Vapor lock nh3

Has anyone ever encountered vapor lock, on a flooded NH3 evaporator? What was done to solve the problem? We use the same evaps in this facility, but the new and improved designs are different then the older ones, which work! Piping changes have been made, but we are still vapor locking. I close the suction valve on the accumulator, build pressure, the temp lowers, then open the suction vlave temp drops more levels off then increases in temp again. Also, by adding more liquor into the accumulator, increasing the static head also helps the liquor move down to the evaps. The evaps are bottom fed, with the wet suction return on the top. Any ideas we are running out of ways to repipe this system.
Thanks for your input and help.

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Originally Posted by rvmitch9927

Has anyone ever encountered vapor lock, on a flooded NH3 evaporator? What was done to solve the problem? We use the same evaps in this facility, but the new and improved designs are different then the older ones, which work! Piping changes have been made, but we are still vapor locking. I close the suction valve on the accumulator, build pressure, the temp lowers, then open the suction vlave temp drops more levels off then increases in temp again. Also, by adding more liquor into the accumulator, increasing the static head also helps the liquor move down to the evaps. The evaps are bottom fed, with the wet suction return on the top. Any ideas we are running out of ways to repipe this system.
Thanks for your input and help.

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I know this may sound stupid but are you sure you have enough refrigerant in your system ?
Flooded means Flooded!
This is not meant as a criticism it's difficult to visualise what you are describing?
Basically you seem to be moving the liquid levels around and what is happening with your pumps, whilst all this is going on?
Fluctuating levels make me think there is a simple answer here.
When you raise or lower this level what is the level of refrigerant within your system / receiver?
Cheers and let us know how you get on please
Grizzly

Is the coil gravity fead or pump fead.? Seems the coils are drying out and not flooding as Grizzly suggested.
If pump fead the coils may have a max flow orifice or hand regulation vav feeding bttom header, that is too small for loads, so when you shut suction allows coil to fill again with no draw off of vapour.

Griz
We are using Subcooled High pressure liquid NH3, @-17 degrees. No pumps, during plant operation there is still ammonia in the HPR. The evaps are votator II by cherry-burrell. It's is hard to describe the set-up. Each system has it's own accumulator which is filled with the SHPL, level maintained by a float, the accumulator gravity feeds the evaps/votator. The latest piping change they had the liquid line at a 45 degree angle. We could watch the liquid line start melting the ice that had formed, which tells me a gas pocket had formed. Restricting the liquid flow. The wet suction (from the votator to the accumulator.) also doesn't form ice on the pipe either. We aren't keeping the evaps flooded. Could the the capacity of the evaps be under sized and be creating this problem. Or is it in the piping design. Thanks for your suggestions GRIZ & MAGOO

Thanks for the explanation Mitch.
I can understand better what the problem is now.
I have not worked on any gravity fed systems.
So maybe Magoo or some of the other Industrial Guys are more qualified to help?

Wild shot but would a blockage in the votator influence in any way?

Good Luck and thanks once again for the explanation.
Please keep us informed ,interesting one this!
Cheers Grizzly

Where has " the gas pocket " formed
, is it in the HPSLL or accumulator ?

If its HPSL line feeding each accumulator can't see how gas pocket can form unless branch off main HPSL is not connected in properly or restricted , favouring the easiest path .

If float in new surge drums is satisfied you sould see ice on liquid and wet return to vessel obviously .
Unless evaporator liquid feed out of bottom of surge drum is going to far into surge drum above float control level ?
Do you have surge drum details ?

What type of float contol do you have ie LLC switch or phillips float ?

How big is the accumulator? Length/diamiter? How much liquid are you holding in the vessel? When the temps are going up on the cherry barrell - are you still seing the float switch made as the accumulator has liquid in it? The float switch - how is it piped up? Maybe it is giving a false level. Ive ran into things like that where the float switch would be piped tied into the dry suction (after the baffel plate). This caused the float column to have liquid pulled up in it when the vessel was actually running lower levels (false level reading). If you have piped this things different ways with liquid & suction & still have problems - look into the level. A sight glass in the column would do no good if the float is the problem. Also where on the accumulator is the float, at what level?

With the new and improved evaporator, the improvement may be that each circuit has a orifice regulator specific to pump fed systems. Not good for gravity fed unless the liquid head is extra high, check coil manufacturers drgs.,details.

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Originally Posted by rvmitch9927

Each system has it's own accumulator which is filled with the SHPL, level maintained by a float, the accumulator gravity feeds the evaps/votator.

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This is a fairly simple gravity flooded system. If you get liquid in the surge drum to maintain a constant level and the feed & return piping to the votator is correct, there is no reason it should not work.

The return piping from the votator comes off of the top of it, right? And the liquid feed line should feed the bottom of the votator. Liquid goes in, gas and liquid come out.

The only other thing that might pose a problem is the suction pressure regulator is set too high or the suction pressure at the compressor(s) is too high.

If you cannot maintain a constant liquid level in the surge drum then you have a liquid supply issue (low receiver level, clogged strainer, or incorrectly set hand expansion valve.

It's pretty hard to screw one of these up.;)

Hi US Iceman.
I agree it is hard to screw up a gravity fed system particually if a repeat of previous installs.
The only variable to system is a change in evaporator design, thats why I suggested a long hard look at differences with new and improved coil configuration.
magoo

Unless something has drastically changed with votator designs it consists of a barrel and the scrapper blades inside of another shell. Only the outside shell is flooded and it should just be a line in and a line out.

If the liquid line enters on the bottom and return line exits on top, there is no way one of these can gas bind (unless something really screwy was done internally).

Ooopps, hi Magoo. my bad manners are now corrected.

Hi again US Iceman.
I think I am totally in the dark with these votator things. Sound like churns for icecream or similar continual process.
I will go away and be quite and very red faced , but watch results of post.
magoo

If the liquid line enters on the bottom and return line exits on top, there is no way one of these can gas bind (unless something really screwy was done internally).

B”H

Votator is a double-walled heat exchanger. It could be that inlet pipe is protracted (welded in) too deep and is very close to the internal tube of the votatot. It would restrict the liquid to enter the chamber. Why do not you speak to the manufacturer?

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Originally Posted by Magoo

Sound like churns for ice cream or similar continual process.

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That is exactly what they are Magoo. A scraped surface heat exchanger. Nothing to be red faced for.;)

Here is a link: http://www.gowcb.com/products/heatex...otsshe_wcb.pdf

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Originally Posted by michaelm

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Originally Posted by michaelm

It could be that inlet pipe is protracted (welded in) too deep and is very close to the internal tube of the votator. It would restrict the liquid to enter the chamber.

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Something like this would do it. The inlet pipe should be flush with the inside shell to allow free flow into the outer chamber.

Brilliant link Iceman.
Complete with schematics on page 10.
As you say in at the bottom and out at the top!
Complete with a description of working level etc.
Brilliant!
Thanks Grizzly

Well, Grizzly... you read more of it than I did.:D I was looking for a picture, found one, and posted it.

They are just fancy ice cream freezers..

Thanks for the input.
1. The gas pocket formed in the LQ suppy to the votator. (We could see the gas form because in piping change #6 the LQ feed to the votator was at 45 degree angle, LQ line should have been full of LQ, but with the pipe at a angel we could see the ice melt off the line and the gas pocket form.)
2. the accumulator was not making up any LQ when we weren't cooling.
3. Votator is LQ feed bottom and gas/wet return top.
The fix PIPING change 7. This is the way it was explained to me. We have 3 votator tubes in a row. The gas return piping was changed so that the tube doing the most work was piped to a header at the accumulator furthest from the the entrance to the accumulator. Then next hardest and the last one. The return off the hardest working tube going in the short header will create a venturi effect pulling on the other two return lines. It worked we came down to temperature.
Thanks for all your help, maybe this will help someone else.

May be it is oil not vapor. Which part of the pipe does defrost first(top or bottom)? I didn't work with this device but thermosyphon coolers sometimes have problem with oil.