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Hydraulik Piping [Bagaimana Mengira Total Head (m)]
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Post Last Edit by dauswq at 28-3-2011 10:06
Mintak sapa yg otai2 sini pasal piping. Mcm mana nak kira Total head (m) yg diperlukan utk mengepam minyak (viscosity 8000) ke satu tempat yg tinggi dalam 10 meter. Apakah parameter2 yg perlu dikenal pasti..... Bagaimana nak kira NPSH.....sapa tau?
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Contoh open tank 1 meter tinggi penuh.....design piping naik sampai 10m tinggi. 3" diameter pipe. Adakah elbow perlu diambil kira |
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Post Last Edit by mr_brown at 24-3-2011 17:17
dude ko kerja kat mana dude....
secara basicnyer kalo ko nak mengepam 10m ke atas, kau hanya memerlukan positif head 10m laaa..... tapi kau kena amik kira pasal losses sepanjang pengepaman tersebut dimana kebanyakkannya berpunca daripada friction within pipe, dan juga pebezaan initial dan final liquid levels.....
secara basicnyer;
H total = H frsuct + H frdis + H distank + H suctank
dimana;
H frsuct = friction head loss in suction piping
H frdis = friction head loss in discharge piping
H distank = height of discharge tank level above pump
H suctank = height of suction tank level above pump (negative when tank level is below pump suction)
elbow tak perlu diambil kira, semua perkiraan dikira vertically.....
kau nak guna pump jenis apa?
kalo untuk minyak memang tak sesuai laa pakai centrifugal pump, kalo nak pakai gak bleh tapi ko kena tambah priming system.....
untuk tinggi2 macam 10 meter tuh biasanya orang pakai gear pump, rotary pump ataupun screw pump....reciprocating pun bleh gak..... |
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Reply 1# penyo.
NPSH (net positive suction head) adalah perbezaan absolute pump inlet pressure dan vapour pressure of the liquid.... vapour pressure nih depend pada temperature so adalah baik untuk dikira semasa operating temperature...
NPSH available = (H atm + H sucttank - H frsuct - H vapress) / absolute pump inlet pressure
dimana;
H atm = atmospheric pressure
H sucttank = tank level from pump (negative when below pump)
H frsuct = friction head loss in suction piping
H vapress = liquid vapour pressure
NPSH dan Head semua adalah dikira dalam unit metre... |
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Post Last Edit by animaniac at 25-3-2011 08:00
bro,gua bukan piping designer tapi nak mencelah sikit dgn reference yg aku rasa cukup senang faham. lebih kurang macam xplaination mr_brown , in fact this is what had been thought in basic fluid mechanics, gua ingat2 lupa sampai jumpa this article.
It turn out that "head" is a very convenient term in the pumping business. Capacity is measured in gallons per minute, and each gallon of liquid has weight, so we can easily calculate the pounds per minute being pumped. Head or height is measured in feet, so if we multiply these two together we get foot- pounds per minute which converts directly to work at the rate of 33,000 foot pounds per minute equals one horsepower.
Pressure is not as convenient a term because the amount of pressure that the pump will deliver depends upon the weight (specific gravity) of the liquid being pumped and the specific gravity changes with temperature, type of fluid, and fluid concentration.
If you will refer to FIG 1, you should get a clear picture of what is meant by static head. Note that we always measure from the center line of the pump to the highest liquid level
To calculate head accurately we must calculate the total head on both the suction and discharge sides of the pump. In addition to the static head we will learn that there is a head caused by resistance in the piping, fittings and valves called friction head, and a head caused by any pressure that might be acting on the liquid in the tanks including atmospheric pressure, called " surface pressure head".
Once we know these heads, we will then subtract the suction head from the discharge head and the amount remaining will be the amount of head that the pump must be able to generate at the rated flow. Here is how it looks in a formula:
System head = total discharge head - total suction head
H = hd - hs
The total discharge head is made from three separate heads:
hd = hsd + hpd + hfd
hd = total discharge head
hsd = discharge static head
hpd = discharge surface pressure head
hfd = discharge friction head
The total suction head also consists of three separate heads
hs = hss + hps - hfs
hs = total suction head
hss = suction static head
hps = suction surface pressure head
hfs = suction friction head
As we make these calculations, you must sure that all calculations are made in either "feet of liquid gauge" or "feet of liquid absolute". In case you have forgotten "absolute means that you have added atmospheric pressure (head) to the gauge reading.
Now we will make some actual calculations:
Figure #2 demonstrates that the discharge head is still measured to the liquid level, but you will note that it is below the maximum height of the piping.
Although the pump must deliver enough head to get up to this maximum piping height, it will not have to continue to deliver this head when the pump is running because of the "siphon effect". There is of course a maximum siphon effect. It is derived from: 14.7 psi (atmospheric pressure) x 2.31 feet / psi = 33.4 feet maximum siphon effect.
We will begin with the total suction head calculation
1. The suction head is negative because the liquid level in the suction tank is below the centerline of the pump:
hss = - 6 feet
2. The suction tank is open, so the suction surface pressure equals atmospheric pressure :
hps = 0 feet gauge
3. You will not have to calculate the suction friction head, I will tell you it is:
hfs = 4 feet at rated flow
4. The total suction head is a gauge value because atmosphere was given as 0,
hs = hss + hps - hfs = -6 + 0 - 4 = -10 feet of liquid gauge at rated flow
The total discharge head calculation
1. The static discharge head is:
hsd = 125 feet
2. The discharge tank is also open to atmospheric pressure, thus:
hpd = 0 feet, gauge
3. I will give you the discharge friction head as:
hfd = 25 feet at rated flow
4. The total discharge head is:
hd = hsd + hpd + hfd = 125 + 0 + 25 = 150 feet of liquid gauge at rated flow
The total system head calculation:
H = hd - hs = 150 - (-10)= 160 feet of liquid at rated flow
example :
Specifications:
1. Transferring 1000 gpm. weak acid from the vacuum receiver to the storage tank
2. Specific Gravity - 0.98
3. Viscosity - equal to water
4. Piping - All 6" Schedule 40 steel pipe
5. Discharge piping rises 40 feet vertically above the pump centerline and then runs 400 feet horizontally. There is one 90° flanged elbow in this line
6. Suction piping has a square edge inlet, four feet of pipe, one gate valve, and one 90° flanged elbow all of which are 6" in diameter.
7. The minimum level in the vacuum receiver is 5 feet above the pump centerline.
8. The pressure on top of the liquid in the vacuum receiver is 20 inches of mercury, vacuum.
To calculate suction surface pressure use one of the following formulas:
inches of mercury x 1.133/ specific gravity = feet of liquid
pounds per square inch x 2.31/specific gravity = feet of liquid
Millimeters of mercury / (22.4 x specific gravity) = feet of liquid
Now that you have all of the necessary information we will begin by dividing the system into two different sections, using the pump as the dividing line.
Total suction head calculation
1. The suction side of the system shows a minimum static head of 5 feet above suction centerline. Therefore, the static suction head is:
hss = 5 feet
2. Using the first conversion formula, the suction surface pressure is:
hps = -20 Hg x 1.133/ 0.98 = -23.12 feet gauge
3. The suction friction head, hfs, equals the sum of all the friction losses in the suction line. Friction loss in 6" pipe at 1000 gpm from table 15 of the Hydraulic Institute Engineering Data Book, is 6.17 feet per 100 feet of pipe.
in 4 feet of pipe friction loss = 4/100 x 6.17 = 0.3 feet
Friction loss coefficients (K factors) for the inlet, elbow and valve can be added together and multiplied by the velocity head:
FITTING K
6" Square edge inlet 0.50
6" 90 flanged elbow 0.29
6" Gate valve 0.11
Total coefficient, K = 0.90
Total friction loss on the suction side is:
hfs = 0.3 + 1.7 = 2.0 feet at 1000 gpm.
4. The total suction head then becomes:
hs = hss + hps - hfs = 5 + (-23.12) - 2.0 = -20.12 feet, gauge at 1000 gpm.
Total discharge head calculation
1. Static discharge head = hsd = 40 feet
2. Discharge surface pressure = hpd = 0 feet gauge
3. Discharge friction head = hfd = sum of the following losses :
Friction loss in 6" pipe at 1000 gpm. from table 15, is 6.17 feet per hundred feet of pipe.
In 440 feet of pipe the friction loss = 440/100 x 6.17 = 27.2 feet
Friction loss in 6" elbow:
from table 32 (a), K = 0,29
from table 15, V2/2g = 1.92 at 1000 gpm.
Friction loss = K V2/2g = 0.29 x 1.92 = 0.6 feet
The friction loss in the sudden enlargement at the end of the discharge line is called the exit loss. In systems of this type where the area of the discharge tank is very large in comparison to the area of the discharge pipe, the loss equals V2/2g, as shown in table 32 (b).
Friction loss at exit = V2/2g = 1.9 feet
The discharge friction head is the sum of the above losses, that is:
hfd = 27.2 + 0.6 + 1.9 = 29.7 feet at 1000 gpm.
4. The total discharge head then becomes:
hd = hsd + hpd + hfd = 40 + 0 + 29.7 = 69.7 feet, gauge at 1000 gpm.
c. Total system head calculation:
H = hd - hs = 69.7 - (-20.2) = 89.9 feet at 1000 gpm.
rujukan dari http://www.mcnallyinstitute.com/07-html/7-01.html |
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Reply 7# animaniac
ade belajar sket psl fluid mechanic..tp basic jek
bernouli + continuity equation + pascal... |
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Reply animaniac
ade belajar sket psl fluid mechanic..tp basic jek
bernouli + continuity equa ...
dauswq Post at 25-3-2011 14:22 
fluid mechanics memang interesting dauswq dan mencabar especially advance fluid mechanics, i rasa budak physics macam u ni senang je nak digest especially on the mathematical solution  |
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Mintak sapa yg otai2 sini pasal piping. Mcm mana nak kira Total head (m) yg diperlukan utk mengepam ...
penyo. Post at 23-3-2011 12:01 
kalau saudara tak keberatan boleh bagi email, saya nak email contoh calculation total head loss |
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Reply 11# sixfor
encik sixfor boleh share di sini jika tdk keberatan....
saya akn bg kredit..klu nak letak red perm pun boleh |
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benda ni notes dia dalam pdf, tapi saya tatau nak buat mcm mana supaya org lain boleh tgk |
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ni link utk sample calculation
sixfor Post at 6-4-2011 00:24
oh....terima kasih banyak2 kerana sudi berkongsi bro!!!! |
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Category: Belia & Informasi
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Post time 23-3-2011 12:01 PM
变色卡
Author
hmy3:
, boleh cerita pasal fluid mechanics ni keja KWSP kejadahnya 
Post time 25-3-2011 02:22 PM
