another refrig question from the shark feeder

[ozmecheng]

ok gents i have recieved another set of questions from the ever so helpful shark feeder.

Heres question 1

http://i158.photobucket.com/albums/t96/s3080722/heatandmassquest1Correction.jpg

I can get a) and b) but am struggling with c) the mass flow rate. Any tips on whats the quickest and simplist way to go about it. Im thinking it has something to to with the compressor details (bore stroke rpm) that he has given.

Any help appreciated. Sorry for the huge image by the way.

Cheers

[US Iceman]

If you get good marks you have to share with us!:D

Compressor displacement will be higher than the volume flow of refrigerant.

Therefore, compressor displacement times the volumetric efficiency equals refrigerant volume flow.

Mass flow equals refrigerant volume flow divided by the gas density (at the inlet conditions to the compressor; temperature and pressure).

I'm signing off for the night. SteinarN will have to take over for me.:p

[ozmecheng]

ok anyone notice anything fishy about the data he has provided when i boot up refrig utilities for R12, the none of the enthalpy values correspond so whos wrong him or RU, but RU gets there data from ASHRAE dont they

[ozmecheng]

update. im having trouble posting big threads but i got the right answer for mass flow thanks all, the only thing that is buggin me now is the wierdo data and i cant seem to get the right answer for mechanical power required. Is this the comp work eaqual to m x (h2 - h1)???

[SteinarN]

update. im having trouble posting big threads but i got the right answer for mass flow thanks all, the only thing that is buggin me now is the wierdo data and i cant seem to get the right answer for mechanical power required. Is this the comp work eaqual to m x (h2 - h1)???

Yes, assuming h2 is corrected for the isentropic efficiency of the compressor.

[SteinarN]

ok anyone notice anything fishy about the data he has provided when i boot up refrig utilities for R12, the none of the enthalpy values correspond so whos wrong him or RU, but RU gets there data from ASHRAE dont they

The entalpy value of different charts and tables may vary. This is because the zero entalpy point is differently choosen. It's the same with degrees C and degrees F. The zero point is choosen different but each degree, C or F, has the same "worth" so to speak. Therefore never mix enthalpy values from different tables and charts. You can choose where to have the zero entalpy in a log P-h chart in Coolpack when you specify the chart for instance.

[ozmecheng]

Does anyone know how i can get cool pack to reporduce the same diagram that i have been given. im sure its something to do with referance but how do i use it, what values to i input.

Cheers
ozmecheng

[Josip]

Hi, ozmecheng :)


Does anyone know how i can get cool pack to reporduce the same diagram that i have been given. im sure its something to do with referance but how do i use it, what values to i input.

Cheers
ozmecheng

You should search RE forums for CoolPack, click on Search button...write down "CoolPack", mark show posts and click button GO and you will get about 170 posts with links shown below .....

but

http://www.et.web.mek.dtu.dk/Coolpac...s/CoolPack.exe (http://www.et.web.mek.dtu.dk/Coolpack/Files/CoolPack.exe)

http://www.et.web.mek.dtu.dk/Coolpack/UK/index.html

enjoy...

Best regards, Josip :)

[US Iceman]

Look at your chart and find where the enthalpy is zero. What temperature does this occur at? That is your reference temperature.

The rest are just isobars and isotherms.

[SteinarN]

Does anyone know how i can get cool pack to reporduce the same diagram that i have been given. im sure its something to do with referance but how do i use it, what values to i input.

Cheers
ozmecheng

Select the reference tap at the box where you select the refrigerant to draw. You can select between 3 different standards, default, Ashrae and IIR.

Edit: Seems to be the Ashrae standard in your table.

[ozmecheng]

ok thanks all im felling so much more confident in this subject than ever now :-)