ammonia suction piping risers

[gwapa]

hi Josip
Could you describe a litlle bit your riser

• 
  Why do you introduse the ends of the small reiser inside the big one?
• Why you make a 45° in smaller riser?
• Why the cut is in the oposite side of the flow?
• What was the drag velocity in both reiser?

Thanks
GWAPA

[nh3wizard]

I think the idea of using penthouses does greatly reduce the riser penalties for pressure losses.

The main problem I see with this is the first cost for the penthouses and roof curbs. These can be expensive with a first cost premium.

A secondary consideration is the use of duct work adding static pressure to fans and increasing the fan input power.

This could be minimized by careful selection of fan types and the air distribution system though.

These also have some extra benefits such as having the piping and valve stations on the roof for easier service and installation.

What has been your experience with these NH3wizard?

Any complaints or helpful suggestions?

I happen to be re-reading this thread and noticed questions being asked But anyway most of our facility's are distribution centers, and a few have blast cells, the main advantage like US Iceman has stated is all of the piping and valve stations are located on the roof, which make find leaks, repairing valves, replacing motors much easier, the initial cost is a bit more, but I feel it is worth it. Plus I feel it is much easier to troubleshoot is you can actually see and put your hands on the valve stations when walking the roof, there is no excuse for not knowing a AHU is not working properly.

Andy let me look for some photo shots of the penthouses and I will post them like you asked earlier in this thread.

[sterl]

Very good discussion.

2-phase risers for R-717 and R-744 are the subject of a current, funded and assigned research study funded by IIAR and ASHRAE. The prevailing math today is as US Iceman indicated from USSR studies in the 50's & 60's of coolant in nuke reactors. Institute at a Russian university named after the man; S. S. Kutateladze.

If you make the translation from the Russian algebra: It leans very heavily on work by Martinelli and Rossi.

The onset of difficulty occurs when the annular velocity on the liquid skin on the pipe wall inside goes negative, or put another way: The gas travels up and the liquid travels down. And 1-pipe steam heating systems have deliberately worked that way for 150 years.

There is an identifiable pressure difference in the riser well above that anticipated for frictional flow. Even at relative low recirculation rates and high vapor velocities, the actual density of the "aerosol" in the pipe is much higher than that of the vapor alone. By field measure, this can represent as much as 5-times what would be calculated for the same length of "dry" pipe passing vapor, and still not log up; that at minus 40 Evap.

Biggest "new" issue in this regard has been VFD on CSW-type evaps as opposed to full speed fan cycling.

And the FMC approach (the LVS) uses a fluid dynamic approach to separation and re-injection of liquid, such that height and separation limitiations are largely overcome. There are minimal controls involved but it works best in a narrow window of load and temperature condition....Move an LTS drum from a minus 50 to a minus 10 load and it basically acts like a tiny surge drum.


We do not use the Trap and Split type double risers except at changes in roof level. And we do not overloop the return main if the evap's pipe is 4-sizes smaller than the main: we side stab it cause the purpose of the up and over is honored by the geometry of the intersecting pipes.

[Icelander]

If I understand your problem right, I think it would be good to drill 3/4" hole under pipe from the evaporator and place a pipe that is connected to a vessel use pump to empty the vessel when the level is high in the vessel. Each pipe from the evaporator to the vessel should have a valve that closes when the evaporator is in defrost.