Energy Harvesting Through Optical Properties of TiO2 and C- TiO2 Nanofluid for Direct Absorption Solar Collectors

Abstract

Nanofluids are tailored suspensions of nanoparticles in a suitable base fluid. The discovery of  nanofluids by Stephen choi opened a new heat transfer mechanism. Since then several research has taken place to explore thermal, electrical and magnetic property of nanofluids. Nanofluids showed enhanced electrical and thermal conductivities. The nanofluids are also proved as a potential candidate for direct absorption solar collectors (DASC). The present work investigates the effect of nanoparticle volume fraction and the associated optical intensity attenuation with a semiconductor laser diode of wavelength 670 nm. Nanoparticles of Titanium dioxide (TiO₂) and Carbon doped Titanium dioxide (C-TiO₂) are prepared by sol gel and characterized by powder XRD, SEM and UV. Since carbon is a good absorption material, TiO₂ are doped with carbon (C-TiO₂) to increase the absorption of incident radiation. Nanoparticles of TiO₂ and C-TiO₂ with two weight fractions such as 0.04 and 0.08 are dispersed in water and ethylene glycol to obtain TiO₂ and C-TiO₂ nanofluids. The nanofluids are investigated for their sedimentation time. Stability of TiO₂ nanofluid is nine times more than C-TiO₂ nanofluid but C-TiO₂ nanofluid are found to be efficient absorbers than TiO₂ nanofluid. A low volume fraction of C-TiO₂  nanofluid  can ensure high stability, low pumping power  and good absorption for a DASC.

 

Keywords- : Nanofluid, TiO₂ C-TiO_2,optical absorption, Laser.DASC

1.Introduction

Increasing consumption and growing demands of electrical appliances across the globe have posed a threat on the non renewable energy resources and has made us exploit the maximum of renewable energy resources, in which solar energy is the ultimate choice. Solar energy has been investigated for photovoltaic and thermal applications (Duffie, 1980) [1]. A major thrust in materials development is to identify new materials in order to increase the efficiency of solar cells. Materials with ultra fine grain size  and nanomaterials have provided an opportunity to tune the band gap and absorption of the existing solar energy. Conventional solar cells transfer the heat from the flat plate to the working fluid and it suffers from the large heat loss. The concept of direct absorption solar collectors in which working fluid acts as absorber and carrier of heat started replacing the conventional solar cells (Otanicar TP,2009) [2]. Since thermal conductivity of pure liquids are extremely less than solid particles, suspension of  microparticles gained  prominence.  But micro-colloidal suspensions has drawbacks like abrasion and sedimentation. Nanofluids were substituted by Robert Taylor (2009) to overcome the above problems  [3].The term Nanofluid was coined by Stephen Choi in 1995.[4] Nanofluids are suspensions of nanosized solid particles (1-100nm) in suitable base fluids. Since 1995,  nanofluids have been explored as a heat transfer fluid and the best results have been reported by Eastman and Stephen Choi in ( 2001). In the past five years nanofluids have been  also explored for their electrical (Suvankar Ganguly 2009)[5] and magnetic properties( John Philip,2009).[6]

Nanofluids can be prepared by two ways, single step method (H Zhu 2004  )[7] or two step method (Eastman 1997) [8]. Single step method is based on simultaneous synthesis of nanoparticle and nanofluid and two step methods involve; the synthesis of nanoparticles in the first step followed by dispersion in a suitable base fluid in the second step. The success of nanofluid for DASC depends on suitable choice of base fluid and nanoparticles. The best nanofluids have high stability, high absorption of sun light and minimum abrasion. In the present work an attempt has been made to identify the best absorption nanofluid.