Estimating density, viscosity and thermal conductivity

In summary, the individual component values for density, viscosity, and thermal conductivity can be found from NIST at the correct pressure and temperature. However, to accurately estimate these properties for a gaseous mixture at 20 bar with 8 components, a weighted average may not be sufficient. The ideal gas law can also be used but may result in inaccurate values. For a more reliable method, the book "Transport Phenomena" by Bird et al offers mixing rules that can be used to calculate these properties.
  • #1
Mark Rice
37
0

Homework Statement


Hi there, I am designing a heat exchanger and I am really struggling to find out how to fairly accurately estimate the density, viscosity and thermal conductivity of a gaseous mixture at ~~20bar. There is 8 components in the mixture: methane, ethane, ethene, ethlyene oxide, CO2, water, argon and O2.

Homework Equations


PV=znRT (for denisty),
kmix = ka Ma + kbMb + knMn (for themal conductivity of mix

I have all the pure component values of density, viscosity and thermal conductivity from NIST at the correct P and T.

The Attempt at a Solution


My initial thought was to just simply do a weighted average of the sum of (properties*molefraction) however I feel this may not be that accurate. I have looked through perry's engineering handbook and some design textbooks and can't find a reliable method to work out these properties. I then tried to use the ideal gas law with the compressibility factor however the values this gave me Z was almost = 1 and my density values were way too low (I know what the values should be roughly as I have modeled it on design software).

Thanks,
 
Last edited:
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  • #2
See Transport Phenomena by Bird et al for mixing rules.
 

FAQ: Estimating density, viscosity and thermal conductivity

1. What is density?

Density is a measure of how much matter is contained in a certain volume. It is typically expressed in units of mass per unit volume, such as grams per cubic centimeter (g/cm3) or kilograms per cubic meter (kg/m3).

2. How is density estimated?

Density can be estimated by dividing the mass of an object by its volume. In a laboratory setting, it can also be measured using specialized equipment such as a balance and a graduated cylinder.

3. What is viscosity?

Viscosity is a measure of a fluid's resistance to flow. It is often described as the "thickness" or "stickiness" of a fluid. Viscosity is typically measured in units of pascal-seconds (Pa·s) or centipoise (cP).

4. How is viscosity estimated?

Viscosity can be estimated by measuring the flow rate of a fluid through a specific area under a certain pressure. In a laboratory setting, it can also be measured using specialized equipment such as a viscometer.

5. What is thermal conductivity?

Thermal conductivity is a measure of a material's ability to conduct heat. It is typically expressed in units of watts per meter-kelvin (W/m·K). Materials with high thermal conductivity can transfer heat more easily than those with low thermal conductivity.

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