Novel air conditioning system

As there have been so many posts lately about A/C systems, does anyone
remember the system
that was developed several decades ago that used compressed air as the
refrigerant?

It came to mind as I was reading these posts.

It was abandoned, probably for a number of reasons, but used no refrigerant
charge at all.

wrote:
> As there have been so many posts lately about A/C systems, does anyone
> remember the system
> that was developed several decades ago that used compressed air as the
> refrigerant?
>
> It came to mind as I was reading these posts.
>
> It was abandoned, probably for a number of reasons, but used no refrigerant
> charge at all.
>
>
I do remember several like that. I flew jet trainers for awhile (until
I washed out), and remember the simple system they used. In fact many
jet planes today simply bleed off a little of the compressor air, expand
it through a heat exchanger, and feed it to the cockpit or cabin.

I have heard that there is an efficiency issue, that air may not give as
efficient a cooling, BTUs per hour of cooling per hp per drive, but I
have never pulled out my old thermo textbooks to confirm this myself. I
do know that a phase change system does make the system a lot smaller,
and in those bleed air systems the air does not change phase.

"Don Stauffer" > wrote in message
...
> wrote:
> > As there have been so many posts lately about A/C systems, does anyone
> > remember the system
> > that was developed several decades ago that used compressed air as the
> > refrigerant?
> >
> > It came to mind as I was reading these posts.
> >
> > It was abandoned, probably for a number of reasons, but used no
refrigerant
> > charge at all.
> >
> >
> I do remember several like that. I flew jet trainers for awhile (until
> I washed out), and remember the simple system they used. In fact many
> jet planes today simply bleed off a little of the compressor air, expand
> it through a heat exchanger, and feed it to the cockpit or cabin.
>
> I have heard that there is an efficiency issue, that air may not give as
> efficient a cooling, BTUs per hour of cooling per hp per drive, but I
> have never pulled out my old thermo textbooks to confirm this myself. I
> do know that a phase change system does make the system a lot smaller,
> and in those bleed air systems the air does not change phase.

Phase change generally gives a lot more heat capacity, as you say. High
pressures
can at least partially offset this fault of compressed air systems.

I seem to remember there were noise issues as well...I would expect there to
be
a goodly whack of ultrasonic energy generated in expanding very high
pressure air.
Although you may not be able to hear it, it is still there, and some people
seem to be
sensitive to it. I'm sure that could be insulated.

A couple of us bombarded the university physics lab one afternoon with
ultrasonic
waves and noted the reaction when students came to class. Some seemed to
'feel'
something was wrong, became agitated. (Others never woke up)

"Don Stauffer" > wrote in message
...
> wrote:
>> As there have been so many posts lately about A/C systems, does anyone
>> remember the system
>> that was developed several decades ago that used compressed air as the
>> refrigerant?
>>
>> It came to mind as I was reading these posts.
>>
>> It was abandoned, probably for a number of reasons, but used no
>> refrigerant
>> charge at all.
>>
>>
> I do remember several like that. I flew jet trainers for awhile (until I
> washed out), and remember the simple system they used. In fact many jet
> planes today simply bleed off a little of the compressor air, expand it
> through a heat exchanger, and feed it to the cockpit or cabin.


The air cycle isn't quite that simple, there are a series of heat bulky
exchangers involved before the bleed air is fed to the cooling turbine. The
temperature of the cooling air available to aircraft heat exchangers is
generally much colder than a car will ever see during the months A/C is
needed and the volume of compressed air to feed the system is only available
from turbine engines.

http://www.boeing-727.com/Data/systems/infoaircon.html