INFLUENCE OF SIZE AND PRESSURE ON THE TEMPERATURE DEPENDENCIES OF THERMODYNAMIC PROPERTIES OF PLATINUM

Основываясь на параметрах парного потенциала межатомного взаимодействия Ми-Леннард-Джонса для Pt, и используя RP-модель нанокристалла, изучены температурные, барические и размерные зависимости следующих свойств: модуля упругости, коэффициента теплового расширения, изобарной теплоемкости и поверхностной энергии. Расчет уравнения состояния Pt показал хорошее согласие с экспериментом. Уравнение состояния было рассчитано вдоль пяти изотерм: T = 300, 1300, 1500, 1700, 1900 К. Впервые с единых позиций выполнены расчеты температурных зависимостей указанных свойств Pt в диапазоне от 0 K до 1500 K вдоль изобар 0 и 50 ГПа. Расчеты указанных зависимостей проведены как для макро-, так и для нанокристалла кубической формы из 306 атомов. Показано, что при изобарно-изотермическом уменьшении размера нанокристалла Pt происходит уменьшение значений модуля упругости и поверхностной энергии, а значения коэффициента теплового расширения и изобарной теплоемкости увеличиваются на исследуемом интервале температур. Based on the parameters of the pair interatomic interaction potential of the Mie-Lennard-Jones for Pt, and using the RP-model of the nanocrystal, the temperature, pressure and size dependencies of the following properties are studied: elastic modulus, thermal expansion coefficient, isobaric heat capacity, and surface energy. The calculation of the equation of state showed good agreement with experiment. The equation of state was calculated along five isotherms: T = 300, 1300,1500, 1700, 1900 K. For the first time, calculations of the temperature dependences of the above properties of Pt in the range from 0 to 1500 K along 0 and 50 GPa isobars were performed from a unified standpoint. Calculations of these dependencies were carried out for both macro- and cubic nanocrystals of 306 atoms. It is shown that with an isobaric-isothermal decrease in the nanocrystal size, the values of the elastic modulus and surface energy decrease, while the values of the thermal expansion coefficient and isobaric heat capacity increase over the investigated temperature range.

Development of a method to improve the calculation accuracy of specific fuel consumption for performance modeling of air-breathing engines

Determination of specific fuel consumption of air-breathing engines is one of the problems of modeling their performance. As a rule, the estimation error of the specific fuel consumption while calculating air-breathing engine performance is greater than that of thrust. In this work, this is substantiated by the estimation error of the fuel-air ratio, which weakly affects thrust but significantly affects the specific fuel consumption. The presence of a significant error in the fuel-air ratio is explained by the use of simplified methods, which use the dependence of enthalpy as a function of mixture temperature and composition without taking into account the effect of pressure. The developed method to improve the calculation accuracy of specific fuel consumption of air-breathing engines is based on the correction of the fuel-air ratio in the combustor, determined by the existing mathematical models. The correction of the fuel-air ratio is made using the dependences of enthalpy on mixture temperature, pressure and composition. The enthalpy of the mixture is calculated through the average isobaric heat capacity obtained by integrating the isobaric heat capacity, depending on mixture temperature, pressure and composition. The calculation accuracy of the fuel-air ratio was verified by comparing it with the known experimental data on the combustion chamber of the General Electric CF6-80A engine (USA). The average calculation error of the fuel-air ratio does not exceed 3 %. The developed method was applied for correcting the specific fuel consumption for calculating the altitude-airspeed performance of the D436-148B turbofan engine (Ukraine), which made it possible to reduce the estimation error of the fuel-air ratio and specific fuel consumption to an average of 3 %

Measurement of the isobar heat capacity of fluids in the critical area by the method of flowing adiabatic calorimeter

With regard to the problem of refining the fundamental equations of state of hydrocarbons, the methodological and design features of the experimental measurement of the isobaric heat capacity in the critical region by the method of a flow adiabatic calorimeter are considered. The pressure measurement system has been improved by introducing a differential manometer into the measuring circuit, which made it possible not only to increase the accuracy of pressure determination, but also to implement a universal scheme of calorimetric experiment. The use of a universal scheme of the calorimetric experiment allows one to determine two values of the isobaric heat capacity at pressures that differ by the value of the pressure loss in the calorimeter. Such an approach in the critical region is relevant, since it makes it possible to quite simply and reliably determine the value of the derivative of the heat capacity with respect to pressure, which is used to estimate not only the error in assigning the value of heat capacity to pressure, but also the equilibrium conditions of the experiment in a flow-through calorimeter. The technique of determining and making a correction for the inhomogeneity of the supply wires of the differential thermocouple, for the throttling of the flow of matter in the calorimeter is considered. Correct relations are obtained for determining the average temperature of the measurement experiment for various methods of measuring the temperature and temperature difference in a flow-through calorimeter. The results of experimental measurements of the isobaric heat capacity of n-pentane in the critical region, obtained using the universal scheme of the calorimetric experiment, for n-pentane were measured on an isobar of 3.400 MPa (critical pressure 3.355 MPa), which is the closest to the critical point at practice of flow calorimetry

Methodology for constructing the equation of state and thermodynamic tables for a new generation refrigerant

A unified fundamental equation of state 2,3,3,3-tetrafluoropropene (R1234yf) has been developed, a fourth-generation ozone safe refrigerant, and a method for constructing the equation has been proposed. In the gas region, this equation transforms into the virial equation of state, and in the vicinity of the critical point it satisfies the requirements of the modern large-scale theory of critical phenomena and transforms into the Widom scale equation. On the basis of a single fundamental equation of state in accordance with GOST R 8.614-2018, standard reference data (GSSSD 380-2020) on the density, enthalpy, isobaric heat capacity, isochoric heat capacity, entropy and sound velocity of R1234yf in the temperature range from 230 K to 420 K and pressures from 0.1 MPa to 20 MPa. A comparison of the calculated values of equilibrium properties with the most reliable experimental data obtained in the famous of the world, and tabular data obtained on the basis of the known fundamental equations of state R1234yf. Uncertainties of tabulated data for saturated vapor pressure, density, enthalpy, isobaric heat capacity, isochoric heat capacity, entropy and speed of sound of 2,3,3,3-tetrafluoropropene are estimated – standard relative uncertainties by type A, B, total standard relative and expanded uncertainties. The results obtained in the work show that the proposed unified fundamental equation of state adequately describes the equilibrium properties of R1234yf in the range of state parameters stated above.