Most of the current predictions of the radiative properties of microalgae use the homogeneous sphere approximation based on the Mie scattering theory, and the refractive indices of the model were ...regarded as fixed values. Using the recently measured optical constants of various microalgae components, we propose a spherical heterogeneous model for spherical microalgae. The optical constants of the heterogeneous model were characterized by the measured optical constants of microalgae components for the first time. The radiative properties of the heterogeneous sphere were calculated using the T-matrix method and were well verified by measurements. It shows that the internal microstructure has a more significant effect on scattering cross-section and scattering phase function than absorption cross-section. Compared with the traditional homogeneous models selected with fixed values as refractive index, the calculation accuracy of scattering cross-section of the heterogeneous model improved by 15%-150%. The scattering phase function of the heterogeneous sphere approximation agreed better with measurements than the homogeneous models due to the more detailed description of the internal microstructure. It can be concluded that considering the internal microstructure of microalgae and characterizing the microstructure of the model by the optical constants of the microalgae components helps to reduce the error caused by the simplification of the actual cell.
In this article, a Ni-Cu-P modified surface is prepared by electroless plating, and the microbial fouling resistance tests on the Ni-Cu-P surface are carried out further. The results show that the ...Ni-Cu-P modified surface has excellent antifouling performance. Compared with carbon steel, the microbial fouling on the Ni-P and Ni-Cu-P modified surface are decreased by 90.6% and 92.0% respectively. Further the effects of temperature, flow rate, and initial bacterial concentration on microbial fouling thermal resistance of Ni-Cu-P modified surface are investigated and analyzed. With the cooling water inlet temperature increasing (25–40°C), the fouling thermal resistance of the Ni-Cu-P modified surface is increased first and then reduced. Among experimental temperature range, there might be an “optimal” temperature for microbial fouling accumulation. With the flow rate increasing (0.2m/s–0.3m/s), the fouling thermal resistance of Ni-Cu-P modified surface is decreased by 78.3%. With the initial bacteria concentration in cooling water increasing (8.364 × 109 CFU/mL −51.456 × 109 CFU/mL), the fouling thermal resistance is increased by 57.4% accordingly. By rationally adjusting the operating conditions, the accumulation of microbial fouling on the Ni-Cu-P modified surface can be further reduced, allowing for long-term cleaning and effective heat transfer of the Ni-Cu-P modified heat exchange surface.
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•A Ni-Cu-P modified surface is designed and prepared for fouling reduction.•The microbial fouling deposition on modified surface is reduced significantly.•The fouling thermal resistance is used to evaluate microbial fouling process.•The modified surface combined operation factors revision foster fouling reduction.
Microbial fouling on heat exchange surface is common for large amount of microorganisms in circulating cooling water. In this article, a modified surface technology is used to suppress and reduce the accumulation of microbial fouling on the heat transfer surface. Firstly a Ni-Cu-P modified surface is prepared by electroless plating, and a Ni-P surface applied commonly in industry is also prepared as a comparison. With the help of the designed and constructed experimental system for dynamic monitoring of microbial fouling, the microbial fouling tests of the Ni-Cu-P, Ni- P and carbon steel surface are carried out. The results show that the Ni-Cu-P modified surface has excellent antifouling performance. Compared with carbon steel, the microbial fouling on the Ni-P and Ni-Cu-P modified surface are decreased by 90.6 % and 92.0 % respectively. Further the effects of temperature, flow rate, and initial bacterial concentration on microbial fouling heat resistance of Ni-Cu-P modified surface are investigated and analyzed. With the cooling water inlet temperature increasing (25–40 °C), the fouling heat resistance of the Ni-Cu-P modified surface is increased first and then reduced. With the flow rate increasing (0.2 m/s-0.3 m/s), the fouling heat resistance of Ni-Cu-P modified surface is decreased by 78.3 %. With the initial bacteria concentration in cooling water increasing (8.364 × 109 CFU/mL −51.456 × 109 CFU/mL), the fouling heat resistance is increased by 57.4 % accordingly. By rationally adjusting the operating conditions, such as regulating the temperature of cooling water far away from the suitable temperature of bacteria and increasing the flow rate of circulating cooling water as much as possible, the accumulation of microbial fouling on the Ni-Cu-P modified surface can be further reduced, allowing for long-term cleaning and effective heat transfer of the Ni-Cu-P modified heat exchange surface.
•The fouling characteristics of IB and SFB in plate heat exchanger are studied.•The effects of working conditions on fouling characteristics are investigated.•The fouling characteristics of bacteria ...mixture are studied.•The synergy between IB and the SFB has been analyzed.
Iron bacteria (IB) and slime-forming bacteria (SFB) are the most common in circulating cooling water. In order to study on the characteristics of microbial fouling in plate heat exchangers, an experimental study was carried out for the fouling characteristics of IB and SFB. The fouling characteristics in the plate heat exchanger under the different flow velocity, temperature and concentration were investigated for these two bacteria and the mixture of them. The results show that the asymptotic value of fouling resistance and the time of reaching the asymptotic value decreases with the increase of fluid velocity. The asymptotic value of fouling resistance increases with the increase of concentration. And the influence of temperature is different for the two kinds of bacteria. When these two bacteria are mixed, the IB and the SFB grow synergistically because the IB have strong ability in microbial fouling and the SFB have the high secretion rate of extracellular polymeric substances.
•Transparent ceramics were obtained from naturally occurring fluorite mineral.•The optical transmissivity reached about 60% in the infrared wavelength range.•Transparent ceramics are 40 mm in ...diameter and 2.5 mm in thickness.•The average grain size was about 100 μm.
A approach to fabricating of transparent polycrystalline fluorite ceramic based on hot pressing sintering of fluorite mineral powders was proposed. Fluorite powders were obtained by ball milling naturally occurring fluorite mineral, and diameters of obtained powders were less than 100 μm. Transparent polycrystalline fluorite ceramic was fabricated by hot pressing sintering at 1100 °C for 3 h. The optical transmissivity reached about 60% in the infrared wavelength range (2.5 mm thickness specimen), and the average grain size was about 100 μm.
Transparent Pr3+ doped Ca1-xGdxF2+x (x = 0, 0.01, 0.03, 0.06, 0.10, 0.15) polycrystalline ceramics with fine-grained microstructures were prepared by the hot-pressing method. The dependence of ...microstructure, optical transmittance, luminescence performances and mechanical properties on the Gd3+ concentrations for Pr3+:Ca1-xGdxF2+x transparent ceramics were investigated. The Gd3+ ions show positive effects on the microhardness of Pr3+:Ca1-xGdxF2+x transparent ceramics as a result of the decrease in the grain sizes. Excited by the Xenon lamp of 444 nm, typical visible emissions located at 484 nm, 598 nm and 642 nm were observed. Furthermore, the incorporation of Gd3+ ions can greatly enhance the photoluminescence performance owing to the improvement in the concentration quenching effect. The quenching concentration of Pr3+ ions in CaF2 transparent ceramics increased to 1 at.% as a result of the positive effect of Gd3+ codoping. The energy transfer mechanism of Pr3+ in the Pr3+:Ca1-xGdxF2+x transparent ceramics has been investigated and discussed.
Er, Yb:CaF2 nanoparticles with different Yb concentrations were synthesized by a coprecipitation method using nitrates as raw materials. X‐ray powder diffraction and transmission electron microscopy ...analysis showed that the nanoparticles were single fluorite phase and the nanoparticle size was found to decrease with increasing Yb concentrations. The obtained nanoparticles were hot‐pressed at 800°C under 30 MPa under vacuum environment to fabricate Er, Yb:CaF2 transparent ceramics. The influence of Yb ion concentrations on the optical transmission, microstructure, and luminescence properties of Er, Yb:CaF2 transparent ceramics were investigated. The addition of Yb ions was found effectively to reduce grain size and has a positive effect on improving the optical transmission of Er, Yb:CaF2 transparent ceramics. The highest transmittance in the near‐infrared spectral region of the Er, Yb:CaF2 transparent ceramic reached about 90%. The green, red, and near‐infrared emission intensities were found to increase with increasing Yb concentration.
Near-infrared pumped up-conversion luminescent PrF3 and YbF3 co-doped SrF2 ceramics were fabricated by the hot-pressing sintering technique, and the pellets were transparent with a primrose yellow ...appearance. The influence of YbF3 co-doping levels on the optical qualities and microstructures of ceramics was investigated. We identified the mechanisms to realize up-conversion luminescence in the visible range from 3P0,1 levels (Pr3+) under near-infrared wavelength pumping sources other than the near ultraviolet to blue region photons. Yb3+ ions inducing a broad and intense absorption band at the 900–1050 nm region, and the absorption coefficient and cross-section at 980 nm are 7.57 cm−1 and 4.19 × 10−21 cm2 in the ceramic co-doped with 15 wt% YbF3, respectively. The intense up-conversion luminescence bands at 480, 520, 540, and 600 nm under 980 nm excitation were attributed to 3P0→3H4, 3P1→3H5, 3P0→3H5 and 1D2→3H4 transitions of Pr3+ ions, respectively.
Yb3+ as sensitizers are introduced into Pr:SrF2 transparent ceramics, and realize intense emission in the visible regions through up-conversion (UC) procedure under the maturely commercial InGaAs laser diode at near-infrared (NIR) pumping source excitation, instead of the near-ultraviolet (NUV) or blue region pumping sources. Two-photon mechanisms are identified to generate UC luminescence for Pr, Yb:SrF2 transparent ceramics. Display omitted
•Yb3+ ions as sensitizers are introduced into Pr:SrF2 ceramics.•Highly transparency Pr, Yb:SrF2 ceramics were fabricated by HP sintering.•Intense UC emission was realized under the maturely InGaAs LD excitation.•Two-photon mechanism is identified to generate UC emission for ceramics.
•Highly transparency Er:SrF2 ceramics were fabricated by HP sintering.•The transmittance at 500 nm and 1200 nm are 87.9 % and 89.5 %, respectively.•The intensity ratio R (Red/Green) increase with ...increasing ErF3 doping levels.•Fracture toughness (KIC) for the Er(5 wt.%):SrF2 ceramic is 0.52 ± 0.08 MPa·m1/2.
Raw SrF2 powders were synthesized by the chemical precipitation method, and the mean particle size was 58.48 nm. Er:SrF2 transparent ceramics were obtained by hot-pressed (HP) technique, and the effect of ErF3 levels on the transparency, microstructure, luminescence spectroscopic and microhardness were studied. The ratio of emission intensities R (Red/Green) increased with the ErF3 doping levels. The addition of ErF3 was found effectively to reduce grain size and has a positive effect on improving the microhardness. The SrF2 ceramic doped with 5 wt.% ErF3 (2 mm thick) showed the best optical transparency, the transmittance at 500 nm and 1200 nm are 87.9 % and 89.5 %, respectively. The average grain size, Vickers hardness (Hv), and fracture toughness (KIC) for the SrF2 ceramic were 21.1 ± 4.5 μm, 1.73 ± 0.04 GPa, and 0.52 ± 0.08 MPa·m1/2, respectively.
Nanoparticles of erbium‐doped calcium fluoride were synthesised by the coprecipitation method. Micromorphology of the obtained nanoparticles was observed by transmission electron microscopy. The ...nanoparticles were hot‐pressed in a vacuum environment to achieve Er:CaF2 transparent ceramic. X‐ray diffraction analysis confirmed the crystallization of a single fluorite phase after sintered. Transmittance spectrum of Er:CaF2 ceramic sample was measured, and the transmittance at 1200 nm reached about 87%. Microstructures were characterized using field‐emission scanning electron microscopy. The luminescence spectrum of Er:CaF2 transparent ceramics under 488‐ and 978‐nm excitation was measured and discussed. It was evidenced that strong cross‐relaxation processes between Er3+ ions occur at high dopant concentration, and favoring the red emission at the expense of the green one.
