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Pump Sizing Example ( Open System)

ဤဥပမာတြင္ Pump Head ကို တြက္ရန္အတြက္ Friction Losses ႏွင့္ Dynamic losses ကိုတစ္မ်ိဳးစီတြက္ၿပီးေပါင္းရန္ၿဖစ္သည္။

Friction Losses သည္ Pipe Size ( Flow Velocity), Pipe Length ႏွင့္ Pipe material တုိ့ေပၚတြင္မူတည္သည္။

Dynamic losses သည္ changes in flow area (Velocity), chages in flow direction ႏွင့္ obstructions တုိ့ေပၚတြင္မူတည္သည္။

Friction Losses ကို ASHRAE Handbook - Fundamental ၏ Friction loss for water in commercial steel pipe Chart မွဖတ္ယူသည့္နည္းၿဖင့္တြက္ယူရန္ၿဖစ္သည္။ Formul ႏွင့္လည္းတြက္ယူနုိင္သည္။

က) Pipe Diameter လုိင္းသည္ ညာဘက္သုိ့ေစာင္းေနေသာ ကန့္လန့္ၿဖတ္လုိင္းမ်ားၿဖစ္သည္။ Pipe Diameter = 300mm လုိင္းသည္ အၿပာလုိင္းၿဖစ္သည္။

ခ) Water Flow rate = 450 CMH = 125 L/s - Volume Flow Rate (L/s) လုိင္းသည္ ေဒါင္လုိက္လုိင္းမ်ားၿဖစ္သည္။ Water Flow rate = 450 CMH = 125 L/s လုိင္းသည္ အနီေရာင္လုိင္းၿဖစ္သည္။

ထုိလုိင္းႏွစ္လုိင္းၿဖတ္မွတ္မွ point တစ္ခုကိုရသည္။ ထုိ point မွ Pressure Drop ( အလ်ားလိုက္အစိမ္းေရာင္လုိင္းမွ) 70Pa/m Pressure Drop ကို ရသည္။ Pipe Length = 100m x 70Pa/m = 7,000Pa သည္ Friction Losses.

ထုိ 300m ပုိက္ထဲတြင္ 125 L/s - Volume Flow Rate သြားလွ်င္ Velocity မွာ 1.7m/sec ၿဖစ္သည္။ Chart ေပၚမွ ဘယ္ဘက္သို့ ေစာင္း ေစာင္းေနေသာ ကန့္လန့္ၿဖတ္လုိင္း (Velocity လုိင္းမွ)ဖတ္ယူနုိင္သည္။

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Dynamic losses

Number of Valve = 6 ( Gate Valve, fully open)

Number of Stariner = 2 ( take pressuer loss to be the same as for fully open globe valve)

Number of pipe bends = 15 ( 90 Degree Standard elbow)

Number of Valve = 6 ( Gate Valve, fully open)

fully opened gate valve ၏ K တန္ဘိုး မွာ အထက္ပါ ဇယားမွာ 300mm ပုိက္ ၾကည့္လွ်င္ 0.05 ၿဖစ္သည္။

Pressure drop for fully opened gate valve = K x density of water x Velocity x Velociyt / 2

Pressure drop for fully opened gate valve = 0.05 x 1000 kg/ cu m x 1.7 m/s x 1.7 m/s/ 2 = 72.25Pa/Gate Valve

For 6 Valves x 72.25Pa/Gate Valve = 433.50Pa

 

Number of Stariner = 2 ( take pressuer loss to be the same as for fully open globe valve)

fully opened globe valve ၏ K တန္ဘိုး မွာ အထက္ပါ ဇယားမွာ 300mm ပုိက္ ၾကည့္လွ်င္ 0.05 ၿဖစ္သည္။

Pressure drop for fully opened globe valve = K x density of water x Velocity x Velociyt / 2

Pressure drop for fully opened globe valve = 5.7 x 1000 kg/ cu m x 1.7 m/s x 1.7 m/s/ 2 = 8236.5Pa

For 2 Strainer x 8236.5Pa = 16473.00 Pa

 

Number of pipe bends = 15 ( 90 Degree Standard elbow)

fully opened globe valve ၏ K တန္ဘိုး မွာ အထက္ပါ ဇယားမွာ 300mm ပုိက္ ၾကည့္လွ်င္ 0.05 ၿဖစ္သည္။

Pressure drop for fully opened globe valve = K x density of water x Velocity x Velociyt / 2

Pressure drop for fully opened globe valve = 5.7 x 1000 kg/ cu m x 1.7 m/s x 1.7 m/s/ 2 = 346.8 Pa/ elbow

For 15 elbow x 346.8 Pa/ elbow = 5202 Pa

 

Pressuer losses across heat exchanger= High of Water (H) x Desity of Water x G = 5m x 1000 x 9.8m = 49,000 Pa

Cooling Tower Static Head = High of Water (H) x Desity of Water x G = 4m x 1000 x 9.8m = 39,200 Pa

 

ပုစၦာတြင္ pipe diameter မေပးထားခဲ့လွ်င္

က) Chart မွဖတ္ယူသည့္နည္းၿဖင့္တြက္ယူရန္ Desing Pressure Drop (သို့ Friction loss) ကို ပိုက္ ၁မီတာလွ်င္ 150 Pa ( 150Pa/m) ကို အေၿခခံ၍တြက္ခ်က္မည္ၿဖစ္သည္။ 150Pa/m Desing Pressure Drop သည္ (1.5ft/100ft) တပ္ဆင္ထားသည္ ပိုက္100ေပလွ်င္ 1.5ft of water Pressure drop ႏွင့္တူညီသည္။

ခ) Water Flow rate = 450 CMH = 125 L/s

ဂ) Pressure Drop လုိင္းသည္ အလ်ားလုိက္လုိင္းမ်ားၿဖစ္သည္။ Volume Flow Rate (L/s) လုိင္းသည္ ေဒါင္လုိက္လုိင္းမ်ားၿဖစ္သည္။ 150Pa/m

ကိုအလ်ားလုိက္လုိင္းမွ 125 L/sကိုေဒါင္လုိက္လုိင္းမွ Chart ေပၚမွာဖတ္လွ်င္ pipe diameter ကိုရရွိနုိင္သည္။

 

Friction Losses ႏွင့္သက္ဆုိင္ေသာ ACMV Lecture မ်ား (6 Lectures)
1 Air Side Friction Losses in Duct 1 Read
2 Water Side Friction Losses in Pipes Read
3 Air Side Friction Losses in Duct 2 Read
4 Air Side Dynamic Losses Read
5 Air Side Duct Static Pressure Loss ( Excel ဖိုင္) Read
6 Pumping System Pressuer Losses for Pump or Pump Head Read
   

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