Greg C. Glatzmaier

Nanofluid heat capacities

Significant increases in the heat capacity of heat transfer fluids are needed not only to reduce the costs of liquid heating and cooling processes, but also to bring clean energy producing technologies like concentrating solar power (CSP) to price parity with conventional energy generation. It has been postulated that nanofluids could have higher heat capacities than conventional fluids. In this work, nano- and micron-sized particles were added to five base fluids (poly-α olefin, mineral oil, ethylene glycol, a mixture of water and ethylene glycol, and calcium nitrate tetrahydrate), and the resulting heat capacities were measured and compared with those of the neat base fluids and the weighted average of the heat capacities of the components. The particles used were inert metals and metal oxides that did not undergo any phase transitions over the temperature range studied. In the nanofluids studied here, we found no increase in heat capacity upon the addition of the particles larger than the experimental ...

Ca(NO3)2—NaNO3—KNO3 Molten Salt Mixtures for Direct Thermal Energy Storage Systems in Parabolic Trough Plants

Molten salts are currently the only thermal energy storage media operating with multiple hours of energy capacity in commercial concentrated solar power (CSP) plants. Thermal energy is stored by sensible heat in the liquid phase. A lower melting point in the range of 60–120 C and a decomposition temperature above 500 _C are desired because such a fluid would enhance the overall efficiency of the plants by utilizing less energy to keep the salt in the liquid state and by producing superheated steam at higher temperatures in the Rankine cycle. One promising candidate is a multicomponent NaNO3—KNO3—Ca(NO3)2 molten salt. Different compositions have been reported in literature as the best formulation for CSP plants based on melting temperature. In this paper, the National Renewable Energy Laboratory (NREL) presents the handling, preparation, thermal properties, and characterization of different compositions for this ternary nitrate salt, and comparisons are drawn accordingly. This system has a high tendency to form supercooled liquids with high viscosity that undergoes glass formation during cooling. When the proportion of Ca(NO3)2 decreases, the formulations become more thermally stable, the viscosity goes down, and the system increases its degree of crystalline solidification. Differential scanning calorimetry (DSC) tests showed the presence of a ternary eutectoid solid–solid invariant reaction at around 100 _C. The eutectic invariant reaction was resolved between 120 and 133 _C as reported in the literature. Based on DSC and viscosity results, the best composition would seem to be 36 wt. % Ca(NO3)2—16 wt. % NaNO3—48 wt% KNO3, which showed a low solidification point. [DOI: 10.1115/1.4023182]

Solar destruction of hazardous chemicals

Abstract The objective of this work was to demonstrate that concentrated solar energy can be used to effectively destroy hazardous chemicals. The study involved the design and construction of a photochemical reactor that was used in a unique solar experiment that utilized concentrated sunlight to destroy a dioxin. Temperatures from 750 to 1000 °C were achieved along with solar flux levels from 500 to 1000 times normal sunlight (50–100 W/cm2). Field testing demonstrated that concentrated sunlight can effectively destroy a hazardous chemical (1,2,3,4‐tetrachlorodibenzo‐p‐dioxin). Significant enhancements were also shown to exist due to the presence of solar photons of wavelength 300–400 nm.

Pilot-Scale Demonstration of an Innovative Treatment for Vapor Emissions

Researchers from the National Renewable Energy Laboratory recently conducted a pilot-scale study at McClellan Air Force Base (AFB) in Sacramento, CA. The objective of the test was to determine the effectiveness of an ambient-temperature, solar-powered photocatalytic oxidation treatment unit for destroying emissions of chlorinated organic compounds from an air stripper. This paper reports test results and discusses applications and limitations of the technology. A 10-standard-cubic-foot-per-minute (SCFM) (28.3 L/min) slip stream of air from an air stripper at Operative Unit 29-31 at McClellan AFB was passed through a reactor that contained a lightweight, perforated, inert support coated with photoactive titanium dioxide. The reactor faced south and was tilted at a 45° angle from vertical so that the light-activated catalyst received most of the available sunlight. An online portable gas chro-matograph with two identical columns simultaneously analyzed the volatile organic compounds contained in the reactor inlet and outlet air streams. Summa canister grab samples of the inlet and outlet were also collected and sent to a certified laboratory for U.S. Environmental Protection Agency Method TO-14 analysis and verification of our field analyses. Three weeks of testing demonstrated that the treatment systems destruction and removal efficiencies (DREs) are greater than 95% at 10 SCFM with UV intensities at or greater than 1.5 milliwatts/square centimeter (mW/cm2). DREs greater than 95% at 20 SCFM were obtained under conditions where UV irradiation measured at or greater than 2 mW/cm2. In Sacramento, this provided 6 hours of operation per clear or nearly clear day in April. A solar tracking system could extend operating time. The air stream also contained trace amounts of benzene. We observed no loss of system performance during testing.

Supercritical CO2 as a Heat Transfer and Power Cycle Fluid for CSP Systems

Concentrating Solar Power (CSP) utilizes solar thermal energy to drive a thermal power cycle for the generation of electricity. CSP technologies include parabolic trough, linear Fresnel, central receiver or “power tower,” and dish/engine systems. The parabolic trough is the most common system with nine Solar Electric Generating Stations (SEGS) operating in southern California for over two decades and new plants online in Nevada and Spain. The resurgent interest in CSP has been driven by renewable portfolio standards in southwestern states and renewable energy feed-in tariffs in Spain. CSP has cost advantages versus solar photovoltaic systems for large, centralized power plants. Certain CSP systems, in particular parabolic troughs and power towers, are also amenable to the incorporation of thermal energy storage. Thermal energy storage is much less expensive than electric storage and allows CSP plants to increase capacity factor and dispatch power as needed — for example, to cover an evening demand peak.Copyright

Thermal Energy Storage and its Potential Applications in Solar Thermal Power Plants and Electricity Storage

With the rapid growth of renewable power generation, economically storing large quantities of solar- and wind-generated electricity may become as important as renewable power itself. The combination of renewable power generation and energy storage can overcome the variability of renewable power generation alone and create the opportunity for renewable generation to provide base-load electricity. For peak power usage, the integration of renewable power and storage of excess electricity has several significant and positive impacts: expanding the renewable energy portion of total electricity generation, improving the peak-load response, and coordinating the electricity supply and demand over the grid. Several energy storage approaches exist, with mechanical, chemical, and electrical methods either in use now or being developed. Comparing their efficiencies as well as their economic uses for different scales and applications helps determine the right technology for the right purpose. This paper will study the possibility of using thermal energy storage as a means for electricity storage, and compare it to other energy storage methods including batteries, flywheels, compressed air, and pumped hydropower.Copyright

Can particle-stabilized inorganic dispersions be high-temperature heat-transfer and thermal energy storage fluids?

Particle-stabilized dispersions are considered as potential high-temperature, high-energy–density heat transfer fluids as well as thermal energy storage materials. To be useful practically, these dispersions need to be stable against coalescence and have low viscosity. We present indirect experimental evidence of particle stabilization of Al–Si in NaCl–NaF dispersions with graphite as the stabilizer. We found no evidence of particle stabilization in the same system with boron carbide, silicon carbide, silica, or zirconia as the stabilizer. We also present indirect experimental evidence of particle stabilization in Al/B2O3/C and Al/NaCl–KCl/Al2O3 dispersed phase/dispersion media/stabilizer systems.

Origin of anomalous strain effects on the molecular adsorption on boron-doped graphene

When compressive strain is applied to a single-layered material, the layer generally ripples along the third dimension to release the strain energy. In contrast, such a rippling effect is not favored when it is under tensile strain. Here, using first-principles density-functional calculations, we show that molecular adsorption on boron-doped graphene (BG) can be largely tuned by exploiting the rippling effect of the strained graphene. Under tensile strain, the adsorption energy of K2CO3, NO2, and NH3 on BG, for which the molecular adsorption is a chemisorption characterized by a covalent B-molecule bond, exhibits a superlinear dependence on the applied strain. In contrast, when microscopic ripples are present in the BG under compressive strain, the adsorption strength is significantly enhanced with increasing the strain. Such a nonlinear and asymmetric effect of strain on the molecular adsorption is a characteristic of two-dimensional systems, because a general elastic theory of molecular adsorption on three-dimensional systems gives a linear and symmetric strain effect on the adsorption strength. We provide the underlying mechanism of the anomalous strain effect on the chemical molecular adsorption on BG, in which the microscopic rippling of the graphene and the creation of the π-dangling bond state near the Dirac point play an important role. Our finding can be used to modify chemical reactivity of graphene with a wide range of application.

Determining the Cost Benefit of High-Temperature Coatings for Concentrating Solar Power Thermal Storage Using Probabilistic Cost Analysis

Probabilistic cost analysis determined the cost benefit for applying a protective coating to the wetted surfaces of stainless steel tank walls for concentrating solar power (CSP) thermal storage applications. The model estimated the total material cost of coated 347 or 310 stainless steel (347/310) and the cost of uncoated Inconel 625, which served as the reference tank wall cost. Model results showed that the cost of the coated 347/310 stainless steel was always statistically less than the cost of the bare Inconel 625 when these materials are used for tank walls at representative tank diameters and temperatures for CSP storage applications.

One-Pot Shear Synthesis of Gallium, Indium, and Indium–Bismuth Nanofluids: An Experimental and Computational Study

Nanofluids are often proposed as advanced heat transfer fluids. In this work, using a one-step nanoemulsification method, we synthesize gallium, indium, and indium–bismuth nanofluids in poly-alpha-olefin (PAO). The size distributions of the resulting nanoparticles are analyzed using transmission electron microscopy (TEM). X-ray diffraction (XRD) analysis of the alloy nanoparticles indicates that their composition is the same as that of the bulk alloy. It was found that oleylamine stabilizes both gallium and indium particles in PAO, while oleic acid is effective for gallium particles only. The microscopic adsorption mechanism of surfactants on gallium and indium surfaces is investigated using density functional theory (DFT) to understand why oleylamine is effective for both metals while oleic acid is effective for gallium only.