Absolute Temperature Scale

The Centigrade and the Fahrenheit scales indicate relative temperature "Absolute" temperature may be measured only when the reading scale starts at a true zero temperature where, because there is no heat, there is no degree of heat.
This "absolute zero" is the basis of two other temperature scales. These are called the "Kelvin" and the "Rankine" scales.
The Kelvin (K) scale is referred to as the "absolute Centigrade scale" and is used in scientific work.
The Rankine (R) scale is the "absolute Fahrenheit scale"

These are the scales whichare applied in refrigeration and air conditioning.
A comparison between the normal scales and the absolute scales for boiling and freezing points is illustrated.

The Kelvin Temperature Scale :
Scientifically, it has been estabilished that a ga decreases 1/273 of its 0 degree Centigrade pressure for each degree that it is cooled. This condition exists for all gases. Thus, the temperature which no pressure is exerted is at the same point as the temperature at which there is no heat, or -273 degrees Centigrade.

Before gases change state, it is also true that a constant pressure there is an expansion (or contraction) of 1/273 of their volume for each degree Centigrade increase (or decrease). Referring to the illustration on which the temperature scales are compared, note that the unit degree on the Kelvin absolute scale is equal in value to the Centigrade degree.

To convert from the Centigrade to the Kelvin scale when the reading is 0 degree Centigrade, or higher, merely add 273 degrees. This is so because the zero reading on the Kelvin scale is located 273 degrees below 0 degree. For example, 35 degrees Centigrade, is equal to 273 + 35, or 308 degrees Kelvin.
The 273 represents the number of Centigrade degrees between absolute zero and the melting point of ice. Since the reading is 35 degrees above 0 degree Centigrade.,35 added to 273 to get the 308 degrees Kelvin value.

On readings which are blow 0 degree Centigrade., subtract the reading from 273 in order to get the Kelvin scale reading. For instance, -15 degrees Centigrade is equal to 273-15, or 258 degrees Kelvin.

The Rankine Temperature Scale:
On the F.scale,absolute zero is 460 Fahrenheit degrees below 0 degree Fahrenheit or -460 degrees Fahrenheit.This is place at which there would be no heat whatsoever and no motion of the molecules. Since the size of the units on the F. and R. scales is the same, ordinary thermometer temperatures in Fahrenheit may be easily changed to R, temperatures.
If the temperature reading is above 0 degree Fahrenheit.,merely add 460 to the reading. When a temperature reading is below 0 degree Fahrenheit., subtarct the reading from 460. The answer will then be in degrees on the R.scale.

EXAMPLE 1 : Change a 50 degrees Fahrenheit reading to R. absolute temperature.
460+50 = 510
Thus,the 50 degrees Fahrenheit. reading is 510 degrees R (Rankine
Absolute)
EXAMPLE 2 : Convert - 20 degrees F. to its equivalent R. value.
460-20 = 440
Thus, the -20 degrees F. reading is 440 degrees R.

The absolute scales must be used when calculating the changes in prossure thar a refrierant ga experiences when being superheated in the evaporator or in a cylinder left out in the hot sun.