Showing papers on "Calorimeter published in 1981"

High-temperature thermodynamic properties of aqueous sodium sulfate solutions

Abstract: A flow calorimeter has been used to measure the heat capacities of aqueous sodium sulfate solutions from 30 to 200/sup 0/C at 1 bar, or the saturated vapor pressure, and at 200 bar. The heat-capacity data have been integrated as a function of temperature to obtain values of the apparent molal enthalpy, the osmotic coefficient, and the mean activity coefficient. Osmotic coefficients obtained in this manner are in good agreement with available literature data over the entire temperature range. These results indicate that heat-capacity measurements can be used reliably to obtain the high-temperature activity properties of electrolyte solutions, provided the enthalpy and Gibbs energy are known at 25/sup 0/C.

Determination of the basal metabolic rate of humans with a whole-body calorimeter

Abstract: The basal metabolic rate (BMR) of a human subject is measured with the subject reclining in a non-adiabatic whole-body calorimeter. Heat losses which occur through the uninsulated wall of the calorimeter chamber during the measurement period are determined in a preliminary calibration step, in the absence of the subject. The BMR measurement is simply made, requiring only the determination of the ambient air and the calorimeter chamber inlet air temperatures, the change of outlet air temperature with time (open circuit), air flow rate, and relative humidity. The use of insulation, sensors in the calorimeter wall and of a circulating water stream to measure temperature increase are unnecessary.

The thermodynamics of the LaNi5-H2 system by differential heat flow calorimetry I: Techniques; the α + β two-phase region

Abstract: The use of a heat flow calorimeter with the differential twin cell configuration to study intermetallic compound-hydrogen reactions is described. The techniques of calibration and operation of both the gas titration system and the calorimeter, which are required to obtain high precision enthalpies, are described and discussed. Enthalpies for the reaction in the two-phase region of the LaNi5-H2 system are independent of the overall composition but exhibit a small hysteresis with ΔHabs = −32.30 ± 0.07 kJ (mol H2)−1ΔHdes = 31.83 ± 0.09 kJ (mol H2)−1 where ΔHabs is the enthalpy of absorption, ΔHdes is the enthalpy of desorption and the errors are the standard deviations. The value of ΔHdes is the best value for the enthalpy of reaction between equilibrium phases with a total probable error of ±0.5 kJ (mol H2)−1.

Isothermal, isobaric, elevated temperature, high‐pressure, flow calorimeter

Abstract: An isothermal, isobaric, flow calorimeter suitable for measuring either endothermic or exothermic heats of mixing from 273 to 423 K and from 01 to 405 MPa is described Energy effects from 015 to 30 J/min can be measured to an accuracy of ±05% for standard test systems at a constant temperature through the use of an automatically controlled heater and a constant cooling Peltier device The calorimeter was tested by measuring the heat of mixing of water‐ethanol at 383 K and 1 MPa and was found to produce data in good agreement with published literature values

Automatic low temperature calorimetry for the range 0.3-320K

Abstract: The authors describe a fully automated process control, data recording and analysing system for measuring heat capacities in the temperature range 0.3K to 320K, using the Nernst method. The DC measuring system employs the CAMAC-norm in conjunction with an on-line-computer system (PDP 11/15-PDP 11/20), shared together with three other types of solid state physics experiments. The apparatus is characterised by a high flexibility to adapt to a wide range of different experimental conditions and has been tested in a series of high precision specific heat measurements. The low temperature calorimeter and the organisation of hardware and software components are described. The performance of the apparatus is illustrated by results obtained on a copper-standard sample.

The Graphite Calorimeter as a Standard of Absorbed Dose for Cobalt-60 Gamma Radiation

Abstract: Absorbed dose to water in a cobalt-60 gamma-ray beam has been determined using a thick-walled graphite ionization chamber. The chamber was calibrated in a graphite phantom against a graphite calorimeter, and the graphite calibration factor was converted to a water calibration factor using published energy absorption coeffi­ cient ratios and a measured replacement factor. Comparisons between the graphite and water measurements were made at pairs of points that were scaled in position according to the ratio of electron densities, so that the photon spectra were the same for the two points in a given pair. Measurements performed in graphite over a wide range of phantom depths, field sizes, and source distances, showed that the calibration factor varies slowly with the phantom depth and field size, and probably has a negligible dependence on source distance. By com­ parison with the thick-walled chamber in a cobalt-60 gamma-ray beam, a secondary ionization chamber can be calibrated in terms of absorbed dose to water with an estimated uncertainty of about ± 1 percent.

High‐temperature calorimetry (1000°–1500 °C): new calorimeter detectors, procedures of mixing, and automatic data exploitation

Abstract: New calorimetric detectors for measurements of enthalpies of formation of liquid ionic and metallic systems in the temperature range 1000°–1500 °C have been designed and assembled. Much attention was paid in designing these new detectors in order to obtain reliable data. The mixing method, used with a stirring device, allows avoidance of parasitic thermal effects, and therefore improves the accuracy of the measured heat of mixing. The acquisition and treatment system of the calorimetric data is described.

Design and performance of a new microcalorimetric system for aerobic cultivation of microorganisms

Abstract: A twin-type heat-conduction calorimeter for an aerobic fermentation process was designed and constructed fermentor both in batch and continuous runs. The time constant of the calorimeter was 3.3 min. The volumetric oxygen transfer coefficient (kLa) of the vessel was measured by a sulfite oxidation method in a continuous flow system under various rotation speeds and gas flow rates. Sufficient thermal stability of the calorimeter was obtained both in batch and continuous runs within the operation time period.

Specific heat anomalies in iron-chromium-nickel alloys

Abstract: The specific heat of FCC Fe-Cr-Ni alloys has been determined in an adiabatic calorimeter between 300 and 1200K. The experimental curves reveal two anomalous maxima at 500K and 800-900K with only a weak concentration dependence. The anomalies can be interpreted by thermally excited electron transitions with energy gaps corresponding to absorption bands that have been found in the infra-red absorption spectrum.

Study of the Phase Situation in 4-n-pentylphenyl-4′-n-heptyloxythiobenzoate (7S5)

Abstract: Results of measurements of the specific heat of 4-n-pentylphenyl-4′-n-heptyloxythiobenzoate in the temperature range from about 90 K to about 370 K are presented. They were carried out with an adiabatic calorimeter, a differential scanning calorimeter and a polarizing microscope. Adiabatic calorimetry revealed four anomalies in the specific heat vs. temperature curve viz., two associated with transitions in the solid phase, one with melting and one with the liquid-crystalline nematic-to-isotropic phase transition. Also, two modifications of the solid, stable and metastable, were found to exist. In addition, the DSC method applied in the 285 K to 370 K range revealed a smectic C phase, but only when the sample is being cooled. The polarizing microscope showed the structural polymorphism of the solid phase in the 297 K to 327 K range to be more complex than would stem from adiabatic calorimetry and DSC measurements alone. It also confirmed the occurence of the Sc phase on cooling as ascertained by ...

Enthalpies and temperatures of transformation for plutonium using a differential scanning calorimeter

Abstract: The enthalpies and temperatures of transformation of high purity plutonium were measured using a differential scanning calorimeter. The results of our study are presented and compared to values obtained by previous methods.

Determination of the Specific Heat Capacities of Aqueous Solutions of Pentose

Abstract: A laboratory-constructed isoperibol twin calorimeter of dry shield type (J. Chem. Thermodyn., 13, 89 (1981)) was used for measurements of the specific heat capacities of aqueous solutions of D-xylose, D-ribose, D-, and L-arabinose at ca. 30 °C. The partial molar heat capacity at infinite dilution, Cp.2∞ was determined. Values of Cp.2∞ obtained are: D-xylose 281±2, D-ribose 271±2, D-arabinose 278±3, and L-arabinose 270±4 J K−1 mol−1. Measurements of the heat capacity of these pentoses in the solid state, Cp.2* were carried out and the parameter ΔCp.2∞≡Cp.2∞–Cp.2* was evaluated. Values of ΔCp.2∞ are smaller than the corresponding values for hexose obtained previously. Similarly as had been the case for hexose, the additivity parameters of the group contribution on Cp.2∞ of solute estimated from the data on other nonelectrolytes were not acceptable for pentose. From this point the interactions working between solute of saccharide and the solvent water are considered to have characters largely different from ...

A procedure for the calculation of enthalpy changes from continuoustitration calorimetric experiments

Abstract: An isoperibolic titration calorimeter has been modified to perform continuous-titration measurements In order to take into account the unavoidable time-lag in the response of the sensor element to temperature changes, the process of heat transfer inside the calorimeter has been schematized A calculation procedure, based on this model, allows the interpretation of the experimental data and the determination of enthalpies of reaction The method has been tested by measurement of the heat of ionization of water and the heat of protonation of aminotris (hydroxymethyl) methane at 298 K The results are in good agreement with previously reported data The stepwise enthalpies of protonation of the phosphate ion in 015 mol dm–3 NaCl at 298 K have also been determined

Transitions of n-alkanes above the melting point

Abstract: The specific heat capacity of a series of n-alkanes was measured in a powercompensated differential scanning Calorimeter with high resolution Above the melting point the specific heat capacity increases strictly linear with temperature until 430 K In this region no transition of first, second or third order could be found Between 450 and 480 K the nalkanes show an exothermic effect bound to the first run with hermetically sealed sample pans It is assumed that this effect is a pressure induced epitactic ordering phenomenon correlative to the surface of the sample pan

Pattern Recognition in Calorimeters

Abstract: It is probable that LEP detectors will often include 4π calorimeters. Since this is a novel technique, not much expertise exists yet in the field of pattern recognition for large calorimeter systems. A fast method to simulate calorimeter signals, based on an analytical parameterization of electromagnetic and hadronic showers, developed by the UA1 software group on calorimetry, is presented. Some reconstruction problems are discussed, in particular the question of disentangling individual showers within an energetic jet.

Clay chemistry: Investigation of thermodynamics of ion exchange reactions by titration calorimetry

Abstract: We have built a titration calorimeter that is suitable for measurements on colloidal suspensions as well as more conventional chemical reactions in solution. This calorimeter has been used for investigation of a number of ion exchange reactions involving kaolinite and montmorillonite clays. Results of these measurements have led to cation exchange capacities, to enthalpies of ion exchange reactions, and also to equilibrium constants for some of these same reactions. These calorimetrically determined cation exchange capacities and equilibrium constants agree well with corresponding quantities obtained by way of conventional methods based on chemical analyses. It has been demonstrated that titration calorimetry is a useful and convenient method for investigation of ion exchange in clays.

Application of a digital computer to data acquisition and shield temperature control of a high‐temperature, adiabatic calorimeter

Abstract: The use of a digital computer, operating under real‐time, time‐sharing mode, for the operation of a high‐temperature (300–1300 K), adiabatic calorimeter is described. The specimen temperature and power to the specimen heater are logged continuously, from which the heat capacity is calculated for specified temperature intervals (e.g., 20 K). The determinate error in the calculated heat capacity is about ±0.6%. The temperature control of the adiabatic shields is quite comparable with that obtained previously with analog controllers. The temperature difference between the specimen and a shield can be maintained to about ±0.1 K. The heat capacity of a pure titanium specimen has been measured from 320 to 1020 K using the computer and also using the analog control. No discernible difference in results can be seen. The heat capacity data scatter about ±1% from a smooth curve fitted through the 325 data points.

Messung der spezifischen Wärme und des Joule-Thomson-Koeffizienten von Kohlendioxid bei Temperaturen von – 40°C bis 200°C und Drücken bis 15 bar

Abstract: In order to improve the experimental data for the thermal properties of carbon-dioxide, the isobaric heat capacity and the adiabatic Joule-Thomson-coefficient of carbon-dioxide have been measured with a flow calorimeter in the temperature range from −40°C to 200°C at pressures up to 15 bar. In the investigated range, the accuracy is better than 0.15 per cent for the heat capacity and 0.5 per cent for the Joule-Thomson-coefficient. The isothermal throttling coefficients at zero pressure, obtained by extrapolation of the experimental values, are consistent with the temperature dependence of the second virial coefficient as measured by A. and C. Michels.

A self-compensating, closed-circuit respiration calorimeter for small mammals and birds.

Abstract: Summary The calorimeter has special features which make it independent of changes in ambient temperature and pressure and therefore able to record precisely not only the integral of respiratory exchange over periods of 24 h but also the rate of oxygen consumption over short periods. Experiments with mice and kestrels (Falco tinnunculus) are presented to illustrate the accuracy of the apparatus.