1 HBD Air Cooling System TK Hemmick for the HBD group 8/25/06.
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Transcript of 1 HBD Air Cooling System TK Hemmick for the HBD group 8/25/06.
1
HBD Air Cooling System
TK Hemmick for the HBD group 8/25/06
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Why is Cooling Needed?
The noise debugging of the HBD showed that RF shield covers must be applied above the pre-amp cards.
These covers give excellent noise performance but trap heat.
The pre-amps & LDO regulators reach 50-60C.
These temperatures are not a fire hazard, but they would limit the lifetime of the pre-amps.
So…we designed a way to cool them.
3
How can cooling be accomplished?
The covers: Block normal convention (the problem). Form a channel for air (the solution).
There are 6 covers around the azimuth and 6 gaps between the covers.
The gaps have sufficient room for a 3/8” tube from which to supply air. How much air? How to deliver air?
4
Overview of Information
System requirements: Power load handling.
Amount of air required (theory) Amount of air required (measurement)
Air handling system. Pressure & Flow (theory) Pressure & flow (measurement)
System parts (Prototype & Proposal) Exploded view of parts. Materials list. MSDS links.
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Power load.
One preamp card requires: +6V at 1.8 A -6V at 1.2 A 18 Watts
LDO regulators on board can handle higher temp, preamps cannot. Pre-amps = +5V at 1.8 A & -5V at 1.2 A 15 Watts.
Air flow should remove 15 Watts from every board.
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Air requirements (theory)
One board… 15 Watts = 15 Joules/sec. Air can be approximated
well as an ideal diatomic gas (CP=7/2 R)
15 Joules in one second. Allow 20 degree rise. Requires 0.64 liters in one
second. Requires ~40 l/min~80 cfh
l
litermolesmoles
V
molesn
n
TnCQ P
64.0040.0
026.0
026.0
20315.82
715
NOTE: Upper limit (ignores natural convective cooling)
7
Air requirements (measurement)
One circuit card was outfitted with a small tube to spread air flow over card.
Tube = 3/8” diameter, 2.5” water, 5 small holes (uniform flow w/ reasonable pressure & small holes)
Pre-amp temp as a function of flow is plotted. 50 cfh is good target for cooling each board. 6 board per side = 300 cfh = 5 cfm per side.
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Pressure and Flow (theory)
P in final tube = 2.5” water Ptot <0.2” water to assure uniform
air delivery. F = 5 cfm, L=15” (conservative) =1.8x10-5 Pascal x sec r = 0.26 inches (d=0.52 inches).
Flow is not purely laminar… Set ID of tubing to ¾”
F 5/6F 4/6F 3/6F 2/6F 1/6F
25.0
4
tot
6
)8(15
8
6
15P
P
LFr
r
LR
FRP
RFP
ii
ii
http://www.google.com/search?hl=en&lr=&client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&q=2*%28%2815*5+cubic+feet+per+minute+*+8+*+1.8E-5+pascal+seconds+*+15+inches%29%2F%286*pi*0.4+torr%29%29%5E0.25+in+inches&btnG=Search
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Pressure & Flow (measurement-1)
Assemble prototype manifold.
All tubing dimensions correct.
Measure air flow parameters.
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Pressure & Flow (measurement-2)
Measured parameters: 5 cfm flow. Pressure in tubes = 2.5”
water. 0.1” water difference
from first to last tube. 6” water is pressure at
supply. Design parameters met
exactly. 100% success.
Air flow uniform in all holes.
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Exploded (Prototype) Part List
Tubing ¾” ID Poly-flow tubing ½” ID Latex (surgical) tubing
Nylon plumbing TEE, coupling; hose barb; elbow; cap.
PTEG Plastic: 3/8” nominal tubing.
Link pointing to MSDS Files:
http://skipper.physics.sunysb.edu/HBD/MSDS/
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Example Commercial Blower…
The above small (2” x 2”) commercial blower meets all the specifications for our needs. http://www.acal-radiatron.com/download/micronel/u51dl-tec.pdf
This will be evaluated and compared to other similar units.
Blower selection will be discussed separately.
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Proposed System
Manifold: PVC pipe, ¾” ID, running underneath
HBD cable tray. Nylon NPT3/8”Hose Barb at 6 locations.
Jumper (manifold individual tube) 3/8” latex surgical tubing.
Flow tube: 3/8” ID mylar tube (0.010” thick wall) Nylon cap.