Carnot Type Research Articles

Orlicz spaces and the large scale geometry of Heintze groups

We consider an Orlicz space based cohomology for metric (measured) spaces with bounded geometry. We prove the quasi-isometry invariance for a general Young function. In the hyperbolic case, we prove that the degree one cohomology can be identified with an Orlicz–Besov function space on the boundary at infinity. We give some applications to the large scale geometry of homogeneous spaces with negative curvature (Heintze groups). As our main result, we prove that if the Heintze group is not of Carnot type, any self quasi-isometry fixes a distinguished point on the boundary and preserves a certain foliation on the complement of that point.

Optimization of the Changing Phase Fluid in a Carnot Type Engine for the Recovery of a Given Waste Heat Source

A Carnot type engine with a changing phase during the heating and the cooling is modeled with its thermal contact with the heat source. In a first optimization, the optimal high temperature of the cycle is determined to maximize the power output. The temperature and the mass flow rate of the heat source are given. This does not take into account the converter internal fluid and its mass flow rate. It is an exogenous optimization of the converter. In a second optimization, the endogenous optimization, the isothermal heating corresponds only to the vaporization of the selected fluid. The maximization of the power output gives the optimal vaporization temperature of the cycled fluid. Using these two optima allows connecting the temperature of the heat source to the working fluid used. For a given temperature level, mass flow rate and composition of the waste heat to recover, an optimal fluid and its temperature of vaporization are deduced. The optimal conditions size also the internal mass flow rate and the compression ratio (pump size). The optimum corresponds to the maximum of the power output and must be combined with the environmental fluid impact and the technological constraints.

Performance Envelope for Fuel Cell Heat Engine Hybrids and Heat Engine Combustors

The performance envelope for fuel cell heat engine hybrid cycles is developed and explored. The benefit of fuel cell heat engine hybrids in conversion of chemical energy was thermodynamically established. Fuel cell hybrids are combination of energy conversion sub-systems – fuel cells and heat engines. Fuel cell hybrids are important for the future for they are the most efficient devices when converting chemical energy of methane from renewable fuels to electricity. The power produced from an ideal fuel cell hybrid is a function of the current and the standard Gibbs free energy at unit activities. On the other side the operation of heat engines heated by a chemical reaction is based on the same principles, however the technical potential of direct electron transport is principally not used. The fuel cell allows an almost reversible operation at ambient temperature while the Carnot type engine operates principally reversible at a reversible Carnot temperature where the free enthalpy of the reaction is zero. Hybrid systems unify the benefits of both technologies and expand the possible range of operation to all temperatures between ambient and the above mentioned reversible Carnot temperature. The fuel cell hybrid performance is always higher than or equal to the heat engine combustor performance. It is higher until the Carnot temperature of 4,300K in the case of hydrogen combustion. By the same token, the fuel cell hybrid performance occurs over a limited temperature range due to the narrow operating temperatures of fuel cells. The practical operating temperature of a fuel cell, and hence the fuel cell heat engine hybrid, is less than 1,400K. At temperatures from 298K to 1,400K, the fuel cell hybrid performance exceeds all other performances, of course. The cooled fuel cell power case exceeds heat combustion performance until around 1,200K. This paper builds from and is an extension of several papers recently published in the Journal of The Electrochemical Society (ECS), ECS Transactions, and the Journal of Fuel Cell Science and Technology, and the International Journal of Hydrogen Energy.

Approximate ecological efficiency with a non-linear heat transfer

The optimisation of a thermal engine performing a Carnot type cycle is considered under the criterion that it should produce high power output with the least possible entropy production in the cycle. It is assumed that the heat transfer between the reservoirs and the engine takes place according to the Dulong and Petit heat transfer law. Also an expression was found for the efficiency as a power series in a parameter that is a function of the compression ratio. It was also shown that this result reduces itself to the ecological efficiency calculated without taking explicitly into account the time of the adiabatic processes.

Trial Manufacturing of a Laminated Frame-Adopted Stirling Engine and Its Characteristics

The Stirling engine is an external combustion engine run by the expansion and contraction of an operating gas by heat, regardless of the source of heat. It used to be called “The Dream Engine” as it is noiseless and is as efficient as the Carnot type in theory. The Stirling engine has been given more credit recently because of its promising characteristics as a clean engine regardless of heat source, with possibili-ties of becoming an ecologically sound engine. Unfortunately, techniques to minimize losses of various natures have not been established yet, even in theory, yet using present machining techniques, which are essential in obtaining high engine efficiency. Our focus was the structure of the frame, in order to increase the efficiency and output of the Stirling engine. Conventionally, frames of monocoque construction were fabricated through machining, which was limited, as to shape, by manufacturing techniques. With an aim to improve the specific output of the Stirling engine, the author, et al proposed a laminated structure frame using two different materials, which made the Stirling engine drastically lighter than the conventional Stirling engine using a monocoque frame. In terms of heat transmission, the laminated frame also presented excel-lent characteristics, proving that it could provide a higher pressure ratio than the monocoque-framed Stirling engine, working advantageously in improving overall output.

SOBOLEV CLASSES AND HORIZONTAL ENERGY MINIMIZERS BETWEEN CARNOT–CARATHÉODORY SPACES

The notion of horizontal energy minimizers between C-C spaces is introduced. We prove the existence of such energy minimizers when the domain is a C2, noncharacteristic bounded open set in a C-C space and the target is a C-C space of Carnot type.

DECOMPOSITION OF BV FUNCTIONS IN CARNOT-CARATHÉODORY SPACES

The aim of this paper is to get the decomposition of distributional derivatives of functions with bounded variation in the framework of Carnot-Carathéodory spaces (C-C spaces in brievity) in which the vector fields are of Carnot type. For this purpose the approximate continuity of BV functions is discussed first, then approximate differentials of L1 functions are defined in the case that vector fields are of Carnot type and finally the decomposition Xu = ∇u · Ln +Xsи is proved, where и ∈ BVx(Ω) and ∇u denotes the approximate differential of u.

A general property of endoreversible thermal engines

In this work we propose that endoreversible Carnot–type heat engines have a general property independent of the heat transfer law used to describe heat exchanges between the working fluid and its thermal reservoirs. This property has to do with the so-called ecological function [F. Angulo–Brown, J. Appl. Phys. 69, 7465 (1991)]. According to this property, the efficiency at the maximum of the ecological function is the semisum of the Carnot and the maximum power efficiencies for any heat transfer law. This result is obtained by using the quasiparabolic behavior of power versus efficiency. From this property, we obtain a corollary over a general quantitative relation between the power (and also the entropy production) of both maximum power and maximum ecological regimes. We also discuss a criterion to find the best ecological function.

静止型磁気冷凍機

The Carnot type magnetic refrigeration in the temperature range from 4.2K to 15K has been studied. This refrigeration system mainly consists of the following components; the magnetic working material, the thermal switches at 4.2K and 15K, and the superconducting pulsed magnet. Gd3Ga5O12 (GGG) single crystal was used as the working material. The entropy diagram and thermal conductivity were obtained. It was concluded that GGG provides large refrigeration capacity (1-3W/mol) in the Carnot cycle. A heat pipe was used as the thermal switch at 4.2K. Thermal conductivity of the heat pipe at 4.2K was as large as that of OFHC copper and switch ratio between 4.2K and 15K was over 103. Some testpieces consist of GGG and the heat pipe were experimented. The difficulty concerning with the thermal resistance between non-metallic material (GGG) and metal (heat pipe) wat solved out by using the specially deviced heat pipe where GGG liquefies directly gaseous helium. The maximum liquefaction efficiency was -70%.Based on these preriminary studies, the Carnot type magnetic refrigerator was constructed. The average liquefaction efficiency for the one-shot demagnetion process was -40%. For continuous operation at 3.1 Tesla between 4.2K and 10K, the refrigeration capacity was 0.34W and the Carnot efficiency was 17%. This efficiency was not taken account of the loss from the superconducting pulsed magnet. This trial magnetic refrigeration system gave the possibility for realizing the small refrigerator with high efficiency at 4.2K.

Quasi-static processes in energy conversion statics

A general treatment of quasi-static processes in the field of energy conversion is developed. The approach is based on a unified theory of energy conversion statics as established in reference 1 with specific emphasis on electromechanical conversion processes. A number of general theorems are developed dealing with reversible and irreversible processes. Maximum work processes are deduced using the dissipation law and a general Carnot type cycle is established. Stability criteria for processes involving any number of coupled sources are set up using energy minimum theorems. The general coverage of the approach is demonstrated with specific case examples involving electromechanical transducers.