Isosteric heat of adsorption and isochoric heat of vaporization and sublimation

Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1316–1317, May, 1996.     

A new heat fluxmeter

The dynamic measurement of beat flux gives a lagged and out of shape electrical response due to the heat transfer through the materials. So, it is necessary to use dynamic correctors to get the real response.To reduce the length of the thermal conductors, we propose to generate the useful electric signal perpendiculary to the heat flux by means of a magnetic induction field.We built a new heat fluxmeter, fitted to a 15 cm cell and based on this thermomagnetoelectric effect. Its main intrinsic time constant is 25 seconds and its sensibility at room temperature is 0.6V/mW.

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Zusammenfassung Die dynamische Messung eines WÄrmeflusses ergibt ein zeitlich verzögertes und amplitudenmÄssig verÄndertes elektrisches Signal. Mit geeigneten dynamischen elektrischen Korrekturgliedern kann das reale Signal approximiert werden. Zur Verringerung der LÄnge der Messanordung wird ein neues thermomagnetoeletrisches Prinzip vorgeschlagen. Unter Verwendung eines magnetischen Induktionsfeldes senkrecht zum WÄrmefluss wird ein zu diesen beiden Flüssen senkrecht stehendes elektrisches Potential erzeugt.Die Konstruktion dieses WÄrmeflussdetektors wird vorgestellt und die Charakteristik wird diskutiert.

     

Review of heat transport properties of solar heat transfer fluids

The present article reviews the test techniques for some of the important heat transport properties of oils such as viscosity, density, specific heat capacity and thermal conductivity mainly used for characterization of heat transfer fluids. It can be seen that while density of oils can be tested at higher temperatures, the other heat transport properties of oils like viscosity, specific heat capacity and thermal conductivity have a limitation of being tested at low temperatures below 100–150 °C. While quite a few number of researchers have reported evaluation of heat transfer properties like specific heat capacity and thermal conductivity of oils by different methods, there remains a huge scope of debate and discussions on the repeatability and reproducibility of such tests, especially in case of oils used in high-temperature applications. A lot of insight has been gathered with respect to testing of thermal conductivity of oils, and several common test methods have been compared with each other. Lastly, two mathematical models, reported in the literature in open domain, have been reviewed and compared with each other. If the oils are to be used at elevated temperatures, like heat transfer fluids used in concentrated solar power generation where temperatures go as high as 400 °C and beyond, there is an urgent need to standardize a laboratory test method for performance evaluation of heat transport properties, which can help in formulating new generation oils based on novel chemistries and technologies like nanofluids, synthetic oils of novel chemistries, molten salts and molten metals.     

Waste heat driven solid sorption coolers containing heat pipes for thermo control

This paper provides a focus on the R&D of solid sorption coolers and heat pumps made in the Luikov Heat & Mass Transfer Institute (CIS Countries Association Heat Pipes) under Thermacore, Inc. Agreement.Commercial and space applications of sorbent systems offer an attractive alternative to compression systems and liquid sorption systems for cooling, heating and air conditioning.MgA zeolites solid sorption systems are analyzed. Some new results are presented.Solid sorption heat pump technology utilizing heat pipe heat recovery with a condensing/evaporating refrigerant holds considerable promise for bivariant (space and domestic) applications due to the variable temperature and variable load capabilities of such machines.     

Electrochemical heat flow calorimeter

A device designed for research of heat phenomena occurring in chemical power sources (CPS) is described. The device includes two functional blocks: electrochemical and calorimetrical, operating under single control, which allows simultaneously performing electrochemical and calorimetric measurements. The calorimetric block is a heat flow calorimeter. The calorimetric chamber design provides the possibility of studying thermal processes in laboratory electrochemical cells and CPS of planar, disk, and prismatic design. The absolute measurement error of the heat flow is ±50 μW at the resolution of 1 μW. The operating temperature range of the calorimetric chamber is 0–90°C. The basis of the electrochemical block is a module of a four–range potentiostat–galvanostat. The maximum polarizing current of the potentiostat is ±200 mA at the maximum voltage on the auxiliary electrode of ±10 V. Multiuser remote access from the user computers over Ethernet to the device is provided for control and treatment of experimental data. Digital deconvolution filters allowing to compensate the response rate of the heat flow meter are used for processing primary data of calorimetric measurements.     

Single run heat capacity measurements

A prior study of single-run differential scanning calorimetry that leads directly to heat capacity results is extended to low temperatures (180 K). The instrument considered was the duPont dual sample differential scanning calorimeter with auto sampler and liquid nitrogen cooling accessary-II. The major error is caused by the low temperature isotherm. After optimizing all parameters, heat capacities of selenium, aluminum, quartz, polystyrene, sodium chloride were measured between 180 to 370 K. The root mean square error of all measurements on comparison with well established adiabatic calorimetry is ±2.9%.

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Zusammenfassung In einer vorangehenden Untersuchung wurde single-run DSC zur direkten Ermittlung von WÄrmekapazitÄtswerten angewendet. Diese Methode wird hier auf den niedrigen Temperaturbereich (180 K) ausgedehnt. Das benutzte GerÄt war ein duPont Doppelproben-DSCalorimeter mit Auto-Sampler und einem Flüssigstickstoff-KühlerzusatzgerÄt-II. Der grö\te Fehler wird durch die Niedrigtemperaturisotherme verursacht. Nach Optimierung aller Parameter wurden im Temperaturbereich 180–370 K die WÄrmekapazitÄten von Selen, Aluminium, Quarz, Polystyrol und Natriumchlorid gemessen. Verglichen mit der gutuntersuchten adiabatischen Kalorimetrie betrÄgt der Standardfehler aller Messungen ±2.9 %.

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On leave from the Dept. of Material Science, Fudan University, Shanghai, China.

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This work was supported by the Division of Materials Sciences, National Science Foundation, Polymers Program, Grant # DMR 8818412 and the Division of Materials Sciences, Office of Basic Energy Sciences, U. S. Department of Energy, under Contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc. In addition, support by the duPont Company in acquisition of the instrumentation is acknowledged.     

Single run heat capacity measurements

A study of single-run differential scanning calorimetry is presented considering baseline repeatability, crosstalk between the calorimeters, positioning of calorimeters, heating rate, sample mass, environment changes, sample pan mass, purge gas flow, instrument lags, and differences in heating rate between the calorimeters. The instrument considered was the du-Pont dual sample differential scanning calorimeter. The major errors are caused by environmental changes. All other errors seem to limit accuracy to±0.3%, a very respectable level. After optimizing all parameters, heat capacities of aluminum, sodium chloride, quartz, polystyrene and selenium were measured between 348 and 548 K. The root mean square error of all measurements on comparison with well established adiabatic calorimetry is±0.8%. This proves that single-run differential scanning calorimetry is possible, as predicted before, and improvements can still be made.

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Zusammenfassung Es wird eine Untersuchung eines single-run DSC vorgestellt, die tagendes berücksichtigt: Grundlinienreproduzierbarkeit, crosstalk zwischen Kalorimetern, Einstellung von Kalorimetern, Aufheizgeschwindigkeit, Probenmasse, Umweltver änderungen, Probenhaltermasse, Spülgasfluss, Instrumentträgheit und Unterschiede in der Aufheizgeschwindigkeit der Kalorimeter. Das fragliche Instrument war ein duPont Doppelproben DS-Kalorimeter. Die grössten Fehler werden durch Umwelteinflüsse verursacht. Alle anderen Fehler scheinen die Genauigkeit auf das akzeptierbare Mass von ±0.3% zu begrenzen. Nach einer Optimierung aller Parameter wurden bei Temperaturen zwischen 348 und 548 K die Wärmekapazitäten von Aluminium, Natriumchlorid, Quarz, Polystyrol, und Selen gemessen. Die Standardabweichung aller Messungen im Vergleich mit der relativ gut bekannten adiabatischen Kalorimetrie beträgt ±0.8%. Dies beweist, dass die single-run DSC, wie schon darauf hingewiesen, prinzipiell möglich ist, Verbesserungen aber noch möglich sind.

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On leave from the Dept. of Material Science, Fudan University, Shanghai, Chine

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This work was supported by the National Science Foundation, Polymer Program Grant #DMR 8818412 and the Division of Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract DE-AC05-84OR21400 with Martin Marietta Systems, Inc. In addition, support by the duPont Company in acquisition of the instrumentation is acknowledged.     

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.     

Low-temperature heat capacity of diglycylglycine

Heat capacity of tripeptide diglycylglycine was measured in a temperature range from 6.5 to 304 K. The results were compared with those for glycine and glycylglycine. Peptide bonding was found not to change C _P(T) virtually above 70 K, where heat capacity does not obey the Debye model. Comparison with literature data allows one to expect a significant difference in the heat capacity for enantiomorph and racemic species of valine and leucine, like it was found recently for D-and DL-serine.     

The minimum heat consumption for heat-driven binary separation processes with linear phenomenological heat transfer law

The optimal performance of heat-driven binary separation processes with linear phenomenological heat transfer law(q∝△(T-1)) is analyzed by taking the processes as heat engines which work between high-and low-temperature reservoirs and produce enthalpy and energy flows out of the system,and the temperatures of the heat reservoirs are assumed to be time-and space-variables.A numerical method is employed to solve convex optimization problem and Lagrangian function is employed to solve the average optimal contr...     

Absorbed heat and heat of formation of dried microbial biomassstudies on the thermodynamics of microbial growth

As represented by equations in which there is a term representing the biomass, the thermodynamics of biological growth processes is difficult to study without knowing the thermodynamic properties of cellular structural fabric. Measurement of the heat capacity data required to determine the standard entropy, So _298,15 or the standard absorbed heat, (H o _298,15 -ΔHo ₀ =Θo _298,15 of biomass requires a low-temperature calorimter, and these are not present in most laboratories. Based on a previously described method for entropy, two equations are developed that enable values of the absorbed heat (Θo _298,15) and the absorbed heat of formation, (Δ _f Θo _298,15) for biomass to be calculated empirically which are accurate to within 1% with respect to the biomass substances tested. These equations depend on a previous knowledge of the atomic composition or the unit-carbon formulas of macromolecules or structural cellular fabric. This revised version was published online in July 2006 with corrections to the Cover Date.     

Metrologically based procedures for the temperature, heat and heat flow rate calibration of DSC

Metrologically based measuring procedures and evaluation methods are recommended as guidance for practical temperature, heat and heat flow rate calibration of DSC instruments which are largely independent of instrumental, test and sample parameters. The relevant terms are defined, the measuring procedures and evaluation methods described, calibration materials and their characteristic data stated and guidance for the sample handling provided. Reference is made to three extended papers on calibration. The recommendations were developed by the working group Calibration of Scanning Calorimeters of the German Society of Thermal Analysis (GEFTA).Recommendation of the working group Calibration of scanning calorimeters of the Gesellschaft für Thermische Analyse e.V. (GEFTA)     

The heat of fusion of polytetrafluoroethylene

The heat of fusion of virgin and melt-processed polytetrafluoroethylene (PTFE) was determined using the Clapeyron equation. Experimental data were obtained from PVT experiments and high-temperature x-ray diffraction measurements. For virgin, as-polymerized PTFE, the melting temperature is given by where, for T_m in degrees Celsius, A = 346.3±1.2, B = 0.095±0.003, and P is the pressure in kilograms per square centimeter. At the end of the atmospheric-pressure melting interval, the amorphous and crystalline specific volumes V₁ and V_c are 0.6517 and 0.492 cm³/g, respectively. Thus the heat of fusion is 24.4 cal/g, or nearly twice the value reported previously. The increases in enthalpy and volume at the melting point both indicate a degree of crystallinity of about 75–80% although infrared, x-ray, and NMR data give much higher levels. Data from calorimetry, NMR, and dynamic mechanical measurements indicate that in virgin PTFE some of the crystals continue to experience torsional oscillations at temperatures below the room-temperature transitions. This indicates that there are at least two kinds of crystalline regions. For previously melted PTFE, T_m is determined by A = 328.5±0.7 and B = 0.095±0.002, the volumes are V_am = 0.6349 and V_cr = 0.4855 cm³/g, and the heat of fusion is 22.2 cal/g. The entropy of fusion for PTFE is much closer to that of polyethylene than was previously believed.     

Model-free temperature scaling for heat capacity

In treating the experimental data on the heat capacity of solids, the essence of any model application is in the searching for the scaling factors (k _i or 1/Θ_i) which transform a set of independent functions C _P,i(T) for every substance into a function C _P(T·k _i) universal for the particular set of substances. DSC heat capacities of I–III–VI₂ compounds at elevated temperatures exceed the upper limit of 12R (3R per mole of atoms) and make impossible application of any model. Nevertheless, the temperature scaling of heat capacity can be solved as a pure mathematical problem without any physical model (theory). The benefits of the model-free scaling are illustrated with the case of four isostructural chalcogenides (LiInS₂, LiInSe₂, LiGaS₂, and LiGaSe₂) measured recently with DSC in a temperature range from 180 to 460 K. The upper limit of C _P(T·k _i) functions was expanded up to 635 K. Low-temperature heat capacity of LiInSe₂ published in 1995 made it possible to derive the thermodynamic functions (enthalpy and entropy) for LiInS₂ (0–590 K), LiGaS₂ (0–640 K), and LiGaSe₂ (0–490 K) and expand those data for LiInSe₂ from 300 to 460 K.     

The heat capacity of NdPO4

The heat capacity of neodymium orthophosphate has been measured in the temperature range (0.6 to 1570) K. From the results the excess (electronic) heat capacity has been derived by subtracting the lattice heat capacity derived from the heat capacity of the isostructural LaPO₄ and GdPO₄, reported earlier. The calculated excess heat capacity thus obtained is in reasonable agreement with that calculated from the crystal field energies.     

Specific heat measurements under non-equilibrium conditions

The application of conduction calorimetry for specific heat measurements on samples under non-equilibrium conditions is reviewed.The influence of a constant rate of temperature decrease on the specific heatc of a TGS ferroelectric crystal doped with a small quantity ofL-alanine (LATGS) is discussed. The relaxation process ofc is likewise analysed.The simultaneous measurement ofc and the dissipative heat powerQ in a LATGS crystal in an alternative electric field which produces hysteresis loops is also discussed. It is shown that this specific heat is the sum of the corresponding equilibrium values plus a term proportional to the derivative ofQ with respect to temperature.     

Effective waste heat recovery from engine exhaust using fin prolonged heat exchanger with graphene oxide nanoparticles

Waste heat recovery is an important alternative to reduce the energy consumption in industrial processes. Heat Exchangers are used effectively for heat recovery. Thus, the role of heat exchangers for waste heat recovery system is crucial. The exclusive of heat transmission of a heat exchanger can be improved by many methods such as by modifying the geometries and using nano-additives of different concentration. In this continuation, a modified geometry of finned heat exchanger is developed with CFD analysis. Modified heat exchanger includes the fins in the internal pipe to improve heat transfer. Nanoparticles of graphene oxide with various concentrations are introduced in working fluid. A steady numerical study is performed by using ANSYS Fluent with k-omega turbulence model for exhaust flow. Variation at inlet velocities of exhaust gas and water, particles concentration and internal fin geometry are considered. The reduction in hot fluid temperature from 6 m/s to 2 m/s enhanced the effectiveness by approximately 33.3%. The decrease in hot fluid velocity to 2 m/s and 6 m/s can reduce its outlet temperature by 100 K and 14 K at 0.03 m/s cold fluid temperature. The inclusion of nanoparticles at 0.1% can enhance the effectiveness by maximum of 7%.     

Measurement of the specific heat and heat of decomposition of a polymer composite to high temperatures

The specific heat and heat of decomposition of a glass-filled phenolformaldehyde (phenolic) resin have been determined from experimental data obtained using a simultaneous thermal analyzer capable of operation to 1500 C. The measurements were conducted on powdered samples of the polymer to temperatures of approximately 1050 C at a rate of 20 deg min^–1 in an argon atmosphere. Both the mass loss and energetics were measured for the virgin component of the material, while only the energetics were measured for the char component. The combination of these data was used to calculate the specific heat of the virgin, char, and decomposing material, as well as the heat of decomposition. Also, in order to establish the accuracy of the instrument, the specific heat of pyroceram 9606 was measured and compared to previously published values.

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Zusammenfassung Die spezifische Wärme und die Zersetzungswärme eines glasgefüllten Phenol-Formaldehyd-Harzes wurden aus experimentellen Daten bestimmt, die mittels eines simultanen ThermoanalyseGerätes für Arbeiten bis 1500 C gewonnen wurden. Die Messungen wurden an gepulverten Polymerproben bis zu Temperaturen von 1050 C mit einer Aufheizgeschwindigkeit von 20 K min^–1 in Argonatmosphäre durchgeführt. Massenverlust und Energieänderungen wurden für das jungfräuliche Material gemessen, die Energieänderung auch für das verkohlte Material. Zur Prüfung der Messgenauigkeit des Geräts wurde die spezifische Wärmekapazität von Pyroceram 9606 gemessen und mit früher publizierten Daten verglichen.

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On sabbatical leave from the University of Rhode Island, Kingston, Rhode Island 02881 U.S.A.     

The heat capacity of BaUO4

The heat capacity of barium uranate BaUO₄ has been measured in the temperature range (1.9 to 1570) K in order to resolve the discrepancy between two existing low-temperature calorimetric studies on this compound. Our results are in good agreement with one of the two earlier studies, and the impact of this finding is discussed.