# Liquid Air and Compressed Air Density

• I
• Anand Sivaram
In summary, normal air has a density of 1.225 kg/m3 at STP, while liquid air has a density of 870 kg/m3, making it 710 times denser. If normal air is compressed to more than 710 atmospheric pressure, it could potentially have a higher density than liquid air. This raises the question of whether it is possible to compress air to such high levels and if the gaseous state can have a higher density than the liquid state. A good resource to research the triple point is the Engineering Toolbox website. The triple point and critical point are important factors in understanding the behavior of air at different temperatures and pressures. If air is cooled to 132.63K at 1bar and then
Anand Sivaram
TL;DR Summary
Liquid Air and Compressed Air Density
Densities of Normal Air is 1.225 kg/m3 at STP, whereas the density of Liquid Air is 870 kg/m3. That means liquid air is 710x denser that normal air.
Then suppose, we compress normal air to more than 710 atmospheric pressure, then it could have a density more than that of liquid air. Is this understanding correct?
Basically, could we compress air to that high level? Can gaseous state have more density that the liquid state? What is the typical or practial maximum pressure achieved in an air compressor? Assuming all isothermal compression used.

I understood the logic of Triple Point and Critical Point. If air is cooled to 132.63K at 1bar and then compress it to 37.858 bar, it would liquefy. Above this temperature there is no liquid phase.
For water it is 647K and 218bar above which it is considered as supercritical fluid.

In that case should air at STP also be considered as supercritical fluid? Also what is the typical pressure obtained from air compressors? Industrial/Scientific ones?

I believe supercritical implies being above critical point in both T and P. So air at STP is just a gas.

Anand Sivaram

## 1. What is the difference between liquid air and compressed air?

Liquid air is the state of air when it is cooled below its boiling point and becomes a liquid. Compressed air, on the other hand, is air that is pressurized and stored in a container.

## 2. How is the density of liquid air and compressed air calculated?

The density of liquid air and compressed air can be calculated using the ideal gas law, which states that the density is equal to the mass of the gas divided by its volume. The mass of the gas can be determined by measuring its weight, and the volume can be calculated using the container's dimensions.

## 3. What factors affect the density of liquid air and compressed air?

The density of liquid air and compressed air is affected by temperature, pressure, and the composition of the air. As the temperature and pressure increase, the density also increases. The composition of the air, such as the amount of water vapor or other gases present, can also impact the density.

## 4. What are the applications of liquid air and compressed air?

Liquid air is commonly used in cryogenic applications, such as in the production of medical gases and in the cooling of electronic components. Compressed air has many industrial uses, such as in pneumatic tools, air compressors, and as a source of energy for vehicles.

## 5. How is liquid air and compressed air stored and transported?

Liquid air is typically stored and transported in insulated containers, as it needs to be kept at extremely low temperatures to remain in its liquid state. Compressed air is stored and transported in pressurized tanks or cylinders, and can also be transported through pipelines.

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