• Welcome, Guest! We hope you enjoy the excellent technical knowledge, event information and discussions that the BMW MOA forum provides. Some forum content will be hidden from you if you remain logged out. If you want to view all content, please click the 'Log in' button above and enter your BMW MOA username and password.

    If you are not an MOA member, why not take the time to join the club, so you can enjoy posting on the forum, the BMW Owners News magazine, and all of the discounts and benefits the BMW MOA offers?

15W-50 instead of 10W-40?

I gotta call BS on that one. 25 years in car dealership shops and I've never even heard mention of a viscosity checker, let alone used one. :scratch

Oil test labs do this type of thing. Here's a discussion of a "viscosity checker":

http://en.wikipedia.org/wiki/Viscometer

It's basically how much fluid flows through an orifice in a given period of time at a specific temperature. I wouldn't think it's a house-hold item, though! :stick
 
Oil test labs do this type of thing. Here's a discussion of a "viscosity checker":

http://en.wikipedia.org/wiki/Viscometer

It's basically how much fluid flows through an orifice in a given period of time at a specific temperature. I wouldn't think it's a house-hold item, though! :stick

I'm almost positive I saw a tech doing the "Falling Sphere Viscometers" test just a week or so ago. And this was when the bike was sitting on top of a Harbor Freight lift no less!! And, this was all performed during a 600 mile service at the request of the OEM!


Falling sphere viscometers


Creeping flow past a sphere.
Stokes' law is the basis of the falling sphere viscometer, in which the fluid is stationary in a vertical glass tube. A sphere of known size and density is allowed to descend through the liquid. If correctly selected, it reaches terminal velocity, which can be measured by the time it takes to pass two marks on the tube. Electronic sensing can be used for opaque fluids. Knowing the terminal velocity, the size and density of the sphere, and the density of the liquid, Stokes' law can be used to calculate the viscosity of the fluid. A series of steel ball bearings of different diameter are normally used in the classic experiment to improve the accuracy of the calculation. The school experiment uses glycerine as the fluid, and the technique is used industrially to check the viscosity of fluids used in processes. It includes many different oils, and polymer liquids such as solutions.
In 1851, George Gabriel Stokes derived an expression for the frictional force (also called drag force) exerted on spherical objects with very small Reynolds numbers (e.g., very small particles) in a continuous viscous fluid by changing the small fluid-mass limit of the generally unsolvable Navier-Stokes equations:

where:
is the frictional force,
is the radius of the spherical object,
is the fluid viscosity, and
is the particle's velocity.
If the particles are falling in the viscous fluid by their own weight, then a terminal velocity, also known as the settling velocity, is reached when this frictional force combined with the buoyant force exactly balance the gravitational force. The resulting settling velocity (or terminal velocity) is given by:

where:
Vs is the particles' settling velocity (m/s) (vertically downwards if , upwards if ),
is the Stokes radius of the particle (m),
g is the gravitational acceleration (m/s2),
ρp is the density of the particles (kg/m3),
ρf is the density of the fluid (kg/m3), and
is the (dynamic) fluid viscosity (Pa s).
Note that Stokes flow is assumed, so the Reynolds number must be small.
A limiting factor on the validity of this result is the roughness of the sphere being used.
A modification of the straight falling sphere viscometer is a rolling ball viscometer which times a ball rolling down a slope whilst immersed in the test fluid. This can be further improved by using a patented V plate which increases the number of rotations to distance traveled, allowing smaller more portable devices. This type of device is also suitable for ship board use. Currently, new equipment is developed for viscosity measurements. This equipment is survismeter and not only measures viscosity only but along with viscosity, it also measures surface tension, interfacial tension, wetting coefficient with high accuracy and precision. The survismeter also measures a new parameter which is noted as friccohesity. The friccohesity establishes an interface between the cohesive forces and the frictional forces within the similar or dissimilar molecules, dispersed in desired medium.Friccohesity is intimately associated with distribution of the particles due to oscillations of the velocity components on gaining kinetic energy. Since friccohesity depicts demonstration of cohesive or potential forces and kinetic or frictional forces together and thus the particle distribution is automatically involved in the behavior of the mixtures. It is similar to melting of the ice or the solid state materials in parts because the particles which gain kinetic energy start moving in x,y,z directions with definite pressure and thus the less is the cohesive force more is the pressure exerted by the kinetically moving molecules which strike the walls. But when the molecules move on the fixed track that is noted under the capillary phenomenon within the rigid wall example is Schr?dinger equation within the solid wall. Thus, the particles distribution occurs in 2 D and in such cases the friccohesity is called restricted friccohesity within boundaries.
 
Back
Top