Microchannel cooling - Update Outline Test of 1st full-scale prototype Hydraulic behaviour Thermal behaviour Layout optimization for the prototype Structural analysis and Manifold Pressure tests Next steps 07 Sep 2010 G. Nüßle

First tests on a full-scale prototype Test sample and numerical model manifold depth 100mm Inlet 1mm Channel cross section 100mm x 100mm Power density 1 W/cm2 (50% nominal) Mass flow 3,66 x 10-3 kg/s (50% nominal) Inlet temperature 18 C Outlet pressure 1bar Laminar flow Outlet 07 Sep 2010 G. Nüßle

First tests on a full-scale prototype Simulated vs. experimental pressure drop 07 Sep 2010 G. Nüßle

First tests on a full-scale prototype Thermal visualization IN OUT Thermograph before injection IN OUT Heat load simulated by a Kapton heater of suited resistance and geometrical dimension Thermograph at injection Thermograph after few seconds of coolant circulation 07 Sep 2010 G. Nüßle

First tests on a full-scale prototype Steady state DT between inlet and surface probes 1 2 3 4 5 6 4 6 5 1 3 2 07 Sep 2010 G. Nüßle

Wedged manifold, depth 150mm, 280mm and 400mm Layout optimization Optimized geometry for uniform and minimal DP CFD models of the geometry presently under tests have been successfully validated. Further optimization of the manifold geometry and of the channel cross section are then performed with CFD analysis in order to reduce the amount of samples to be produced for testing purposes Inlet Wedged manifold, depth 150mm, 280mm and 400mm Outlet 07 Sep 2010 G. Nüßle

Layout optimization Effect of inlet manifold geometry on DP Wedged manifold, 1.6 mm Max width, 150 mm deep, opposed inlet & outlet Wedged manifold, 1.6 mm Max width, 280 mm deep, opposed inlet & outlet Rectangular manifold, 1 mm wide, 100 mm thick, central inlet & outlet Wedged manifold, 1.6 mm Max width, 400 mm deep, opposed inlet & outlet 07 Sep 2010 G. Nüßle

Layout optimization 07 Sep 2010 G. Nüßle

Structural analysis Experiments “Sacrificial” samples with different manifold widths are produced and brought to collapse by gradually increasing pressure under a high speed camera in order to determine the limit pressure and the exact breaking mechanics. 60 3 0.05 0.025 varying width 07 Sep 2010 G. Nüßle

Structural analysis Numerical simulations vs. tests A simplified ANSYS 2D parametric model has been developed and calculations are checked against experimental results in order to validate the model for further forecasts, including the effect of wall thinning or of geometrical variations Yield stress ~25 MPa [ICES 2009] 07 Sep 2010 G. Nüßle

Structural analysis Extrapolations 07 Sep 2010 G. Nüßle

Next steps Immediate future Perform full-scale thermal tests in cold (vacuum vessel) Define the details and properties of the Si-Si fusion bonding process and verify with a new series of tests Advance in the integration study of the GTK module 07 Sep 2010 G. Nüßle

Back Up 07 Sep 2010 G. Nüßle

Thermo-fluid dynamic basic calculations The cooling fluid circulating in the micro-channels is the perfluorocarbon C6F14, which is widely used as coolant medium in LHC detectors. They exhibit interesting properties for cooling applications in high radiation environment such as thermal and chemical stability, non-flammability and good dielectric behaviour. In particular C6F14 is liquid at room temperature and is used as single phase cooling fluid in the inner tracking detectors of CMS. Properties C6F14 @ -25°C Density r [kg/m3] 1805 Viscosity n [10-7 m2/s] 8.2 Heat capacity cp [J/(kg K)] 975 Thermal conductivity l [10-2 W/(m K)] 6.275 Based on the properties of C6F14, a mass flow of 7.325*10-3 kg/s is required to extract the heat dissipated by the readout chips (~32 W) with a temperature difference of 5K between the inlet and outlet temperature of the coolant The results from the analytical calculations performed indicate that the suited range of the micro channel geometry is the following: Width: between 100 mm and 150 mm Height: between 80 mm and 120 mm Fin width: between 25 mm and 75 mm Between 300 and 500 channels to cover the area Flow rate attained with 2 bar Dp vs. channel width for a fixed height of 90 mm 07 Sep 2010 G. Nüßle

Layout optimization Summary table two inlets 07 Sep 2010 G. Nüßle

Proposed solution Schematic of the layout of the proposed m-channel cooling plate the coolant will enter and exit the straight channels via manifolds positioned on top and bottom. The channels, distribution manifold and openings for the inlet and outlet connectors are etched into a silicon wafer, which is then coupled to a second wafer closing the hydraulic circuit. The final goal is to have both wafers in silicon bonded together by fusion bonding to produce a monolithic cooling element An alternative design, in case of technical difficulties with the fusion bonding process, relies on a flat Pyrex cover 50 µm thick anodic-bonded to the silicon wafer carrying the hydraulic circuit. On top of this flat plate, an additional silicon frame (surrounding the beam area) will be again anodic-bonded. In this way the global structure of the cooling wafer will be symmetric, the effects of coefficient of thermal expansion (CTE) mismatching between silicon and Pyrex will be minimized and the same resistance to pressure and manipulation as in the baseline case will be attained 07 Sep 2010 G. Nüßle

Approach to the problem Take advantage of recent results obtained in two different fields of development: m-channel cooling devices have started to be actively studied for future applications for high power computing chips or 3D architectures. Thin and light m-fluidic devices in silicon are largely in development for bio-chemical applications. Anyway for the first case, where the power densities are extreme, the mass of the device (hence its material budget) is an irrelevant parameter. In the second case the typical values of the flow rate and pressure are much lower. Furthermore, the presence of a low temperature fluid and possibly of a high radiation level is unique to the HEP detector case. dedicated R&D is nevertheless unavoidable for the specific application under study. 07 Sep 2010 G. Nüßle

Approach to the problem The procedure followed to tackle the different challenges and to converge in a limited time on a single device satisfying all the requirements is to move in parallel along different lines of R&D in a “matrix” approach, where the intermediate results of one line are used to steer the parallel developments. Fabrication technique studies Possible layouts Common specs Thermo-fluid dynamic simulations Optimal layout Numerical structural simulations Pressure limits Experimental tests 07 Sep 2010 G. Nüßle

m-fabrication process START: Czochralski silicon wafer polished on both sides (4′′ diameter, 380 μm thick, 0.1-0.5 ohm-cm p-type). A layer of 1 µm of oxide (SiO2) is grown on both sides of the wafer Clariant AZ-1512HS photoresist is spin coated on one side of the wafer at 2000 rpm and lithography is performed to obtain an image of the channels in the photoresist Dry etching of the top layer oxide is used to transfer the micro-channels pattern A second lithography is performed with frontside alignment to image two fluid transfer holes, 1.4 mm diameter, for fluid injection and collection from the two manifolds. Deep Reactive Ion Etching (DRIE) is used to partially etch the access holes down to 280 µm The photoresist is stripped in Microposit Remover 1165 at 70°C and DRIE is used to anisotropically etch 100 μm deep channels separated by 25 µm wide structures in silicon Subsequently the oxide layers are removed by wet etching in BHF 7:1 for 20 min at 20°C At present, the processed Si wafer and an unprocessed Pyrex wafer (4” diameter and 525 µm thick) are then cleaned in a Piranha bath (H2SO4 + H2O2) at 100°C and anodic bonding is performed to close the channels with the Pyrex wafer 07 Sep 2010 G. Nüßle

m-fabrication process The anodic bonding is performed at ambient pressure and T is raised to 350°C then lowered to 320°C. At this stage a constant voltage of 800 V is applied between the Si and Pyrex wafer. In the final production both the processed and the unprocessed wafers will be in 525 µm thick silicon. The bonded wafer undergoes a further processing: this includes a final local etching to obtain a thinner region in the beam acceptance area The resulting wafer is diced according to alignment marks previously etched in Si to obtain a cooling plate with precise external references for integration into the electromechanical assembly 1 mm .... 30 mm Scanning Electron Microscope image of the cross-section of 50 x 50 mm channels etched in silicon bonded to a Pyrex wafer Finally, PEEK connectors (NanoPort® assemblies from Upchurch Scientific) are aligned, together with a gasket and a preformed adhesive ring to the inlet and outlet on the silicon and clamped. They undergo a thermal treatment at 180°C for 2 hours to develop a complete bond between the connectors and the silicon substrate. 07 Sep 2010 G. Nüßle