Empirical Investigation of the Thermal Performance of Nanofluid-Enhanced Flat-Plate Solar Collectors Under the Climatic Conditions of North Central Nigeria

Despite the established theoretical advantages of nanofluids as heat transfer fluids in solar thermal systems, empirical validation under the specific climatic and operational conditions of tropical African environments remains limited, creating a gap between laboratory findings and practical deployment potential in Nigeria. This study presents an empirical investigation of the thermal performance improvement achievable in flat-plate solar collectors using alumina-water and copper oxide-water nanofluids at volume concentrations of 0.1, 0.25, and 0.5 percent, tested under the solar irradiance and ambient temperature conditions of Lafia, Nasarawa State, in the North Central geopolitical zone. A purpose-built experimental collector test rig conforming to the ASHRAE 93 standard was constructed, and comparative performance tests were conducted between nanofluid and distilled water baseline working fluids under identical operating conditions. Instantaneous collector efficiency, useful heat gain, heat removal factor, and overall heat loss coefficient were determined and compared across fluid types and concentrations. Results demonstrated that alumina-water nanofluid at 0.5 percent volume concentration improved mean collector efficiency by 9.3 percentage points over the water baseline, while copper oxide-water at the same concentration yielded an 11.7 percentage point improvement. Pressure drop penalties associated with nanofluid use were characterised and incorporated into net system performance calculations. Statistical regression models relating collector efficiency to incident radiation, inlet temperature differential, and nanofluid concentration were developed and validated against independent test data. Findings provide empirically grounded guidance for nanofluid selection in solar thermal applications across the North Central climate zone. Keywords: nanofluid, flat-plate solar collector, thermal performance, alumina, North Central Nigeria.