In the present work, a nanofluid based volumetrically absorbing solar receiver having reflecting inner surfaces has been tested under outdoor conditions. Carbon soot nanoparticles from used motor oil dispersed in paraffin oil forms the working fluid. Results show that steady-state thermal efficiency peaks at an optimum nanoparticles volume fraction (η_th = 59 ± 4% at f_v = 1%). Furthermore, the as-prepared nanofluid shows excellent stability i.e. it retains its optical characteristics and particle size distribution even after undergoing pumping and thermal cycles and moving in flow loops (circulation through pipes/valves) during on-sun testing. Moreover, the as-prepared nanofluid has negligible impact on the surface and optical properties of solar receiver constituent materials. Overall, the proposed receiver design and the as-prepared nanofluid stability represent significant steps towards realization of practical nanofluid based volumetric absorption solar thermal systems.

在本工作中，已经在室外条件下测试了具有反射内表面的基于纳米流体的体积吸收太阳能接收器。来自用过的机油的碳烟灰纳米颗粒分散在石蜡油中，形成工作流体。结果表明，稳态热效率峰值在最佳的纳米粒子的体积分数（η_个 = 59±4％在˚F _v = 1％）。此外，所制备的纳米流体表现出优异的稳定性，即，即使在进行日晒测试期间经历了泵送和热循环并在流动回路中移动（通过管道/阀门循环）后，它仍保留了其光学特性和粒径分布。而且，所制备的纳米流体对太阳能接收器构成材料的表面和光学性质的影响可忽略不计。总的来说，所提出的接收器设计和所准备的纳米流体稳定性代表了实现基于实际纳米流体的体积吸收太阳能热系统的重要步骤。