An experimental study on MWCNT-water nanofluids flow and heat transfer in double-pipe heat exchanger using porous media

This paper presents the results of an experimental investigation on the heat transfer characteristics of multi-walled carbon nanotube aqueous nanofluids inside a countercurrent double-pipe heat exchanger using porous media. Aluminum porous media (epsilon=67%) were used because of the construction of the medium, with porous plate media at the center of the inner tube and with three porous plates on the walls of the inner tube. The effects of operating parameters including flow rate (4600<7600), mass fractions of nanofluids (0.04-0.25mass%), and inlet temperature of nanofluids (Tin=50 degrees C) on the heat transfer coefficient were investigated. The results indicate that imposing the plate porous media increases the heat transfer coefficient significantly, and the highest increase in the heat transfer coefficient is 35% which is obtained in the test of the lowest mass fraction (0.04mass%) with three-plate porous media in the experiment range. As the mass fractions increased, the value of heat transfer enhancement assisted by porous media gradually decreased. Also the lower range 100 (Lh(-1)) of the volume flow rate has a powerful enhancement on the enhancement coefficient, while the higher ranges 300 (Lh(-1)) have low influence.