An isothermal heat flow calorimeter for large-volume applications

Design, construction, calibration, and testing of a new isothermal heat flow calorimeter suitable for investigation of large-volume specimens are presented. The measuring vessel has the volume of 1370?cm³, and the calorimeter allows for the measurement at surrounding air temperatures of 5?C60?°C. A practical application of the device is demonstrated at the determination of specific hydration heat of cement paste and concrete with silica-aggregate size of up to 16?mm, having the same water/cement ratio. The differences over the whole measuring time period of about 100?h are lower than 2% which indicates a good potential of the calorimeter for the measurement of total hydration heat of composite materials. A reference measurement of hydration heat of cement paste using common isothermal heat flow calorimeter with the measuring vessel of 1?cm³ shows an agreement within ±7%, which seems acceptable, taking into account the heat transport processes in the far larger specimens. The designed calorimeter may find use in future also in other applications where larger specimens are required, such as the measurement of adsorption heat, solution heat, various reaction heats, and enthalpy of liquid?Csolid transition in heterogeneous systems with large representative elementary volumes.     

Micro flow calorimeter for thermoelectrical detection of heat of reaction in small volumes

A micro chip element with an integrated flow channel and thin film thermopiles was developed in order to realize a micro calorimeter for small volumes in a flow arrangement. The flow channel consists of two inlets, a mixing region, a measurement region, and one outlet. Thermopiles of BiSb/Sb thermocouples were used as thermal transducers because of their extraordinary high thermopower. A thin film heater of a NiCr alloy was integrated in order to yield the possibility of internal electrical calibration. In addition, this heater can be used for thermal modulation of the whole measurement system. The calorimeter was prepared using vacuum evaporation, PECVD and magnetron sputtering for thin film deposition and photolithography as well as chemical wet etching for microstructuring. The function of the device was tested to neutralize 400 nmole, 100 nmole and 10 nmole NaOH by H₂SO₄.     

Micro-combustion calorimetry employing a Calvet heat flux calorimeter

Two micro-combustion bombs developed from a high pressure stainless steel vessel have been adapted to a Setaram C80 Calvet calorimeter. The constant of each micro-bomb was determined by combustions with benzoic acid NIST 39j, giving for the micro-combustion bomb in the measurement sensor k_m=(1.01112±0.00054) and for the micro-combustion bomb in the reference sensor k_r=(1.00646±0.00059) which means an uncertainty of less than 0.06 per cent for calibration. The experimental methodology to get results of combustion energy of organic compounds with a precision also better than 0.06 per cent is described by applying this micro-combustion device to the measurement of the enthalpy of combustion of the succinic acid, giving Δ_cH^∘_m(cr, T=298.15 K)=−(1492.89 ± 0.77) kJ · mol⁻¹.     

A constant heat-flux calorimeter for measuring heat transfer data

A new isothermal calorimeter, designed especially for simultaneously measuring the heat of reaction and the heat transfer data in a reaction solution, is described. The system, called a Constant Heat-Flux Calorimeter, is similar to a differential scanning calorimeter in terms of direct calorimetric measurement of the energies of reaction, but differs from the conventional calorimeters described in the literature. With this device, one recorded output in a temperature control circuit is a linear function of change in energies of reaction, and second in a differential temperature control circuit is found to be proportional to a resistance to heat transfer in a solution. The performance of the calorimeter was evaluated on the basis of some results on heat transfer data of aqueous solution of polyethylene glycol and on solution polymerization of styrene at constant temperatures.     

A compact differential isoperibol calorimeter with variable heat shields

The dynamic characteristics of an isoperibol solution calorimeter with electrical heating are discussed on a theoretical basis.The design requirements of a solution calorimeter are briefly reviewed. A calorimeter which satisfies these requirements was conducted and is described here. The dynamics of solutions heating by an electrical heater are mathematically developed and computer generated heating curves are compared to experimental curves.     

Determination of heat of mixing and heat of vaporization with a differential scanning calorimeter

A simple method is presented for measuring the heat of mixing and the heat of vaporization of volatile liquids at temperatures below their boiling point. It consists in introducing liquids by a microsyringe into a nearly closed cell of the DSC. The relative standard deviation for 4 to 5 runs is ca. 5% for heat of mixing and ca. 2% for heat of vaporization.     

An adiabatic low-temperature calorimeter for heat capacity measurement of small samples

A small sample adiabatic calorimeter for measuring heat capacities in the temperature range 60–350 K using the Nernst method has been constructed. The sample cell of the calorimeter is 6 cm³ in the internal volume, equipped with a miniature platinum thermometer and surrounded by two adiabatic shields. Two sets of 6-junction chromel-copel thermocouples were mounted between the cell and the shields to indicate the temperature differences between them. The adiabatic conditions of the cell were automatically controlled by two sets of temperature controller. A mechanical pump was used to pump out the vapour of liquid nitrogen in the cryostat to solidify N₂ (1), and 60 K or even lower temperature was obtained. The performance of this apparatus was evaluated by heat capacity measurements on α-alumina. The deviations of experimental results from a smoothed curve lie within ±0.2%, while the inaccuracy is within ±0.5% compared with the recommended reference data in the wole temperature range.     

Pulse microcatalytic setup with a reactor inside a flow calorimeter

A pulse microcatalytic setup, whose reactor is placed inside a Thiane-Calvet microcalorimeter is suggested. This setup permits to carry out simultaneous measurements of thermal effect and kinetic parameters of heterogeneous catalytic experiments during one experiment.

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Fuzzy control for the precision water bath of the heat exchange calorimeter

Fuzzy inference approach was applied to select the control input for the precision water bath of the heat exchange calorimeter used at a non-air-conditioned laboratory. The thermal fluctuation of the bath water was necessary to be kept within a narrow range. The cooling water or coolant kept at a temperature lower than the set temperature was circulated in the bath. The deviation corresponding to the difference between the set temperature and the observed temperature was observed as the input signal. The output or control input to be given to the heather element in the water bath was calculated by the fuzzy modus. The output function was simplified by means of circulating the cooling water. The contribution of each membership function was changed according to the thermal progress of the observed temperature of the water. The whole system including the control programs was examined by a practical water bath, and fairly good results were obtained. Reasonable recoveries were also shown for external thermal disturbances given to the controlled system.

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Zusammenfassung Zur Wahl des Regel-Inputs des Präzisionswasserbades für ein Wärmeaustauschkalorimeter in einem nicht klimatisierten Laboratorium wurde eine Unschärfeschlußnäherung angewendet. Die thermischen Schwankungen des Wassers im Wasserbad müssen in engen Grenzen gehalten werden. Das Kühlwasser oder Kühlmittel mit einer niedrigeren Temperatur als die eingestellte Temperatur wird im Bad zirkuliert. Die Abweichung durch die Differenz zwischen der eingestellten Temperatur und der gemessenen Temperatur wird als Input-Signal beobachtet. Der an das Heizelement im Wasserbad weiterzuleitende Output oder Regel-Input wird mittels des Unschärfe-Modus berechnet. Die Output-Funktion wird durch das Zirkulieren des Kühlwassers vereinfacht. Der Beitrag jeder Teilfunktion wird in Abhängigkeit vom thermischen Verlauf der gemessenen Wassertemperatur geändert. Einschließlich der Regelprogramme wurde das gesamte System an einem praktischen Wasserbad erprobt und man erhielt recht gute Ergebnisse. Akzeptable Diagnosen konnten auch für externe thermische Störeinflüsse gezeigt werden, denen das geregelte System ausgesetzt wurde.

     

Design, Calibration, and use of convective air flow dynamic calorimeter

A new type of calorimeter has been developed that continously monitors the rate of heat emission from a heat source by following the rate of convective air flow induced by the emitted heat. For this purpose a thermistor version of a hot-wire anemometer connected to a strip chart recorder is positioned to measured the flow of incoming air. Details are given for the construction, calibration, and operation of a form of the calorimeter designed for studying the upward burning of unrestrained fabric samples under conditions closely approximating natural burning.     

A new version of differential flow heat capacity calorimeter; tests of heat loss corrections and heat capacities of aqueous NaCl from T = 300 K to T = 623 K

A new differential flow heat capacity calorimeter was constructed. It is designed to operate at temperatures up to 700 K and pressures up to 35 MPa and its primary use is for determining the massic heat capacities at constant pressure of dilute aqueous solutions. The instrument works in the so-called isoperibol regime, where the fluid sample flowing through the cell is heated by an electrical heater and the power necessary to provide a constant temperature rise is measured relative to that for a reference fluid (water). From the two values of power for sample and water the ratio of massic heat capacities of the sample to that of water can be calculated. A thorough investigation of calibration techniques showed that the calorimetric performance is very sensitive to the thermal conductivities of the sample and reference fluids. Measurements under turbulent flow conditions are questionable since there is no guarantee that by changing the flow rate the experiments and the calibrations would be performed at the same flow conditions. The procedure is very accurate and sensitive when measuring the difference in heat capacity between a solvent and a dilute solution of solute in the same solvent. The calorimeter was used to measure heat capacities of aqueous solutions of NaCl at eight temperatures up to 623 K and pressures to 30 MPa. The newly obtained values show consistency with previously published results and enlarge the database of experimental values aboveT =  573 K, where experimental data are rare.     

A fully automated adiabatic calorimeter for heat capacity measurement between 80 and 400 K

A fully automated adiabatic calorimeter controlled on line by a computer used for heat capacity measurements in the temperature range from 80 to 400 K was constructed. The hardware of the calorimetric system consisted of a Data Acquisition/Switch Unit, 34970A Agilent, a 7 1/2 Digit Nano Volt /Micro Ohm Meter, 34420A Agilent, and a P4 computer. The software was developed according to modern controlling theory. The adiabatic calorimeter consisted mainly of a sample cell equipped with a miniature platinum resistance thermometer and an electric heater, two (inner and outer) adiabatic shields, two sets of six junction differential thermocouple piles and a high vacuum can. A Lake Shore 340 Temperature Controller and the two sets of differential thermocouples were used to control the adiabatic conditions between the cell and its surroundings. The reliability of the calorimeter was verified by measuring the heat capacities of synthetic sapphire (α-Al₂O₃), Standard Reference Material 720. The deviation of the data obtained by this calorimeter from those published by NIST was within ±0.1% in the temperature range from 80 to 400 K.     

新型热量计的研制及其在吸热型碳氢燃料热沉测定中的应用

建立并完善了一套高温流动型热导式量热装置,实现了量热与色谱在线分析的有机结合。对该系统的仪器常数、热量常数、时间常数进行了精确的标定,并采用标准物质氮气、正庚烷等对仪器的准确性进行了考察,测量结果误差在2.2%～4.7%之间。同时还实测了吸热型碳氢燃料S-1,R-1等的热裂解热沉值。S-1在700℃时的热沉为2.99MJ/kg,而R-1的热沉为2.82MJ/kg。     

Determination of the specific heat capacity of hemoglobin- and methemoglobin-water mixtures using an adiabatic calorimeter

The specific heat capacity of bovine hemoglobin-, methemoglobin-, and thermally denatured hemoglobin-water mixtures were measured in the temperature range from 10 to 80°C. The partial specific heat capacities for mass fractions of the protein between 0 and 1 were computed. Significant differences of the partial quantities were obtained for the native, respectively denatured state of protein and for the protein in the native state in fluid mixtures, respectively in rather dry mixtures. For mixtures with protein mass fractions up to 0.45, exceeding the value in living human red cells, partial specific heat capacities of either components are found to be constant. The accuracy of the used adiabatic calorimeter will be described briefly.     

Advanced two-channel ac calorimeter for simultaneous measurements of complex heat capacity and complex thermal conductivity

The advanced construction of a two-channel ac calorimeter for simultaneous measurements of frequency-dependent complex heat capacity C(ω) and complex thermal conductivity λ(ω) is presented. In the new calorimeter, the number of interfaces with thermal-wave reflections was reduced. Thus, the new construction can be easily calibrated with higher precision and is simpler in handling than the previous one. The new construction allows to measure thermal conductivity in steady-state mode, as well as frequency-dependent complex thermal properties in ac mode, in the same measuring cell. The capabilities of this technique were demonstrated, being applied for simultaneous measurements of complex effusivity, diffusivity, heat capacity, and thermal conductivity of glycerol in the glass transition region. The so-called ac and dc thermal conductivities of glycerol were measured as a function of temperature. It was shown that the double-channel ac calorimetry is a technique, which can be used for reliable distinguishing of relaxation processes related to relaxing thermal conductivity or relaxing heat capacity.In the region apart from phase transitions, the calorimeter provides the unique possibility of simultaneous measurements of the thermal contact properties together with the sample’s thermal parameters. The improvement of the accuracy gave us the possibility to observe the thermal contact resistance, leading to a step of 1 and 5% in the temperature-modulation amplitude at the cell/sample interface in the case of liquid samples such as Apiezon™-H grease and glycerol, respectively. A step of 25% was observed in the case of a dry thermal contact between the cell and an ethylene-1-octene copolymer sample. Thus, the thermal contact resistance must be taken into account in the temperature-modulated calorimetry, especially in the case of a dry cell/sample contact.     

汽体流动量热计: 苯汽化热与苯汽体热容的测量

介绍了根据Pitzer型汽体流动量热计和Newsham型汽化热量热计建立的一套同时测定汽化热和汽态热容的汽体流动量热计. 该量热计可用于测定有机化合物及其混合物在不同温度下的汽化热、从沸点到200℃范围内的汽体热容. 量热计用苯标定, 汽化热的精度达到0.5%以上, 汽体热容的精度约1%.     

Adsorption micro calorimeter

In this work, it is described an innovative heat flux micro calorimeter Tian-Calvet type designed to measure adsorption heats and reactions as well as adsorption isotherms. It consists in an adsorption instrument for volumetric gases, which is coupled to the micro calorimeter. The changes in the pressure are monitored by means of high sensitivity and high precision pressure transducers. The micro calorimeter has thermo elements that work by a Seebeck effect, in a twin cells system. The cells are inside a box in which the temperature can be adjusted from 77 to 300 K. The sensitiveness of the calorimeter is established by applying a perfectly known electric work. The results corresponding to the electric calibration, the base line stability determination and the time constant in the equipment are shown.     

An improved technique for accurate heat capacity measurements on powdered samples using a commercial relaxation calorimeter

We have modified our earlier technique for accurate PPMS heat capacity measurements on powdered samples by means of applying Wakefield grease or small copper strips in the sample preparation instead of using Apiezon N high-vacuum grease. For the Wakefield grease measurements, we put a small amount of Wakefield thermal compound in a copper cup instead of potting with Apiezon N, and the accuracy of measurements on powdered benzoic acid was determined to be ±1% and ±4% in the temperature ranges of 10 K < T < 280 K and 280 K < T < 300 K, respectively. The Wakefield grease was found to improve the accuracy somewhat but overall there was no noticeable improvement in the “grease region” above T = 220 K. To overcome the known shortcomings of using Apiezon N grease above 220 K, we have replaced the Apiezon N grease with small copper strips in the sample preparation to aid thermal conductivity, which results in a less time-intensive two-step technique for the PPMS heat capacity measurement but with an accuracy, based on measurements of benzoic acid, that is ±1% from T = (10 to 300) K and, more importantly, the elimination of the “grease problem”. As an additional test of the new technique, the heat capacity of powdered bulk rutile has been measured twice within the temperature range from (2 to 300) K using the PPMS, and its standard entropy at T = 298.15 K was calculated to be (50.39 ± 0.50) and (50.31 ± 0.50) J · K^?1 · mol^?1, which deviates 0.08% and ?0.08% from the measurement results of our low-temperature adiabatic and semi-adiabatic calorimeters, respectively. We recommend that this technique become the standard for accurate heat capacity measurements on insulating powdered samples using a PPMS system and the corresponding thermodynamic calculations.     

Microcomputer-aided optimal selection of control input for the precision water bath of a heat exchange calorimeter

In heat exchange calorimetry, sample and reference vessels are fixed differentially in a water bath. The heat evolved in the sample vessel is exchanged freely with the ambient water. The accuracy and precision of the calorimetry depend on the temperature range of the drift and fluctuation in the bath water. In the present report, a simple temperature-control system with no empirical factors is proposed for the precision water bath. The heat exchange between the inside of the vessels and the ambient water is expressed by a differential equation or a Newtonian cooling equation. Similarly, the thermal behaviour of a water bath placed in a non-air-conditioned laboratory was also considered to be expressed by the same equation. The heat exchanged with the surroundings, the non-stationary heat flow from warm stirrer motors, and other thermal factors were considered to be part of the heat sources. Cooling water about 2°C lower than the set temperature was circulated in the water bath. The difference between the set temperature and the observed temperature was fed into a microcomputer every second. The latest four data points were used to fit a modified Newtonian equation by the common method of least-squares. The control input to the bath was calculated and given to the heater circuit after power amplification. The program written in basic was about 3.3 kbyte. The controlled range of drift and fluctuation was almost the same, or better, as that previously reported.