Hot Disk Thermal Constant Analyzer Research Articles

压实膨润土的导热特性研究

利用Hot disk热常数分析仪测定了压实新疆阿尔泰膨润土在不同条件下的导热性能。探讨了干密度、含水量、孔隙度、饱和度与导热性能的关系，并运用了多种模型对热传导系数进行了预测对比分析。结果表明：阿尔泰膨润土的热传导系数、热扩散系数和体积比热均随着干密度和含水量的增大而增大；相同含水量条件下，均随孔隙度的增大而减小；在饱和度大于20%时，饱和度与热传导系数、热扩散系数和体积比热具有明显的指数关系。通过对比，得到实验所得方程与Kahr模型能较好地预测阿尔泰膨润土的热传导系数。 To analyze the relationship between dry density, water content, porosity, saturation and thermal properties, Hot disk thermal constants analyzer is used to measure the thermal properties of compacted Xinjiang Altay bentonite under different conditions. The test results of thermal conductivity are analyzed by several models. The experimental results show that thermal conductivity, thermal diffusivity and volumetric specific heat increase as the dry density and water content increase, and for the same water content, the thermal conductivity, thermal diffusivity and volumetric specific heat decrease as the porosity increase. When the saturation is more than 20%, exponential relationships between saturation and the thermal conductivity, thermal diffusivity, volumetric specific heat are observed respectively. By contrast, the equation obtained by experiments and Kahr’s model is more suitable for predicting the thermal conductivity of Xinjiang Altay bentonite.

Effect of Cryogenic Treatment on Thermal Behavior of WC-9Ni-xCeO2 Cemented Carbides

A series of specimens of WC-9Ni-xCeO2 cemented carbides were prepared. The influences of CeO2 addition and cryogenic treatment (CT) on thermal conductivity, thermal diffusion coefficient, and heat capacity of the alloys were investigated using a Hot Disk thermal constant analyzer, a X-ray diffractometer (XRD), and a scanning electron microscope (SEM) coupled with an energy dispersive X-ray detector (EDS). The results indicated that with the increase in CeO2 content in WC-9Ni-xCeO2 cemented carbides, the thermal conductivity and thermal diffusion coefficient first increase and then decrease. The change in heat capacity of the cemented carbides, however, does not show obvious regularity. CT tends to increase the thermal conductivity, thermal diffusion coefficient, and decrease the heat capacity of WC-9Ni-xCeO2 cemented carbides. Notably, the degree of influence of CT on thermal properties of the cemented carbides with various CeO2 contents is obviously different. After CT, with an increase in the CeO2 content, the variation of amplitude of thermal conductivity decreases. Similar situations also appear in the other two kinds of thermal properties.

Effect of nano CdS dispersion on thermal conductivity of PS/PVC and PS/PMMA polymeric blend nanocomposites

The effect of dispersion of CdS nano-filler particles in respective PS/PVC and PS/PMMA polymer blend matrices on the effective thermal conductivity has been studied through Hot Disk Thermal Constant Analyzer based on transient plane source (TPS) technique. The thick film samples have been prepared by dispersing nano-filler particles of CdS (6 wt%) in respective PS/PVC and PS/PMMA binary blend matrices. The nanocomposite nature of prepared samples ascertained through small angle X-ray scattering (SAXS) as well as transmission electron microscopy (TEM) measurements. It is observed that at room temperature nano CdS dispersed polymeric blend samples offer higher effective thermal conductivity.

Preparation of carbon-coated iron nanofluid and its application in radiofrequency ablation.

Carbon-coated iron nanoparticles (Fe@C CCINs) were synthesized by carbon arc discharge method and were studied via X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that CCINs have good core-shell structure and are in size of 40-50 nm. Also, carbon-coated iron nanofluid (CCINs-nanofluid) was prepared via two-step method by dispersing as-prepared CCINs and polyvinylpyrrolidone (PVP) into physiological saline. Its dispersion stability and thermal conductivity were detected by gravity sedimentation method and Hotdisk thermal constant analyzer respectively. The results indicated that CCINs-nanofluid possesses good dispersity and stability. Moreover, CCINs-nanofluid showed enhanced thermal conductivity compared with its base fluid physiological saline. The enhancement of thermal conductivity even reaches 41%. Additionally, CCINs-nanofluid injection aided radiofrequency ablation (RFA) was carried out. The relation between tissue temperature and ablation time revealed that by injecting CCINs-nanofluid into pork livers during RFA, target tissue temperatures were less than 100°C. Dissected pork livers showed that there was little or no tissue charring around the ablation probe. Results of ablation area calculation showed that the ablation area of CCINs-nanofluid injection aided RFA was 67% larger than that of saline injection aided RFA, indicating that a larger-volume tumor tissue necrosis at a single session can be achieved by CCINs-nanofluid injection aided RFA.

Fabrication of self-assembled hierarchical flowerlike zinc stannate thin film and its application as liquefied petroleum gas sensor

In the present communication, hierarchical flowerlike zinc stannate architectures have been fabricated using sol–gel spin coating process. X-ray diffraction analysis confirms the formation of zinc stannate with minimum crystallite size ∼7nm. The particle size distribution was determined with the help of acoustic spectroscopy using acoustic particle sizer (APS-100). Surface morphology exhibits the formation of porous hierarchical structure having a number of gas adsorption sites. Optical characterizations were recorded using UV–visible absorption spectroscopy and Fourier transforms infrared spectroscopy. Thermal properties were studied using a hot disk thermal constants analyzer (TPS-500). Further, the fabricated thin film was investigated with the exposure of liquefied petroleum gas (LPG) at room temperature (25°C). The maximum sensitivity of the sensor was found 2.5. The response and recovery times were found ∼180 and 240s, respectively. Maximum percentage sensor response of the sensor was 143. Improved sensitivity and percentage sensor response, small response time and good reproducibility identify that the fabricated LPG sensor is challenging for the detection of LPG at room temperature.

Effects of surfactant on the stability and thermal conductivity of Al2O3/de-ionized water nanofluids

Al2O3/de-ionized water nanofluids of different volume fractions with different surfactant mass fractions are prepared by two-step method. Thermal conductivities of the suspensions are measured by a Hot Disk thermal constant analyzer. The uncertainty of liquid thermal conductivity measurement is within 1.5% at room temperature according to the accuracy verification test of de-ionized water. Effects of two kinds of surfactants — sodium dodecyl sulphate (SDS) and polyvinylpyrrolidone (PVP) — on the stability and thermal conductivity of Al2O3/de-ionized water nanofluids are analyzed respectively. Results show that surfactant plays an important role in dispersing the nanoparticles into the base fluid and improving the stability of Al2O3/de-ionized water nanofluids. Non-ionic surfactant PVP shows better positive effects than anionic surfactant SDS on the dispersion and stability of the nanofluids. The highest thermal conductivity occurred at an optimal concentration ratio of surfactant mass fraction and particle volume fraction, where the ratio is partly associated with the particle size and decreases with the increase of particle volume fraction.

An Accuracy Estimation Method for Composite Thermal Conductivity Based on Experiments

Proposed an accuracy estimation method combined thin films section of hot disk thermal constants analyzer and Fourier transform formula, saves the requirement that heat capacity must be given in advance when use anisotropic model hot disk thermal constants analyzer to test the thermal conductivity of materials with coating. Use the anisotropic model of hot disk thermal constants analyzer and heat transfer experiment to testify the accuracy of this method.

Evaluation of Morphological Effect on Thermal and Mechanical Performance of PS/PMMA/CdS Nanocomposite Systems

In the present paper an effort has been made to investigate effect of dispersion of CdS nanoparticles on the thermal and mechanical properties of PS/PMMA blends. Samples have been prepared through dispersion of CdS nanoparticles (prepared separately) during solution casting blend fabrication processing. These nanocomposites samples are structurally characterized through Wide angle X-ray Scattering (WAXS) and Small Angle X-ray Scattering (SAXS) techniques. Scanning Electron Microscopy (SEM) analyses of these samples have been carried out in lieu of surface morphological characterization. The measurements of glass transition temperature and stress-strain analyses have been performed through Dynamic Mechanical Analyzer (DMA). The thermal conductivity of nanocomposite samples has been determined using Hot Disk Thermal Constants Analyzer. The study shows that the incorporation of dispersed CdS nanoparticles in PS/PMMA blend matrix significantly alter their glass transition behaviour, thermal conductivity and tensile properties.

Effect of Phase-Change Materials on Thermal and Mechanical Properties of Asphalt Mixtures

Abstract The use of phase-change materials (PCMs) in asphalt mixture is expected to solve some problems related to asphalt-pavement temperature, such as rutting behaviors and urban heat island effect. This study mainly evaluated the thermal and mechanical properties of asphalt mixtures with and without various PCMs (PCM-L, PCM-Z) using laboratory performance tests. The experimental tests included thermal conductivity and diffusivity, volumetric heat capacity, indoor temperature changes versus time when heated or cooled, indirect tensile strength, high-temperature rutting, and low-temperature cracking. In addition, a hot disk thermal constants analyzer was used to measure the thermal constants of asphalt mixtures. The results showed that different PCMs had different effects on the thermal constants of asphalt mixtures. Compared with control sample, the sample with PCM-L showed a higher thermal conductivity, whereas the sample with PCM-Z had a lower thermal conductivity. Moreover, PCM-Z exhibited a more-significant phase-change adjusting-temperature effect on asphalt mixtures than PCM-L. However, the addition of PCM to asphalt mixtures resulted in a decreased indirect tensile strength and a weakened rutting resistance, but the effect of PCM-Z was smaller than that of PCM-L. In addition, the asphalt mixture with PCM-Z exhibited better cracking resistance than the mixture with PCM-L and control mixture. Therefore, it is recommended to use PCM-Z in asphalt mixtures to solve the problem of pavement at high temperatures.

An investigation of melting/freezing characteristics of nanoparticle-enhanced phase change materials

The aim of this study is to investigate the melting/freezing characteristics of paraffin by adding Cu nanoparticles. Cu/paraffin composite phase change materials (PCMs) were prepared by a two-step method. The effects of Cu nanoparticles on the thermal conductivity and the phase change heat transfer of PCMs were investigated by the Hot Disk thermal constants analyzer and infrared monitoring methods, respectively. The maximum thermal conductivity enhancements up to 14.2% in solid state and 18.1% in liquid state are observed at the 2 wt% Cu/paraffin. The photographs of infrared monitoring suggest that the melting and freezing rates of Cu/paraffin are enhanced. For 1 wt% Cu/paraffin, the melting and freezing times can be saved by about 33.3 and 31.6%, respectively. The results provide that adding nanoparticles is an efficient way to enhance the phase change heat transfer of PCMs.

Applications of some thermo-analytical techniques to glasses and polymers

Thermal characterization of materials provides conclusions regarding the identification of materials as well as their purity and composition, polymorphism, and structural changes. Analytical experimental techniques for thermal characterization comprise of a group of techniques, in which physical properties of materials are ascertained through controlled temperature program. Among these techniques, traditional differential scanning calorimetry (DSC) is a well-accepted technique for analyzing thermal transitions in condensed systems. Modulated DSC (MDSC) is used to study the same material properties as conventional DSC including: transition temperatures, melting and crystallization, and heat capacity. Further, MDSC also provides unique feature of increased resolution and increased sensitivity in the same measurement. “Hot disk thermal constant analyzer”, based on Transient Plane Source (TPS) technique, offers simultaneous measurement of thermal transport properties of specimen, which are directly related to heat conduction such as thermal conductivity (λ) and thermal diffusivity (χ). This method enables the thermal analysis on large number of materials from building materials to materials with high thermal conductivity like iron. The temperature range covered so far extends from the liquid nitrogen point to 1000 K and should be possible to extend further. This review also presents some interesting results of phase transition temperature of miscible (CPI/TPI) and immiscible (PS/PMMA) polymeric systems carried out through dynamic mechanical analyzer along with the thermal transport properties obtained for cis-polyisoprene (CPI), trans-polyisoprene (TPI), and their blends determined by TPS technique.

Heat conduction enhanced shape-stabilized paraffin/HDPE composite PCMs by graphite addition: Preparation and thermal properties

In this study, the thermal conductivity of shape-stabilized paraffin/high density polyethylene (HDPE) composite phase change material (PCM) was improved by addition of graphite powder (GP) and expanded graphite (EG). GP and EG in different mass fractions were added to PCM, and thermal conductivities of paraffin/HDPE/GP and paraffin/HDPE/EG composites were measured by a Hot Disk Thermal Constant Analyzer. An almost linear relationship between mass fractions of GP and EG additives and thermal conductivity of PCMs was found. Furthermore, the physical structures and thermal properties of the composite PCMs were investigated by scanning electron microscope (SEM) and differential scanning calorimetry (DSC), respectively. The experimental results showed that the thermal conductivities of the shape-stabilized paraffin/HDPE composite PCMs could be greatly improved by addition of EG. When the addition of EG was in the ratio of 4.6 wt%, the thermal conductivity of the PCM was up to 1.36 W m −1 K −1, more than 4 times of that without any additives, which was much better than that by addition of GP. The latent heat of the heat conduction enhanced PCMs decreased little due to small amount of EG, and good uniformity structure was confirmed by SEM in this paper.

Effect of expanded graphite on properties of high-density polyethylene/paraffin composite with intumescent flame retardant as a shape-stabilized phase change material

The shape-stabilized phase change material (PCM) based on paraffin and high-density polyethylene (HDPE) is used as a storage media in thermal energy storage. This storage media can retain the shape even when paraffin is in the liquid state, and no paraffin is observed, but it has a low thermal conductivity and is easily flammable, which limits the utility area in thermal energy storage. The motivation of this study was to improve thermal conductivity and flame retardant property of shape-stabilized PCM. A flame retardant shape-stabilized PCM made of paraffin, HDPE, expanded graphite (EG) and intumescent flame retardant (IFR) was presented. To characterize the resulting product, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), hot disk thermal constants analyzer, attenuated total reflectance fourier transform infrared (ATR-FTIR) and cone calorimeter measurements were employed to investigate their microcosmic shapes, crystalline behaviors and thermal properties. The SEM results indicated that paraffin and EG were well dispersed in the network formed by HDPE. The thermal conductivity and the flame retardant efficiency of IFR could be improved by adding EG. The possible flame retardant mechanism for paraffin/HDPE/IFR/EG as a shape-stabilized PCM was proposed.

Influence of moisture content on measurement accuracy of porous media thermal conductivity

AbstractThe thermal conductivity measurement accuracy of sand was experimentally studied with a hot disk thermal constant analyzer and water morphologies, distribution, and evolution at the pore scale were observed with a charge coupled device (CCD) combined with a microscope. It was found that thermal conductivities of samples with low moisture content (<25%) could not be accurately measured. For samples with low moisture content, the analysis showed that the water in the region adjacent to the analyzer sensor mainly existed as isolated liquid bridges between/among sand particles and would evaporate and diffuse to relatively far regions because of being heated by the sensor during measurement. Water evaporation and diffusion caused the sample constitution in the region adjacent to the sensor to vary throughout the whole measurement process, and accordingly induced low accuracy of the obtained thermal conductivities. Due to high water connectivity in pores, the rate of water evaporation and diffusion in porous media of high moisture content was relatively slow when compared with that of low moisture content. Meanwhile, water in the relatively far regions flowed back to the region adjacent to the sensor by capillary force. Therefore, samples consisting of the region adjacent to the sensor maintained the constant and thermal conductivities of porous media with relatively high moisture content and could be measured with high accuracy. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20272

Synergistic effect of iron and intumescent flame retardant on shape-stabilized phase change material

This paper deals with the preparation of paraffin/high density polyethylene (HDPE)/intumescent flame retardant (IFR)/iron as flame retardant shape-stabilized phase change material (FSPCM). The influences of iron for FSPCM on morphology, flammability property, latent heat and thermal conductive property were characterized by scanning electron microscopy (SEM), cone calorimeter, differential scanning calorimetry (DSC) and hot disk thermal constants analyser. It was found that iron could be well dispersed into the composite formed by HDPE and paraffin; the flame retardant efficiency of IFR could be improved by adding iron; the thermal conductivity of FSPCM could be increased due to the high thermal conductivity of iron. At the same time, the possible flame retardant mechanism for paraffin/HDPE/IFR with iron as a FSPCM was proposed.

Dispersion behavior and thermal conductivity characteristics of Al2O3–H2O nanofluids

Abstract Nanofluid is a kind of new engineering material consisting of solid nanoparticles with sizes typically of 1–100 nm suspended in base fluids. In this study, Al2O3–H2O nanofluids were synthesized, their dispersion behaviors and thermal conductivity in water were investigated under different pH values and different sodium dodecylbenzenesulfonate (SDBS) concentration. The sedimentation kinetics was determined by examining the absorbency of particle in solution. The zeta potential and particle size of the particles were measured and the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory was used to calculate attractive and repulsive potentials. The thermal conductivity was measured by a hot disk thermal constants analyser. The results showed that the stability and thermal conductivity enhancements of Al2O3–H2O nanofluids are highly dependent on pH values and different SDBS dispersant concentration of nano-suspensions, with an optimal pH value and SDBS concentration for the best dispersion behavior and the highest thermal conductivity. The absolute value of zeta potential and the absorbency of nano-Al2O3 suspensions with SDBS dispersant are higher at pH 8.0. The calculated DLVO interparticle interaction potentials verified the experimental results of the pH effect on the stability behavior. The Al2O3–H2O nanofluids with an ounce of Al2O3 have noticeably higher thermal conductivity than the base fluid without nanoparticles, for Al2O3 nanoparticles at a weight fraction of 0.0015 (0.15 wt%), thermal conductivity was enhanced by up to 10.1%.

Effective Thermal Conductivity of Moist Porous Sintered Nickel Material

The effective thermal conductivity of capillary structures is an important parameter in the thermal performance analysis of loop heat pipes (LHP). In this paper, the effective thermal conductivity of porous sintered nickel material filled with water, ethanediol, and glycerin were measured by means of the hot disk thermal constant analyzer. The measured data were compared with similar measured data and calculated values from models in the literature. The results indicate that the thermal conductivity of the porous material depends on the thermal conductivity of the fluid, the filled ratio, and the porosity of the material.

Parameter estimations for measurements of thermal transport properties with the hot disk thermal constants analyzer

The objective of this work is to improve measurements of transport properties using the hot disk thermal constants analyzer. The principle of this method is based on the transient heating of a plane double spiral sandwiched between two pieces of the investigated material. From the temperature increase of the heat source, it is possible to derive both the thermal conductivity and the thermal diffusivity from one single transient recording, provided the total time of the measurement is chosen within a correct time window defined by the theory and the experimental situation. Based on a theory of sensitivity coefficients, it is demonstrated how the experimental time window should be selected under different experimental situations. In addition to the theoretical work, measurements on two different materials: poly(methylmethacrylate) and Stainless Steel A 310, with thermal conductivity of 0.2 and 14 W/mK, respectively, have been performed and analyzed based on the developed theory.

Recent developments and applications of the hot disk thermal constants analyser for measuring thermal transport properties of solids

When thermal conductivity and diffusivity are measured with the hot disk thermal constants analyser, hot disk sensors or G-probes of different designs are used. The design of these sensors can be described as a double spiral etched out of a 10 μm thick metal foil sandwiched between two thin insulating sheets of an electrically insulating material. So far mostly nickel and in a few instances platinum foil have been used as the sensing' material, For experiments from 30 K up to about 450 K the polyimide Kapton with a thickness of 25 μm has been used as insulating material while for temperatures beyond 450 K and up to about 1200 K a 100 μm thick mica material is used. Attempts are presently being made also to use other insulating materials, which might further increase the temperature range of the sensors. Beside work on the further development of the sensors, work is going on to extend the application of this experimental technique to cover new experimental situations, Presently, some options in addition to the standard system can be utilised. These options include possibilities to measure the thermal transport properties of anisotropic bulk materials, thin insulting sheets of low conducting materials, and slabs of material with medium to high thermal conductivity. in addition there is a facility to measure the specific heat capacity of different materials directly. When the standard experimental technique is applied, the usual experimental arrangement is to place one piece of the sample material on either side of the sensor. However, attempts have recently been made to cover one side of the sensor with a material with known thermal properties and then place the material with unknown properties in contact with the other side of the probe.