Test report of PS-Pack cooling system for ATLAS TGC
B.J.Ye(1), T.Ohska(2) and T.Takashita(3)
(1)ICEPP, University of Tokyo, Japan
(2)International Collaboration Office, KEK, Japan
(3)Department of Physics , Shinshu University, Japan
________________________________________________________
1. PS-Pack set up and measurement system
The test PS-Pack set up includes 4 sub-PS-Packs, that is,
it consists of 4 mother Patch Panel (PP) boards, 8 daughter PP
boards and 8 Slave Boards(SLB). The length of set up is one meter
in four layers. According to the present design, the PS-Pack has
two kinds of modules: normal module and upside-down module. All
PC-boards are supported by the aluminum pillars as shown in Fig.1
in its cross section. The support frame of PS-Pack set up is made
of 4 mm thick aluminum plate. The cover is 1 mm thick aluminum
as shown in Fig.1a and Fig. 1b
Figure 1 : (a and b) Cross section of the test module
On the PC board of mother PP and SLB, there installed nine
resistors(3 parallel resistor-chains each made of 3 series 220Ohm
resistors) and on each daughter board there are 4 resistors (2
parallel resistor-chains each made of 2 series 220Ohm resistors).
Each board, therefore, had 220Ohm equivalent resistance. The total
resistance is 9.5Ohm. AC voltage was imposed on each board simultaneously
to heat up the boards. Since there were 24 boards in this set
up, supplied 15V of AC voltage causes 23.7W heat delivered.
The water flow rate was adjusted by a needle valve of a flow meter.
A temperature-controlled cooling bath was used to set the temperature
of cooling water. Two kinds of cooling pipes were tested in the
measurements: copper pipes with 2inches inner diameter and aluminum
pipes with double holes as shown in Fig.1.
The temperature was measured by a high precision (about 0.01C)
temperature sensor with a computer at several points. The set
up was placed in an air-conditioned room where room temperature
was stable to within 0.5 degree in a day.
The supplied power on PS-Pack is estimated from the electronic
design. It is about 15mW/channel for PP, 15mW/channel for SLB
and 13mW/channel for LVDS termination. The lengths of the real
PS-Pack are 5m for doublet and 3.2m for triplet in the 1/24 of
a wheel. Total channels for 1/24 wheel are 4342 and 2123 channels
for the doublet and the triplet, respectively. It is estimated
to be 37W/meter and 27W/meter at average for the doublet and the
triplet, respectively.
Figure 2: test bench with cables.
2. E-shape copper pipes
We use copper pipes as the cooling pipes and make an E-shape cooling route in which the length of cooling pipes has been increased. For one meter PS-Pack, the length of the E-shape cooling pipe is about 4 meters as shown in Fig.3. The temperature was measured at 5 points: water in, water out, ambience and two PC boards. The heat removed can be estimated from temperature difference between water out and water in.
Figure 3: E-shaped cooling pipie made of copper.
2.1 Water flow rate
Water flow rate is one of the important factors for the cooling
system. We measured total heat removed by cooling water under
different water flow rates which varied from 150cc/min to 350
cc/min as shown in Fig.4. We have fixed the water temperature
to 18C and power supplied to be 24W. The room temperature was
about 23C. Total heat removed increases with increasing of water
flow rate as expected. In flow rate to be 300cc/min, the cooling
system can remove 24.6W which is about 103% of power supplied.
Total heat removed is a sum of two parts: one is heat removed
from ambience and the other is that from PC-board. Heat removed
from ambience can be extrapolated in the case of with no AC power
supplied. So that the heat removed directly from PC-board is estimated
by subtracting the heat removed from ambience from the total heat
removed. Heat removed from PC-board directly is estimated about
12.5W which is constant except for the case of the flow150cc/min.
Fig.4 : Total heat removed varying with water
flow rate
2.2 Water temperature
The temperature of the cooling water should be an important
factor for cooling sytem. We have measured heat removed in 3 temperature
settings of 18C, 20C and 22C as shown in Fig.5. With increasing
the temperature of the cooling water, total heat removed increased
by 2.5W/degree and the heat removed from PC-board decreases about
0.3W/degree. Current cooling system can remove as much amount
of heat by controling the coolant temperature and its flow rate.
The temperature of cooling water is limited by operating gas in
TGC chambers, because the dew point of the operating gas mixture
of TGC is 17C. Therefore, it should be a suitable selection for
the temperature of cooling water to be 17C or 18C. In fact, the
length of PS-Pack is about 3.2m for triplet and 5m for doublet
so long, temperature of coolant outlet would be very high. For
example, for a 5m PS-pack, the temperature of cooling water at
out point is about 5C higher than that of the inlet. The cooling
efficiency (if we take it as a calculation of the heat removed
divided by the heat produced) will decrease from 103% for the
first 1m at 18C to 55% for the last 1m at 22C. The average cooling
efficiency is about 80% for 5m PS-Pack in condition of water temperature
18C and water flow rate 300cc/min.
2.3 Power supplied
We have measured the heat removed by cooling system changing with power supplied as shown in Fig.6. When no power is supplied on PC-board, cooling system can remove 12.4W heat from ambience. With increasing of power supplied on PC-board, heat remove by cooling system increases. In 24W power supplied, cooling system can remove 25W heat. In triplet PS-Pack in which is about 27W power per meter, cooling system can remove same amount of heat which is produced in the PS-PAck. In doublet PS-Pack in which is about 37W per meter, the cooling system can remove 31W. Fig.7 shows the cooling efficiency decreased with increasing of power supplied.
Fig.6 : Heat removed by cooling system varying with power supplied<
Fig.7 : Cooling efficiency varying with power supplied
2.4 E-shape cooling pipes of 2m
In order to know the cooling efficiency as a function of the length of the PS-Pack, we made a two meter set up which is made to combine normal and upside down modules. Total length of cooling pipes for 2m PS-Pack is about 8 meters. We measured heat removed by cooling system varying with the power supplied in the conditions of water temperature 18C and flow rate 300cc/min. When no power supplied on PC-boards, the cooling system can remove about 25W heat from ambience. With increasing of power supplied, the cooling system can remove more amount of heat from system as shown in Fig.8. But cooling efficiency decreases with the increasing of power supplied as shown in Fig.9. For 2 meters of the triplet PS-Pack in which generated power is about 64W, the present cooling system can removed 50W heat. For 2 meters doublet PS-Pack in which generated power is about 76W, cooling system can remove 61W of heat. In present condition, that is, water temperature to be18C, water flow rate to be 300cc/min and ambience temperature to be 23C, the cooling efficiency is about 80%. In order to increase cooling efficiency, we can reduce cooling water temperature to 17C and increase flow rate to 500cc/min. Besides, ambience temperature also is a important factor. The cooling efficiency should be increased with increasing of ambience temperature, which will be discussed in below.
Fig.8 : Heat removed by cooling system varying with power supplied
Fig.9 : Cooling efficiency varying with power
supplied
2.5 Room temperature
The average temperature of ATLAS hall is supposed to be around 25C. The temperature on top of hall should be a few degree difference with bottom of hall because heat always gang up on the top. Cooling efficiency should increase with increasing of ambience temperature. We have measured heat removed by cooling system varying with the ambience temperature as shown in Fig.10. Measurement was done in conditions of water temperature 18C, flow rate 300cc/min and 47W power supplied on the 2m PS-Pack. A systematics can be deduced from the measured results as following:
Htotal = -112.03+6.908*Troom
It can be estimated that the heat removed by cooling system is about 61W in the temperature 25C of ATLAS hall and in 47W power supplied.
Fig.10 : Heat removed by cooling system varying with ambience temperature
3 Double U-shape cooling system
E-shape copper pipes can remove most amount of heat produced on PC-board, but it is difficult to install the E-shape cooling pipes under Al support base, because it has too much bend points. The surface area of cooling pipes also is an important factor to remove heat from system. The surface area of copper pipes is not enough large. In order to increase the surface area of cooling pipes, we choose a kind of aluminum support bar with two holes in it as cooling pipes as shown in Fig.11. The weight is 1.4kg/m and price is $28/m. Double U-shape cooling system is shown in Fig.12.
Fig. 11 : Al cooling pipe and its install
Fig. 12 : Double U-shape cooling system
and one meter PS-Pack
Fig. 13 : Measurement system of PS-Pack
cooling system and isolation box
In order to understand the heat neutral, we made an isolation
box with size 1.4*1*0.6m3 as shown in Fig.13 and Fig.14. We put
the PS-Pack in the isolation box and test the equilibrium temperature
of the air inside the box. The cooling system should be "OK",
if it is about the room temperature after power supplied on PC-board.
It should be called the thermal neutral.
We use 3 temperature sensors to measure the air temperature inside
box in 3 points: bottom, middle and top as shown in Fig.14. We
use mean value of 3 temperatures as the temperature of inside
box. Heat removed by cooling system was estimated using temperature
difference between two points: water out from PS-Pack and water
into PS-Pack.
Fig.14 : Isolation box and temperature measured points
3.1 Water flow rate
In order to select a suitable water flow rate, we measured heat removed by cooling system in different water flow rate. The temperature of cooling water was set at 17C and a constant AC power 33W was supplied on PC-board. Water flow rate was decreased from 500cc/min to 100cc/min at a step of100cc/min. Each stage kept about 1.5 hour in which it is enough to reach thermal equilibrium. Heat removed by cooling system was about 35W for the flow rate of 500cc/min. With decreasing of the water flow rate, the heat removed decreases about 2W/100cc as shown in Fig.15. Therefore, the mean temperature inside of box increases with the decreasing of flow rate as shown in Fig.16. We select 500cc/min as the flow rate of the cooling system.
Fig.15 : Heat removed changed with water flow rate
Fig.16 : Mean temperature inside of box changed with water flow rate
3.2 Power supplied
For 1m PS-Pack, the mean electronic power is about 32W. The maximum power is estimated to be 44W/m in some special part of PS-Pack. We measured the temperatures of inside box varying with the power supplied as shown in Fig.17. PS-Pack is standing up inside box as shown in Fig.14. The water flow rate is 500cc/min and temperature ofthe cooling water is 17C. At 22W power supplied, all temperatures in 3 points were below the ambience temperature. At 32W power supplied, the temperature at top point was over ambience temperature, but average temperature of inside box was 23.7C which was below ambience temperature. At 43W power supplied, the temperature was 25.4C which was a degree higher than the ambience temperature and the average temperature of inside box was 24.7C which was 0.3 higher than the ambience temperature. Heat removed by cooling system was shown in Table.1. The cooling system can remove 35W heat at 32W power supplied and 39W heat at 43W power supplied.
Fig.17 :Temperatures inside box varied with power supplied
Fig.18 :Average temperature inside box varying with power supplied
Table 1: Heat removed varying with power
supplied
The total number of PS-Pack for one side doublet and triplet is 24. Because the orientation of PS-Pack can be at different angles, we also need know the cooling efficiency at different orientation of PS-Pack. We changed the isolation box and set up as shown in Fig.19. Other conditions of measurements were kept as same as that used in the cse of standing up. We changed power supplied from 22W to 51W and measured the heat removed by the cooling system. The air temperatures of inside box were shown in Fig.20. The results was better than that in case of standing up. Even in 43W power supplied, the temperature of the top point was only over a little of the ambience temperature and average temperature was about 24.2C which is lower than that of ambience as shown in Fig.21. This is due to the distance of heat passing to cooling pipes is shorter than that in standing up.
Fig.20 : solation box and set up in lie plat
Fig.21 : Temperatures of inside box varied with power supplied
Fig.22 : Average temperature of inside box varied with power supplied
3.3 Water temperature
The temperature of cooling water has selected at 17C. As we known, the length of PS-Pack is 5m for doublet and 3.2m for triplet. But it is very difficult to make a so huge PS-Pack to measure the cooling system. The aim of this measurement is to understand the cooling efficiency varied with temperature cooling water. A 5m PS-Pack can be regarded as 5 PS-Packs with one meter in length as shown in Fig.23. The cooling water flow into the second PS-Pack is come from the pipe of the first PS-Pack and so on. In a good approximation, we can estimate the cooling efficiency for 5m PS-pack in this way shown in Fig.23.
The measurement was done in conditions of water flow rate of 500cc/min, power supplied of 32W and set up in standing up case. the Fig.24 shows the air temperatures of inside box varied with the temperature of cooling water. With increasing of temperature of cooling water, all temperatures of inside box increases slowly. The average temperature of inside box varied with the temperature of cooling water was shown in Fig.25. At temperature 19C of the cooling water, the average temperature is over the temperature of ambience about 0.3C. We hope that the temperature of cooling water is not higher than 19C. For a 5m PS-Pack, the temperature of cooling water at fourth meter as shown in Fig.17 was about 20C. We plan to use two units of cooling system in one PS-Pack set, that is, each unit of cooling water supplied is 2.5 meters as shown in Fig.26(A). Another a scheme for cooling water supplied is shown in Fig.26(B), which is more easy to install than scheme (A). In this case, we estimated, almost all heat produced on PC-board can be removed by cooling system. For triplet PS-Pack set, we suggest that it use a unit for cooling water supplied because the total length of PS-Pack is 3.2m.
4 Summary
The present measurement shows the double-U shape of cooling system can meet the requirement of ATLAS. Almost all amount of heat produced on PS-Pack can be removed by the cooling system after using two supplied units of cooling water for doublet PS-Pack. For triplet we still use one unit because heat produced on triplet PS-Pack is less than that in double. Besides, the length of triplet PS-Pack is shorter than that of doublet. The obliquity of PS-Pack placement can change the cooling efficiency. In the position of the horizontal set up, heat can be removed more effectively than in standing up placement. In addition, we suggest that Al cooling pipes can replace the support bar of PS-Pack in which can reduce weight and price of PS-Pack.
Fig. 24 : Temperatures of inside box varied with the temperature of cooling water
Fig.25 : Average temperature of inside box varied with temperature of cooling water
Fig.26 : Two kinds of scheme for cooling water supplied in doublet PS-Pack
