Question about temperature and Specific Weight

[petersun825]

Hello,

I know there are many different representations of temperature, there's 4, 1) Fahrenheit 2) Kelvin 3) Celsius then there's 4) T = 460 + F

In my fluid dynamics review book To calculate specific weight γ= P(pressure) / (R * T) = lb/ft^3, it explained that T should be absolute temp so I used 2) kelvin, but the book used 4) T = 460+F

Can somebody explain what 460 + F stands for??

Thanks,
Peter

 

[Borek]

Absolute in this context means any scale for which zero is at absolute zero. 460+F is also known as a Rankine scale.

 

[petersun825]

So Rankine scale goes with british units lb/ft^3 and kelvin scale goes with international units like kg/m^3?

 

[Borek]

Not necessarily. Units used will change the R value - it can be calculated to use any combination of mass, length and temperature units (http://en.wikipedia.org/wiki/Ideal_gas_constant - see the table on the right). The only important thing is that the temperature scale is absolute (as explained in my previous post).

 

[dawin]

So Rankine scale goes with british units lb/ft^3 and kelvin scale goes with international units like kg/m^3?

Generally, yes, you'll see those pairings. Not necessarily just those units--other units will be used besides lbs/ft^3. Fahrenheit is usually used by those that use US Customary units, and we happen to also use lbs, inches/ft, etc, so the pairing is usually natural.

1 °Ra is equivalent to a change of 1 °F. Whereas 1 Kelvin is equal a change of 1 °C.