Approach to solution of tank with hydrogen peroxide pressurization by its decomposition products

Aim. To find and confirm the possibility of hydrogen peroxide tank pressurization using high-temperature pressurization gas (~1100К) with a high percentage of steam (up to 70%) without its losses. Research methods. Mathematical modeling of pressurization system parameters with the theory of mass transfer and thermodynamic of variable mass bodies have been used. Results. The conducted research allowed us to find and confirm the possibility of using a new pressurization method with additional sources of heat and elaborate recommendations for its appliance during pressurization time. Scientific novelty. The main processes have been determined, which prevent implementation of the efficient high-temperature pressurization system of the tank with the hydrogen peroxide using peroxide decomposition products. The main obstacle is the volume condensation of vapor in the free volume of the tank when heat exchange processes with boundary surfaces take place. For the first time, by means of theoretical calculations, the expediency and rationality of using the additional sources of heat such as high-temperature combustion product of solid-fuel gas generator based on sodium azide have been proved. Using of this additional source for the first 30 seconds of engine operation has been proved. Practical value. Methodology of pressurization system parameters’ calculation was supplemented with discovered thermodynamic relation, which allowed us to calculate the amount of vapor and take some measures to eliminate the condensation. Results of the research allowed the designation of the pressurization system for the highly concentrated hydrogen peroxide tank with a high value of length to diameter relation with its high-temperature decomposition products.

Gradient and GENERIC time evolution towards reduced dynamics

Reduction of a mesoscopic dynamical theory to equilibrium thermodynamics brings to the latter theory the fundamental thermodynamic relation (i.e. entropy as a function of the thermodynamic state variables). The reduction is made by following the mesoscopic time evolution to its conclusion, i.e. to fixed points at which the time evolution ceases to continue. The approach to fixed points is driven by entropy, that, if evaluated at the fixed points, becomes the thermodynamic entropy. Since the fixed points are parametrized by the thermodynamic state variables (by constants of motion), the thermodynamic entropy arises as a function of the thermodynamic state variables and thus the final outcome of the reduction is the fundamental thermodynamic relation. This reduction process extends also to reductions in which the reduced theory still involves the time evolution (e.g. reduction of kinetic theory to hydrodynamics). The essence of the extension is the replacement of the mesoscopic time evolution of the state variables with the corresponding mesoscopic time evolution of the vector field (i.e. of the fluxes). The fixed point in this flux time evolution is the vector field generating the reduced mesoscopic time evolution. The flux-entropy driving the flux time evolution becomes, if evaluated at the fixed point, the flux fundamental thermodynamic relation in the reduced dynamical theory. We show that the flux-entropy is a potential related to the entropy production. This article is part of the theme issue ‘Fundamental aspects of nonequilibrium thermodynamics’.

Gravitational thermodynamics of causal diamonds in (A)dS

The static patch of de Sitter spacetime and the Rindler wedge of Minkowski spacetime are causal diamonds admitting a true Killing field, and they behave as thermodynamic equilibrium states under gravitational perturbations. We explore the extension of this gravitational thermodynamics to all causal diamonds in maximally symmetric spacetimes. Although such diamonds generally admit only a conformal Killing vector, that seems in all respects to be sufficient. We establish a Smarr formula for such diamonds and a ``first law" for variations to nearby solutions. The latter relates the variations of the bounding area, spatial volume of the maximal slice, cosmological constant, and matter Hamiltonian. The total Hamiltonian is the generator of evolution along the conformal Killing vector that preserves the diamond. To interpret the first law as a thermodynamic relation, it appears necessary to attribute a negative temperature to the diamond, as has been previously suggested for the special case of the static patch of de Sitter spacetime. With quantum corrections included, for small diamonds we recover the ``entanglement equilibrium'' result that the generalized entropy is stationary at the maximally symmetric vacuum at fixed volume, and we reformulate this as the stationarity of free conformal energy with the volume not fixed.

Magnetic properties of the non-stoichiometric TbCo2Nix alloys

The magnetic and magnetothermal properties of the non-stoichiometric TbCo2Nix (0 ≤ x ≤ 0.2) alloys were studied. It was found that the concentration dependence of the Curie temperature and magnetic moment of the 3d-sublattice have a maximum at x = 0.025. The obtained experimental magnetic properties of the TbCo2Nix alloys were discussed under assumption that the Co magnetic moment in the compounds changes with increasing x. The magnetic entropy change was determined using the temperature dependences of the magnetization and Maxwell’s thermodynamic relation. The obtained results for TbCo2Nix were compared with those for the ErCo2Mnx alloys.

s-Wave holographic superconductor in different ensembles and its thermodynamic consistency

In this paper, we analytically study the consistency between the Ginzburg–Landau theory of the holographic superconductor in different ensembles and the fundamental thermodynamic relation, we derive the equation of motion of the scalar field which depicts the superconducting phase in canonical ensemble (CE) and a consistent formula to connect the holographic order-parameter to the Ginzburg–Landau coefficients in different thermodynamic ensembles, and we also study the spatially nonuniform Helmholtz free energy.

MODELING OF THE SURFACE TENSION OF COLLOIDAL SUSPENSIONS

Surface tension is one of the fundamental properties of the colloids, which can be altered by concentration and size of colloidal particles. In the current work, modeling of the surface tension of suspension as it would be analyzed by maximum bubble pressure method has been performed. A new modified equation to correlate the surface tension with the bubble pressure is derived by applying fundamental thermodynamic relation considering the presence of particles in suspension and curvature of the interface between the particles and bubbles inside liquid. Moreover, the change of particles concentration in air–water interface due to capillary force is also considered. The predicted surface tension using the developed model has been verified by numerous experimental data with deviation less than 5% in most of cases. It was found that the calculated surface tension is altered by contact angle and particle radius as well as particle concentration. The obtained model may have potential application to predict the surface tension of colloidal suspension.

Effects of Constitutive Properties on Pressure and Extent of Reaction

The paper applies the theory of mixtures to the chemical reaction rate. Concerning the time dependence of pressure, it is shown that pressure increases, is constant or decreases depending on the analogous behaviour of mole numbers. The results are established analytically and then numerically for the ideal gas, the van der Waals and the truncated virial equations. Next, in connection with the ideal gas model, Denbigh assumption is established by starting from the thermodynamic relation between (partial) pressure and Helmholtz free energy. Moreover, it is pointed out that the chemical potential does not exactly equal the partial derivative of the Gibbs free energy with respect to the corresponding mole number. This in turn is shown to imply that the evolution of a reaction is provided by the chemical potentials rather than by the derivative of the Gibbs free energy. Subject to the assumption of ideal gas for the constituents, as a thermodynamic requirement it is shown that if the number of moles increases the reaction is favoured by low pressures, and viceversa, and explicit estimates are established.

Moisture desorption isotherms of cucumber seeds: modeling and thermodynamic properties

Hygroscopic equilibrium curves or sorption isotherms are important in order to define dehydration limits of the product, estimate moisture content alterations under environment conditions and to acquire moisture content values for safe storage. This work aimed to determine desorption isotherms of cucumber seeds stored at different temperature (10, 20, 30, 40 and 50 ºC) and relative humidity (0.11 to 0.96) and the thermodynamic properties of this process. Mathematical models were fitted to experimental data in order to represent the agricultural products hygroscopicity. Net isosteric heat of desorption was performed based on the Clausius-Clapeyron thermodynamic relation and Gibbs free energy through the Van't Hoff equation. Based on statistical parameters, Modified Henderson model was the one that best represented hygroscopicity of cucumber seeds. Equilibrium moisture content of cucumber seeds decreased with temperature increment at a constant value of relative humidity. Differential enthalpy values, representing the energy required to remove moisture from the cucumber seeds, ranged from 2923 to 2469 kJ. kg-1. Values of differential entropy and Gibbs free energy decreased with moisture content increase. Enthalpy-entropy compensation theory is valid for the sorption of cucumber seeds, in which the water sorption mechanism in cucumber seeds can be considered to be enthalpy controlled.