Na'urar Tufafi da Turancin Dukkana
Draught yana ita ce farkon tsafta wanda ke kula tsakiyar hawa da kuma gaso daga baya zuwa baya a cikin systemin boiler. Draught yana bukatar a cikin systemin boiler saboda biyu na dalilai.
Don bayar hawa da kyau don kammala combustion.
Don fitar da flue gases daga systemi ba da combustion da kuma heat exchange.
An samu biyu na abubuwan draught wadanda ake amfani da su a cikin systemin boiler.
Natural draught
Forced draught
Zan iya hada a nan cikin wannan article game da natural draught. Natural draught yana da muhimmanci saboda ba ake bukata kan yi aiki da kudin ba, musamman idan an samun gajerar da ya kai. Natural draught yana bayar hawan da ya gane a cikin systemin boiler. Natural draught yana neman da ya gane mai girma ta chimni.
Na iya karin cewa maimakon girma da ya fi sace a cikin chimni don natural draught don systemin boiler. Don haka, zan iya karin duwatsu masu gajerar tsafta ga gaso. Dukata suna da biyu:
Amsa, “P” yana nufin tsafta ga hawa ko gaso, “ρ” yana nufin girma ga hawa ko gaso, “g” yana nufin constant na gravity, da “h” yana nufin girma ga head.
Amsa, “V” yana nufin volume ga hawa ko gaso, “m” yana nufin mass ga gaso, “T” yana nufin temperature a matsayin Kelvin, da “R” yana nufin gas constant.
Duka (2) zan iya rubuta shi a haka:
A cikin processin combustion a cikin furnace, carbon yana ci oxygen (O2) na hawar da kuma yana da carbon dioxide (CO2). Volume solid carbon da ake bukata saboda reaction yana da kyau saboda volume hawa da ake bukata. Saboda haka, zan iya cewa volume hawa da ake bukata yana da kyau da volume flue gases da aka fara a cikin combustion idan ana iya kawo fahimta cewa temperature a matsayin sama a cikin waɗannan lokutan. Amma wannan babu alama. Hawan da ake bukata a cikin combustion chamber zai samu volume extra saboda temperature combustion. Volume hawan da aka samu zai da kyau da volume flue gases da aka fara a cikin combustion.
Zan iya cewa, ρo yana nufin girma ga hawa a 0oC ko 273 K, da za a cewa To
Amsa, P yana nufin tsafta ga hawa a 0oC ko 273 K, wanda aka cewa To K.
Idan an kawo P da ya fi sace, relation bayan girma da temperature ga hawa ko gaso zan iya rubuta shi a haka:
Amsa, ρa da ρg yana nufin girma ga hawa a temperature Ta da Tg K respectively.
Daga equation (1) da (5) zan iya rubuta expression of pressure at point “a” outside the chimney, as
Volume of the air at the temperature Tg would be
Let us assume, m kg of air is required to burn 1 kg of carbon then the density of the flue gas would be
The pressure of the flue gas inside the cheimny from equation (1) and (8), would be
The pressure difference between outside and inside of the chimney from equation 96) and (9) would be
Here, “h” is the minimum height of the chimney to be constructed for the draught ΔP. The flue gas will flow upwards through the chimney due to this pressure difference. So, by calculating this pressure difference one can easily calculate the approximate height of the chimney to be constructed. The pressure difference can be represented as a formula for calculating the height of the chimney for a natural draught.
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