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Egzergia, strumień egzergii i sprawność wykorzystania energii promieniowania elektromagnetycznego

Sieniutycz S., Kuran P.

Prace Wydziału Inżynierii Chemicznej i Procesowej Politechniki Warszawskiej

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2011

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Vol. 35, z. 1

31-56

PL

Egzergia promieniowania określa górną granicę pracy, którą promieniowanie może wykonać. W publikacji wykazano, że istniejące w literaturze równania nie opisują poprawnie egzergii przenoszonej przez strumień promieniowania słonecznego. Bazując na analizie termodynamicznej i kinetycznej, uzyskano ścisłe wyrażenie na strumień egzergii promieniowania elektromagnetycznego, zgodne z termodynamiką ogólną.

EN

Energy of radiation defines an upper bound for work which can be done by the radiation. In this paper it is shown that the energy formulae existing in the literature do not describe correctly the exergy transferred with the flux of solar radiation. With the help of thermodynamic and kinetic analysis an exact formula for exergy flux of electromagnetic radiation is found. The result agrees with the general thermodynamics.

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Limiting power in imperfect systems with fluid flow

Sieniutycz S.

Archives of Thermodynamics

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2004

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Vol. 25, no. 2

69-80

EN

We develop a simple formula for the efficiency of imperfect energy converters and then apply it to the irreversible extension of the classical problem of maximum mechanical work. The work is the cumulative effect obtained from a system composed of: a resource fluid at flow, a set of sequentially arranged engines, and an infinite bath. In the engine mode the fluid's temperature T decreases along the path, thus tending to the bath temperature [T^e]. In the heat-pump mode the process direction is inverted and the fluid is heated (thermal utilization). In a related classical problem the process rates vanish due to the reversibility; here, however, finite rates und unavoidable losses of the work potential are admitted. The method of variational calculus leads to a finite-rate generalization of the maximum-work potential called the finite-rate exergy. This finite-rate exergy is a function of the usual thermal coordinates and the overall number of transfer units tau. The resulting bounds onthe work delivered or supplied are stronger than the reversible bounds predicted by the classical thermodynamics.

3

Thermodynamic limits for work-assisted and solar assisted mass transfer operations

Sieniutycz S.

Archives of Thermodynamics

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2001

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Vol. 22, nr 3-4

17-36

EN

We displey a basic thermodynamic approach to endoreversible limits' of work that may be produced or consumed by a single resource flowing in an open system. To evaluate these limits we consider sequential work-assisted unit operations, in particular those of heating, evaporation and drying which run jointly with 'endoreversible' thermal machines (e.g. heat pumps.) We also compare structures of optimization criteria describing these limits in conventional operations of mass transfer and in work-assisted operations. Mathematical analogies between entropy production expressions in these two sorts of operations are helpful to formulate optimization criteria in both cases. In work-assisted unit operations, total power input is minimized at constraints which take into account dynamics of heat and mass transport and rate of work consumption. Finite-rate, endoreversible models include irreducible losses caused by thermal resistances to the classical exergy potential. Functions of extremum work, which incorporate residual minimum entropy production, are formulated in terms of initial and final states, total duration and (in discrete processes) number of stages. With a radiative engine as an example, extension of the present approach to thermodynamic limits of nonlinear processes is also discussed.

4

Thermodynamic Criteria for Optimization of Work-Assisted and Conventional Drying Operations

Sieniutycz S., Szwast Z.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2000

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Vol. 48, nr 3

315-332

EN

This work presents thermodynamic criteria for optimization of work-assisted drying operations and compares these criteria with those conventional drying operations in sequential systems. For the work-assisted operations, which run jointly with thermal machines, such as heat pumps, total power input is minimized at constrains which describe dynamics of energy and mass exchange. Finite-rate models take into account irreducible consumption of the classical exergy caused by lossy elements in the system. Optimal work functions, which incorporate a residual entropy production, are found in terms of end states, duration and (in discrete processes) number of stages. Mathematical analogies between entropy production expressions in work-assisted and conventional operations are helpful to formulate optimization criteria of the former.