Angstrom Method Research Articles

How to Accurately Measure the Effective Thermal Diffusion Conductivity of Vapor Chamber by Angstrom Method

How to Accurately Measure the Effective Thermal Diffusion Conductivity of Vapor Chamber by Angstrom Method

HiPIMS obtained carbon nano-coatings on copper foil and their thermal conductivity

To prevent overheating of high-power electronic devices, effective cooling and thermal management is a key issue. Owing to the extraordinarily high thermal conductivity of graphene structure in nature, an approach for growth of carbon nano-coating with multiplex layer architecture on copper foil by using high power impulse magnetron sputtering (HiPIMS), as an alternative to the conventional chemical vapor deposition process, is reported for heat-spreading purposes. For successful deposition, a high peak current of 600 A with a short pulse of 30 μs at a relatively low substrate temperature of 600 °C was applied. Moreover, growth mechanisms without and with applying copper for Cu/carbon (Cu/C) nano-coating periodic deposition are revealed and discussed. Based on the measurement results using Angstrom's method, under optimum deposition time, the HiPIMS prepared carbon nano-coating with multiplex layer architecture, which contains in-plane-oriented multilayer graphene structure and the following out-of-plane-oriented turbostratic graphene structure, can enhance the heat spreading ability of the copper foil, reaching a thermal diffusivity value of 1.05 cm2/s. For Cu/C nano-coating periodic deposition, copper can act as catalyzing ingredient to inhibit amorphous carbon formation and promote the crystalline graphene-like structure growth, resulting in a further increase in the thermal diffusivity up to 1.21 cm2/s, twice that of the bare copper foil.

Algorithms for thermal diffusivity measurement of heterogeneous 1D materials based on Infrared Microscopy Enhanced Angstrom Method

An infrared microscopy enhanced Angstrom method has been develpoed to measure the thermal diffusivity. Infrared microscopy technique can acquire temperatures of multiple points at one shot. Two algorithms for calculating thermal diffusivity were proposed and compared in practice. One is based on global temperature data and the other is based on local temperature data. The according calculated thermal diffusivities are denoted as and . Three 1D materials of different heterogeneity (Cu wire, Ni-Cu wire and PVA-CNT fiber) were measured on the experimental platform. The calculated and values show that for homogeneous material such as Cu, these two algorithms give similar results, while for heterogeneous ones (Ni-Cu and PVA-CNT), they come to be discrepant. The data fluctuation analysis of zooms in the discrepancy and verifies that is more sensitive to local property change and more competent in revealing heterogeneous properties.

Thermal conductivities of solid and molten silicates: Implications for dynamos in mercury-like proto-planets

Remanent magnetization and active magnetic fields have been detected for several telluric planetary bodies in the solar system (Earth, Mercury, Moon, Mars) suggesting the presence of core dynamos active at the early stages of the planet formation and variable lifetimes. Among the factors controlling the possibility of core dynamos generation, the dynamics of the surrounding silicate mantle and its associated thermal properties are crucial. The mantle governs the heat evacuation from the core and as a consequence the likeliness of an early thermally driven dynamo. In the case of planets with a thick mantle (associated with supercritical Rayleigh numbers), the core heat is efficiently removed by mantle convection and early thermally-driven dynamos are likely. At the opposite, planets with a thin mantle (associated with subcritical Rayleigh numbers) might evacuate their inner heat by diffusion only, making early thermally-driven dynamos difficult. Within the Solar System, Mercury is a potential example of such a regime. Its small mantle thickness over the planet radius ratio might be inherent to its small orbital semi-axis and hence, might be ubiquitous among the terrestrial objects formed close to their star.To constrain the likeliness of a thermally driven dynamo on “Mercury-like” planets (i.e. with large Rc/R), we present new thermal diffusivity measurements of various solid, glassy and molten samples. We applied the Angstrom method on cylindrical samples during multi-anvil apparatus experiments at pressures of 2 GPa and temperatures up to 1700 K. Thermal diffusivities and conductivities were estimated for solid and partially molten peridotites, with various melt fractions, and for basaltic and rhyolitic glasses and melts. Our study demonstrates that melts have similar thermal properties despite a broad range of composition investigated. The melts reveal much lower thermal conductivities than the solids with almost an order of magnitude of decrease: 1.70 (±0.19) to 2.29 (±0.26) W/m/K against 0.18 (±0.01) to 0.41 (±0.03) W/m/K for peridotites at high temperatures and various melts respectively. Partially molten samples lie in between and several predictive laws are proposed as a function of the melt fraction and solid/melt texture.Using our results into forward calculations of heat fluxes for dynamo generation for Mercury-like planets, we quantify the effect of mantle melting on the occurrence of thermally driven dynamos. The presence of a mushy mantle and partial melting could significantly reduce the ability of the mantle to evacuate the heat from the core and can prevent, shut or affect the presence of a planetary magnetic field. The buoyancy and fate of molten material in such bodies can thus influence the magnetic history of the planet. Future observations of Mercury-like planets accreted near their star and the detections of their magnetic signatures could provide constraints on their inner state and partial melting histories.

Microscale heat-flux meter for low-dimensional thermal measurement and its application in heat-loss modified Angstrom method

A microscale heat-flux meter is designed based on micro-hotwire and infrared thermal microscopy. Its feasibility in low-dimensional thermal measurement is verified by its application in heat-loss modified Angstrom method for simultaneous measurement of thermal diffusivity, thermal conductivity and specific heat. The hotwire and the sample under test are placed in a vacuum chamber. Through an observation window, the infrared microscopy can capture the thermal image including the hotwire and the sample. When the hotwire is heated, the temperature distribution along the wire is acquired by the readings extracted from the thermal image, which enables the determination of nonlinear and local temperature gradient. This gradient, according to Fourier's Law, can be used to calculate the local heat flux. When a sample is attached to the middle of the hotwire, the attached point is appeared to be a singularity in the temperature distribution along the hotwire, which poses a rigorous challenge to calculate the heat flux flowing into the sample. Here we tried some approaching strategies and verified that the local heat flux at second derivative minima around the singularity is a good enough approximation. The mathematical and physical origins for this approximating strategy are also discussed. This microscale heat-flux meter is a general technique, which is promising for an extension to other thermal measurements.

An analytically based method to estimate the effective thermal diffusivity of a heat pipe

An analytically based method is proposed to estimate the equivalent thermal diffusivity (α) of a heat pipe. This novel method, which enables real-time screening, features simple, fast, inexpensive and accurate characteristics in obtaining the corresponding α value. Different from the traditional Angstrom method, which uses a sinusoidal pulse heating source for measuring the offset of two separate waves triggered in an intermittent time span; the proposed method merely uses a water bath as the heating source with the derived closed-form solution as a core computing algorithm, and the correct α value can be obtained. The examination process only takes less than 30 s and can be deployed in production lines for real-time screening. The closed-form analytical solution is associated with an infinite power series and is validated with heat pipes of 6 mm in diameter and 260 mm in length. The equivalent thermal diffusivity of the heat pipe is 0.00382 m2 s−1, which is about 35 times higher than copper and 3.6 times higher than graphite. The analytical predictions are in line with experimental results for the transient temperature rise of the heat pipe.

A Thermo-electric Apparatus for Thermal Diffusivity and Thermal Conductivity Measurements

In this study, a one-dimensional heat transfer measurement device is developed based on the mathematical theory of the Angstrom method. To conform to the mathematical assumption, it is required that the device precisely controls the heat source to generate sinusoidal temperature signal. A thermo-electric module is used as the heat source for the measurement platform. This module is connected to a computer for program control, such that the temperature can be controlled quickly, precisely, and dynamically. In this study, five common heat-conducting materials are tested to verify the proposed one-dimensional heat transfer measurement device. By substituting the experimental results into the mathematical model of the Angstrom method, the thermal diffusion and thermal conductivity of the test material is calculated. The experimental results are compared with the physical properties of the materials, and the accuracy error is extremely low. This study confirmed that the Angstrom method theory applied thermal diffusivity and thermal conductivity measurement, which can be realized by thermo-electric temperature control technology.

Measurement of Hair Thermal Diffusivity with Infrared Microscopy Enhanced Ångström's Method

While heat acts as an essential component of various hair care processes, the thermal properties of hair are little studied and these properties dictate how heat is spread and stored in hair. Here, the infrared microscopy enhanced Angstrom's method is introduced for accurate measurement of thermal diffusivity of hair. Four factors that could influence the thermal diffusivity were statistically tested: (1) hair type, (2) the specific fiber from the same hair type, (3) the specific locations along the same hair fiber (i.e., near the root vs. near the tip), and (4) the humidity level at which the hair is conditioned. The results indicate that the average thermal diffusivity of hair across the types measured is 0.148 mm2/s, which is in good agreement with the published data. Also, hair type, fiber, and location had no statistically significant impact on the thermal diffusivity, while increasing humidity level significantly reduced the thermal diffusivity. This seems to be due to the higher specific heat capacity of water than air, which dominates the heat transport and lowers the effective thermal diffusivity of hair which contains both.

Opto-thermal technique for measuring thermal conductivity of polyacrylonitrile based carbon fibers

Thermal conductivity of carbon fibers (CFs) is an important property because CFs are used as heat dissipation fillers in composites for aerospace and electronics applications. However, evaluating thermal conductivity of a single filament of CFs is an arduous task due to dimensional issue of specimens and limitations of conventional measurement system. Therefore, we suggest an opto-thermal technique using Raman spectroscopy to measure thermal conductivity of commercial polyacrylonitrile based CFs (T300, T700SC and T800H). The opto-thermal technique used that G band from Raman spectroscopy of carbon materials is shifted depending on temperature. For verifying an accuracy of the technique, the laser absorbance of CFs were estimated, and the thermal conductivity was measured depending on the length of CF. The measured data were reflected in the thermal conductivity calculation formula. It was demonstrated that the method provides more reasonable thermal conductivity values compare to a conventional Angstrom method. In addition, this simple technique confirmed that graphitic structure of CFs played a critical role in their thermal conductivity.

Application of the Basalt Powder as a Filler for Polypropylene Composites With Improved Thermo‐Mechanical Stability and Reduced Flammability

The influence of the basalt powder (BP) on mechanical properties as well as on thermal stability and flammability of the isotactic polypropylene (iPP) composites was investigated. Thermo‐mechanical stability of the pure polypropylene and composite materials containing from 5 up to 40 wt% BP was defined in static and dynamic testing conditions with the use of the heat distortion temperature measurement, vicat softening point temperature test, and dynamic mechanical thermal analysis. All measurements showed, unequivocally, a significant improvement of thermo‐mechanical stability of the composite materials which was directly related to an increasing amount of inorganic filler. A research conducted on the mechanical properties revealed that stiffness and hardness of polypropylene‐based composites was affected by the addition of the filler, leading to a strong increase of both mechanical parameters. Moreover, the application of thermogravimetric analysis and cone calorimetry measurements allowed to determine the composites with highest thermal stability, which was dependent on the concentration of the filler. Changes observed in the polypropylene‐based composites properties were related to an increase of thermal diffusivity caused by presence of the BP measured by modified Angstrom method. POLYM. ENG. SCI., 59:E71–E79, 2019. © 2018 Society of Plastics Engineers

Performance evaluation of a coupled method for the estimation of daily global solar radiation on a horizontal surface

The accurate estimation of the amount of global solar radiation potential on the earth’s surface is one of the most important parameters for solar energy investments and long-term climate studies. The most accurate solar radiation data are generally available in some ground stations where they are obtained by using direct measurement. However, the estimation of global solar radiation data can be conducted by some estimation methods in the areas that do not have this information. This study compares and discusses some approaches to identify the most accurate method for daily global solar radiation reaching on a horizontal surface. The comparisons are carried out between some selected conventional empirical methods taken from the related literature, the satellite-based HELIOSAT method and the coupled (hybrid) method which uses both ground data and satellite images. These selected methods have been tested previously and declared most accurate by many researchers for Turkey. The performance results were compared with ground-measured data and all methods were analyzed by using statistical errors in the selected site. According to the last six years of data results, the coupled method is better than the others (except the Angstrom method), with daily difference values (91%) and daily absolute difference values lower than 2.5 MJ m –2 day.

Criteria for accurate measurement of thermal diffusivity of solids using the Angstrom method

This paper presents criteria for accurately measuring the thermal diffusivity of a solid material using the Ångström method. In this technique, a periodic heat load is supplied at one end of the sample and temperatures are measured at different locations along the sample. The thermal diffusivity is estimated from the measured amplitude and phase of the temperature oscillations at various locations along the sample. Criteria are presented for important measurement parameters namely as periodic heat load power, waveform and frequency. Since more than two sensors are used, the accuracy is further improved since the linearity of the phase and amplitude data can be verified. We experimentally establish that a sinusoidal input heat load with a frequency as defined by the criteria established in this paper results in improved measurement accuracy. Based on these criteria, the experiment was performed with a range of materials spanning low to high thermal diffusivities namely Teflon, G10, Titanium Alloy (Ti6Al4V), Stainless steel (SS316) and Aluminium Alloy (Al6061-T6). The results indicate that the measured thermal diffusivity values deviate from the literature data at room temperature by less than 2.1%.

Important factors affecting the thermal resistance and thermal diffusivity of vapor chambers

This paper discusses a number of important parameters associated with the measurement of thermal resistance and thermal diffusivity in vapor chambers (VCs). Thermal resistance and thermal diffusivity are representative indicators of VC performance. In this paper, we measured thermal resistance using four distinct Experiment Setups. Our empirical results demonstrate that thermal resistance values depend largely on how the experiment is set up. We also examined two different condensation methods in the measurement of thermal resistance. Condensation condition 1 uses cooling water with an input temperature fixed at 20°C and the flow rate fixed at 10g/s. Condition 2 involved fixing the temperature of the top surface of the vapor chamber by adjusting the temperature of the cooling water according to the input power. In experiments, the lowest thermal resistance was 0.135°C/W under condensation condition 1 and 0.023°C/W under condensation condition 2.We also developed a device for the measurement of thermal diffusivity based on the Angstrom method. We then measured (under experimental conditions) the thermal diffusivity of four pure metals for comparison with standard reference values. The thermal diffusivity values were measured as follows: VC (44.04cm2/s) and copper plate (1.219cm2/s).

Paper Thermoelectrics: Merging Nanotechnology with Naturally Abundant Fibrous Material.

The development of paper-based sensors, antennas, and energy-harvesting devices can transform the way electronic devices are manufactured and used. Herein we describe an approach to fabricate paper thermoelectric generators for the first time by directly impregnating naturally abundant cellulose materials with p- or n-type colloidal semiconductor quantum dots. We investigate Seebeck coefficients and electrical conductivities as a function of temperature between 300 and 400 K as well as in-plane thermal conductivities using Angstrom's method. We further demonstrate equipment-free fabrication of flexible thermoelectric modules using p- and n-type paper strips. Leveraged by paper's inherently low thermal conductivity and high flexibility, these paper modules have the potential to efficiently utilize heat available in natural and man-made environments by maximizing the thermal contact to heat sources of arbitrary geometry.

Heat-loss modified Angstrom method for simultaneous measurements of thermal diffusivity and conductivity of graphite sheets: The origins of heat loss in Angstrom method

Angstrom method is a steady-state measurement for thermal diffusivity α using ac heating. Since thermal conductivity λ is a better-known quantity, measured diffusivity α is sometimes transformed into λ based on relation λ=Cvα using recorded or DSC measured Cv. However, Angstrom method itself is principally possible to extend to specific heat measurements, yet the accuracy is not promising due to the complexity of heat loss. Here we present a modified method for simultaneous measurements of thermal diffusivity and thermal conductivity with high accuracy by taking heat loss into account. A linear heat loss term m2T is introduced into the diffusion equation and the thermal conductivity λ can be directly measured instead of specific heat. The measured thermal properties of commercial graphite sheets agree well with their nominal value. The origins of m2 are also discussed. m2 can be divided into amplitude independent and dependent part. From the basics of radiation and convection, the first-order radiation and convection comprise the amplitude independent part, while the dependent part includes higher order (dominated by second-order) radiation. Although the amplitude independent part agrees well with the extrapolated value of m2 at zero amplitude, the second-order radiation cannot fully cover the measured amplitude dependent part. This discrepancy is further explained by floating temperature baseline variation due to residual heat during heat oscillation.

Multiscale Thermal Characterization of Mechanically Loaded Ceramic Matrix Composite

Ceramic Matrix Composites (CMC) are very attractive for structural applications at high temperatures or under temperature gradients. For these reasons, the mechanical properties must be considered together with the thermophysical properties. The aim of this work is to demonstrate the thermal characterization capabilities of IR thermography in multiscale damage assessment for CMCs. A first device was developed for the thermomechanical characterization at the level of fiber bundle. The longitudinal effective thermal diffusivity was monitored in-situ using the Angstrom method during a tensile test. In a second device, we implemented flash methods for the estimation of longitudinal and transverse diffusivities during tensile tests of 2D woven SiC/SiC composites. The macroscopic results corroborate the microscopic ones, but they also give complementary indications about composite’s behavior. Morevover, these methods offered the possibility to map the distribution of transverse thermal diffusivity.

Thick Graphene Embedded Metal Heat Spreader with Enhanced Thermal Conductivity

In this paper, a copper foil-thick grapheme (thin graphite sheet)-copper foil structure is reported to achieve mechanically strong and high thermal conductive layer suitable for heat spreading components. Since graphene provides much higher thermal conductivity than copper, thick graphene embedded copper layer can achieve higher effective thermal conductivity which is proportional to graphene/copper thickness ratio. Since copper is nonreactive with carbon material which is graphene, chromium is used as adhesion layer to achieve copper-thick graphene-copper bonding for graphene embedded copper layer. Both sides of thick graphene were coated with chromium as an adhesion layer followed by copper by sputtering. The copper foil was bonded to sputtered copper layer on thick graphene. Angstrom's method was used to measure the thermal conductivity of fabricated copper-thick graphene-copper structure. The thermal conductivity of the copper-thick graphene-copper structures is measured as <TEX>$686W/m{\cdot}K$</TEX> which is 1.6 times higher than thermal conductivity of pure copper.

Theoretical description of the photopyroelectric technique in the slanted detector configuration for thermal diffusivity measurements in fluids

• A model for photopyroelectric thermal characterization of fluids is presented. • A slanted detector configuration is considered with a finite measurement cell. • The mean temperature distribution in the photopyroelectric detector, as function of the beam spot position, is calculated. • The influence of the excitation beam spot size, the thermal diffusion length and size of the sample is discussed. • The high lateral resolution of the method observed in experiments is explain. This work presents an extended description about the theoretical aspects related to the generation of the photopyroelectric signal in a recently proposed wedge-like heat transmission detection configuration, which recreates the well-known Angstrom method (widely used for solid samples) for accurate thermal diffusivity measurement in gases and liquids. The presented model allows for the calculation of the temperature profile detected by the pyroelectric sensor as a function of the excitation beam position, and the study of the influence on it of several parameters, such as spot size, thermal properties of the absorber layer, and geometrical parameters of the measurement cell. Through computer simulations, it has been demonstrated that a narrow temperature distribution is created at the sensor surface, independently of the lateral diffusion of heat taking place at the sample's surface.

Thermal diffusivities of MgSiO3 and Al-bearing MgSiO3 perovskites

Thermal diffusivities of MgSiO3 perovskite (MgPv) and MgSiO3 perovskite containing 2 wt% Al2O3 (Al-MgPv) were measured at ambient conditions using the micro-spot heating angstrom method. The obtained values of thermal diffusivities of MgPv and Al-MgPv are 2.6 ± 0.1 and 2.4 ± 0.1 mm2/s, respectively. Present result for MgPv is much higher than previously reported value of 1.7 mm2/s. Substitution of aluminum into MgPv has little effect on its thermal diffusivity at ambient conditions, and such an impurity effect would remain insignificant at high pressures and high temperatures corresponding to the Earth’s lower mantle.

A method for thermal diffusivity measurement in fluids

A technique is proposed for thermal diffusivity measurement in fluids. It is based on the Angstrom method, but with excitation of thermal waves by electromagnetic energy absorption and pyroelectric detection. The good agreement between measured thermal diffusivity of air and some test liquids with literature values shows the validity of the method. It is free of some limitations of conventional photopyroelectric technique with length scanning because it is free of moving parts inside the sample and because it avoids problems associated with the non-parallelism between thermal wave generator surface and sensor. It does not require any data normalization procedure or special sample preparation.