Optical properties of a solar-absorbing molten salt heat transfer fluid. [Eutectic mixture of KNO3, NaNO2, and NaNO3 with particle suspensions of cobalt oxides or copper oxides]
The optical absorption properties of a high temperature molten salt heat transfer fluid were measured from 0.35 ..mu..m to 2.5 ..mu..m using both hemispherical transmission and reflection techniques. This fluid has application as a direct-absorbing working fluid in a high temperature central receiver solar energy facility. The absorption spectrum of the pure molten fluid--a eutectic mixture of KNO/sub 3/, NaNO/sub 2/, and NaNO/sub 3/, known as Hitec (Du Pont trade name)--displays a fundamental absorption edge near 410 nm, which was found to shift to longer wavelength linearly with temperature. Throughout the remainder of the visible spectrum, the fluid is transparent. To enhance its solar absorption, particulate metallic oxides of Co or Cu were introduced into the fluid. Absorption spectra of these oxide particle suspensions in the molten salt were determined as a function of dopant concentration ranging from 0 to 0.1 wt% metal nitrate added to the Hitec. These measurements were carried out at 200/sup 0/C under flow conditions to cause a homogeneous suspension of particles. Special transmission and reflection flow cells were designed and constructed to handle 200/sup 0/C fluids. The suspended particles cause an additional optical absorption throughout the visible spectrum which is characteristic of the particular metallic oxide and closely follows a Beer-Lambert concentration dependence. The solar averaged absorption in a fixed layer thickness was calculated for various concentrations of the fluid-oxide mixtures. The fluid without oxide particles absorbs approximately 8% of the solar spectrum per cm of path length. Addition of 0.1 wt% of Co(NO/sub 3/)/sub 2/.6H/sub 2/O increases this absorption to approximately 90% per cm. Of the oxides studied, Co/sub 3/O/sub 4/ particle suspensions offer better solar absorption characteristics than CuO. Effects of particulate scattering on the measurements are discussed.
- Research Organization:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
- DOE Contract Number:
- EY-76-C-04-0789
- OSTI ID:
- 7296394
- Report Number(s):
- SAND-77-0938
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CENTRAL RECEIVERS
WORKING FLUIDS
MOLTEN SALTS
OPTICAL PROPERTIES
POTASSIUM NITRATES
SODIUM NITRATES
ABSORPTIVITY
COBALT OXIDES
COPPER OXIDES
EUTECTICS
HEAT TRANSFER
LIGHT SCATTERING
PARTICLES
SUSPENSIONS
TOWER FOCUS COLLECTORS
TOWER FOCUS POWER PLANTS
ALKALI METAL COMPOUNDS
CHALCOGENIDES
COBALT COMPOUNDS
COPPER COMPOUNDS
DISPERSIONS
ENERGY TRANSFER
FLUIDS
NITRATES
NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
POTASSIUM COMPOUNDS
POWER PLANTS
SALTS
SODIUM COMPOUNDS
SOLAR COLLECTORS
SOLAR POWER PLANTS
SOLAR THERMAL POWER PLANTS
TRANSITION ELEMENT COMPOUNDS
CSP
Concentrating Solar Power
140702* - Solar Thermal Power Systems- Central Receiver
141000 - Solar Collectors & Concentrators