Effectiveness Study of a Shell and Tube Heat Exchanger Operated with Nanofluids at Different Mass Flow Rates

Abstract

Several challenging issues, such as global warming, greenhouse effect, fuel security, and the high price of energy, motivate people to think about energy savings. Energy can be saved by effectively using available materials and facilities. Heat exchangers play a significant part in the field of energy conservation, conversion, and recovery. Nanofluids can be used in the heat exchangers to reduce global energy losses. Thermal performance of a shell and tube heat exchanger operated with nanofluids has been analytically investigated at different mass flow rates and compared with water as the base fluid. Suspensions of ZnO, CuO, Fe₃O₄, TiO₂, and Al₂O₃ nanoparticles in water (W) at 0.03 volumetric fractions have been considered. It is found that, for a certain mass flow rate (50 kg/min) of tube side and shell side fluid, the highest heat transfer coefficient (h) belongs to Al₂O₃-Wnanofluid and the lowest to CuO-W nanofluid. However, maximum energy effectiveness (ϵ) improvement took place by 43% for ZnO-W nanofluid and minimum ϵ improvement that was around 31% happened for Al₂O₃-W nanofluid. Furthermore, this energy effectiveness also improved with the decrease of the mass flow rates of nanofluids and increasing the mass flow rates of the base fluid. However, changing the base fluid's mass flow rate has a limited effect on this improvement of energy effectiveness. For example, a maximum overall heat transfer coefficient was found to vary from 18.31 to 18.35 W/m² · K for Al₂O₃-W nanofluid when changing the mass flow rate of nanofluid from 50 to 70 kg/min. On the other hand, with the same changes of hot water mass flow rates, a maximum overall heat transfer coefficient was obtained to shift from 18.31 to 22 W/m².K for the same nanofluid. Viscosity and specific heat of nanofluids are responsible for these phenomena. However, energy effectiveness of the shell and tube heat exchanger can be increased by using metal oxide nanofluids, and better performance can be achieved by maintaining higher mass flow rates of shell side fluid and lower mass flow rates for tube side fluid.

Acknowledgments

The authors would like to acknowledge the Ministry of Higher Education Malaysia (MoHE) for its financial support. This work was supported by the UM-MoHE High Impact Research Grant Scheme (HIRG) (Project No.: UM.C/HIR/MOHE/ENG/40 (D000040-16001)).