Acetone working fluid

GlynnHeeswijk

Is it possible to use acetone as the working fluid in a Rankine cycle engine (like steam engine)?
How efficent would it be? I want to use it becasuse it boils at just 56.5C.
many thanks.

tuananh3ap

i think: have many reason the acetone doesn't use like a power example: expensive, steam fast, don't produce many etc
but i know have many engine working by alcohol

Mech_Engineer

I'm finding it relatively difficult to find available thermophysical propeties of pure Acetone, but I can tell you that boiling temperature of the fluid has little effect on the overall efficiency of the cycle when compared to things like superheat, operating pressure, and pumping efficiency.

Why do you want to use Acetone? It's poisonous, flammable, and not generally used in this application; where as water is non-flammable, non-toxic, and thermodynamic data is readily available. There are also many fluids with low boiling temperatures that are relatively safe and have lots of available data, like refrigerants.

GlynnHeeswijk

Hi thanks for the reply i'll have a look at diffrent refrigerants. It can be any liquid has long as it has a low boilling point and would be reasonably efficent.
many thanks.

stewartcs

My version of REFPROP (from NIST) has acetone properties if you are interested.

CS

Mech_Engineer

I checked NIST's online database, but they don't have Acetone properties there.

Are you able to generate a h-P chart (Enthalpy on the x-axis, Pressure on the log-scale y-axis) with Temperature, saturated liquid/vapor, specific volume, and entropy contour lines on the chart? Using such a chart would enable the calculation of basic effciencies and flow rates for the system being discussed.

Similar to the attached Propane properties chart I have attached.

Attached Files

Thermodynamic Properties of Propane.pdf (172.4 KB, 5 views)

stewartcs

Yes. The plot export is hard to read though.

CS

EDIT: Just noticed it won't let me include anything but the Enthalpy and Pressure. I'll play around and see if I can get more on it somehow.

Attached Thumbnails

 

stewartcs

OK, I think this should have enough information on it.

Still hard to read though.

CS

Attached Thumbnails

 

Mech_Engineer

Stewart-

Thanks for the charts, but after thinking about it some I realized it's premature to try and do any calculation without first understanding more about what the OP is trying to accomplish.

I think you may be missing a critical point in the design of Rankine Cycle engine- it's efficiency will be limited by the "boiler's" maximum temperature and ambient temperature.

I suspect you are wanting a working fluid with a low boiling temperature so you can use waste heat from something that is at a relatively low temperature. If this is the case, this would mean that you can find the maximum possible efficiency of the cycle by finding the Carot Cycle Efficiency between a hot and cold reservoir.

[tex]\eta=1-\frac{T_{C}}{T_{H}}[/tex]
http://en.wikipedia.org/wiki/Carnot_cycle

In the case of Acetone, if we assume the heat source heats the Acetone to saturated vapor at 56.5 C (329 K) and the fluid is then cooled in the condenser to ambient of about 22 C (295 K), that would mean that the absolute maximum efficiency the system could achieve would be 10% (this approximation doesn't work anyway, since saturated Acetone vapor at 56.5 C is at 1 ATM, and your turbine needs a pressure difference to run). Because this is a maximum, your efficiency would be less due to losses in the turbine, pump, condenser, and "boiler."

Basically, you need to get the "high" temperature as high as possible to get your system efficiency up. What fluid is being used in the process is just a matter of selection based on thermodynamic properties.

So, what we really need to know is what heat source you're planning on using, mainly it's available temperature.

GlynnHeeswijk

I have a water cooled electric motor, and i have measured the heat output (using specific heat capacity of water) and calulated it gives out about 6Kw of waste heat and the water goes to 65C. And i wanted to see how much of that energy could be harnessed (its not for any purpose just a little experiment), i looked at thermoelectric which would be a good option but there is little i could find on high power devices.

Mech_Engineer

Well if the heat source is at 65 C, and your "cold-sink" is ambient air at about 22 C, the maximum efficiency you can get out of the system is 12.7%. Odds are you would get about half to three-quarters of that, so maybe 7%. If the motor is indeed putting off 6kW of heat (that sounds like a lot of waste heat, what's the total power output of the motor?), then you will probably be able to get about 400W back.

GlynnHeeswijk

The motor draws 26Kw (under high load (what i tested water temp with) ) and can run at 18kw all day. It runs at 72v.
I wont do it on the electric motor because the efficency is so low but may try a higher temp system for fun.
Thank you very much for the help Mech_Engineer, stewartcs and tuananh3ap.