Volume 48, Issue 4

The wide-spread opinion is that original quantum mechanics is a reversible theory, but this statement is only true for undecomposed systems that are those systems for which sub-systems are out of consideration. Taking sub-systems into account, as it is by definition necessary for decomposed systems, the interaction Hamiltonians –which are absent in undecomposed systems– can be a source of irreversibility in decomposed systems. Thus, the following two-stage task arises: How to modify von Neumann’s equation of undecomposed systems so that irreversibility appears, and how this modification affects decomposed systems? The first step was already done in Muschik (“Concepts of phenomenological irreversible quantum thermodynamics: closed undecomposed Schottky systems in semi-classical description,” J. Non-Equilibrium Thermodyn. , vol. 44, pp. 1–13, 2019) and is repeated below, whereas the second step to formulate a quantum thermodynamics of decomposed systems is performed here by modifying the von Neumann equations of the sub-systems by a procedure wich is similar to that of Lindblad’s equation (G. Lindblad, “On the generators of quantum dynamical semigroups,” Commun. Math. Phys. , vol. 48, p. 119130, 1976), but different because the sub-systems interact with one another through partitions.

The main attention is paid to the analytical analysis of an oblique shock wave in a turbulent adiabatic gas flow. For this purpose, a modified Rankine–Hugoniot model was obtained. On its basis, a solution was derived for the Rankine–Hugoniot conditions for a gas flow with various degrees of turbulence, as well as the equation of the modified Hugoniot adiabat. The behavior of the velocity of an adiabatic turbulent gas flow during its passage through an oblique shock wave at different levels of turbulence is demonstrated. A modification of Prandtl’s law for the velocity coefficients was obtained. The shock polar was also analyzed. The relationship between the angular gas flow and the angle of the shock wave was derived. Finally, the condition for the appearance of an outgoing bow shock wave was obtained.

This study examines the effect of a short term rotation on a system of constant volume. Adsorption of CO 2 is performed on Activated Carbon (AC) at 281, 293 and 298 K with a special designed device that allows rotation. The adsorption isotherms were conducted up to 10 bar for both No Rotational (NoROT) and Rotational (ROT) cases. The ROT case refers to 60 s of rotation at 5000 rpm. The experimental results were fitted to Langmuir as well as to Dubinin–Astakhov (D–A) models with the latter presenting the best fit. A detailed thermodynamic analysis is performed in order to quantify the overall contribution of the rotation on gas adsorption compared to static case. For the ROT case, the maximum amount adsorbed ( q max ) is by 12 % higher than the NoROT counterpart, while a decrease in chemical potential as surface loading is increased, indicates that the process after rotation is entropy driven. The outcome of this work suggests that rotation enables gas molecules to access previously inaccessible sites, thus gaining more vacancies due to better rearrangement of the adsorbed CO 2 molecules.

Any real physical process that produces entropy, dissipates energy as heat, or generates mechanical work must do so on a finite timescale. Recently derived thermodynamic speed limits place bounds on these observables using intrinsic timescales of the process. Here, we derive relationships for the thermodynamic speeds for any composite stochastic observable in terms of the timescales of its individual components. From these speed limits, we find bounds on thermal efficiency of stochastic processes exchanging energy as heat and work and bound the rate of entropy change in a system with entropy production and flow. Using the time set by an external clock, we find bounds on the first time to reach any value for the entropy production. As an illustration, we compute these bounds for Brownian particles diffusing in space subject to a constant-temperature heat bath and a time-dependent external force.

While genetic mutations, natural selection and environmental pressures are well-known drivers of enzyme evolution, we show that their structural adaptations are significantly influenced by energy dissipation. Enzymes use chemical energy to do work, which results in a loss of free energy due to the irreversible nature of the process. By assuming that the catalytic process occurs along a potential barrier, we describe the kinetics of the conversion of enzyme-substrate complexes to enzyme-product complexes and calculate the energy dissipation. We show that the behaviour of the dissipated energy is a non-monotonic function of the energy of the intermediate state. This finding supports our main result that enzyme configurations evolve to minimise energy dissipation and simultaneously improve kinetic and thermodynamic efficiencies. Our study provides a novel insight into the complex process of enzyme evolution and highlights the crucial role of energy dissipation in shaping structural adaptations.

In order to commercialize aqueous two-phase systems (ATPSs), not only the equilibrium data is essential, but also the knowledge of separation mechanisms, kinetics, settling time, and operational conditions are needed. Mixing duration and settling time are the most critical factors affecting separation and biomolecule partitioning in terms of economic aspects. This research aimed to find the desired conditions for separating cephalexin in an ATPS consisting of acetonitrile, glucose, and water. Firstly, the evolution of the interphase region was observed. Hereafter, to examine the effect of time on the experimental tie-lines and partition coefficient in non-equilibrium states, the settling time was varied from 2 min to 24 h. In addition, centrifugation was applied to help the separation at different time intervals and rotational speeds. The results of tie-lines slope and partitioning coefficients showed that the system approaches equilibrium after 5 h. However, using the centrifuge separation at 4000 rpm improved the separation time to 45 min, reaching 80 % of the actual partition coefficient. It can be concluded that with an acceptable tolerance in the partition coefficient, a remarkably diminished settling time is available for economic productivity in industrial units.

Radiative heat transport involving complex geometries is an important area of investigation. The formulation of the transport phenomenon is more involved and consideration of the proper treatment of the irregular geometry becomes necessary for accurate estimation of heat transfer rates. Therefore, the present study focuses on the modeling and the solution of the radiative transfer equation (RTE) in an absorbing, emitting, and isotropically scattering, participating media for complex geometries using the body-fitted coordinates. The RTE in an orthogonal coordinate system is formulated and is then numerically solved in conjunction with a numerically generated, body-fitted, curvilinear coordinate system. The geometries are considered to be opaque and, in the analysis, both the radiative as well as the non-radiative equilibrium cases are considered. The formulation is validated through the previously published results. Notable agreement is observed between the results and those reported earlier for different complex geometries and various properties of the participating media.

Based on the irreversible Otto cycle model, applying finite-time-thermodynamic theory, this paper takes power and efficiency as the objective functions, further studies the cycle performance under the condition of non-ideal gas working fluid, analyzes the effects of different loss items and freedom degree ( d ) of monatomic gas on the cycle performance, and compares performance differences of ideal gas and non-ideal gas under different specific heat models. The results demonstrate that, with the increase of d , the maximum-power-output ( P max ), the maximum-thermal-efficiency ( η max ), the corresponding optimal compression-ratio ( ( γ opt ) p ${({\gamma }_{\text{opt}})}_{p}$ ) and efficiency ( η P ) at the P max point, and the corresponding optimal compression ratio ( ( γ opt ) η ${({\gamma }_{\text{opt}})}_{\eta }$ ) and power ( P η ) at the η max point will all increase; the P max , ( γ opt ) p ${({\gamma }_{\text{opt}})}_{p}$ , η max , ( γ opt ) η ${({\gamma }_{\text{opt}})}_{\eta }$ , η p and P η will decrease with the increases of three irreversible losses; the specific heat model has only quantitative effect on cycle performance but no qualitative effect; under condition of non-ideal gas specific heat model, the power and efficiency are the smallest.

Some of the previous investigations neglect the mass transfer contribution of the hydrophilic layer for modeling the Janus membrane that is used for direct contact membrane distillation (DCMD). This work studies the impact of adding such resistance on the performance of the DCMD, especially on the temperature polarization coefficient (TPC), thermal efficiency, and permeate flux. The commercial software Ansys 2020 was used to describe the transport behavior through the Janus membrane. The bulk-flow model was employed to evaluate the permeate flow through the hydrophilic layer for the first time. Simulation results were compared with the experimental results from the literature for validating the model, and a satisfactory agreement was found. Results demonstrated that the permeate flux increased by about 61.3 % with changing the porosity of the hydrophilic layer from 0.5 to 0.9 for the membrane with the lowest hydrophilic layer thickness. Moreover, the thermal conductivities of both layers contribute significantly to the DCMD’s overall performance enhancement. Vapour flux might be enhanced by increasing the hydrophilic layer’s thermal conductivity while decreasing the hydrophobic layer’s thermal conductivity. Finally, the DCMD thermal efficiency was investigated, for the first time, in terms of both layer characteristics.