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John McGru
16-02-2004, 09:44 AM
hihi all!

I'm encountered a problem during studying the compressor's volume efficiency.

I have grabbed data from Bitzer's software into text-formatted file, the data grabbed and taken into further condiferation are:
* T_ev (evaporation temperature),
* T_cond (condensing temperature),
* dT_oh (overheating temperature, fully used),
* Q_0 (evaporator capacity),
* QVb (displacement)
for all the range of semi-hermetic reciprotating compressors.

Then I calculated the enthalpy difference between the boiling point and suction point, the density of vapor at suction point, and the refrigerant mass flow (for mass flow, my calculations differ from Bitzer's ones on value less than 1%).
Then, using formula
qV = Q_0 / (dH * D)
or
qV = qm / D
(where qV - volume capacity of refrigerant, Q_0 - heat capacity at evaporator, dH - enthalpy difference calculated above, D - density of vapor calculated above)
and dividing it onto compressor's displacement, I have get the "volume efficiency" (as i think it should be):
lambda = qV/QVb

Then I composed the graph lambda=lambda(P_cond/P_ev), (P_condensing and P_evaporation have been calculated for T_cond and T_ev correspondingly).

As I read from literature, the "almost ideal" compressor should have this dependance (lambda(Pc/Pev)) been linear. But I see the strange behaviour of a line - it depends also on T_ev...
Pls, loot at the picture: http://mcgru.remholod.com/rx/2cc-3-2.jpg
It also does not fully correlate with T_ev...

Please, check it and tell me if I was somewhere wrong with calculations, or if I missed something important during calculations, or if it is some physical dependance...

Thank you in advance,
John