# Can air compressors be used to boil water?

I was just reading an article about how air compressors can be used as an energy source. As the air is compressed, its temperature increase significantly, and this energy stored as heat can be used to do useful work. However, I was wondering whether we can use air compressors to boil water when it gets in contact with this incredibly hot air. Also, are these devices viable for home uses as heat sources?

• Is that the most efficient use of the energy? Jan 26 at 13:18
• I acknowledge that this is not the most efficient use. I was just wondering whether it is possible or not. Also, I wanted to know whether it is safe for home use. Jan 26 at 13:25
• Waste heat from any process can be used in another process. Jan 26 at 13:55
• I understand that. I am asking if the air can be heated to enough temperature to boil water and whether it is safe or not. Jan 26 at 14:10
• Air can be heated due to compression to cause a fuel to self-combust - check out diesel engines. As for safe - who knows how you will operate any machinery. Jan 26 at 14:13

This is probably technically feasible (albeit requires a high level of sophistication and there are a lot of asterisks attached to it) but as mentioned above not practical or economical. Air has a very small density ($$1.3 \frac{kg}{m^3}$$)and a relatively small heat capacity ($$700\; J/kg$$), on the contrary water has many times larger density ($$1000 \frac{kg}{m^3}$$)and one of the highest heat capacities $$4180\; J/kg$$.

As a result about 1 kg of water has the same thermal capacity of approximately 7000 $$m^3$$ of air.

The point I am trying to come across is even though you can bring air to 100 degrees (you go a higher without a reaction) the heat inside the air would not be able to heat up sufficiently a mass of water more that 1 gr (and that's assuming that all the heat from the air is transferred to the water, which is not).

So, it would be possible to create warm water at best, but boiling (i.e. the evaporation heat) is probably out of the question.

what you propose is capturing the waste heat given off by the cooling fins on the outside of an air compressor's cylinders while the compressor is running. This is certainly feasible, but note the following:

We take the example of a Dayton two-cylinder air compressor driven with a 1 HP electric motor, working into a tank rated for an operating pressure of 120 PSI (I know this unit well).

It requires about one minute to run the tank up to 120 PSI. At the end of this cycle, the pump shuts down and if you put your hand on the cooling fins, they will feel quite warm but not hot enough to burn your fingers- certainly not warm enough to boil water.

Now if you had a water jacket surrounding the cylinders you could certainly use the compressor heat to preheat the water flowing into a conventional water heater and recoup those losses- but the money saved will be just a small fraction of the operating cost of the water heater without the preheat.

Yes, submerge the hot parts in water. If you can reach over 100 C, the water will eventually start to boil. You could keep the water at a constant level using a fill valve, such as the type you find in WC cisterns. Then you've basically created a steam boiler.