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Mark Baldry
School of Physics University of Sydney Sydney New South Wales Australia

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Full paper
Published: 30 March 2021 in Plasma Processes and Polymers
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Precise control of capacitively coupled radiofrequency (CCRF) plasma reactors is required to achieve desired outcomes in surface functionalisation and material synthesis processes. This necessitates detailed mapping of the large process parameter space and a thorough understanding of spatial and temporal variations of the plasma throughout the reactor. These goals can only feasibly be achieved with accurate numerical modelling. Previous numerical studies of CCRF discharges have implemented a range of simplifying assumptions to improve numerical tractability, such as small electrode spacing, radial uniformity, fewer active species and simplified boundary conditions, while neglecting self‐bias formation. Although this approach is useful in developing the methodology for continuum plasma modelling, it poses challenges for direct comparison with experimental data and for understanding the behaviour of plasma processes employed in the surface treatment of large, complex objects, or the synthesis of nanoparticles. Here we report the development of a two‐dimensional axisymmetric continuum model for a CCRF reactor with a pure argon 13.56‐MHz discharge using the finite element method. The large electrode spacing and reactor design result in two distinct discharge regions and the formation of a strong DC self‐bias on the powered electrode. The plasma discharge is studied as the pressure is varied from 0.1 to 0.3 Torr, over the radiofrequency input power range of 25–100 W, which leads to consistent enhancements of the electron density and self‐bias. The impact of the electron energy distribution function (EEDF) on the discharge is assessed, with the assumption of a Druyvesteyn EEDF resulting in a bulk electron density and temperature of 3.4 × 1015 m−3 and 3.3 eV, respectively, compared with 8.1 × 1015 m−3 and 1.9 eV in the Maxwellian case. The asymmetric power distribution throughout the reactor is quantified to build a reduced domain model with a lower computational cost. The effect of an electrically floating parallel plate electrode is assessed, resulting in a 42% higher bulk plasma potential as compared with the grounded case. The inclusion of resonant and 2p excited states of argon is shown to have a major impact on the discharge dynamics, leading to an order of magnitude reduction in bulk electron density. This study proposes a robust numerical model of a CCRF argon plasma discharge to facilitate future simulations of more complex discharges with important implications in plasma surface engineering and synthesis of materials.

ACS Style

Mark Baldry; Laura L. Haidar; Behnam Akhavan; Marcela M. M. Bilek. Continuum modelling of an asymmetric CCRF argon plasma reactor: Influence of higher excited states and sensitivity to model parameters. Plasma Processes and Polymers 2021, 18, e2000243 .

AMA Style

Mark Baldry, Laura L. Haidar, Behnam Akhavan, Marcela M. M. Bilek. Continuum modelling of an asymmetric CCRF argon plasma reactor: Influence of higher excited states and sensitivity to model parameters. Plasma Processes and Polymers. 2021; 18 (6):e2000243.

Chicago/Turabian Style

Mark Baldry; Laura L. Haidar; Behnam Akhavan; Marcela M. M. Bilek. 2021. "Continuum modelling of an asymmetric CCRF argon plasma reactor: Influence of higher excited states and sensitivity to model parameters." Plasma Processes and Polymers 18, no. 6: e2000243.

Journal article
Published: 02 December 2020 in Journal of Thermal Science and Engineering Applications
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The rapid development of metal 3D printing techniques has enabled the exploration of complex free-convection heat sink designs. Small free-convection heat sinks with pin-fin arrays (or novel geometries) are widely employed at different orientations in a variety of electronic devices, yet there is limited understanding of how orientation impacts their heat transfer behavior. This article characterizes the orientation-dependent performance of a small, tapered pin, free-convection heat sink (named HS17) manufactured with direct metal laser sintering for use with a thermoelectric scalp cryotherapy device for the prevention of chemotherapy-induced alopecia. A validated numerical model and custom-built free-convection test rig were used to investigate the heat sink’s performance over the orientation range of 0 deg to 135 deg. HS17 maintained relatively robust performance over the 0 deg to 90 deg range; however, the thermal resistance (Rth) at 112.5 deg and 135 deg was 6% and 11% higher compared to the 90 deg case, respectively. The heat sink design was modified to include a 22.5 deg wedge base (named HS17-W) to mitigate this performance decline, which is important to ensure safe and continued operation of the cryotherapy device. Compared to the flat base heat sink, the wedge-base design successfully reduced Rth from 11.9 K/W, 12.5 K/W, and 12.8 K/W to 11.5 K/W, 11.8 K/W, and 12.3 K/W at 90 deg, 112.5 deg, and 135 deg, respectively. These results demonstrate the effectiveness of the current proposed design to improve the performance of free-convection heat sinks at downward-facing orientations.

ACS Style

Mark Baldry; Victoria Timchenko; Chris Menictas. The Effect of Orientation on the Performance of Small Free-Convection Heat Sinks for Use With a Thermoelectric Cryotherapy Device. Journal of Thermal Science and Engineering Applications 2020, 13, 1 -23.

AMA Style

Mark Baldry, Victoria Timchenko, Chris Menictas. The Effect of Orientation on the Performance of Small Free-Convection Heat Sinks for Use With a Thermoelectric Cryotherapy Device. Journal of Thermal Science and Engineering Applications. 2020; 13 (4):1-23.

Chicago/Turabian Style

Mark Baldry; Victoria Timchenko; Chris Menictas. 2020. "The Effect of Orientation on the Performance of Small Free-Convection Heat Sinks for Use With a Thermoelectric Cryotherapy Device." Journal of Thermal Science and Engineering Applications 13, no. 4: 1-23.

Journal article
Published: 16 October 2020 in Sustainability
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Human health is a key pillar of modern conceptions of sustainability. Humanity pays a considerable price for its dependence on fossil-fueled energy systems, which must be addressed for sustainable urban development. Public hospitals are focal points for communities and have an opportunity to lead the transition to renewable energy. We have reimagined the healthcare energy ecosystem with sustainable technologies to transform hospitals into networked clean energy hubs. In this concept design, hydrogen is used to couple energy with other on-site medical resource demands, and vanadium flow battery technology is used to engage the public with energy systems. This multi-generation system would reduce harmful emissions while providing reliable services, tackling the linked issues of human and environmental health.

ACS Style

Nicholas Gurieff; Donna Green; Ilpo Koskinen; Mathew Lipson; Mark Baldry; Andrew Maddocks; Chris Menictas; Jens Noack; Behdad Moghtaderi; Elham Doroodchi. Healthy Power: Reimagining Hospitals as Sustainable Energy Hubs. Sustainability 2020, 12, 8554 .

AMA Style

Nicholas Gurieff, Donna Green, Ilpo Koskinen, Mathew Lipson, Mark Baldry, Andrew Maddocks, Chris Menictas, Jens Noack, Behdad Moghtaderi, Elham Doroodchi. Healthy Power: Reimagining Hospitals as Sustainable Energy Hubs. Sustainability. 2020; 12 (20):8554.

Chicago/Turabian Style

Nicholas Gurieff; Donna Green; Ilpo Koskinen; Mathew Lipson; Mark Baldry; Andrew Maddocks; Chris Menictas; Jens Noack; Behdad Moghtaderi; Elham Doroodchi. 2020. "Healthy Power: Reimagining Hospitals as Sustainable Energy Hubs." Sustainability 12, no. 20: 8554.

Journal article
Published: 17 April 2020 in Applied Sciences
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The world is moving to the next phase of the energy transition with high penetrations of renewable energy. Flexible and scalable redox flow battery (RFB) technology is expected to play an important role in ensuring electricity network security and reliability. Innovations continue to enhance their value by reducing parasitic losses and maximizing available energy over broader operating conditions. Simulations of vanadium redox flow battery (VRB/VRFB) cells were conducted using a validated COMSOL Multiphysics model. Cell designs are developed to reduce losses from pump energy while improving the delivery of active species where required. The combination of wedge-shaped cells with static mixers is found to improve performance by reducing differential pressure and concentration overpotential. Higher electrode compression at the outlet optimises material properties through the cell, while the mixer mitigates concentration gradients across the cell. Simulations show a 12% lower pressure drop across the cell and a 2% lower charge voltage for improved energy efficiency. Wedge-shaped cells are shown to offer extended capacity during cycling. The prototype mixers are fabricated using additive manufacturing for further studies. Toroidal battery designs incorporating these innovations at the kW scale are developed through inter-disciplinary collaboration and rendered using computer aided design (CAD).

ACS Style

Nicholas Gurieff; Declan Finn Keogh; Mark Baldry; Victoria Timchenko; Donna Green; Ilpo Koskinen; Chris Menictas. Mass Transport Optimization for Redox Flow Battery Design. Applied Sciences 2020, 10, 2801 .

AMA Style

Nicholas Gurieff, Declan Finn Keogh, Mark Baldry, Victoria Timchenko, Donna Green, Ilpo Koskinen, Chris Menictas. Mass Transport Optimization for Redox Flow Battery Design. Applied Sciences. 2020; 10 (8):2801.

Chicago/Turabian Style

Nicholas Gurieff; Declan Finn Keogh; Mark Baldry; Victoria Timchenko; Donna Green; Ilpo Koskinen; Chris Menictas. 2020. "Mass Transport Optimization for Redox Flow Battery Design." Applied Sciences 10, no. 8: 2801.

Preprint
Published: 26 March 2020
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The world is moving to the next phase of the energy transition with high penetrations of renewable energy. Flexible and scalable redox flow battery (RFB) technology is expected to play an important role in ensuring electricity network security and reliability. Continuous performance improvements will further enhance their value by reducing parasitic losses and maximizing available energy conversion over broader operating conditions. Concentration overpotentials from poor internal reactant distribution at high and low states of charge (SOC) limit power densities and are thus an important area of investigation. However, efforts to address these coupled electrochemical phenomena can compromise mechanical performance. Modelling and simulation of cell design innovations have shown it is possible to reduce losses from pump energy while increasing the availability of active species where required. The combination of wedge-shaped cells with static mixers investigated in this paper can reduce pressure drop and improve energy efficiency. Toroidal vanadium redox flow battery (VRB/VRFB) designs incorporating this innovation are presented for further development to improve community engagement with the technology.

ACS Style

Nicholas Gurieff; Declan Finn Keogh; Mark Bladry; Victoria Timchenko; Donna Green; Ilpo Koskinen; Chris Menictas. Mass Transport Optimization for Redox Flow Battery Design. 2020, 1 .

AMA Style

Nicholas Gurieff, Declan Finn Keogh, Mark Bladry, Victoria Timchenko, Donna Green, Ilpo Koskinen, Chris Menictas. Mass Transport Optimization for Redox Flow Battery Design. . 2020; ():1.

Chicago/Turabian Style

Nicholas Gurieff; Declan Finn Keogh; Mark Bladry; Victoria Timchenko; Donna Green; Ilpo Koskinen; Chris Menictas. 2020. "Mass Transport Optimization for Redox Flow Battery Design." , no. : 1.

Journal article
Published: 02 July 2019 in Applied Thermal Engineering
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Metal additive manufacturing technologies are increasingly being adopted for rapid prototyping and to build geometrically complex designs for thermal management. This paper develops and experimentally validates a numerical model to design a high performance, small-scale heat sink for use with a thermoelectric cooling cap. The design was constrained by a heat load of 2.15 W, and a target average base temperature of 45°C as a compromise between avoiding burn injury and reducing heat dissipation requirements. Over successive numerical iterations, an optimal natural convection heat sink was developed with an estimated thermal resistance of 10.9 K.W-1 and base temperature of 44.4°C. This design featured an internal cavity in a tapered pin array, and was able to achieve a steady state base temperature that was 11.7°C cooler than a conventional design, with 51% less surface area and significantly less material.

ACS Style

Mark Baldry; Victoria Timchenko; Chris Menictas. Optimal design of a natural convection heat sink for small thermoelectric cooling modules. Applied Thermal Engineering 2019, 160, 114062 .

AMA Style

Mark Baldry, Victoria Timchenko, Chris Menictas. Optimal design of a natural convection heat sink for small thermoelectric cooling modules. Applied Thermal Engineering. 2019; 160 ():114062.

Chicago/Turabian Style

Mark Baldry; Victoria Timchenko; Chris Menictas. 2019. "Optimal design of a natural convection heat sink for small thermoelectric cooling modules." Applied Thermal Engineering 160, no. : 114062.

Journal article
Published: 01 August 2018 in Journal of Thermal Biology
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This study presents a novel, thermoelectric cryotherapy cap that aims to provide effective and controlled scalp cooling to prevent hair loss for chemotherapy patients. The cap's design consists of multiple thermoelectric coolers (TECs) evenly spaced and bonded to a soft thermal interface material, tightly fitted to a patient's head. A numerical model is developed to assess the performance of alternative cap designs in relation to their ability to achieve hair follicle hypothermia. Under ideal conditions, 26.5 W of heat removal from the scalp is required to achieve the clinically-significant follicle temperature target of 22 °C. Temperature maps of the subcutaneous tissue are generated to visualise the development of hypothermic follicles, and thereby assess the effectiveness of the cap design. Transient studies show that cooling to the therapeutic temperature can be achieved within 40 minutes. To avoid the possibility of cold-induced tissue damage, individual thermoelectric cooling modules should not be operated at a cooling flux beyond approximately 3,175 W/m2. This may be achieved with 38 modules evenly spaced in a checkerboard arrangement, each providing 0.7 W of cooling to the scalp.

ACS Style

Mark Baldry; Victoria Timchenko; Chris Menictas. Thermal modelling of controlled scalp hypothermia using a thermoelectric cooling cap. Journal of Thermal Biology 2018, 76, 8 -20.

AMA Style

Mark Baldry, Victoria Timchenko, Chris Menictas. Thermal modelling of controlled scalp hypothermia using a thermoelectric cooling cap. Journal of Thermal Biology. 2018; 76 ():8-20.

Chicago/Turabian Style

Mark Baldry; Victoria Timchenko; Chris Menictas. 2018. "Thermal modelling of controlled scalp hypothermia using a thermoelectric cooling cap." Journal of Thermal Biology 76, no. : 8-20.