Previous Page  20 / 28 Next Page
Basic version Information
Show Menu
Previous Page 20 / 28 Next Page
Page Background

Capitolo 5

Il bilancio entropico

64

7XWWDYLD FRPH LQGLFDWR VFKHPDWLFDPHQWH LQ )LJXUD QHOOH WUDVIRUPD]LRQL ULJXDUGDQWL

VLVWHPL FKLXVL SUHYDOH O¶DVSHWWR WHPSRUDOH FLRq HVVH VDUDQQR FDUDWWHUL]]DWH GD XQ

prima

e un

dopo

RYYHUR GD XQ

inizio

e una

¿QH

GHOOD WUDVIRUPD]LRQH DQFKH VH PDJDUL HVVD FRPSRUWD XQR

VSRVWDPHQWR QHOOR VSD]LR

Stato

i

Stato

f

Tempo

Figura 5.1

,QYHFH FRPH LQGLFDWR LQ )LJXUD QHO FDVR GL WUDVIRUPD]LRQL ULJXDUGDQWL VLVWHPL DSHUWL

LQ UHJLPH SHUPDQHQWH SUHYDOH O¶DVSHWWR VSD]LDOH H FL VDUj XQ

qui

e un

FLRq XQ¶

entrata

e una

uscita

D SUHVFLQGHUH GDO IDWWR FKH LO WUDQVLWR GDOO¶LQJUHVVR DOO¶XVFLWD ULFKLHGD XQ FHUWR WHPSR

,Q HQWUDPEL L FDVL VL SRWUj FRPXQTXH SHQVDUH D

trasformazioni chiuse

GHWWH DQFKH

tra-

sformazioni cicliche

FDUDWWHUL]]DWH GDO IDWWR FKH DOOD ¿QH GHO SURFHVVR VL ULWRUQD QHOOH FRQ

-

GL]LRQL LQL]LDOL 7DOL WUDVIRUPD]LRQL ULYHVWRQR XQ¶LPSRUWDQ]D WDOH GD PHULWDUH XQD WUDWWD]LRQH

SL DSSURIRQGLWD

Spazio

Entrata

Uscita

dm

e

dm

u

Figura 5.2

5.2

LE TRASFORMAZIONI CICLICHE

,Q EDVH D TXDQWR DSSHQD GHWWR VL SRWUj UHDOL]]DUH XQD

trasformazione chiusa

o

trasforma-

zione ciclica

VLD PHGLDQWH XQ VLVWHPD FKLXVR FLRq SULYR GL VFDPEL GL PDVVD FKH FRPSLH XQD

VHULH GL WUDVIRUPD]LRQL SDU]LDOL FKH OR ULSRUWDQR QHOOH FRQGL]LRQL GL SDUWHQ]D )LJXUD

VLD

PHGLDQWH XQD VXFFHVVLRQH GL VLVWHPL DSHUWL LQ UHJLPH VWD]LRQDULR FKH IDQQR Vu FKH OD VRVWDQ]D

FKH OL DWWUDYHUVD DVVXPD QXRYDPHQWH OH FRQGL]LRQL LQL]LDOL )LJXUD

,Q HQWUDPEL L FDVL VL

WUDWWHUj GL PRGXODUH RSSRUWXQDPHQWH JOL VFDPEL GL FDORUH H GL ODYRUR DL TXDOL YLHQH DVVRJJHW

-

WDWR LO VLVWHPD FKLXVR R OD VXFFHVVLRQH GL VLVWHPL DSHUWL LQ PRGR GD FKLXGHUH LO FLFOR

1HO FDVR GL XQ VLVWHPD FKLXVR SHU FLDVFXQD WUDVIRUPD]LRQH SDU]LDOH LO ELODQFLR HQHUJHWLFR

FRPSRUWD FKH

Q

if

= (

U

T

,

f

U

T

,

i

) +

L

if

GRYH DO VROLWR FRQ

Q

si indicano gli scambi termici, con

L

JOL VFDPEL GL ODYRUR H FRQ

U

T

la

YDULD]LRQH GL HQHUJLD WRWDOH GHO VLVWHPD 0D QHO FDVR GL XQD VHULH GL WUDVIRUPD]LRQL SDU]LDOL

FKH FRPSOHVVLYDPHQWH VL FKLXGRQR VX Vp VWHVVH GDQGR OXRJR DG XQD WUDVIRUPD]LRQH FLFOLFD VH

VL VRPPDQR PHPEUR D PHPEUR OH VLQJROH HTXD]LRQL

VL RWWLHQH

™

Q

if

™

L

if

(5.2)