Efficiency of a volumetric receiver using aqueous suspensions of multi-walled carbon nanotubes for absorbing solar thermal energy

Abstract This paper analytically investigates the efficiency of a nanofluid volumetric receiver (NVR) for absorbing solar thermal energy considering the experimentally measured extinction coefficient of aqueous suspensions of multi-walled carbon nanotubes (MWCNT) according to the wavelength from 200 to 2000 nm. For this purpose, considering the spectral behavior of nanofluids, we obtained analytical solutions of temperature fields as well as the efficiency of the NVR based on the condition of fully developed flow between the two plates. The aqueous MWCNT nanofluids were prepared using the two-step method, and their extinction coefficients were experimentally measured by the UV/Vis/NIR spectrophotometer according to the wavelength. With the analytical equations, we identified those key engineering parameters that affect the efficiency of an NVR: the Nusselt number of heat loss, the concentration of nanoparticles, the Peclet number, and aspect ratio. Also, we systematically observed the effects of key engineering parameters on the temperature fields and on the efficiency of the NVR. The current results clearly show that the efficiency calculated under the assumption of plug-flow through an NVR reported by previous researchers is overestimated in the case of high heat loss. Moreover, the present results show that NVR efficiency is proportional to the Peclet number as well as to the concentration of nanoparticles, while it is inversely proportional to the Nusselt number of heat loss and aspect ratio. The results of this study may be helpful to design and predict the efficiency of an NVR.

[1]  Z. Kam,et al.  Absorption and Scattering of Light by Small Particles , 1998 .

[2]  Robert A. Taylor,et al.  Nanofluid-based direct absorption solar collector , 2010 .

[3]  Robert A. Taylor,et al.  Nanofluid optical property characterization: towards efficient direct absorption solar collectors , 2011, Nanoscale research letters.

[4]  N. Arai,et al.  Development of a “volume heat-trap” type solar collector using a fine-particle semitransparent liquid suspension (FPSS) as a heat vehicle and heat storage medium Unsteady, one-dimensional heat transfer in a horizontal FPSS layer heated by thermal radiation , 1984 .

[5]  Robert A. Taylor,et al.  Applicability of nanofluids in high flux solar collectors , 2011 .

[6]  Soteris A. Kalogirou,et al.  Solar thermal collectors and applications , 2004 .

[7]  Seok Pil Jang,et al.  A Review of Thermal Conductivity Data, Mechanisms and Models for Nanofluids , 2010 .

[8]  Abraham Kribus,et al.  Experimental evaluation of a non-isothermal high temperature solar particle receiver , 2004 .

[9]  Alexander Mitsos,et al.  Concentrated solar power on demand , 2011 .

[10]  Andrej Lenert.  Nanofluid-based receivers for high-temperature, high-flux direct solar collectors , 2010 .

[11]  P. Lettieri,et al.  An introduction to heat transfer , 2007 .

[12]  G. M. Hale,et al.  Optical Constants of Water in the 200-nm to 200-microm Wavelength Region. , 1973, Applied optics.

[13]  Seung-Hyun Lee,et al.  Extinction coefficient of aqueous nanofluids containing multi-walled carbon nanotubes , 2013 .

[14]  A two-dimensional heat transfer analysis of the thermal-trap collector , 1988 .

[15]  E. Wang,et al.  Optimization of nanofluid volumetric receivers for solar thermal energy conversion , 2011 .

[16]  Fletcher Miller,et al.  Thermal Modelling of Small Particle Solar Central Receiver , 2000 .

[17]  Bong Jae Lee,et al.  Radiative Heat Transfer Analysis in Plasmonic Nanofluids for Direct Solar Thermal Absorption , 2012 .

[18]  Dennis G. Zill,et al.  Advanced Engineering Mathematics , 2021, Technometrics.

[19]  E. Sani,et al.  Carbon nanohorns-based nanofluids as direct sunlight absorbers. , 2010, Optics express.

[20]  Qunzhi Zhu,et al.  Characterization of Thermal Radiative Properties of Nanofluids for Selective Absorption of Solar Radiation , 2013 .

[21]  E. Wang,et al.  Analytical model for the design of volumetric solar flow receivers , 2012 .

[22]  F. Martelli,et al.  Absorption and scattering properties of carbon nanohorn-based nanofluids for direct sunlight absorbers , 2011, Nanoscale research letters.

[23]  John E. Harries,et al.  Physics of the Earth's radiative energy balance , 2000 .

[24]  J. Minardi,et al.  Performance of a “black” liquid flat-plate solar collector☆ , 1975 .

[25]  Seok Pil Jang,et al.  Flow and convective heat transfer characteristics of water-based Al2O3 nanofluids in fully developed laminar flow regime , 2009 .

[26]  H. Tyagi,et al.  Predicted Efficiency of a Low-Temperature Nanofluid-Based Direct Absorption Solar Collector , 2009 .

[27]  E. Palik.  Handbook of Optical Constants of Solids , 1997 .