Question about temperature and Specific Weight

  1. 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
     
  2. jcsd
  3. Borek

    Staff: Mentor

    Absolute in this context means any scale for which zero is at absolute zero. 460+F is also known as a Rankine scale.
     
  4. So Rankine scale goes with british units lb/ft^3 and kelvin scale goes with international units like kg/m^3?
     
  5. Borek

    Staff: Mentor

    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).
     
  6. 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.
     
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