Predicted Efficiency of a Low-Temperature Nanofluid-Based Direct Absorption Solar Collector

Abstract

Due to its renewable and nonpolluting nature, solar energy is often used in applications such as electricity generation, thermal heating, and chemical processing. The most cost-effective solar heaters are of the “flat-plate” type, but these suffer from relatively low efficiency and outlet temperatures. The present study theoretically investigates the feasibility of using a nonconcentrating direct absorption solar collector (DAC) and compares its performance with that of a typical flat-plate collector. Here a nanofluid—a mixture of water and aluminum nanoparticles—is used as the absorbing medium. A two-dimensional heat transfer analysis was developed in which direct sunlight was incident on a thin flowing film of nanofluid. The effects of absorption and scattering within the nanofluid were accounted for. In order to evaluate the temperature profile and intensity distribution within the nanofluid, the energy balance equation and heat transport equation were solved numerically. It was observed that the presence of nanoparticles increases the absorption of incident radiation by more than nine times over that of pure water. According to the results obtained from this study, under similar operating conditions, the efficiency of a DAC using nanofluid as the working fluid is found to be up to 10% higher (on an absolute basis) than that of a flat-plate collector. Generally a DAC using nanofluids as the working fluid performs better than a flat-plate collector, however, much better designed flat-plate collectors might be able to match or outperform a nanofluids based DAC under certain conditions.

Solar steam generation by heat localization

“…The steam thus generated is usually in thermal equilibrium with the bulk liquid. Nanofluids-fluids seeded with nanoparticles-as another alternative have been studied [5][6][7] as volumetric absorbers, potentially minimizing the surface energy loss by uniform temperature in the fluid 6 and enhanced thermal conductivity of nanofluid 8,9 . Local generation of steam in a cold bulk liquid can be achieved through high concentrations or illumination of nanofluids by electromagnetic waves (generally, lasers) with high power intensity [10][11][12][13][14][15][16][17][18] .…”

Optimization of nanofluid volumetric receivers for solar thermal energy conversion

“…The efficiency of a solar thermal receiver is the ratio of collected thermal energy to the total incident energy (Tyagi et al, 2009) …”

“…Kumar and Tien (1990) developed a model for particle-laden falling liquid films (1-5 mm thick) incorporating the spectral and directional radiative properties of the particles, and provided a framework for future modeling studies. More recently, Tyagi et al (2009) numerically investigated a low temperature nanofluid receiver inside a mini-channel; while, Otanicar et al (2009b) extended this model to include multiple and dependent scattering, and size-dependent optical properties. Otanicar et al (2010) also experimentally demonstrated the use of different nanofluids in a micro-channel solar collector.…”

Investigation and Measurement of Copper Nanofluid Impact on Thermal Efficiency of Solar Collectors

“…Tyagi investigated the efficiency of a direct absorption solar collector containing nanofluids under numerical comparison with a conventional flat plate collector. He used aluminum nanoparticles, and in this collector model, he showed that performance under normal operations was almost 10% more than performance of the conventional flat plate collector under similar conditions [2]. Otanicar carried out an experimental study on the effects of using nanofluids in a microsized direct absorption collector and showed that it had a positive effect of about 5% on collector efficiency [3].…”