Measurement of the critical properties of thermally unstable substances and mixtures by the pulse-heating method

Nikitin, Eugene D.; Pavlov, P. A.; Скрипов, П. В.

doi:10.1006/jcht.1993.1084

Cited by 102 publications

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“…The methods for measuring critical parameters of thermally unstable fluids or reactive compounds (flow method; transient pulse-heating thin wire probe) have been proposed by various authors (see, for example, Refs. [74][75][76][77][78][79]). These methods are capable of residence times between 0.01 ms and 30 s. Unfortunately, these methods have not been applied to the measurement of the critical parameters of methanol.…”

Section: Critical Parametersmentioning

confidence: 99%

Thermodynamic Properties of Methanol in the Critical and Supercritical Regions

et al. 2005

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The isochoric heat capacity of pure methanol in the temperature range from 482 to 533 K, at near-critical densities between 274.87 and 331.59 kg · m −3 , has been measured by using a high-temperature and high-pressure nearly constant volume adiabatic calorimeter. The measurements were performed in the singleand two-phase regions including along the coexistence curve. Uncertainties of the isochoric heat capacity measurements are estimated to be within 2%. The single-and two-phase isochoric heat capacities, temperatures, and densities at saturation were extracted from experimental data for each measured isochore. The critical temperature (T c = 512.78 ± 0.02 K) and the critical density (ρ c = 277.49 ± 2 kg · m −3 ) for pure methanol were derived from the isochoric heat-capacity measurements by using the well-established method of quasi-static thermograms. The results of the C V V T measurements together with recent new experimental PVT data for pure methanol were used to develop a thermodynamically self-consistent Helmholtz free-energy parametric crossover model, CREOS97-04. The accuracy of the crossover model was confirmed by a comprehensive comparison with available experimental data for pure methanol and values calculated with various multiparameter equations of state and correlations. In the critical and supercritical regions at 0.98T c T 1.5T c and in the density range 0.35ρ c ρ 1.65ρ c , CREOS97-04 represents all available experimental thermodynamic data for pure methanol to within their experimental uncertainties.

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Section: Critical Parametersmentioning

confidence: 99%

Thermodynamic Properties of Methanol in the Critical and Supercritical Regions

et al. 2005

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“…The critical temperature and pressure evaluated in such a way were substituted into formula (1), and the parameter A was calculated by the use of the literature vapour pressures. Further formulae given previously (1,2) were used to calculate corrections to the apparent values of p' c (t*) and T' c (t*), and then the values of p c (t*) and T c (t*) themselves. After that the new dependence p c (t*) (curve 2 in figure 2a) was extrapolated to zero time, and the value of p c2 was estimated.…”

Section: Methodsmentioning

confidence: 99%

“…Then the temperatures of the attainable superheat T*(p c1 , t*) were found (figure 1). Next the dependence T*(p c1 , t*) was extrapolated to zero time with the help of the formula given previously (1) (figure 2b, curve 1). The critical temperature and pressure evaluated in such a way were substituted into formula (1), and the parameter A was calculated by the use of the literature vapour pressures.…”

Section: Methodsmentioning

confidence: 99%

“…Owing to the thermal decomposition it is impossible to measure the critical constants of ethene glycols by standard methods; therefore we used the pulse-heating method. (1) Recently the critical properties of n-alkanes from heptadecane to tetracosane (2) and (oligopropene oxides + carbon dioxide) (3) were measured by this method.…”

Section: Introductionmentioning

confidence: 99%

“…The critical constants of monoethene glycol were determined by us earlier. (1) The choice of polyethene glycols as the object of investigation is explained by the availability of samples with a sufficiently narrow molar-mass distribution. Owing to the thermal decomposition it is impossible to measure the critical constants of ethene glycols by standard methods; therefore we used the pulse-heating method.…”

Section: Introductionmentioning

confidence: 99%

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(Gas + liquid) critical temperatures and pressures of polyethene glycols from HOCH2CH2OH to H(OCH2CH2)ν≈13.2OH

Nikitin

Pavlov

Popov

1995

The Journal of Chemical Thermodynamics

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Heat pulse monitoring of curing and polymer–gas systems

Скрипов

Puchinskis

Begishev

et al. 1994

J of Applied Polymer Sci

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SYNOPSISAn implantable thermal probe is used to study the reaction of molten polymers and curing systems to pulse heat release. At the heating rates T 2 5 -lo5 K/s, a polymer system shows the response to pulse heating that is confined in time and reproducible with respect to temperature. This response is related to the abrupt change in the conditions of the contact between the probe and a substance. The temperature of the response T* is determined by the polymer properties and depends on the pressure and T. The pulse thermal probe method, which includes two measuring procedures, complementing each other, has been used to monitor a number of processes in polymeric systems. The variation of the values of T* and the thermal activity of a polymer is compared with the variation of its molecular weight (A& -10'-lo6), the molecular weight distribution, and the concentration of a low molecular weight component. The method allows one to trace the kinetics of polymerization and curing and the kinetics of dissolution of volatile impurity and polymer devolatilization, and to determine the limit of supersaturation of gas solutions in molten polymers. The pulse repetition frequency is changed from 0.1 to 1 Hz. The heated volume of a substance is mm3. 0 1994 John Wiley & Sons, Inc. INTRODUCTIONThe methods of the study of the substance properties and characteristics of processes based on the recording and analysis of the system response to some perturbation ( mechanical, acoustic, electrical) have found a wide application for polymers.' We used for these purposes the method of pulse heating of a substance on the surface of a wire probe2s3 and revealed the response confined in time and reproducible with respect to temperature of a polymeric system to heat release. The nature of this response is related to an abrupt violation of the conditions of the probe contact with a substance. The temperature of the response depends on the instantaneous composition and physicochemical properties of a substance. Its value is above the traditional temperature range for experiments with polymers. By the character of the response, the observed phenomenon is similar to that of spontaneous nucleation in superheated low * To whom correspondence should be addressed. , but shall discuss the possibilities of the practical use of the method of pulse heating for the evaluation of a number of parameters of polymeric systems and processes, in particular, the value of the molecular mass and polydispersity, kinetics of curing, kinetics of dissolution or removal of volatile impurities, and the boundaries of the stability of a condensed state of an oligomer supersaturated with a gas. The prospects of effective use of the method are based on its speed, microquantity of the analyzed substance, independence of the observed parameter (T* ) on the medium temperature, and compactness and noise im-munity of the equipment employed. The characteristic time of heating is of the order of 10-4-10-5 s, and the heated volume is of the order of 10 p4 mm3. The pulse repetit...

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Measurement of the critical properties of thermally unstable substances and mixtures by the pulse-heating method

Cited by 102 publications

References 0 publications

Thermodynamic Properties of Methanol in the Critical and Supercritical Regions

Thermodynamic Properties of Methanol in the Critical and Supercritical Regions

(Gas + liquid) critical temperatures and pressures of polyethene glycols from HOCH2CH2OH to H(OCH2CH2)ν≈13.2OH

Heat pulse monitoring of curing and polymer–gas systems

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