Performance enhancement of photovoltaic/thermal system using hybrid nanofluid

Abstract

Nanofluids are an emerging class of colloidal suspension with nanometer-sized particles. Nanomaterials of high surface area in comparison to their volume can enhance the heat transfer potential of the base fluid in which they are dispersed. A hybrid photovoltaic/thermal system (PV/T) is a cutting-edge and environmentally friendly technology that combines photovoltaics (PV) and solar thermal collectors. This study investigates the performance enhancement in PV/T, achieved using nanofluids.

Carbon quantum dots (C-dot), MXene, and novel MXene/C-dot hybrid nanofluids were synthesized during the study. Nanomaterial characterization was conducted to study the morphology, phase structure, and chemical composition. Similarly, nanofluid characterizations were carried out to study the thermal characteristics, optical properties, corrosion characteristics, and dispersion stability. From the characterization data, semi-empirical correlations were coined to predict the thermal conductivity and specific heat of nanofluids. Thermophysical and economic parameters were taken into consideration to optimize the nanofluid concentration to be used as heat transfer fluid (HTF) in PV/T. Optimized concentrations of C-dot, MXene, and MXene/C-dot hybrid, were found to be 0.15, 0.1, and 0.15wt%, respectively. Maximum thermal conductivity enhancement achieved over base fluid with optimized MXene, hybrid and C-dot nanofluids were 29.1, 28.7, and 32.4%, respectively. Hybrid nanofluid was found to be economical, exhibit lower property degradation rate and higher stability.

An indoor experimental test rig was fabricated to conduct the experimentation on PV/T with the optimized nanofluids. Multi-day test was performed under a solar simulator at various irradiance levels (350, 500 and 650 Wm-2). Energy analysis shows that the hybrid nanofluid produced an improvement of 9.45 % over DI water and had a thermal efficiency of 57.45%, at moderate irradiation (500 Wm-2), high flow rate (2.5 lpm) and low inlet temperature (15℃) conditions. Nanofluids were discovered to have a minor impact on the electrical efficiency of PV/T. The maximum total energy efficiency was 65.61 (at 350Wm-2), 71.13 (at 500Wm-2), 69.93 (at 500Wm-2), and 75.36% (at 500Wm-2) for PV/T with DI, C-dot, MXene, and hybrid nanofluids, respectively. The surface temperature of PV/T over DI water was lowered by a hybrid nanofluid by around 3.4°C. This study has successfully developed a validated CFD model in ANSYS Fluent, to predict the performance of the nanofluid-based PV/T system at operating conditions that are difficult to simulate experimentally. Experimentally derived thermophysical properties of the proposed nanofluids were imported into the model.

The research has also explored the feasibility of the synthesised nanofluids as a HTF in a direct absorption solar collector (DASC). The photothermal conversion performance of the nanofluids was investigated in a parabolic trough DASC using an outdoor experimental test rig. The research concludes that the proposed nanofluids could improve the heat transfer efficiency, and overall performance of PV/T in comparison to conventional HTFs. Nanofluids were also found to be a potential candidate for DASCs.

Date of Award	Jan 2024
Original language	English
Sponsors	Department for the Economy
Supervisor	Nikhilkumar Shah (Supervisor), Jayanta Mondol (Supervisor), Neil Hewitt (Supervisor) & Supriya Chakrabarti (Supervisor)