Ngā Huringa Enthalpy i roto i ngā Pūnaha Wera i roto i te Hangarau Mīhini
I te ao hangarau miihini, he hononga tata tonu ngā kōrero mō te pūngao ki ngā pūnaha wera pēnei i ngā kohua, ngā tāwhana mamaoa, ngā pūwero, ngā whakakōpeke, ngā whakawhiti wera, me ngā miihini mura ā-roto. Ko tētahi o ngā rahinga wera e whakamahia whānuitia ana hei tātari i te whakawhiti pūngao i roto i ēnei taputapu ko te enthalpy. He tino whai hua te enthalpy nā te mea he maha ngā tukanga i roto i ngā taputapu wera ka puta i roto i te rere wai (te rōrahi whakahaere), kaua i roto i te pūnaha kati (te papatipu whakahaere). Nō reira, ko te mārama ki ngā huringa enthalpy te mea nui ki te mārama ki te wāhi e haere ai te pūngao i roto i tētahi tukanga.
1. Te Mārama ki te Enthalpy me tōna Tikanga Ā-tinana
E ai ki te whakamāramatanga, ko te enthalpy (H) he rahinga thermodynamic i hangaia penei:
H = U + pV
me:
– U = pūngao ā-roto
– p = pēhanga
– V = rōrahi
Mō te tātari i ngā pūnaha rere, ka whakamahia te puka motuhake:
h = u + pv
ko h te enthalpy motuhake (kJ/kg). Ko te kupu pv tāpiri ka whakamāramahia pinepinetia ko te pūngao e pā ana ki te "mahi rere," arā, ko te mahi e hiahiatia ana hei neke i te wai ki roto, ki waho rānei i te rōrahi whakahaere. Koia te take he tino watea te enthalpy mō te tātari i ngā taputapu pēnei i ngā tāpine, ngā pūwero, ngā kaiwhakawhiti, ngā papu, me ngā pūwero.
2. Te Huringa Enthalpy (Δh) i roto i ngā Tukanga Wera
I roto i te mahi miihini, ehara i te mea ko te uara enthalpy anake te mea nui, engari ko te huringa o te enthalpy:
Δh = h₂ − h₁
E whakaahua ana tēnei panoni i te panoni o te nui o te pūngao o tētahi wai nā te whakamahana, te whakamatao, te whakawhanui, te pēhi, te panoni āhua rānei (hei tauira, te wai ki te mamaoa). I roto i te maha o ngā wāhanga wera, e pā tika ana te panoni enthalpy ki te wera me te mahi e pā ana.
Hei tauira:
– I roto i te pōro, ka piki te enthalpy nā te mea ka whiwhi te wai i te wera.
– I roto i ngā tāpoi, ka heke te enthalpy nā te mea ka hurihia te pūngao wai hei mahi poro.
– I roto i te pūwhakamātao, ka heke te enthalpy nā te mea ka tukuna te wera e te mamaoa ki te taiao, ki te reo whakamatao rānei.
3. Te Enthalpy i roto i te Whārite Pūngao Rere Tūmau
Ko te tātaritanga tino noa o ngā pūnaha wera miihini ko te rere-pūmau. Ko te whārite pūngao mō te rōrahi whakahaere rere-pūmau (Steady Flow Energy Equation/SFEE) ka tuhia penei:
q − w = (h₂ − h₁) + (V₂² − V₁²)/2 + g(z₂ − z₁)
me:
– q = te wera mō ia wae papatipu (kJ/kg)
– w = mahi mō ia wae papatipu (kJ/kg)
– V = te tere rere (m/s)
– z = teitei (m)
– g = te whakaterenga nā te kaha ā-papa (m/s²)
I roto i te maha o ngā tono hangarau mīhini, he iti noa iho ngā panonitanga o te pūngao nekeneke me te pūngao pūmanawa ki te whakataurite ki te panonitanga o te enthalpy, nō reira ka whakangawaritia kia penei:
q − w ≈ h₂ − h₁
He tino kaha tēnei whanaungatanga māmā: ki te mōhio tātou ki te āhua o te wera me te mahi, ka taea e tātou te whakatau tata i te huringa enthalpy; ki te mōhiotia rānei ngā raraunga enthalpy (hei tauira, mai i ngā ripanga mamaoa), ka taea e tātou te tatau i te mahi tāpine, i te mana rānei e hiahiatia ana e te kōpeketanga.
4. Ngā Huringa Enthalpy i roto i ngā Wāhanga Matua o tētahi Pūnaha Wera
a) Pūwero me te Whakamahana
I roto i te pōro, ka whakamahanatia te wai kia huri rā anō hei mamaoa. Tērā pea ka uru atu ki te tukanga:
1) te whakamahana i te wai wai (te whakamahana mohio),
2) te mimiti (te whakamahana huna),
3) te whakamahana nui (te whakamahana atu i te mamaoa).
Ka whakanuia rawatia te enthalpy e ēnei tokotoru. I roto i te ariā:
q_in ≈ h_out − h_in
Ka teitei ake te pēhanga me te pāmahana o te putanga o te pōro, ka nui ake te enthalpy o te mamaoa e puta ana, ā, ko te tikanga ka teitei ake te mahi pūmanawa ka taea te tango i roto i te tāpine.
b) Ngā Tāpine Kohu me ngā Tāpine Hau
I roto i te tāpine, ka mahi te wai i runga i ngā mata me te kakau. I raro i ngā āhuatanga adiabatic (kāore he whakawhiti wera):
w_out ≈ h_in − h_out
Ko te tikanga o tēnei, ko te whakahekenga enthalpy i roto i te tāpine he hononga tika ki te mahi i puta. Mō ngā tāpine mamaoa, ko ngā raraunga enthalpy ka riro mai i ngā ripanga, i ngā hoahoa Mollier (hs) rānei. Mō ngā tāpine hau, ka tatauhia te enthalpy mā te whakamahi i te kaha wera motuhake, mā te whakamahi i te huarahi hau pai.
c) Ngā Papu me ngā Pūwhakakorikori
Me whai mahi whakauru ngā papu (mō ngā wai) me ngā pūwero (mō ngā hau). Mō ngā papu, nā te mea he tata kore e taea te pēhi i ngā wai, he iti noa te huringa enthalpy, ā, he maha ngā wā ka whakatauhia mā te:
w_in ≈ v (p₂ − p₁)
I roto i ngā pūwero hau, ka nui te pikinga o te enthalpy, ā, e pā ana ki te pikinga o te pāmahana nā te pēhanga. I roto i te pūwero adiabatic:
w_in ≈ h_out − h_in
Ko te pikinga o te enthalpy e tohu ana i te pūngao e tāpirihia ana ki te wai mā te mahi o te pou.
d) Pūwhakamātao
Ka tangohia e te pūwhakamātao te wera mai i te mamaoa kia whakamātao rā anō hei wai. Ina kore he mahi o te pou:
q_puta ≈ h_in − h_puta
He nui te hekenga o te enthalpy i roto i te pūwhakamātao nā te mea kei roto ko te tukunga o te wera huna i te wā o te pūwhakamātao, he tino kaha tēnei ki te whakataurite ki te hekenga pāmahana noa.
e) Takirere Whakawhanui (Takirere Whakatere)
He mea noa te kitea o ngā takirere whakawhanui i roto i ngā pūnaha whakamatao me ētahi pūnaha mamaoa. He āhuatanga nui tō te tukanga whakawhāiti: te enthalpy pumau (isenthalpic) i raro i ngā āhuatanga hangarau maha.
h₁ ≈ h₂
Ahakoa kāore te enthalpy i rerekē, ka tino heke te pēhanga, ā, ka rerekē pea te āhua o ētahi o te wai (hei tauira, ka huri hei ranunga wai-kohu). He mea nui tēnei i roto i ngā huringa whakamatao nā te mea ka iti ake te pāmahana i muri i te whakawhanuitanga.
5. Te Enthalpy me ngā Huringa Āhua o ngā Wai Mahi
Ko ngā huringa enthalpy te mea tino kitea i roto i ngā tukanga e pā ana ki ngā huringa ā-wāhanga, pērā i:
– ka huri te wai kohua hei mamaoa,
– ka whakapūpū te mamaoa hei wai,
– ka mimiti te hau whakamatao i roto i te mīhini whakamomona.
Ka hua ake te pikinga o te enthalpy i te wera huna o te mimiti, te hauhautanga rānei, engari kāore he pikinga nui o te pāmahana i raro i te pēhanga pumau. Nō reira, he mea nui te tātari enthalpy i roto i te hoahoa i ngā kohua, i ngā whakapūmau, i ngā whakamomona, me ngā whakawhiti wera e rua-wāhanga.
6. Te Whakamahinga o ngā Raraunga Enthalpy i roto i te Mahi Hangarau Mīhini
I roto i te nuinga o ngā āhuatanga o te ao tūturu, kāore ngā kaihangarau e tatau i te enthalpy mai i te tātai taketake, engari ka whakamahia:
– ngā tēpu mamaoa,
– te hoahoa hs (Mollier),
– pūmanawa āhuatanga pāmahana (REFPROP, EES, CoolProp),
– ngā raraunga a te kaihanga.
Ka taea e ngā hapa iti i roto i ngā pānui enthalpy te hanga rerekētanga nui i roto i ngā whakatau tata o te mana o te tāpine, ngā whakaritenga wahie, te kaha whakamatao rānei. Nō reira, he mea nui te whiriwhiri i ngā āhuatanga whakahaere tika (pēhanga/pāmahana) me te mārama ki te kounga o te mamaoa.
7. Whakamutunga
Ko te huringa enthalpy he ariā matua i roto i te tātari pūnaha wera miihini, nā te mea e hono tika ana i ngā āhuatanga o te wera, te mahi, me ngā huringa āhua wai i roto i ngā taputapu rere. Mā te whakamahi i te whārite pūngao āhua pumau, ka taea te whakamahi i te huringa enthalpy hei tatau i te mahi tāpine, te mana kōpeke, te wera i tāpirihia ki te poiha, me te wera i panaia i roto i te condenser. Ko te enthalpy he "reo" mahi mā ngā miihini kia mārama ai ki te mahi me te whai huatanga o ngā huringa wera pēnei i a Rankine, Brayton, me ngā pūnaha pouaka whakamātao. Ko te matatau ki te huringa enthalpy ko te kaha ki te pānui me te hoahoa i ngā pūnaha wera kia tika ake, kia haumaru, kia whai hua ake hoki.
Ki te hiahia koe, ka taea e au te tāpiri i ngā tauira tatau māmā (hei tauira, ngā tāhūhū mamaoa, ngā pūwero rānei) kia pai ake ai te whakamahi i te tuhinga, kia tata ake ai hoki ki ngā hiahia o ngā kauhau/mahi ā-ringa.
