Performance evaluation of evacuated tube solar collector using boron nitride nanofluid

Nanofluids are the most fascinating and efficient approach to strengthen the thermal performance of a heat exchanger device. Herein, this contemporary experimental investigation exhibited the impact of water based hexagonal Boron Nitride nanofluid (hBN/water) on the thermal performance of a U-tube evacuated tube solar collector. The hBN nanoparticles of 50 nm size are dispersed and ultrasonicated in distilled water to obtain hBN/water nanofluid of varying volumetric concentrations (0.25, 0.50, 0.75, 1, 1.25, 1.50, 1.75, and 2 vol%). For stability improvement of nanofluid, six different surfactants (i.e. TWEEN20, SPAN20, SDS, SDBS, CTAB, and TTAB) are mixed with nanofluid at a different mixture ratio (i.e. 4:2, 3:2, 2:3, and 1:4) and zeta potential test was performed to inspect the stability of the mixture. The thermophysical properties (i.e. thermal conductivity, viscosity, and specific heat) of hBN/water nanofluid were analyzed at above volumetric concentration and varying temperature ranges (i.e. 25, 30, 35, 40, 45, and 50 degrees C). The collector's thermal performance is analysed at varying mass flow rates (0.0085, 0.01667, 0.0255, 0.034, 0.0425 and 0.051 kg/s) and obtained the maximum energy efficiency (72.14 % at 1.5 vol% and 0.051 kg/s), which is approximately 84 % higher than water at the same flow conditions.