1. University of Colorado – Boulder
Pixel cooling
Kevin Stenson
University of Colorado – Boulder
Cooling Meeting – July 3, 2008

2. Monday
On Monday afternoon started opening lines on the pixel detector.
All TA valves set to 1.0 (out of 5.0); should be low rate.
We see coolant levels in reservoir drop (good sign that air is being removed)
After opening about 10 lines, pump can no longer maintain pressure and eventually trips off.
Pump was restarted and we finished for the evening but apparently the pump tripped off again Monday night and was restarted Tuesday morning by Carsten.

3. Tuesday
Tuesday morning I observed mostly air in PP0 bypasses and was worried about getting air out before our Wednesday test.
Stopped opening lines after 14 of the 18 were open
Started increasing TA valve on 2 lines in –z. Was told by Carsten that a setting of 2 or 2.5 would be plenty. Ended at 2.5 for the night.
Was told to make sure bypass line stayed above 35% or so to make sure pump could handle job
Sasha suggested a valve hidden above the cooling plant was in the wrong position, not allowing air to escape. Wrote an ELOG entry. Sasha also found a big leak on a pressure relief valve on the return line (and fixed it).

4. Wednesday
Some time in the morning Carsten opened the valve allowing air from the return to the reservoir
I continued to increase the flow on 2 –z lines to ensure there would not be any bubbles. By 11am they were fully open.
Finally around 6pm we got access to PP0.
The lines which had been running for 2 days at a TA valve setting of 1–1.6 were still mostly air
The lines which were at higher settings appeared to be fully liquid, no bubbles.

5. Our setup PI Detector valve Flow meter PO PIX-11 (aka PD.2.2.4) Return
TA valve
40 m
PIX (aka PD.2.2.4)
Supply

6. Strange results from test
With valve wide open and no apparent bubbles, pressure gauges jumped between 0 and 1 bar and flow meter jumped between 100 and 120 cc/sec.
After closing the detector valve some amount, bubbles appeared in the flow meter (downstream of valve). Pressure gauges settled down some.
Tried closing off all lines other than the one we were checking to avoid any interference. No effect on our line.
Closing the detector valve results in pressure gauges jumping between 0 and 4 bar.
What is going on?!

7. Questions
Exactly what leak tests were done on the pixel system? Do we need to make additional checks?
What is the cause of the bubble appearance?
What is the cause of the pressure fluctuations?
Why is it so difficult to remove air from the lines at rates less than full?
How can we check that the air has been removed and there are no bubbles?
Put in a transparent section?
Put in flow meters?
Put in pressure gauges?

8. Near term plans
See if it is possible to safely remove air from the lines (as when the detector is in place)?
Perhaps one line at a time, monitoring the pressure?
Should we hook up some pressure gauges to the calibrated orifices?
After air is removed, turn up pressure and increase flow to do the cleaning part of the test.
If it is difficult to remove air, is it possible to keep coolant in the lines when we remove the bypass to insert the detector?
Remote readout of the cooling plant
Connected to our DCS?
Or accessed separately?

9. What was decided
Previous slides were based on what I presented at the cooling meeting. Below is what was decided.
Need to understand relationship between pressure regulator (remotely adjustable but currently at 2.5 bar) and the pressure relief valve (mechanically adjustable but value unknown and adjustment procedure unknown).
Start up flow on all lines at what we think is nominal flow rate (1.5 on TA valve)
Connect pressure gauges on a supply and return line to monitor pressure and presence of air