Calculations on the compressed air to an engine cycle

[Forhorse]

No it's just that heating a house in the heat of summer is pointless ... so the yield of the solution is variable.

[Eric DUPONT]

I do not think I am mistaken in saying that all the losses which cause a drop in yield are thermal, whether mechanical friction, heating of electric cables by the passage of current, etc. ... During a production of potential mechanical energy, whether by raising a mass to take advantage of gravity, compressing air to take advantage of the pressing force, or rotating a mass at high speed to take advantage of its inertial energy, etc. ... If we recover all of the dissipated thermal energy, we obtain a yield of 100%, is that correct?

it depends on how you count the energy and what you want to do with it. Numerically yes, the energy is conserved, so if you are the losses + the mechanical work recovered, you will find everything that has been supplied to the machine

To stay on topic (Calculations on the cycle of compressed air for an engine), if we compress air in order to run a compressed air engine, we produce about 65% of mechanical force in the form of compressed air stored in a tank, and 35% of heat is produced, of which 94% can be recovered (this is what is done in industry) for heating, hot water production, hot air , etc ... Even if the energies produced are different, from the moment they are used, they are not losses but rather "useful" energy. We can therefore compress air using 97% of the starting energy. I find that pretty good! The fact of not recovering the heat during the compression makes the use of compressed air not very profitable, and this is the case I believe with Guy Nègre's car.

It remains to be seen the performance of the engine ...

if you do an isothermal compression by spending 1 kwh at 10 ° c for example you have to dissipate 1 kwh of heat at 10 ° C, which is impossible but at 10,0001 ° c yes ... in theory. if the heat is evacuated to 20 ° C or 30 ° c to heat a house as much use a heat pump and compress the air to 10 ° c isothermally separately.

[Remundo]

Of course, by introducing a notion of nobility it lowers the yield ... Unless it is for you only a way of expressing that you do not like compressed air?

Neither I like nor I don't like.

We can have absolutely compressed air, or not, we can absolutely need low temperature heat, or not ...

It all depends on useful need. Thermodynamics has no mood.

If you like compressed air, there are large-scale storage (CAES: compressed air energy storage), and sometimes when the trigger is on, you burn fuel oil to swing everything in a gas turbine.
https://en.wikipedia.org/wiki/Compresse ... gy_storage

it is a well documented and long known technical field.

[obelix39]

No it's just that heating a house in the heat of summer is pointless ... so the yield of the solution is variable.

Fortunately, the industry needs heat all year round, and they do not recover heat from the heat wave ...

[obelix39]

if you do an isothermal compression by spending 1 kwh at 10 ° c for example you have to dissipate 1 kwh of heat at 10 ° C, which is impossible but at 10,0001 ° c yes ... in theory. if the heat is evacuated to 20 ° C or 30 ° c to heat a house as much use a heat pump and compress the air to 10 ° c isothermally separately.

I do not understand your calculation well? Could you explain it to me, please?

Otherwise, with a compressor, you can heat water, up to + 70 °. The operating temperature of a screw compressor is approximately 80 °.

[Remundo]

there is heat et heat...

there are some industrial processes which are satisfied with ambient temperatures, but the majority of them require very higher temperatures (X00 ° C) and no isothermal compression of ambient air can then meet the needs.

This is what I call "the nobility", you have to understand that not all forms of energy are created equal, with orderly mechanical / electrical work, we do what we want, with high temperature calories, we do a lot of things, with low temperature calories, it becomes very tight.

what I'm explaining here is a summarized, watered down and popularized version of the 1st and 2nd principles of thermodynamics. Must work thermodynamics not to say or imagine too much nonsense in the matter.

[Remundo]

if you do an isothermal compression by spending 1 kwh at 10 ° c for example you have to dissipate 1 kwh of heat at 10 ° C, which is impossible but at 10,0001 ° c yes ... in theory. if the heat is evacuated to 20 ° C or 30 ° c to heat a house as much use a heat pump and compress the air to 10 ° c isothermally separately.

I do not understand your calculation well? Could you explain it to me, please?

Otherwise, with a compressor, you can heat water, up to + 70 °. The operating temperature of a screw compressor is approximately 80 °.

this precisely means that we are very far from isothermal compression, and we are not in the adiabatic either since we allow ourselves to heat water to 70 ° C

In summary it promises a very bad compression performance, with low temperature calories, which even if they are recovered, do not allow much other than taking a hot bath or thermising a home ...

A well-used heat pump would do the job with far greater efficiency.

And a very neat compressor with isothermal evolution would compress air with an efficiency close to 100%

Eric is absolutely right here.

[obelix39]

Of course, by introducing a notion of nobility it lowers the yield ... Unless it is for you only a way of expressing that you do not like compressed air?

Neither I like nor I don't like.

We can have absolutely compressed air, or not, we can absolutely need heat low temperature, or not...

It all depends on useful need. Thermodynamics has no mood.

I do not find that 70 ° is a "low temperature", but it is relative (like the rest) ...

[obelix39]

if you do an isothermal compression by spending 1 kwh at 10 ° c for example you have to dissipate 1 kwh of heat at 10 ° C, which is impossible but at 10,0001 ° c yes ... in theory. if the heat is evacuated to 20 ° C or 30 ° c to heat a house as much use a heat pump and compress the air to 10 ° c isothermally separately.

I do not understand your calculation well? Could you explain it to me, please?

Otherwise, with a compressor, you can heat water, up to + 70 °. The operating temperature of a screw compressor is approximately 80 °.

this precisely means that we are very far from isothermal compression, and we are not in the adiabatic either since we allow ourselves to heat water to 70 ° C

In summary it promises a very bad compression performance, with low temperature calories, which even if they are recovered, do not allow much other than taking a hot bath or thermising a home ...

A well-used heat pump would do the job with far greater efficiency.

And a very neat compressor with isothermal evolution would compress air with an efficiency close to 100%

Eric is absolutely right here.

Regarding the use of recovered heat, there are not only hot baths and central heating, there are also industrial uses.

And this recovery is just so as not to waste it. The goal is to obtain compressed air which will pump a maximum of heat on decompression by using the heat given off by a combustion engine with poor performance (those with which we drive today). The aim of the operation is to produce a thermal equilibrium between two motors, one thermal (internal combustion consuming gasoline or diesel) producing unnecessary heat, and the other pneumatic requiring this heat to provide a full yield. My goal is not to use a compressed air engine to move a vehicle, it's just to use the 60% energy that an internal combustion engine wastes. Maybe it's silly?

[Forhorse]

Regarding the use of recovered heat, there are not only hot baths and central heating, there are also industrial uses.

What industrial use are you thinking of? Because having worked a lot in the industry, in various fields, I have not seen many processes that were content with 70 ° C ... hot water for washing in the food industry perhaps, and still ...