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MEL 411:
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The cours e involv e s t he study andm e asur e m e nts of t he prop e rtie s of liquid fu e ls.It d e als wit h the m e asur e m e nt fu e ls pr e ssur e, te mp e ratur e le ve l, flow , sp ee d , we ig h t , ar e a , volum e, viscosity , st e am quality and products of combustion. It also includ e s t he study and
analysis of fu e ls and lubricants.
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VISCOSITY - the fluid r e sistanc e to s he ar or flow- a m e asur e of t he ad he siv e/ co he siv e or frictionalfluid prop e rty
APPLICATION:
- nee de d for prop e r d e sign of r e quir e dte mp e ratur e s for storag e, pumping or inj e ction of fluids
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TWO RELATED MEASURES OF FLUID VISCOSITY
ABSOLUTE (D Y NAMIC) VISCOSITY - is a m e asur e of t he int e rnal r e sistanc e- is t he tang e ntial forc e pe r unit ar e a r e quir e d tomov e on e h orizontal plan e with re sp e ct to t he
ot he r at unit v e locity w he n maintain e d a unitdistanc e apart by t he fluid- the ratio of s he ar int e nsity to v e locity gradi e nt
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Formula:
= dc/dy where:
shearing stress dynamic viscosity
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UNITS OF MEASUREMEN TSSI syst e mN-s / m 2
Pa -skg / m -s
CGS syst e m g/cm-sdyne - s/cm 2
poise (p)
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Conv e rsion:1 poise = dyne-s/cm 2
= g/cm-s
= 1 / 10 Pa-s= 100 cp (centipoise)
Constant:absolute viscosity of water (68.4F = 2 0 .2C)
= 1 cp
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K INEMATIC VISCOSI TY - is t he ratio of absolut e or dynamic viscosity to t he mass d e nsity of fu e ls
Formula: = /
where:
- kinematic viscosity - absolute or dynamic viscosity - density
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SI syst e mm 2 / sS toke ( S t)1 S t = 10 -4 m 2 /s
= 100 cS t (centistokes)1 cS t = 10 -6 m 2 /s
Constant:
kin e matic viscosity of wat e r (68.4 oF) - for all practicalpurpos e s= 1 .0 cS t.
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Othe r Commonly us e d Viscosity Units
Saybolt Univ e rsal S e conds ( SSU )
- is us e d to m e asur e viscosity- The e fflux tim e is Saybolt Univ e rsal S e conds ( SUS ) re quir e d for 60millilit e rs of a p e trol e um product to flow t h roug h the calibrat e d orific e of aSaybolt Univ e rsal viscom e te r
Re lations h ip of kin e matic and dynamic viscosity = 4.63 / SG
where:
v kinematic viscosity, SSU
dynamic viscosity, CpSG
specific gravity
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VISCOSITY OF COMMON LIQUIDS
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Typical liquid Saybolt S e condUniv e rsal( SSU )
ce ntiStok e s(cS t)
Wat e r (20 oC) 31 1
MilkSAE 20 Crankcas e OilSAE 75 G e ar Oil
40 4.3
# 4 FUEL OIL 80 15.7
SAE 30 crankcas e oilSAE 85 GEAR OIL
500 110
SAE 90 GEAR OIL 1000 220
SAE 140 GEAR OIL 2000 440
SAE 250 GEAR OIL 5000 1100
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Probl e m:
Calculat e the absolut e viscosity of air at 1 bar and 40C , kin e matic viscosity of 16.97cSt.
Give n:P = 1 bar
T = 40C
cSt = 16.97
Solution:
= p / R T
= ( 10 5 N /m 2 ) / ((287 J/kg/K) (273 oC + 33 0 C)
= 1 .11 3 kg/m 3
Absolute viscosity is,
= ( 1 .11 3 kg/m 3 ) ( 1 6.97 10 -6 m 2 /s)
= 1 .88 10 -5 kg/m s
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Conv e rt kin e matic viscosity from SSU tocSt.
cS t = 0 .226 SSU - 1 9 5 / SSU
SSU < 100
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cS t = 0 .22 0 SSU - 1 3 5 / SSU SSU > 100
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For liquids - viscosity d e cr e as e s wit h te mp e ratur e
for gas e s viscosity incr e as e s wit h te mp e ratur e
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Probl e mA solid circular cylind e r slid e s insid e a v e rtical smoot h pip e .The spac e be twee n t he cylind e r and t he pip e is lubricat e dwith an oil film. Calculat e the te rminal v e locity of t he cylind e r.
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Solution
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BOARD WORK
Probl e mA cylindrical tank mad e of st ee l is 6 ft long and 1.5 m in diam e te r. Ane ngin e h as fu e l rat e consumption of 1000 g / min at 27 API fu e lsp e cific gravity. D e te rmin e the numb e r of days t he tank can supplythe e ngin e?
Give nm fu e l = 1000 g / minAPI = 27h = 6 ftd = 1.5 m
Re quir e m e ntNo.of days
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BOARD WORK
SolutionVfu e l = m fu e l / de nsity fu e l
Vf = Vt = 3.23 cu.m
d e nsity fu e l = SG 15.6 C (d e nsity wat e r)
= 0.893 (1000 kg / cu.m)
= 893 kg / cu.m
Vfu e l = 60 kg /h r / 893 kg / cu.m
= 0.067 cu.m /h r
# of h rs = 3.23 cu.m / 0.067 cu.m /h r
= 48.21 h rs
# of days = 2 days
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H ydrom e te r
- a d e vice us e d for m e asuring som e ch aract e ristics of a liquid suc h as itsde nsity and sp e cific gravity.
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Application
The d e vice consist of a w e ig h te d , s e al e d , and long -n e ck e d glass tub e th at is imm e rs e d in t he liquidbe ing m e asur e d (www.britannica.com) .
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