Oil density and viscosity a 20°C

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Discussion Overview

The discussion centers around the viscosity and density of oil at 20°C, with participants exploring methods to extrapolate viscosity from available data at 40°C and seeking precise density values. The conversation touches on standards such as SAE and ISO, and the implications of oil composition on viscosity and density.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant seeks to extrapolate oil viscosity at 20°C from data available at 40°C, questioning the methods for doing so.
  • Another participant suggests using the temperature dependence of liquid viscosity as a resource for extrapolation, but later asks for the formula parameters needed for calculations.
  • Some participants note that SAE standards do not provide exact viscosity values, emphasizing that they are meant to indicate suitability for applications rather than precise measurements.
  • It is mentioned that viscosity can change over time due to chemical degradation and contamination, suggesting that a range of viscosities is more practical than a single exact value.
  • Concerns are raised about the variability of oil densities based on type and additives, with a recommendation to consult manufacturers for specific values.
  • A participant expresses uncertainty about whether they need to contact oil suppliers for formula coefficients, indicating a belief that such coefficients should be included in oil classification standards.

Areas of Agreement / Disagreement

Participants generally agree that viscosity and density can vary and that exact values may not be readily available. However, there is no consensus on the best method to extrapolate viscosity at 20°C or on the availability of formula coefficients in standards.

Contextual Notes

Limitations include the lack of specific formula parameters for extrapolation and the dependence on the definitions and classifications of oil types. The discussion does not resolve the uncertainty regarding the availability of exact values or coefficients.

serbring
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Hi,

I'm performing some calculations and I need oil viscosity at 20°C. I have checked in some standards like SAE or ISO, but the lowest temperature I have found is 40°C. How may I extrapolate the viscosity a 20°C? Moreover I need a precise value of oil density, does someone know this value?

Thanks
 
Last edited:
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Mugambo said:
Please refer to the temperature dependence of liquid viscosity on wikipedia:

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

Plug in the already available data (40°C) to extrapolate required data (20°C)

thanks for the posted link, however where can I get the formula parameters?

There an ISO standard for each ISO oil type?
 
The commonly referenced SAE standards are not meant to give "exact values". They are a way to label oils so that a particular brand of oil is known to be suitable for a particular application.

The viscosity changes over the working life of an oil as its chemical composition degrades and it dissolves contaminants from its environment, so the practical requirement is to stay within a RANGE of viscosities for a minimum amount of time (before the oil is changed), not to have an "exact" value of viscosity.

Oil densities can vary widely depending on the type of oil and the additives it contains.

If you want "exact" values for a particular brand of commercially available oil, the best source of information would be the manufacturer's technical services department.
 
AlephZero said:
The commonly referenced SAE standards are not meant to give "exact values". They are a way to label oils so that a particular brand of oil is known to be suitable for a particular application.

The viscosity changes over the working life of an oil as its chemical composition degrades and it dissolves contaminants from its environment, so the practical requirement is to stay within a RANGE of viscosities for a minimum amount of time (before the oil is changed), not to have an "exact" value of viscosity.

Oil densities can vary widely depending on the type of oil and the additives it contains.

If you want "exact" values for a particular brand of commercially available oil, the best source of information would be the manufacturer's technical services department.

So, do I have to ask to oil supplier for getting the formula coefficients? I believed in oil classification standards there are formula coefficients too. I haven't the standard, and so before to buy it I want to understan if it is really useful for my application.
Thanks
 

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