July 4th 2006 1Moritz Kuhn (TS/CV/DC/CFD)

CERN July 4th 2006

Moritz Kuhn

Cooling of the P326 Gigatracker silicon pixel detector (SPIBES)

CFD – Cooling Simulation

July 4th 2006 2Moritz Kuhn (TS/CV/DC/CFD)

Initial Situation• Case A: without cooling plane

• Case B: with cooling plane and with different thermal contact resistances between the solids

• Total Heat Load of 2 W/cm²

Case Cooling plane Thermal conductivityk [W/(cm K)]

B1 Toray M55J 1.5

B2 Carbon-Carbon 2.5

B3 Thornel 8000X panels

8.0

B4 Thornel K-1100 10.0

July 4th 2006 3Moritz Kuhn (TS/CV/DC/CFD)

Simplifications / Assumptions

• Because the problem is an one-dimensional thermal conduction problem, only a small strip is modeled.

• Due to the symmetry, only one half (18 mm) of the chip is modeled

• As the chip is operating in vacuum, it is only a conduction / radiation problem

• Because there is no definitive temperature difference between Sensor and Pixel ASIC, radiation can be neglected. Temperature of the outer walls of the vacuum container are not considered

July 4th 2006 4Moritz Kuhn (TS/CV/DC/CFD)

Results with ideal contact between materialsCase

A

B1

B2

B3

B4

July 4th 2006 5Moritz Kuhn (TS/CV/DC/CFD)

Temperature gradient of the Silicon Pixel detector in dependence of the thermal conductivity of the cooling plane

0

10

20

30

40

50

60

70

80

0 2 4 6 8 10 12 14

Thermal conductivity, cooling plane [W/(cm K)]

Tem

pera

ture

gra

dien

t [K

]

July 4th 2006 6Moritz Kuhn (TS/CV/DC/CFD)

Thermal Contact Resistance• To consider the thermal contact resistance Rt,c two different values for the contact between every material are assumed. *

• Rt,c = 0.2 x 10-4 m2K/W and Rt,c = 0.9 x 10-4 m2K/W

• Values for contact without thermal grease

• Because the temperature gradient in the case of the cooling plane made of “Toray M55J” and “Carbon-Carbon” was already to large, only the “Thornel” was considered.

* Values taken from: P. Incropera, P. DeWitt; Fundamentals of Heat and Mass Transfer, 4th edition John Wiley & Sons; Table 3.2

July 4th 2006 7Moritz Kuhn (TS/CV/DC/CFD)

Results with thermal resistance between materials

July 4th 2006 8Moritz Kuhn (TS/CV/DC/CFD)

Influence of the thermal resistance• It is quite difficult to calculate the real thermal resistance of the contact surfaces between the materials.

• Differences between hand calculation and CFD-Simulation, show the influence of the bumps.

Case A B1 B2 B3 B4

ΔT, hand calculation 72.0 54.0 46.3 25.9 22.3

ΔT, CFD-Simulation 80.0 59.6 49.5 26.6 23.7

ΔT with thermal contact resistance Rt,c= 0.2 x 10-4 m2K/W

-- -- -- 33.9 28.4

ΔT with thermal contact resistanceRt,c= 0.9 x 10-4 m2K/W

-- -- -- 37.5 31.6

July 4th 2006 9Moritz Kuhn (TS/CV/DC/CFD)

Cooling

• Demand: tmax = - 10 °C

• Refrigerants commonly used at TS/CV/DC: C3F8 (evaporation),

C6F14 (subcooled liquid), R404A (evaporation)

July 4th 2006 10Moritz Kuhn (TS/CV/DC/CFD)

Imaginable Cooling Solution

• Assuming a ΔT of 30 K in the detector

• Assuming a tmax of -10 °C

• Assuming a cooling pipe of ø 1.27 cm and 4.8 cm length, refrigerant C6F14, subcooled liquid, 3 m/s

• a ΔT of 24 K between inlet and outlet of the pipe is necessary to remove the heat

• Inlet Temperature of C6F14 tin = -70 °C

• Evaporation in the pipe would be better