Optimization of Solar Still Performance Using CuO and ZnO Nanoparticles as Thermal Enhancers

Abstract

This research presents an experimental study on optimizing the performance of a single-slope solar still using copper oxide (CuO) and zinc oxide (ZnO) nanoparticles as thermal conductivity enhancers. Experiments were conducted at three different water depths (4 cm, 6 cm, and 8 cm) using 11° inclined glass cover under summer climatic conditions in Gwalior, India. The nanofluids were prepared with 0.1% concentration of CuO and ZnO nanoparticles and added to the basin water to improve heat absorption and evaporation rate. Results showed that basin water temperatures increased significantly with the addition of nanoparticles, with CuO achieving a peak temperature of 59?°C at 6 cm depth, compared to 58?°C for ZnO. Correspondingly, the highest daily distillate yield was 3.45?L/m² for CuO and 3.38?L/m² for ZnO at 6 cm depth, outperforming conventional water-based systems by over 35%. While CuO exhibited higher thermal efficiency at shallower depths, ZnO showed slightly better performance at deeper levels. The findings confirm that both CuO and ZnO nanoparticles significantly enhance the thermal behavior and freshwater productivity of solar stills. The optimal results at 6 cm depth indicate an effective balance between thermal energy absorption and evaporation rate, highlighting the potential of metal oxide nanofluids in sustainable water desalination applications.

Introduction

1. Introduction

• Freshwater scarcity is a major global issue, worsened by population growth, urbanization, industrialization, and climate change.

• Solar distillation is a sustainable and low-energy water purification method that mimics the natural water cycle through evaporation and condensation.

• The main limitation of solar stills is low thermal efficiency and limited water output.

2. Role of Nanoparticles

• Metal oxide nanoparticles, especially Copper Oxide (CuO) and Zinc Oxide (ZnO), improve the thermal performance of solar stills due to their:

  • High thermal conductivity

  • Stability

  • Cost-effectiveness

• These nanoparticles enhance solar energy absorption, evaporation rate, and freshwater yield.

3. Experimental Setup

• A single-slope solar still was tested in Gwalior, India under natural sunlight.

• CuO and ZnO nanofluids were prepared at 0.05%, 0.1%, and 0.2% concentrations and tested at three water depths: 4?cm, 6?cm, and 8?cm.

• Key measurements included temperatures (ambient, water, glass) and distillate yield from 9?AM to 6?PM.

4. Key Findings

A. Thermal Performance

• Nanofluids raised basin water temperature significantly, particularly during peak solar hours (11?AM–2?PM).

• CuO outperformed ZnO at shallow depths (4?cm, 6?cm), while ZnO performed better at 8?cm due to better dispersion in deeper water.

• Average temperature gains over baseline:

  • CuO: +6.2?°C

  • ZnO: +5.8?°C

B. Distillate Yield (Daily Output at 0.1% concentration)

• The CuO-ZnO hybrid (0.05% each) showed the best performance due to synergistic effects, combining CuO’s conductivity with ZnO’s stability.

5. Optimization and Limitations

• Optimal nanoparticle concentration: 0.1% for individual types, 0.05% each for the hybrid.

• At >0.2%, performance plateaued and agglomeration was observed, which decreased system efficiency.

• The hybrid nanofluid was most efficient, cost-effective, and stable, making it ideal for long-term use.

Conclusion

The incorporation of CuO and ZnO nanoparticles into the basin water of solar stills significantly enhanced the thermal performance and freshwater productivity. Experimental results demonstrated that nanofluids improve heat transfer by increasing the thermal conductivity of the working fluid, resulting in higher basin water temperatures and accelerated evaporation rates. Among the tested configurations, the hybrid nanofluid composed of 0.05% CuO and 0.05% ZnO (total 0.1% concentration) delivered the best overall performance, increasing the daily distillate yield by 35.8% compared to the conventional still using pure water. This improvement confirms the synergistic effect of combining CuO and ZnO nanoparticles, balancing superior thermal conductivity with dispersion stability. The optimized nanoparticle concentration prevented sedimentation and agglomeration issues observed at higher loadings, ensuring sustained performance. The findings highlight the practical feasibility of employing metal oxide nanofluids as cost-effective thermal enhancers for solar distillation systems. Overall, this study contributes to the development of sustainable and efficient solar desalination technologies, offering a promising solution to freshwater scarcity, especially in remote and water-stressed regions. Future work should focus on the long-term stability of nanofluids, environmental impact assessments, and integration with other solar energy enhancement methods to further boost system efficiency.

References

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Copyright

Copyright © 2025 Jitendra Kumar Tiwari, Amit Agrawal. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.