Ukuze athole ukuthi angakhuphula kanjani ukusebenza kahle kwenjini yokushisa , usosayensi waseFrance ogama lakhe linguSadi Carnot (1796-1832) wahlola umshini wekhalori ofanele ngo-1824. Ngaleso sikhathi, umthetho wokuqala we-thermodynamics wawungakakhiwa, noma umthetho wesibili we-thermodynamics. Umthetho wokuqala awukakhiwa ngoba ososayensi abakakazi ukuthi ukushisa kungamandla. Ngemva kokuba uJoule nozakwabo bevivinye ngawo-1830, ososayensi bathola ukuthi ukushisa kungamandla ahamba ngenxa yokwehluka kwezinga lokushisa. Ngakho-ke, umthetho wokuqala we-thermodynamics wakhiwa ngemva kuka-1830. USadi Carnot wayecwaninga ngenjini yekhalori efanelekile ngo-1824. Ucwaningo lwakhe empeleni lwaluwukwandisa ukusebenza kahle kwenjini yomusi. Izinjini eziningi zomusi zangaleso sikhathi zazingasebenzi kahle.
Umjikelezo enjinini yokushisa efanele yomcabango kaSadi Carnot ubizwa ngokuthi umjikelezo weCarnot. Ngaphambi kokufunda umjikelezo weCarnot, saqonda inqubo engenakuguqulwa futhi. Yonke inqubo yokushintsha kwamandla kanye nokudluliselwa kwamandla kwenzeka ngokungenakushintshwa. Isibonelo, sihlikihla izandla ukuze izandla zifudumale. Ukushisa kukhiqizwa ngomsebenzi esiwenzayo. Inqubo ayinakuguqulwa. Ukushisa akukwazi ukuhlikihla izandla.
Inhloso yenjini yokushisa ukuguqula enye yale nqubo, lapho ukushisa kungasetshenziswa khona ukwenza umsebenzi ngokusebenza kahle kakhulu. Ukuze injini yokushisa ibe nokusebenza kahle kakhulu, khona-ke kumelwe sigweme zonke izinqubo ezingaguquki. Ukudluliselwa kokushisa ngokwemvelo akunakuguquki ukuze ukunyakaza kokushisa kungenzeki.
Uma injini ithatha ukushisa (Q H ) ekushiseni okuphezulu (T H ), uketshezi olusebenzayo emshinini kumele lube ekushiseni kwe-T H. Ngokufanayo, uma injini ikhipha ukushisa kwe-Q L ekushiseni okuphansi (T L ), uketshezi olusebenzayo emshinini kumele lube ekushiseni kwe-T L. Ngakho-ke, noma iyiphi inqubo ehilela ukudluliselwa kokushisa kumele ibe yi-isothermal (izinga lokushisa elifanayo). Ngokuphambene nalokho, uma izinga lokushisa lomsebenzi emshinini liphakathi kwe-T H ne-T L , akukho ukudluliselwa kokushisa okwenzekayo phakathi komshini lapho indawo inokushisa kwe-T H (umhlinzeki wokushisa) nendawo enokushisa kwe-T L (ukukhishwa). Ngoba ukushisa akuhambi, khona-ke inqubo kumele yenziwe ngokushesha.
Umjikelezo weCarnot uqukethe izinqubo ezimbili eziguquguqukayo ze-isothermal kanye nezinqubo ezimbili eziguquguqukayo ze-adiabatic.
Isithombe ohlangothini yi-The piston Carnot cycle for a perfect gas. Okokuqala, ukushisa kuyamuncwa ngesikhathi sokwanda kwe-isothermal (ab). Ngesikhathi sokwanda kwe-isothermal, izinga lokushisa legesi ku-cylinder lihlala linjalo.
Okulandelayo, igesi iyanda ngokwe-adiabatic ukuze izinga lokushisa lehle kusuka ku-T H liye ku-T L (bc). I-T H = izinga lokushisa eliphezulu, i-T L = izinga lokushisa eliphansi. Ngesikhathi sokwandiswa kwe-adiabatic, akukho ukushisa okungena noma okuphumayo kwisilinda. Ngemva kwalokho, igesi icindezelwa ngokwe-isothermal (cd). Ngesikhathi sokucindezela kwe-isothermal, izinga lokushisa legesi ligcinwa lingaguquki. Igesi bese icindezelwa ngokwe-adiabatic (da). Ngenxa yokuthi icindezelwa ngokwe-adiabatic, izinga lokushisa legesi liyakhuphuka. Izinga lokushisa legesi liyakhuphuka ukuze ingcindezi yegesi nayo ikhuphuke. Yonke inqubo emjikelezweni we-Carnot iyaguqulwa.
Ngesikhathi sokwanda kwe-isothermal kanye nokucindezela kwe-isothermal, izinga lokushisa legesi lihlala linjalo. Umgomo ukugwema noma yikuphi ukwehluka kwezinga lokushisa. Ukuba khona kokwehluka kwezinga lokushisa kungabangela ukudluliselwa kokushisa (inqubo engaguquki). Ukuze inqubo ye-isothermal yenzeke (izinga lokushisa legesi lihlala linjalo) igesi kumele ikhuliswe kancane kancane noma icindezelwe. Eqinisweni, ukwanda, noma ukucindezelwa kwegesi, kwenzeka ngokushesha okukhulu. Lokhu kungenxa yokuxokozela (khumbula izinto ezishintshashintshayo zoketshezi), ukungqubuzana, i-viscosity, njll. Ngenxa yalokho, inqubo ephelele ye-isothermal ngeke ibe khona. Ngokuphambene nalokho, ukwanda nokucindezelwa kwe-adiabatic kuyashesha.
Umgomo uwukugcina ukushisa kungangeni kusilinda noma kuphume kusilinda. Ukuba khona kokungqubuzana, ukujiya, njll. akubangeli ukwanda okuphelele kwe-adiabatic kanye nokugcizelela. Khumbula ukuthi injini yeCarnot imane nje iyinkolelo-mbono. Umshini weCarnot awukho empilweni yethu. Nakuba kuyinkolelo-mbono kuphela, ukuba khona kwenjini yeCarnot kuyintuthuko enenzuzo ye-thermodynamics. Okungenani kungaziwa nganoma yiziphi izinqubo ezingalungiseki ezingase zenzeke ngesikhathi senqubo futhi kuzanywe ukuzinciphisa ukuze ukusebenza kahle kwenjini kube phezulu.
Umphumela obalulekile wenjini yeCarnot uwukushisa kwenjini okuphelele, ukushisa okutholakele (Q H ) kuhambelana nokushisa okuphezulu (T H ), kanti i-exhaust encibilikisiwe (Q L ) ihambelana nokushisa okuphansi (T L ). Ngakho-ke, ukusebenza kahle kwenjini yokushisa ephelele yilokhu:
Lesi yisibalo sokusebenza kahle kwenjini yokushisa ephelele.
Umbuzo 1:
Injini yomusi isebenza phakathi kuka-500 o C no-300 o C. Nquma ukusebenza kahle okufanele (ukusebenza kahle kweCarnot) kwenjini yomusi.
Isixazululo
Izinga lokushisa kufanele liguqulwe libe yisilinganiso sikaKelvin.
I-T H (izinga lokushisa eliphezulu) = 500 o C = 500 + 273 = 773 K
TL (izinga lokushisa eliphansi) = 300 o C = 300 + 273 = 573 K
Ukusebenza kahle kwenjini yokushisa ephelele esebenza phakathi kuka-500 °C no-300 °C kungu-26%. Uma imishini esiyisebenzisayo empilweni yethu yansuku zonke isebenza phakathi kuka-500 °C no-300 °C, ukusebenza kahle okukhulu imishini engakufeza kucishe kube ngokusebenza kahle okulungile okuphindwe ka-0.7 (18.2%).
Umbuzo 2:
Injini yokushisa ithola ama-J angu-600 ekushiseni okungu-300 °C, yenza umsebenzi (W) ama-Joules angu-100 bese ikhipha ama-J angu-500 ku-100 °C. Nquma ukusebenza kahle kwangempela kanye nokusebenza kahle okufanelekile (ukusebenza kahle kwe-Carnot) kwalo mshini.
Izinga lokushisa kufanele liguqulwe libe isikali sikaKelvin
I-T H (izinga lokushisa eliphezulu) = 300 o C — 300 + 273 = 573 K
TL (izinga lokushisa eliphansi) = 100 o C — 100 + 273 = 373 K
Q H = 600 J
Q L = 500 J
Ukusebenza kahle kwenjini:
Ukusebenza kahle kwale mishini:
Ukusebenza kahle kwenjini yokushisa ephelele esebenza phakathi kuka-300 °C no-100 °C kungu-35%. Ukusebenza kahle okuphezulu umshini ongakufeza ngokuvamile kuphindwe izikhathi ezingu-0.7 kunokusebenza kahle okufanele = 0.7 x 35% = 24.5% (24.5% x 600 J = 147 J ukushisa okusetshenziselwa ukwenza umsebenzi).
Ukusebenza kahle kwangempela kwalomshini kungu-17% (ukushisa okungu-100 J kuphela okusetshenziselwa ukwenza umsebenzi). Kusekhona ukushisa okungu-147 J – 100 J = 47 J okungasetshenziswa ukwenza umsebenzi.
Umbuzo 3:
Umshini uthola ama-calories angu-1000 e-Joule futhi ukhiqiza ama-Joule angu-400 omsebenzi emjikelezweni ngamunye. Lo mshini usebenza phakathi kuka-500 o C no-200 o C. Bala ukusebenza kahle kwangempela kanye nokusebenza kahle kwalo mshini.
Isixazululo
I-T H (izinga lokushisa eliphezulu) = 500 o C — 500 + 273 = 773 K
TL (izinga lokushisa eliphansi) = 200 o C — 200 + 273 = 473 K
Q H = 1000 J
Q L = 400 J
Ukusebenza kahle kwenjini:
Ukusebenza kahle kwale mishini:
Ukusebenza Kahle Kwe-Carnot = 40%. Ukusebenza kahle kwenjini yangempela = 60%. Lo mshini awukho. Ukusebenza kahle komshini bekungeke kube ngaphezu kokusebenza kahle kwe-Carnot.
Umbuzo 4:
Ukuze ukusebenza kahle kwenjini yeCarnot kufinyelele ku-100% (1), lingakanani izinga lokushisa lokukhipha elidingekayo (T L )?
Isixazululo
Ukuze injini isebenze kahle kahle ifinyelele ku-100% (konke ukushisa kungasetshenziswa ukwenza umsebenzi), khona-ke izinga lokushisa eliphansi (T L ) kufanele libe ngu-0 Kelvin.
Akunakwenzeka ukufinyelela izinga lokushisa likaKelvin elingu-0. Lesi sitatimende siwumthetho wesithathu we-thermodynamics.
Njengoba i- 0 Kelvin ngayinye ingenakwenzeka, injini yokushisa ephelele ingase ingabi nokusebenza kahle okungu-100%. Njengoba injini yokushisa ingenakukwazi ukufezwa ukusebenza kahle okungu-100%, kungaphethwa ngokuthi akunakwenzeka ukusebenzisa konke ukushisa (Q H ) ukwenza umsebenzi. Kumele kube nokushisa okulahlekile (Q L ).
Akunakuba khona injini yokushisa (esebenza ngomjikelezo) engaguqula konke ukushisa kube ukusebenza (Umthetho wesibili we-thermodynamics, isitatimende sikaKelvin-Planck).
Le grafu ikhombisa inqubo ye-isothermal (ukwanda kwe-isothermal) eyenzeka esigabeni esisodwa kuphela. Kule nqubo, konke ukushisa (Q) kungaguqulwa kube umsebenzi (W). Inani lomsebenzi owenziwe = indawo enomthunzi.
Injini yokushisa kumele isebenze njalo (inqubo kumele yenzeke ngokuphindaphindiwe, ayikwazi ukwenzeka ngesinyathelo esisodwa nje). Isibonelo, injini yomusi yohlobo olushintshanayo. I-piston enjinini yomusi eshintshanayo kumele ihambe iye kwesokudla nakwesobunxele njalo, ukuze amasondo akwazi ukuzungeza (angasetshenziswa ukuhambisa okuthile). Amasondo awakwazi ukuzungeza lapho i-piston inyakaza iyema ngakwesokudla ngaleso sikhathi (inqubo yenzeka esigabeni esisodwa kuphela). Uma inqubo yenzeka ngokuphindaphindiwe, akunakwenzeka ukuthi konke ukushisa kungaguqulwa kube umsebenzi (isitatimende sikaKelvin-Planck).
Igrafu engakwesobunxele ibonisa ukwanda kwe-isothermal (umcibisholo ophansi) kanye nokucindezelwa kwe-isothermal (umcibisholo ophakeme). Inqubo yenzeka ngokuqhubekayo i-isothermal (Akukho msebenzi okhiqizwayo). Igrafu engakwesokunene inqubo yokwandiswa kwe-isothermal (umcibisholo ophansi), inqubo yokucindezela i-isobaric (umcibisholo ongakwesokunxele) kanye nenqubo ye- isohroric (umcibisholo ophakeme). Kula magrafu amabili, kubonakala sengathi ngenqubo eqhubekayo, kuhlala kukhona ukushisa okuchithekayo.
