1 st VS 2 nd Laws of Thermodynamics

Transcription

1 t VS nd Law f hemdynamic he fit Law Enegy cneatin Quantity pint f iew - In tem f Enegy Enegy cannt be ceated detyed, but it alway cnee - If nt, it ilate t law f themdynamic Enegy input Enegy utput Enegy ted 00% utput w/ any l he ecnd Law Diectin f a pce Quality pint f iew - In tem f Entpy Entpy geneatin alway inceae - If nt, it ilate nd law f themdynamic A pce inceae Entpy high à Ieeibility high A pce inceae Entpy lw à Ieeibility lw Ht à Cld (O); Cld à Ht (X)

2 t law f hemdynamic Cntl ma (Cled Sytem) Cntl lume (Opened Sytem) Ming bunday (cled Sytem) E ma V D W + D Q DU + D KE + DE D W + D Q + DE ( DE ) DU + D KE + DE ma bunday D W + D Q DH + D KE + DE If yu ytem i a tatinay ytem D W + D Q D U D W + D Q + DE ( DE ) DU DW + DQ DH ma bunday

3 Sme Remak abut Entpy. cee can ccu in a cetain diectin nly, nt in any diectin. A pce mut pceed in the diectin that cmplie with the inceae f entpy pinciple, that i, S gen 0.. Entpy i nn-cneed ppety, and thee i n uch thing a the cneatin f entpy pinciple. 3. he pefmance f engineeing ytem i degaded by the peence f ieeibility, and entpy geneatin i a meaue f the magnitude f the ieeibility' peent duing that pce

4 Week. Ga we Cycle I

5 Objectie. Ealuate the pefmance f ga pwe cycle f which the wking fluid emain a ga thughut the entie cycle. Deelp implifying aumptin applicable t ga pwe cycle 3. Dicu bth appximate and exact analyi f ga pwe cycle 4. Reiew the peatin f ecipcating engine 5. Sle pblem baed n the Ott, Dieel, Stiling, and Eicn cycle 6. Sle pblem baed n the Baytn cycle; the Baytn cycle with egeneatin; and the Baytn cycle with intecling, eheating, and egeneatin 7. Analyze jet-ppulin cycle 8. Identify implifying aumptin f ecnd-law analyi f ga pwe cycle 9. efm ecnd-law analyi f ga pwe cycle

6 Fuel Cmbut And Cycle Heat we Output Chemical Enegy hemal Enegy Mechanical Enegy Lw Heat Value empeatue ie eue ie Rtatinal tque Cmbutin Mechanical linkage Cmbut Extenal Cmbut Intenal Cmbut Stiling Engine Steam Engine Galine Engine (Spak-ignitin) Dieel Engine (Cmpein-ignitin) Ga ubine Jet Engine Stiling Cycle Rankine Cycle Ott Cycle Dieel Cycle Baytn Cycle Jet-ppulin Cycle

7 Baic Cnideatin in the Analyi f we Cycle he analyi f many cmplex pcee can be educed t a manageable leel by utilizing me idealizatin he idealizatin and implificatin cmmnly emplyed in the analyi f pwe cycle can be ummaized a fllw:. he cycle de nt inle any fictin. heefe, the wking fluid de nt expeience any peue dp a it flw in pipe deice uch a heat exchange.. All expanin and cmpein pcee take place in a quai-equilibium manne. 3. he pipe cnnecting the aiu cmpnent f a ytem ae well inulated, and heat tanfe thugh them i negligible. 4. Neglecting the change in kinetic and ptential enegie f the wking fluid i anthe cmmnly utilized implificatin in the analyi f pwe cycle.

8 he Cant Cycle And It Value in Engineeing he Cant cycle i the mt efficient cycle that can be executed between a heat uce and a ink It i cmped f fu ttally eeible pcee: Ithemal heat additin, Ientpic expanin, Ithemal heat ejectin, and Ientpic cmpein It themal efficiency h th, Cant - L H Example 9-(hw that the themal efficiency f a Cant cycle peating between the tempeatue limit f H and L i lely a functin f thee tw tempeatue) he eal alue f the Cant cycle cme fm it being a tandad againt which the actual the ideal cycle can be cmpaed - and - diagam f a Cant cycle

9 Ai-Standad Aumptin he wking fluid i ai, which cntinuuly ciculate in a cled lp and alway behae a an ideal ga All the pcee that make up the cycle ae intenally eeible he cmbutin pce i eplaced by a heat-additin pce fm an extenal uce he exhaut pce i eplaced by a heatejectin pce that ete the wking fluid t it initial tate Ai ha cntant pecific heat whe alue ae detemined at m tempeatue (5 C) ß cld ai tandad aumptin

10 Entpy Change f Ideal Gae du d d + dh d - d d d c + R d d cp - R ( ) du dh he diffeential entpy change f an ideal ga - ò ò c c ( ) p d d + R ln - R ln R c c p d d he entpy change f a pce btained by integating

11 Cntant Specific Heat (Appximate Analyi) he entpy change elatin f ideal gae unde the cntant pecific heat aumptin - c, ag ln + R ln c - p,ag ln R ln (kj/kg K) Entpy change can al be expeed n a unit mle bai - c, ag ln + R ln u c - p,ag ln Ru ln (kj/kml K)

12 Ientpic cee f Ideal Gae (Appximate Analyi) - c, ag ln + R ln cp,ag ln - R ln æ ö æ ö ç ç è ø è ø cnt. ( k -) k (ideal ga) nd ientpic elatin R æ ln - ln Þ ln ln c ç è c p R c -, Þ R p c k k - c c æ ö æ ö ç ç è ø è ø cnt. k - (ideal ga) t ientpic elatin ö ø R c æ ö æ ö ç ç è ø è ø cnt. k (ideal ga) 3 d ientpic elatin Cmpact fm k - ( -k) k k cntant cntant (ideal ga) cntant

13 Vaiable Specific Heat (Exact Analyi) ò ò c p 0 ( ) d d c p ( ) - he entpy change elatin f ideal gae unde the aiable pecific heat aumptin R ln (kj/kg K) It i expeed n a unit-mle bai Ru ln (kj/kml K)

14 Ientpic cee f Ideal Gae (Exact Analyi I) 0 ln R ) exp( R ln R + ø ö ç è æ ø ö ç è æ - R R R exp exp exp Relatie peue cnt. ø ö ç ç è æ cnt ø ö ç ç è æ Relatie pecific lume / Stictly alid f ientpic pcee f ideal gae nly he alue f and ae lited f ai in able A-7

15 Ientpic cee f Ideal Gae (Exact Analyi II) he alue f and lited f ai in able A-7 ae ued f calculating the final tempeatue duing an ientpic pce