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Full-Text Articles in Mechanical Engineering
Thermodynamic Analysis Of Closed Steady Or Cyclic Systems, Jim A. Mcgovern
Thermodynamic Analysis Of Closed Steady Or Cyclic Systems, Jim A. Mcgovern
Articles
Closed, steady or cyclic thermodynamic systems, which have temperature variations over their boundaries, can represent an extremely large range of plants, devices or natural objects, such as combined heating, cooling and power plants, computers and data centres, and planets. Energy transfer rates can occur across the boundary, which are characterized as heat or work. We focus on the finite time thermodynamics aspects, on energy-based performance parameters, on rational efficiency and on the environmental reference temperature. To do this, we examine the net work rate of a closed, steady or cyclic system bounded by thermal resistances linked to isothermal reservoirs in …
Non-Intrusive Second Law Performance Evaluation Of A Domestic Freezer, Jim Mcgovern, S. Oladunjoye
Non-Intrusive Second Law Performance Evaluation Of A Domestic Freezer, Jim Mcgovern, S. Oladunjoye
Conference Papers
This paper describes non-intrusive performance testing and second law, exergy-based, performance evaluation of a small, contemporary domestic freezer that used R600a refrigerant. The methodology presented is associated with logging of temperatures and the instantaneous power consumption. It gives a ‘second law of thermodynamics’ perspective on operating performance by providing rational efficiency values and by localizing and quantifying the instantaneous exergy destruction rates. This approach is compared to a more conventional ‘first law’ energy analysis. Suggestions are made for the standardization of such an approach in order to enhance the sustainability of domestic freezers. Keywords: Domestic freezer, Performance testing, Performance evaluation, …
Rational Efficiency Of A Heat Exchanger, Jim Mcgovern, Brian P. Smyth
Rational Efficiency Of A Heat Exchanger, Jim Mcgovern, Brian P. Smyth
Articles
The authors propose a new and unique definition for the rational efficiency of a heat exchanger. This new rational efficiency is defined in terms of its sub-rational efficiencies: a heat transfer rational efficiency and a friction rational efficiency for each of the fluid systems comprising the heat exchanger. The heat transfer rational efficiency is based on the definition of a mean temperature for the heat source and a mean temperature for the heat sink and reflects the exergy supplied and the exergy received, due to heat transfer only. The friction rational efficiency for each fluid system of the heat exchanger …
Termes De Signes Positif Et Négatif En Analyses Exergétiques Des Flux De Chaleur, Jim Mcgovern, Pierre Le Goff
Termes De Signes Positif Et Négatif En Analyses Exergétiques Des Flux De Chaleur, Jim Mcgovern, Pierre Le Goff
Articles
In various technical plants there are heat transfer rates at temperatures above that of the environment and other simultaneous heat transfer rates at temperatures below the temperature of the environment. This is the case in cryogenic industrial processes where a cooling effect is produced from a heat source. This is also the case for all absorption refrigeration plants or absorption plants that provide refrigeration and heat pumping, notably for air-conditioning of buildings. In these cases exergetic analysis leads to equations in which some terms are positive and others are negative. This can pose problems in the definition of exergetic, or …
Exergetic Cost Analysis Of A Mechanical Exergy Recycle, Jim Mcgovern
Exergetic Cost Analysis Of A Mechanical Exergy Recycle, Jim Mcgovern
Conference Papers
A mechanical plant that involves an exergy recycle is presented for analysis. It consists of gearboxes and a fluid coupling. There is one input of shaft power to the plant and there are three separate outputs of shaft power. An exergetic cost analysis approach is outlined and applied to the plant.
A Virtual-System Concept For Exergy Analysis Of Flow Network Plant; Part I: Principles, Jim Mcgovern, Francis O'Toole
A Virtual-System Concept For Exergy Analysis Of Flow Network Plant; Part I: Principles, Jim Mcgovern, Francis O'Toole
Conference Papers
A new type of virtual system, named a flow constraint system (FCS), is proposed to facilitate, clarify, and simplify exergy analyses of plant that involve material flow networks. The need for the virtual system is outlined and the concept is demonstrated by applying it to a CHP steam cycle. The FCS concept allows the physical constraints on the exergy interactions associated with flow streams to be taken into account fully. It also simplifies the treatment of bifurcations in material flows and considerably reduces the need for absolute exergy evaluations. The new concept follows from the work already published by the …
A Virtual-System Concept For Exergy Analysis Of Flow Network Plant; Part Ii: Exergetic And Exergonomic Analysis Illustration, Jim Mcgovern, Francis O'Toole
A Virtual-System Concept For Exergy Analysis Of Flow Network Plant; Part Ii: Exergetic And Exergonomic Analysis Illustration, Jim Mcgovern, Francis O'Toole
Conference Papers
This paper is a continuation of Part I — Principles, to which it refers extensively. The virtual system concept and the methodology introduced in Part I are illustrated by means of a numerical example. This is an exergetic and exergoeconomic analysis of the CHP steam plant that was described in Part I without operating values and parameters. Matrix methods developed by Valero et al. (1986) are adapted to the new concept. It is shown that these methods are made simpler and less subjective. Bond-graph-type diagrams for exergetic and economic costs are presented.