The creation of nanofluids containing palladium (Pd) and silver (Au) nanoplates for the volumetric absorption of intense solar radiation in concentrating solar power plants (CSPs) with parabolic trough collectors (PTCs) is the subject of a new study published in the journal. Energy and fuels.
Study: Are nanofluids suitable for volumetric absorption in PTC-CSP plants? An exemplified and realistic assessment with characterized metal-oil nanofluids. Image credit: Sergio Sergo/Shutterstock.com
Concentrating solar power (CSP) can significantly reduce carbon dioxide emissions by minimizing the intermittent nature of photovoltaic and wind electricity, expanding its role in today’s power generation landscape.
The minimum energy conversion efficiencies of CSP plants set a lower limit for their practical applications. An improvement in these efficiencies can considerably accelerate the commercialization of CSP technology. The use of nanofluids as new heat transfer fluids (HTFs) has recently been suggested for this function, provided that the physical parameters governing the convective heat flow are appropriately increased.
Nanofluids: Why are they important?
The transformation of solar to thermal energy is a very prominent application area in which nanofluids, which are already known for their use in complex applications, can be used for heat transmission, thermal energy retention or the volumetric absorbance.
The physical qualities of heat transfer fluids (HTFs) influence the performance, affordability and reliability of solar-to-thermal energy conversion systems. It is widely recognized and well documented in the literature that the adoption of innovative HTFs such as nanofluids can greatly benefit applications that rely on solar energy conversion.
This is also true for concentrated solar power (CSP) plants, a new renewable energy generation technique for long-term and possibly dispatchable electricity production severely hampered by poor power transfer efficiency solar to thermal energy.
Improving the performance of CSP plants using nanofluids
As heat transfer fluids or latent heat storage compounds, nanofluids can significantly increase the effectiveness of CSP systems. Thermal lubricants and molten salts are critical components of the power production processes of CSP plants. As such, they are attractive base fluids for developing nanofluids to increase the reliability and thermophysical characteristics of CSP plants.
The receiver operating fluid in CSP facilities using parabolic trough collectors (PTCs), the most developed and frequently used form of collector, is usually a eutectic and azeotropic combination of biphenyl oxide and diphenyl
The creation of nanofluids from this natural thermal oil has recently received intense attention, with important work dedicated to its synthesis, stability study and evaluation of thermal and physicomechanical properties.
Nanofluids as new volumetric absorbers in CSP plants
The use of nanofluids as volumetric absorbers for immediate solar-to-thermal energy transfer is optimal without the conventions of surface-treated materials. Since local overheating does not occur with volumetric absorbers, the pumping energy can be reduced while the temperature differential between the surface absorbers and the fluid remains minimal, resulting in lower emissive losses.
However, for volumetric absorption to be effective, solar absorption with nanofluids must be continuous along the optical path of the radial orientation of the parabolic trough collector.
Several studies have been carried out to characterize the optical characteristics of nanofluids, some with an emphasis on their possible use in CSP-PTC plants. As a general rule, opaque and dark nanofluids are suitable for this purpose.
This work thoroughly investigates the feasibility of using nanofluids containing Au and Pd nanoplates as volumetric absorbers and HTFs in CSP-PTC systems. The researchers also compare conventional HTF A and nanofluids based on critical characteristics such as projected PTC efficiency, heat exchange effectiveness, and overall system performance.
Important results of the study
The perfect distribution of mass fractions enhances the spectral attenuation throughout the visible light spectrum, implying that the produced nanofluids, especially those containing Pd nanoplates, are well suited for volumetric absorption. Furthermore, without any rheological cost, nanoparticles can significantly increase the thermal conductance and heating value of CSP-PTC plants, suggesting that nanofluids are potentially attractive possibilities for heat transfer applications.
The researchers successfully gave a realistic assessment of the ramifications of using these nanofluids in PTC for CSP plants using some mathematically basic but relevant expressions accessible in the literature.
It was shown that nanofluids containing Pd nanoplates could improve plant efficiency by up to 31.6 percent while reducing pumping requirements by 15 percent, keeping structural disturbances to a minimum and preserving structural stability avoiding overheating of the surface collector.
reference
Carrillo-Berdugo, I. et al. (2022). Are nanofluids suitable for volumetric absorption in PTC-CSP plants? An exemplified and realistic assessment with characterized metal-oil nanofluids. Energy and fuels. Available at: https://pubs.acs.org/doi/10.1021/acs.energyfuels.2c01759
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