Experimental and numerical investigations of thermal performance of Al₂O₃/water nanofluid for a combi boiler with double heat exchangers

This study aims to focus on usage of Al₂O₃/water nanofluid as working fluid in a combi boiler. The plate heat exchanger located at the bottom of the combi boiler has been used for heating the domestic water in the present study. Al₂O₃/water nanofluid has also been used in obtaining of the heat energy provided from combustion. Therefore, thermal performance of Al₂O₃/water has been determined by comparing water and nanofluid-water mixture. The present study also investigates heat transfer rates as numerical and experimental for varying cold side outlet temperatures, comparatively.

The present study has included both experimental and numerical methodologies. The experimental setup consists of main heat exchanger, atmospheric burner, circulation pump and plate-type heat exchanger in which the Al₂O₃/water nanofluid was used as working fluid to heat the domestic water. In the numerical part of the study, a commercial computational fluid dynamic code has been used to model heat rate and thermal efficiency of the heat exchanger used.

It has been concluded that the predicted results are in satisfactorily good agreement with the measured data. In the experimental part of the study, the flow rate of Al₂O₃/water nanofluid was kept constant during the experiments. The flow rates of the water by which the heated Al₂O₃/water nanofluid mixture was cooled via the plate heat exchanger have been changed as 3, 4, 5 and 6 lpm. The domestic water temperatures that were kept constant have also been changed as 40°C, 45°C, 50°C, 55°C and 60°C. It has been concluded that the Al₂O₃/water nanofluid thermal efficiency has been 16 per cent better than pure water.

The main originality of the present study is that thermal efficiency of the plate-type heat exchanger when Al₂O₃/water mixture nanofluids are used as there are limited studies related to the usage of Al₂O₃/water mixture nanofluids in the plate-type heat exchanger not only experimental but also numerical methodologies.