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vipxing0811
27-01-2009, 05:29 PM
I am using refrigerant R410A. The sight glass is located before the TXV. I checked the subcooling temperature, and it's about 12 degree Celsius. But when I run the system, I can see many bubbles in the sight glass. I don't understand becuase there is enough subcooling. And because of this, the mass flow meter also didn't work. Could anyone explain this?

SteinarN
27-01-2009, 05:56 PM
If it is noncondensables like air or nitrogen in the system you will have subcooling and bubbles simultaneously.

I suppose it's a small AC system?

Grizzly
27-01-2009, 06:30 PM
Unless you KNOW that your system is fully loaded a sight glass is useless as a indicator for charge level.
In fact if I had a choice I would rip out sight glasses on the smaller A/c.
Basically a sight glass can only be used as a rough indication. Further measurement need to be taken to confirm system charge.

Simply put increase the duty until the system is fully loaded (doing some work) then you can use your sight glass as an indication.
Grizzly

nicolacozma
27-01-2009, 06:58 PM
Which are the indication of the other parameters?
The system is operating properlly, except the bubbles?
Could be flash-gas due to an restriction just before sight-glass. A restriction on the liquid line will give you a good subcooling.
(filter-drier, on-off valve,...).
As SteinarN says check also for noncondensables.

Brian_UK
27-01-2009, 08:36 PM
Do we assume that this is a college question and you are working on a test rig ?

Before you worry about bubbles in the sight glass establish that the evaporator load has been satisfied.

Grizzly
27-01-2009, 10:13 PM
Do we assume that this is a college question and you are working on a test rig ?

Before you worry about bubbles in the sight glass establish that the evaporator load has been satisfied.

Thanks Brian!
Grizzly:off topic:

Brian_UK
27-01-2009, 11:45 PM
Sorry Grizzly, just re-read your earlier post and it covered my answer already.

I must stop speed-reading, it doesn't always work. :eek:

vipxing0811
28-01-2009, 06:09 AM
Yes, I am doing a testing in the university. The capacity of my unit is 3 ton. As for the noncondensable, since I have evacuated the system a couple of times so I think there should be no noncondensable. The test conditioning for cooling mode: outdoor unit 25C, indoor 30C. I chose the temperature because I just want to make the system run easy. I think I will evacuate the system and charge again. Actually I am wondering that could over charging and under charging be the reason of bubbles?

Grizzly
28-01-2009, 08:07 AM
Sorry Grizzly, just re-read your earlier post and it covered my answer already.

I must stop speed-reading, it doesn't always work. :eek:


:off topic:Crossed wires here Brian.
I was thanking you for backing up my statement.
It must be our age?



The test conditioning for cooling mode: outdoor unit 25C, indoor 30C. I chose the temperature because I just want to make the system run easy. I think I will evacuate the system and charge again. Actually I am wondering that could over charging and under charging be the reason of bubbles?


Vipxing.
Given the extra info above I suspect you already know the cause.
I definatly have a problem with the split across the evap and condensor.
In my mind that is a non load situation?
What does anyone else think?
Good Luck Grizzly

Brian_UK
28-01-2009, 09:48 PM
A few thoughts ------

Do you evacuate using a Torr guage or digital vacuum gauge and if so to what level do you reach?

Is the liquid line undersized ?

Are you charging in liquid state or vapour state ?

With the constant evacuating and recharging that this system is/has received, has the filter/drier been replaced or is it an old, well used, one ?

vipxing0811
28-01-2009, 10:27 PM
A few thoughts ------

Do you evacuate using a Torr guage or digital vacuum gauge and if so to what level do you reach?

Is the liquid line undersized ?

Are you charging in liquid state or vapour state ?

With the constant evacuating and recharging that this system is/has received, has the filter/drier been replaced or is it an old, well used, one ?

I am using pressure transducers from Setra System Inc. I have calibrated these transducers and when I evacuated, the pressure went down to almost zero.

As for the size of liquid line, I am using the same size as the manual suggests.

I charged the system in liquid state because R410A is azeotropic mixture.

The unit I am using is a brand new one, never used before. So I think there should be no problem with the filter.

Today I did the test again, the air flow rate for my indoor unit is about 800cfm, but the manual suggests 1600 cfm. I am wondering this might be the reason for not fully loaded?

Brian_UK
29-01-2009, 12:34 AM
I am using pressure transducers from Setra System Inc. I have calibrated these transducers and when I evacuated, the pressure went down to almost zero. OK, but was is range of readings? Saying they were almost at zero tells us nothing; if with a range of, say, 0 to 100 psi or 0 to 50 bar then that means that the sensor is no good for measuring vacuum.


As for the size of liquid line, I am using the same size as the manual suggests. OK


I charged the system in liquid state because R410A is azeotropic mixture.Good, just testing :D


The unit I am using is a brand new one, never used before. So I think there should be no problem with the filter.Fair enough, but you have removed and replaced the refrigerant charge several times already. Have you been allowing the system to be open at atmospheric pressure ?


Today I did the test again, the air flow rate for my indoor unit is about 800cfm, but the manual suggests 1600 cfm. I am wondering this might be the reason for not fully loaded?If you have not built the system according to the specification then do not expect it to behave correctly.

vipxing0811
30-01-2009, 04:31 PM
I have evacuated the system and charged new refrigerant again. Now there is no bubble in the sight glass. I think the bubbles was due to noncondensables. Thank you very much for everyone!

Grizzly
30-01-2009, 04:51 PM
See what happens when you assume that someones does everthing correctly the first time!!!!!
Grizzly

Brian_UK
30-01-2009, 07:49 PM
Still no figures to work to but never mind, it's Friday ;)

wambat
30-01-2009, 08:07 PM
I always get suspecious when someone says they think this or that. That is a totally irrelivent statement.

frederik79
08-02-2009, 12:46 AM
r u sure it are bubbles and not oil ...
if subcool temp is ok then there is no problem ...

uhmm the condenser fan is it freq regulated ??

Gary
08-02-2009, 06:53 PM
Here is the info needed to properly evaluate the system:

Evap air in temp
Evap air out temp
Saturated suction temp (converted from pressure)
Suction line temp

Cond air in temp
Cond air out temp
Saturated condensing temp (converted from pressure)
Liquid line temp

We can't see the system from here. All we know is what you tell us and you have told us very little.

Gary
08-02-2009, 07:05 PM
Today I did the test again, the air flow rate for my indoor unit is about 800cfm, but the manual suggests 1600 cfm. I am wondering this might be the reason for not fully loaded?

The evap air in and air out temps will reveal the answer to this question.

imran ansari
09-02-2009, 01:34 PM
Yes, I am doing a testing in the university. The capacity of my unit is 3 ton. As for the noncondensable, since I have evacuated the system a couple of times so I think there should be no noncondensable. The test conditioning for cooling mode: outdoor unit 25C, indoor 30C. I chose the temperature because I just want to make the system run easy. I think I will evacuate the system and charge again. Actually I am wondering that could over charging and under charging be the reason of bubbles?system is undercharge if bubble is large quantity and continous its means over charge

imran ansari
09-02-2009, 01:36 PM
how to seperate water if its mix with R 123

nike123
09-02-2009, 02:34 PM
system is undercharge if bubble is large quantity and continous its means over charge


There are several reasons for bubbles in the sight glass. If one of the traditional refrigerants showed vapor in the sight glass it often meant there wasn't enough liquid refrigerant being fed to the valve, and more refrigerant was added to the system.
Blends could show flashing for the same reason, however, they can also flash when there is plenty of liquid in the receiver. Ironically, this liquid in the receiver could be causing the problem, particularly when the equipment is in a hot environment. Blends will come out of the condenser slightly subcooled - at a temperature below the saturated temperature of the blend at the existing high side pressure.
Yet when the blend sits in the receiver, it can "locally fractionate," or change composition slightly by shifting one of the components into the vapor space of the receiver. This will effectively produce a saturated liquid in the receiver, at the same pressure you had before, which flashes when it hits the expanded volume of the sight glass. In most cases these bubbles will collapse when the blend gets back into the tubing which feeds the valve, and the system will operate just fine.

amitsaxena
24-02-2009, 06:50 AM
Its majorly because blend properties as you are confirming the subcooling is proper then only possibility is that in the eqilibrium state one of the blend refrigerants is in Vapor stage.