Showing papers on "Calorimeter published in 1973"

Heat capacity of seawater solutions from 5° to 35°C and 0.5 to 22‰ chlorinity

Abstract: The specific heat of seawater solutions from 0.5 to 22‰ chlorinity has been determined at 5°, 15°, 25°, and 35°C by using a new precision heat capacity calorimeter (Picker et al., 1971). The concentration dependence Cl (‰) of the specific heats cp has been fit to cp = cp° + ACp Cl (‰) + BCp Cl (‰)3/2, where cp° is the specific heat of pure water and ACp and BCp are temperature-dependent constants. The specific heats fit this equation with an average deviation of ±0.0002 joule deg−1 g−1 between 15° and 25°C and ±0.0005 joule deg−1 g−1 at 5°C. The specific heats determined in this study are in excellent agreement (±0.002 joule deg−1 g−1) with the results of Cox and Smith (1959) and Bromley et al. (1967, 1970). The apparent equivalent heat capacity ΦCp for sea salt has been determined from these heat capacities, and the concentration dependence (Im is the molal ionic strength) has been analyzed by ΦCp = ΦCp° + SCpIm1/2 + bCpIm, where ΦCp° is the infinite dilution equivalent heat capacity of sea salt (related to ion-water interactions), SCp is the Debye-Huckel limiting law slope (related to ideal ion-ion interactions), and bCp is an empirical constant (related to deviations from the Debye-Huckel limiting law). The relative apparent equivalent heat capacity ΦJ = ΦCp − ΦCp° calculated from our results is in good agreement with the temperature dependence of the enthalpy of seawater ΦJ = ∂ΦL/∂T calculated from the apparent equivalent enthalpy data ΦL of Millero et al. (1973). Young's (1954) rule, ΦCp = ∑EiφCp(i), has been used at 25°C to estimate the ΦCp of sea salt by using data on the major components of seawater in pure water. The estimated ΦCp and cp are in excellent agreement with the measured values.

Calorimetric Study of the Glassy State. VIII. Heat Capacity and Relaxational Phenomena of Isopropylbenzene

Abstract: The heat capacities of isopropylbenzene were measured with an adiabatic calorimeter for the crystal from 14 to 177.13 K (Tm), for the glassy state from 14 to around 126 K (glass transition temperature: Tg) and for the liquid from Tg to 313 K, with a sample of 99.93% purity. The heat and entropy of fusion were found to be 7326 J mol−1 and 41.36 J K−1 mol−1, respectively. Based on these data, a set of thermodynamic functions are tabulated at rounded temperatures. In addition to the primary glass transition phenomenon, a secondary enthalpy relaxation as well as a step-like heat capacity anomaly was observed at around 70 K. These facts were discussed in correlation with the β-relaxation already observed by dielectric measurement. Gonfigurational entropies of the supercooled liquid and of the glassy state were calculated to investigate a relation with relaxational properties. The agreement is found between the temperatures where catastrophe occurs in viscosity (T0), and where the configurational entropy vanish...

An Isothermal Titration Microcalorimeter

Abstract: An isothermal titration microcalorimeter having a volume of 4 ml and capable of temperature control to ± 2 × 10−5 °C is described. Major components include a constant temperature water bath controlled to ± 3 × 10−4 °C, a platinum reaction vessel, and an isothermal control circuit consisting of constant Peltier thermoelectric cooling and variable Joule heating controlled by a thermistor in an ac Wheatstone bridge circuit. The calorimeter was tested by measuring the heat of ionization of water and was found to produce data accurate to ±0.1% for this system. The instrument is ideally suited for measuring heats where small samples are used such as in the investigation of many biological systems.

Automatic Calorimetry in the 3–30 K Range. The Specific Heat of Copper

Abstract: Automatic data acquisition is by means of a slightly modified version of a hard‐wired system described previously (Martin and Snowdon, 1970) combined with an on‐line minicomputer which controls the calorimeter heating rate and computes temperature and specific heat. The new cryostat, calorimeter assembly, and adiabatic shield control are briefly described. Experiments to verify the accuracy of germanium thermometry with the automatic ac bridge are detailed. Operation of the system is illustrated by results on pure copper which show a standard deviation of 0.3% (mostly due to temperature scale defects rather than inherent lack of precision) and agree well with the Copper Reference Equation below 20 K but above this temperature agree more closely with the results of Cetas, Tilford, and Swenson [Phys. Rev. 174, 835 (1968)].

Heat capacity of molten polymers

Abstract: Heat capacities of molten polyethylene, polypropylene, poly-1-butene, polystyrene, and poly(methyl methacrylate) were measured over a wide range of temperature by using a differential scanning calorimeter. The upper limit of temperature was established for each polymer at about 10°K below the beginning of thermal decomposition. For poly-1-butene and poly(methyl methacrylate) the solid-state heat capacity was also measured starting from room temperature. Several samples of each polymer were used so that average values of heat capacities could be established (reported in 10°K intervals). The data revealed for all polymers a nearly linear increase of heat capacity with increasing temperature over the whole temperature range investigated.

An Absolute Method of Measuring Energy Outputs from CO2 Lasers

Abstract: In the energy meter described here the CO2 laser radiation is almost completely absorbed by an Al2O3 surface on an aluminum plate. The high absorption of the surface (≥95%) eliminates the need for calibration and the laser energy is computed by measuring the temperature rise of a plate with known thermal capacity. Experimentally we find that the calorimeter noise level corresponds to an energy density of about 2 mJ/cm2. Calculations indicate that the instrument is capable of measuring the energy of a single pulse that is 1 nsec wide, provided the pulse contains an average energy density of 10 mJ/cm2. We have estimated the radiation and convection losses and found them to be negligible. The calorimeter is good for radiation between 8.5 and 11 μ; however, with modifications the bandwidth could easily be increased.

A Plasma Calorimetric Probe

Abstract: A high‐temperature calorimetric probe was shown to be a reliable method of measuring temperatures in argon and helium plasma jets in the range 2000 to 10 000 K. A number of simple corrections were found to be necessary to account for the heat transfer interactions between the calorimeter, its insulating jacket, and its water‐cooled support, as well as for the flow of heat to the nose section of the calorimeter. At the high temperature level (12 000 K), the probe measurements agreed with the spectroscopic data reported in the literature, while the values in the lower temperature range were confirmed by thermocouple measurements. The probe could also be used to measure gas composition and gas velocity, and results of typical applications are given.

Calorimetric study of flammable fabrics. I. Instrumentation and measurements

Abstract: A calorimeter has been designed, calibrated, and tested to measure the total amount of heat released and the rate of heat released from the combustion of fabrics in air. Calibration of the calorimeter gave a reproducibility of ±3% for total heat measurements and ±5% on rate measurements. Consideration of systematic errors gives an expected accuracy of ±7% for total heat and ±10% for combustion rate measurements. Measurements on cotton show that 90% of the standard heat of combustion is released when cotton is burned in air. The rate of heat release for cotton is independent of fabric weight. The constancy of rate of heat release as determined calorimetrically confirmed the result implied by the 45° test measurements on flame spread rate. The rate and amount of heat release of other commercial fabrics and blends were also measured.

Calorimetry of Small Samples with Low Thermal Diffusivity

Abstract: A system for measuring small specific heats of samples with low thermal diffusivity is described. A simple method for treating data obtained using discontinuous heating when temperature drifts and thermal nonequilibrium are large is introduced. The measurements on a copper sample deliberately in poor thermal contact with a calorimeter provided a test of the system and data handling.

Heat Capacities of Polyethylene from 2 to 360 K. I. Standard Samples of Linear and Branched Polyethylene Whole Polymer.

Abstract: Heat capacities of two well characterized polyethylene samples have been measured from 2 to 360 K in a precision vacuum adiabatic calorimeter. The two samples are derived from the same stocks from which NBS standard reference materials (SRM) 1475 and 1476 for linear and branched polyethylene whole polymers, respectively, were established. Both samples have been studied in the conditions as received. The branched polyethylene sample has also been studied following various thermal treatments in the calorimeter. The effect of thermal history on the behavior of branched polyethylene has also been studied by differential scanning calorimetry.

An absolute calorimeter for high power CO2 laser

Abstract: An easy to operate absolute calorimeter has been successfully built and calibrated in order to measure the energy output of a high power TEA CO2 laser The laser beam is completely absorbed in a plastic foil glued on a copper plate A thermocouple measures the difference of temperature between two separate sandwiches of Plexiglas and copper plates, one of them taken as reference Tested between 1 and 15 J at 106 mu m, the device showed an accuracy of 5% In the best case, the maximum absorbed power could reach 80 MW cm-2 without any visible damage to the calorimeter Such calorimeters are particularly convenient for the energy measurement of a high power laser with large beam cross section

Studies on a dynamic adiabatic calorimeter. I. Heat leakage at high temperatures

Abstract: In dynamic adiabatic calorimetry, the heat exchange between the calorimeter and its surroundings has been measured from room temperature to 800 degrees C, and the effects of heating method, atmosphere, heating rate and heat content of the sample upon the heat leakage are discussed. From these measurements, it is concluded that the necessary conditions for absolute measurement are that the heat leakage be minimal and constant. This may be achieved by using external heating of the sample and controlling the heating rate.

An Adiabatic Twin Calorimeter Using Electron Beam Heating

Abstract: An adiabatic twin calorimeter is described in which sample and dummy are heated by bombarding them with 5 keV electrons. The electron beam coming from outside the adiabatic jacket is directed alternatingly to sample and dummy. The heating power generated in the sample is varied by changing the hold‐up time of the beam at the sample with respect to that at the dummy. The required measurement of the ratio of heating powers in sample and dummy is replaced by a time measurement. The calorimeter is capable of measuring the ratio of the heat capacities of sample and dummy with a resolution better than 10−3. By measuring the specific heat of nickel and comparing the result with literature data the systematic error of the calorimeter was found to be less than 1%.

High temperature specific heats of iron-rich iron-titanium alloys between 600 and 1150K

Abstract: High temperature specific heats of iron-titanium alloys with up to 4.78 at.% Ti were measured with a heat exchange calorimeter. All samples show a pronounced sharp λ-peak in the specific heat. The Curie temperature, as determined from the position of this peak is, within experimental accuracy, independent of titanium concentration.

Liquid Bismuth Calorimetry: Enthalpies of Solution of Copper, Indium, and Tellurium, and Enthalpies of Formation of Cuprous Selenides

Abstract: An isoperibol liquid metal solution calorimeter in which samples are introduced below the surface of the melt is described. Enthalpies of solution in liquid bismuth at ca. 625°K in kcal mol−1 were ...

Calorimeter for picosecond laser pulses.

Abstract: Calorimeters have been designed and constructed that can measure the energy content of picosecond 1.06-μm laser pulses ranging in energy from ~13 μJ to 200 J. Noise levels are approximately 55 dB below individual instruments’ upper limits. The thermopile output voltage peaks in less than 2 sec and recovers with a time constant of ~50 sec or less.

Study of the radiation post-polymerization of solid n-phenylmaleimide with a diathermal calorimeter☆

Abstract: The PMI, recrystallized from dry benzene, had m.p. 89-90 °. For the calorimetric investigation we used the diathermal calorimeter described in reference [3]. Some minor changes in design (increase of the power of the heater, improvement in the thermal insulation etc.) enabled the working temperature range to be extended to 370°K. The PMI samples were irradiated in the calorimeter cells by 6°Co y-radiation at a dose rate of 4.5 Mrad]hr, at 77°K. The irradiated cell containing the monomer was transferred to the calorimeter at 77°K and the calorimetric melting curve was recorded at a uniform rate of warming up. After melting of the contents the cell was opened and the yield of polymer was determined gravimetrieally.

A differential calorimeter for studies of polymer-monomer interactions in solution and for the measurement of heats of mixing

Abstract: The construction, operation and performance of a twin-cell differential calorimeter is described. The calorimeter was constructed primarily to detect the changes of enthalpy resulting from specific interactions between polymers in solution and monomers and thus to identify systems in which the monomer is likely to polymerize at an enhanced rate on the polymeric 'template'. It is shown that with this calorimeter it is also possible to measure the heats of mixing at high dilution of liquids of low molecular weight with fair accuracy. The heats of mixing so obtained for several pairs of liquids agree well with values given in the literature.

Design of a Calorimeter for the Continuous Study of Heat Production during Anaerobic Microbial Growth

Abstract: A conduction type calorimeter has been designed to chase microbial growth in batch system. The calorimeter is of a twin structure having thermopile plates as a temperature sensor. The heat evolution during the microbial growth at a required temperature can be observed as an output-voltage generated at thermopile terminals with a sensitivity of 58.5mV K-1 A stainless steel cell with a volume of 300cm3 serves as a culture cell which is capable of being autoclaved prior to the initiation of calorimetric run, taking out from the calorimeter body. Because of the twin structure, the apparatus works with sufficient stability in detecting small heat evolution for long duration. Its operation has been demonstrated with the growth of Sacch. cerevisiae grown on liquid synthetic medium under anaerobic condition.

Isothermal Titration Calorimeter

Abstract: The construction and performance of an isothermal titration calorimeter is described. It is based on continuous automatic balancing of constant Peltier cooling with variable Joule heating. By using this arrangement the short response time (∼5 s) obtained, makes this instrument particularly suitable for applications to solution kinetics and for thermometric titrations.

Heat capacity of amorphous polyhexene-1 between 20 and 300°K: Intramolecular vibrational contribution to Cv below the glass transition

Abstract: The heat capacity of polyhexene-1 was measured between 20 and 300°K. The apparatus, an adiabatic calorimeter giving results with a random error of 0.2–0.4%, is briefly described. The characterization of the sample by x-ray diffraction patterns established that it was amorphous at all temperatures. Gold foil was incorporated with the sample to increase the apparent thermal diffusivity and so to decrease the time needed for the measurements. The glass transition temperature was found to be 215.5 ± 1°K. On the Cp curve, no subglass anomaly was detected, unlike the results of experiments described elsewhere. The calculation of Cv is discussed, and an explanation is given for the choice of the number of intramolecular vibrational modes per monomer which are assumed to contribute to Cv. A linear continuum model with characteristic temperature θ1 = 736°K allows us to fit the experimental curve over a temperature range of 140°K.