26 registered members (DaHen, aleneros, carviewsonic, Bogdon, Bailes1992, CATERHAM, 2 invisible),
1,244
guests, and 29
spiders. 
Key:
Admin,
Global Mod,
Mod


Forums67
Topics301,894
Posts5,204,873
Members70,798

Most Online4,538 Jan 20th, 2020



Determining Viscosity
#4341288
02/27/17 03:02 PM

Joined: Jun 2002
Posts: 20,910
MolaKule
OP
Global Moderator

OP
Global Moderator
Joined: Jun 2002
Posts: 20,910 
This exercise is a bit more involved and requires a Scientific Calculator and is open to all. One way of measuring viscosity is to use a "Rotating Concentric Cylinder" viscosimeter, sometimes called a, "Couette" viscosimeter. A rotating cylinder (the Inner Cylinder), is placed inside another ( outer) cylinder and the fluid whose viscosity is to be measured in poured into the gap, g. The Inner Cylinder is rotated at a specific RPM and the amount of Torque to rotate the Inner Cylinder is measured. Note: * is multiplication and X^n is a number raised to the "nth" power since we don't have an equation editor in BITOG. The viscosity is given by: u = T*g/(4*pi^2*R^3*n*L) = Absolute Viscosity in SI units of N.s/m^2 T is torque, measured at 1.8 N.m, g is gap between Inner and Outer Cylinder, or 0.15 cm, Outer Diameter of Inner Cylinder is 12 cm, L is length of each each cylinder which is 40 cm long, n is RPM, 300 RPM R is Radius of Inner Cylinder. Hints: Use 39.48 for 4*pi^2; Convert all given units to meters and seconds; answer will be in N.s/m^2. We will disregard any "end" effects. The result will be a 30 Grade motor oil at ~ 40C.
Last edited by wwillson; 03/10/17 06:15 AM. Reason: insert graphics



Re: Determining Viscosity
[Re: MolaKule]
#4342055
02/28/17 11:20 AM

Joined: Jun 2002
Posts: 20,910
MolaKule
OP
Global Moderator

OP
Global Moderator
Joined: Jun 2002
Posts: 20,910 
Hints: Use 39.48 for 4*pi^2; Convert all given units to meters and seconds; answer will be in N.s/m^2.
I'm a Student Pilot. Frightening, isn't it?



Re: Determining Viscosity
[Re: MolaKule]
#4342247
02/28/17 03:41 PM

Joined: Dec 2009
Posts: 28,128
Garak

Joined: Dec 2009
Posts: 28,128 
Showing units: 1.8 N.m × 0.0015 m / [4 × pi^2 × (0.06m)^3 × 5 rev/s × 0.4m] = 0.158314349 N.s/m^2 = 0.2 N.S/m^2, given one significant figure. Calculating through the units does indeed show the units you asked for are obtained.
Last edited by Garak; 02/28/17 03:42 PM.
Plain, simple Garak.
2008 Infiniti G37  Shell ROTELLA T6 MultiVehicle 5w30, Wix 57356 1984 F150 4.9L  Quaker State GB 10w30, Wix 51515



Re: Determining Viscosity
[Re: MolaKule]
#4342256
02/28/17 03:51 PM

Joined: Jul 2016
Posts: 666
Ohle_Manezzini

Joined: Jul 2016
Posts: 666 
Force?
Newton * second / square meters



Re: Determining Viscosity
[Re: Ohle_Manezzini]
#4342306
02/28/17 04:50 PM

Joined: Dec 2009
Posts: 28,128
Garak

Joined: Dec 2009
Posts: 28,128 
Newtons are the force, this expression is a dynamic viscosity, where 1 N.s/m^2 = 10 P or 1000 cP.
Plain, simple Garak.
2008 Infiniti G37  Shell ROTELLA T6 MultiVehicle 5w30, Wix 57356 1984 F150 4.9L  Quaker State GB 10w30, Wix 51515



Re: Determining Viscosity
[Re: Ohle_Manezzini]
#4342399
02/28/17 06:47 PM

Joined: Jun 2002
Posts: 20,910
MolaKule
OP
Global Moderator

OP
Global Moderator
Joined: Jun 2002
Posts: 20,910 
Force?
Newton * second / square meters Excellent Garak. RPO, had I given you the density you could have determined the Kinematic Viscosity in the SI units of m^2/s or cgs units of centistokes or cSt, with proper conversion coefficients.
I'm a Student Pilot. Frightening, isn't it?



Re: Determining Viscosity
[Re: MolaKule]
#4342645
02/28/17 10:34 PM

Joined: Jul 2016
Posts: 666
Ohle_Manezzini

Joined: Jul 2016
Posts: 666 
So the answer can also be expressed as 200 cP at 40C... Or:
In cst is 200 In Poise is 2 In stokes is 2 In SSU is 927
RPO
Last edited by Ohle_Manezzini; 02/28/17 10:41 PM.



Re: Determining Viscosity
[Re: MolaKule]
#4342695
02/28/17 11:14 PM

Joined: Dec 2009
Posts: 28,128
Garak

Joined: Dec 2009
Posts: 28,128 
Thanks. Technically, I shouldn't have put rev/s as a unit in my equation, since revs really aren't a unit. To be rigorous, I should have just used the unit of s^1.
Plain, simple Garak.
2008 Infiniti G37  Shell ROTELLA T6 MultiVehicle 5w30, Wix 57356 1984 F150 4.9L  Quaker State GB 10w30, Wix 51515



Re: Determining Viscosity
[Re: MolaKule]
#4342742
03/01/17 05:16 AM

Joined: Dec 2009
Posts: 28,128
Garak

Joined: Dec 2009
Posts: 28,128 
There, Mola. I made it look pretty, albeit a bit larger than I intended.
Plain, simple Garak.
2008 Infiniti G37  Shell ROTELLA T6 MultiVehicle 5w30, Wix 57356 1984 F150 4.9L  Quaker State GB 10w30, Wix 51515



Re: Determining Viscosity
[Re: MolaKule]
#4342794
03/01/17 07:29 AM

Joined: Jul 2016
Posts: 666
Ohle_Manezzini

Joined: Jul 2016
Posts: 666 
And the range for a 30 weight oil @ 40C is: 55cP to 82cP! So, this oil isn't a 30 grade at all Sorry Mola, could't resist, just grabbed a coffee Cqd,, RPO



Re: Determining Viscosity
[Re: Ohle_Manezzini]
#4343087
03/01/17 03:36 PM

Joined: Jun 2002
Posts: 20,910
MolaKule
OP
Global Moderator

OP
Global Moderator
Joined: Jun 2002
Posts: 20,910 
And the range for a 30 weight oil @ 40C is: 55cP to 82cP! So, this oil isn't a 30 grade at all Sorry Mola, could't resist, just grabbed a coffee Cqd,, RPO RPO, you need more than coffee. Look at F.M. White's, Fluid Mechanics, McGrawHill, 2003. He has a chart of various fluids (Viscosity vs. Temperature) expressed in Absolute Viscosity or N.s/m^2, and the SAE 30 oil [email protected] does indeed pass through the answer given by Garak.
I'm a Student Pilot. Frightening, isn't it?



Re: Determining Viscosity
[Re: MolaKule]
#4343742
03/02/17 01:57 PM

Joined: Jun 2002
Posts: 20,910
MolaKule
OP
Global Moderator

OP
Global Moderator
Joined: Jun 2002
Posts: 20,910 
A viscosity curve will pass through various values of Absolute Viscosity verses temperature.
For Garak's roundup value of 0.2, the curve is right on at 20C.
At 0.1583 N.s/m^2, the curve passes through 26C because of it's slope.
I accepted any numerical value between 0.158 N.s/m^2 and 0.2 N.s/m^2.
Last edited by MolaKule; 03/02/17 02:01 PM.
I'm a Student Pilot. Frightening, isn't it?



