arXiv subjects

Zeng-Yuan Guo

Publications and source records attributed to Zeng-Yuan Guo.

5 recordsLinked to original sources

arXiv2023

Maximum Power and The Corresponding Efficiency for A Carnot-like Thermoelectric Cycle Based on Fluctuation Theorem

Here, we investigate the maximum power and corresponding efficiency of thermoelectric generators through devising a set of protocols for the isothermal and adiabatic processes of thermoelectricity to build a Carnot-like thermoelectric cycle, with the analysis based on fluctuation theorem (FT). First of all, the Carnot efficiency can be readily obtained for the quasi-static thermoelectric cycle, with the vanishing power. Moreover, the maximum power-efficiency pair of the finite-time thermoelectric cycle is derived, which is found to have the identical form to that of Brownian motors characterized by the stochastic thermodynamics. However, it is of significant discrepancy compared to the linear-irreversible and endoreversible-thermodynamics-based formulations. The distinction compared to the linear-irreversible-thermodynamics case could result from the difference in the definitions of Peltier and Seebeck coefficients in the thermoelectric cycle. As for the endoreversible thermodynamics, we argue the applicability of endoreversibility could be questionable for analyzing the thermoelectric cycle here, due to the incompatibility of the endoreversible hypothesis that attributes the irreversibility to finite heat transfer with thermal reservoirs, though the distinction of the mathematical expressions can vanish with the assumption that the ratio of thermoelectric power factors at the high and low temperatures is equal to the square root of the temperature ratio (this condition could significantly deviate from the practical case).

physics.app-ph↗

arXiv2023

Re-recognition of the ideal gas and real gas

Ideal gas is the most fundamental and simple system in thermodynamics, which has extensive applications in energy research and engineering. By reviewing the physical concept of ideal gas, it is found that the current understanding of ideal gas is still inappropriate and ambiguous, making it challenging to reveal the essential difference between ideal and real gases. Therefore, the macro and microscopic definitions and properties of ideal gas need to be reconceptualized. On the microscopic level, an ideal gas is a hypothetical collection of classical masses in irregular motion, which does not involve quantum mechanics; on the macroscopic level, any real gas cannot strictly obey the equation of state of ideal gas. Moreover, the heat capacity is a constant which should be an endogenous attribute of ideal gas model in order to unify the macroscopic and microscopic definitions of ideal gas. Finally, according to the law of heat capacity, the real gas can be divided into three categories: far-ideal, near-ideal, and quasi-ideal. This makes it easier to perform thermodynamic calculations with the assistance of ideal gas. Among them, the far-ideal gas heat capacity is a function of temperature and pressure, the near-ideal gas heat capacity is a single-valued function of temperature, and the quasi-ideal gas heat capacity is a constant.

physics.class-ph↗

arXiv2022

Lyapunov function for non-equilibrium transport processes

Irreversibility is a critical property of non-equilibrium transport processes. An opinion has long been insisted that the entropy production rate is a Lyapunov function for all kinds of processes, that is, the principle of minimum entropy production. However, such principle is based on some strong assumptions that are rarely valid in practice. Here, the common features of parabolic-like transport processes are discussed. A theorem is then put forward that the dot products of fluxes and corresponding forces serve as Lyapunov function for parabolic-like transport processes. Such fluxes and forces are defined by their actual constitutive relations (e.g., the Fourier's law, the Fick's law, etc.). Then, some typical transport processes are analyzed. Particularly for heat conduction, both the theoretical and numerical analyses demonstrate that its Lyapunov function is the entransy dissipation rather that the entropy production, when the Fourier's law is valid. The present work could be helpful for further understanding on the irreversibility and the mathematical interpretation of non-equilibrium processes.

cond-mat.stat-mech↗

arXiv2021

Equation of state from symmetry

Equation of state (EOS) describes the thermodynamic properties of substances. It has important applications in many fields such as power mechanics, geophysics, astrophysics, and detonation physics. Currently, most EOSs have been constructed using the ideal gas EOS as the base framework. However, this is inappropriate for the substances with high pressures or low temperatures that are far from the ideal gas state. Here we extract a concept of "ideal solid" that is symmetrical with ideal gas and propose its EOS. We verify that the ideal solid EOS represents the thermodynamic properties of the high-pressure and low-temperature limiting state. It indicates that the thermodynamic properties of substances have symmetrical characteristic. Then we develop a universal model by interpolation of the ideal gas and the ideal solid limits. We verify that the universal EOS has high description accuracy in a wide region. The concept of ideal solid and its EOS potentially provides a new direction for the development of the EOS theory.

cond-mat.stat-mech↗

arXiv2020

Reversible Reciprocal Relation of Thermoelectricity

The first Kelvin relation that states the Peltier coefficient should be equal to the product of temperature and Seebeck coefficient is a fundamental principle in thermoelectricity. It has been regarded as an important application and direct experimental verification of Onsager reciprocal relation (ORR) that is a cornerstone of irreversible thermodynamics. However, some critical questions still remain: why Kelvin's proof that omits all irreversibility within a thermoelectric transport process can reach the correct result, how to properly select the generalized-force-flux pairs for deriving the first Kelvin relation from ORR, and whether the first Kelvin relation is restricted by the requirement of linear transport regime. The present work is to answer these questions based on the fundamental thermodynamic principles. Since the thermoelectric effects are reversible, we can redefine the Seebeck and Peltier coefficients using the quantities in reversible processes with no time derivative involved, which are renamed as "reversible Seebeck and Peltier coefficients". The relation between them (called "the reversible reciprocal relation of thermoelectricity") is derived from the Maxwell relations, which can be reduced to the conventional Kelvin relation, when the local equilibrium assumption (LEA) is adopted. In this sense, the validity of the first Kelvin relation is guaranteed by the reversible thermodynamic principles and LEA, without the requirement of linear transport process. Additionally, the generalized force-flux pairs to obtain the first Kelvin relation from ORR can be proper both mathematically and thermodynamically, only when they correspond to the conjugate-variable pairs of which Maxwell relations can yield the reversible reciprocal relation. The present theoretical framework can be further extended to other coupled phenomena.

cond-mat.stat-mech↗