Showing papers on "Calorimeter published in 2003"

Thermodynamic Properties of 1-Butyl-3-methylimidazolium Hexafluorophosphate in the Condensed State

Abstract: Thermodynamic functions for 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]) are reported in a range of temperatures from (5 to 550) K, based on new measurements by calorimetry. Heat capacities of the crystal, glass, and liquid phases for [C4mim][PF6] were measured with a pair of calorimeters. A vacuum-jacketed adiabatic calorimeter was used at temperatures between (5 and 310) K, and a heat bridge-scanning calorimeter was used from (300 to 550) K. With the adiabatic calorimeter, the fusion Tfus = 283.51 K, = 19.60 kJ·mol-1, and the glass transition Tg = 190.6 K were observed. The [C4mim][PF6] test sample was determined to have a mole fraction purity of 0.9956 by a fractional melting analysis. Densities of the liquid were measured in a range of temperatures from (298 to 353) K with a pycnometer equipped with a capillary neck. An unexpected endothermal transition, with a very small enthalpy change of 0.25 J·g-1 (0.071 kJ·mol-1), was observed in a range of temperatures from (394 to 412) K. He...

Measurement and calculation of arc power and heat transfer efficiency in pulsed gas metal arc welding

Abstract: This study investigates the heat transfer efficiency of the pulsed gas metal arc welding (GMAW-P) process. The arc power and heat input were calculated from arc current and voltage measurements and the heat input was also measured with a liquid nitrogen calorimeter. The measured heat transfer efficiency for GMAW-P varied slightly over a wide range of pulse parameters, with an average value of 70%, a maximum of 72% and a minimum of 68%. Welding heat transfer efficiency based on arc power calculated as the product of average current and voltage was too high (averaging 82%), while that calculated using the product of the root mean square (RMS) of the average current and voltage was too low (averaging 61%). Both also varied significantly with pulsing parameters. Mathematical analysis shows that average instantaneous power values must be used when current and voltage vary significantly with time. The experimental differences between the average instantaneous power and the other calculated values are ex...

A high-sensitivity differential scanning calorimeter with magnetic field for magnetostructural transitions

Abstract: We have developed a differential scanning calorimeter capable of working under applied magnetic fields of up to 5 T. The calorimeter is highly sensitive and operates over the temperature range 10–300 K. It is shown that, after a proper calibration, the system enables determination of the latent heat and entropy changes in first-order solid–solid phase transitions. The system is particularly useful for investigating materials that exhibit the giant magnetocaloric effect arising from a magnetostructural phase transition. Data for Gd5(Si0.1Ge0.9)4 are presented.

Enthalpy of Fusion of Indium: A Certified Reference Material for Differential Scanning Calorimetry†

Abstract: An adiabatic calorimeter was used to measure the enthalpy of fusion of a very pure sample of indium. The new value of the enthalpy of fusion was determined to be ΔfusH = (28.6624 ± 0.0076) J·g-1, where the uncertainty corresponded to a 95% confidence interval. The temperature of fusion of this sample was found to not differ from the ITS-90 assigned value within the accuracies of the thermometry used in the present study. A comparison with previous determinations is made.

Performance of the ATLAS electromagnetic calorimeter end-cap module 0

Abstract: The construction and beam test results of the ATLAS electromagnetic end-cap calorimeter pre-production module 0 are presented. The stochastic term of the energy resolution is between 10% GeV^1/2 and 12.5% GeV^1/2 over the full pseudorapidity range. Position and angular resolutions are found to be in agreement with simulation. A global constant term of 0.6% is obtained in the pseudorapidity range 2.5 eta 3.2 (inner wheel).

Precision calorimetry for the accurate measurement of inverter losses

Abstract: High precision calorimetry permits the direct measurement of losses in power electronic systems This paper describes improvements to the design of a double- jacketed, closed type calorimeter in order to make these measurements Calibration tests have confirmed that the new design can measure losses to an accuracy of better than 05 W in 200 W This calorimeter has been used to verify the accuracy of models for inverters for use in variable speed drives for domestic appliances Verification has been undertaken at a range of switching frequencies and confirms the ability of the models to predict inverter performance without recourse to physical prototypes

A New Small-Scale Reaction Calorimeter That Combines the Principles of Power Compensation and Heat Balance

Abstract: We developed a new prototype reaction calorimeter with an integrated infrared−attenuated total reflection (IR−ATR) probe that has a sample volume of 45 mL and uses a metal block as an intermediate thermostat. Isothermal conditions are maintained using the power compensation principle. An additional heat balance using Peltier elements is implemented to compensate for changes of the reactor-sided heat-transfer coefficient and to circumvent corresponding calibration steps. The new calorimeter has been tested using the neutralization of NaOH with H2SO4 and the hydrolysis of acetic anhydride. These experiments showed the precision of the new calorimeter and its capability to deal with fast and highly exo- or endothermic reactions. The kinetic parameters obtained from the IR and calorimetric measurements agree well with each other and with literature values. Even for the investigated simple reaction schemes, the IR−ATR probe provided additional information from what is obtained from the calorimetric signal alone.

Helium adsorbed on carbon nanotube bundles: one-dimensional and/or two-dimensional solids?

Abstract: Heat capacity measurements of 4He adsorbed on closed-end single-wall carbon nanotube bundles in the temperature range 1.5 K

A study of microsegregation in Al-Cu using a novel single-pan scanning calorimeter

Abstract: A single-pan scanning calorimeter has been developed that eliminates the smearing of latent heat that occurs in a conventional two-pan heat-flux differential scanning calorimeter (DSC) In the new calorimeter, accurate enthalpy/temperature data was obtained in pure Al without smearing, and excellent sensitivity to new phases was obtained in a multicomponent Al alloy (LM25) The calorimeter has been used to investigate microsegregation in an Al-445 wt pct Cu alloy The enthalpy/temperature data fell between that calculated, assuming no mixing in the solid (Scheil) and complete mixing in the solid (equilibrium solidification) The amount of segregation agreed well with that calculated using a diffusion-based model of microsegregation The difficulty of getting the fraction solid from the enthalpy data is discussed, and it is concluded that it is not possible to do so without using a microsegregation model In addition, it is concluded that it is wrong to assume that the enthalpy of an alloy can be given by a specific heat term and a constant latent heat term that depend on fraction liquid as is assumed in most casting models

Enthalpy of formation and heat capacity of Fe-Mn alloys

Abstract: The partial and integral enthalpies of mixing of liquid Fe-Mn alloys were measured as a function of the atomic fraction of iron (x) within the range of 0≤x≤0.45 at 1700±5 K, using a laboratory-built, high-temperature isoperibolic calorimeter. The minimum integral enthalphy of mixing at x=0.5 is about −820±45 J mol−1. The enthalpy of formation of solid γ-Fe-Mn alloys with 30.0, 40.0, 50.0, and 57.0 at. pct Mn was determined indirectly, using the same calorimeter, by dissolving these alloys in liquid aluminium at 1409±3 K, and the minimum value amounts to −1940±70 J mol−1 at x=0.5. The heat capacities of these alloys as well as the heat capacity of pure iron and α-Fe-Mn alloys with 0.95, 2.03, 2.73, and 4.30 at. pct Mn, were measured by a differential thermal analysis (DTA) technique and are described using a new analytical representation of the magnetic contribution. The composition dependencies of heat content, Curie and Neel temperatures, enthalpy of formation of α-Fe-Mn alloys, magnetic contribution to the enthalpy of pure Fe and its change due to the addition of Mn, as well as the change of enthalpy upon the γ → α transformation, were deduced from the experimental data. The results obtained were compared with experimental information available in the literature.

Initial hydration of cementitious systems using a simple isothermal calorimeter and dynamic correction

Abstract: A simple isothermal calorimeter ideal to study hydration of cementitious systems is described together with an ampoule design to allow addition of water and mixing with the ampoule inside the calorimeter. An overview of dynamic corrections is given, and the utilisation of the different dynamic corrections on the calorimeter output is discussed. Correction of data on b-hemihydrate hydration to form gypsum has shown good kinetic agreement with data from synchrotron X-ray diffraction.

Textured silicon calorimetric light detector

Abstract: We apply the standard photovoltaic technique of texturing to reduce the reflectivity of silicon cryogenic calorimetric light detectors. In the case of photons with random incidence angles, absorption is compatible with the increase in surface area. For the geometrically thin detectors studied, energy resolution from athermal phonons, dominated by position dependence, is proportional to the surface-to-volume ratio. With the CaWO4 scintillating crystal used as light source, the time constants of the calorimeter should be adapted to the relatively slow light-emission times.

Isochoric heat capacities of alkanols and their aqueous mixtures

Abstract: Isochoric heat capacities (c v ) of methanol, ethanol, and 1-propanol and binary mixtures of water with each of these alkanols were measured in the temperature range from 280 to 420 K and at pressures up to 30 MPa. The measurements were carried out on liquid-phase samples with a twin-cell type adiabatic calorimeter. Liquid densities were also reported in this work on the basis of the mass of the sample and the volume of the calorimetric cell. The experimental expanded uncertainty (with a coverage factor k = 2) of temperature measurements is ±13 mK, and that of pressure measurements is ±8 kPa. The expanded relative uncertainty for isochoric heat capacity is estimated to be ±2.2% for the liquid-phase measurements, and for density it is ±0.16%. The behavior of c v is anomolous, indicating that alkanol + water mixtures are strongly associated due to the influence of hydrogen bonds.

Measurements of Heat Transfer to a Massive Cylindrical Calorimeter Engulfed in a Circular Pool Fire

Abstract: A large-scale experiment was performed to measure heat transfer to a massive cylindrical calorimeter engulfed in a 30 minute circular-pool fire. This test simulated the conditions of a truck-sized nuclear waste transport package in a severe fire. The calorimeter inner surface temperature and the flame environment emissive power were measured at several locutions us functions of time. An inverse heat conduction technique was used to estimate the net heat flux to the calorimeter. Tall porous fences surrounded the test facility to reduce the effect of wind on the fire. Outside the fences, 2.9 m/s winds blew across the calorimeter axis at the beginning of the test but decreased with time. The wind tilted and moved the fire so that the initial flame environment emissive power was substantially less on the windward side than the leeward side. The calorimeter became more uniformly engulfed as the winds decreased. The maximum heat flux to the calorimeter was 150 MW/m 2 on the leeward side at the beginning of the fire, and generally decreased with time. The local variations of calorimeter temperature and heat flux were closely related to the local flame environment emissive power.

A Textured Silicon Calorimetric Light Detector

Abstract: We apply the standard photovoltaic technique of texturing to reduce the reflectivity of silicon cryogenic calorimetric light detectors. In the case of photons with random incidence angles, absorption is compatible with the increase in surface area. For the geometrically thin detectors studied, energy resolution from athermal phonons, dominated by position dependence, is proportional to the surface-to-volume ratio. With the CaWO4 scintillating crystal used as light source, the time constants of the calorimeter should be adapted to the relatively slow light-emission times.

ac nanocalorimeter for measuring heat capacity of biological macromolecules in solution

Abstract: A precise calorimeter has been developed to measure the heat capacity of a small amount of liquid using a novel ac calorimetric method in which the effect of heat loss from a sample cell is corrected using the phase of the ac temperature. The sample cell is made of a fine glass tube, whose outer surface is plated with a nickel film as an ac heater. The ac temperature of the sample is detected precisely with a microbead thermistor attached to the middle of the tube. The resistance of the thermistor is measured with an ac Wheatstone bridge which is composed of resistors with a low temperature coefficient of ±1 ppm/K. The unbalance ac signal of the bridge is measured with a lock-in amplifier. To reduce the drift of measured values caused by the variation of room temperature, the amplifier and measuring instruments with temperature coefficients of >1 ppm/K are kept at constant temperature. Moreover, the gain of the amplifier is calibrated at every measuring point. Consequently, the heat capacity of 10 μl liqu...

A method to determine mixing enthalpies by DSC

Abstract: A method has been developed that utilizes a special custom-made mixing device and HPLC micro liter syringe to perform mixing experiments of liquid systems directly in open measuring cells of differential scanning calorimeters. The present paper describes how to determine mixing enthalpies from time scans of the isothermal heat flux during an exothermal or endothermal process. Using ethylene glycol and the slightly volatile component water to calibrate the mixing calorimeter, the mixing enthalpy of the binary system poly(ethylene glycol) 400/water could be determined with sufficient precision compared to the results of measurements with a conventional flow calorimeter.

The differential reaction calorimeter: examples of use

Abstract: A new kind of calorimeter, commercialized by SETARAM SA and operating in isoperibolic mode, appeared 2 years ago: the differential calorimeter DRC ® . This DRC was developed by Aventis Pharma in their own laboratories and has been used as standard tool for 10 years. The Swiss Institute for the promotion of safety and security (Organic Process Research and Development (2002) to be published) has also studied this calorimeter. In order to show the accuracy of this apparatus, we can compare the DRC with the RC1 from Mettler Toledo which is the reference for safety studies. We can demonstrate the exactitude of results in a wide range of reactions: with one step (neutralization) or two steps (aldolisation–crotonisation), semi-batch reactions with addition of one reagent or simultaneous additions of two reagents, slightly or very exothermic reactions. In each situation, DRC will obtain the same data and results in less time with a smaller amount of raw materials.

Calorimeter probe for the DIII-D divertor

Abstract: Heat flux measurements of the DIII-D divertor plate have been obtained with 6 mm spatial resolution using a calorimeter probe. These measurements complement the infrared camera system normally used for heat flux measurements on DIII-D but at higher-spatial resolution. The calorimeter probe is inserted into the tokamak from below to a position which is flush with the lower divertor plate tiles using the divertor materials experimental station (DiMES). The DiMES mechanism allows for retraction of the probe behind a gate valve and removal from the tokamak for modification or calibration. A 6 mm diameter insulated graphite cylinder for collecting energy is mounted within a standard DiMES sample. A 0.8 mm diameter thermocouple, installed 4 mm below the surface, provides a measurement of the temperature during and after the plasma exposure. The 80 ms time constant for the measurement is fast enough to determine heat flux changes during the 5 s plasma discharge and heat flux profiles have been obtained using both fixed strike points and slow strike point sweeps across the calorimeter. Special electronics and isolation is necessary as the sample is in direct electrical contact with the plasma. The calorimeter observes approximately 100 °C temperature rise over one tokamak discharge. The thermocouple signals are typically less than 1 mV and must be amplified near the vacuum feedthrough, passed through a low-pass filter to eliminate magnetic pickup, isolated, and sent to the data acquisition system approximately 8 m away. Initial measurements are included.

DSC Curves and Further Evaluations

Abstract: A Scanning Calorimeter measures heat flow rates in dependence of temperature or time. Modern DSCs are nowadays always connected with a data acquisition system and a powerful computer (PC). This allows one to present the measured data online on a monitor in form of a curve. Normally the heat flow rate versus the program temperature (or time) is plotted, but it is also possible to calculate other quantities from the originally measured values and draw the respective graphs on the screen as well. Modern computer techniques make it possible to do even complicated evaluations of the just measured values in the background while the measurement runs.