Investigations on optical and photo-thermal conversion characteristics of BN-EG and BN/CB-EG hybrid nanofluids for applications in direct absorption solar collectors

Direct absorption using a nanofluid is an efficient way of harnessing solar energy. Present works aim to inves-tigate hexagonal boron nitride-ethylene glycol (BN-EG) nanofluids and BN mixed with carbon black (CB) in EG (BN/CB-EG) hybrid nanofluids for applications in direct absorption solar collectors (DASCs). Nanofluids were prepared by using the two-step method. Stability and homogeneity were inspected photographically after storage of one month. The optical properties of the nanofluids were measured and computed under varying concen-tration mixing ratios (CMRs). An absorbed energy fraction of 98.92% was obtained in a 2.0 cm height of 90 ppm/15 ppm BN/CB nanofluid. Photo-thermal conversion performances of the nanofluids were investigated using a small in-house built experimental collector. Temperature-rises in the working fluids were measured under varying durations of exposure to a fixed irradiance, fluid height, and CMRs of the nanoparticles. An enhancement of 34.55% photo-thermal conversion efficiency over that of EG alone was obtained in the 90 ppm/15 ppm BN/CB nanofluid after 1200 s exposure to 437 W/m(2) incident irradiance. Some basic approaches for designing a DASC in an optimized manner are also discussed. It is concluded that BN/CB-EG hybrid nanofluids can be the prospective working fluids in DASCs.

Automated summary

This study investigates hexagonal boron nitride-ethylene glycol (BN-EG) nanofluids and BN mixed with carbon black (CB) in EG (BN/CB-EG) hybrid nanofluids for applications in direct absorption solar collectors (DASCs). The experimental results show that the hybrid nanofluids outperform pure ethylene glycol in terms of photo-thermal conversion efficiency.