Appunti Fisica Tecnica Industriale 1

1 Università di Roma Tor Vergata – corso Coppa/Petracci

Federico Casucci Federico Casucci ©2

1 Sommario

1 Termodinamica _______________________________________________________________________________________________________ 7

• 1.1 Lavoro termodinamico ____________________________________________________________________________________________ 8
• 1.2 Calore, temperatura ed equilibrio termico _______________________________________________________________________ 8
• 1.3 Primo principio della termodinamica conservazione dell’energia per i sistemi chiusi _____________________ 9
• 1.4 Conservazione della massa per sistemi aperti _________________________________________________________________ 10
• 1.5 Primo principio della termodinamica conservazione dell’energia per i sistemi aperti __________________ 10
• 1.6 Secondo principio della termodinamica ________________________________________________________________________ 11
• 1.6.1 Formulazione analitica del secondo principio ____________________________________________________________ 12
• 1.7 Entropia ___________________________________________________________________________________________________________ 12
• 1.7.1 Teorema di aumento dell’entropia ________________________________________________________________________ 13
• 1.7.2 Calore in termini di entropia _______________________________________________________________________________ 13
• 1.7.3 Energia interna ed entalpia in termini di entropia _______________________________________________________ 13
• 1.7.4 Lavoro in termini di entropia ______________________________________________________________________________ 13

2 Sistemi tecnici ______________________________________________________________________________________________________ 15

• 2.1 Sistemi tecnici chiusi _____________________________________________________________________________________________ 15
• 2.1.1 Sistema motore _____________________________________________________________________________________________ 15
• 2.1.2 Sistema frigorifero __________________________________________________________________________________________ 15
• 2.1.3 Sistema pompa di calore ___________________________________________________________________________________ 16
• 2.2 Sistemi tecnici aperti _____________________________________________________________________________________________ 16
• 2.2.1 Espansore o turbina ________________________________________________________________________________________ 17
• 2.2.2 Compressore o pompa _____________________________________________________________________________________ 17
• 2.2.3 Valvola di laminazione _____________________________________________________________________________________ 18
• 2.2.4 Miscelatore __________________________________________________________________________________________________ 19
• 2.2.5 Scambiatore _________________________________________________________________________________________________ 19
• 2.2.6 Condotti, ugelli e diffusori __________________________________________________________________________________ 20
• 2.3 Sistemi tecnici nei diagrammi ed __________________________________________________________________ 20

3 Proprietà delle sostanze _______________________________________________________________________________________ 21

• 3.1 Coefficienti di dilatazione e compressione _____________________________________________________________________ 21
• 3.2 Coefficienti calorimetrici ________________________________________________________________________________________ 21
• 3.3 Potenziali termodinamici ________________________________________________________________________________________ 22
• 3.4 Equazioni di Maxwell ____________________________________________________________________________________________ 22
• 3.5 Energia interna in variabili di stato _____________________________________________________________________________ 23
• 3.6 Entalpia in variabili di stato _____________________________________________________________________________________ 24
• 3.7 Calore in variabili di stato _______________________________________________________________________________________ 24
• 3.8 Entropia in variabili di stato _____________________________________________________________________________________ 24
• 3.9 Relazione di Mayer _______________________________________________________________________________________________ 24
• 3.10 Diagramma ________________________________________________________________________________________________ 25
• 3.11 Diagramma ________________________________________________________________________________________________ 26

4 Gas perfetti _________________________________________________________________________________________________________ 28

• 4.1 Trasformazione isoentropica ___________________________________________________________________________________ 28

Federico Casucci © 3

• 4.2 Trasformazioni politropiche ____________________________________________________________________________________ 29
• 4.3 Diagramma per i gas perfetti ____________________________________________________________________________ 30

5 Passaggi di stato per sostanze pure _________________________________________________________________________ 32

• 5.1 Liquido-vapore nel diagramma __________________________________________________________________________ 32
• 5.2 Liquido-vapore nel diagramma _________________________________________________________________________ 33
• 5.3 Liquido-vapore nel diagramma _________________________________________________________________________ 33
• 5.4 Piano delle fasi ___________________________________________________________________________________________________ 33

6 Miscele di aria umida _____________________________________________________________________________________________ 35

• 6.1 Psicrometro _______________________________________________________________________________________________________ 36
• 6.1.1 Diagramma psicrometrico _________________________________________________________________________________ 37
• 6.2 Trasformazioni di miscele di aria umida _______________________________________________________________________ 37
• 6.2.1 Riscaldamento isotitolo ____________________________________________________________________________________ 37
• 6.2.2 Miscelazione ________________________________________________________________________________________________ 38
• 6.2.3 Raffreddamento isotitolo ___________________________________________________________________________________ 39
• 6.2.4 Raffreddamento con deumidificazione ___________________________________________________________________ 39
• 6.2.5 Umidificazione adiabatica con raffreddamento __________________________________________________________ 40
• 6.2.6 Umidificazione isoterma ___________________________________________________________________________________ 41

7 Cicli motore termici a combustione interna ______________________________________________________________ 43

• 7.1 Ciclo Otto __________________________________________________________________________________________________________ 43
• 7.1.1 Ciclo reale e semplificazioni termodinamiche ____________________________________________________________ 44
• 7.1.2 Parametri di valutazione ___________________________________________________________________________________ 45
• 7.2 Ciclo Diesel ________________________________________________________________________________________________________ 45
• 7.2.1 Ciclo reale e semplificazioni termodinamiche ____________________________________________________________ 46
• 7.2.2 Parametri di valutazione ___________________________________________________________________________________ 47
• 7.2.3 Confronto Otto vs Diesel ___________________________________________________________________________________ 48
• 7.3 Ciclo misto Sabathé ____________________________________________________________________________________________ 49
• 7.4 Ciclo Joule _________________________________________________________________________________________________________ 50
• 7.4.1 Parametri di valutazione ___________________________________________________________________________________ 51

8 Cicli motore a vapore ____________________________________________________________________________________________ 54

• 8.1 Ciclo di Carnot ____________________________________________________________________________________________________ 54
• 8.1.1 Parametri di valutazione ___________________________________________________________________________________ 55
• 8.1.2 Limiti realizzativi del ciclo di Carnot ______________________________________________________________________ 55
• 8.2 Ciclo Hirn o Rankine a vapore surriscaldato _________________________________________________________________ 55
• 8.2.1 Parametri di valutazione ___________________________________________________________________________________ 57
• 8.2.2 Confronto Hirn vs Carnot __________________________________________________________________________________ 57

9 Impianti misti _______________________________________________________________________________________________________ 59

• 9.1 Impianto a ciclo combinato ______________________________________________________________________________________ 59
• 9.2 Impianto di cogenerazione ______________________________________________________________________________________ 59

10 Cicli frigoriferi _________________________________________________________________________________________________ 60

• 10.1 Ciclo frigorifero a compressione di vapore ____________________________________________________________________ 60
• 10.1.1 Parametri di valutazione ___________________________________________________________________________________ 61

Federico Casucci ©4

• 10.1.2 Fluidi refrigeranti ___________________________________________________________________________________________ 61
• 10.2 Impianto frigorifero in cascata __________________________________________________________________________________ 62

11 Termofluidodinamica _________________________________________________________________________________________ 63

• 11.1 Conservazione della massa ______________________________________________________________________________________ 63
• 11.2 Equazione di Bernoulli generalizzata principio in forma meccanica ___________________________________ 64
• 11.3 Misurazione della pressione ____________________________________________________________________________________ 65
• 11.4 Carico potenziale per attrito come caduta di pressione _______________________________________________________ 66
• 11.5 Viscosità __________________________________________________________________________________________________________ 66
• 11.6 Esperienza di Reynolds __________________________________________________________________________________________ 67
• 11.7 Perdite di carico __________________________________________________________________________________________________ 68
• 11.7.1 Perdite di carico distribuite ________________________________________________________________________________ 68
• 11.7.2 Perdite di carico concentrate ______________________________________________________________________________ 71
• 11.7.3 Perdite di carico totali ______________________________________________________________________________________ 71

12 Trasmissione del calore ______________________________________________________________________________________ 72

• 12.1 Conduzione _______________________________________________________________________________________________________ 72
• 12.1.1 Conduzione in regime permanente monodimensionale _________________________________________________ 73
• 12.1.1.1 Lastra piana ____________________________________________________________________________________________ 74
• 12.1.1.2 Cilindro cavo ___________________________________________________________________________________________ 74
• 12.1.1.3 Lastre piane affacciate ________________________________________________________________________________ 74
• 12.1.1.4 Cilindri cavi affacciati _________________________________________________________________________________ 76
• 12.1.2 Conduzione a parametri concentrati ______________________________________________________________________ 77
• 12.1.2.1 Solido a contatto con un fluido _______________________________________________________________________ 78
• 12.2 Irraggiamento ____________________________________________________________________________________________________ 78
• 12.2.1 Corpo nero __________________________________________________________________________________________________ 79
• 12.2.2 Intensità di radiazione di un corpo nero __________________________________________________________________ 80
• 12.2.3 Corpi reali ___________________________________________________________________________________________________ 81
• 12.2.4 Legge di Kirchhoff __________________________________________________________________________________________ 81
• 12.2.5 Scambio termico per irraggiamento – fattori di vista ____________________________________________________ 82
• 12.2.6 Irraggiamento in cavità nere _______________________________________________________________________________ 84
• 12.3 Convezione _______________________________________________________________________________________________________ 84
• 12.3.1 Convezione naturale ________________________________________________________________________________________ 85
• 12.3.2 Numero di Nusselt per la convezione naturale ___________________________________________________________ 85
• 12.3.3 Numero di Nusselt per la convezione forzata ____________________________________________________________ 86
• 12.3.4 Convezione e regime di moto ______________________________________________________________________________ 88

13 Comfort termoigrometrico _________________________________________________________________________________ 90

• 13.1 Corpo umano _____________________________________________________________________________________________________ 90
• 13.1.1 Bilancio termico del corpo umano _________________________________________________________________________ 91
• 13.2 Equazioni del comfort di Fanger ________________________________________________________________________________ 93
• 13.2.1 Intervallo di comfort ________________________________________________________________________________________ 94

14 Impianti ad acqua _______________________________________________________________________________________________ 96

• 14.1 Tipologie di impianti ad acqua calda ___________________________________________________________________________ 96

Federico Casucci © 5

• 14.2 Componenti degli impianti ad acqua calda _____________________________________________________________________ 97
• 14.2.1 Caldaia _______________________________________________________________________________________________________ 97
• 14.2.2 Corpi scaldanti ______________________________________________________________________________________________ 97
• 14.2.3 Vaso di espansione _________________________________________________________________________________________ 98
• 14.2.4 Pompa _______________________________________________________________________________________________________ 99
• 14.2.5 Tubazioni ___________________________________________________________________________________________________ 100
• 14.2.6 Altri componenti ___________________________________________________________________________________________ 101
• 14.3 Dimensionamento di un impianto di riscaldamento ad acqua calda ________________________________________ 101
• 14.3.1 Dimensionamento di un impianto di circolazione a 2 tubi _____________________________________________ 101
• 14.3.2 Dimensionamento di un impianto a ritorno inverso e ad anello _______________________________________ 103
• 14.3.3 Dimensionamento di un impianto ad un solo tubo ______________________________________________________ 103
• 14.3.4 Dimensionamento di un impianto a collettore complanare ____________________________________________ 105
• 14.4 Regolazione di un impianto di riscaldamento ad acqua calda _______________________________________________ 105
• 14.5 Installazione delle pompe in un impianto di riscaldamento ad acqua calda _______________________________ 106

15 Impianti di teleriscaldamento ____________________________________________________________________________ 108

• 15.1 Centrale di cogenerazione ______________________________________________________________________________________ 108
• 15.2 Tipologia di rete _________________________________________________________________________________________________ 109
• 15.3 Componenti degli impianti di teleriscaldamento _____________________________________________________________ 109
• 15.3.1 Tubazioni ___________________________________________________________________________________________________ 109
• 15.3.2 Fluidi termovettori ________________________________________________________________________________________ 109
• 15.3.3 Vaso di espansione ________________________________________________________________________________________ 110
• 15.3.4 Serbatoi o accumulatori ___________________________________________________________________________________ 110
• 15.4 Dimensionamento di un impianto di teleriscaldamento _____________________________________________________ 110
• 15.5 Posizionamento della pompa ___________________________________________________________________________________ 111

16 Impianti ad aria ________________________________________________________________________________________________ 113

• 16.1 Componenti degli impianti ad aria _____________________________________________________________________________ 113
• 16.1.1 Scambiatori di calore ______________________________________________________________________________________ 113
• 16.1.2 Umidificatori _______________________________________________________________________________________________ 113
• 16.1.3 Deumidificatori ____________________________________________________________________________________________ 113
• 16.1.4 Filtri _________________________________________________________________________________________________________ 114
• 16.1.5 Bocchette o diffusori _______________________________________________________________________________________ 115
• 16.1.6 Condotti ____________________________________________________________________________________________________ 115
• 16.1.7 Ventilatori __________________________________________________________________________________________________ 116
• 16.2 Tipologie di impianti ad aria ___________________________________________________________________________________ 116
• 16.2.1 Impianti a tutta aria _______________________________________________________________________________________ 116
• 16.2.1.1 Im