Temperature increases in photovoltaic (PV) panels are one of the primary issues preventing PV systems from being used extensively. When a photovoltaic module overheats, its output power performance drops by 0.4%–0.5% for every degree Celsius above its rated temperature. Lowering the operating temperature of the PV surface using a cooling medium is an efficient technique to increase electrical performance and decrease the rate of thermal degradation of a PV module. To prevent this performance loss, researchers have worked on cooling photovoltaic panels with fluids such as air, water, and nanofluids. In this study, the effects of cooling on photovoltaic panels with water and nanofluid were investigated. The experiment was carried out by fixing the pipe and fins to the back surface of the panel. Al₂O₃‐water and TiO₂‐water nanofluids were used as working fluid due to their cost effectiveness. Nanofluids prepared in three different volumetric fractions (0.01%, 0.1%, and 1%), the current and voltage values obtained from the panels were recorded, and the panel efficiency was calculated. The experimental results showed that the cooling increased the panel voltage and decreased the current. The results indicated that using TiO₂ nanofluid was more effective than Al₂O₃ nanofluid in terms of electrical efficiency. It was also found that the fluids prepared as 0.01% and 1% gave the most efficient results. It has been observed that it is possible to increase the panel efficiency by 8.32% by cooling the panel.

The thermal conductivity of recently produced hexagonal boron nitride (hBN)-containing nanofluids is comparatively higher than their viscosity, indicating that these materials belong to a relatively novel class. In this study, hBN–water nanofluids in stable and dispersed concentrations were used in parallel and counterflow experiments at volumes of 0.01%, 0.1%, and 1%, as well as at various flow rates and Reynolds numbers. When employing hBN–water nanofluid in a counter-flow heat exchanger instead of distilled water, the results showed a 16.7% increase in the overall heat transfer coefficient. The findings also showed that, in comparison to a counter-flow heat exchanger, employing hBN nanofluid as the cold fluid in a parallel-flow heat exchanger produced superior results in terms of an increase in heat transfer. The effects of nanofluid concentration on pressure drops were investigated through experiments conducted in both parallel- and counter-flow conditions.

This article experimentally and numerically analyzes the effect of turbulators with different geometries (Type I, Type II, Type III, and Type IV) located at the inlet of the inner pipe in a concentric-type heat exchanger. Experiments were performed at parallel-flow conditions in the same and opposite directions to investigate the impact of manufactured turbulators on heat transfer and pressure drop. In the numerical study, ANSYS 12.0 Fluent code program was used, and basic protection equations were solved in the steady-state, three-dimensional, and turbulence-flow conditions. Results were obtained from numerical analysis conducted at different flow values of air (7, 8, 9, 10, 11, and 12 m³/h). The distribution of temperature, velocity, and pressure was demonstrated as a result of numerical analyses. Experimental and numerical results were compared, and it was observed that they were in conformity with each other. When the data obtained from the analyses were examined, the highest heat transfer, pressure drop, and friction factor increase were detected to be in the Type IV turbulator.

This study investigated the effects of using nanofluids prepared with hexagonal boron nitride (hBN) nanoparticles on the thermal performance and pressure drop of a concentric tube heat exchanger. Experiments were carried out with water-hBN nanofluids for stable, dispersed, 0.01%, 0.1% and 1% volume concentrations, at different flow rates and Reynolds numbers under parallel and counter-flow conditions. When the experimental results were examined, the exergy loss was higher in the parallel-flow heat exchanger compared to the counter-flow heat exchanger. The highest exergy loss value was obtained for distilled water at the highest Reynolds number (Re = 8,700) for parallel flow operation at 170 W. The exergy loss of water at the highest Reynolds number (Re = 8,700) for parallel flow operation increased by 15.7%, 24.8% and 49.8% for hBN-water concentrations of 0.01%, 0.1% and 1%, respectively. Exergy loss of water at the highest Reynold number (Re = 8,700) for counter flow operation increased by 11.3%, 17.3% and 29.2% for hBN-water concentrations of 0.01%, 0.1% and 1%, respectively. When evaluating the exergy analysis of the system, exergy losses due to pressure drops were negligible for both flows (parallel and counter).

Among the various approaches, the use of nanofluids−suspensions of nanoparticles in base fluids−has emerged as an effective method for improving the thermal performance of solar collectors. Metal oxide nanoparticles, such as cerium oxide (CeO₂) and zinc oxide (ZnO), have gained significant attention due to their high thermal conductivity, chemical stability, low cost, and environmental compatibility. The aim of this study is to evaluate and compare the thermal and exergetic performance of CeO₂−water and ZnO−water nanofluids at varying volumetric concentrations (0.01%, 0.1%, and 1%) and flow rates (50, 150, and 250 L/h) in a flat-plate solar collector. Both experimental and numerical analyses (CFD) were conducted to assess parameters such as collector efficiency, temperature−irradiance−time behavior, entropy generation, and exergy destruction. The ZnO−water nanofluid at 1% concentration and 250 L/h flow rate yielded the highest thermal efficiency, showing a 28% improvement compared to water. In contrast, the CeO₂−water nanofluid at 0.01% concentration and 50 L/h flow rate demonstrated only an 8% efficiency increase. The CFD results showed strong agreement with experimental data. The findings confirm that both CeO₂ and ZnO nanofluids enhance the thermal and exergetic performance of flat-plate solar collectors, with ZnO demonstrating superior efficiency due to its higher thermal conductivity.