View Full Version : VC or not VC

01-02-2002, 04:43 PM
Can a multi phase fluid at entry centrifugal compressor with a secondary stage liquid booster pump be correctly described as a vapour compression cycle.

Best suggestion so far is a multiphase reverse rankine.....

Your go!:confused:

Prof Sporlan
01-02-2002, 07:41 PM
The vapor compression cycle is the idealized cycle for most modern air conditioning and refrigeration systems, i.e., isentropic compression; isobaric heat rejection; isobaric/isothermal heat rejection (condensation); isenthalpic expansion; isobaric/isothermal heat addition (evaporation).

The Rankine cycle is closely approximated in actual steam turbine plants. Its basic cycle is: isentropic compression; isobaric heat addition; isobaric/isothermal heat addition (evaporation); isentropic expansion; isobaric/isothermal heat rejection (condensation).

The Prof doesn't recall running across an idealized cycle described as "reversed Rankine", though no doubt it could be put on paper. Since it would seem the turbine would have to be reversed in such a cycle, it would seem an isentropic expansion process would be needed.

But if we have a vapor compressed by a centrifugal compressor, then condensed, then boosted by a pump, then the idealized cycle should read: isentropic compression; isobaric heat rejection; isobaric/isothermal heat rejection (condensation); isentropic compression...... with a few more steps to be added.

Your "multi-phase" fluid term is confusing. You mean a fluid at its triple point, i.e., solid, liquid and vapor coexist? Or a fluid that will change from vapor to two-phase to liquid states doing the cycle?

02-02-2002, 12:42 AM
Give us a lot more information

ie !! D values on all refrigerants used and the type of recognition that it would require:rolleyes:

02-02-2002, 03:20 AM
Originally posted by Fridgetech
Is Derek referring to organic gases as fluids, per the henry valve fellow?

Multi phase? Perhaps a screw turbine is more tollerant of vapour/liquid mixes, a turbine/impeller not as, for erosion.

Why would it matter to the nature of the cycle, being multi or not multi phase? Inefficiency by wasted throughput maybe? How is that important to the question, or is it just hapstance?

erosiIntuitively, lol, it IS, surely, a Revere Rankine cycle. Superheating before the turbine is required for at least one reason, to avoid turbine on. Superheating by the impeller is unavoidable.

Purhaps some of the fluids used in organic rankine cycles do partially condense on their way, isentropically, through the turbine and this has promted you to consider wet fluids entering an impeller? In that case, if it were dry vapour entering the impeller it might be the equivalent of a single phase reverse rankine, reverse rankine since there is a liquid pump, of course :)

Dan would normally ask these type questions but he seems to be away? :)

I give up, what's the answer? :) [SIZE=3]

02-02-2002, 10:21 PM

Do you realy know what you are talking about or are you just a WIND UP MERCHANT

All the best JASPER:D :D :D :rolleyes: :eek:

02-02-2002, 10:32 PM
One other point MARC is the henry your talking about ELECTRICAL or mechanical

:p :p

06-02-2002, 12:53 PM

Without giving the game away

Get out an R11 Ph chart (no I'm not using that just pretend)

Point 1 is 0.1 Mpa at 360 kg/kj Inlet Turbine
Point 2 is 0.6 Mpa at 450 kg/kj Condenser (air)
Point 3 is 0.56 Mpa at 270 kg/kj Pump
Point 4 is 0.8 Mpa at 290 kg/kj Orifice
Point 5 is 0.11 Mpa at 280 kg/kj Evap

Its not that I know the answer but if I put it all down in writing I don't want some smarta**e giving me a lecture on cycles.

08-02-2002, 04:11 AM
Dan would normally ask these type questions but he seems to be

LOL. Just got back into town. I am out of my league here, but the first thoughts that came to my mind were how the components and processes compare between a vapor compression refrigeration cycle and the rankine cycle. After all, a motor and a generator are the same at a basic level.

pump=compressor (some of the duty, anyway)
turbine=throttling device? desuperheater circuit in the condenser? Hmmmm.

LOL! I have the metering device in front of the condenser! I am not thinking backwards enough.

It does require mirror thinking.... where some things reverse and others don't appear to.

Whereas, with a compressor we want a dry feed to the unit, we want a wet feed to a pump.

Whereas, with a turbine, we want a dry feed but a wet feed to an expansion valve...

The Rankine cycle doesn't appear to rely on large pressure differentials.... perhaps it would more easily be compared to an absorption system running backwards.

Nice ponderosity, Derek.

Prof Sporlan
08-02-2002, 04:15 AM
Without giving the game away
Since we have flow thru an orifice, and this flow apparently does not assist with the turbine operation, we cannot have a Rankine cycle, or a reversed Rankine cycle. Flow thru an orifice will be isenthalpic, not isentropic as required by the Rankine cycle.

It would seem we have a standard vapor compression cycle, with a secondary isentropic compression. An idealized refrigeration system with an LPA if you will.

08-02-2002, 04:25 AM
Can a multi phase fluid at entry centrifugal compressor with a
secondary stage liquid booster pump be correctly described as a
vapour compression cycle.

I may not understand the question. I would say "Yes." after rereading your first post, Derek. You have vapor, a compressor and an expansion device just like I see all the time in vapor compression systems. Forget my other post. I wondered away.:)

12-02-2002, 06:33 PM
Wow Marc

Moderator with attitude.

No I just had to admit that I'm not perfect and someone queried the use of vapour when in practice its not. I could baffel with bull **** but I ain't paid for that.

I'm sticking with cycle as VC just thought you'd like the discussion.

OK perfect gas cycles are just that and real life is well different. Tell you when it goes to print and see if the knockers will accept that saying it can't be done is just a challenge to me.

Dan and Prof ...the beers are in! :cool: