Drying agricultural produce consumes a considerable amount of energy. As an energy-efficient system, a heat pump can improve the energy efficiency of the drying process and hence reduce the energy consumption, especially in South Africa, where both sub-tropical and temperate weather conditions dominate. The objective of this research is to experimentally investigate the impacts of weather conditions on the operational conditions and thermal performance of an open-loop air-source heat pump drying system. The experimental investigation was conducted in a climate chamber where the climate conditions were simulated from −10 °C to 20 °C with an interval of 10 °C for the typical temperature range of the harvesting season in South Africa. The findings indicate that ambient temperatures have a significant impact on both the operating conditions and thermal performance of an open-loop heat pump system; the change in ambient temperatures from −10 °C to 20 °C leads to a 141.6% improvement in the suction pressure, a 214.2% increase in the discharge pressure, and 30.1% increase in the compression ratio, as well as a consequent increase of 130.6% in the refrigerant mass flow rate (from 0.0067 to 0.0155 kg/s), resulting in a corresponding increase in the coefficient of performance (COP) of the heat pump drying system by about 42.1%. Therefore, this study suggests that, while using an open-loop air-source heat pump drying system utilising R134a refrigerant is feasible in South Africa, it may be practically limited to regions with warm climates or during warmer seasons.

This study investigates the impact of optimizing refrigeration systems using an environmentally friendly refrigerant, isobutane (R600a), which has a low global warming potential (GWP) and zero ozone depletion potential (ODP), coupled with bio-nanofluid. The utilization of this natural refrigerant, combined with a bio-nanofluid developed from agricultural produce, introduces the innovative concept of this study and has the potential to enhance the global market. The incorporation of synthesized biodegradable waste significantly enhances the performance characteristics, including the coefficient of performance (COP), reduced compressor energy consumption, and improved refrigerating effect (RE). Bio-nanoparticles from mango peels (MP) and mango leaves (ML) were extracted using aluminium sulphate (Al₂(SO₄)₃) as the inorganic salt, and experimental examination was achieved with 0.1, 0.5, and 1.0% volume concentrations of the bio-nanofluid. The vapour compression refrigeration system (VCRS) performance was evaluated under an ambient temperature value of 26 °C. The results indicate that the system’s performance operating with a 0.5% volume concentration of aluminium oxide (Al₂O₃) nanoparticles from MP improved significantly compared to the base fluid, with 62% COP enhancement and 17.6% reduction in energy consumption. The lowest evaporator temperature of -23 °C was attained in 120 min.

The utilization of biomass-coal briquettes offers a promising approach for improving the sustainability and performance of solid-fuel combustion systems. This study experimentally investigated the combustion characteristics of sawdust-coal briquettes in a fixed-bed reactor to evaluate the influence of fuel composition on combustion behavior. Briquettes containing 0–60 wt.% coal at 10 wt.% intervals were produced and combusted under a constant air mass flux of 0.10 kg/m²s. Combustion performance was assessed using temperature distribution, mass-loss history, ignition time, flame propagation speed, and burning rate. Temperature profiles exhibited a single dominant peak, indicating substantial overlap of fuel heating, devolatilization, volatile combustion, and char oxidation processes. Peak bed temperatures decreased from 813 °C for briquettes containing 40 wt.% sawdust to 657 °C for pure sawdust briquettes, while combustion duration decreased from 26 to 21 min with increasing sawdust content. Mass-loss rate, flame propagation speed, and burning rate increased with increasing sawdust content, while ignition time decreased progressively. Overall, higher sawdust contents promoted earlier ignition, faster fuel conversion, and greater combustion reactivity, whereas higher coal contents resulted in elevated combustion temperatures and longer combustion durations. These findings provide insights for optimizing biomass-coal briquette formulations for fixed-bed combustion applications.