Rick, Jason, & Jeff B.
This morning we ran a test on the PSL 70w cooling circuit to see if we could lower the flow rate and thereby reduce the line pressure (and turbulence noise) while maintaining proper cooling of the laser.
Setup: Connected two thermocouples, one to the supply line and one to the return line of the 70w amp. Allowed both temperatures to stabilize. Then swapped the leads between the two meters to discover if there was any difference between the two. No difference in the base line readings were noted between the meters.
Test: Recorded the base line temperature, pressure, and flow rate of the 70w amp. Next, using the 70w amp cooling circuit’s pressure regulator, lowered the flow rate by ~ 27% (did not want to drop the flow any lower without talking to the manufacture) and observed the changes in the supply and return line temperatures over a 40 minute period.
After the test, removed the thermocouples and returned the flow rate back to the manufacture’s specification.
|
Elapsed time |
Flow Rate |
Supply Pressure |
Supply Temp C |
Return Temp C |
|
0 |
2.2lpm |
56psi |
20.8 |
21.8 |
|
|
|
|
|
|
|
2 |
1.6lpm |
53psi |
20.9 |
21.9 |
|
5 |
|
|
20.8 |
21.9 |
|
10 |
|
|
20.8 |
21.9 |
|
15 |
|
|
20.9 |
22.1 |
|
20 |
|
|
20.9 |
21.9 |
|
25 |
|
|
20.9 |
21.9 |
|
30 |
|
|
20.9 |
22.0 |
|
35 |
|
|
20.9 |
22.0 |
|
40 |
|
|
20.8 |
22.0 |
Conclusion:
While hardly an exhaustive study, the data shows there appears to be room to turn down the water flow in the 70w amp circuit and still maintain proper cooling of the laser. Before lowering the flow rate in the 70w amp, we needed to: (1) Run this same study over a much longer time to guarantee the cooling circuit temperature will stabilize at an acceptable level, and (2) Speak with the manufacture of the laser to ensure there are no issues with a reduced water flow.
If the noise data shows an improvement at these lower flow and pressure levels, we should look into the possibility of similar changes to the frontend and the external shutter cooling circuits. These two cooling circuits are currently running at 1.8lpm and 1.7lpm so there may not be much noise advantage to flow reductions. However, these two circuits are running at 64psi line pressure. As some of the fittings on these circuits are rated at a max 75psi, lowering the line pressure by 10 to 15% would have several benefits.
There are several more tuning changes planned for the PSL chiller circuits, which will be rolled in as time and opportunity allow. Lowering flows and pressures in these cannot but help to lower the cooling system noise in the PSL.