Thermal measurements in Glasgow Richard Bates, Isaac Bonad, Craig Buttar

Contents In plane thermal conductivity measurements –Apparatus –Method –Results

Early photograph of the apparatus, before the experiment was inside the vacuum tank, but while the area was tidy

Thermal studies Plastic insulating supports DUT H2OH2O V,I measured Electrical Heaters Water cooled Cu block Al thermal shield PT100s RTD1 RTD2RTD3

Details of the measurement Radiation reduction –Radiation shield around the sample –Polystyrene balls filler –Cool outside of tank to Copper block temperature Conduction reduction –RTD wire 44SWG Manganin tied to the cooling block –Thermally insulating mounts for apparatus Convection reduction –Vacuum tank Accuracy –4 wire temperature sensors and heater –Careful calibration of RTDs against each other (temperature differences important)

Measurement details Sample size –Defined by thermal shield size and vacuum tank –Presently : 10cm x 1 cm –Max length at present : 20cm (limited by vac tank) Heater power –Max at present 0.5W –Easy to manage temperatures in the shield and only small changes in sample temperature –Requires accurate temperature measurements (TPG ΔT = 0.5C) Cooling –Use anti-freeze based chiller : -20C minimum temperature –Peltier elements to further reduce temperature

The experiment Sample and thermal shield clamped to cold block Copper tower to clamp PT100 wires to cold block Heaters on sample and shield removed Pocofoam under test Thermal shield Cooling block PT100 with Manganin wire

Experiment sits inside a vacuum tank to isolate it from the external environment Vacuum Chamber Support/Insulation (polystyrene)

SolidWorks drawing of the experiment Experiment draw in SolidWorks Exported to Ansys for thermal simulation

Simulation Ansys FEA simulation performed on the simulation –Radiation losses to the environment included –Conduction losses to the environment included –Convection losses ignored Detailed simulation performed for sample of known thermal conductivity –Understand all heat loss paths to reproduce experimental results –Undesired heat paths removed as much as possible

Ansys thermal simulation of the experiment Simulation includes all know heat sources, except convection Thermal profile of simulation and experiment shown to agree better than 2%

Reduction of parasitics Cold Block Heater Sample length P=0 P1 T0T0 ΔT1ΔT1 ΔT2ΔT2

Analysis method Impossible to remove all parasitic heat paths, p, to the sample For zero intentional power have ΔT 1 Apply power P –Keep central temperature constant T 0 As long as ΔT 2 is not much larger than ΔT 1 then parasitic effects cancel

Results Measured –TPG as a function of temperature –Pocofoam –Carbon-carbon –C-SiC Copper

Through-plane thermal conductivity measurements V,I measured Water cooled Cu block Heated Cu block PT100s Plastic thermal insulation System in a vacuum and surrounded by polystyrene for thermal insulation DUT size: 1 cm x 1 cm x 100um Measure thickness with a travelling microscope DUT Pressure gauge Load cell Screw, to apply pressure Vacuum vessel

Future work System undergoing an upgrade –Extension of the operating range away from room temperature (-20C to -50C) –Additional radiation shield around the set-up –Improved vacuum tank (aim 1x10 -6 mbar) –Use of Peltier elements to lower temperature –Goal to test to -50C or lower