PDA

View Full Version : Tube pitch squared/staggered







Friobernal
15-12-2002, 11:57 AM
Hi all,

Does anybody knows why the tube pitch for ammonia evaporators use to be squared instead of staggered ( as for *****s)?

P.D. I think that the efficiency of the fin is bigger when is staggered, because it creates a bigger turbulence in the air ... :confused:

Andy
15-12-2002, 10:31 PM
Hi, Friobernal:)
please enlighten us on chiller construction, with regards to what tube pitch is and where the finning would be.
Regards. Andy.

Friobernal
16-12-2002, 10:39 AM
Hi Andy;

"Tube pitch" is an expresion i have read Idonotwhere, but i mean the geometry of the tubes in an air coil evaporator, that for *****s are always staggered, and for ammonia´s coils are squared, being the fin less efficient.

I´ve being thinking that a possible reason could be the higher K, and more frosting....

Regards:confused: (Again)

Prof Sporlan
16-12-2002, 06:53 PM
The Prof would think of tube pitch to be its degree of slope, which would have some implications with the suction line, but not the evaporator. By chance are you referring to how the tubes in the coil are circuited, e.g., counter-flow? Most ammonia coils are designed and used for recirc duty instead of DX, and there are some issues ergarding coil circuiting for each.

Friobernal
16-12-2002, 07:40 PM
Let me see if i could explain it better in my poor english:
The geometry i´m talking about, you can see in:
http://www.ari.org/std/individual/410-2001.pdf
(page 4) Staggered tubes and parallel (in line) tubes

I´m attaching a brochure of a european manufacturer, where you can see (page 2) differents tubes arrangements, and for ammonia; in-line geometry is prefered.

I know (from a book) that the compactness of staggered is a 16% higher than parallel tubes, so we obtain less efficiency....
why using in-line instead staggered????
:confused:

:confused:

Thanks for all Prof and Andy

Friobernal
16-12-2002, 07:47 PM
Sorry, I cannot to attach.

www.guentner-online.de/guentner-shop/pics/pdf/gco.pdf

Regards

Andy
16-12-2002, 09:18 PM
Hi, Friobernal:)
the professor is correct, I was thinking about water chilling, thats what I get for working on a burst chiller all last week. The inline holes is just as the Professor says for Pumped or Flooded circulation.
On DX or LPR NH3 (Low Pressure Recevier a bit like DX only the suction from the cooler has liquid in it) the tubes are in slope type formations, the liquid having to make a number of passes (usually 2-4) before it is boiled off, this is the same as DX ***** coolers.
The square or in line passes are in pump circ or flooded coolers were the liquid enters the suction to be separated else where.

Remember the only coolers which are sloped pitch that have liquid leaving them not dry gas are on LPR systems, which is a modified DX system anyways.
Hope this helps Regards. Andy.:eek:

Kathleen
30-12-2002, 06:05 PM
Originally posted by Friobernal

"Tube pitch" is an expresion i have read Idonotwhere, but i mean the geometry of the tubes in an air coil evaporator, that for *****s are always staggered, and for ammonia´s coils are squared, being the fin less efficient.


Hi Friobernal,

With ammonia coil we work with carboned steel, stainless, aluminium tubing and aluminiun fins the efficiency is poored compare with cooper tubing, therefore defrost is more difficult. At low temperature (below freezing) flat fin as better result in defrost and in fouling factor efficiency than staggered.

We just encountered a problem this summer the manufacture as supplied us straggered aluminiun fins with carboned steel tubing,and the defrost cycle was terrible. We change the coil with flat fins and no more problem. Our range of temperature was of 40dF (4.4dC) entering and 27dF (-2.8dC) leaving air.

truly yours

Kathleen

Friobernal
03-01-2003, 09:46 AM
hi Kathleen

What do you mean with "and the defrost cycle was terrible"?

Does terrible mean long?

Thanks all and regards

Andy
03-01-2003, 05:56 PM
Hi, Friobernal:)
yes I would say that is what Kathleen means.
Another reason for the square pitch would be cost and size, the square pitch is simplier to make and with NH3 the cooler will have smaller diamentions for a given kW capacity, so the size issue may not come into it, just the cost.
As I stated earlier on Low Pressure Receiver Systems we use the sloped pitch, with no defrost problems, defrost problems will be associated with the fin spacing, if you had close finning and a slope pitched tube arrangement the evaporator would not be correct for low temperature work, but more than adequate for high or possibly medium temperature duty.
Hope this helps, Regards. Andy.

Kathleen
04-01-2003, 04:00 AM
Originally posted by Friobernal
Does terrible mean long?


Friobernal,

time between each defrost was short because the effeciency of the coil drop from the moment that ice started to built on it.

Defrost was also long.

We had to defrost every 45 minutes to keep efficiency, and air flow.

Kathleen