Showing papers on "Calorimeter published in 1972"

Heat Capacity Measurements on Small Samples at Low Temperatures

Abstract: We describe a new calorimeter for measuring heat capacity in the range 1–35 K, using a silicon chip bolometer as sample holder, temperature sensor, and sample heater. The apparatus is capable of measuring very small samples (1–500 mg), and may be used with a number of different experimental methods.

Heat Capacity and Thermodynamic Properties of o‐Terphenyl Crystal, Glass, and Liquid

Abstract: The heat capacity of o‐terphenyl has been measured with an adiabatic calorimeter for the crystal from 2°K to Tm (329.35°K), for the glasses from 2°K to Tg (around 240°K) and for the liquid from Tg to 360°K, on a sample with less than 0.005 mole % impurity. The heat of fusion and the entropy of fusion are 17 191 J mole−1 and 52.20 J°K−1· mole−1, respectively. The residual entropy of the glasses at 0°K is about 15 J°K−1· mole−1. Above 170°K, the heat capacity of the o‐terphenyl crystal is nearly proportional to the temperature to within 1%. Configurational entropy of the supercooled liquid, estimated from the result of this investigation, is used to relate the relaxation properties of glass‐forming liquids according to the theory of Adam and Gibbs. Good agreement is found for both viscosity and NMR correlation frequency data.

Influence of temperature and composition on some physical properties of milk and milk concentrates. I. Heat capacity

Abstract: An isothermal jacket calorimeter was set up and apparent heat capacities of skim-milk, half-and-half milk, whole milk, and their concentrates up to about 30 % total solids were measured throughout the 5–70°C temperature range. Above the butterfat melting interval, the heat capacity of every sample was linearly related to temperature and a linear regression equation was found to relate heat capacity and total solids content for each one of the 3 milk sets. By means of an overall approximation, a single expression relating heat capacity, temperature and total solids content was also derived. To facilitate calculations of relative heat content for practical purposes, an average apparent heat capacity was computed for the whole temperature range and a nomogram was constructed for its determination from fat and solids-not-fat contents in any sample.

A Reference Calorimeter for Laser Energy Measurements.

Abstract: Principles and detailed procedures are described for measuring laser energy and power in terms of electrical energy based on voltage, resistance, and frequency standards. The construction of a small isoperibol calorimeter used for the measurements is described. The calorimeter will accommodate 0.01 to 20 J and 4 × 10-5 to 1 W cw and is limited to a maximum pulse intensity of 0.1 J/cm2. The standard deviation of comparison measurements using two calorimeters and a beam splitter is 0.08 percent when the smaller energy input is not less than 0.3 J. The estimated limits of systematic error for one calorimeter are ± 1.0 percent of the laser energy measured by the calorimeter.

The peak pool boiling heat flux from a sphere

Abstract: A hydrodynamic prediction is formulated for the peak nucleate boiling heat flux on spheres. It employs no empirical constants but it is justified by an experimental correlation of the vapor blanket thickness at the equator of the sphere. The prediction compares very favorably with 27 original data obtained by the transient calorimeter method in both water and N2 on spheres of different sizes. It also compares well with the data of prior investigators for a large range of size, gravity, and boiled liquids. Assumptions as to the vapor removeal configuration are supported with photographic observations of the boiling procss.

Calorimeters for heat of solution and low-temperature heat capacity measurements

Abstract: __________________________________________ _ Introduction ________________________________________ _ Acknowledgments ___________________________________ _ Low-temperature heat capacity calorimeter _____________ _ Cryostat components ____________________________ _ Submarine _________________________________ _ Electrical lead wires _________________________ _ Heat station ________________________________ _ Helium reservoir ____________________________ _ Isothermal shield ____________________________ _ Helium economizer __________________________ _ Floating ring _______________________________ _ Vacuum elevator and heat switch _____________ _ Adiabatic shield _____________________________ _ Calorimeter ________________________________ _ Thermometer _______________________________ _ Heater _____________________________________ _ Cryostat hoist_ _____________________________ _ Vacuum systems ________________________________ _ Adiabatic shield controller ________________________ _ Assembly ______________________________________ _ Temperature-energy measurements circuit_ _________ _ Operation and data reduction _____________________ _ Heat capacity results for Calorimetry Conference benzoic acid _____________________________________________ _ Page

Heat Flux Measurement Using Swept Null Point Calorimetry

Abstract: A new technique for measuring the heat flux incident on models tested in high-pressure arc heaters has been developed and demonstrated. The technique consists of sweeping an appropriately designed null point calorimeter across the jet at a rate sufficiently fast not to melt, yet slow enough to permit proper instrument response. This approach has the advantages of 1) measuring the heat flux profile across the entire jet, and 2) saving the instrument for reuse. Numerical heat conduction analyses of null point calorimeters were performed to assess a variety of potential measurement errors and to verify the feasibility of the swept approach. The swept null point technique was utilized to successfully measure the heat flux profile (with q peaks as high as 18k Btu/ft sec) across the AFFDL 50 MW RENT arc jet.

An Isothermal Displacement Calorimeter for Measuring Enthalpies of Mixing

Abstract: An isothermal displacement calorimeter of the Van Ness type has been constructed. The calorimeter was tested on three systems, benzene+cyclohexane, cyclohexane+n-hexane, and benzene+dichloromethane, at 25°C, and the performance of the calorimeter was discussed in connection with the literature values. The precision of the new calorimeter was within 0.5%; this was equal to, or better than, that of calorimeters of a similar type which have been constructed by several investigators.

Partial Heats of Mixing in the Bi-Sn system

Abstract: Partial heats of mixing have been measured at 725 K for liquid Bi-Sn alloys using a liquid metal solution calorimeter. Integral heats of mixing were calculated and were found to be endothermic. The experimental data are analyzed using the subregular model and the modified quasichemical model.

The Heat of Adsorption from Solution. I. The Heat of Adsorption of Benzene on Silica Gel from the Benzene-Cyclohexane Solution

Abstract: The sensitivity and reliability of the improved-flow micro-calorimeter have been examined by supplying given amounts of electric energy to the calibration heater inserted in the calorimeter. The detection limit of the heat amount was found to be 0.01 meal, and its probable error to be ±0.5 and ±0.3% at the heat evolutions of 10 and 40 meal respectively. The heat of the adsorption of benzene on silica gel from a cyclohexane solution has been measured at 30°C by the calorimeter thus constructed. The adsorption calorimetry indicates that benzene is adsorbed reversibly on silica gel, and that the differential heat of the adsorption of benzene is independent of the amount of adsorbed benzene, but that it depends strongly on the pretreatment temperature of the silica gel. The heats of adsorption were found to be 1.2, 1.6, 2.0, and 3.8 kcal/mol on silica gel samples treated at 100, 300, 500, and 800°C respectively. The findings on the heats of adsorption have been elucidated in terms of the interaction between b...

Heat flow calorimeter

Abstract: This invention generally relates to heat flow calorimeter devices for measuring heat liberated from or absorbed by an object and particularly concerns a calorimeter device capable of measuring the thermal output of sealed nickel-cadmium batteries or cells during charge-discharge cycles thereof. In the preferred embodiment, the invention contemplates the provision of a thermally isolated calorimeter vessel into which an object, such as a nickel-cadmium cell, is placed, heat exchange taking place between the object and the vessel. An elongated metal heat conducting rod is coupled between the calorimeter vessel and a heat sink, thus providing the only heat exchange path from the calorimeter vessel itself. Heater wires disposed within the calorimeter vessel supply additional heat to the vessel to maintain a constant temperature head therein or, more specifically, to maintain a constant temperature differential between the vessel and the heat sink. Any variation in the amount of heat supplied to the vessel and specifically any variation in power supplied the calorimeter vessel heater besides that necessary to maintain the constant temperature difference between the vessel and the heat sink is equal to the amount of heat liberated or absorbed by the object within the vessel itself, and means are provided for measuring this heater power. The apparatus is constructed into electrically insulated split halves so that the heat conducting rod and other components of the system are themselves utilized to conduct power to and from nickel-cadmium cell disposed within the calorimeter vessel.

Isothermal calorimetry method and apparatus therefor

Abstract: Method and apparatus for isothermal calorimetry in which the temperature within the calorimeter is maintained at a constant value by the application of energy in the form of pulses of constant power, which pulses are counted and summated, the number of pulses per unit time being determined by temperature control means.

Method for determining thermo-physical properties of specimens

Abstract: The square root of the product of thermophysical properties rho , c and k, where rho is density, c is specific heat and k is thermal conductivity, is determined directly on a test specimen such as a wind tunnel model. The test specimen and a reference specimen of known specific heat are positioned a given distance from a heat source. The specimens are provided with a coating, such as a phase change coating, to visually indicate that a given temperature has been reached as well as to ensure that both specimens have the same absorbtivity and thus receive the same heat rate. A shutter interposed between the heat source and the specimens is opened and a motion picture camera is actuated to provide a time record of the heating step. The temperature of the reference specimen is recorded as a function of time. The heat rate to which both the test and reference specimens have been subjected is determined from the temperature time response of the reference specimen by the conventional thin-skin calorimeter equation. This heat rate is then used to determine 2ROOT rho ck of the test specimen from the transient one dimensional heat conduction equation for a semi-infinite solid subjected to a step heat input at a constant heat rate. A model, such as a wind tunnel model, can be tested directly thus eliminating the costly and inaccurate method of making test models solely for the purpose of determining 2ROOT rho ck.

Calorimetry of Spark Energy

Abstract: A new calorimeter of balanced heat transfer type for the spark energy measurement has been designed and tested, and the calorimeter has been proved to exhibit a satisfactory performance, in accuracy and reproducibility of the measurements, as compared with conventional calorimeters of transient heat transfer type. The construction, experimental procedure and some results of this new type of calorimeter are described. Theoretical relations, which explain the results and will be helpful in the design of this type of calorimeter for different heat input and size, are also introduced.

Thermal Behavior of Solid CH3D in the Region T <10°K

Abstract: An attempt was made to determine the heat capacity of isotopically pure CH3D in the temperature regime where a Schottky‐type anomaly was known to occur. Before measurements were performed, the calorimeter system was usually kept at about T=20°K for 24 h or so. The results did not agree with extensive ones obtained earlier by Colwell for CH3D of normal isotopic purity nor were they reproducible from day to day. It had been suggested by Colwell that conversion occurs between the nuclear spin species of this methane at low temperatures and that his results corresponded to the equilibrium mixture at each temperature. Some experiments were therefore done with isotopically and chemically pure CH3D to which had been added 0.17% of O2, the object being to try to catalyze the conversion. While the addition of the O2 had a small effect, the heat capacities were still not reproducible. A subsequent detailed study of a specimen of CH3D of normal isotopic purity disclosed a slow evolution of energy (characteristic time ≥30 min) when the specimen was first cooled below T=10°K. If the calorimeter vessel was held at temperatures of 4°K or less for several hours, then the heat capacities became reproducible and similar to but not identical with those obtained by Colwell. The cause of the slow process cannot be established with certainty but the magnitude of the energy released and the fact that the process can be reversed suggest that conversion between the spin species of CH3D is involved. Several experimental tests showed that the process could not be associated with the λ‐type anomalies that occur in solid CH3D at T=16.1 and 23.1°K nor with pathological behavior of the calorimeter system.

Heater Lead Error in Calorimetry

Abstract: A summary of previous work is followed by an examination of the effects of radiation from heater leads. Solutions of the exact differential equation for particular experimental configurations have been obtained by a numerical method. For certain simple situations the solutions can be checked against partial or complete analytical solutions of the equation. It is shown that even for low temperature calorimeters a large part of the electrical energy dissipated in heater leads may be radiated unless the lead resistance is kept very low. If a significant part of the total energy supplied to the calorimeter is radiated, systematic errors may arise because, for a given calorimeter heating rate, the heater lead radiation loss will differ in the ``full'' and ``empty calorimeter'' experiments.

WR15 Microwave Calorimeter and Bolometer Unit

Abstract: Descriptions of the principal changes in the calorimeter and bolometer unit from the WR28 models of a microwave serving as National Bureau of Standards standard for power measurements in the frequency range 50 to 75 GHz.

Boundary cooled rocket engines for space storable propellants

Abstract: An evaluation of an existing analytical heat transfer model was made to develop the technology of boundary film/conduction cooled rocket thrust chambers to the space storable propellant combination oxygen difluoride/diborane. Critical design parameters were identified and their importance determined. Test reduction methods were developed to enable data obtained from short duration hot firings with a thin walled (calorimeter) chamber to be used quantitatively evaluate the heat absorbing capability of the vapor film. The modification of the existing like-doublet injector was based on the results obtained from the calorimeter firings.

Heat Capacities of Aqueous Solutions of Ethylene Glycol, Propylene Glycol and 1, 3-Butanediol

Abstract: A calorimerter composed of a Dewar vessel and a Beckmann thermometer was constructed. By means of this calorimeter, the heat capacities of aqueous solutions of ethylene glycol, propyrene glycol, and butanediol were measured at 30d C. It was confirmed by the measurement of heat capacities of n-heptane that the errors due to the evaporation were negligible. The partial molar heat capacities at the infinite dilution were obtained for the respective solutes. The structural changes of water caused by the dissolution of these solutes were discussed,

Pulsed‐Current Control and Measurement System for Precision Microcalorimetry

Abstract: Instrumentation for heat measurement in differential microcalorimetry is described in sufficient detail so the electronic apparatus can be built and used reliably with various calorimeters. Theory and calibration techniques are explained for calculating endothermic and exothermic heats from indicated digital data for reaction calorimetry and temperature scan calorimetry (including DTA). The cooler of twin calorimeter cells is heated electrically to counteract thermal effects of the system being measured. This heating is by pulses of current, all identical, whose rate of occurrence is controlled proportionally to the small residual intercell temperature gradient; counting pulses gives heat indication directly as numbers. The heat per pulse is known accurately, and the pulsed (indicated) heat is related to effects of the system under study; the relation is by a constant, near unity factor (such as 1.010) which can be calculated using easily measured calorimeter parameters. The factor is constant because hea...