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Liquid Cooled
Cold Plates
Aluma Cop
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Vette Thermal Technologies
Subject: Study On Using Vette Tubes
Patent
Pending (Proprietary information)
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1.0 LABORATORY TESTING OF THE Vette
TUBE
The purpose of the lab tests was to obtain hydraulic
and thermal measurements and use this information
to compare and correlate with the analytical calculations.
The basic test apparatus is shown in Figures 1.1
and 1.2.
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Figure 1.1: Schematic of the
laboratory test apparatus |
Figure 1.2: Actual test apparatus
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Four resistance
heaters were used in a double-sided cooling configuration.
The heaters supplied constant power input to the tube
while steady state measurements were made. The measurements
included voltage drop, current, coolant pressure drop,
coolant flow rate, coolant temperature rise, and several
tube surface temperatures.
Three tests were performed:
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TEST ONE
500 watts total heat transfer, thermal and hydraulic
measurements were made at flow rates of 1, 2,
3, and 4 gpm.
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TEST TWO
Zero power input, only hydraulic measurements
were made at flow rates between 0.5 and 5.0 gpm
in increments of 0.25 gpm.
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TEST THREE
800 watts total heat transfer, thermal and hydraulic
measurements were made at flow rates between 0.5
and 5.0 gpm in increments of 0.5 gpm.
Only the second and third sets
of tests were used in the study, as the first set
contained redundant information.
Further details of the individual test parameters
are given below.
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Cooling Tube.
9-in length Vette Tube. The tube stock was taken
from leftover tubes from a previous shipment from
Vette.
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Coolant Supply.
50/50 WEG supplied at room temperature, at flow
rates between 0.5 and 5.0 gpm.
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Electrical
Supply. DC power distributed evenly between
4 resistors. The footprint of the resistors was
1.965in X 0.660in. Voltage drop was measured using
a multimeter, and current was measured using a
current probe.
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Fluid Measurements.
A flow meter calibrated for 50/50 WEG was used.
Electronic pressure sensors were located at the
tube inlet/outlet. Additional pressure measurements
were made using analog gages located at the inlet/outlet.
Thermocouples were used at the inlet/outlet to
measure the bulk fluid temperature.
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Surface Temperature
Measurements. Thermocouples were used
to measure surface temperature at several locations
beneath the heat sources. The TCs were mounted
inside drilled holes in copper spreader plates.
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Heat Spreaders.
Thin copper plates with the same footprint as
the heat source, sandwiched between the heat sources
and the tube surface.
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Thermal Interface
Material. Thermagon T-Grease 401 was
applied to both sides of the heat spreader plates.
A clamping pressure of 25 psi was used.
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Insulation.
Several small pieces of insulation material were
placed around the entire apparatus to minimize
heat loss to the surroundings.
2.0 EXPERIMENTAL AND ANALYTICAL
RESULTS
Data from Test Two was used to determine the coolant
pressure drop and compared to the Analytical predictions.
Table 2.1 summarizes the parameters used in the analytical
calculations. |
Table 2.1: Parameters used
in the thermal calculations |
The
pressure drop according to the analytical calculation
was compared to the measurements, and the results
are shown in Figure 2.1 below. |
Figure 2.1: Measured and predicted
pressure drop for the 9-in Vette tube. |
Data from Test Three was used to correlate the
thermal resistance (sink to ambient resistance,
based on max sink temperature). Figure2.2 shows
the measured and predicted thermal resistance over
the range of coolant flow rates.
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Figure 2.2: Measured and predicted
thermal resistance for the Vette tube. |
From inspection of Figures 2.1 and 2.2 it is clear
that the analytical results are in very good agreement
with the measured data. In fact, the thermal predictions
are excellent; the largest deviation between the
measured and predicted result is about 10%, which
occurred at 1 gpm. The hydraulic predictions are
excellent at the lower flow rates, but not as good
at the higher flow rates, mainly due to the different
flow models used in the laminar and turbulent flow
regimes (the laminar model is used at the lower
flow rates, the turbulent model is used at the higher
flow rates).
From the pressure drop data in Figure 2.1, it appears
that the flow regime is laminar below about 2 gpm,
and turbulent above about 3 gpm. Although for these
tests the flow remained laminar up to 2 gpm.
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