Measurement Of Thermal Properties Research Articles

Measurement of thermal properties of bulk materials and thin films by modulated thermoreflectance (MTR)

Thermal conductivity and thermal diffusivity of materials must be known at high accuracy for thermal engineering applications, in order to understand energy dissipation in devices and engines. Thermal conductivity libraries can be unreliable since their reported values may not reflect the complexities of the samples under investigation, and new materials may not yet be listed. Over the past three decades, modulated thermoreflectance (MTR) has emerged and evolved as a reliable, non-contact, and noninvasive technique to measure the thermal properties of a wide range of bulk and thin film materials and their interfaces. This Tutorial discusses the basis of, and recent advances in, the MTR technique, and its applications in the thermal characterization of a variety of materials. MTR experiments use two micrometer-wide laser beams. Experimental data (amplitude and phase vs the offset between the pump and the probe) give information about heat diffusion around the heat source along several tens of micrometers. Heat diffusion equations are used to fit the experimental data and extract the required thermal properties. Importantly, best fit procedures are not always needed because some analytical approximations provide evidence of the required thermal properties. We present many examples (bulk materials, layered sample, etc.) which illustrate this.

Tribological and thermal properties of plasma nitrided Ti45Nb alloy

In this study, the effects of plasma nitriding surface treatment on the structural, tribological and thermal properties of Ti45Nb Beta alloy were investigated experimentally. Plasma nitriding process of Ti45Nb alloy was performed in 25% Ar-75% N2 gas mixture, for treatment times of 1–4 hours at the temperatures of 700–750 °C. The tribological tests of the plasma nitrided alloy were performed in dry sliding conditions. Thermal property measurements were applied to the plasma nitrided samples to determine their thermal conductivity and specific heat capacity. The TiNbN2 phase was observed in the compound layer formed after the nitriding process, and the compound layer and diffusion layer thicknesses increased depending on the nitriding temperature and duration. The highest microhardness was obtained for the sample nitrided at 750 °C for 4 hours and the hardness approximately twice increased compared to the untreated alloy. Due to its high surface hardness and nitride layer with sufficient thickness, the lowest wear rate was obtained for the nitrided sample under these conditions. As a result, the most effective parameter on the wear properties of Ti45Nb alloy after nitriding was determined as the process temperature. After the plasma nitriding process, thermal conductivity, thermal diffusion and specific heat capacity values decreased due to the formation of a nitride layer on the surface with a relatively lower thermal conductivity compared to the untreated alloy.

Role of the electron–phonon coupling in tuning the thermal boundary conductance at metal-dielectric interfaces by inserting ultrathin metal interlayers

Varying the thermal boundary conductance at metal-dielectric interfaces is of great importance for highly integrated electronic structures such as electronic, thermoelectric and plasmonic devices where heat dissipation is dominated by interfacial effects. In this paper we study the modification of the thermal boundary conductance at metal-dielectric interfaces by inserting metal interlayers of varying thickness below 10 nm. We show that the insertion of a tantalum interlayer at the Al/Si and Al/sapphire interfaces strongly hinders the phonon transmission across these boundaries, with a sharp transition and plateau within ∼1 nm. We show that the electron–phonon coupling has a major influence on the sharpness of the transition as the interlayer thickness is varied, and if the coupling is strong, the variation in thermal boundary conductance typically saturates within 2 nm. In contrast, the addition of a nickel interlayer at the Al/Si and the Al/sapphire interfaces produces a local minimum as the interlayer thickness increases, due to the similar phonon dispersion in Ni and Al. The weaker electron–phonon coupling in Ni causes the boundary conductance to saturate more slowly. Thermal property measurements were performed using time domain thermo-reflectance and are in good agreement with a formulation of the diffuse mismatch model based on real phonon dispersions that accounts for inelastic phonon scattering and phonon confinement within the interlayer. The analysis of the different assumptions included in the model reveals when inelastic processes should be considered. A hybrid model that introduces inelastic scattering only when the materials are more acoustically matched is found to better predict the thickness dependence of the thermal boundary conductance without any fitting parameters.

Multicriteria Methodology for Open Space Analysis

This paper describes an urban analysis method for the evaluation of the diversity of open spaces. Diversity is understood as the variety of options that a public space offers to the users, giving them the opportunity to choose the area which best suits their needs, activities, and personal preferences. The method facilitates an environmental quality assessment and comparative evaluation between spaces. Decision support tools based on data analysis are developed to facilitate technical urban design decisions. The methodology is based on a multi-criteria analysis of a public square in Madrid, Spain. Field measurements of climatic data and thermal properties of materials, the activities carried out by people and their location, as well as factors related to urban design are collated in the analysis. Data are complimented with bioclimatic and simulation tools. The analysis identifies differentiated thermal profiles, as well as patterns of use of the space. This enables the identification of specific locations currently favored by citizens and the microclimatic and spatial variety of the square.

Thermal transport properties of Ni–Co-based superalloy

We report systematic measurements of thermal transport properties of a Ni–Co-based superalloy at temperatures ranging from room temperature to around 800 K. In this temperature range, the thermal diffusivity and conductivity of the superalloy monotonically increase with an increase in the temperature, while the specific heat capacity is almost temperature-independent. We found that the observed thermal conductivity of the Ni–Co-based superalloy is higher than the electronic thermal conductivity expected from the Wiedemann–Franz law, indicating the substantial contribution of phonon thermal conductivity. The temperature dependence of the phonon thermal conductivity for the Ni–Co-based superalloy was observed to be weaker than that for other Ni-based alloys, which can be qualitatively explained by enhanced phonon scattering due to small γ′-phase precipitates in the superalloy. This result suggests possible tuning of the thermal conductivity of the superalloy based on phonon transport engineering.

Printability, Mechanical and Thermal Properties of Poly(3-Hydroxybutyrate)-Poly(Lactic Acid)-Plasticizer Blends for Three-Dimensional (3D) Printing.

This paper investigates the effect of plasticizer structure on especially the printability and mechanical and thermal properties of poly(3-hydroxybutyrate)-poly(lactic acid)-plasticizer biodegradable blends. Three plasticizers, acetyl tris(2-ethylhexyl) citrate, tris(2-ethylhexyl) citrate, and poly(ethylene glycol)bis(2-ethylhexanoate), were first checked whether they were miscible with poly(3-hydroxybutyrate)-poly(lactic acid) (PHB-PLA) blends using a kneading machine. PHB-PLA-plasticizer blends of 60-25-15 (wt.%) were then prepared using a corotating meshing twin-screw extruder, and a single screw extruder was used for filament preparation for further three-dimensional (3D) fused deposition modeling (FDM) printing. These innovative eco-friendly PHB-PLA-plasticizer blends were created with a majority of PHB, and therefore, poor mechanical properties and thermal properties of neat PHB-PLA blends were improved by adding appropriate plasticizer. The plasticizer also influences the printability of blends, which was investigated, based on our new specific printability tests developed for the optimization of printing conditions (especially printing temperature). Three-dimensional printed test samples were used for heat deflection temperature measurements and Charpy and tensile-impact tests. Plasticizer migration was also investigated. The macrostructure of 3D printed samples was observed using an optical microscope to check the printing quality and printing conditions. Tensile tests of 3D printed samples (dogbones), as well as extruded filaments, showed that measured elongation at break raised, from 21% for non-plasticized PHB-PLA reference blends to 84% for some plasticized blends in the form of filaments and from 10% (reference) to 32% for plasticized blends in the form of printed dogbones. Measurements of thermal properties (using modulated differential scanning calorimetry and oscillation rheometry) also confirmed the plasticizing effect on blends. The thermal and mechanical properties of PHB-PLA blends were improved by the addition of appropriate plasticizer. In contrast, the printability of the PHB-PLA reference seems to be slightly better than the printability of the plasticized blends.

Hydroxyapatite/polyetheretherketone nanocomposites for selective laser sintering: Thermal and mechanical performances

Abstract In this article, the thermal and mechanical properties of hydroxyapatite (HA)/polyetheretherketone (PEEK) nanocomposites were investigated. The surface of the HA particles was modified by stearic acid. Subsequently, the modified HA and PEEK were ultrasonically dispersed in ethanol and then subjected to drying and ball milling treatments. By controlling the concentration of modified HA, HA/PEEK nanocomposite powders containing various amounts of modified HA were successfully prepared. The tensile strength, impact strength, and flexural strength of the nanocomposite reached maximum values at 2.5 wt% HA and were 18.5%, 38.2%, and 5.7% higher than those of the pure PEEK, respectively. Moreover, the flexural modulus of the HA/PEEK nanocomposites increased at 2.5 wt% HA and was approximately 30% higher than that of the pure PEEK. The thermal property measurements (differential scanning calorimetry and thermogravimetric analysis) showed that the nanocomposites with 2.5 wt%-modified HA exhibited enhanced thermal stability as compared to the pure PEEK, showing potential for selective laser sintering.

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.