis of $\mathrm{BaMnS}{\mathrm{b}}_{2}$. Data analysis indicates that the oscillations result from a single band, and the system can reach the first Landau level at high H. Evidence for Zeeman splitting is also observed at low Landau levels, which yields the Land\'e factor $g\ensuremath{\sim}8.9\ensuremath{-}10.4$. In addition, thermal property measurements reveal very low phonon thermal conductivity and moderate thermopower. The coupling between charge, spin and lattice is discussed.

A novel analytical model for the thermal behavior of a fiber-reinforced plastic pulley in a front-end accessory drive

This research proposes an innovative model for calculating the temperature distribution of a composite pulley inside a belt drive. The main advantage of the proposed model is a significant reduction in the costs of calculation resources and time. This model adopts two classical theories to determine the heat generation flux and subsequent thermal flow into the pulley. Then, ordinary differential equations are developed in this model according to the irregular geometric structures of a pulley to describe the thermal flow inside this component. Afterward, analytical solutions of the ordinary differential equations are derived to provide final temperature distributions of the pulleys. Moreover, measurements of thermal properties are conducted to reduce the influence of errors. To improve the reliability of the results, experimental temperature measurements were performed on a composite pulley of a designed belt drive system in an engine dynamometer system to validate this analytical model under various operating conditions. The temperature data measured at multiple locations indicate good agreement with the corresponding analytical results. Therefore, the temperature distribution provided by this model can be utilized for the development of high-thermal resistance composite. It can also be used for thermal fatigue simulations of composites under numerous load cases.

NiO@C and Ni@C Nanoparticles: Synthesis, Characterization and Magnetic Properties

Carbon-coated nickel oxide nanoparticles (NiO@C) were synthesized by near-critical hydrothermal method using starch and nickel nitrate as precursors. Also,carbon-coated Ni nanoparticles (Ni@C) were obtained by annealing NiO@C nanoparticles in hydrogen atmosphere. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy(TEM), Raman spectroscopy, simultaneous thermal analysis (STA) and physical property measurement system (PPMS). The average sizes of the NiO and Ni nanoparticles were 18[Formula: see text]nm and 15[Formula: see text]nm according to the XRD analysis, respectively. Raman spectroscopy and thermogravimetric analysis demonstrated that the carbon shells of NiO@C and Ni@C nanoparticles were composed of amorphous and partially graphitized carbon. The formation mechanism of NiO@C and Ni@C nanoparticles was briefly discussed. The Ni@C nanoparticles have enhanced coercive force than bulk nickel, and their coercive force has shown a linear dependence on the square root of temperature.

Thermoelectric properties and thermal expansion of quaternary layered compound SrFZnSb

Abstract Layered semiconductors have received increased attention recently due to the potential as high-performance thermoelectric materials. The quaternary layered compound SrFZnSb adopts ZrSiCuAs-type structure with insulating [Sr2F2]2+ layers and conductive [Zn2Sb2]2+ layers alternately stacked along the c-axis. As a narrow band-gap p-type semiconductor, SrFZnSb has a higher electrical conductivity and smaller Seebeck coefficient in comparison with isostructural thermoelectric compound BiOCuSe. Thermal properties measurements for pristine SrFZnSb reveal that its total thermal conductivity drops to 1.33 W m−1 K−1 at 773 K with the lattice thermal conductivity fitting the law of T−1. The maximum thermoelectric figure of merit ZT for SrFZnSb reaches 0.17 at 773 K. In addition, SrFZnSb presents the bulk thermal expansion coefficient of 1.2–1.5 × 10−5 K−1 within the temperature range of 300–700 K, smaller than 6.74 × 10−5 K−1 for BiOCuSe.

Efficacy of alkyl ketene dimer modified microcrystalline cellulose in polypropylene matrix

In this study, microcrystalline cellulose (MCC), which is a completely bio-derived material, was modified. An alkyl ketene dimer was used for the modification. The improved performance is beneficial for polymer matrices and advantageous with regard to the color and oxygen permeability; thus, the produced composites can be widely used in industries. The objective of this study was to improve the performances of the polypropylene matrix. Composites were successfully prepared by adding modified MCC and MCC via an extrusion process. Subsequently, the properties of the composites were analyzed according to their compositions. To confirm the difference by modification, structural analyses and thermal-property measurements were conducted. The thermal and mechanical properties of the prepared composites were measured to investigate the effects of the MCC modification and the amount, and to determine the crystallinity. Additionally, oxygen-permeability and color-difference measurements were conducted to confirm that the composites would be suitable for industrial applications.

Depth Thermography: Noninvasive 3D Temperature Profiling Using Infrared Thermal Emission

We introduce a technique based on infrared thermal emission, termed depth thermography, that can remotely measure the temperature distribution beneath the surface of certain objects. Depth thermography utilizes the thermal-emission spectrum in the semitransparent spectral region of the target object to extract its temperature as a function of depth, in contrast with conventional thermography, which uses the spectrally integrated thermally emitted power to measure the surface temperature. Coupled with two-dimensional imaging, e.g., using an infrared hyperspectral camera or scanning a single-pixel spectrometer, this technique can yield volumetric temperature distributions. We carried out a proof-of-concept experiment on an asymmetrically heated fused-silica window, extracting the temperature distribution throughout the sample. Depth thermography may enable noncontact volumetric temperature measurements of microscopic objects such as multilayer electronic devices or macroscopic volumes of liquids and gasses as well as simultaneous all-optical measurements of optical and thermal properties.