Experimental study of friction factors of multi-walled carbon nanotubes/water flow inside helical double-pipe heat exchangers

This study presents the findings of experiments on the impact of multi-walled carbon nanotubes on the pressure drop of the flow in helical annuli. The exterior of the heat exchanger is insulated. The nanofluid travels through the annulus as hot water flows through the inner helical tube. Two double-pipe cases are produced, each with a different curvature ratio. Several experiments are conducted to assess the effect of the coiled annuli geometry on the flow pressure drop. Additionally, the effects of the Dean Number and nanotube concentration are examined. The results indicated that the friction factors related to the nanofluid flow are higher than those of water, but our previous study demonstrated that they have superior heat transfer coefficients. Therefore, the performance evaluation criteria are achieved. In all the cases, they are higher than unity showing the superiority of this kind of heat exchanger.