H. Saygin¹, ² and A. Sisman^2
1 Istanbul Technical University, Informatics Institute, 80626-Maslak, Istanbul, Turkey
² Istanbul Technical University, Nuclear Energy Institute, 80626-Maslak, Istanbul, Turkey

An overview of various thermodynamic gas cycles working at quantum degeneracy conditions is presented. It is well known that an ideal gas deviates from its classical behaviour under quantum degeneracy conditions (sufficiently low-temperature or high-density conditions). Although the gas is still an ideal gas, it obeys Bose-Einstein or Fermi-Dirac statistics instead of Maxwell-Boltzmann statistics. Under quantum degeneracy conditions, the corrected equation of state is valid instead of the classical ideal gas equation of state. The corrected equation of state is obtained by considering the quantum degeneracy of gas particles and it is reduced to classical ideal gas equation of state at the classical ideal gas conditions (sufficiently high-temperature or low-density conditions). In thermodynamic analyses of ideal gas cycles, efficiency (except the Carnot efficiency) and work expressions are derived by using the classical ideal gas equation of state and some generalisations are obtained by using the results of these analyses. Analyses of gas cycles working with ideal Bose and Fermi gases allow us to investigate how these expressions and generalisations are effected by the quantum degeneracy. In literature, various gas cycles working with ideal Bose (⁴He) and Fermi (³He) gases have been thermodynamically analysed at quantum degeneracy conditions. Here, heat, work and entropy expressions for isothermal, isobaric, isochoric and isentropic processes under the quantum degeneracy conditions are introduced. The behaviour of Carnot and Ericsson power and Brayton refrigeration cycles working with ideal Fermi and Bose gas are reviewed by using these expressions. For these cycles, advantage or disadvantage of the use of Fermi and Bose gases are also given in a brief summary. This overview provides a general picture of the physics of the cycles working under quantum degeneracy conditions.

I.K. Smith and N. Stosic
Centre for Positive Displacement Compressor Technology,
School of Engineering, City University, London, EC1V 0HB, U.K.

The development of two-phase expanders with adiabatic efficiencies of more than 70% has been the goal of many research workers for more than 30 years. The applications for such devices are almost exclusively for power recovery from low temperature heat resources. The inherently poor conversion efficiencies associated with low temperature energy conversion implies that such expanders must be cheap to be economically viable.
This paper describes the results of a long term R and D programme carried out at City University, London, which has resulted in the development of twin screw machines of great simplicity which have expansion efficiencies greater than 70% and which can be manufactured at low cost.
Two applications are given for these.
The first is in a high efficiency system for the recovery of power from low temperature sensible heat sources, such as liquid geothermal brines.
The second is as a throttle valve replacement in large refrigeration and air conditioning plant where a device called an "Expressor" has been developed by the authors. This combines power recovery from the two-phase expansion and recompression of part of the vapour formed during the expansion in a self driven sealed unit containing only a single pair of rotors. Manufacturers’ cost estimates for batch production of expressor units are indicate that simple payback times for them are less than six months
Details are given of both analytical and experimental work on both expander and expressor units.

THERMODYNAMIC ANALYSES OF HEAT ENGINES BASED ON THE CASIMIR EFFECT AT FINITE TEMPERATURE

A. Sisman ¹ and H. Saygin ^1,2
1 Istanbul Technical University, Nuclear Energy Institute, 80626-Maslak, Istanbul, Turkey,
² Istanbul Technical University, Informatics Institute, 80626-Maslak, Istanbul, Turkey

There is an attractive force between two parallel neutral conducting plates at a distance d, even at absolute zero temperature and no matter is present in the gap separating them. This effect is called the Casimir effect and it is due to the quantum vacuum fluctuations of the zero point electromagnetic field. At finite temperatures (K), pressure and also the other thermodynamic properties (like as entropy, energy and etc.) become temperature dependent besides the distance d. Hence, it is theoretically possible to design some heat engines based on the Casimir effect at finite temperature. In this work, thermodynamic analysis of a Carnot heat engine based on the Casimir effect at finite temperature is aimed to understand the thermodynamic structure of this kind of machines. Two parallels, neutrals, perfectly conducting plates are considered as a heat engine device. For low () and high () temperature limits, heat and work exchange expressions for isothermal, isobaric, isochoric and isentropic processes are derived by taking the Casimir effect into account. It is seen that working fluid is the classical (three-dimensional) black-body radiation (BBR) at high temperature limit, while it is two-dimensional BBR at low temperature limit. By using the derived expressions, maximum work and maximum work density of a Carnot power cycle are calculated. Numerical results are compared at both high and low temperature limits. It is shown that maximum work at low temperature limit, at which the Casimir effect becomes dominant, is much less than the maximum work at high temperature limit. On the other hand, opposite of this situation is valid for maximum work density. These results provides to understand the behaviours of heat engines based on the Casimir effect and they can also be used if such heat engines based on the nano-technology are designed in the near future.

N. Mugabi¹, A. Machida¹, H. Fukumoto¹, M. Fukamura¹, Y. Takeda², K. Sanno^2
1 Mayekawa Mfg. Co. Ltd. Advanced Technology Lab.,2000, Tatsuzawa, Moriya Machi Kitasooma-gun, Ibaraki, 302-0118, Japan
Tel : 81- 297-48-1364, Fax : 81-297-48-5170
² Kansai Electric Power Co. ,Technical Research Center, 3-11-20 Nakoji, Amagasaki, Japan.

Ice thermal storage systems are being developed and marketed as one of the means of electric load levelling . Conventional ice thermal storage systems are of static type. These systems are reported to have bad responses to heat load and require big pipings to deliver cold heat. This makes initial investment and running costs high. Dynamic Ice systems have been developed to offset some of the disadvantages of the conventional static systems. Dynamic ice is mainly produced by using brine solutions. These solutions not only lower the solidification temperatures , thus lowering COPs, most of them are not friendly to the environment.
We have developed a highly efficient slurry ice generation and transportation system using both environmentally friendly ammonia as the refrigerant and water as the coolant. Water is super cooled to –1.5°C before its delivered to a super cool releaser where slurry ice is produced. By using water, the COP is not only improved as compared with brines, the application range of the system widens from air conditioning to cover other areas such as the food industry and machinery.
This paper reports on the development and application of a 66kW cooling capacity system with a COP of 3.5.

W. Bolek, E. Slifirska and T. Wisniewski
Institute of Power Engineering and Fluid Mechanics, Wroclaw University of Technology,
ul. Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland
email : tadewis@pwr.wroc.pl

There exists a need to measure the content of a gas mix called trimix, which is composed of three components : helium, oxygen and nitrogen. Trimix is used for breathing in hyperbaric exposures. The main difficulty in measuring this gas is that there are no simple devices available on market, which allows measuring concentration of helium or nitrogen.
The thermodynamic state of a three component mixture is given by four values: e.g. two thermodynamic quantities and concentration of two components. This state might be also given as three independent thermodynamic quantities and one concentration. Moreover there exists a relation between quantities in both descriptions. It means, if it is possible to measure these three quantities and one concentration then it would be possible to evaluate contents fraction of remaining components.
This is the idea to build the device evaluating helium content. It occurs, that three independent thermodynamic quantities (temperature T, pressure p and sound speed ad) and oxygen concentration are easily measured. Simple sensors, which measure these quantities, are available on the market.
This paper is devoted to verification of this idea. In order to know precisely the helium concentration before the measurement the method was verified on the mixture of air and helium (helair). The constant ratio of nitrogen and oxygen allows assessing the precision of the method.
The relation of helium concentration on sound speed and temperature for helair was approximated by polynomials. The true values for this approximation were taken from electronic thermodynamic tables, which are available in a Promix software. The actual helium concentration is evaluated based on oxygen sensor. The measurement is made at the ambient pressure and this variable is not taken into account in evaluations.
A small laboratory stand was made in order to conduct the measurements. The examined gas is introduced into a vertical cylinder under ambient pressure. The sound speed is measured parallel to the vertical axis of a cylinder. The ultrasonic distance sensor is placed on the top of the cylinder. The temperature measurement was made by resistance sensor Pt100. These two measurements are led into a PC through an A/D converter board. The computer evaluates on-line the current value of helium based on an approximate relation.
During the measurements, the examined gas was slowly introduced into a cylinder. The evaluated values of helium concentration were monitored until they stabilised. The time of stabilisation was due to the volume of cylinder. The gas inlet was cut off. The value read in this moment was taken as a measured value and compared with a true value obtained by oxygen sensor. The helair mixes up to 30% of helium were examined. The relative error was lower than 2%.
The undertaken experiments shown, that it is possible to make a concentration sensor based on the sound speed measurement. In the future work, the specialised devise will be made. It will work on microprocessor controller without any PC.

LE CAPTEUR ULTRASONIQUE POUR LA MESURE DE LA TENEUR DE L'HELIUM DANS LE MELANGE DES GAZ

Il est nécessaire de mesurer la teneur des constituant dans le mélange ternaire contenant hélium, azote, oxygène, utilisé par les plongeurs en exposition hyperbarique.
La difficulté principale à mesurer un gaz est un manque d'appareils nécessaires qui permettent de mesurer la concentration d'hélium ou d'azote.
L'état thermodynamique du mélange ternaire est déterminé par quatre grandeurs, par exemple : par deux variables thermodynamiques et par la concentration de deux constituants ou par trois variables indépendantes thermodynamiques et une concentration.
Il existe une relation entre ces deux descriptions. Ainsi, s'il est possible de mesurer la température, la pression, la vitesse sonique et une concentration dans le mélange, il sera possible d'évaluer la teneurs des autres constituants.
C'est sur ce concept qu'a été réalisé un capteur pour la mesure de la teneur en hélium du mélange. Par suite de cela, on a élaboré une méthode qui permet d'évaluer le pourcentage d'hélium dans le mélange, fondée sur la mesure de la température, de la pression, de la vitesse sonique et de la concentration en oxygène. On peut réaliser facilement ces mesures en utilisant les appareils commerciaux.
Cet article présente la validation expérimentale de ce concept de mesure. La vérification a été menée pour le mélange hélium-air. Le rapport constant de la teneur d'azote et d'oxygène permet d'estimer facilement la précision de la méthode.
Pour conduire les recherches, on a construit un banc d'essais dans lequel le gaz étudié est introduit dans un cylindre vertical sous la pression atmosphérique. La vitesse sonique est mesurée le long de l'axe vertical du cylindre à l'aide du capteur de distance qui est installé en haut du cylindre. La mesure de la température est réalisée à l'aide du capteur à résistance.
Les résultats des mesures sont transmis dans l'ordinateur par l'intermédiaire de la carte du convertisseur analogique - digital.
L'ordinateur évalue la concentration d'hélium en mélange d'après un polynome d'interpolation, dont les coefficients ont été identifiés sur les valeurs réelles issues du logiciel Promix. Ces coefficients sont calculés en fonction de la vitesse sonique et de la température.
La méthode proposée a été vérifiée en tenant compte de la connaissance de la proportion dans le mélange hélium-air. Cette proportion a été obtenue à l'aide du capteur de l'oxygène.
Des mélanges contenant jusqu'à 30% d'hélium ont été testés et l'erreur relative de la mesure est restée inférieure à 2%.

A. Chisacof
Mechanical Engineering Faculty, University "Politehnica" of Bucharest, 313, Spl. Independentei, RO- 77206 Bucharest, Romania

The large amount of used fluids which is released every day in the atmosphere by the industrial plants and current activity, could modify , in the medium to long term the local climate, and this could, in different ways, strongly impact the human activities. Concerning the emission from the industrial plants, especially from the power plants and chemical layout, which use the important quantities of fossil fuels and row materials, the important amounts of fluids containing the vapour-gas mixture, having a low or moderate temperature (in the range of 100°C to 250°C), are evacuated into the surroundings. The limitation of this negative impact may by realised by an advanced recovery of available heat of the multiphase mixture, and also by the condensation of vapour components from gas-vapour system. In this mode a part of the pollutant or of the reusable fluids, may be stored in the special reservoirs or recovered, and reinserted in the technological layout.
ln this paper is proposed a combined system for the advanced recovery of heat and of the condensable components of gas-vapour mixture. The proposed system consists in the initial compression of the gas-vapour mixture in aim to increase the mean temperature and the dew point of the medium. On this way, the level of temperature during the heat transfer processes increases, the amount of recovered heat increases too, due of the heat of condensation extracted from the vapour phase. By this system we find the possibilities to use its thermal energy by co-generation in the own plant, or in the other cooling, refrigeration or heating systems. The dry gas obtained after the condensation is expanded in a turbine. On this way a reduction of external work input for compression is realised.
The paper presents the range of the efficiency of the proposed system in function of the mixture composition, of the compression ratio. The evolution of the recovered heat and of the mass fraction of recovered liquid is presented, in function of initial composition of gas-vapour mixture.

RENOUVELER L'ÉNERGIE THERMIQUE DES FLUIDES POLYPHASIQUES PAR UN SYSTÈME DE COMPRESSION - CONDENSATION

Des grandes quantités de fluides sont évacués tous les jours dans l'atmosphère soit par les usines, soit due aux activités courantes, ce qui peut modifier le climat en ayant un fort impact sur les activités humaines. En ce qui concerne les émissions données par les grandes plates-formes industrielles, par les usines chimiques et les centrales électriques, consommateurs des importantes quantités de combustibles fossiles, les fumées évacuées dans l'environnement contiennent des fractions élevées de vapeur d'eau à basse ou moyenne température (entre 100°C et 250°C). Dans le but de réaliser une limitation significative de cet impact négatif sur l'environnement, il est nécessaire d'introduire dans la chaîne industrielle des installations de récupération avancée de la chaleur contenue dans les mélanges polyphasiques par la condensation de la vapeur contenue par ceux-ci. De cette manière une partie de fluides polluants est récupérée, et peut être stocké dans des réservoirs ou réintroduite dans la chaîne technologique.
Dans ce travail on propose un système combiné pour la récupération avancée de la chaleur des composants condensables du mélange gaz-vapeur. Le système proposé utilise une compression initiale du mélange gaz-vapeur, ce qui a comme but l'augmentation de la température moyenne et de celle du point de rosée du milieu. Par conséquent, on obtient un niveau élevé de la température du milieu pendant le déroulement du processus de transfert thermique et d'autre part, due à la condensation de la vapeur, la quantité de chaleur récupérée augmente aussi. Le système proposé permet l'utilisation de la chaleur par co-génération dans l'installation elle-même, respectivement dans d'autre système de chauffage ou de réfrigération. Les fumées sèches, issues de système de compression-condensation, sont détendues dans une turbine. Par cette méthode on diminue l'apport de l'extérieur de travail mécanique nécessaire à la compression du mélange diminue.
Dans le travail sont données les valeurs de l'efficacité thermique du système proposé en fonction de la composition du milieu et de taux de compression. Aussi, sont présentées les évolutions de la chaleur récupérée et de la fraction de liquide obtenue par condensation en fonction de la composition du mélange.