IMPROVEMENT OF PERFORMANCE OF HEAT RECOVERY UNITS BY USING MAGNETIC NANOFLUID

Waste heat recovery units are systems that are widely used in the preheating of clean air, which is needed in industrial and waste heat facilities, without contact with polluted air, especially during the pandemic period. In this study, it is aimed to increase the operating temperature range by improving the performance of a heat exchanger consisting of a heat pipe bundle and an integrated heat recovery unit. The originality of the work is in the use of NiFe₂O₄/water, ZnFe₂O₄/water, and CoFe₂O₄/water nanofluids as the working fluid in the heat pipes and the improvement rates in the heat recovery unit's thermal performance were determined compared to pure water, which is the basic fluid. The turbulence of the flows in the channel prevented the establishment of a linear relationship between the Reynolds number and the thermal improvement in performance. However, by using nanofluids instead of pure water, thermal performance improvement was achieved for all Reynolds numbers. According to the results obtained it is seen that higher performances are obtained in the case of using nanofluids compared to pure water. The average performance values are 14%, 18%, 19%, and 20% for water, NiFe₂O₄, ZnFe₂O₄, and CoFe₂O₄ nanofluids, respectively, according to the Re number on the cold fluid side, while the average performance improvement rates of NiFe₂O₄, ZnFe₂O₄, and CoFe₂O₄ nanofluids compared to the base fluid (pure water) are 29%, 38%, and 44%, respectively. When the Re number in the hot air flow channel is taken into account, it is seen that the average performance values are 13%, 19%, 20%, and 22% in the same order, while the improvement rates are 48%, 57%, and 72%. Therefore, according to the average performance and improvement values, the CoFe₂O₄ nanofluid was found to be a more suitable fluid than the others.