The twin screw compressor can be actually considered as one of the most efficient and commonly used machines for compressed air production, cooling and refrigeration, due to its high efficiency, reliability and compactness. This thesis is mainly focused on a thorough performance analysis of six positive displacement machines (manufactured by Bitzer), with the working fluid R134a. The analysis has been carefully carried out by means of a 0-D simulation model, after tuning the model for each compressor. Inputs for the model are represented by several parameters to be optimized in order to minimize the simulation error in terms of mass flow rate, power consumption and outlet temperature, to validate the lowest difference among the model outputs and what the manufacturer declares. Different parameters are taken into account: heat transfer coefficients at the inlet section, at the outlet section and with the environment, the Built-In Volume Ratio (BVR), a fictitious leakage area, the displacement and two coefficients which account for possible power losses. By means of several plots, the percentage errors for both flow rates and power consumptions have been studied in order to highlight that the difference between the model outputs and Bitzer data are always acceptable (within ±5%). After setting the parameters for each machine, some possible similarity laws among the parameters themselves and displacement (and/or flow rates) can possible. Further, next steps could aim at analysing a broader range of compressors, by taking into consideration other manufacturers and different working fluids.
Il compressore a doppia vite è una macchina ampiamente adottata nei settori della produzione di aria compressa, refrigerazione e condizionamento, per efficienza, affidabilità e compattezza. Questo lavoro di tesi affronta l’analisi delle prestazioni di sei macchine volumetriche di costruzione BITZER, operanti con fluido di lavoro R134a. Tale studio è stato condotto attraverso l’ausilio di un modello di simulazione 0-D, che è stato calibrato su ognuno dei compressori sopracitati. Il modello richiede in input dei parametri da ottimizzare per minimizzare l’errore previsionale in termini di portata elaborata, potenza assorbita e temperatura del fluido alla mandata, allo scopo di verificare la minima differenza tra le grandezze ottenute dal codice di calcolo e quelle dichiarate dal costruttore. Diversi parametri sono presi in esame: coefficienti di scambio termico all’ammissione, all’uscita e con l’ambiente, il rapporto volumetrico di compressione (anzidetto BVR), un’area di trafilamento, la cilindrata, due specifici coefficienti utili per la simulazione della potenza persa. Per mezzo di grafici specifici sono stati studiati gli errori percentuali di portate e potenze, al fine di mostrare come la discrepanza fra le grandezze calcolate e quelle fornite sia accettabile e sempre compresa entro il ±5%. Calibrati i parametri di ciascuna macchina, si è cercato di individuare delle possibili relazioni di similitudine tra i parametri stessi e grandezze fondamentali quali portata e/o cilindrata. La tesi lascia aperte prospettive di sviluppo future, in modo da migliorare i risultati fin qui presentati, estendendo l’analisi su compressori di altri costruttori, eventualmente operanti con fluidi diversi da R134a.
Simulazioni di compressori a vite in vista di leggi di similitudine
FACCHINO, VINCENZO
2014/2015
Abstract
The twin screw compressor can be actually considered as one of the most efficient and commonly used machines for compressed air production, cooling and refrigeration, due to its high efficiency, reliability and compactness. This thesis is mainly focused on a thorough performance analysis of six positive displacement machines (manufactured by Bitzer), with the working fluid R134a. The analysis has been carefully carried out by means of a 0-D simulation model, after tuning the model for each compressor. Inputs for the model are represented by several parameters to be optimized in order to minimize the simulation error in terms of mass flow rate, power consumption and outlet temperature, to validate the lowest difference among the model outputs and what the manufacturer declares. Different parameters are taken into account: heat transfer coefficients at the inlet section, at the outlet section and with the environment, the Built-In Volume Ratio (BVR), a fictitious leakage area, the displacement and two coefficients which account for possible power losses. By means of several plots, the percentage errors for both flow rates and power consumptions have been studied in order to highlight that the difference between the model outputs and Bitzer data are always acceptable (within ±5%). After setting the parameters for each machine, some possible similarity laws among the parameters themselves and displacement (and/or flow rates) can possible. Further, next steps could aim at analysing a broader range of compressors, by taking into consideration other manufacturers and different working fluids.File | Dimensione | Formato | |
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2015_09_Facchino.pdf
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Descrizione: Testo della tesi
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https://hdl.handle.net/10589/109941