arXiv subjects

Alexander Franke

Publications and source records attributed to Alexander Franke.

4 recordsLinked to original sources

arXiv2025

Spatio-Temporal Life Cycle Analysis of Electrolytic H2 Production in Australia under Time-Varying CO2 Management Schemes

The transition to sustainable energy is critical for addressing global climate change. Hydrogen production, particularly via electrolysis, has emerged as a key solution, offering the potential for low-carbon energy across various sectors. This paper presents a novel approach to enhancing hydrogen production by aligning it with periods of low-carbon intensity on the electricity grid. Leveraging real-time data from the Electricity Mapping database and real-time electricity cost data from the AEMO database, the model dynamically adjusts hydrogen output to minimize both emissions and production costs. Furthermore, the integration of hydrogen tax credits significantly enhances cost-effectiveness, offering a viable pathway for widespread adoption. A comprehensive Life Cycle Assessment (LCA) framework is employed to assess the environmental impacts, emphasizing the need for real-time data incorporation to more accurately reflect hydrogen production's carbon footprint. The study concludes that dynamic, real-time operation, coupled with financial incentives, provides a promising method to enhance the sustainability and economic viability of hydrogen production.

eess.SY↗

arXiv2024

Measurement of the thermal accommodation coefficient of helium on a crystalline silicon surface at low-temperatures

Next-generation gravitational wave observatories are expected to use cryogenically cooled, pendulum-suspended 200 kg test mass mirrors from a crystalline material such as crystalline silicon. During operation of the observatories, these mirrors undergo heating due to the absorption of laser radiation of up to a watt. Low noise cooling techniques need to be developed. Low-pressure helium exchange gas at 5 K might contribute to the challenging task. Here, we report the measurement of the helium accommodation coefficient $\alpha(11\,\mathrm{K} 0.7$ for temperatures < 20 K, which increases the cooling power compared to recently used assumptions. The idea of free molecular flow helium gas cooling is thus supported and might find application in some observatory concepts.

physics.ins-det↗

arXiv2023

Self-calibrating gas pressure sensor with a 10-decade measurement range

Recent years have seen a rapid reduction in the intrinsic loss of nanomechanical resonators (i.e., chip-scale mechanical oscillators). As a result, these devices become increasingly sensitive to the friction exerted by smallest amounts of gas. Here, we present the pressure-dependency of a nanomechanical trampoline resonator's quality factor $Q$ over ten decades, from $10^{-7}$ to $10^{3}\,\mathrm{mbar}$. We find that the measured behavior is well-described by a model combining analytical and numerical components for molecular and viscous flow, respectively. This model relies exclusively on design and typical material parameters, together with measured values of intrinsic resonance frequency $f_\mathrm{in}$ and quality factor $Q_\mathrm{in}$. Measuring $f_\mathrm{in}$ and $Q_\mathrm{in}$ at a pressure $<\!10^{-7}\,\mathrm{mbar}$ self-calibrates our sensor over its entire measurement range. For a trampoline's fundamental out-of-plane vibrational mode, the resulting deviation between measured and simulated pressure dependencies of the quality factor and resonance frequency is within $15\,\%$ and $4\,\%$, respectively. The resulting error for pressure values inferred from quality factor and frequency measurements is $<10\,\%$, for pressures between $\sim 10^{-6}$ and $\sim 10^{-1}\,\mathrm{mbar}$, and $<25\,\%$ for the complete 10-decade measurement range. Exceptions are two outliers with increased measurement errors, which might be related to the limited accuracy of our commercial pressure gauge. Based on investigations with helium, we demonstrate the potential for extending this sensing capability to other gases, thereby highlighting the practical use of our sensor.

physics.app-ph↗

arXiv2021

Gas cooling of test masses for future gravitational-wave observatories

Recent observations made with Advanced LIGO and Advanced Virgo have initiated the era of gravitational-wave astronomy. The number of events detected by these "2nd Generation" (2G) ground-based observatories is partially limited by noise arising from temperature-induced position fluctuations of the test mass mirror surfaces used for probing spacetime dynamics. The design of next-generation gravitational-wave observatories addresses this limitation by using cryogenically cooled test masses; current approaches for continuously removing heat (resulting from absorbed laser light) rely on heat extraction via black-body radiation or conduction through suspension fibres. As a complementing approach for extracting heat during observational runs, we investigate cooling via helium gas impinging on the test mass in free molecular flow. We establish a relation between cooling power and corresponding displacement noise, based on analytical models, which we compare to numerical simulations. Applying this theoretical framework with regard to the conceptual design of the Einstein Telescope (ET), we find a cooling power of 10 mW at 18 K for a gas pressure that exceeds the ET design strain noise goal by at most a factor of $\sim 3$ in the signal frequency band from 3 to 11 Hz. A cooling power of 100 mW at 18 K corresponds to a gas pressure that exceeds the ET design strain noise goal by at most a factor of $\sim 11$ in the band from 1 to 28 Hz.

physics.ins-det↗