Condensation Temperature?

[Indy2010]

Forgive my noob question but

How can you determine the condensation temperature of a gas in a light commercial refrigeration condenser?

and is the saturation point effected by pressure?

[marc5180]

Connect your gauges and use a PT comparator ( or measure the temperature of the middle passes of the condensor)

The saturation point varies with the pressure

[marc5180]

Maybe have a read here;

http://www.refrigeration-engineer.co...ad.php?t=19701

[Indy2010]

Thanks I have read the 101 thread and found it verg interesting and informative unfortunately I could not find an explanation to my above question. Remember I'm a noob here. Seems that the liquid line connection for the high side gauge will be influenced by subcooling to some degree.
Will a p/t chart indicate the saturation point from vapor to liquid based upon pressure? Is this point called the bubble point?

[Indy2010]

Dupont has p/t charts that show bubble point for some gases yet not for others (I'm thinking they may be blends) is that a reason?

Also back to the bubble point. Is this the point at which a gas vapor shows the first sign of condensing ?

[TRASH101]

Indy,

Bubble point = evaporation, boils, phase change from liquid to gas.

Dew point = Condensation, mists, phase change from gas to liquid.

[marc5180]

Dupont has p/t charts that show bubble point for some gases yet not for others (I'm thinking they may be blends) is that a reason?

Also back to the bubble point. Is this the point at which a gas vapor shows the first sign of condensing ?

Hopefully this will help;

http://www2.dupont.com/Refrigerants/...temp_glide.pdf

[Tayters]

Copied from this web page.

http://www.refrigerants.com/faq.htm#nine:

Bubble point is the temperature where the saturated liquid starts to boil off its first "bubble" of vapor. (Picture a pot of liquid with the first bubbles starting to appear.) It is also called the "liquid side temperature/ pressure relationship." Dewpoint is the temperature where saturated vapor first starts to condense, or the last drop of liquid evaporates. (Picture a room full of vapor with a few drops forming on the ceiling.) This is also called the "vapor side temperature/ pressure relationship."

The condensing temperature is usually 15 to 20K above ambient for an air cooled condenser. Most commercial stuff seems to be around the 40*C mark unless there is something wrong.
Temperature is the important part. The pressure helps you determine condensing temperature.

Hope that helps,

Andy.

[Indy2010]

Cool thanks guys for all the explanations

Just when I think I'm getting a handle on what's going on I then have a bunch more questions...

Thanks again for all the help, much appreciated

[Indy2010]

Ok perhaps I've been over thinking this one.

Let' see if I understand now, if we take the pressure reading from the liquid line service port and convert it to a temperature using the gas P/T chart the result is for all practicable purposes the dew point (assuming no pressure loss through the condenser) which is the answer to my OP question.


How am I doing?

[Gary]

For a given pressure, every liquid has a boiling temperature.

For example, at atmospheric pressure (0 psi) water boils at 100C/212F. We could say this is it's "boiling temperature", or since we are turning it into a vapor we could say this is it's "evaporating temperature", or since vapor bubbles are forming we could call this it's "bubble point temperature". All mean the same thing.

If we take hot steam at atmospheric pressure (0 psi) and cool it to that same 100C/212F it condenses to a liquid, so we could call this it's "condensing temperature", or since it is forming liquid droplets (dew) we could call this it's "dewpoint temperature".

All of these terms describe the same temperature point for water at 0 psi, but also describe whether we are adding or removing heat.

What if both liquid and vapor are present and we are neither adding nor removing heat? What do we call this temperature then? If we are simply describing the temperature at which the process could be driven in either direction (liquid to vapor or vapor to liquid) for water at 0 psi, we call this it's "saturation temperature".

Which terminology we use depends on whether we are simply describing the temperature point or also describing the process... so...

The saturation temperature for water at 0 psi is 100C/212F.

The evaporating temperature for water at 0 psi is 100C/212F.

The condensing temperature for water at 0 psi is 100C/212F.

[Gary]

Taking this a step further, "dewpoint temperature" and "bubble point temperature" are terms we use to describe a mixture of refrigerants which have different saturation temperatures (zeotropic mixture).

Let's say we have two refrigerants.

The saturation temperature for refrigerant "A" at 0 psi is 10C/50F.

The saturation temperature for refrigerant "B" at 0 psi is 15C/59F.

If we mix these two together and are in the process of adding heat (at 0 psi), the mixture will start to bubble at 10C/50F and will finish evaporating at 15C/59F.

If we are in the process of removing heat from the mixture (at 0 psi), it will start to form dew at 15C/59F and finish condensing at 10C/50F.

The bubble point for this mixture at 0 psi is 10C/50F.

The dewpoint for this mixture at 0 psi is 15C/59F.

The difference between bubble point temperature and dewpoint temperature is called the "glide" which in this case is 5K/9F.

[Gary]

And then there is pressure.

If we raise the pressure, we raise the saturation temp. If we lower the pressure, we lower the saturation temp.

The pressure/temperature (P/T) chart (aka comparator) for our refrigerant tells us the saturation temp for a given pressure. Or for zeotropic refrigerant mixtures, it tells us the bubble point and/or dewpoint.

[Gary]

Ok perhaps I've been over thinking this one.

Let' see if I understand now, if we take the pressure reading from the liquid line service port and convert it to a temperature using the gas P/T chart the result is for all practicable purposes the dew point (assuming no pressure loss through the condenser) which is the answer to my OP question.


How am I doing?

Pretty close. If this is a mixed zeotropic refrigerant (R400 series), it finishes condensing at the bubble point temperature... and this is the important number on the P/T chart. On the low side, we would need to know the dewpoint temperature, since this is where the mixture has finished evaporating.

If this is an azeotropic blend (R500 series) or a single refrigerant (everything else series), then the P/T chart is showing us the condensing temperature. The low side pressure would show us the evaporating temperature.

Hope this all makes sense.

[Indy2010]

Absolutely all makes sense thank you so much. Now I see where my confusion came from..

I was considering R507 (an azeotropic blend) and now understand why it has listed only one Pressure column.


Gary, I've been attempting to purchase your book (pdf format would be great) unfortunately the links no longer function

[Gary]

Try this link:

http://prostores1.carrierzone.com/se...com/StoreFront

[Indy2010]

Taking this a step further, "dewpoint temperature" and "bubble point temperature" are terms we use to describe a mixture of refrigerants which have different saturation temperatures (zeotropic mixture).

Let's say we have two refrigerants.

The saturation temperature for refrigerant "A" at 0 psi is 10C/50F.

The saturation temperature for refrigerant "B" at 0 psi is 15C/59F.

If we mix these two together and are in the process of adding heat (at 0 psi), the mixture will start to bubble at 10C/50F and will finish evaporating at 15C/59F.

If we are in the process of removing heat from the mixture (at 0 psi), it will start to form dew at 15C/59F and finish condensing at 10C/50F.

The bubble point for this mixture at 0 psi is 10C/50F.

The dewpoint for this mixture at 0 psi is 15C/59F.

The difference between bubble point temperature and dewpoint temperature is called the "glide" which in this case is 5K/9F.

This is a great explanation thanks Gary

The P/T chart is making more sense now

[Indy2010]

How come I can't edit any post??

[Brian_UK]

How come I can't edit any post??

Because your post count is still low.

It is a forum safety thing, when your count increases more things are possible.

[Indy2010]

Cool thanks

[snow_man]

Hi Garry ..After reading your replies here and on Refrigeration 101 I have purchased your Books .If the books are as good as your replies I will be delighted .

[SkyWalker]

http://www.achrnews.com/Articles/Ser...00f932a8c0____ this is a good read regarding superheat and subcooling, and where you apply the info above

[Gary]

http://www.achrnews.com/Articles/Ser...00f932a8c0____ this is a good read regarding superheat and subcooling, and where you apply the info above

Back in the mid 1980's I wrote a column for the ACH&R News in which I first introduced the TECH Method of troubleshooting. My greatest fear back then was that competitors would come out with the MECH Method, the TRECH Method or the WHAT THE HECH Method. After all these years, I see that my fears were totally unfounded. They still don't get it.

[moideen]

why dont give the "moderator post" to gary?i think he is the super star in this forum........

[Gary]

I have found that the key to superstardom is to avoid getting involved in the many subjects about which I am totally clueless. I don't think the forum has, should have, or needs to have superstars. We all help when we can and where we can.

Moderator? No, thanks. I am far too irresponsible.