Engine Room Blower Fan Capacity Calculation

သေဘ္ာအသစ္ေတြတည္ေဆာက္တဲ႔အခါ၊ Technical Data ေတြ၊ Specification ေတြေပါါမူတည္လို႔၊ တြက္ခၽက္ ရပါတယ္။ အဲဒီတြက္တာခၽက္တာေတြ ထဲက၊ Engine Room မွာ တတ္ဆင္အသံုးၿပဳမယ္႔ Blower Fan ရဲ႕ capacity တြက္နည္းကေလးကို၊ ေဖာ္ၿပခၽင္ပါတယ္။  

သေဘ္ာဟာ DWT ၆၃၀၀ တန္ရိွတဲ႔၊ Product tanker တစီးၿဖစ္ၿပီး၊ Technical data အရ၊ engine room မွာတတ္ဆင္တာေတြကို၊

(၁)။ 1471 KW ရိွတဲ႔၊ Main Engine (၂) လံုး။
main engine ရဲ႕ total output = 2 x 2000 PS = 4000 PS ( 1 PS = 0.7355 KW)

(၂)။ 320 KW ရိွတဲ႔၊ generator Engine (၂) လံုး။
generator ရဲ႕ total output = 2 x 435 PS = 870 PS ( 1 PS = 0.7355 KW)

(၃)။ 2500 KW ရိွတဲ႔ Thermal oil heater (၁) လံုး
thermal oil heater ရဲ႕ total output = 3399 PS ( 1 PS = 0.7355 KW)

(၄)။ Main engine exhaust gas pipe diameter/ length = 800mm/ 25 Mtr, Generator engine exhaust gas pipe diameter/ length + 300mm/ 35 Mtr ဆိုၿပီး ေတြ႔ရပါတယ္။ 

engine room မွာတတ္ဆင္အသံုးၿပဳမယ္႔ blower fan ရဲ႕ capacity ဟာ၊ engine room ရဲ႕ total combustion air flow နဲ႔ total air flow for removing heat တို႔ေပါါမူတည္ေနပါတယ္။ တနည္းအားၿဖင္႔

Blower Fan Capacity = Total Combustion Air Flow + Total Air Flow For Removing Heat 

ရယ္လို႔ေၿပာနိဳင္ပါတယ္။ engine room အတြက္ total combustion air flow Qc ကို၊ ယူနစ္အေနနဲ႔ Cu. Mtr/ min နဲ႔သတ္မွတ္ပါတယ္။ total air flow for removing heat Qh ကိုလည္း၊ ယူနစ္အေနနဲ႔ Cu. Mtr/ min နဲ႔သတ္မွတ္ ပါတယ္။

Total Combustion Air Flow Qc = Qme + Qae + Qoh 

မွာ, Qme = combustion air flow for main engine, Qae = combustion air flow for generator engine နဲ႔ Qoh = combustion air flow for thermal oil heater ရယ္လို႔တြက္ယူ နိဳင္ပါတယ္။

Qme = Combustion Air Flow For Main Engine = 0.85 (F x V x M x P / 60) Cu. mtr/ min 

ဆိုတဲ႔ ပံုေသနည္းအရ

Qme = combustion air flow for main engine
F = fuel consumption rate of the engine at MCR = 0.128 Kg/ PS. h
V = air quantity for burning fuel oil of 1 kg completely = 12 Cu. mtr/ Kg
M = main engine calorific value = 3.6
P = maximum continuous output = 4000 PS
Power factor = 0.85 တို႔ကိုအစားသြင္းလိုက္တဲ႔အခါ၊
Qme = 0.85 (0.129 x 12 x 3.6 x 4000/ 60) = 315.8 Cu. mtr/ min ရယ္လို႔ရလာပါတယ္။

Qae = Combustion Air Flow For Generator Engine = 0.85 (F x V x M x P / 60) Cu. mtr/ min 

ကိုလည္း၊ အထက္ပါအတိုင္း F = 0.165 Kg/ PS. h, V = 12 Cu. mtr/ Kg, M = 1.2 ~ 2, P = 870 PS နဲ႔ Power factor = 0.85 ဆိုၿပီး၊ အစားထိုးတြက္ႀကည္႔တဲ႔အခါ၊

Qae = 0.85 (0.165 x 12 x 2 x870/ 60) = 48.8 cu. mtr/ min ဆိုၿပီးရလာပါတယ္။ အလားတူ

Qoh = Combustion Air Flow For Thermal Oil Heater = 0.85 (F x V x M x P / 60) Cu. mtr/ min

ကိုလည္း၊ အထက္ပါအတိုင္း, F = 0.165 Kg/ PS. h, V = 12 Cu. mtr/ Kg, M = 1.2 ~ 2, P = 3399 PS နဲ႔ Power factor = 0.85 ဆိုၿပီး၊ အစားထိုး တြက္ႀကည္႔တဲ႔အခါ၊  

Qoh = 0.85 (0.165 x 12 x 2 x3399/ 60) = 190.68 cu. mtr/ min ဆိုၿပီးရလာပါတယ္။ အဲဒီအခါ

Total Combustion Air Flow Qc = Qme + Qae + Qoh 

Qc = 315.8 + 48.8 + 190.68 = 552.28 cu. mtr/ min ဆိုၿပီး၊ total combustion air flow ဆိုတဲ႔၊ engine ေတြ၊ thermal oil heater ေတြအတြက္ ေမာင္းနွင္ဖို႔လိုအပ္မယ္႕ air flow ပမာဏကို၊ ရရိွလာ ပါတယ္။

Total Air Flow For Removing Heat Qh = { Rh/ (P x Cp x T) } - 0.4 {(Qme + Qae + Qoh)}  

ၿဖစ္ပါတယ္။

Rh = Heat Evacuation = Rme + Rae + Roh + Rex 

ဆိုတဲ႔ပံုေသနည္းမွာ

Rme = Heat evacuation for main engine = {Pme x Udme}/ 100
Pme = main engine total output KW = 2 x 1471 Kw
Udme = main engine percentage of heat loss = 1.307 KW ရယ္လို႔ technical specification အရ၊ သိရတာေႀကာင္႔ main engine ရဲ႕ heat evacuation Rme = {Pme x Udme}/ 100 = {2 x 1471 x 1.307}/ 100 = 38.2 Kw ရယ္လို႔တြက္ယူနိဳင္ပါတယ္။

Rae = Heat evacuation for generator engine ကို
Pae = generator engine total output KW = 2 x 320 = 640 KW
Udae = generator engine percentage of heat loss = 4.571 KW
generator engine ရဲ႕ heat evacuation Rae = {Pae x Udae}/ 100 = {2 x 320 x 4.571}/ 100 = 29.25 KW နဲ႔

Roh = Heat evacuation of thermal oil heater ကိုလည္း
Poh = thermal oil heater total output KW = 2500 KW
Udoh = thermal oil heater percentage of heat loss = 1.307 KW
thermal oil heater ရဲ႕ heat evacuation Roh = {Poh x Udoh}/ 100 = {2500 x 1.307}/ 100 = 32.67 KW ဆိုၿပီး၊ တြက္ယူနိဳင္ပါတယ္။ 

Rex = Heat evacuation for exhaust gas pipe = {main engine exhaust gas pipe heat evacuation} + {generator engine exhaust gas pipe heat evacuation} + {thermal oil heater exhaust gas pipe heat evacuation}  

ဆိုတဲ႔၊ ပံုေသနည္းမွာ၊ exhaust gas pipe အတြက္၊ ရရိွထားတဲ႔ technical data ေတြကိုအစားသြင္းၿခင္းၿဖင္႔

Rex = {0.75 KW x 25 mtr} + {0.23 KW x 35 mtr} + {0.23 KW x 35 mtr} = 35 KW ဆိုၿပီး၊ ရရိွလာပါတယ္။

အဲဒီကတဆင္႔ Rh = Heat evacuation = Rme + Rae + Roh + Rex = {38.2 + 29.25 + 32.67 + 45} KW = 145.12 KW တနည္းအားၿဖင္႔ 145.12 KJ/ Sec ကိုတြက္ယူရရိွပါတယ္။

P = air density = 1.164 Kg/ cu. mtr @ 45 Deg. C, Cp = 1.01 KgJ/ KgoC specific heat of dry air @ 45 Deg. C, T = allowable temperature rise 7 ~ 10 Deg. C for engine room ဆိုၿပီး၊ ရရိွထားတဲ႔ data ေတြအရ total air flow for removing heat Qh ကို၊ တြက္ယူတဲ႔အခါ၊

Qh = { Rh/ (P x Cp x T) } - {0.4 (Qme + Qae + Qoh)}

Qh = {145.12 KgJ/ Sec./ (1.165 Kg/ cu. mtr x 8 Deg. C)} - 0.4 {(315.8 + 48.8 + 190.68) Cu. mtr/ min}
Qh = {15.42 Cu. mtr/ Sec.} - {221.1 Cu. mtr/ min}
Qh = {15.42 x 60 Cu. mtr/ min} - {221.1 Cu. mtr/ min}
Qh = {925.2 Cu. mtr/ min} - {221.1 Cu. mtr/ min}
Qh = 703.1 Cu. mtr/ min ဆိုၿပီးရရိွလာပါတယ္။ ဆက္လက္ၿပီး တတ္ဆင္မယ္႔ blower fan ရဲ႕ capacity ကို

Blower Fan Capacity = Total Combustion Air Flow + Total Air Flow For Removing Heat

ဆိုတဲ႔ပံုေသနည္းအရ ရွာေဖြတဲ႔အခါ၊

Blower Fan Capacity = Qc + Qh

blower fan capacity = 552.28 cu. mtr/ min + 703.1 Cu. mtr/ min
blower fan capacity = 1258. 38 Cu. mtr/ min

Safety 20 % fan capacity = 1.2 x 1258.38 = 1510.06 Cu. mtr/ min
Safety 20 % fan capacity = {1510.06 Cu. mtr/ min} x 60
Safety 20 % fan capacity = 90603 Cu. mtr/ Hr ဆိုၿပီးရရိွလာတာမို႔၊ 5000 Cu. mtr/ Hr capacity ရိွတဲ႔၊ blower fan (၂) လံုးကို၊ ေရြးခၽယ္တတ္ဆင္ခဲ႔ပါတယ္။

အေသးစိတ္ကို၊ ISO : 8861 - Shipbuilding -- Engine-room ventilation in diesel-engined ships - Design requirements and basis of calculations မွာ၊ ဆက္လက္ေလ့လာနိဳင္ပါတယ္။ အလားတူ Ducting နဲ ႔ပက္သက္လို႔၊ ISO : 7547 - Air Conditioning and Ventilation of Accommodation Spaces  မွာ၊ ဆက္လက္ေလ့လာနိဳင္ပါတယ္။

Credit to : ကိုထြန္း
 
Reference : ISO : 8861, ISO : 7547, www.jimarine.com.sg