It should be intuitively true that if you have two substances that are equally "sticky" but one is "heavier", the "heavier" one is going to have a stronger resistance due to inertia. Physically, the viscosity coefficient represents the sort of "strength" of the fluid's resistance to shear. And if density is constant then constant mu also implies constant nu - they're identical statements so your distinction here doesn't make much sense. If the density is variable then mu matters. Who is "people"? If you're dealing with a constant density flow, then nu is the parameter that matters. I am just trying to understand why people favor the constant mu over constant nu assumption How is that relevant to the question? Obviously if you are considering a problem with two totally different fluid properties then assuming constant viscosity or constant density are both very wrong. Consider two fluids in a container with low miscibility, the viscosity clearly non-uniform and dependent on local composition or density, while the temperature can be assumed constant I can come up with an example for the case I described. Off hand, you're probably okay with constant viscosity if you're operating in lower mach numbers. If that's "small" then assuming constant viscosity probably won't negatively impact you, particularly for high Reynolds number flows. If you're talking standard air, then look at Sutherland's law and compute the viscosity difference for your expected temperature differences. I'm wondering if these assumptions has any physical basis. I've seem derivations taking mu out of the spatial derivatives in compressible N-S equation. Maybe that's equivalent to the weakly compressible formulations? If you have density variations that's going to need some equation of state and coupling to the first law of thermodynamics, which makes assuming constant temperature a dubious idea. I'm sure someone somewhere formulates their governing equations like this, but it's not common, as far as I'm aware. The bath consists of a cylindrical glass vessel with a stainless steel cover with 50.8 mm diameter holes, motor stirrer, refrigerating coil with water connections, heating system, contact thermometer, external protection and insulating base. NOTE: 81-PV0116/A viscometer bath includes six holders for Cannon-Fenske viscometers.If the temperature is kept constant, but density may vary (compressible) Used to maintain theĬapillary type viscometers at a uniform temperature. Viscometer bath is used in the determination of both the kinematic and dynamic viscosity. Supplied complete with calibration certificate.įor determining the kinematic viscosity, all the above viscometers have to be introduced in the 81-B0116/A Viscometer bath by the appropriate Holder 81-B0116/H2 for Zeitfuchs cross-arm models and 81-B0116/H3 for BS U-Tube models. Used for the determination of kinematic viscosity of liquid asphalts (bitumen) road oil and distillation residues of liquid asphalts and asphalt cements at 135☌. Supplied complete with calibration certificate.īS U-Tube modified reverse flow viscometers Used for the determination of kinematic viscosity of liquid asphalts (bitumens) road oil and distillation residues of liquid asphalts and asphalt cements at 135☌. Supplied complete with calibration certificate. Cannon-Fenske Opaque models are suitable for opaque liquids. Used for the determination of kinematic viscosity of liquid asphalts (bitumens) and road oils at 60☌ and distillation residue of liquid asphalts and asphalt cements at 135☌.
0 Comments
Leave a Reply. |