Liphetoho tsa Enthalpy Litsamaisong tsa Thermal ho Boenjiniere ba Mechanical
Lefatšeng la boenjiniere ba mechini, lipuisano tsa matla li hokahane ka mokhoa o ke keng oa aroloa le litsamaiso tsa mocheso tse kang liboiler, li-turbine tsa mouoane, li-compressor, li-condenser, li-heat exchanger, le lienjine tsa ho chesa ka hare. E 'ngoe ea bongata ba thermodynamic bo sebelisoang khafetsa ho sekaseka phetiso ea matla lisebelisoa tsena ke enthalpy. Enthalpy e na le thuso haholo hobane lits'ebetso lisebelisoa tsa mocheso hangata li etsahala ka har'a phallo ea mokelikeli (bophahamo ba taolo), ho fapana le ka har'a sistimi e koetsoeng (boima ba taolo). Ka hona, ho utloisisa liphetoho tsa enthalpy ke senotlolo sa ho utloisisa hore na matla a ea kae ts'ebetsong.
1. Ho Utloisisa Enthalpy le Moelelo oa Eona oa 'Mele
Ka tlhaloso, enthalpy (H) ke bongata ba thermodynamic bo entsoeng ka tsela ena:
H = U + pV
ka:
– U = matla a ka hare
– p = khatello
– V = bophahamo ba modumo
Bakeng sa tlhahlobo ea litsamaiso tsa phallo, foromo e itseng hangata e sebelisoa:
h = u + pv
moo h e leng enthalpy e itseng (kJ/kg). Lentswe le eketsehileng la pv hangata le hlaloswa e le matla a amanang le "mosebetsi wa phallo," ke hore, mosebetsi o hlokahalang ho tsamaisa mokelikeli ho kena kapa ho tswa ho bophahamo ba taolo. Ke ka lebaka leo enthalpy e leng bonolo haholo bakeng sa ho sekaseka disebediswa tse kang diturbine, di-nozzle, di-diffuser, dipompo le di-compressor.
2. Phetoho ea Enthalpy (Δh) Mekhoeng ea Thermal
Mokhoa oa boenjiniere ba mechini, ntho ea bohlokoa ka ho fetisisa ha se feela boleng ba enthalpy, empa le phetoho ea enthalpy:
Δh = h₂ − h₁
Phetoho ena e hlalosa phetoho ea matla a mokelikeli ka lebaka la ho futhumatsa, ho pholisa, ho atoloha, ho hatelloa, kapa phetoho ea mohato (mohlala, metsi ho ea mouoane). Likarolong tse ngata tsa mocheso, phetoho ea enthalpy e amana ka ho toba le mocheso le mosebetsi o amehang.
Mohlala:
– Ka har'a boiler, enthalpy ea eketseha hobane mokelikeli o fumana mocheso.
– Ka har'a liturbine, enthalpy ea fokotseha hobane matla a mokelikeli a fetoloa mosebetsi oa shaft.
– Ka har'a condenser, enthalpy ea fokotseha hobane mouoane o ntša mocheso tikolohong kapa sebakeng se pholisang.
3. Enthalpy ho Tekanyo ea Matla a Phallo e Tsitsitseng
Tlhahlobo e tloaelehileng haholo ea litsamaiso tsa mocheso tsa boenjiniere ba mechini ke phallo e tsitsitseng. Tekanyo ea matla bakeng sa bophahamo ba taolo ea phallo e tsitsitseng (Steady Flow Energy Equation/SFEE) hangata e ngoloa tjena:
q − w = (h₂ − h₁) + (V₂² − V₁²)/2 + g(z₂ − z₁)
ka:
– q = mocheso ka boima ba yuniti (kJ/kg)
– w = mosebetsi ka yuniti e le nngwe (kJ/kg)
– V = lebelo la phallo (m/s)
– z = bophahamo (m)
– g = ho potlaka ka lebaka la matla a khoheli (m/s²)
Lits'ebetsong tse ngata tsa boenjiniere ba mechini, liphetoho tsa kinetic le matla a ka bang teng li nyane haholo ha li bapisoa le phetoho ea enthalpy, kahoo hangata li nolofalloa ho:
q − w ≈ h₂ − h₁
Kamano ena e bonolo e matla haholo: haeba re tseba hore na mocheso le mosebetsi li etsahala joang, re ka hakanya phetoho ea enthalpy; kapa ka lehlakoreng le leng, haeba lintlha tsa enthalpy li tsejoa (mohlala, ho tsoa litafoleng tsa mouoane), re ka bala mosebetsi oa turbine kapa litlhoko tsa matla a compressor.
4. Liphetoho tsa Enthalpy Likarolong tse ka Sehloohong tsa Sistimi ea Thermal
a) Boiler le Heater
Ka boiler, metsi a futhumatsoa ho fihlela a fetoha mouoane. Ts'ebetso e ka kenyelletsa:
1) ho futhumatsa metsi a metsi (ho futhumatsa ka mokhoa o utloahalang),
2) mouoane (ho futhumatsa ho patehileng),
3) ho futhumatsa haholo (ho futhumatsa ka mouoane o mong hape).
Ka boraro ba tsona di eketsa enthalpy haholo.
q_in ≈ h_out − h_in
Ha kgatello le mocheso wa sehokelo sa boiler di le hodimo, enthalpy ya mouoane e hlahiswang e ba kgolo, mme ka kakaretso mosebetsi o ka ntshwang ka hara turbine o ba moholo.
b) Liturbine tsa mouoane le liturbine tsa khase
Ka har'a turbine, mokelikeli o sebetsa holim'a makhasi le shaft. Tlas'a maemo a adiabatic (hoo e ka bang ha ho na phetisetso ea mocheso):
w_out ≈ h_in − h_out
Sena se bolela hore phokotso ea enthalpy ka har'a turbine e amana ka ho toba le mosebetsi o hlahisoang. Bakeng sa liturbine tsa mouoane, data ea enthalpy hangata e fumanoa litafoleng kapa litšoantšong tsa Mollier (hs). Bakeng sa liturbine tsa khase, enthalpy hangata e baloa ho sebelisoa bokhoni bo itseng ba mocheso, ho sebelisoa mokhoa o loketseng oa khase.
c) Lipompo le Li-compressor
Lipompo (bakeng sa lino tse metsi) le li-compressor (bakeng sa likhase) li hloka mosebetsi oa ho kenya. Bakeng sa lipompo, kaha lino tse metsi li batla li sa hatelloe, phetoho ea enthalpy e nyane haholo 'me hangata e hakanyetsoa ka:
w_in ≈ v (p₂ − p₁)
Ho di-compressor tsa khase, keketseho ya enthalpy e ka ba kgolo mme e amana le keketseho ya mocheso ka lebaka la kgatello. Ho compressor ya adiabatic:
w_ka hare ≈ h_out − h_ka hare
Keketseho ea enthalpy e bontša matla a eketsoang mokelikeling ka mosebetsi oa shaft.
d) Sekontiri
Sekontiri se tlosa mocheso mouoaneng ho fihlela o fetoha mokelikeli. Ha ho se na ts'ebetso ea shaft:
q_out ≈ h_in − h_out
Ho fokotseha ha enthalpy ho condenser ka kakaretso ho hoholo hobane ho kenyelletsa ho lokolloa ha mocheso o patehileng nakong ea ho kolobisoa, e leng ntho e matla haholo ha e bapisoa le ho fokotseha ho tloaelehileng ha mocheso.
e) Valve ea Katoloso (Valve ea Throttling)
Li-valve tsa katoloso li atisa ho fumanoa lits'ebetsong tsa sehatsetsing le lits'ebetsong tse ling tsa mouoane. Ts'ebetso ea ho phunya e na le tšobotsi ea bohlokoa: enthalpy e sa fetoheng (isenthalpic) tlas'a maemo a mangata a boenjiniere.
h₁ ≈ h₂
Leha enthalpy e sa fetohe, kgatello e theoha haholo, mme karolo e nngwe ya mokelikeli e ka fetoha mohato (mohlala, ya fetoha motswako wa mokelikeli le mouwane). Sena se bohlokwa dipotolohong tsa sehatsetsing hobane se fella ka mocheso o tlase kamora katoloso.
5. Liphetoho tsa Enthalpy le tsa Mokhahlelo oa Metsi a Sebetsang
Liphetoho tsa enthalpy li hlahella haholo lits'ebetsong tse amanang le liphetoho tsa mekhahlelo, joalo ka:
– metsi a belang a fetoha mouoane,
– mouoane o fetoha metsi,
– sehatsetsi se fetoha mouoane ka har'a evaporator.
Mocheso o patehileng oa mouoane kapa ho kolobisoa ha moea o hlahisa keketseho ea enthalpy ntle le keketseho e kholo ea mocheso tlas'a khatello e sa khaotseng. Ka hona, tlhahlobo ea enthalpy e bohlokoa haholo ho raleng liboiler, li-condenser, li-evaporator le li-heat exchange tse peli.
6. Tšebeliso ea Lintlha tsa Enthalpy ho Mekhoa ea Boenjiniere ba Mekaniki
Maemong a mangata a sebele, baenjiniere ha ba bale enthalpy ho tsoa foromong ea motheo, empa ho e-na le hoo ba sebelisa:
– litafole tsa mouoane,
– setshwantsho sa hs (Mollier),
– software ea thepa ea thermodynamic (REFPROP, EES, CoolProp),
– tlhahisoleseding ea moetsi.
Liphoso tse nyane lipalo tsa enthalpy li ka etsa phapang e kholo likhakanyong tsa matla a turbine, litlhoko tsa mafura, kapa bokhoni ba ho pholisa. Ka hona, ho khetha maemo a nepahetseng a ts'ebetso (khatello/mocheso) le ho utloisisa boleng ba mouoane ke tsa bohlokoa.
7. Kesimpulan
Phetoho ea enthalpy ke mohopolo oa mantlha tlhahlobong ea litsamaiso tsa mocheso tsa boenjiniere ba mechini hobane e hokahanya ka kotloloho liketsahalo tsa liphetoho tsa boemo ba mocheso, mosebetsi le mokelikeli lisebelisoa tsa phallo. Ka ho sebelisa equation ea matla a tsitsitseng, phetoho ea enthalpy e ka sebelisoa ho bala mosebetsi oa turbine, matla a compressor, mocheso o ekelitsoeng ho boiler, le mocheso o haneloang ka har'a condenser. Enthalpy e sebetsa e le "puo" e sebetsang bakeng sa baenjiniere ho utloisisa ts'ebetso le katleho ea lipotoloho tsa mocheso tse kang Rankine, Brayton, le litsamaiso tsa sehatsetsing. Ho tseba phetoho ea enthalpy ho bolela ho khona ho bala le ho rala litsamaiso tsa mocheso ka nepo, ka mokhoa o sireletsehileng le ka katleho.
Haeba o batla, nka eketsa mehlala e bonolo ea lipalo (mohlala, li-turbine tsa mouoane kapa li-compressor) ho etsa hore sengoloa se sebetse haholoanyane le haufi le litlhoko tsa lipuo/mosebetsi o sebetsang.
