The kinematic viscosity of any medium would be found by following the formula: The unit of kinematic viscosity is Stokes (St) or centistokes (cSt). Kinematic viscosity is the oil resistance to flow created internally due to shear & gravity. And the measurement of viscosity is also different for these two types of viscosity. Oil viscosity units are different for both types. There are two types of viscosity, one is kinematic viscosity & another is dynamic viscosity. Just like this if any oil moves more slowly than other oil, that means the oil is more viscous than the other oil. For example, if you pour Olive oil & Honey from the same place then you will see that olive oil is going faster than honey, this is because of the higher viscosity of honey. Shortly you can also say that viscosity is the internal resistance of oil to flow. When working to higher temperatures the problems are less.This is the basic parameter of oil by which we can understand how much thicker or thinner the oil is. These should also be values taken from the oil to be tested rather than the typical values given for the oil grade. Thus, if you wish to use the Reynolds or ASTM D341 equations to find the viscosity of an oil at around 32☏(?) then you need to c calibrate the equations with viscosities appropriate to that temperature which the standard viscosities at 40☌ and 100☌ are not. I think the point here, relative to KimWonGung's original enquiry, is that pretty well any equation where the reference viscosities are at temperatures much above the target temperature at which you wish to know the viscosity, will give out unreliable results. This assumption may or may not work well for other types The Reynolds formula is best usedīetween two known v/T points, and it assumes a linear variation in the Lubricants used in industrial bearings typically do have their viscosityĭrop significantly as they get hotter. Temperature range one should not count on it without prior validation. The Reynolds formula is fine for its intended use, but using it outside that RE: Viscosity Chart for SAE 30 Oil jmw (Industrial) 6 Mar 11 07:01 10%) and these will certainly turn any calculations to mush. Manufacturers can supply lubricants with significant tolerances (e.g. The big risk is deviating to far away from the reference temperatures used to establish the equation (usually the viscosity at 4o☌ and at 100☌) and in extrapolating outside these values, especially when extrapolating to significantly lower temperatures.Īlso, one should note that the values used in the xlrotor equation are the nominal values for the lubricants. this is a very important caveat and is equally applicable to the ASTM D341 equation - under some conditions it is an excellent method but under others it can act like a random number generator. The temperature ranges that bearing lubricants typically operate in.Īdequate results for Reynolds formulation can be obtained if the knownĬhosen at the oil inlet temperature and below the maximum film temperature It two temperature/visc points as a baseline. Viscosity equation" and it is often used in the analysis of journal bearingsīecause it is computationally convenient. I believe some refer to this formula as "Reynolds The formula used to compute viscosity can be seen in the cells of the RE: Viscosity Chart for SAE 30 Oil jmw (Industrial) 4 Mar 11 18:43 So I'll have to do some research on this and for the moment withdraw the comment that ASTM D341workss for lubricants. I need to delve into my records for that report. unless (and it's a long time ago) we only compared at common temperatures and not calculated values. and that means I have to explain why the Castrol Blend 42 equation for lubricants tested out against ASTM D341 in process measurements. I an understand a significant viscosity at at much lower temperatures than the reference temperatures in an ASTM D341 equation, but not the significant errors between the temperatures.this would suppose than not only has the slope been adjusted but the entire temperature viscosity relationship. but I can't think why using numerical equivalents in kg/m 3 should give different answers of such significance at 230☏. So, can anyone explain why the temperature density and temperature viscosity relationships for lubricants should be different to other hydrocarbons? I'll know more if I can convert those weird density units. numerically equivalent to 8.17 x 10 -5sn/in 3 at 60☏ (817.35kg/m 3at 15☌)I get 756.6kg/m 3 at 230☏ while the number in the Xrotor spreadsheet is 7.62 x 10 -5.? I haven't found a conversion for the density units yet but if I take 817kg/m 3(i.e.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |