ANALYSIS OF LOW-TEMPERATURE EXPANSION PROCESSES OF NON-IDEAL GASES

An energy analysis of the processes of obtaining and using artificial cold in chemical technology is presented. The most well-known methods of obtaining and applying the cooling effect are considered: adiabatic expansion of vapor and gaseous bodies in expanders, throttling. Special attention is paid to the effect of object deviation from the ideal gas model.

Continuum Thermodynamics of Constrained Reactive Mixtures

Mixture theory models continua consisting of multiple constituents with independent motions. In constrained mixtures all constituents share the same velocity but they may have different reference configurations. The theory of constrained reactive mixtures was formulated to analyze growth and remodeling in living biological tissues. It can also reproduce and extend classical frameworks of damage mechanics and viscoelasticity under isothermal conditions, when modeling bonds that can break and reform. This study focuses on establishing the thermodynamic foundations of constrained reactive mixtures under more general conditions, for arbitrary reactive processes where temperature varies in time and space. By incorporating general expressions for reaction kinetics, it is shown that the residual dissipation statement of the Clausius-Duhem inequality must include a reactive power density, while the axiom of energy balance must include a reactive heat supply density. Both of these functions are proportional to the molar production rate of a reaction, and they depend on the chemical potentials of the mixture constituents. We present novel formulas for the classical thermodynamic concepts of energy of formation and heat of reaction, making it possible to evaluate the heat supply generated by reactive processes from the knowledge of the specific free energy of mixture constituents as well as the reaction rate. We illustrate these novel concepts with mixtures of ideal gases, and isothermal reactive damage mechanics and viscoelasticity, as well as reactive thermoelasticity. This framework facilitates the analysis of reactive tissue biomechanics and physiological and biomedical engineering processes where temperature variations cannot be neglected.

The phenomenon of relay race molecular transfer of the amount of motion and its relationship with the diffusion phenomenon

The very fact of molecular transfer of the amount of motion, including in an ideal gas in an equilibrium state, has long been well known. However, this fact is still not realized as a physical phenomenon of transfer, equivalent to such transfer phenomena as diffusion, thermal conductivity and viscosity. The key concept used in this paper when describing the phenomenon of relay race molecular transfer of the amount of motion is the concept - “molecular relay race type of motion”. A molecular relay race model of an ideal gas in an equilibrium state is proposed, as well as a molecular relay race model of a mixture of two ideal gases at constant temperature and pressure. It is shown that the value of the velocity modulus of diffusion flows is one of the physical characteristics of the mixture as a whole. It is also shown that the total density of the substance carried by the diffusion flows is many orders of magnitude less than the total density of the inhomogeneous multicomponent mixture.

MATHEMATICAL MODEL OF HOT-AIR BALLOON STEADY-STATE VERTICAL FLIGHT PERFORMANCE

Vertical flight performance of Lighter-than-Air free hot-air balloons is derived and discussed. Novel mathematical model using lumped-parameters has been used to model balloon flight dynamics and steady-state performance in particular. Thermal model was not treated as the super-heat is under the control of aeronauts/pilots. Buoyancy or gross lift, net or effective lift, specific lift, and excess specific lift were derived for a general single envelope balloon and can be applied to hot-air, gas and hybrid balloons. Rate-of-climb, absolute ceiling, rate-of-descent, and the maximum rate-of-descent or the uncontrolled terminal descent have all been modeled and sample computations performed for AX8 or AX9 FAI-class hot-air balloons. Lifting index or the specific net/effective lift have been computed treating ambient and hot air as ideal gases at various pressure altitudes and representative envelope temperatures. Drag coefficient in upward and downward vertical flights have been chosen based on best available data. Experimental scale and full-scale flight tests are suggested for more accurate estimates of external aerodynamics in vertical balloon flights. CFD computations of coupled inner- and external-flows are also recommended in future efforts. Knowledge of free balloon’s vertical performance is essential in flight planning and operational safety of flight.

Modeling of thermodynamic processes using the properties of matter presented in the form of spreadsheets

New thermodynamic cycles are developed in which the working fluid used cannot be considered as an ideal gas. This applies to oxy-fuel combustion cycles. In these cycles, oxygen is separated from the air prior to combustion. The combustion chamber is supplied with fuel and pure oxygen. The required temperature at the outlet of the combustion chamber is achieved by supplying some other substances from which it is easy to separate the CO2 formed during the combustion of the fuel. Commonly, CO2, or H2O, or their mixture is used as such substances. Thus, there are no exotic substances in the composition of the working fluid, but such a range of parameters is chosen for such cycles that the working fluid at certain points of the cycle can be both gaseous and liquid, or in a supercritical state. To model thermodynamic processes in such cycles, it is unacceptable to use the polytropic equation of ideal gases. A technique for integrating differential equations describing the state of the working fluid is proposed. This technique is based on the presentation of the thermodynamic properties of pure substances that make up the working fluid in the form of spreadsheets. The proposed technique is implemented in a software-computing module.

El uso de representaciones múltiples en clases de Ciencias Naturales para fortalecer la competencia argumentativa

RESUMEN La presente investigación, busca identificar la manera como las representaciones múltiples pueden incidir en el fortalecimiento de la competencia argumentativa en estudiantes de básica secundaria. La fundamentación metodológica en la cual se sustenta tiene como soporte, el enfoque cualitativo-comprensivo y, la estrategia de investigación bajo el método estudio de caso; perspectivas que orientan adecuadamente el ejercicio investigativo en el campo de la educación, porque permiten ofrecer recursos y herramientas favorables para tal actividad. Teniendo en cuenta lo anterior, se realizó un proceso de intervención pedagógica, con un enfoque investigativo, relacionado con la ley general de gases ideales, mediante la ejecución de los elementos presentados en el ciclo didáctico. Entre tanto, en las técnicas utilizadas para el proceso de intervención se encuentran: la observación participante, el grupo de discusión y la encuesta. De manera específica se retoman como instrumentos para la construcción de los datos; la entrevista semiestructurada y la guía de preguntas. La investigación se llevó a cabo con la participación, equitativa, de doce estudiantes de la básica secundaria, pertenecientes a ambas instituciones educativas de la ciudad de Medellín. En cuanto a las conclusiones, se encuentra que el uso sistemático de las representaciones múltiples posibilita una mayor comprensión de la temática ley general de gases ideales, permite alcanzar un mejor nivel argumentativo y desarrollar un lenguaje más cercano a las ciencias. ABSTRACT This research seeks to identify how multiple representations can influence the strengthening of argumentative competence in high school students. The methodological foundation on which it is based is supported by the qualitative-comprehensive approach and the research strategy under the case study method; perspectives that adequately guide the research exercise in the field of education, because they allow offering favorable resources and tools for such activity. Considering the above, a process of pedagogical intervention was carried out, with an investigative approach, related to the general law of ideal gases, through the execution of the elements presented in the didactic cycle. Among the techniques used for the intervention process were: participant observation, discussion group and survey. Specifically, the semi-structured interview and the guide of questions were used as instruments for the construction of the data. The research was carried out with the equal participation of twelve high school students from both educational institutions in the city of Medellin. As for the conclusions, it is found that the systematic use of multiple representations enables a better understanding of the general law of ideal gases, allows reaching a better argumentative level and developing a language closer to science.

$$\mu PT$$ statistical ensemble: systems with fluctuating energy, particle number, and volume

Within the theory of statistical ensemble, the so-called $$\mu PT$$ μ P T ensemble describes equilibrium systems that exchange energy, particles, and volume with the surrounding. General, model-independent features of volume and particle number statistics are derived. Non-analytic points of the partition function are discussed in connection with divergent fluctuations and ensemble equivalence. Quantum and classical ideal gases, and a model of Bose gas with mean-field interactions are discussed as examples of the above considerations.