Selected water thermal properties from molecular dynamics for engineering purposes

Modeling, simulation and performance evaluation of a PVT system for the Kenyan manufacturing sector

Manufacturing is an end-use sector that uses the most delivered energy, accounting for around 50% of all transported fuel globally and 40% of carbon dioxide emissions worldwide. Solar photovoltaic-thermal (PVT) energy can substitute the transported energy to meet thermal and electrical energy requirements, mitigating high energy costs and climatic problems. This research aimed to develop, simulate, and evaluate the capabilities of a solar photovoltaic-thermal system for potential use in Kenya's manufacturing sector. A multistage cluster sampling technique was used in the study to characterize the manufacturing industry. Additionally, a PVT system was simulated using MATLAB Simulink to ascertain the relationship of temperature and the PV electrical efficiency. The impact of incorporating a thermal collector into the PV system on electrical, thermal, and overall system efficiency, and also the system's potential for use in thermal processes in manufacturing, were assessed. From the characterization results, the agro-processing sector dominates with 35% representation, and the small-scale thermal energy category dominates at 80%. The simulation findings show that a small temperature increase leads to a small increment in short circuit current but a significant decline in open circuit voltage. As a consequence, the maximum power (Pmax) of the PV decreases, lowering its electrical efficiency. However, the integration of PV with thermal collector improved the electrical, thermal, and the entire system efficiencies by, 16.01%, 20%, and 36.13%, respectively. More than 75% of the electrical and thermal energy processes fall in the small energy category. Hence, the PVT system is suitable for small-scale low-to-medium heat thermal energy categories or as a substitute system for higher temperature processes to raise feed water temperatures and reduction of thermal energy cost. This study gives a new approach of the application of PVT system for thermal industrial applications.

Influence of Nanoparticles on Thermophysical Properties of Hybrid Nanofluids of Different Volume Fractions

Nanofluids are frequently employed in numerous heat transfer applications due to their improved thermophysical properties compared to a base fluid. By selecting suitable combinations of nanoparticles, hybrid nanofluids can have better thermophysical properties than mono nanofluids. Thus, this study examines the effect of volume fractions of hybrid nanofluids on different thermophysical properties, such as density, thermal conductivity, specific heat, and dynamic viscosity. Thermophysical properties of copper–nickel (Cu–Ni) water-based hybrid nanofluids are determined using molecular dynamic (MD) simulation for different volume fractions of 0.1–0.3%. Results show that the density, thermal conductivity, and viscosity of Cu–Ni hybrid nanofluids increase with volume fraction, whereas the specific heat capacity at a constant pressure decreases with volume fraction. These properties are validated for the base fluid, mono nanofluids, and hybrid nanofluids. Results are in good agreement with previous findings. The thermophysical properties of Cu–Ni hybrid nanofluids significantly improve and have better characteristics for cooling fluids than the base fluid.

Initial-position-driven opposite directional transport of a water droplet on a wedge-shaped groove

The transport direction of water droplets on a functionalized surface is of great significance due to its wide applications in microfluidics technology. The prevailing view is that a water droplet on a wedge-shaped groove always moves towards the wider end. In this paper, however, molecular dynamics simulations show that a water droplet can move towards the narrower end if placed at specific positions. It is found that the direction of water droplet transport on a grooved surface is related to its initial position. The water droplet moves towards the wider end only when it is placed near the wider end initially. If the water droplet is placed near the narrower end, it will move in the opposite direction. The novel phenomenon is attributed to the opposite interactions of the groove substrate and the groove upper layers with water droplets. Two effective models are proposed to exploit the physical origin of different transport directions of water droplets on a wedge-shaped groove surface. The study provides an insight into the design of nanostructured surfaces to effectively control the droplet motion.