REFRIGERATION CYCLES WITH VAPOR TREATED WITH THE DIRECT METHOD FROM FINITE SPEED THERMODYNAMICS (TFS)

Autor/autori: Catalina DOBRE, Stoian PETRESCU, Monica COSTEA

Rezumat: Lucrarea prezinta o abordare complet noua si originala a analizei ireversibilitatilor generate in timpul func?ionarii masinilor frigorifice cvasi-Carnot cu vapori. Schema de calcul dezvoltata in aceasta lucrare este bazata pe algoritmul Metodei Directe elaborata in cadrul Termodinamicii cu Viteza Finita (TFS). Metoda Directa consta in analiza unui ciclu ireversibil, pas cu pas, prin integrarea ecuatiei Primului Principiu pentru procesele cu viteza finita pe fiecare faza a ciclului. In acest articol sunt dezvoltate expresii pentru calculul sursei interne de generare a entropiei si a coeficientului de performanta, in functie de viteza finita a procesului si de al?i parametri,precum temperatura vaporilor, raportul de comprimare/destindere, debitul masic si proprietatile vaporilor pentru fiecare proces ce se desfasoara cu viteza finita in masinile frigorifice ireversibile cvasi-Carnot. Este prezentat un studiu comparativ (patru cicluri in care ireversibilitatile sunt introduse progresiv) cu scopul de a ilustra maniera de utilizare a acestor expresii pentru a evalua generarea interna de entopie si totodata pentru a calcula performantele masinii. In cadrul acestor calcule sunt luate in considerare proprietatile gazului real. Aceasta abordare, bazata pe Metoda Directa, propune o alternativa viabila pentru proiectarea si optimizarea acestui tip de masini.

Cuvinte cheie: generarea de entropie, ciclu cvasi-Carnot ireversibil, Metoda Directa, masini frigorifice,Termodinamica cu Viteza Finita.


Abstract: The paper presents a completely new and original approach of quasi-Carnot refrigeration machines working with vapor. 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. It provides expressions for calculating the internal entropy generation source and COP, as a function of the finite speed of the process and other parameters such as temperature of the vapor, compression/expansion ratio, mass flow rate and vapor properties for each finite speed process of the reversed irreversible quasi-Carnot cycle refrigeration machines. The real gas properties are considered in these calculations. This approach, based on the Direct Method, becomes an important issue in design and optimization of such machines. An example of a comparative study (four cycles in which irreversibilities are gradually introduced) is presented in order to illustrate the use of these expressions to assess the internal entropy generation and also the evaluation of the machine performance. The real gas properties are considered in these calculations. This approach, based on the Direct Method, becomes an important tool in design and optimization of such machines.

Keywords: entropy generation, irreversible quasi-Carnot cycle, reversed irreversible cycle, finite speed processes, Direct Method, refrigeration machines, Thermodynamics with Finite Speed

 

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