Efficiencies of compressor in industrial chiller system.

[chonvlc]

Homework Statement

Data: http://postimage.org/image/4bb6y6jrd/
Variables: http://postimage.org/image/sk8xnrru5/

Question asks to find mechanical, volumetric and isentropic efficiencies.

The test facility is based around a chiller of nominal cooling capacity of 25 kW. The chiller is equipped with shell and tube heat exchangers, an externally equalised thermostatic expansion valve, a 4 cylinder hermetic compressor designed for use with R404A and appropriate controls. The compressor displacement is 33.07 m3/hr at 1450 rpm.

Homework Equations

n(isentropic)=isnetropic work per unit mass of compressed fluid/actual work per unit mass of compressed fluid.

n(volumetric)=actual vol of fresh gas infuced/compressor swept volume.

n(mechanical)=work on gas/work delivered to shaft.

work on gas=massflowrate (h2-h1) where h2 is enthalpy after comrpession and 1 is before compression.


If you could just show me how to do the first one, or explain the method that'd be great.
e-mail chonssdw@gmail.com for steam tables, or assume random values just to show the point.

 

[Valkarie]

The Attempt at a Solution Isentropic Efficiency:n(isentropic) = (h2-h1)/(h2s-h1)Where h2 and h1 are the enthalpies of the gas after and before compression, and h2s and h1 are the isentropic enthalpies corresponding to the same temperatures and pressures. The isentropic enthalpy can be found using steam tables or assuming random values. For example, assume h2=2500 kJ/kg, h1=1000 kJ/kg, h2s=2500 kJ/kg, and h1s=1000 kJ/kg. n(isentropic) = (2500-1000)/(2500-1000) = 1.0 Therefore, the isentropic efficiency is 1.0.