Thermal Probe Technique Research Articles

Thermal conductivity of MX80 powders-granules mixture and its prediction for high-level radioactive waste repository

Bentonite granules and their mixtures with powders are considered to be a preferred sealing material for filling gaps between buffer layer and surrounding rock in high-level radioactive waste (HLW) repository. Due to continuous release of decay heat from nuclides, thermal conductivity of bentonite granules must be assessed. In this study, the effects of water content, dry density, temperature on the thermal conductivity in the directions parallel (λpar) and perpendicular (λperp) to the bedding plane of MX80 powders-granules mixture (PGM) were investigated by thermal probe technique. Test results showed that the thermal conductivity of powdered bentonite (PB) was higher than that of PGM and λpar was higher than λperp. With increasing water content, the difference rate (δPSD) in thermal conductivity between PB and PGM increased, and anisotropy coefficient α (a ratio of λpar to λperp) decreased, while the effects of dry density and temperature on δPSD and α were not obvious. The factor importance was analyzed, and results showed that the effects of water content, dry density, temperature, and particle size distribution decreased successively. A modified geometric mean (MGM) model for predicting thermal conductivity of PGM with temperature is proposed and it predicted thermal conductivity of MX80 PGM well.

Experimental Investigations on the State-Dependent Thermal Conductivity of Sand-Rubber Mixtures

Soil-rubber mixtures are potential construction materials for use in civil engineering applications such as the thermal insulation layer for buried pipelines in the permafrost zone and underground energy storage systems. Currently, however, the thermal conductivity of soil-rubber mixtures in various stress, saturation, and void ratio conditions is not fully understood. In this study, a stress-controlled apparatus based on the thermal needle probe technique was developed. It was employed to study the influence of the aforementioned factors on the thermal conductivity of sand-rubber mixtures. Thirty-four tests were completed with a wide range of net stresses (0–600 kPa), initial degrees of saturation (0%–100%), void ratios (0.45–0.95), and rubber contents (0%, 10%, and 20%). Three replicates were used in each condition. The results showed that the thermal conductivity was strongly dependent not only on void ratio, rubber content, and degree of saturation but also on net stress. For instance, the thermal conductivity of a dry sand-rubber mixture increased by 30% when the stress increased from 0 to 600 kPa. This increase in thermal conductivity can mainly be attributed to an increase in interparticle contact area, accounting for about 25% of the 30% increase; the reduction in void ratio played a minor role. A semiempirical equation was proposed to calculate the thermal conductivity of sand-rubber mixtures at different stress levels.

Measurement and Modeling of Tissue Thermal Conductivity With Variable Water Content and Compression

The effects of water content and compression level on tissue thermal conductivity were studied. These effects are important in electrosurgery, as tissue is subjected to both compression and thermal heating. Ex vivo canine spleen tissue was used in this study. A thermal diffusion probe technique was employed to measure the tissue thermal conductivity in three different conditions. First, the tissue thermal conductivity with different water content levels was measured. The measured thermal conductivity decreased as the percentage of water within the tissue decreased. Second, the tissue thermal conductivity under compression, up to 77%, was measured and it showed a 9% reduction as the load was applied. Third, desiccated tissue was compressed, and the thermal conductivity was measured. The compression effect on thermal conductivity was less prominent in the desiccated tissue because less water was squeezed out due to compression. A three-phase Maxwell–Eucken model was developed to predict the tissue thermal conductivity for varying water content and compression levels. The model used the ratio of air, tissue fiber, and water to predict the thermal conductivity and showed a good agreement with the experimental data.

An Alternating-Current Voltage Modulated Thermal Probe Technique for Local Seebeck Coefficient Characterization

An ac voltage-modulated thermal probe technique based on the atomic force microscope is developed to measure local Seebeck coefficients (S) of thermoelectric bulk and films. The characterization principle is based on the strictly quadratic relationship between the excited local dc Seebeck voltage and the applied ac voltage at high frequency. Excellent agreement is found between local S values and their corresponding macro-S values of thermoelectric bulk and thin films. This thermoelectric probe technique provides a very convenient, promising tool for local thermoelectric parameters with sub-micrometer scale resolution.

Anisotropic thermal conductivity of natural Boom Clay

The thermal conductivity of host rocks is an important parameter in the design of deep geological disposal of heat-emitting radioactive waste. Due to bedding, heat transfer in sedimentary rocks is affected by their transversally isotropic structure. In this work, an experimental program is run to measure the thermal conductivities of Boom Clay along various orientations with respect to the bedding plane by using the needle thermal probe technique. Measurements were performed on specimens obtained from cores drilled from the HADES Underground Research Laboratory (URL) at Mol, Belgium, at a depth of 223m. The thermal conductivity values obtained are in good agreement with those previously published, confirming the thermal anisotropy of Boom Clay. Moreover, the observed changes in thermal conductivity with respect to the distance to the gallery provide further evidence on the extent of the Excavation Damaged Zone around the gallery.

Basic Problems in Thermal-Conductivity Measurements of Soils

The thermal conductivity of pozzolanic soil (a fine sandy, unconsolidated, alluvial soil from Lazio, Italy, based on volcanic ash) and blue marlstone rocks (from Alba, Piedmont, north Italy) was measured, using a thermal probe technique, over a wide range of temperatures from $${-}20\,^\circ \mathrm{C}$$ to $${+}20\,^\circ \mathrm{C}$$ . Unfrozen pozzolanic soil thermal-conductivity data display surprisingly low values about 3 to 4 times smaller than water; for frozen soils, the data are just slightly higher than for the unfrozen state but they are still 2 to 3 times lower than for water and seven times lower than for ice. This outcome is probably due to a high internal porosity of individual volcanic ash particles. The influence of the bulk soil porosity on the measured thermal conductivity was found to be rather negligible; the observed slight variation of the thermal conductivity is possibly due to the diverse grain size distribution of soil samples excavated from different depths of the ground. The blue marlstone rock has a considerably higher thermal conductivity than pozzolanic soil, likely due to its very small porosity, consolidated structure, and different implicated minerals. The frozen rock has just about a 30 % higher thermal conductivity than that for the unfrozen state. A temperature-dependent thermal conductivity is observed in the freezing state only. Test results show how heat transfer between the thermal probe and surrounding soil is influenced by storage of heat in the tested material, conduction heat flow, water evaporation due to heating, and finally by vapor diffusion and circulation.

Thermal Giant Gravitons

We study the giant graviton solution as the AdS_5 X S^5 background is heated up to finite temperature. The analysis employs the thermal brane probe technique based on the blackfold approach. We focus mainly on the thermal giant graviton corresponding to a thermal D3-brane probe wrapped on an S^3 moving on the S^5 of the background at finite temperature. We find several interesting new effects, including that the thermal giant graviton has a minimal possible value for the angular momentum and correspondingly also a minimal possible radius of the S^3. We compute the free energy of the thermal giant graviton in the low temperature regime, which potentially could be compared to that of a thermal state on the gauge theory side. Moreover, we analyze the space of solutions and stability of the thermal giant graviton and find that, in parallel with the extremal case, there are two available solutions for a given temperature and angular momentum, one stable and one unstable. In order to write down the equations of motion, action and conserved charges for the thermal giant graviton we present a slight generalization of the blackfold formalism for charged black branes. Finally, we also briefly consider the thermal giant graviton moving in the AdS_5 part.

Thermal conductivity probe length to radius ratio problem when measuring building insulation materials

Thermal conductivity probes are assessed in relation to measuring the effective thermal conductivity of building insulations as samples or in situ. Thermal conductivity and volumetric heat capacity results are given for a range of building insulations, including open and closed cell materials. It was found that the thermal probe technique had potential to be a valuable tool in helping measure, manage and reduce the energy demand of buildings but that traditional solutions for probe length to radius ratios need revision before reliable results can be consistently achieved.

Thermal Conductivity of Standard Sands II. Saturated Conditions

A non-stationary thermal probe technique was used to measure the thermal conductivity of three saturated standard sands (Ottawa sand C-109, Ottawa sand C-190, and Toyoura sand) in a range of soil porosities (n) from 0.32 to 0.42, and temperatures (T) from 25 °C to 70 °C. The sand thermal conductivities at full saturation (λ sat) increased with decreasing n (increasing compaction, 1 − n). In addition, a declining λ sat(T) n=const trend was observed. The peak λ sat values and highest decreasing rate of λ sat with T were observed at the heaviest compaction and lowest tested T. This trend gradually diminished with increasing T and expanding volume of water (larger n) due to the markedly lower ability of water to conduct heat than quartz. A series-parallel model, containing three parallel paths of heat flow (through continuous solids, continuous fluid, and solids plus fluid in series), was successfully applied to predicted λ dry and λ sat data. The model by de Vries, with new fitted grain shape values, also closely followed measured λ sat data. The corresponding square root of the relative mean squared errors varied from 2.9 % to 3.4 % for C-109, from 1.9 % to 3.0 % for C-190, and from 2.3 % to 2.4 % for Toyoura sand. The use of a weighted geometric mean model also provided good λ sat estimates with errors ranging from 3.1 % to 3.5 % for C-109 and C-190 and 8.3 % for Toyoura sand. This paper also discusses a successful attempt to model λ sat as a product of thermal conductivity of the solid fraction (quartz plus other minerals) and a thermal conductance factor of water.

Validation of data analysis routines for a thermal probe apparatus using numerical data sets

Most thermal properties of construction materials used in the analysis of building performance have been measured under laboratory conditions, using a guarded hot box or hot plate apparatus. As a consequence, these properties seldom reflect the impact of actual conditions (especially moisture content) on the values of thermal conductivity and diffusivity. Hence there is a need to develop techniques that take into account local conditions, and measure building material properties in situ. One option available is the use of a thermal probe. The thermal probe technique is based on creating a line source in a material sample and measuring the temperature rise in the sample in reaction to heat being applied. Obviously the data analysis routines used to calculate thermal conductivity and diffusivity based on the temperature rise observed are crucial to the success of the technique. This work has used transient thermal simulation of a model representing a line source in an infinite material sample to generate a set of numerical data sets to validate analysis routines in conjunction with an experimental thermal probe apparatus. Findings show that by careful application of these routines, a close agreement with simulation input values can be achieved, with errors of less than one percent. This validates the analysis routines and provides a deeper appreciation of the theoretical behaviour of a thermal probe.

Sustainable earth walls to meet the building regulations

The thermal conductivity and diffusivity of un-fired clay bricks, a straw clay mixture and straw bales have been measured using a thermal probe technique, with an iterative method for data analysis. The steady-state air-to-air thermal transmittance, or U-value, and the time-dependent thermal properties of some proposed sustainable earth wall constructions are presented. Sustainable cavity walls of un-fired clay bricks with paper, straw or wool cavity insulation have thermal transmittances less than 0.35 W/m 2 K, and therefore meet the current United Kingdom Building Regulations. A review of possible methods for thermally up-grading existing earth walls, by adding an internal insulated timber frame construction, again demonstrates possible compliance with the current UK thermal regulations.

Scaling of Tg and reaction rate with film thickness in photoresist: A thermal probe study

A thermal probe technique, local thermal analysis, was used to measure the glass transition temperature (Tg) and reaction rate as a function of film thickness in chemically amplified photoresists. Using this technique, heat loss into a resist film was monitored as the temperature of the probe was ramped from ambient to temperatures as high as 200 °C. The thermal events, glass transition temperature or heat evolved during reaction, were recorded as a function of the probe temperature. The Tg of the photoresists UVN 30, UV6, UV3, KRS, and KRS-XE was measured for thick films and for ultrathin films approximately 50 nm thick. The measured Tg in ultrathin resist films was 4–22 °C higher relative to that measured in thick films. We also investigated the behavior of polyhydroxystyrene films, and found that crosslinking to the substrate can increase Tg by a large amount. The photoresist films were then exposed with x-ray radiation at the same dose (950 mJ/cm2) for both thick and ultrathin films to ensure a constant photogenerated acid concentration with thickness. The exposed areas of the films were heated with the thermal probe, and an increase in heat flow into the exposure area, attributed to the heat of reaction, prior to the glass transition temperature was measured. Kinetic rate constants were estimated with data from the power supplied to the probe as a function of temperature using a first order reaction model. The results indicate that the rate of reaction in ultrathin resist films is smaller than in thicker films for resists processed at the same postexposure bake temperature. We find that Tg and reaction rate depend on film thickness in ultrathin photoresist films; the differences in these properties are expected to lead to large changes in the processing conditions used for ultrathin films relative to thick films.

Lock-in contact thermography investigation of lateral electronic inhomogeneities in semiconductor devices

Dynamic precision contact thermography (DPCT) is a thermal scanning probe technique with pulsed heating of the sample and lock-in signal detection. It enables the lateral imaging of weak leakage- and injection currents in large-area electronic devices. After summarizing the basic principles of this investigation technique, recent results of investigating a silicon solar cell and MOS wafers are presented.

Psychophysical responses to a speech stressor: Correlation of plasma beta-endorphin levels at rest and after psychological stress with thermally measured pain threshold in patients with coronary artery disease

Objectives. We tested the hypothesis that psychological stress alters plasma levels of opioid peptides and that these plasma levels are related to pain perception in patients with coronary artery disease.Background. Public speaking psychological stress has previously been shown to be associated with silent ischemia.Methods. After instrumentation and a 30-min rest period, venous blood samples for beta-endorphin were obtained before and immediately after psychological stress in 20 patients with coronary artery disease. Pain threshold was then assessed using a thermal probe technique at baselin and immediately after stress. Patients gave three brief speeches lasting a total of 15 min about real-life hassle situations.Results. Psychological stress significantly increases plasma beta-endorphin levels (4.3 ± 0.9 pmol/liter [mean ± SE] at rest to 8.3 ± 2 pmol/liter after stress, p < 0.05). There was a significant positive correlation between pain threshold and beta-endorphin levels after stress (r = 0.577, p = 0.008). This significant positive correlation was still present while rest blood pressure and change in blood pressure during stress were controlled for by analysis of covariance techniques.Conclusions. In patients with coronary artery disease and exercise-induced ischemia, public speaking produces psychological stress manifested by increased cardiovascular reactivity and causes an increase in plasma beta-endorphin levels that is significantly correlated with pain thresholds. These findings may explain the predominance of silent ischemia during psychological stress in patients with coronary artery disease.

Editorial comment: Mental stress, pain perception and risk of silent ischemia

testing has been frequently utilized to evaluate the effects of mental stress induced in the laboratory on hemodynamic variables and the risk of developing myocardial ischemia. The results of these studies had revealed that commonly used psychologic stressors, such as mental arithmetic, color stroop test and the task of public speaking (about unpleasant life experiences), frequently result in development of regional wall motion abnormalities, which are thought to occur secondary to myocardial ischemia in patients with coronary artery disease. It is of interest to note that most patients do not experience chest pain in association with the wall motion abnormalities induced during periods of mental stress. The precise mechanism responsible for lack of symptoms in association with ischemic episodes induced by mental stress in the laboratory, or silent ischemia encountered during daily life, has not been fully elucidated. It has been postulated that alteration in pain threshold might account for the silent nature of ischemic episodes during daily life and during periods of mental stress. However, there has been little evidence to support this hypothesis. The report by Sheps et al. (1) in this issue of the Journal provides valuable information in this area by demonstrating the significance of alterations in pain threshold as well as exploring the role of the opioid system in pain perception in patients with coronary artery disease. The present study. In their study, Sheps et al. (1) have evaluated the effects of psychological stress produced by public speaking on pain threshold and plasma beta-endorphin levels in patients with established diagnosis of coronary artery disease. Pain threshold was measured using a thermal probe technique previously validated by the investigators. Most patients (80%) had a history of stable angina pectoris; 60% had

1028-121 Stressful Public Speaking Elevates Plasma β-Endorphins

Public speaking psychological stress has previously been shown to be associated with silent ischemia. To test the hypothesis that psychological stress elevates plasma β-endorphin and that this changes pain threshold, we studied 20 patients with documented CAD and exercise induced ischemia, Following instrumentation and a 30 minute rest period, venous blood samples for β-endorphin were obtained prior to and immediately post psychological stress, Pain threshold was then assessed using a thermal probe technique at baseline and immediately post psychological stress. Patients gave 3 brief speeches lasting a total of 15 minutes about real life hassle situations.Empty CellBaselinePeak StressEmpty CellSBP (mmHg)138 ± 4180 ± 4HR (Beats/min)65 ± 378 ± 4Double Product9,047 ± 50814,240 ± 844Plasma β-endorphin (pMoI/L)4.3 ± 0.98.3 ± 2p &lt; 0.05Pain Threshold (C°)45.0 ± 0.545.4 ± 0.5P = 0.18 There was a significant positive correlation between pain threshold post stress and β-endorphin post stress (r = 0,58, p = 0.008) In patients with CAD and exercise induced ischemia 1) public speaking produces psychological stress manifested by increased cardiovascular reactivity 2) public speaking causes an increase in plasma β-endorphin which is significantly correlated with pain thresholds 3) this may explain the predominance of silent ischemia during psychological stress in patients with CAD.

Polyolefins ‐ poly(ethylene oxide) blends: Structure and properties

AbstractStructure and properties of polyolefins‐poly(ethylene oxide) (PEO) blends were studied by combination of thermal analysis, light microscopy and fluorescence probe technique. Mixing and preparation conditions influence the calorimetric behavior, changing heat and temperature of melting and crystallinity degree of blended polymers. Values of the static mechanical parameters as well as flow characteristic parameters of the blends are lower for the higher PEO fraction in the samples. Fluorescence investigation of pyrene (changes in the vibrational fine structure) showed a nonhomogeneous distribution of the probe molecules between polyolefin and PEO environment. From these data the partition coefficient between polyolefin and PEO phase can be calculated and correlated with the crystallinity changes of the mixture composition.

In situ thermal conductivity measurements of Precambrian, palaeozoic and Mesozoic rocks on Bornholm, Denmark

Abstract The thermal conductivities of 13 rock units of Precambrian, Palaeozoic and Mesozoic age on the island of Bornholm (Denmark) have been measured in situ by the cylindrical thermal conductivity probe technique. Results from the individual Precambrian rocks show narrow distributions with an overall range of 2.4–3.8 W/(m K). As a comparison with theoretical predictions based on mineral compositions indicates accordance within reasonable limits of accuracy, the measured thermal conductivities are considered to be representative for the rocks in question. In contrast to the Precambrian crystalline rocks the younger sedimentary rocks show a wider range of thermal conductivities (1.2–6.2 W/(mK)). In addition to the presentation of results, some special field conditions are considered.

Apparent thermal conductivity of glass-fibre insulant: effects of compression and moisture content

The line source thermal probe technique was validated and used to measure the apparent thermal conductivities of commercially available dry and moist glass-fibre blankets under various compressions. For the dry insulant, a minimum apparent thermal conductivity of 0·039 W m −1 K −1 occurred at ∼ 20°C for optimal values of bulk density—and consequently of volume voidage—of 0·45 kg m −3 and 0·985, respectively. Observations for the apparent thermal conductivities of moist insulants did not agree with theoretical predictions but were corroborated by the experimental results of other investigators.