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Absolute Temperature
Absolute temperature is the temperature of air or gas measured starting at absolute zero. Absolute zero is the lowest possible temperature, where internal energy and ideal entropy are at their lowest values. The value for absolute zero comes from the temperature at which an “ideal” gas at a constant pressure would reach zero volume. In reality, gases compress into liquids or solids before this point.
Absolute temperature is essential for air compressors because some calculations, like air density and flow rate, require the temperature to be in absolute temperature units. Otherwise, the calculations would yield the wrong values and impact decision-making processes.
FAQs
Kelvin (K) and Rankine (°R) are the scales used for measuring absolute temperature. Kelvin is related to the centigrade scale, so an increase of one degree Kelvin would also be an increase of one degree Celsius. Rankine is related to the Fahrenheit scale in the same way.
The absolute temperature formula depends on whether you begin with Celsius or Fahrenheit. Here are the formulas for both:
Kelvin (K) = degrees Celsius (°C) + 273.15
Degrees Rankine (°R) = degrees Fahrenheit (°F) + 459.67
Since the scales are related, the conversion only requires addition. This formula shows that 0 K equals -273.15°C and 0°R equals -459.67°F.
Absolute temperature is most valuable in scientific and engineering calculations. It is especially beneficial for those involving gases and thermodynamics, such as the ideal gas law, which incorporates absolute temperature. This law is essential for relating air pressure, volume and the number of moles of gas.
Here are a few metrics relevant to air compressors:
- Air density: The air density impacts how much air a compressor can take in during each cycle. Compressors working with low-density air might need to run longer or harder to achieve the same output.
- Flow rate: This value is typically measured in cubic feet per minute (CFM). It details the volume of air delivered by the compressor each minute. You can use the CFM to determine if your compressor meets your application’s demands.
- Pressure: Compressors provide air at a particular force, sometimes represented by pounds per square inch (psi). Different processes require a specific pressure to operate effectively.
Using absolute temperature enables them to simplify equations, especially those involving gases, heat transfer and thermodynamics. Since absolute temperature begins at the lowest possible temperature, you will never have a negative value as you would when using Celsius or Fahrenheit. These negative values could create errors in calculations.
Ambient or operating temperatures are the temperatures at which air compressors operate, typically measured using Celsius or Fahrenheit. By contrast, absolute temperature isn’t used in everyday operations.
For example, the ideal operating temperature for an air compressor is between 50°F and 85°F (10°C to 29°C). You wouldn’t usually see these represented by absolute temperature because the numbers aren’t as understandable at first glance. They are also much larger: 50°F is 509.67°R, which is unwieldy.