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Revista de Chimie, Volume 63, Issue 1, pp. (2012)

STOIAN PETRESCU, CATALINA DOBRE, CAMELIA STANCIU, MONICA COSTEA, GEORGIANA TIRCA-DRAGOMIRESCU, MICHEL FEIDT The Direct Method from Thermodynamics with Finite Speed used for Performance Computation of quasi-Carnot Irreversible Cycles. I.Evaluation of coefficient of performance and power for refrigeration machines with mechanical compression of vapour


This paper is dealing with the performances (Coefficient of Performance, COP and Power) evaluation for a quasi-Carnot irreversible cycle, namely the Irreversible Refrigeration Cycle with Mechanical Compression of Vapour. The present computation scheme is based on recent developments of the Direct Method from Finite Speed Thermodynamics (FST). The Direct Method consists in analyzing any irreversible cycle, step by step, by writing the corresponding equation of the First Law of Thermodynamics for finite speed processes and integrating it on the whole cycle, for each process. The First Law expression for finite speed processes includes three of the main sources of internal irreversibilities, namely: finite speed interaction between the piston and the gas/vapour, friction due to the finite piston speed within the cylinder, throttling processes in the valves. The new expression of the First Law for processes with finite speed is used here in order to get equations that relate the vapour properties for each irreversible process that occurs with finite speed of the piston in the compressor, in a Refrigeration Machine Cycle with Mechanical Compression of Vapour. These equations are used later for calculating entirely analytically the performances of the cycle, as a function of the finite speed of the piston and also as a function of other parameters such as: vapour temperatures and pressures in the evaporator, respectively in the condenser, compression ratio and mass flow rate. Note that the present analysis will differ from the previously reported one <1>, because here the real properties of vapour in the cycle will be considered, for the first time in using the Direct Method, by using a correction for departure of vapour behaviour from the behaviour of perfect gases. The previous analysis used only the perfect gas properties. Therefore, these results can be used for optimization and design of refrigeration machines and heat pumps. Keywords: reversed irreversible quasi-Carnot cycle, finite speed processes, Direct Method, refrigeration machines with finite speed, Thermodynamics with Finite Speed

Issue: 2012 Volume 63, Number 1
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