901 publications from this institution
The minimum theoretical refrigerator power for cooling mechanical supports for a cryogenic apparatus is determined with the calculus of variations. A mathematical approach is developed that can be used to evaluate the thermal performance of any mechanical support which has fixed geometry. Four practical, non-optimum cooling arrangements are compared with the minimum power case. The comparison shows that a smaller refrigerator power is required when continuous cooling is provided at intermediate temperatures along the conducting support. A combination of two gas streams in series closely approximates the thermodynamically optimum cooling arrangement.
Constructal theory is applied to the cooling of a disc where heat is uniformly generated. The disc size and the total volume occupied by the ducts (distributing the flow from the centre to the periphery) are constrained. It is shown that when the objective is to minimise the global thermal resistance, the best design is the one built with radial ducts. On the other hand, the minimisation of the pumping power leads to tree-shaped structures. The results show that the two optimisation approaches, thermal and fluid-mechanical, generate results with nearly the same global performance. Yet, when the scale of the problem becomes smaller and smaller and dendritic flows perform better, demonstrating the usefulness and robustness of tree-shaped structures.
Enclosures heated from the side are most representative of porous systems that function while oriented vertically, as in the insulations for buildings, industrial cold-storage installations, and cryogenics. As in the earlier chapters, we begin with the most...
This is an analytical and numerical study of the exergy that can be delivered by a solar collector installation with temporary energy storage capability. In the first part of the study, the method of variational calculus is used to show that under conditions of time-dependent inlet and outlet flow rates, the total exergy delivered by the installation is maximum when the collector temperature is maintained at an optimum constant level throughout the insolation period. More realistic models of solar collectors with storage capability are analyzed in the second and third parts of the study. In each of the models considered, the analysis shows that the relative timing of the filling and discharge processes has a significant effect on the total exergy delivered by the installation. The main conclusion of the study is that the daily regime of operation of the collection/storage installation can be selected by design in order to maximize the harvesting of solar exergy per unit of collector area.
Thermodynamics is brief, simple, unambiguous and improving.Yet, confusion reigns in the field.The word "entropy" is pasted on almost any new thing, without any respect for its proper definition in thermodynamics.Every author bows to his own maximum or minimum principle, even when it contradicts English, not just thermodynamics.Minimizing resistance cannot be the same as maximizing resistance.Minimizing entropy generation cannot be the same as maximizing entropy generation.Because of the word "entropy", many believe that entropy generation minimization and maximization are covered by the second law, which is incorrect, twice.Because for an isolated system (or an adiabatic closed system) the second law states that the system entropy inventory increases during changes inside the system, many believe that the second law accounts for organization, evolution, and the arrow of time.This too is incorrect.It is time for a reality check, and this means to take a look at nature, at the physics, at the science of all the natural things that "happen".Here then is a review of the few, the noble, the laws with which in science we cover the few distinct phenomena that nature is made of.
In this chapter we focus on the equation that expresses the first law of thermodynamics in a porous medium. We start with a simple situation in which the medium is isotropic, and where radiative effects, viscous dissipation, and the work done by pressure changes are...
Introduction to Thermal System Design. Thermodynamics, Modeling, and Design Analysis. Exergy Analysis. Heat Transfer, Modeling, and Design Analysis. Applications with Heat and Fluid Flow. Applications with Thermodynamics and Heat and Fluid Flow. Economic Analysis. Thermoeconomic Analysis and Evaluation. Thermoeconomic Optimization. Appendices. Index.
This paper shows that thermodynamic optimization provides a common theoretical basis for the existence of the finely tuned frequencies of pulsating processes of animals. In respiration and circulation, the minimization of mechanical power consumption subject to finite contact area and mass transfer (metabolic) rate constraints also explains why frequencies decrease as the body size (M) increases. For example, it is shown that the optimal breathing and heartbeat time intervals should increase as M 0.24, which is in excellent agreement with experimental data. It is also shown that the breathing and heartbeat time intervals should be of the same order of magnitude. In ejaculation, the maximization of the mechanical power transmitted to the ejected seminal fluid explains the existence of an optimal bursting time interval. The deterministic method of thermodynamic optimization predicts temporal organization in Nature, and extends thermodynamics to the field of biology.
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The objective of the Journal of Mechanics is to provide an international forum to foster exchange of ideas among mechanics communities in different parts of world.
No abstract is provided for this article.
This paper presents a new concept for generating the multi-scale structure of a finite-size flow system that has maximum heat transfer density–
This article is about evolutionary design and freedom and is based on my new book, Freedom and Evolution: Hierarchy in Nature, Society and Science [1]. There is a lot to say about this broad subject, therefore I’ve reduced it to the topics of thermodynamics, freedom and evolution, diversity and hierarchy, and science and freedom. First, I will present the terminology, which will be followed by the applications of the evolution of cooling technology for high-density heat-generating components in a packet. Finally, I will show why this book is important for you, the reader, as well as for the practitioner.
1. Natural form, questioning, and theory 2. Mechanical structure 3. Thermal structure 4. Heat trees 5. Fluid trees 6. Ducts and rivers 7. Turbulent structure 8. Convective trees 9. Structure in power systems 10. Structure in time: rhythm 11. Transportation and economics structure 12. Shapes with constant resistance About the author Author index Subject index.
Constructal theory complements the analysis of thermodynamic systems by focusing on the flow configuration of the system, and on the relationship between configuration (design) and global performance. The design progress made in this emerging field is reviewed in a new book [1]. In this paper we outline our progress on developing flow architectures for a new class of smart materials: composites with vascular channels that provide volumetric flowing (bathing) and cooling.
It has been proposed to extract energy from the subterranean hot dry rock bed (HDR) by creating one or more narrow fractures in the rock and circulating cold water through the fractures. In time, the temperature of the rock region surrounding the crack drops under the influence of time-dependent conduction. This study presents the most basic thermodynamic aspects (first law and second law) of the HDR energy extraction process. It shows which parameters most influence the amount of useful energy (exergy) extracted from the HDR reservoir over a fixed time interval. For example, the water flow rate can be selected optimally in order to maximize the delivery of energy over the lifetime of the HDR system.
In this paper we describe a natural language processing system which is able to predict whether or not a patient exhibits a specific phenotype using the information extracted from the narrative reports associated with the patient. Furthermore, the phenotypic annotations from our report dataset were performed at the report level which allows us to perform the prediction of the clinical phenotype at any point in time during the patient hospitalization period. Our experiments indicate that an important factor in achieving better results for this problem is to determine how much information to extract from the patient reports in the time interval between the patient admission time and the current prediction time.
