scholarly journals Thermometric bridge circuits for measuring thermophysical properties

2020 ◽  
Vol 6 (2) ◽  
pp. 127-136
Author(s):  
Ihor Vasylkivskyi ◽  
◽  
Vasyl Fedynets ◽  
Yaroslav Yusyk
Keyword(s):  
Thermal Conductivity ◽  
Thermophysical Properties ◽  
Measurement Range ◽  
Measurement Result ◽  
Informative Parameters ◽  
Wide Range ◽  
Properties Of Materials ◽  
Methodological Approaches ◽  
Bridge Circuits ◽  
Electricity Transfer

The article presents the designs of a number of devices for measuring the thermal conductivity of solids developed using the new methodological approaches proposed by the authors, which enable measurements in a wide range of thermal conductivity values with better accuracy. The proposed approaches rely on the principle of invariance, which consists in ensuring the compensation of the effect of various non-informative parameters on the measurement result. For calculating the developed thermometric bridge circuits (balanced, unbalanced and partially balanced), there was applied the theory of thermal circuits based on the similarity between heat transfer and electricity transfer. The design of thermometric devices based on thermometric bridge circuits makes it possible to raise significantly the accuracy of measuring thermophysical properties of materials due to the reduced errors stemming from the effect of non-informative parameters on the measurement result. This, in turn, allowed the extended measurement range for the thermal conductivity, increased reliability and reduced cost of the devices owing to the simplified measuring circuit.

Development of high-insulating materials with aerogel for protective clothing applications – an overview

2021 ◽  
Vol 112 (2) ◽  
pp. 164-172
Author(s):  
Agnieszka Greszta ◽  
Sylwia Krzemińska ◽  
Grażyna Bartkowiak ◽  
Anna Dąbrowska
Keyword(s):  
Thermal Conductivity ◽  
Thermal Insulation ◽  
Protective Clothing ◽  
State Of The Art ◽  
Knitted Fabrics ◽  
Insulating Materials ◽  
Textile Materials ◽  
Wide Range ◽  
Properties Of Materials ◽  
Hot Environments

Abstract Aerogels are ultra-light solids with extremely low thermal conductivity (even lower than air), thanks to which they have a huge potential in a wide range of applications. The purpose of this publication is to present the state-of-the art knowledge of the possibility of using aerogels to increase the thermal insulation properties of clothing materials intended for use in both cold and hot environments. Various methods of aerogels application to textile materials (non-woven, woven and knitted fabrics) are discussed, indicating their advantages and limitations. Numerous research studies confirm that aerogels significantly improve the thermal insulation properties of materials, but due to their delicate and brittle structure and their tendency to dusting, their application still poses considerable problems.

scholarly journals Variations of thermophysical properties and heat transfer performance of nanoparticle-enhanced ionic liquids

2019 ◽  
Vol 6 (4) ◽  
pp. 182040 ◽  
Author(s):  
Fang-Fang Zhang ◽  
Fei-Fei Zheng ◽  
Xue-Hong Wu ◽  
Ya-Ling Yin ◽  
Geng Chen
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Mass Fraction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Measurement Range ◽  
Maximum Enhancement ◽  
Wide Range ◽  
Mass Fractions ◽  
Classical Models

The ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([EMIm]Ac) was investigated as a promising absorbent for absorption refrigeration. To improve the thermal conductivity of pure [EMIm]Ac, IL-based nanofluids (ionanofluids, INFs) were prepared by adding graphene nanoplatelets (GNPs). The thermal stability of the IL and INFs was analysed. The variations of the thermal conductivity, viscosity and specific heat capacity resulting from the addition of the GNPs were then measured over a wide range of temperatures and mass fractions. The measured data were fitted with appropriate equations and compared with the corresponding classical models. The results revealed that the IL and INFs were thermally stable over the measurement range. The thermal conductivity greatly increased with increasing mass fraction, while only slightly changed with increasing temperature. A maximum enhancement in thermal conductivity of 43.2% was observed at a temperature of 373.15 K for the INF with a mass fraction of 5%. The numerical results revealed that the dispersion of the GNPs in the pure IL effectively improved the local heat transfer coefficient by up to 28.6%.

Thermophysical Properties of Molybdenum Copper Multilayer Composites for Thermal Management Applications

2015 ◽  
Vol 825-826 ◽  
pp. 297-304 ◽  
Author(s):  
Martin Seiss ◽  
Tobias Mrotzek ◽  
Norbert Dreer ◽  
Wolfram Knabl
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Management ◽  
Thermophysical Properties ◽  
Copper Content ◽  
Coefficient Of Thermal Expansion ◽  
Strong Anisotropy ◽  
Multilayer Composites ◽  
Properties Of Materials ◽  
Materials Used

The key properties of materials used for thermal management in electronics are thermal conductivity and the coefficient of thermal expansion. These properties can be tailored by stacking molybdenum and copper layers. Here, molybdenum copper multilayer composites with varying copper content, from 63 to 88 wt%, have been investigated. It is demonstrated, that thermal conductivity and coefficient of thermal expansion, can be adjusted by the copper content. Two flash methods for measuring the thermal conductivity are compared and the validity of the results is discussed since measurements on thin materials with strong anisotropy require a certain setup of the measurement device. For the studied compositions the thermal conductivity was determined to be between 220 to 270 W/m/K and the coefficient of thermal expansion between 6.1 to 11.5 ppm/K.

scholarly journals Identification of the Measuring Situation when Determining Thermal Properties of Solid Materials under Uncertainty

2021 ◽  
Vol 27 (4) ◽  
pp. 516-527
Author(s):  
Z. M. Selivanova ◽  
K. V. Skomorokhov
Keyword(s):  
Thermal Conductivity ◽  
Thermophysical Properties ◽  
Optimization Problem ◽  
Measuring System ◽  
Solid Materials ◽  
Information Measuring System ◽  
Properties Of Materials ◽  
Main Factors ◽  
Intelligent Information ◽  
System Operating

The main factors characterizing the uncertainty of the measuring situation during thermophysical measurements are considered. An approach is proposed for determining the parameters of the thermophysical properties of materials and the measurement error under uncertainty. A conceptual model of the formation of a measuring environment for an intelligent information-measuring system of thermophysical properties of materials in a situation of uncertainty has been created. The solution of the optimization problem of identification of the measuring situation when determining the thermophysical properties of solid materials of various ranges of thermal conductivity is presented. An information model has been developed to identify a measurement situation in an intelligent information and measurement system operating under conditions of uncertainty.

Thermal Conductivity Measurements of Ultra-Thin Amorphous Poly(Methyl Methacrylate) (PMMA) Films

2013 ◽  
Author(s):  
Ickchan Kim ◽  
Mihai G. Burzo ◽  
Pavel L. Komarov ◽  
Peter E. Raad
Keyword(s):  
Thin Film ◽  
Thermal Conductivity ◽  
Methyl Methacrylate ◽  
Data Storage ◽  
Thermophysical Properties ◽  
Dielectric Materials ◽  
Magnetic Data ◽  
Poly Methyl Methacrylate ◽  
Wide Range ◽  
Intrinsic Thermal Conductivity

As technology progresses towards smaller and higher density microelectronic devices, we are faced with working with atomic-scale dimensions that present us with challenges but also opportunities. Since mechanical and chemical properties of ultra-thin polymeric films can vary dramatically from their bulk, the thermophysical properties of thin films are also expected to vary. Ultra-thin poly(methyl methacrylate) (PMMA) films have been the focus of numerous investigations in recent years as a data storage medium. Employing Atomic Force Microscopy (AFM) technology, it is possible to store data bits by heating a target zone until it melts, which leaves a nano-dimple indentation in the PMMA polymer film. The AFM technology has great potential because it possesses considerable data density when compared to conventional magnetic data storage. Since the amount of heat that needs to be used to melt the nanoscale region of the polymer needs to be precisely controlled, knowing the thermophysical properties of such films is a critical factor in advancing this technology. It is known that heat carriers such as electrons and phonons in metallic and dielectric materials, respectively, are influenced by the “size effect” in the micro and nano-scale dimensions. Therefore, a goal for this investigation is to determine whether any dependence exists between the PMMA’s film thickness and its thermal conductivity. In this work we investigated whether a “scale effect” on intrinsic thermal conductivity actually exists for amorphous PMMA films with thicknesses ranging from 40 nm to 2 μm. The approach is based on the transient thermoreflectance (TTR) method, where the change in the surface temperature is measured by detecting the change in the reflectivity of the sample. The sample is heated by laser irradiation and probed using a continuous-wave laser that detects changes in the reflectivity of the heated material surface. The experimentally obtained transient temperature signature is then used to extract unknown values of thermal properties. Based on our previous experience with measuring a wide range of thin-film materials and the data available in the literature, we expected a lower thin-film thermal conductivity as compared to the bulk value. Surprisingly, the results show that the intrinsic thermal conductivity of layers thinner than 40 nm PMMA film deposited on native silicon oxide is about three times higher than the bulk PMMA value. A similar trend was observed for all ultra-thin (sub 100 nm) films.

scholarly journals Computer simulation of logarithmic transformation function to expand the range of high-precision measurements

2021 ◽  
Vol 2 (9 (110)) ◽  
pp. 27-36
Author(s):  
Volodymyr Shcherban’ ◽  
Ganna Korogod ◽  
Oksana Kolysko ◽  
Mariana Kolysko ◽  
Yury Shcherban’ ◽  
...  
Keyword(s):  
Relative Error ◽  
Measurement Accuracy ◽  
Experimental Studies ◽  
Measurement Range ◽  
Measurement Result ◽  
Threefold Increase ◽  
Radiation Fluxes ◽  
Wide Range ◽  
Controlled Flow ◽  
The Relationship

Studies of the effect of normalized radiation fluxes on the measurement result revealed the most influential one. The value of the normalized flow F0 was shown to have a greater effect on the relative measurement error than ΔF0. This allows investigating the relationship between the controlled Fx and the normalized flow F0. Experimental studies have confirmed that by a threefold increase in the normalized flow F0 relative to the controlled flow Fx, it becomes possible to increase the measurement accuracy in a wide range. In particular, it was found that at the flux value F0=0.16×10-3 W, it becomes possible to measure the controlled flow in a wider range Fх=(0.16×10-3÷0.97×10-3) W with a relative error of thousandths of a percent. The effect of the reproduction error on the measurement result under the condition of a threefold increase in the normalized flow F0 relative to the controlled flow Fх is shown. It was found that an increase in the reproduction error of the normalized radiation fluxes by 1 order leads to a narrowing of the range in which the value of the relative error tends to zero. It is shown that in the absence of a threefold increase in the normalized flow F0, an increase in the reproduction error of the normalized flows by 1 order leads to individual cases of reduction in the relative error to small-order values. The latter, by the way, applies to cases where the ratio between the normalized F0 and controlled flow Fx, as 3 to 1, is ensured. It is shown that the reproduction error of the dark flow does not affect the measurement result.Thus, there is reason to believe that it is possible to expand the measurement range, in which the value of the relative error is thousandths of a percent, even for 1 measurement cycle

Recycling and Reuse in the Roman Economy

2020 ◽  
Keyword(s):  
Building Materials ◽  
Computational Modelling ◽  
Late Antique ◽  
Roman Economy ◽  
Wide Range ◽  
The Status ◽  
Recent Developments ◽  
Methodological Approaches ◽  
First Time ◽  
Site Types

The recycling and reuse of materials and objects were extensive in the past, but have rarely been embedded into models of the economy; even more rarely has any attempt been made to assess the scale of these practices. Recent developments, including the use of large datasets, computational modelling, and high-resolution analytical chemistry, are increasingly offering the means to reconstruct recycling and reuse, and even to approach the thorny matter of quantification. Growing scholarly interest in the topic has also led to an increasing recognition of these practices from those employing more traditional methodological approaches, which are sometimes coupled with innovative archaeological theory. Thanks to these efforts, it has been possible for the first time in this volume to draw together archaeological case studies on the recycling and reuse of a wide range of materials, from papyri and textiles, to amphorae, metals and glass, building materials and statuary. Recycling and reuse occur at a range of site types, and often in contexts which cross-cut material categories, or move from one object category to another. The volume focuses principally on the Roman Imperial and late antique world, over a broad geographical span ranging from Britain to North Africa and the East Mediterranean. Last, but not least, the volume is unique in focusing upon these activities as a part of the status quo, and not just as a response to crisis.

scholarly journals A Resonant Pressure Microsensor with a Wide Pressure Measurement Range

Micromachines ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 382
Author(s):  
Chao Xiang ◽  
Yulan Lu ◽  
Chao Cheng ◽  
Junbo Wang ◽  
Deyong Chen ◽  
...  
Keyword(s):  
Chemical Mechanical Planarization ◽  
Measurement Range ◽  
Silicon On Insulator ◽  
Anodic Bonding ◽  
Pressure Measurements ◽  
Quality Factors ◽  
Deep Reactive Ion Etching ◽  
Wide Range ◽  
Form Pressure ◽  
Silicon Islands

This paper presents a resonant pressure microsensor with a wide range of pressure measurements. The developed microsensor is mainly composed of a silicon-on-insulator (SOI) wafer to form pressure-sensing elements, and a silicon-on-glass (SOG) cap to form vacuum encapsulation. To realize a wide range of pressure measurements, silicon islands were deployed on the device layer of the SOI wafer to enhance equivalent stiffness and structural stability of the pressure-sensitive diaphragm. Moreover, a cylindrical vacuum cavity was deployed on the SOG cap with the purpose to decrease the stresses generated during the silicon-to-glass contact during pressure measurements. The fabrication processes mainly contained photolithography, deep reactive ion etching (DRIE), chemical mechanical planarization (CMP) and anodic bonding. According to the characterization experiments, the quality factors of the resonators were higher than 15,000 with pressure sensitivities of 0.51 Hz/kPa (resonator I), −1.75 Hz/kPa (resonator II) and temperature coefficients of frequency of 1.92 Hz/°C (resonator I), 1.98 Hz/°C (resonator II). Following temperature compensation, the fitting error of the microsensor was within the range of 0.006% FS and the measurement accuracy was as high as 0.017% FS in the pressure range of 200 ~ 7000 kPa and the temperature range of −40 °C to 80 °C.

scholarly journals Thermophysical Properties of Cement Mortar Containing Waste Glass Powder

Crystals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 488
Author(s):  
Oumaima Nasry ◽  
Abderrahim Samaouali ◽  
Sara Belarouf ◽  
Abdelkrim Moufakkir ◽  
Hanane Sghiouri El Idrissi ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Specific Heat ◽  
Thermophysical Properties ◽  
Glass Powder ◽  
Cement Mortar ◽  
Soda Lime ◽  
Waste Glass ◽  
Soda Lime Glass ◽  
Volumetric Specific Heat ◽  
Waste Glass Powder

This study aims to provide a thermophysical characterization of a new economical and green mortar. This material is characterized by partially replacing the cement with recycled soda lime glass. The cement was partially substituted (10, 20, 30, 40, 50 and 60% in weight) by glass powder with a water/cement ratio of 0.4. The glass powder and four of the seven samples were analyzed using a scanning electron microscope (SEM). The thermophysical properties, such as thermal conductivity and volumetric specific heat, were experimentally measured in both dry and wet (water saturated) states. These properties were determined as a function of the glass powder percentage by using a CT-Meter at different temperatures (20 °C, 30 °C, 40 °C and 50 °C) in a temperature-controlled box. The results show that the thermophysical parameters decreased linearly when 60% glass powder was added to cement mortar: 37% for thermal conductivity, 18% for volumetric specific heat and 22% for thermal diffusivity. The density of the mortar also decreased by about 11% in dry state and 5% in wet state. The use of waste glass powder as a cement replacement affects the thermophysical properties of cement mortar due to its porosity as compared with the control mortar. The results indicate that thermal conductivity and volumetric specific heat increases with temperature increase and/or the substitution rate decrease. Therefore, the addition of waste glass powder can significantly affect the thermophysical properties of ordinary cement mortar.

Study of Method for Determination of Thermal Conductivity of Automotive Interior Materials

2014 ◽  
Vol 526 ◽  
pp. 46-51
Author(s):  
Li Xiong Zhang ◽  
Rong Gang Gao
Keyword(s):  
Thermal Conductivity ◽  
Conductivity Measurement ◽  
Transient Heat Conduction ◽  
Traditional Theory ◽  
Infinite Plane ◽  
Plane Source ◽  
Transient Plane Source ◽  
Wide Range ◽  
Automotive Interior

Based on the traditional theory of transient plane source for thermal conductivity measurement, this paper designed and developed a new pattern of heating and temperature sensing probe, presented the study of transient heat conduction of half-infinite plane while being heated, established a modified mathematical model of transient plane source method, and achieved the measurement of thermal conductivity of automotive interior material sample by the data processing method of mathematical iteration and liner regression using the modified transient plane source probe. According to the data of experiments, the instrument which this paper designed has a high precision of 5% and a wide range of 0.003-1W/(mK).This paper provides a practicable way for heat capacity determination of automotive interior materials.

Sign in / Sign up

Export Citation Format

Share Document