Volume 44, Issue 4

Measurements of Thomson (later Lord Kelvin) coefficients are made in an evacuated region on a silver sample with a novel transducer in temperature intervals T A ± 20 K{T_{A}}\pm 20\hspace{0.1667em}\text{K}, where the T A {T_{A}} are very carefully controlled ambient temperatures. This is the first systematic examination of Thomson coefficients in these temperature intervals. The Thomson coefficients when plotted against T , the temperature of measurement, are found to be discontinuous precisely at T A {T_{A}}. When the Thomson coefficients are multiplied by a transformation involving T and T A {T_{A}}, a linear curve in T results. Examinations here of measurements of Thomson coefficients produced by others show multiple values at T in some cases and odd behavior in other cases. Multiplying the results of others by the transformation discovered here almost always produces linear curves. The conclusions are the following. (1) Thomson’s explicit assumption that the Thomson effect involves no energy exchange with surroundings was wrong. (2) Any non-equilibrium thermodynamic approach to deriving the Thomson effect must take into account the energy exchange with the surroundings and consequently must be made in three dimensions. (3) From the work here and that of others, the energy exchange with the environment is probably mostly thermal radiation.

The present work models MHD three-dimensional flow in a rotating channel. The energy expression is characterized by heat generation/absorption and radiation effects. Homogeneous-heterogeneous features are also accounted for. The obtained non-dimensional systems are numerically computed via the NDSolve based Shooting technique. Graphs are plotted to visualize the impact of various influential variables on velocity, temperature and concentration. In addition, skin friction and the Nusselt number are numerically estimated. Here temperature increases for increasing estimations of heat generation/absorption and radiation parameters. Furthermore, skin friction is reduced in the case of large Reynold number and rotation parameter.

Entropy fluctuations with time occur in finite-sized time-evolving dissipative systems. There is a need to comprehend the role of these fluctuations on the fluctuations-averaged entropy generation rate, over a large enough observation time interval. In this non-equilibrium thermodynamic investigation, the Fluctuation Theorem (FT) and Principle of Least Action are re-visited to articulate their implications for dissipative systems. The Principle of Maximum Entropy Production (MaxEP: the entropy generation rate of a dissipative system is maximized by paths of least action) is conceptually identified as the Principle of Least Action for dissipative systems. A Thermodynamic Fusion Theorem that merges the FT and the MaxEP is introduced for addressing the role of fluctuations in entropy production. It identifies “entropy fluctuations” as the “least-action path” for maximizing the time-averaged entropy production in a dissipative system. The validity of this introduced theorem is demonstrated for the case of entropy fluctuations in Rayleigh–Taylor flow instability.

Through altering the ambient environment of the iron conductor with respect to the copper conductor of an iron-copper thermocouple, the output emf of the thermocouple was reduced by a factor of almost two. This reduction was apparently a result of a Benedicks emf. Such a Benedicks emf was produced here in a continuous iron conductor. The Benedicks emf produced was about half the expected Seebeck emf from the copper-iron couple. The source of the Benedicks emf can be explained as a Seebeck charge separation produced by the effect of ambient radiation in one conductor of the thermocouple, while the effect of ambient radiation was deliberately removed in the other part of the conductor. The effect of ambient radiation was removed by matching the surface temperature gradient of the second part of the conductor point for point with an external (or ambient) temperature gradient. The conclusions of this research contradict the assumption made by William Thomson [1] that the ambient surroundings have no effect on thermocouple behavior. This assumption, which was made almost two hundred years ago, has never been experimentally refuted. The idea of using such a temperature match arose from a lesson learned from observations of directly measured Thomson coefficients by Jacovelli et al. [2]

The main purpose of this numerical investigation is to estimate energetically the thermo-magnetohydrodynamic (MHD) irreversibility arising in Stokes’ second problem by successfully applying the first and second thermodynamic laws to the unsteady MHD free convection flow of an electrically conducting dissipative fluid. This fluid flow is assumed to originate periodically in time over a vertical oscillatory plate which is heated with uniformly distributed temperature and flowing in the presence of viscous dissipation and Ohmic heating effects. Moreover, the mathematical model governing the studied flow is formulated in the form of dimensional partial differential equations (PDEs), which are transformed into non-dimensional ones with the help of appropriate mathematical transformations. The expressions of entropy generation and the Bejan number are also derived formally from the velocity and temperature fields. Mathematically, the resulting momentum and energy conservation equations are solved accurately by utilizing a novel hybrid numerical procedure called the Gear-Generalized Differential Quadrature Method (GGDQM). Furthermore, the velocity and temperature fields obtained numerically by the GGDQM are exploited thereafter for computing the entropy generation and Bejan number. Finally, the impacts of the various emerging flow parameters are emphasized and discussed in detail with the help of tabular and graphical illustrations. Our principal result is that the entropy generation is maximum near the oscillating boundary. In addition, this thermodynamic quantity can rise with increasing values of the Eckert number and the Prandtl number, whereas it can be reduced by increasing the magnetic parameter and the temperature difference parameter.

A novel realistic Work Criteria Function (WCF) approach has been used to analyze the ideal air-standard Diesel cycle. The WCF formulation gives rise to a new performance criterion which is termed as efficient power density (EPD). Thermodynamic analysis under maximum efficient power density (MEPD) conditions has been performed and compared with other available performance criteria using variable specific heats of the working fluid. The results obtained from this analysis prove that the engine designed under MEPD conditions is very efficient and the size of the engine is reduced significantly compared to those designed under maximum efficient power (MEP), maximum power density (MPD), and maximum power (MP) criteria. Harmful emissions like NO x {\mathrm{NO}_{\mathrm{x}}} may decrease considerably at higher values of the maximum cycle temperature ratio ( ξ ). The effect of variable specific heats of operational fluid on the actual cycle’s performance has a significant impact on engine performance and should be incorporated when evaluating practical cycle engines. The results obtained in the current study have scientific importance and could be an essential guide for the design of real Diesel engines by engine manufacturers.

The Stochastic Novikov engine is an endoreversible model for heat engines where the heat supply takes place at a fluctuating temperature. These fluctuations can be observed for example at solar thermal power plants. While recently the influence of the temperature fluctuations on the engine’s performance has been studied for Newtonian heat transport, the relation between the used heat transport type and the performance measures remained open. Therefore, we here consider a Stochastic Novikov engine with Fourier heat transport. Based on a short summary of the concept of a Stochastic Novikov engine and the corresponding different control types, the maximum work output and the corresponding efficiency are derived. In particular, we discuss the influence of the distribution’s parameters on the engine’s performance assuming a uniform temperature distribution. We find that the heat transport type has a significant effect on some of the engine’s fundamental properties.

The current work presents a concept that deals with the production of entropy generated by non-equilibrium processes in consequence of mass and energy transfer. The often used concept of endoreversible thermodynamics is based on the non-realistic conjecture that the entire entropy production is realized at the system boundary. In this contribution, an open system in a thermodynamically non-equilibrium state is assumed. Production of entropy is generated due to non-equilibrium processes accompanied by energy conversion. The steady state of the system is maintained by a negative entropy flux. The conclusions for expansion energy conversion, i. e., thermal machines, confirm the general outcomes of the endoreversible thermodynamics. However, the presented conclusions related to non-expansion energy conversion offer a new perspective on the principle of minimum entropy production and the corresponding stability conditions at steady state. The analysis of the energy conversion in closed cycles is presented for fuel cells, i. e., non-expansion energy conversion. The efficiency of the energy conversion is maximal at zero power output. Moreover, the efficiency of the fuel cells, and consequently the efficiency of all non-expansion energy conversion processes, depends on the load and then the maximal possible efficiency can be determined.

Thermal energy transfer in combined thin films consisting of silicon and diamond is considered. The combined films are thermally disturbed by a temperature oscillation at the silicon left edge and the influence of pulse length of temperature oscillation on energy transport characteristics is investigated. A nano-size gap with varying length is adopted at the films interface. The Boltzmann equation is adopted for the predictions of phonon intensity in the combined structure. The cut-off mismatch model is accommodated formulating interface conditions. The contribution of the near field radiation, due to evanescent waves, is also included at the interface. Equivalent equilibrium temperature is used quantifying phonon intensity distribution in the combined structure. It is found that the influence of the temperature oscillation on the phonon transport is significant at the silicon interface, i. e., increasing pulse length reduces phonon intensity at the silicon interface. Temporal behavior of equivalent equilibrium temperature is similar to the temperature oscillation introduced at the left edge of the silicon. The rise in temperature in the combined film is faster in the beginning of the heating cycle.