July 4 th 20061Moritz Kuhn (TS/CV/DC/CFD) CERN July 4 th 2006 Moritz Kuhn Cooling of the P326 Gigatracker silicon pixel detector (SPIBES) CFD – Cooling Simulation

July 4 th 20062Moritz 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 CaseCooling planeThermal conductivity k [W/(cm K)] B1Toray M55J1.5 B2Carbon-Carbon2.5 B3Thornel 8000X panels 8.0 B4Thornel K

July 4 th 20063Moritz 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 4 th 20064Moritz Kuhn (TS/CV/DC/CFD) Results with ideal contact between materials Case A B1 B2 B3 B4

July 4 th 20065Moritz Kuhn (TS/CV/DC/CFD) Temperature gradient of the Silicon Pixel detector in dependence of the thermal conductivity of the cooling plane

July 4 th 20066Moritz Kuhn (TS/CV/DC/CFD) Thermal Contact Resistance To consider the thermal contact resistance R t,c two different values for the contact between every material are assumed. * R t,c = 0.2 x m 2 K/W and R t,c = 0.9 x m 2 K/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 4 th 20067Moritz Kuhn (TS/CV/DC/CFD) Results with thermal resistance between materials

July 4 th 20068Moritz 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. CaseAB1B2B3B4 ΔT, hand calculation ΔT, CFD-Simulation ΔT with thermal contact resistance R t,c = 0.2 x m 2 K/W ΔT with thermal contact resistance R t,c = 0.9 x m 2 K/W

July 4 th 20069Moritz Kuhn (TS/CV/DC/CFD) Cooling Demand: t max = - 10 °C Refrigerants commonly used at TS/CV/DC: C 3 F 8 (evaporation), C 6 F 14 (subcooled liquid), R404A (evaporation)

July 4 th Moritz Kuhn (TS/CV/DC/CFD) Imaginable Cooling Solution Assuming a ΔT of 30 K in the detector Assuming a t max of -10 °C Assuming a cooling pipe of ø 1.27 cm and 4.8 cm length, refrigerant C 6 F 14, 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 C 6 F 14 t in = -70 °C Evaporation in the pipe would be better