Te Whakamahinga o te Ture Tuarua o te Thermodynamics ki ngā Mīhini Wera
Ko te mīhini wera tētahi o ngā mea tino nui i hangaia i roto i te hītori o te hangarau nā te mea i taea ai e te tangata te huri i te pūngao wera hei mahi miihini whai hua. Mai i ngā mīhini mamaoa o te Huringa Ahumahi ki ngā tāpine hau me ngā mīhini mura ā-roto i roto i ngā waka hou, kei te mau tonu te ariā taketake o te mīhini wera: he pūtake wera, he totohu wera, me te mahi i puta. Engari ka taea te huri i te wera katoa hei mahi 100% o te wā? He aha i noho tonu ai ngā "ngaronga" kāore e taea te karo? Kei roto i te Ture Tuarua o te Thermodynamics te whakautu. Ehara tēnei ture i te ture ariā noa iho, engari he rohe taketake e whakatau ana i te pai o te mahi a te mīhini wera me te āhua o te hoahoa.
He Tirohanga Whānui mō ngā Mīhini Wera
I te whakarapopototanga, he pūnaha te miihini wera e mahi ana i runga i te huringa hei huri i ētahi o te pūngao wera e haere mai ana hei mahi. I roto i te huringa kotahi, ka mimiti te miihini i te wera mai i tētahi puna wera (hei tauira, te tahu wahie, te tauhohenga karihi rānei), ka whakaputa mahi (hei tauira, te huri i te rakau), kātahi ka panaia te wera e toe ana ki tētahi puna matao (hei tauira, te hau o waho, te wai whakamatao rānei). Ko ēnei huānga e toru—he puna wera, he miihini, me tētahi puna matao—kei roto tonu i tētahi miihini wera tūturu.
Mena ka whakamahia e tātou te tuhipoka noa:
– Ka mimiti te mīhini i te wera mai i tētahi pūtake wera e rite ana ki te Qₕ (te whakauru wera).
– Ka mahi te mīhini i te mahi a W.
– Ka tukuna e te mīhini te wera ki te taiao, ki te pūtake makariri rānei i te nui o te Q𝑐.
E ai ki te Ture Tuatahi o te Thermodynamics (te tiaki i te pūngao), ka pā ēnei ki:
Qₕ = W + Q𝑐
Ko te tikanga o tēnei, ko te mahi e puta ana ko te rerekētanga i waenga i te wera e whakaurua ana me te wera e ngaro ana. Heoi, kāore te Ture Tuatahi e whakamārama he aha e kore ai e taea te kore a Q𝑐. Koinei te wāhi e whai wāhi nui ai te Ture Tuarua.
Te Whakapuakitanga o te Ture Tuarua o te Thermodynamics
Ka taea te kī i te Ture Tuarua o te Thermodynamics i roto i ētahi āhua ōrite, engari ko ngā kōrero e rua e tino pā ana ki ngā miihini wera ko:
1. Te kōrero a Kelvin–Planck:
Kāore e taea te hanga i tētahi mīhini wera e mahi ana i roto i tētahi huringa, ā, ka tahuri i te wera katoa e mimitihia ana mai i tētahi puna wera hei mahi, me te kore e maka atu i te wera ki tētahi atu puna wera.
Ara, e kore e taea e te miihini wera te whai hua 100%.
2. Te kōrero a Clausius:
Kāore e taea te whakawhiti wera mai i tētahi mea makariri ki tētahi mea wera me te kore he mahi o waho.
Koinei te take e hiahia ai ngā pouaka whakamātao/hauātanga ki te pūngao hiko: hei "aki" i te wera kia neke ki tōna ahunga tūturu.
E whakaahua ana ngā kōrero e rua i tētahi mātāpono kotahi: he ahunga tō ngā tukanga taiao (kāore e taea te hoki whakamuri), ā, he herenga taketake anō hoki mō te hurihanga o te pūngao wera hei pūngao whai hua.
Te Entropi me te Aronga Tukanga
Ko tētahi ariā matua e puta mai ana i te Ture Tuarua ko te entropy (S), he rahinga e māramahia ana he ine i te tohatoha o te pūngao, i te nui rānei o te koretake, ahakoa he ōkawa ake tōna whakamāramatanga thermodynamic. Mō tētahi tukanga whakahurihuri, ko te huringa o te entropy ka tautuhia penei:
dS = δQ_rev / T
E ai ki te Ture Tuarua, mō tētahi pūnaha motuhake, kāore te entropy katoa e heke iho:
ΔS_tapeke ≥ 0
I roto i te horopaki o te mīhini wera, ina rere te wera mai i te pūtake wera ki te pūtake makariri, ka piki ake te entropy katoa. Kia puta ai he mahi i te mīhini, ka whakamahia e ia tēnei "rerenga" o te pūngao wera, engari me tutuki tonu ki te whakaritenga kia kaua e heke te entropy katoa. Nō reira, me maka tonu ētahi wera ki te puna makariri. Ehara tēnei maka i te mate hangarau noa iho, engari he whakaritenga taketake kia tutuki ai te whakaritenga entropy.
Te Whai Hua o te Mīhini Wera me te Herenga Carnot
Ko te whai huatanga wera o te miihini wera e tautuhia ana ko te ōwehenga o te mahi i puta ki te wera i mimitihia mai i te pūtake wera:
η = W / Qₕ = (Qₕ − Q𝑐) / Qₕ = 1 − (Q𝑐 / Qₕ)
Ko te Ture Tuarua e whakawhāiti ana i te uara mōrahi o η. Ko te miihini wera tino whai hua ko te miihini Carnot, he miihini tino pai e mahi ana i waenga i ngā puna wera e rua i ngā pāmahana Tₕ (wera) me T𝑐 (matao) i Kelvin. Ko te whai huatanga Carnot mōrahi ka hoatuhia e:
η_Carnot = 1 − (T𝑐 / Tₕ)
E whakaatu ana tēnei tātai i ngā mea nui e rua:
1. Ko te tino whai huatanga e whakawhirinaki ana ki te pāmahana o te puna wai anake, ehara i te momo wai mahi, i ngā taipitopito hoahoa rānei o te miihini.
2. Hei whakanui ake i te whai huatanga, me whakanui ake te Tₕ, me whakaiti rānei te T𝑐. Heoi, he herenga ēnei e rua e ngā rauemi, te haumaru, te utu, me ngā āhuatanga taiao.
Tauira: mēnā ko Tₕ = 900 K, ā, ko T𝑐 = 300 K, kāti:
η_Carnot = 1 − 300/900 = 1 − 1/3 = 0,667 (66,7%)
Koinei te rohe tino pai. Ka iti ake te whai huatanga o ngā miihini tūturu nā te waku, te ngaronga wera, te tahunga kāore i oti, me ētahi atu āhuatanga kāore e taea te whakakore.
Te kore e taea te hoki whakamuri i roto i ngā Mīhini Tuturu
E whakamārama ana hoki te Ture Tuarua he aha ngā miihini tūturu kāore e eke ki te whai huatanga Carnot. Ko te take matua ko te kore e taea te huri, koinei te tukanga e whakaputa ana i te entropy. Ko ētahi o ngā pūtake o te kore e taea te huri i roto i ngā miihini wera ko:
– Te waku ā-mīhini i runga i ngā toki, ngā peera me ngā wāhanga e neke ana.
– Ko te whakawhiti wera mā roto i tētahi rerekētanga pāmahana nui, hei tauira, ko te wera mai i tētahi rūma tahunga wera rawa atu ki tētahi wai mahi; ka nui ake te entropy ka puta mai i tēnei momo whakawhiti i tētahi tukanga pai rawa atu.
– Te aueue me te ngaronga o te pēhanga i roto i te rere o te wai i roto i ngā paipa, ngā takirere me ngā tāpine.
– Te ranunga kore e taea te hoki whakamuri o te hau me te hau, o ngā hua tahunga rānei.
– He tukanga tino kore e taea te whakakore te tahunga tonu.
Ka whakanuia e ēnei mea katoa te entropy katoa, ka "whakapau" i te pūmanawa ki te whakaputa mahi, ā, ka heke te whai huatanga.
Te Whakamahinga i roto i ngā Mīhini Tahunga ā-roto me ngā Whare Hiko Mamao
I roto i ngā miihini mura ā-roto (pērā i ngā miihini penehīni me te tīhiera), ka puta te pūtake wera mai i te tauhohenga mura i roto i te rango. Ka mimiti te miihini i te wera (whai hua) i ngā pāmahana teitei i te wā mura, kātahi ka panaia te wera mā roto i ngā hau putanga me te pūnaha whakamatao (radiator). E whakamārama ana te Ture Tuarua he aha i puta tonu ai te wera para i ngā miihini waka: kāore e taea te huri i te kaha katoa o te wahie hei mahi rakau.
I roto i tētahi tipu hiko-mama (PLTU), ka whakamahanahia te wai hei mamaoa pēhanga teitei hei huri i tētahi tāpine. I muri i te haere i roto i te tāpine, ka whakamataohia te mamaoa i roto i tētahi pūwhakamātao kia hoki ai ki te wai, ā, ka taea te papu anō. Ka mahi tēnei pūwhakamātao hei puna matao. He tokomaha e whakaaro ana he "moumou pūngao" te pūwhakamātao, engari i roto i te thermodynamics, he whakaritenga te whakamararatanga wera kia haere tonu ai te huringa, kia kore ai hoki te entropy katoa e takahi i te Ture Tuarua. Nō reira, ko ngā PLTU ka hangaia i te nuinga o te wā i te taha o ngā puna wai nui hei whakamatao, ka whakamahia rānei ngā pourewa whakamatao.
Ngā Rautaki Whakapai Ake i te Mahi e Hangai Ana ki te Ture Tuarua
Nā te mea he herenga kei te Ture Tuarua, ko ngā whakapainga ki ngā miihini wera e aro ana ki te whakaiti i te kore e taea te huri me te whakawhānui i te awhe pāmahana whai hua. Ko ētahi rautaki noa ko:
– Te whakamahana nui me te whakamahana anō i te huringa Rankine (PLTU) hei whakanui ake i te pāmahana o te tāhūhū.
– Te whakaora (whakamahana wai whāngai) hei whakamahi i te wera para hei whakamahana i te wai whāngai, hei whakaiti i te hiahiatanga wera o te poihā.
– Huringa whakakotahi (huringa hau-korohū whakakotahi), ka whakamahia te wera putanga mai i te tāpine hau hei whakaputa korohū hei taraiwa i te tāpine korohū. Mā tēnei ka pai ake te whakamahinga o te pūngao wera, ā, ka tata ake te pūnaha ki ōna rohe whai hua teitei ake.
– Ngā rauemi kua whakapaitia kia taea ai e ngā wāhanga te mahi i ngā pāmahana teitei ake me te kore e pakaru, ā, ka piki ake te Tₕ.
– Whakaitihia te waku me ngā ngaronga rere mā te hoahoa ā-rangi o te tāpine, te hinu whakahinuhinu pai ake, me te arotau i te ara wai.
Ko ēnei mahi katoa he tono mahi tūturu nō te Ture Tuarua: te whakahaere i te entropy me te pehi i te whakaputanga entropy kia taea ai te huri i te pūngao wera hei mahi.
Whakamutunga
Mā te whakamahinga o te Ture Tuarua o te Thermodynamics ki ngā miihini wera e whakaatu ana i tētahi rohe taketake e kore e taea e tētahi hangarau te wikitoria: kāore he miihini e taea te huri i te wera katoa hei mahi i roto i te huringa kotahi. Ko te noho mai o ngā puna makariri me ngā totohu wera ehara i te mea he hapa hoahoa noa iho, engari he hua tika o te ahunga taiao o te tukanga me te pikinga o te entropy. Mā roto i ngā ariā o te whai huatanga, te rohe Carnot, me te tātari i te kore e taea te hoki whakamuri, ka whakaratohia e te Ture Tuarua he aratohu matua mō te hoahoa i ngā miihini whai hua ake - mai i ngā miihini motuka ki ngā tipu hiko nui. Mā te mārama ki te Ture Tuarua, ehara i te mea ka mōhio noa tātou "he aha i iti ai te whai huatanga" engari me "te wāhi hei whakapai ake" kia tata ake ai ngā miihini wera ki te mahi tino pai e whakaaetia ana e te taiao.
