Cooling of GEM detector

CFD-2012-03_GEM2012/03/06

E. Da Riva CFD-2012-3_GEM 1

1. Geometry and

material properties

E. Da Riva CFD-2012-3_GEM 2

Geometry and material properties

Copper, k = 400 W m-1 K-1

PCB, FR-4, k = 0.25 W m-1 K-1

E. Da Riva 3CFD-2012-3_GEM

A single chip is considered in the CFD simulations

Geometry and material properties

Soldered = perfect thermal contact Gap-pad k = 2 W m-1 K-1

Chip, silicon, q = 1 W

Water, T = 18°CAll surfaces are adiabatic but the inner surface of the pipe

E. Da Riva 4CFD-2012-3_GEM

Geometry and material properties

Connector k = 0.27 W m-1 K-1

Volume including the GEM sensors is not taken into account.This surface is assumed as adiabatic.

E. Da Riva 5CFD-2012-3_GEM

2. Schematic and estimations

E. Da Riva CFD-2012-3_GEM 6

E. Da Riva CFD-2012-3_GEM 7

Schematic of the problem

18°CWater heattransfer coefficient

TCu strip

T T

Gap-pad PCB

Tchip

q = 1W

TGEM

PCB, connectors, etc.

q = 0 W

The temperature of the GEM sensors will be the same as the PCB. In order to reduce the sensor temperature, the thermal resistances must be reduced:-) higher water flow rate -> higher heat transfer coefficient-) shorter Cu strip or larger “cross section”-) Thinner gap-pad or higher thermal conductivity-) good thermal contact Cu strip/gap-pad and gap-pad/PCB

Water in the pipe

E. Da Riva CFD-2012-3_GEM 8

Di [mm]

Vel.[ms-1]

Flow rate[kg s-1]

Temp. rise[K]

Re[-]

HTC [Wm-2K-1]

Δp (2 m pipe)[bar]

6 1 0.028 0.29 5700 4700 0.066 1.8* 0.051 0.16 10200 8200 0.174 1 0.013 0.65 3800 4500 0.114 1.8* 0.023 0.36 6800 8400 0.28

• Heat load per VFAT chip = 1 W• # VFAT chips = 30• Total heat load = 1 W * 30 + 4 W = 34W

* Erosion limit for copper pipe

Low water temperature rise is good to achieve a uniform sensor temperature. The diameter of the pipe may be reduced if needed because of geometrical constraints.

3. Simulation results

E. Da Riva CFD-2012-3_GEM 9

E. Da Riva CFD-2012-3_GEM 10

With water at 18°C, the temperature of the GEM sensor is expected to be around 60°C.

E. Da Riva CFD-2012-3_GEM 11

The dominant thermal resistance is due to the low PCB thermal conductivity and the small interface area between chip and PCB

E. Da Riva CFD-2012-3_GEM 12

The resistance due to water heat transfer coefficient is negligible (wall temperature very close to water temperature)

E. Da Riva CFD-2012-3_GEM 13

Schematic of the problem 2

18°CWater heattransfer coefficient

TCu strip

T T

Gap-pad PCB

Tchip

TGEM

PCB, connectors, etc.

Negligible ~ 10 K Dominant thermal resistance

Increase heat contact area

-) Increase Cu thickness-) Increase Cu width

E. Da Riva CFD-2012-3_GEM 14

Conclusions

• The dominant thermal resistance is between the chip and the PCB

• Direct thermal contact between the copper strip and the chip may be needed (putting the chip above the PCB instead of below?)

• A further step may be increasing the thickness and the width of the copper strip

• The diameter of the pipe may be slightly reduced if needed.