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The Applications of Nanofluids
in Solar Energy
Reporter: Qin Lianwei
Nanofluids:
Suspensions of nanoparticles in base fluids
 solid–liquid composite materials
 consisting of nanometer sized
solid particles suspended in
different 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 basefluids with additives
• Controlling interactions using different “mixing”
methods and thermal-, flow-, catalyst-, and other fieldconditions
Preparation of nanofluids
 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.
Conventional solid-liquid suspensions
compared to nanofluids
Criteria
Conventional
Nanofluids
Stability
Settle
Stable
Surface/volume ratio
Low
High
Thermal Conductivity
Low
High
Clogging
High
Low
Pumping Power
Large
Small
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)
Factors influencing thermal conductivity of
nanofluids:
Particle material
Particle Size
Base fluid material
Thermal Conductivity
Temperature
pH
Particle volume
concentration
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 the nanofluid-based direct
absorption solar collector
Schematic of nanofluid-based concentrated
parabolic solar collector
Conclusions
 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.