Showing papers on "Calorimeter published in 1976"

Isothermal high pressure flow calorimeter

Abstract: An isothermal flow calorimeter suitable for measuring heats of reaction and heats of mixing at high pressure is described. With the calorimeter endothermic or exothermic processes can be studied from 0 to 70 °C and from 1 to 400 atm. Energy effects from 0.15 to 30 J/min are measured with a precision of ±0.4% at a constant temperature through the use of an automatic controlled variable heater and a constant cooling Peltier device. A complete heat‐of‐mixing curve can be generated from a single run. The calorimeter was tested by measuring the heats of neutralization of HClO4–NaOH and HClO4–TRIS and the heat of mixing of n‐hexane‐cyclohexane, and was found to produce data in very good agreement with published literature values.

Heat capacities of aqueous electrolytes: eight 1:1 electrolytes and ΔCp0 for ionization of water at 298 K

Abstract: We have made measurements with a flow calorimeter leading to apparent molal heat capacities of aqueous solutions of NaCl, HCl, KBr, KCl, KOH, NaBr, HBr, and NaOH at 298 K. Results have been used to...

High pressure calorimetry as applied to piezothermal analysis

Abstract: This paper describes an apparatus which can be used to determine bulk thermal expansion coefficients of liquids as a function of temperature and pressure up to 10 kilobar in a temperature range from −20° to 100 °C. The principle of the method consists in measuring the heat of compression by a step by step procedure. The apparatus is a Joule twin calorimeter which is composed of a high pressure vessel and a reference cylinder. Temperature differences between these two components can be detected at better than 10−5 K by means of a gas thermometer, thus providing high sensitivity. Results are given for liquid n‐hexane and ethyl alcohol.

Portable tissue equivalent calorimeter.

Abstract: A portable tissue equivalent calorimeter has been constructed and employed to measure absorbed dose in a mixed fast‐neutron and γ-ray field. Design details and measurement techniques are described along with the limits of precision and absolute accuracy. Experiments have been carried out with a cyclotron produced neutron beam using the 9Be(d,n)10B reaction at dose rates ranging from 3 to 25 rad/min. A series of ten measurements at a dose rate of approximately 10 rad/min were performed with a precision of ±2% (standard deviation about the mean). The compact design of this calorimetric dosimeter system facilitates transport to other laboratories for the measurement of absorbed dose in several complex radiation fields.

Absolute reference calorimeter for measuring high power laser pulses

Abstract: A calorimeter for making absolute energy measurements of high power laser pulses is described. The calorimeter, based on volume absorption in a solid, is calibrated electrically and requires no window or vacuum environment. An error analysis is included giving the systematic and random errors of the instrument for a laser measurement. Briefly, the following performance is typical of the 32-mm x 32-mm aperture calorimeter: range 0.4-15-J; random error +/-0.2% (one standard deviation); systematic error +/-2.3%; and an upper operational limit of 3 J/cm(2). Most of the volume absorber documentation is applicable for 1.06 microm; however, the calorimeter should be useful from the near ir through the visible. Absorbers for use with CO(2) lasers in the 9-11-microm range are also discussed.

Microcalorimetric measurements of heat production in human erythrocytes. IV. Comparison between different calorimetric techniques, suspension media, and preparation methods.

Abstract: Monti, M. & Wadso, I. Microcalorimetric Measurements of Heat Production in Human Erythrocytes. IV. Comparison between Different Calorimetric Techniques, Suspension Media and Preparation Methods. Scand. J. clin. Lab. Invest. 36, 573–580, 1976.Heat production in human erythrocytes from healthy subjects has been measured under different experimental conditions. Simultaneous measurements were made on the same samples using different types of microcalorimeters: a static ampoule calorimeter, an air perfusion calorimeter, and a flow calorimeter. Obtained heat effect values for specified standard conditions, Pd`, were within uncertainty limits the same for the different calorimeters. Cells were suspended either in autologous plasma or in a phosphate buffer. Pd` values for buffer suspensions were significantly higher than those for plasma suspensions. Erythrocyte samples prepared by the column adsorption technique gave higher Pd` values than those obtained by a conventional centrifugation procedure.

The thermodynamic parameters of formation of lanthanide squarate complexes

Abstract: The thermodynamic parameters of complexation of the lanthanide ions by squarate anions have been measured by potentiometric and calorimetric titrations. The design and operation of the calorimeter is described as it has some unique features. The complexes are weaker than analogous complexes with other hydroxy-keto ligands due to a more endothermic enthalpy of complexation.

Comparisons of calorimetric and ionometric measurements in graphite irradiated with electrons from 15 to 50 MeV.

Abstract: Extensive experimental comparisons of calorimetric and ionometric measurements have been made that cover a broader range of electron energies and depths in graphite than previously reported. Electron beams of 15, 20, 25, 30, 40, and 50 MeV were used. Calorimetric absorbed-dose measurements and ionometric specific-charge measurements in air were compared in graphite at depths from 1 to 51 g/cm2. The medium was irradiated with uncollimated electron beams produced by scattering after passing through a 0.1-g/cm2 aluminum vacuum window, various thicknesses of lead foils, and air. The variation in the quotient of the two measurements was studied as a function of lead-foil thickness, depth in the medium, beam energy, foil-to-detector distance, and off-axis distance. These studies permitted the measurements to be corrected and compared with theoretical calculations that assume a broad medium irradiated with broad, parallel, monoenergetic electron beams. The overall experimental uncertainty is estimated to be 1%. The results are generally in good agreement with theoretical and experimental results of other investigators. The calorimeter received close to 1 Mrad during preliminary measurements and from 1 to 2 Mrad during the measurements reported. The results showed no detectable heat defect in graphite after prolonged periods of exposing the calorimeter to air at atmospheric pressure.

Broad spectral electromagnetic radiation calorimeter: Centimeters to microns

Abstract: A specially designed calorimeter is presented capable of measuring total electromagnetic radiated power, in a single pulse mode over the complete spectral range, microwaves to far infrared. The device is assembled in the shape of a pyramid made from thin sheets of graphite absorber, giving it an operating range from centimeter wavelengths to the infrared region with an absorption coefficient of 0.99 at 1.25 cm wavelength. The calorimeter is capable of yielding a linear voltage response from less than 8 mJ up to at least 35 J with an overall sensitivity of 0.05 V/J. The device has the added feature of yielding information on waveguide modes. An example of the calorimeter use is presented.

Improved flow microcalorimeter for biophysical studies.

Abstract: The flow version of the Beckman model 190 microcalorimeter has been improved by replacing the original platinum tubes with Teflon tubing and a Kel‐F mixing chamber, and introducing a physically identical reference system into the thermopile. This modification abolishes the occurrence of spontaneous and irreproducible heat effects probably due to catalytic reactions of the platinum with sulfhydryl groups of the biochemical systems, and permits operation of the instrument as a differential calorimeter. The time constant of the instrument is 50 sec and the useful sensitivity is 6 μcal/min as demonstrated by calibration experiments employing HCl‐neutralization and sucrose dilution. The calibration constant has been shown to be independent of the magnitude of the heat effects, the flow rate, and the mode of operation by continuous flow or pulsed flow experiments. The accuracy of experiments on biophysical problems has been illustrated by the good agreement of the binding enthalpies for the association of NADH ...

The heat capacities and heat content of molten cerium by levitation calorimetry

Abstract: A 15 kVa, 450 kHz radio frequency generator was used to levitate and melt cerium samples ranging in size from 0.4 to 1.7 g. The molten cerium samples were then dropped into a copper block calorimeter contained in isothermal surroundings. The cerium data between 1400 and 1700/sup 0/K indicated a nonlinear heat content function as described by the equation: H/sub T/ -- H/sub 298/./sub 15/ = --0.01255 T/sup 2/ + 75.305 T -- 32,995.401 J/mol. The correlation coefficient for the curve fitting process was 0.81. The data between 1700 and 2500/sup 0/K indicated a linear heat content function as described by the equation: H/sub T/ - H/sub 298/./sub 15/ = (31.616 +- 0.596)(T - 1077) + (38,917.267 +- 575.049) J/mol. The average percent deviation between this and the experimental values was 0.67. Experimental heat contents were corrected for convection and radiation heat losses during the fall of the sample from the levitation chamber into the calorimeter. The maximum estimated error for the levitation calorimetry work was +-2.5 percent.

Flow calorimeter cell for measuring heats of solution of solids

Abstract: A novel flow calorimeter cell has been designed to allow insertion of soluble solids into the stream of the flowing solvent fluid. Only small amounts (∼1 mg) of solid material are required. A model of the flow cell has been constructed for use within a Tian–Calvet microcalorimeter. Effective thermal equilibrium of the flowing fluid is achieved by a counterflow technique developed by Gill, Nichols, and Wadso in a similar system for study of heats of slightly soluble liquids. A precision of 1–2% is obtained by measurements of the heat of solution for diketopiperazine and several purine and pyrimidine compounds at 25 and 40 °C.

Calorimeters for making measurements at pressures above 1000 bars

Abstract: A calorimeter for measuring the latent energy of a sample at a pressure of at least 1,000 bars has a test chamber enclosed in a substantially adiabatic enclosure. It has thick walls able to withstand the very high pressure, and is connected by capillary tubing to means for holding it at a set pressure. The test chamber and a reference body which is thermally equivalent to the chamber are surrounded by respective adiabatic jackets and symmetrically arranged in an isothermal enclosure which is held at a set temperature. A differential gas thermometer has bulbs in contact with the test chamber and with the reference body, and a two-input differential pressure measuring unit has each input connected by a capillary tube to one of the bulbs. The pressure measuring unit has a manometer capsule with a respective input on each side of a flexible membrane, a capacitive pickup for sensing the position of the membrane, and electronic readout means. It is enclosed in a thermally insulative case.

The standard enthalpies of hydrolysis and formation of tricyanophosphine

Abstract: By use of a solution calorimeter the standard enthalpy of hydrolysis of P(CN)3(c) at 298.15 K has been determined as –44.9 ± 0.1 kcal mol–1 and the derived standard enthalpy of formation as 117.9 ± 6.0 kcal mol–1. The enthalpy of sublimation of P(CN)3 was determined by effusion manometry as 18.0 ± 0.7 kcal mol–1 and the P–CN mean bond dissociation energy was estimated as 84 kcal mol–1.

Compact calorimeter for measuring laser absorption coefficients of small samples

Abstract: A relatively simple calorimeter has been designed for measuring laser absorption coefficients on samples of small cross‐sectional area. This instrument has proven useful in studies of absorption or scattering within samples by microscopic defects, where bulk samples of small volume are required.

Calorimeters for pulsed lasers: calibration

Abstract: A calibration technique is developed and tested in which a calorimeter used for single-shot laser pulse energy measurements is calibrated with reference to a cw power standard using a chopped cw laser beam. A pulsed laser is required only to obtain the relative time response of the calorimeter to a pulse. With precautions as to beam alignment and wavelength, the principal error of the technique is that of the cw standard. Calibration of two thermopiles with cone receivers showed −2.5% and −3.5% agreement with previous calibrations made by the National Bureau of Standards.

Calibration and performance of a small animal gradient layer calorimeter box.

Abstract: Calorimetry, using the gradient layer technique, has become well established in the study of energy metabolism. The use of a commercially constructed gradient layer box within a calorimetry system designed to measure directly and indirectly the metabolic sequelae of thermal injury in rats, is described. Variations in the signal output were discovered. These were found to be dependent upon: (a) stability of the ambient temperature (b) stability of the gradient layer box water jacket temperature (c) position and size of the calibrating heat source.

Variable-aperture calorimeter for an unstable resonator.

Abstract: A new technique for measuring the output power from a cw edge-coupled unstable resonator has been developed and applied to a cw DF laser. An internal-cavity calorimeter was used that permits measurement of output power with a variable rectangular mode geometry while containing the radiation inside the resonator. The variable aperture calorimeter absorbing scraper (VACAS) device consists of an absorbing copper plate calorimeter assembly, which replaces the 45 degrees output coupling mirror of a conventional edge-coupled unstable cavity. A rectangular hole in the plate of variable width w and height h defines a rectangular mode of variable width Mw and height Mh within the geometric optics approximation, where M is the magnification. Two important applications of VACAS are (1) the determination of the optimum mode geometry for a cw diffusion-type chemical laser where there is significant variation in gain across the unstable resonator mode and (2) the determination of the power tradeoff between mode width and the number of folds in a folded unstable resonator configuration.

Fast rise-time calorimeter for relativistic electron beam diagnostics

Abstract: A 10‐μsec rise‐time calorimeter using an infrared optical pyrometer for temperature measurement is described. The present equipment is suitable for pulsed high‐energy electron beam diagnostics in graphite targets over the range from 100 to 4000 J/g and includes provisions for temperature calibration and optical alignment. Measurement procedures and applications of the equipment are described. These applications include high‐speed energy absorption diagnostics and measurement of absorbed energy profiles versus target penetration. Improvements over conventional calorimetric dosimeter accuracy appear to be possible for some types of measurements with this approach. The present work demonstrates better than ±3% accuracy for measurement of absorbed energy in a series of experiments.