Collection of UNISA electronic theses and dissertations. https://ir.unisa.ac.za/handle/10500/506 2026-10-14T10:59:50Z 2026-10-14T10:59:50Z Kumi, Ebenezer Nyarko https://ir.unisa.ac.za/handle/10500/33131 2026-10-14T10:57:30Z 2026-07-03T00:00:00Z

Thermodynamic optimisation of ORC systems using hybrid renewable energy sources and nanofluid-zeotropic mixtures2 Kumi, Ebenezer Nyarko This study examines the thermodynamic performance of a hybrid solar–biomass Organic Rankine Cycle system, focusing on the selection of the working fluid and the integration of nanoparticle-enhanced zeotropic mixtures. The work is motivated by the need for decentralised renewable energy systems in regions such as sub-Saharan Africa, where solar potential is high but inconsistent, and biomass provides a reliable complementary resource. A simulation framework was developed using ASPEN Plus V14, with the Peng–Robinson Equation of state used to estimate thermophysical properties. The hybrid heat source configuration combines evacuated-tube solar collectors with a biomass-fired boiler, stabilised by a buffer tank to ensure a consistent thermal input to the ORC evaporator. System performance was assessed under solar-dominant, balanced, and biomass-dominant scenarios, with operating temperatures ranging from 120 to 200 °C. Two sets of zeotropic mixtures were evaluated; transitional refrigerants (R245fa/R123, R245fa/R1233zd(E), and R1233zd(E)/R123) and newer low-GWP alternatives (R1224yd(Z)/R1233zd(E), R1224yd(Z)/R1336mzz(Z), and R1233zd(E)/R1336mzz(Z)). Performance metrics included thermal efficiency, net power output, and heat absorption, supported by system-level indicators such as condenser load and specific work. Nanoparticles of Ag, Al₂O₃, CuO, TiO₂, and ZnO were introduced at varying concentrations to examine their effect on thermal conductivity and cycle stability. Results show that zeotropic mixtures significantly improve thermal matching in heat exchangers through temperature glide, thereby reducing irreversibility and enhancing cycle efficiency. Among the tested fluids, R1233zd(E)/R123 and R1224yd(Z)/R1233zd(E) demonstrated the best performance, delivering higher net power and efficiency across a range of conditions. Ag nanoparticles provided the most substantial enhancement, achieving up to a 16% efficiency improvement at optimal concentrations; however, higher mass fractions introduced viscosity penalties and stability concerns. Oxide nanoparticles yielded modest but more stable performance. The findings demonstrate the technical feasibility of hybrid solar–biomass ORC systems using advanced fluid formulations. While the study is limited to ii thermodynamic modelling, it provides a reproducible foundation for future experimental validation and techno-economic assessments. The work contributes to ongoing efforts to develop sustainable, decentralised energy systems suitable for regions with variable renewable resources.

2026-07-03T00:00:00Z Roets, Andre https://ir.unisa.ac.za/handle/10500/33130 2026-10-14T09:18:18Z 2025-12-29T00:00:00Z

A conceptual model for improving public perceptions of traffic police professional image in South Africa: an empirical investigation Roets, Andre Enhancing the professionalism of traffic policing in South Africa is a difficult task, but it will increase the effectiveness and legitimacy of the profession. There is a need for strict traffic law enforcement to ensure road safety; nevertheless, contemporary South Africa faces persistent institutional shortcomings and the normalisation of deviant behaviour. The operational interface between the motoring public and Traffic Police Officers (TPOs) has been fundamentally damaged. Traffic-public interactions are generally challenging encounters defined by acute public apprehension or capiophobia (fear) rather than partnership-based cooperation for safety. This thesis presents the proposed Public Satisfaction Model as a guide to restoring traffic policing and improving the professional image of TPOs. A convergent mixedmethods strategy was used, collecting quantitative survey data (491 valid responses) and qualitative one-to-one interviews (13 participants). The convergence of these datasets provided a robust criminological analysis of the contemporary traffic law enforcement situation. The analysis found a significant gap between statutory expectations and practical realities, with TPOs failing to meet the required standard. Systemic bribery, extortion and a socio-cultural normalisation of deviance gravely damage their professional image. Corrupt transactions cross demographic boundaries. The absence of procedural fairness, opportunistic policing for monetary gain and abuse of state resources erode public trust and even undermine the visual authority of the uniform. Public anxiety during nocturnal stops is further inflamed by the danger of imitative traffic police officers and secondary media narratives. The study recommends that institutional credibility can be restored through the use of bilateral accountability instruments, including body-worn cameras, 24-hour visible policing, and mandatory rehabilitation for repeat offenders. Future research should examine the socio-economic determinants of public complicity in bribery and the internal occupational problems faced by TPOs.

2025-12-29T00:00:00Z Donda, Elliot Mandlakayise https://ir.unisa.ac.za/handle/10500/33129 2026-10-14T09:06:12Z 2026-08-22T00:00:00Z

Performance of the Compact Turbo and the Alicoco spiral separators in the recovery of Zircon at the Wet Circuit of the Grande Côte Opérations Donda, Elliot Mandlakayise

2026-08-22T00:00:00Z Gazi, Luntukazi https://ir.unisa.ac.za/handle/10500/33128 2026-10-13T18:12:10Z 2026-02-01T00:00:00Z

The lived experiences of female street vendors during COVID-19 restrictions in the Eastern Cape Province Gazi, Luntukazi This study explores the lived experiences and coping mechanisms of female street vendors in the Eastern Cape Province during the COVID-19 lockdown restrictions. The pandemic and subsequent restrictions significantly disrupted the informal economy, placing female street vendors in a position of economic vulnerability and psychosocial strain. Drawing on Feminist Theory, Informal Economy Theory and the Transactional Model of Stress and Coping, this qualitative study examines how inequalities and economic precarity intersected with the health crisis to shape the experiences of female vendors. A constructivist paradigm and phenomenological qualitative design were adopted. Data were collected through face-to-face semi-structured interviews and analysed thematically. The findings reveal that profound economic disruption, heightened caregiving burdens, fear of infection and psychological distress, alongside evidence of resilience, adaptive coping strategies and reliance on community and faith-based support systems. The study concludes that while female street vendors demonstrated considerable resilience, structural vulnerabilities exacerbated their distress. Recommendations are offered for gender-sensitive psychosocial interventions, community-based support structures and policy reforms to strengthen protection for informal workers during future crises. Text in English with summaries in English and Xhosa

2026-02-01T00:00:00Z