Temperature calibration of an electrical compensation DSC on cooling using thermally stable high purity liquid crystals

Temperature calibration of DSCs is usually carried out on heating. In order to accurately control the temperature during cooling experiments, the calibration has to be carried out on cooling. Therefore, three high-purity, thermally stable liquid crystals were used to perform a temperature calibration of an electrcial compensation DSC on cooling. All three liquid crystals have several liquid crystalline phases, and they all were purified to a 99.9% lovel. Temoperatures of the isotropic to nematic or cholesteric and the mesophase to mesophase transitions were used. It was verified that these liquid crystals have sufficient thermal stability for carrying out the calibration on cooling. The dependence of the real temperature on the indicated temperature has been established for all the combinations of the heating and cooling rates of practical interest. It is also shown that the vant's Hoff equation can only be applied to the crystal to a liquid crystal transition, but not to the liquid crystal to liquid crystal or liquid crystal to isotropic transitions.     

Use of salts for calibration of the neutron flux

The advantage of using slats as e.g. NaBr, KBr, AlI₃ for monitoring the fluxes of both thermal and epithermal neutrons is discussed and compared with the accepted usual methods. The main advantages are the possible use for fast determination, the use for a large range of fluxes and the lower propagation error than Zr target in the case of relatively low thermal to epithermal fluxes (>10).     

Temperature calibration of thermo-balances with nickel-iron-nickel-bimetal

The behaviour of Ni?Fe?Ni sandwich material was investigated in air atmosphere up to 850°C with the NETZSCH microbalance TG 209. The aim was to determine if this substance is suitable for calibration. The results show that nickel-iron-nickel-bimetal makes it possible to calibrate thermobalances whilst expending a minimum of time and effort.     

Temperature calibration of differential scanning calorimeters

Journal of Thermal Analysis and Calorimetry - A procedure for calibrating the temperature scale of a DSC is described. A different calibration trend was obtained using the transition points of...     

灰污热流探针模拟锅炉受热面灰沉积的研究

基于傅里叶导热定律,设计了一简单实用的灰污热流探针,以神木煤、黄陵煤、新汶水煤浆和新汶黑液水煤浆为研究对象,在0.25MW热态实验炉上用灰污热流探针模拟了灰沉积过程,研究了四种燃料灰沉积过程中的热流变化特性和灰沉积机理。结果表明,灰污探针能很好地模拟不同燃料的灰污形成过程,模拟结果与实际情况相吻合;灰粒的沉积速率和吸收热流的衰减速率主要取决于燃料本身特性,同时也受烟气温度的影响;通过对探针上灰污的表观物理特性、微观结构、元素构成和矿物相的分析,发现四种燃料的灰沉积机理是不同的,黑液水煤浆灰污中Na、K含量较高,主要物相为熔融温度很低的富Na霞石和无水芒硝,黄陵煤灰污含有较高的Fe、Ca、S,而水煤浆燃烧时Fe的沉积和富集是灰污形成的主要因素;四种实验燃料中,黑液水煤浆和黄陵煤的结渣趋势强于神木煤和水煤浆。     

On the quantitative reliability of heat flux DSC

In an attempt to explain how the calibration factor of a heat flux DSC cell depends both on the standard utilized and on the experimental variables, a study has been undertaken of the entire DSC trace.This report deals with the second half of the peak and shows that, other experimental conditons being fixed, the peak area increases with increasing heating rate.This accounts for the observed decrease in the calibration factors with increasing heating rate.

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Zusammenfassung Die gesamte DSC-Kurve wurde untersucht, um zu klären, wie der Eichfaktor einer Wärmefluss-DSC vom verwendeten Eichstandard und von den Versuchsbedingungen abhängt. Der vorliegende Teil behandelt den zweiten Abschnitt eines DSC-peaks (vom Maximum an). Es wird gezeigt, dass bei Konstanthalten aller anderen Versuchsbedingungen die peak-Flächen mit steigender Aufheizgeschwindigkeit zunehmen. Das wird als Ursache für die beobachtete Verringerung des Eichfaktors mit steigender Aufheizgeschwindigkeit angesehen.

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Measurement of critical heat flux conditions under vacuum

Determination of optimum conditions for waste oil (used motor oils, transformer oils) regeneration using vacuum distillation was attempted including the search for the optimum temperature difference between the heating surface and the boiling point of the liquid. Optimum temperature allowed the distillation equipment to operate at maximum performance. Equipment suitable for the measurement of boiling curves under atmospheric pressure and vacuum conditions was assembled. These curves were used to determine the optimum temperature difference of various substances including waste oils. Properties of pure substances, for example water, ethanol, hexane, heptane, isooctane, decane, or dodecane, were measured with this equipment under atmospheric pressure. Results of various liquids measurements under vacuum and atmospheric pressure are presented.     

Micro-combustion calorimetry employing a Calvet heat flux calorimeter

Two micro-combustion bombs developed from a high pressure stainless steel vessel have been adapted to a Setaram C80 Calvet calorimeter. The constant of each micro-bomb was determined by combustions with benzoic acid NIST 39j, giving for the micro-combustion bomb in the measurement sensor k_m=(1.01112±0.00054) and for the micro-combustion bomb in the reference sensor k_r=(1.00646±0.00059) which means an uncertainty of less than 0.06 per cent for calibration. The experimental methodology to get results of combustion energy of organic compounds with a precision also better than 0.06 per cent is described by applying this micro-combustion device to the measurement of the enthalpy of combustion of the succinic acid, giving Δ_cH^∘_m(cr, T=298.15 K)=−(1492.89 ± 0.77) kJ · mol⁻¹.     

Uncertainty budget for high temperature heat flux DSCs

This study addresses the lack of published information regarding uncertainty for high temperature heat flux differential scanning calorimeters. No data were found in the existing literature stating an uncertainty budget for temperatures above 1,000 °C. The presented results identify the main influencing factor for uncertainty with the instruments used—measurement repeatability—up to a temperature of 1,400 °C. Results show findings from analyzing a series of repeated baseline and sapphire measurements and the influence from different working equations. The uncertainty budget for temperature calibration of DSCs is crucial in cases where accuracy in temperature is significant. Data are also provided from repeated temperature calibrations on the melting point of pure metals from a supplied standard set that comes with the instrument. In addition, carbon eutectics have been used to address an issue resulting from the lack of available calibration materials for high temperatures up to 1,500 °C (above the melting point of gold).     

Oxidation of lipios studied by isothermal heat flux calorimetry

The exothermic reaction of the autoxidation of lipids has been studied by isothermal heat flux calorimetry at temperatures between 80°C and 160°C. A number of lipid samples have been kept in the calorimeter under excess of oxygen for 1 or 2 hours. The capabilities of the method are illustrated by examples exhibiting different thermal behaviour, where the influence of temperature and the role of unsaturation and of antioxidants are presented for selected lipids.     

Experimental and numerical analysis in heat flow sensors calibration

Journal of Thermal Analysis and Calorimetry - The 2010/31/CE directive has highlighted the necessity to improve the energy efficiency in buildings, since they are responsible for 40% of energy...     

Metrologically based procedures for the temperature, heat and heat flow rate calibration of DSC

Metrologically based measuring procedures and evaluation methods are recommended as guidance for practical temperature, heat and heat flow rate calibration of DSC instruments which are largely independent of instrumental, test and sample parameters. The relevant terms are defined, the measuring procedures and evaluation methods described, calibration materials and their characteristic data stated and guidance for the sample handling provided. Reference is made to three extended papers on calibration. The recommendations were developed by the working group Calibration of Scanning Calorimeters of the German Society of Thermal Analysis (GEFTA).Recommendation of the working group Calibration of scanning calorimeters of the Gesellschaft für Thermische Analyse e.V. (GEFTA)     

Experimental study of woods under external heat flux by autoignition

Piloted ignition of woods has been commonly investigated, which is accelerated by a spark plug. Autoignition is a complex phenomenon that combustible materials are ignited by internal heating, without the spark plug. Compared with piloted ignition, process of autoignition is closer to the development of real fire. Very few studies have focused on the prediction of ignition time and average mass loss rate by autoignition. Therefore, ignition time and mass loss rate on six species of commonly used wood samples, namely pine, beech, cherry, oak, maple, and ash, were studied under external heat flux by autoignition in a cone calorimeter. Three mass loss stages of woods under external heat flux was observed. Empirical models of ignition time and average mass loss rate for woods under external heat flux were developed. These empirical models can be used not only for fire risk evaluation, but also for modeling input and validation.     

Temperature calibration of a high-pressure DSC for measurements in ammonia

In this paper the temperature calibration of a Mettler Toledo DSC27HP high-pressure DSC for measurements in an ammonia atmosphere is described. Measurements were performed on the melting process of three reference substances in golden crucibles: indium, tin and lead. The procedure described by the German Society for Thermal Analysis and Calorimetry, GEFTA, was applied: to correct for temperature gradients in the DSC-cel extrapolated onset temperatures of the endothermic melting peaks were measured as a function of heating rate to find by extrapolation the extrapolated onset temperature at zero heating rate, which should be a temperature corrected for temperature gradients. However, measurements performed at different pressures (between 1.5 and 8.4 bar) showed that the evaluated extrapolated onset temperatures at zero heating rate decreased with increasing pressure. This observation cannot be explained by the known dependence of melting temperatures on pressure. Therefore pressure dependence of the extrapolated onset temperatures must be caused by experimental issues. It is assumed that, although the results were extrapolated to zero heating rate, results are still influenced by temperature gradients in the DSC-cell. As a mean value, the extrapolated onset temperatures at zero heating rate decreased by 0.053°C when the pressure was raised by 1 bar. Since the software package does not allow for the pressure dependence of calibration parameters, measurement results must be corrected manually for this effect.     

Temperature calibration of a mass spectrographic evolved gas analysis system

Because of the vacuum used in mass spectrographic evolved gas analysis, the usual effects of temperature lag between actual and apparent sample temperatures are exaggerated. Factors contributing to this temperature difference are discussed. The melting point of various metals in the range 110–1100°C are used to obtain insights and estimates regarding these temperature discrepancies at different heating rates, utilizing a variety of sample holders. In general, if the sample is in good contact with the heated supporting surface, the agreement between the observed and reported equilibrium melting temperatures is good at heating rates of ? ～ 20°C min. At higher heating rates the differences become larger (?10°C) and the effect increases with increasing temperature of melting. For sample holders which are not in good contact with the sample, hot spots can develop at high temperatures due to unequal thermal radiation. Under these circumstances the apparent melting point can be considerably lower than the actual equilibrium temperature and less dependent upon heating rate.     

Evaluation of the calibration errors on cooling of a differential scanning calorimeter using different sets of standard metals

The temperature calibration on cooling of thermal analysis instruments is important for the accurate study of the non-isothermal crystallization kinetics of semi-crystalline polymers. In previous works, a methodology was proposed for performing the calibration on cooling of differential scanning calorimeters (DSCs) with standard metals, and the calibration errors were checked using transitions of high-purity liquid crystals. In this work, alternative, physically meaningful, procedures for carrying out the calibration on cooling are analyzed and validated. The calibration errors are evaluated also with liquid crystalline transitions, when the calibration is performed with standard metals, in a wide temperature range, and when due account is taken for the need of isothermal corrections to the temperature measurements. It is shown that any pair of standard metals may be used to calibrate on cooling, that the calibration errors increase for wider working temperature ranges and that, providing that certain conditions are fulfilled, both calibration procedures yield similar results.     

Temperature dependence of the heat diffusivity of proteins

In a combined experimental-theoretical study, we investigated the transport of vibrational energy from the surrounding solvent into the interior of a heme protein, the sperm whale myoglobin double mutant L29W-S108L, and its dependence on temperature from 20 to 70 K. The hindered libration of a CO molecule that is not covalently bound to any part of the protein but is trapped in one of its binding pockets (the Xe4 pocket) was used as the local thermometer. Energy was deposited into the solvent by IR excitation. Experimentally, the energy transfer rate increased from (30 ps)(-1) at 20 K to (8 ps)(-1) at 70 K. This temperature trend is opposite to what is expected, assuming that the mechanism of heat transport is similar to that in glasses. In order to elucidate the mechanism and its temperature dependence, nonequilibrium molecular dynamics (MD) simulations were performed, which, however, predicted an essentially temperature-independent rate of vibrational energy flow. We tentatively conclude that the MD potentials overestimate the coupling between the protein and the CO molecule, which appears to be the rate-limiting step in the real system at low temperatures. Assuming that this coupling is anharmonic in nature, the observed temperature trend can readily be explained.     

Comparison of heat flux in wild-type and genetically-engineered Chinese Hamster ovary cells

It is claimed, though not without dispute, that genetically engineered mammalian cells grow more slowly than their progenitor cells because the recombinant gene system causes a metabolic burden. This was found to be the case for CHO cells transfected with expression vectors forcytochrome b5. The slower growth was associated with lower metabolic activity measured by heat flux and mitochondrial activity (rhodamine 123 fluorescence). The calorimetric-respirometric ratio was similar for all cell types, implying that the greater fluxes of glucose and glutamine in the recombinant cells was channelled to biosynthesis. This demand probably restricted the supply of pyruvate to the mitochondria in these cells.The authors are grateful to the BBSRC for grant no. 2/3680 and to the University for support from the Senate Research Fund.     

Local stress and heat flux in atomistic systems involving three-body forces

Local densities of fundamental physical quantities, including stress and heat flux fields, are formulated for atomistic systems involving three-body forces. The obtained formulas are calculable within an atomistic simulation, in consistent with the conservation equations of thermodynamics of continuum, and can be applied to systems with general two- and three-body interaction forces. It is hoped that this work may correct some misuse of inappropriate formulas of stress and heat flux in the literature, may clarify the definition of site energy of many-body potentials, and may serve as an analytical link between an atomistic model and a continuum theory. Physical meanings of the obtained formulas, their relation with virial theorem and heat theorem, and the applicability are discussed.