The Applications of Nanofluids in Solar Energy Reporter: Qin Lianwei

 solid–liquid composite materials  consisting of nanometer sized solid particles suspended in different base fluids Nanofluids: Suspensions of nanoparticles in base fluids

Properties of Nanofluids Advanced flow and heat transfer fluids Enhancing functions and properties by combining and controlling interactions Combining different nanoparticles in different base- fluids with additives Controlling interactions using different “mixing” methods and thermal-, flow-, catalyst-, and other field- conditions

 The single-step method The single step simultaneously makes and disperses the nanoparticles directly into a base fluid. Nanoparticles agglomeration is minimized. Only suitable for low vapor pressure fluid.  The two-step method (widely used) Nanoparticles was first produced and dispersed into the base fluids. Good for oxides nanoparticles. Not suitable for metallic nanoparticles. Preparation of nanofluids

CriteriaConventionalNanofluids StabilitySettleStable Surface/volume ratioLowHigh Thermal ConductivityLowHigh CloggingHighLow Pumping PowerLargeSmall Conventional solid-liquid suspensions compared to nanofluids

Four Characteristic Features of Nanofluids Nanofluids have an unprecedented combination of four characteristic features desired in energy systems: –Increased thermal conductivity (TC) at low nanoparticle concentrations –Strong temperature-dependent TC –Non-linear increase in TC with nanoparticle concentration –Increase in boiling critical heat flux (CHF)

Thermal Conductivity Particle material Particle Size Base fluid material TemperatureParticle volume concentration pH Factors influencing thermal conductivity of nanofluids:

TEM Characteristics of Copper Nanofluids By the single-step method very small copper particles (about 10 nm) Very little agglomeration and sedimentation Bright-field TEM micrograph of Cu nanoparticles produced by direct evaporation into ethylene glycol

Applications of Nanofluids in Solar Energy Schematic of nanofluid-based concentrated parabolic solar collector Schematic of the nanofluid-based direct absorption solar collector

 Nanofluids provide a promising technical selection for enhancing heat transfer.  Pioneering nanofluids research has inspired physicists, chemists, and engineers around the world.  These characteristic features of nanofluids make them suitable for the next generation of flow and heat-transfer fluids. Conclusions