Abstract
Nanofluids have great potential for solar energy harvesting due to their suitable optical and thermophysical properties. One of the promising applications of nanofluids is utilization in solar collectors with the direct absorption of light (DASC). The design of a DASC requires detailed knowledge of the optical properties of nanofluids, which can be significantly affected by the particle size distribution. The paper presents the method to take into account the particle size distribution when calculating nanofluid extinction spectra. To validate the proposed model, the particle size distribution and spectral absorbance were measured for aqueous suspension with multi-walled graphite nanotubes; the minimum size of primary nanoparticles was 49 nm. The proposed model is compared with experiments demonstrating the concentration averaged and maximum discrepancies of 6.6% and 32.2% against 12.6% and 77.7% for a model assuming a monosized suspension.
Highlights
The last few decades have been characterized by an ever-growing interest of the world community in renewable energy, solar energy, as one of the most promising renewable energy sources [1]
The influence of agglomerates with medium sizes within the range from 400 nm to 1 μm is more considerable than Fig. 4A due to the relatively high volume fraction of such particles
The large particle agglomerates with sizes above 1 μm do not contribute to the absorbance since their volume fraction is meager (Fig. 1B, curve “2”)
Summary
The last few decades have been characterized by an ever-growing interest of the world community in renewable energy, solar energy, as one of the most promising renewable energy sources [1]. Several devices have been developed to convert solar radiation energy into thermal energy—the socalled solar collectors They differ structurally, but the general principle of operation is to transfer thermal energy from a blackened receiver, heated by solar radiation, to the coolant. The blackened surfaces of the volumes inside which the coolant flows or the outer surfaces of the tubes through which the coolant flows can be used as a receiver The disadvantage of such systems is an overheated outer surface, which loses a significant part of the received energy into the environment. New designs of such devices and different ways to enhance the efficiency of existing technical solutions are proposed [5–8]. The nanofluids and nanoparticle suspensions have found multiple applications in microelectronics [16,17,22–24], nuclear power generation [25], medicine [26,27], chemical technology [28], etc
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