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The UC Research Repository collects, stores and makes available original research from postgraduate students, researchers and academics based at the University of Canterbury.
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Thermal and emission performance studies on premixed meso-combustors for thermophotovoltaic applications.
(2025) Rong, Hui
This study focuses on the thermal and emission performance of small-size premixed combustors by investigating the combustion and flow characteristics of various carbon-free and classical hydrocarbon fuels, including ammonia, hydrogen, and methane. More attention is given to the influence of combustor structure and inlet parameters on thermodynamic and emission performance. These novel structural designs demonstrated obvious improvements in combustor performance, offering valuable insights into the optimization of small-scale combustion systems.
One of the designs include a reverse flow single-channel inlet and double-channel outlet (SIDO) combustor aining to enhance its thermal performances. Increasing the inlet pressure (Pin) improves thermal performance and exergy efficiency while reducing nitrogen oxide emissions. Increasing the inlet velocity (Vin) can enhance the temperature uniformity of the combustor wall. Increasing the equivalence ratio (Φ) leads to a reduction of nitrogen oxide emissions, and the micro-combustor has better overall performance, when Φ = 1.0. Increasing the blending ration of hydrogen give rise to a decayed advection but enhanced diffusion, and the pressure loss (Ploss) can be reduced.
Another design is applying porous medium (PM) in the small-size combustors. In comparison with the system without PM, the application of PM is found to lead to a significant improvement on thermal performances. It is found that there is a substantial 37.5% reduction in the standard deviation of the outer wall temperature (ST,W) at Vin = 2.0 m/s. The optimal thermal performance is achieved as Φ=0.9. A higher porosity (σ) gives rise to a lower entropy production within the PM. The lowest entropy production resulting from heat conduction is shown to be achieved when σ = 0.8. By implementing PM, the exergy efficiency (ηexergy) is found to be increased by 23.9% at Vin = 2.0 m/s. In general, this present investigation shed physical insights on the entropy production and thermodynamic exergy performances of ammonia/methane-fueled micro-combustion systems with and without PM.
For comparison, we proposed and studied a double-channel inlet and double-channel outlet (DIDO) combustor, which is shown to be capable of generating a vortex at the outlet, thereby reducing NOx emissions. Specifically, at a ammonia volumetric flow rate of 900 mL/min, the NO concentration at the outlet can be curtailed by 29.23%. The DIDO combustor yields a substantial enhancement in thermal performance, achieving a 51% reduction in ST,W when ammonia volumetric flow rate is set at 500 mL/min which significantly enhances the uniformity of wall temperature. The peak of thermal performance and maximum radiation efficiency (ηradiation) is reached at Φ = 0.9.
Finally, we proposed and investigated a reverse-flow Tesla channel applied in a counter-flow combustor. It is found that such structured combustor has a remarkable improvement of 72.6% to the combustor wall temperature at hydrogen volume flow rate of 100 mL/min. The diodicity (Di) of the Tesla valve is found to be increased with higher hydrogen volume flow rate, and a lower Φ contributes to a higher Di. Besides, Di decreases when Φ goes up, stabilizing at Φ = 0.9. The reverse-flow Tesla valve exhibits a more uniform pressure distribution and entropy production than the forward-flow Tesla valve. At Φ = 0.9, the hydrogen-to-air ratio maximized heat release, producing the highest entropy. Tesla-valve structured combustors demonstrate near complete combustion before Φ reaching 0.9, the combustion efficiency (ηcombustion) gradually decreasing after Φ getting to 1.0. Additionally, the effect of blending ammonia with various ratio of hydrogen was studied. To achieve a stable ammonia-hydrogen combustion within the reverse and forward flow Tesla valves, ammonia ratio can reach 20% for the reverse flow Tesla valve, whereas the ratio for a stable combustion in the forward flow configuration is 10%. The increased flow resistance inside the reverse flow structure promotes more complete fuel-depleted combustion, thereby increasing the wall temperature. In contrast, the forward flow structure, due to its lower flow resistance, extends the flame area of the mixed fuel, thereby improving wall temperature uniformity. The Double-layer Tesla Valve structure improves wall temperature uniformity by over 55% across varying flow rates. Both double-layer and single-layer structures demonstrate a significant enhancement in the combustor's thermal performance and overall performances characterized with Nusselt and Peclet numbers.
The effectiveness of cognitive and behavioural interventions including parental involvement for anxiety in autistic youth : a systematic review.
(2025) Walker, Tyler
The diagnostic prevalence of autism is growing with a considerable increase shown globally (Maenner et al., 2023; Zeiden et al., 2022) over previous decades (Russell et al., 2022). Moreover, the rates in which anxiety co-occurs with autism is high, with estimates thought to range between 40% to 50%. Anxiety is seen to exacerbate core autism features and impact social and emotional adaptation, relationships, educational performance (Fujii et al. 2012; Reaven et al. 2011; Wood et al. 2015), and the individual’s quality of life (van Steensel et al., 2012). Parental involvement is argued to have significance clinically when treating autistic youth, with research arguing that including parents has the potential to enhance interventional outcomes. The current review aims to evaluate the effectiveness of cognitive and behavioural interventions including parental involvement for anxiety in autistic youth. This was achieved by evaluating the two primary research questions. This review seeks to investigate the effectiveness of parental involvement within cognitive and behavioural interventions targeting anxiety in autistic youth, evaluating outcomes across all measures, not only anxiety. A secondary aim for this review was to investigate whether the degree of parental involvement was impactful upon intervention effects. Studies were included if they: identified anxiety as their primary outcome measure, aimed to reduce or treat anxiety in youth who were school aged (4-18 years) with either a diagnosis of autism and heightened anxiety, included parents, used quantitative research methods, measured at least at pre-intervention and post-intervention. A systematic search of several electronic databases including PsychINFO, PubMed, SCOPUS, embase, and Cochrane Library yielded 3610 citations. Following removal of duplicates, abstract and title screening, full text review, and forward and backward citation searches, 18 studies met eligibility criteria and were included. Of these studies 13 were Randomised Control Trials (RCT) and five were quasi-experimental (QE). Risk of bias was assessed using both the Risk of Bias 2 (RoB2) and the Risk of Bias in Non-randomised Studies of Intervention – version 2 (ROBINS-IV2). The review found marked improvements across all measures of anxiety. The results consistently highlighted reductions in primary anxiety scores, clinical severity of anxiety, and notable improvements in functional measures. Although, some sub-scales demonstrated minimal and insignificant improvement or decline. Moreover, some intervention gains were seen in the broader familial unit. Some limitations were present including broad inclusion criteria, and issues with generalizability. The review included studies that showed a broad range of participant ages, not accounting for developmental differences. Finally, some issues with generalisability may be present as the participants were predominantly male. However, this limitation was to be expected as males are over represented in autism diagnosis.
Student reflections on the transition from primary to intermediate school: exploring expectations, coping and Kiwi Can participation.
(2025) Selwood, Olivia
The transition from primary to intermediate school represents a significant period of change and opportunity for early adolescents, who must adjust to an unfamiliar environment while also navigating a critical developmental milestone: the onset of puberty. Many students face social, academic, and emotional challenges that can impact their overall wellbeing. Despite its significance, research has predominantly focused on other school transitions, leaving a gap in understanding students’ lived experiences. Informed by the Transactional Model of Stress and Coping and Resilience Theory, this qualitative research explored students’ reflections on their transition, focusing on their expectations, adjustment, and coping. It also examined students' perspectives on the Graeme Dingle Foundation’s Kiwi Can program and its application to their primary-intermediate school transition. Ten year-seven students participated in semi-structured interviews, and students’ primary caregivers completed a questionnaire with similar open-response questions as the student interviews for a supplementary data source. The findings revealed that students primarily held negative expectations about intermediate school, often shaped by external sources. Social concerns were particularly salient; however, the extent of peer conflict and complex social dynamics was unexpected. Although academic difficulty increased, the changes were often overestimated. A positive aspect of the transition to intermediate school was the opportunity to participate in extracurricular activities and novel subjects, fostering self-expression. Students were proficient at identifying their coping strategies, particularly relying on peer support and self-directed emotional regulation. Some students attributed their application of resilience and social-emotional skills to Kiwi Can, while others did not consciously make direct links. Findings on expectations, lived experience, and coping aligned with literature on intermediate transitions, offering rich qualitative insights to inform practices and policies that promote a smooth transition.
Forming metal organic framework glass membranes for gas separation.
(2025) Stone, Dana M.
This thesis investigates the fundamental factors affecting the use of glass transformations to repair defective crystalline metal organic framework (MOF) membranes. This work aims to clarify our understanding of the major limitation that prevents MOF materials being used for gas separation membranes: intercrystalline defects. The research aimed to produce MOF membranes within tubular ceramic supports and evaluate the differences in gas separation performance between crystalline and glass (ag) forms. A four-stage method was adapted to produce glass membranes, including the use of an -alumina tubular support, ZnO precursor deposition via Atomic Layer Deposition (ALD), in-situ solvothermal synthesis of ZIF-62, and defect healing through glass transformation. The gas separation performance of ZIF-62 and agZIF-62 membranes showed low permeance (10⁻⁸ & 10⁻¹⁰ mol m⁻²s⁻¹Pa⁻¹ respectively) and selectivities (e.g. H₂/CO₂ of 3.5 & 4.3 respectively) which were seen as significant areas for improvement. To address the low permeance, ALD conditions to control membrane thickness were developed, reducing crystalline membranes thicknesses from 38 μm to 16 μm. The glass transition process led to further membrane thinning, down to 2 μm, due to a capillary effect. To address low selectivity, the relationship between isothermal hold times, porosity, and macroscopic melting was examined via PALS, adsorption studies, and visual imaging. These results showed that only limited retention of porosity was possible, and that isothermal treatments offered no control over pore structure. These results highlighted challenges in reproducibility during glass transformation by revealing the variability in agZIF-62 samples, including pore aperture size which ranged from 3.2 to 3.7 Å. Finally, a pioneering alternative synthesis approach using chemical vapor deposition (CVD) was explored for the multi-ligand ZIF-62 to address the poor quality of ZIF-62 membranes. However, the polymorphic nature and high energy state of ZIF-62 prevented its synthesis via CVD, instead resulting in the formation of the dense ZIF-zni. Overall, this research provides foundational insights for enhancing the performance and scalability of ZIF-based membranes for gas separation.
Jesting boundaries : the impact of context on offensive humor and censorship.
(2025) Robertson, K. L.
This research examines the psychology behind people supporting censorship and
“cancelling” of comedians for telling “offensive” jokes. We argue that people don’t cancel comedians
because of bad jokes, but because of the inferred meaning behind the jokes, and what the audience
thinks a joke reveals about the comedian’s mind (Gray, et al., 2012; Waytz, et al., 2010). Sometimes
the way a joke is told reveals more about the person’s character than the words in the joke itself. We
used a model of mind perception, the Heuristic of Sufficient Explanation (HOSE) to help unpack when
jokes reveal bad character versus not (Vonasch, et al., 2024). We predicted that people will be more
likely to be offended and support censorship when they are told a joke with offensive content that is
not justified by context in how the joke is being told. Results from two experimental studies showed
that missing context led to the audience misperceiving the intentions of the comedian, their mind,
and their overall character due to greater offense taken, and thus audiences were more likely to
support censorship in conditions where the context was missing. However, the extent to which they
supported censorship across all contexts was minimal, supporting the hypothesis that a vocal
minority of people are driving support for censorship of comedians telling offensive jokes (Mustafaraj
et al., 2011). Understanding why individuals and groups may choose to censor comedy it allows us to
examine the balance between protecting societal sensitivities and preserving comedy’s vital role in
promoting free expression, challenging norms, and fostering democratic discourse.