An experimental investigation on the effect of pH variation of MWCNT–H2O nanofluid on the efficiency of a flat-plate solar collector

The effect of pH variation of MWCNT–H2O nanofluid on the efficiency of a flat-plate solar collector was investigated experimentally. The experiments were carried out using 0.2 wt.% MWCNT with various pH values, 3.5, 6.5, and 9.5, and Triton X-100 as additive. The procedure of ASHRAE standard was used for testing the thermal performance of flat-plate solar collector. Results show that by increasing or decreasing the pH values with respect to the pH of isoelectric point, the positive effect of nanofluid on the efficiency of solar collector is increased.

► At pH = 3.5 the efficiency of the solar collector is higher than that for pH = 6.5.
► At high temperature differences, FRUL parameter is more dominant in collector efficiency.
► At lower temperature differences, FR(τα) parameter is more dominant in collector efficiency.
► The positive effect of MWCNT nanofluid at pH = 6.5 is lower than other pH values.
► As the nanofluid become more acidic or basic, the positive effect of nanofluid become higher.