Here's a Neat One

Techman

That's what I did on board the submarine SS-346, and that's where I started my ACR training.We had 2-50ton r-12 units ,water cooled of course!I'm stuck in the "requirers some thought "mode, so I'll get back to you when I get unstuck.

Eugene Silberstein 3

Requires Some Thought

Here's a neat question to ask perspective employees:

What will happen to your subcooling calculation if non-condensable gases gets into the system? Why?

Care to take a stab?

don_182

i would

think it would act like a undersize or dirty condenser.
Low subcooling and possible flashing.
I also wonder if the surface area was pretty big would we still not see some subcooling along with the added heat of compression.

Empire_2

I'll stab at this one.

Due to Non-Condensables, the head pressure will be higher than normal. as a result you will see a large increase in your sub-cool reading, but that is only because the head pressure is eronious,....The sub cool effectively will be the same, but your brain will tell you different. Now you start adding ref. to lower the S/C and find your head is way out of wack, conclusion, must be a restriction,....Now you look and look and when you think you got it, BAM... the same thing.

If able, pump er down and check the TP chart for correlation.

My .02 Bare in mind I answered off the top of my noggen. Ask my wife, she say's sometimes I don't think, but I thought of the first thing that came to me.;-)


Mike T.

Eugene Silberstein 3

I would have figured....

I figured that the "three musketeers" (Don, Terry and Mike) would have been the first three to chime in on this one.

Hmmmmmmmmmmm

Seems like there is some dissension in the ranks....

Wouls anyone else like to voice an opinion on this one?

Techman

How's this?

Professor,I think the subcooling stays the same. Higher (than normal)cond temps would increase subcooling,decreased condensing surface,but higher temps transfer quicker, so, s/c stays the same.NOW,HAVING SAID THAT, I think I'll go into my library and take out my copy of "Pressure/Enthalpy Without Tears " and see if I have to do a little more reading. Well Professor,Thumbs Up or Thumbs Down?!?!?!

Techman

Musketeers

Hi You Two! Who's Moe? Who's Larry? Who's Curley? Oh !! Not those Three? Well, anyway ,Enjoy your day!

Empire_2

T Man

"Why CERTAINLY"!!! na, na na,.....Woo,b woob woob.

Mike T.

Funny thing, the PC said the text I typed looks like Polish and would I like to convert to same???? "Why Certainly"!!!!! I love Polish Sausage......

Techman

Certanitly!

I happen to be of Polish heritage!Enjoy your dayski!

Empire_2

OK Gene,...Time to spill the answer.......

If we Waite to long we get bored.........

Mike T.

don_182

Hey Mike

he likes to make it a cliff hanger.

I too would like to know what effects air has on the subcool temps.Never ever try checking them when running into noncondensible.

I also wonder what other effects it would have on a system
being meter with a orfice verse one with a txv.

I always hear lots of people make claim that the air with set in the upper part of the condenser and not travel thru
out the system.

I've herd guys over the years make claim that they have high
subcool temps and high superheat reading with non condensible.I also herd that it does travel and it will make a txv hunt when it enter first and then the freon finally gets there it act normal.

Then one will hear that yes it effects orfice system more so
then it does a txv because of the higher pressure, not the air.

As you can tell by our replys the brave,the proud,the fearless three amigos that, the opinions are across the board.

Empire_2

Good point's Don

The way I see it,...since you can compress air, but not make it change into a liquid form, the Non-Condensables will usually show up at different points in the system through out the cycle. My thinking at the point of compression, there will be an increase in head pressure which immediately effects the S/C reading, but only as a temp reading vs head pressure. That is why I stated that some will add ref to lower the S/C when in actuality there is nothing wrong with the S/C, BUT the hi head tell you so. Bottom line if there is non condensables in the system you cannot possibly determine the proper sub-cooling because there is non Cond in the system.

I think I'm gonna go and find Gene and strap him to the ladder racks, drive around town until he gives up the answer...:-)

Mike T.

Eugene Silberstein 3

The answer

Thanks to our friend Dalton, and his gas law (that states that the total - vapor - pressure in a sealed vessel is equal to the sum of the pressures of all of the individual vapors in the mixture in the vessel), we will find that, with non-condensables in the system, our subcooling calculation will be higher than normal.

As Mike mentioned, the actual subcooling of the refrigerant will take place but, because the head pressure is abnormally high (thanks to Dalton), the calculation result will be excessive.

Don, you also mentioned that you have heard a number of different opinions regarding non-condensables on the low side of the system. Here is my take on the situation.

On a properly piped evaporator, the refrigerant should, for the most part, be piped into the bottom of the coil and should leave the coil from the top. The reason for this is that we have a saturated refrigerant at the inlet of the coil and as the refrigerant passes throug the coil, it vaporizes. The refrigerant vapor is less dense than the saturated liquid, rises up in the coil and helps refrigerant flow. Since the refrigerant is flowing up and the vapor itself is trying to push up, we are able to maintain the velocity of the refrigerant.

If we fed refrigerant from the metering device into the top of the coil, the velocity of the refrigerant would be reduced. The liquid refrigerant will be pushing doen in the coil, while the vaporized refrigerant will be pushing up as it is less dense than the liquid. Since the liquid and the vapor are pushing in opposite directions, the velocity will be reduced.

So, if there is air in the low side of the system, it will rise toward the top of the coil. Since the outlet of the coil is at the top, the air or other non-condensable gas will flow freely out of the coil. This is why the evaporator superheat will be very close to normal. There is rarely an accumulation of non-consables gas in the evaporator coil of a properly piped system. Now for the high side.

Since the condenser has vapor refrigerant at its inlet and liquid at its outlet, the hot gas from the compressor is piped into the top of the condenser and the liquid leaves the condenser coil from the bottom. Here's the neat part.

If there is non-condensable gas being discharged from the compressor, it will enter the condenser along with the hot discharge gas. As the refrigerant condenses, it will push down in the coil, as the liquid refrigerant is more dense than the vapor. Now, since the non-condensable gas cannot condense, it remains a vapor that is less dense than the liquid. The non-condensables cannot, therefore, reach the outlet of the condenser coil, which is at the bottom.

So, in a nutshell, the superheat readings on the low side of the system will be very close to normal as there are no non-condensables on the low side. The condenser subcooling, on the other hand, will be excessive thanks to Dalton.

Whew!

Empire_2

Thanks Eugene,.....:-)

I'm turning the truck around now. I wont put you up on the rack's after all,....But Ya think I could have some gas money???? I was almost at your house....


Mike T.

Eugene Silberstein 3

Too Funny

You're definitely welcome to continue your journey... I just ordered dinner!

Techman

Odd Man Out

I would join y'all for dinner,BUT,I'm stuck her re-re-reading my "P/E without tears " book (By Professor Silberstein).Darn, I missed another one! Enjoy your dinner!!!

Eugene Silberstein 3

You can come to the next one!

You're more than welcome to come to the next one... You are definitely a lot closer to me than Mike T. is!