Entropy Equation for a Control Volume

Transcription

1 Fudamtals of Thrmodyamcs Chaptr 7 Etropy Equato for a Cotrol Volum Prof. Syoug Jog Thrmodyamcs I MEE

2 Thrmal Egrg Lab. 2 Q ds Srr T Q S2 S1 1 Q S S2 S1 Srr T t t T t S S s m 1 2 t S S s m tt S S ( S S ) s m s m 2 1 tt t C. V ( S S ) s m s m Q S t t t Tt t dscv. Q ms ms Srr dt T tt t C. V rr rr

3 Thrmal Egrg Lab Th scod law of thrmodyamcs for a cotrol volum

4 Thrmal Egrg Lab Th stady-stat procss ad th trast procss Stady-stat procss dscv. 0 dt Q 0 m s m s S T Q m s m s S T g g Q ms ms T Sgl lt & sgl xt q s s sg T for a adabatc procss s s s s g s CV. CV.

5 Thrmal Egrg Lab. 5 Ex. 7.1 Stam trs a stam turb at a prssur of 1 MPa, a tmpratur of 300, ad a vlocty of 50 m/s. Th stam lavs th turb at a prssur of 150 kpa ad a vlocty of 200 m/s. Dtrm th work pr klogram of stam flowg through th turb, assumg th procss to b rvrsbl ad adabatc.

6 Thrmal Egrg Lab. 6 Ex. 7.2 Cosdr th rvrsbl adabatc flow of stam through a ozzl. Stam trs th ozzl at 1 MPa ad 300, wth a vlocty of 30 m/s. Th prssur of th stam at th ozzl xt s 0.3 MPa. Dtrm th xt vlocty of th stam from th ozzl, assumg a rvrsbl, adabatc, stady-stat procss.

7 Thrmal Egrg Lab. 7 Ex. 7.3 A vtor rports havg a rfrgrato comprssor that rcvs saturatd R-134a vapor at -20 ad dlvrs th vapor at 1 MPa, 40. Th comprsso procss s adabatc. Dos th procss dscrbd volat th scod law?

8 Thrmal Egrg Lab. 8 Ex. 7.4 A ar comprssor a gas stato (s Fg. 7.4) taks a flow of ambt ar at 100 kpa, 290 K ad comprsss t to 1000 kpa a rvrsbl adabatc procss. W wat to kow th spcfc work rqurd ad th xt ar tmpratur.

9 Thrmal Egrg Lab. 9 Ex. 7.5 A dsuprhatr works by jctg lqud watr to a flow of suprhatd stam. Wth 2 kg/s at 300 kpa, 200, stam flowg, what mass flow rat of lqud watr at 20 should b addd to grat saturatd vapor at 300 kpa? W also wat to kow th rat of tropy grato th procss.

10 Thrmal Egrg Lab. 10 Trast procss dscv. Q m s m s S dt T 0 t tgrato g Q ( m s m s ) m s m s dt S T t cv c. v g

11 Thrmal Egrg Lab. 11 Ex. 7.6 Assum a ar tak has 40 L of 100 kpa ar at ambt tmpratur 17. Th adabatc ad rvrsbl comprssor s startd so that t chargs th tak up to a prssur of 1000 kpa ad th t shuts off. W wat to kow how hot th ar th tak gts ad th total amout of work rqurd to fll th tak.

12 Thrmal Egrg Lab Th stady-stat sgl flow procss 2 2 V V q h gz h gz w 2 2 Tds q Ts dh vdp g tgrato q ( h h ) vdp T s T s g g L (Lost work) 2 2 ( V V ) L w ( h h ) vdp w ( h h ) g( z z ) 2 w 2 2 ( V V ) vdp g( z z ) w 2 for rvrsbl procss w ( V V ) L w vdp g( z z) 2 L

13 Thrmal Egrg Lab ( V V ) w vdp g( z z) 2 glgbl K.E & P.E dffrc w vdp

14 Thrmal Egrg Lab. 14

15 Thrmal Egrg Lab. 15 for comp. & w V V v( P P ) g( Z Z) V V P gz P gz (Broull Eq.) 2 2

16 Thrmal Egrg Lab. 16 ( 1) l l w vdp C dp P C P P Pv P Pv P v P v P P v P P C dp P C vdp w ) ( C P v C Pv 1 1 cost vdp w * 적분과정

17 Thrmal Egrg Lab. 17 Ex. 7.7 Calculat th work pr klogram to pump watr stropcally from 100 kpa, 30 to 5 MPa.

18 Thrmal Egrg Lab. 18 Ex. 7.8 Cosdr a ozzl usd to spray lqud watr. If th l prssur s 300 kpa ad th watr tmpratur s 20, how hgh a vlocty ca a dal ozzl grat th xt flow?

19 Thrmal Egrg Lab Prcpl of th cras of tropy ds dt C. V ds dt surr m s m s dst dsc. V ds dt dt dt 1 1 Q T T0 Q 0 T0 T Q 0 T0 T dst 0 dt surr m s m s S rr Q S T Q T0 rr, CV

20 Thrmal Egrg Lab. 20

21 Thrmal Egrg Lab. 21 Ex. 7.9 Saturatd vapor R-410A trs th usulatd comprssor of a hom ctral ar-codtog systm at 5. Th flow rat of rfrgrat through th comprssor s 0.08 kg/s, ad th lctrcal powr put s 3 kw. Th xt stat s 65, 3000 kpa. Ay hat trasfr from th comprssor s wth th ambt vromt at 30. Dtrm th rat of tropy grato for ths procss.

22 Thrmal Egrg Lab Egrg applcatos - ffccy th W Q turb t H w h h w h h a s, s P,s = P (Ext prssur of th stropc procss = Ext prssur of th actual procss)

23 Thrmal Egrg Lab. 23 Ex A stam turb rcvs stam at a prssur of 1 MPa ad a tmpratur of 300. Th stam lavs th turb at a prssur of 15 kpa. Th work output of th turb s masurd ad s foud to b 600 kj/kg of stam flowg through th turb. Dtrm th ffccy of th turb.

24 Thrmal Egrg Lab. 24 Ex Ar trs a gas turb at 1600 K ad xts at 100 kpa, 830 K. Th turb ffccy s stmatd to b 85%. What s th turb lt prssur?

25 Thrmal Egrg Lab. 25 Comprsso procss comp w h s h w h h, s coold comp wt w

26 Thrmal Egrg Lab. 26 Ex Ar trs a automotv suprchargr at 100 kpa, 300 K ad s comprssd to 150 kpa. Th ffccy s 70%. What s th rqurd work put pr klogram of ar? What s th xt tmpratur?

27 Thrmal Egrg Lab. 27 Nozzl /2 ozzl V V s /2 2 2,

28 7.6 Summary of gral cotrol volum procss Formulato Stps (S pag 296~297) 1. Mak a physcal modl of th systm wth compots ad llustrat all mass flows, hat flows, ad work rats. 2. Df a cotrol mass or cotrol volum by placg a cotrol surfac that cotas th substac you wat to aalyz. 3. Wrt dow th gral laws for ach of th chos cotrol volums. 4. Wrt dow th auxlary or partcular laws for whatvr s sd ach of th cotrol volums. 5. Fsh th formulato by combg all th quatos. 6. Th quatos ar ow solvd for th ukows by wrtg all trms wth ukow varabls o o sd ad kow trms o th othr. Thrmal Egrg Lab. 28

29 Homwork Problms 2017: 15, 24, 27, 36, 41, 45, 57, 69, : 18, 21, 27, 36, 39, 42, 57, 66, 75, 105, 128 Thrmal Egrg Lab. 29

30 Thrmal Egrg Lab. 30 Problm 7.41

31 Thrmal Egrg Lab. 31 * w q q Tds q q Fl Fl Fl w L q 윗식을 Fl q w a w du ( h d h L pdv w du a a w a dh vdpw w L pdv w ) 의유도과정 까지적분 L L vdp Fl * a : ktc rgy 와 pottal rgy 를갖는 cotrol mass