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Effect of temperature gradient on calorimetric measurements during gas-loading experiments

This study examines the impact of temperature gradient on calorimetric measurements during gas-loading experiments, specifically focusing on the effects of hot and cold spots. The results show that these temperature variations can lead to measurement artifacts and must be taken into consideration for accurate results. The study also suggests using inert gas to mitigate temperature measurement artifacts.

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Effect of temperature gradient on calorimetric measurements during gas-loading experiments

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  1. Effect of temperature gradient on calorimetric measurements during gas-loading experiments O. Dmitriyeva1,2, R. Cantwell1, M. McConnell1, G. Moddel2 1 Coolescence, LLC, Boulder, CO, USA 2 University of Colorado – Boulder, CO, USA 10th Workshop - Siena

  2. Motivation (June 2011) • Ni catalyst • H2 pressurization • Cooling & heating observed 10th Workshop - Siena

  3. Motivation (February 2012) 390oC under 1200 torr H2 H2 H2 H2 D2 D2 D2 50 mW • ZrO-Ni from Dr. Brian Ahern • H2 & D2 pressurizations • 50 mW excess power 2 hours 10th Workshop - Siena

  4. Motivation • Excess heat generation: • at high temperatures (>250oC) • same for H2 and D2 • no decline over time (4 days!) • depends on vessel location 10th Workshop - Siena

  5. Questions to answer • What causes baseline shift? • Can we enhance effect intentionally? • excess heat • excess cold • Independent of gas type? • Applicable to other gas-loading experiments? 10th Workshop - Siena

  6. Gas-loading system • Precision of temperature control 10 mK • 6g of material • Pressure up to 1200 torr • Chamber temperature 40 - 390˚C to vacuum pump pressure gauge reference Ma sample under test temperature acquisition thermistors H2 D2 He isothermal chamber HP 5890 gas chromatographer 10th Workshop - Siena

  7. Thermal gradient in chamber Cold spot Air fan Hot spot 10th Workshop - Siena

  8. Hypothesis 10th Workshop - Siena

  9. Hot spot coupling vacuum gas Gas convection Hot spot Hot spot T1 T2 T1 T3 Thermocouples T2 < T3 10th Workshop - Siena

  10. Forming hot spot intentionally • Hot spot: 150 Ohm resistor: • 1 watt • 4 watt 4 W effect resistor 1 W effect 10th Workshop - Siena

  11. For our configuration: 0.90oC -> 0.8 W apparent excess heat 20% 0.21oC -> 0.17 W apparent excess heat 17% Effect of hot spot in the presence of gas a) 4 W b) 1 W 0.90oC 0.21oC 0 W no resistor – no hot spot H2 H2 H2 10th Workshop - Siena

  12. Independent of gas type • Chamber at 100oC • H2, He 1200 torr • Hot spot 1 watt • H2 and He runs show same exothermic shift of the baseline • H2 runs show spikes: loading/unloading in Ni 10th Workshop - Siena

  13. Cold spot coupling vacuum gas Gas convection Cold spot Cold spot T1 T2 T1 T3 Thermocouples T2 > T3 10th Workshop - Siena

  14. Forming cold spot intentionally • Peltier element - cooling Peltier 0.8 W to Peltier 10th Workshop - Siena

  15. Forming cold spot intentionally • For our configuration: 0.025oC -> 0.013 W apparent excess cooling 1.6% 0.025oC 10th Workshop - Siena

  16. Creating hot spot by heat sleeve 2oC Heat sleeve • For our configuration: • 2oC -> 1.2 W • Apparent excess heat 3% 10th Workshop - Siena

  17. Summary • Temperature gradient causes measurement artifact • Conditions were recreated by • Resistor – hot spot – baseline shifts upwards • Peltier elem. – cold spot – baseline shifts downwards • Heat sleeve: apparent excess heat 3% 10th Workshop - Siena

  18. Conclusion Inert gas must be used to rule out temperature measurements artifacts 10th Workshop - Siena

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