The optimal performance of a generalized Carnot cycle for a generalized heat transfer law

The finite time thermodynamic performance of a generalized Carnot cycle, in which the heat transfer between the working fluid and the heat reservoirs obeys the generalized law Q∝( Δ T) m , is studied. The optimal configuration and the fundamental optimal relation between power and efficiency of the cycle are derived. Some special examples are discussed. The results can provide some theoretical guidance for the design a practical engine.

Reversible Carnot cycle outside a black hole

A Carnot cycle outside a Schwarzschild black hole is investigated in detail. We propose a reversible Carnot cycle with a black hole being the cold reservoir. In our model, a Carnot engine operates between a hot reservoir with temperature Ti and a black hole with Hawking temperature TH. By naturally extending the ordinary Carnot cycle to the black hole system, we show that the thermal efficiency for a reversible process can reach the maximal efficiency 1 - TH/T1. Consequently, black holes can be used to determine the thermodynamic temperature by means of the Carnot cycle. The role of the atmosphere around the black hole is discussed. We show that the thermal atmosphere provides a necessary mechanism to make the process reversible.

Performance characteristics of low-dissipative generalized Carnot cycles with external leakage losses

Under the assumption of low-dissipation, a unified model of generalized Carnot cycles with external leakage losses is established. Analytical expressions for the power output and efficiency are derived. The general performance characteristics between the power output and the efficiency are revealed. The maximum power output and efficiency are calculated. The lower and upper bounds of the efficiency at the maximum power output are determined. The results obtained here are universal and can be directly used to reveal the performance characteristics of different Carnot cycles, such as Carnot heat engines, Carnot-like heat engines, flux flow engines, gravitational engines, chemical engines, two-level quantum engines, etc.

Entransy and Exergy Analyses for Optimizations of Heat-Work Conversion with Carnot Cycle

The concept of entransy has been newly proposed in terms of the analogy between heat and electrical conduction and could bc useful in analyzing and optimizing the heat-work conversion systems. This work presents comparative analyses of entransy and exergy for optimizations of heat-work conversion. The work production and heat transfer processes in Carnot cycle system are investigated with the formulations of exergy destruction, entransy loss, work entransy, entransy dissipation, and cfficiencics for both cases of dumping and non-dumping of used source fluid. The effects of source and condensation temperatures on the system performance arc systematically investigated for optimal condition of producing maximum work or work cntransy.

Association between tropospheric temperature and tropical cyclone peak intensity over the North Pacific and North Atlantic

As natural weather disasters,tropical cyclones(TCs)are destructive in proportion to their peak intensity.This study investigates the association of North Atlantic,western North Pacific,and eastern North Pacific TC peak intensities with tropospheric air temperature,respectively,by applying NCEP–NCAR and MERRA reanalysis data.Both the correlation between TC peak intensity and air temperature and the difference in air temperature between strong and weak TC peak intensity conditions reveal that significant cooling of the tropopause and uppertropospheric warming are accompanied by strengthening TC peak intensity for North Atlantic TCs,suggesting an important effect of upper-tropospheric static stability on TC peak intensity.However,warming in the lower troposphere is associated with strong TC peak intensity for eastern North Pacific TCs,indicating a major effect of lower-tropospheric static stability on TC peak intensity.The peak intensity of western North Pacific TCs is mainly affected by vertical wind shear,not the atmospheric temperature.

Predicting the Curvature of the Cosmos, and Point of Volume Contraction in a Big Bounce Scenario

Based on the latest Planck surveys, the universe is close to being remarkably flat, and yet, within observational error, there is still room for a slight curvature. If the curvature is positive, then this would lead to a closed universe, as well as allow for a big bounce scenario. Working within these assumptions, and using a simple model, we predict that the cosmos may have a positive curvature in the amount, Ω0=1.001802, a value within current observational bounds. For the scaling laws associated with the density parameters in Friedmann’s equations, we will assume a susceptibility model for space, where, , equals the smeared cosmic susceptibility. If we allow the to decrease with increasing cosmic scale parameter, “a”, then we can predict a maximum Hubble volume, with minimum CMB temperature for the voids, before contraction begins, as well as a minimum volume, with maximum CMB temperature, when expansion starts. A specific heat engine model for the cosmos is also entertained for this model of a closed universe.

The Generalized Thermodynamic Temperature and the New Expressions of the First and the Second Law of Thermodynamics

The classical thermodynamics reflects the significant relationship between the heat and the temperature. On the basis of the relationships, according to the mathematical derivation, this paper structures the conceptions of generalized heat, generalized thermodynamic temperature, generalized entropy and so on. The series of conceptions in the classical thermodynamics is merely a special case of the generalized thermodynamics. Based on these conceptions of generalized thermodynamics, this paper presents the new expressions of the first law and the second law of thermodynamics. In other words, these expressions are endued with new explanations. The Eq. LZ = kTS given by this paper provides theoretical basis for these new expressions.