1. Cooling of GEM detector CFD-2012-03_GEM 2012/03/06 E. Da RivaCFD-2012-3_GEM1

2. 1. Geometry and material properties E. Da RivaCFD-2012-3_GEM2

3. 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 Riva3CFD-2012-3_GEM A single chip is considered in the CFD simulations

4. 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°C All surfaces are adiabatic but the inner surface of the pipe E. Da Riva4CFD-2012-3_GEM

5. 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 Riva5CFD-2012-3_GEM

6. 2. Schematic and estimations E. Da RivaCFD-2012-3_GEM6

7. E. Da RivaCFD-2012-3_GEM7 Schematic of the problem 18°C Water heat transfer coefficient T Cu strip TT Gap-padPCB T chip q = 1W T GEM 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

8. Water in the pipe E. Da RivaCFD-2012-3_GEM8 Di [mm] Vel. [ms -1 ] Flow rate [kg s -1 ] Temp. rise [K] Re [-] HTC [Wm -2 K -1 ] Δp (2 m pipe) [bar] 610.0280.29570047000.06 61.8*0.0510.161020082000.17 410.0130.65380045000.11 41.8*0.0230.36680084000.28 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.

9. 3. Simulation results E. Da RivaCFD-2012-3_GEM9

10. E. Da RivaCFD-2012-3_GEM10 With water at 18°C, the temperature of the GEM sensor is expected to be around 60°C.

11. E. Da RivaCFD-2012-3_GEM11 The dominant thermal resistance is due to the low PCB thermal conductivity and the small interface area between chip and PCB

12. E. Da RivaCFD-2012-3_GEM12 The resistance due to water heat transfer coefficient is negligible (wall temperature very close to water temperature)

13. E. Da RivaCFD-2012-3_GEM13 Schematic of the problem 2 18°C Water heat transfer coefficient T Cu strip TT Gap-padPCB T chip T GEM PCB, connectors, etc. Negligible~ 10 KDominant thermal resistance Increase heat contact area -) Increase Cu thickness -) Increase Cu width

14. E. Da RivaCFD-2012-3_GEM14 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.