Temperature-dependent particle stability behavior and its effect on radiative transfer in water/SiO2 nanofluids

Layth Al-Gebory

doi:10.18186/thermal.990645

Abstract

Radiative transfer is one of the methods of energy transport that includes in a wide range of applications and we feel it in our daily lives. Thermal radiation transfer plays an effective role in the utilization of renewable energy. The radiative and optical properties, as well as the nature of the radiative scattering, are the basic principles of the thermal radiation transfer. The unique properties of nanofluids offer the unmatched potential for use in energy utilization, the working temperature has a dominant effect on the stability and radiative properties of such type of suspensions. In this research, the radiative transfer (optical properties, the independent and dependent scattering, and radiative properties) in water/SiO2 nanofluids are investigated; taking into consideration the effect of working temperature on the stability of the particles. The effect of the temperature on the stability ratio and particle agglomeration is determined by estimating the radius of gyration of particle agglomerates using the scaling law based on the stability (DLVO) method. The single-scattering approximation (SSA) is used to calculate the radiative properties in the case of independent scattering, while the quasi-crystalline approximation (QCA) is used for this purpose in the case of dependent scattering. The results show that the temperature has a significant effect on the stability of particles and radiative transfer in nanofluids. It was observed by comparing the results from the two approximation methods in the Rayleigh regime. Particle size affects the physical and scattering cross-sectional areas which give a general understanding of the scattering mechanism from small to large particles.

Highlights

The suspension of particles with nano-size in base fluids, so named nanofluids, have shown significant enhancement in thermal behavior because of their unique radiative and thermophysical properties compared with regular fluids
This research shows the importance of the temperature on the stability of nanofluids, which in turn affects the radiative transfer
The different particle agglomerates under the effect of different working temperatures show a considerable change in the radiative properties of water-SiO2 nanofluids

Summary

INTRODUCTION

The suspension of particles with nano-size in base fluids, so named nanofluids, have shown significant enhancement in thermal behavior because of their unique radiative and thermophysical properties compared with regular fluids. The optical and radiative properties of nanofluids are strongly affected by different parameters such as the radiation wavelength, particle size, particle volume fraction, and particle type They depend on the pressure and temperature of the media. The Lorenz-Mie theory is used (3) to calculate the radiative properties of water/SiO2 nanofluids, the two approximations SSA and QCA are applied based where εr is the relative dielectric constant of base fluids, ε0 is the dielectric constant of the free space, ψs is the surface charge, and κ is the Debye parameter which is the inverse of the Debye length [30]: on the scattering behavior. From the stability ratio modeling of the nanofluids based on DLVO theory, Fig. 3 shows the effect of the temperature on the agglomeration of SiO2 nanoparticles dispersed in water with the concentration of particle (0.5% v/v), these results are obtained by applying Eq 6. The ratio of the scattering to the extinction of incident radiations, the single-scattering albedo, which explains the scattering contribution in the radiative transfer in particulate suspensions [23]:

RESULTS AND DISCUSSION

CONCLUSIONS

DATA AVAILABILITY STATEMENT