Enhanced thermal efficiency of solar liquid tin receiver with carbon black-reinforced carbon nanotube absorber

Abstract

Carbon nanotube (CNT) heat absorbers were developed to enhance the direct solar heating of liquid tin as a heat-transfer fluid in ground solar receivers. To improve the thermal transfer of absorbed solar energy to tin, absorbers reinforced with carbon black (CB) were fabricated by compression molding. As the compressive strength increased, the CNT absorber formed denser nanotube arrays, which increased the thermal conductivity by 1.68 times. Increasing the CB content further enhanced the conductivity by 1.19 times through grape cluster-like structures. The thermal properties of CNT absorbers predominantly depend on the compressive strength and CB content, and a correlation is proposed for predicting the conductivity. The most effective absorber was prepared at 50 kPa with a CB/CNT ratio of 1.0. The heat absorption characteristics of the solar receivers (50 mm i. d., 60 mm high) with the prepared CNT absorbers were determined. Tin temperatures with CNT absorbers rose more steeply than in bare tin systems, exhibiting a higher temperature increase per irradiance. The efficiency of the bare tin system improved from 24.8 % to 45.4 % using absorbers at 50 kPa and to 46.4 % using a CB/CNT ratio of 0.75 at 20 kPa. Under wind-free conditions, the receiver with the highest thermal conductivity achieved 67.7 % efficiency, a 1.69-fold increase over a tin-only receiver. This study confirmed that the improved thermal conductivity of the CNT absorbers significantly enhanced the receiver efficiency by facilitating rapid solar-energy transfer to liquid tin.