Kuchinja kweEnthalpy muThermal Systems muMechanical Engineering
Munyika yeinjiniya yemakanika, hurukuro dzesimba dzakabatana zvisingaparadzaniswe nehurongwa hwekupisa hwakadai semaboiler, maturbine esteam, macompressor, macondenser, maheat exchangers, uye mainjini ekupisa mukati. Imwe yehuwandu hwethermodynamic hunoshandiswa zvakanyanya kuongorora kutamiswa kwesimba mumidziyo iyi i enthalpy. Enthalpy inonyanya kubatsira nekuti maitiro ari mumidziyo yekupisa anowanzoitika mukati mekuyerera kwemvura (control volume), kwete mukati mesystem yakavharwa (control mass). Saka, kunzwisisa shanduko dze enthalpy kwakakosha kuti unzwisise kuti simba rinoenda kupi mukuita.
1. Kunzwisisa Enthalpy uye Zvainoreva Panyama
Netsanangudzo, enthalpy (H) ihuwandu hwe thermodynamic hwakagadzirwa se:
H = U + pV
ne:
– U = simba remukati
– p = kumanikidzwa
– V = vhoriyamu
Pakuongorora masisitimu ekuyerera kwemvura, fomu chaiyo inowanzo shandiswa:
h = u + pv
apo h ndiyo enthalpy chaiyo (kJ/kg). Izwi rekuwedzera repv rinowanzo tsanangurwa sesimba rinobatanidzwa ne "basa rekuyerera," kureva, basa rinodiwa kufambisa mvura ichipinda kana kubuda muhuwandu hwekudzora. Ndosaka enthalpy iri nyore kwazvo pakuongorora zvishandiso zvakaita sematurbine, ma nozzles, ma diffuser, mapombi, uye ma compressor.
2. Kuchinja kweEnthalpy (Δh) muThermal Process
Mukudzidzira kweinjiniya yemakanika, chinhu chakakosha hachisi kukosha kwe enthalpy chete, asi shanduko mu enthalpy:
Δh = h₂ − h₁
Kuchinja uku kunotsanangura kuchinja kwehuwandu hwesimba mumvura nekuda kwekupisa, kutonhora, kuwedzera, kudzvanywa, kana kuchinja kwechikamu (semuenzaniso, mvura kuita utsi). Muzvinhu zvakawanda zvekupisa, kuchinja kwe enthalpy kwakabatana zvakananga nekupisa nebasa rinosanganisirwa.
Sebokai muenzaniso:
– Muboiler, enthalpy inowedzera nekuti mvura yacho inogamuchira kupisa.
– Mumaturbine, enthalpy inoderera nekuti simba remvura rinoshandurwa kuita basa remugodhi.
– Mukondensa, enthalpy inoderera nekuti utsi hunoburitsa kupisa kunzvimbo inotonhorera kana kuti panzvimbo inotonhorera.
3. Enthalpy muSteady Flow Energy Equation
Ongororo inonyanya kutaurwa yezvemainjiniya ekugadzira magetsi emagetsi ndeyekufamba-famba kwakasimba. Equation yesimba yehuwandu hwekudzora kufamba-famba kwakasimba (Steady Flow Energy Equation/SFEE) inowanzo nyorwa seizvi:
q − w = (h₂ − h₁) + (V₂² − V₁²)/2 + g(z₂ − z₁)
ne:
– q = kupisa pahuremu hweyuniti (kJ/kg)
– w = basa pahuremu hweyuniti (kJ/kg)
– V = kumhanya kwekuyerera (m/s)
– z = kukwirira (m)
– g = kukurumidza nekuda kwegiravhiti (m/s²)
Mumashandisirwo mazhinji einjiniya yemakanika, shanduko musimba rekinetic nerinogona kushandiswa idiki zvichienzaniswa neshanduko mu enthalpy, saka dzinowanzo nyorerwa kuita:
q − w ≈ h₂ − h₁
Hukama uhwu huri nyore hune simba guru: kana tikaziva kuti kupisa nebasa zvinoitika sei, tinogona kufungidzira shanduko ye enthalpy; kana zvakasiyana, kana data re enthalpy richizivikanwa (semuenzaniso kubva pamatafura emhepo), tinogona kuverenga mashandiro e turbine kana zvinodiwa nesimba re compressor.
4. Kuchinja kweEnthalpy muZvikamu Zvikuru zveSystem yeThermal
a) Boiler neHeater
Muchibhoyira, mvura inodziiswa kusvika yashanduka kuita utsi. Maitiro acho anogona kusanganisira:
1) kupisa mvura yemvura (kupisa zvine musoro),
2) kupwa kwemvura (kupisa kwakavanzika),
3) kupisa zvakanyanya (kuwedzera kupisa kwemhepo ine mhute).
Zvese zvitatu zvinowedzera enthalpy zvakanyanya.
q_in ≈ h_out − h_in
Kana kumanikidzwa uye tembiricha yemuchina wekubuditsa bhaira yakakwira, enthalpy yemhepo inogadzirwa inowedzera, uye kazhinji kacho basa rinogona kuburitswa muturbine rakawedzera.
b) Maturbine emhepo neMaturbine egasi
Mu turbine, mvura inoshanda pamashizha nemugodhi. Kana mamiriro ekunze asina kupisa (hapana kutamiswa kwekupisa):
w_out ≈ h_in − h_out
Izvi zvinoreva kuti kuderedzwa kwe enthalpy mu turbine kwakabatana zvakananga nebasa rinogadzirwa. Kune ma turbine emhepo, data re enthalpy rinowanzo kuwanikwa kubva pamatafura kana madhayagiramu eMollier (hs). Kune ma turbine egasi, enthalpy inowanzo verengerwa uchishandisa mukana chaiwo wekupisa, uchishandisa nzira yakanaka yegesi.
c) Mapombi nemaCompressor
Mapombi (ezvinwiwa) uye macompressor (emagasi) anoda basa rekuisa. Kune mapombi, sezvo zvinwiwa zvisinganyanyi kumanikidzwa, shanduko ye enthalpy idiki uye inowanzofungidzirwa ne:
w_in ≈ v (p₂ − p₁)
Muma compressor egasi, kuwedzera kwe enthalpy kunogona kuva kukuru uye kune chekuita nekuwedzera kwekushisa kunokonzerwa nekumanikidzwa. Mu compressor ye adiabatic:
w_mukati ≈ h_kunze − h_mukati
Kuwedzera kwe enthalpy kunoratidza simba rinowedzerwa mumvura kuburikidza nekushanda kwemugodhi.
d) Chinotonhodza
Kondensa inobvisa kupisa kubva muutsi kusvika yaita mvura. Kana pasina kushanda kwemubato:
q_out ≈ h_in − h_out
Kudzikira kwe enthalpy mu condenser kunowanzo kuve kukuru nekuti kunosanganisira kuburitswa kwekupisa kwakavanzika panguva yekudziya, uko kunonyanya kukosha kana tichienzanisa nekudzikira kwekupisa kwakajairika.
e) Vharuvhu Yokuwedzera (Vharuvhu Yokupotsera)
Mavharuvhu ekuwedzera anowanzo kuwanikwa mumasisitimu ekutonhodza uye mune mamwe masisitimu eutsi. Maitiro ekudhonza ane hunhu hwakakosha: enthalpy inogara iripo (isenthalpic) pasi pemamiriro akasiyana-siyana einjiniya.
h₁ ≈ h₂
Kunyangwe enthalpy ichiramba isina kuchinja, kumanikidzwa kwayo kunoderera zvakanyanya, uye imwe yemvura inogona kuchinja chimiro (semuenzaniso, kuva musanganiswa wemvura-utsi). Izvi zvakakosha mukutenderera kwefiriji nekuti zvinoguma nekupisa kwakaderera mushure mekuwedzerwa.
5. Kuchinja kweEnthalpy uye Chikamu cheMafuta Anoshanda
Kuchinja kwe enthalpy kunonyanya kuonekwa mumabasa anosanganisira kuchinja kwechikamu, akadai se:
- mvura iri kufashaira inoshanduka kuita utsi,
– mhute inoungana mumvura,
- mufiriji unopwa mu evaporator.
Kupisa kwakavanzika kwekupfuta kana kudziya kunoita kuti enthalpy iwedzere pasina kuwedzera kwakanyanya kwekushisa pasi pekumanikidzwa kwakasimba. Saka, kuongorora enthalpy kwakakosha pakugadzira maboiler, macondenser, ma evaporator, uye ma heat exchangers maviri.
6. Kushandiswa kweEnthalpy Data muMechanical Engineering Practice
Muzviitiko zvakawanda zvepasirese, mainjiniya haaverenge enthalpy kubva mufomura yekutanga, asi vanoshandisa:
- matafura emhepo,
– dhayagiramu yehs (Mollier),
- software ye thermodynamic property (REFPROP, EES, CoolProp),
- ruzivo rwemugadziri.
Zvikanganiso zvidiki mukuverenga kwe enthalpy zvinogona kuita mutsauko mukuru mukufungidzira kwesimba re turbine, zvinodiwa nemafuta, kana kugona kutonhodza. Saka, kusarudza mamiriro akakodzera ekushanda (pressure/tembiricha) uye kunzwisisa mhando yemhepo inopisa kwakakosha.
7. Kesimpulan
Kuchinja kwe enthalpy ipfungwa huru mukuongorora masisitimu ekupisa einjiniya yemakanika nekuti inobatanidza zvakananga zviitiko zvekuchinja kwekupisa, basa, uye mamiriro emvura mumidziyo inoyerera. Nekushandisa equation yesimba re steady-state, kuchinja kwe enthalpy kunogona kushandiswa kuverenga basa re turbine, simba re compressor, kupisa kunowedzerwa ku boiler, uye kupisa kunorambwa mu condenser. Enthalpy inoshanda se "mutauro" unoshanda kumainjiniya kuti vanzwisise mashandiro uye kushanda zvakanaka kwema thermal cycles akadai seRankine, Brayton, uye ma refrigeration systems. Kugona kuchinja kwe enthalpy zvinoreva kukwanisa kuverenga nekugadzira masisitimu ekupisa zvakanyatsonaka, zvakachengeteka, uye zvinobudirira.
Kana muchida, ndinogona kuwedzera mienzaniso iri nyore yekuverenga (semuenzaniso maturbine emhepo kana macompressor) kuti chinyorwa chive chinoshanda zviri nani uye chiri pedyo nezvinodiwa nehurukuro/basa rekushanda.
