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[en] A novel chitosan magnetic adsorbent was prepared with chemical cross linking and seed swelling method. The adsorption performance of the adsorbent for Hg2+ and UO22+ was investigated. The results show that the diameter of the magnetic adsorbent is 50-80 μm and the mass fraction of ferric oxide is about 16%. Selective separation of Hg2+ and UO22+ is achieved at pH<2.5. The adsorption capacity increase with pH increase. The adsorption isotherm data are analyzed by the Langmuir equations as: ceq/Qeq=0.4405 ceq/Qm + 0.5840 (Hg2+, r=0.9960); ceq/Qeq=0.5256 ceq/Qm + 1.3434 (UO22+, r=0.9906). The values of maximum adsorption capacity (Qm) are 2.27 mmol/g for Hg2+ and 1.90 mmol/g for UO22+. The adsorption kinetic data are fitted by the Lagergren equations as: lg(Qeq-Q)=0.3612-0.0155 t (Hg2+, r=0.9821); lg(Qeq-Q)=0.3027-0.0112 t (UO22+, r=0.9925). The value of the adsorption rate constents (kad) are 0.036 min-1 for Hg2+ and 0.026 min-1 for UO22+. Regeneration of the adsorbent is achieved using 1 mol/L H2SO4 with the desorption efficiency of more than 90%. The reproductive performance of the adsorbent is excellent. (authors)
[en] Fe3O4/chitosan magnetic microspheres were prepared with inverse-phase suspension dispersion method. It was modified through the reaction with poly(ethyleneimine) to increase the content of amine group of the adsorbent. The samples were characterized by X-ray diffraction (XRD), FT-IR, and thermogravimetric analysis (TGA). Adsorption performance of the modified chitosan microspheres toward Hg2+ and UO22+ was investigated. The results showed that the concentration of amine group of the adsorbent was 6.47 mmol/g. The adsorption rate was fast due to their small size (15-30 μm). Selective separation of Hg2+ and UO22+ was achieved at pH < 3. This was due to the fact that Hg2+ was able to form complexing anion (HgCl3-) with Cl- and adsorb onto the modified chitosan adsorbent through ion-exchange mechanism, but UO22+ could not. The maximum adsorption capacity (qm) was 2.19 mmol/g for Hg2+ and 1.38 mmol/g for UO22+. The adsorption rate constant calculated by Lagergrent equation was 0.087 min-1 for Hg2+, 0.055 min-1 for UO22+. More than 90% desorption efficiency for UO22+ and Hg2+ was achieved using 1 mol/L H2SO4 and for UO22+ using 2 mol/L HC1. (authors)
[en] Highlights: • Electrical performance of MJ solar cells immersed by silicon oil was studied under 500×. • Theoretical cell photocurrent losses caused by silicon oil absorption were estimated. • Cell performance changes operated in silicon oil (1.0–30.0 mm) were analyzed. • Critical silicon oil thickness on top of MJ solar cells was estimated to be 6.3 mm. - Abstract: In order to better apply direct liquid-immersion cooling (LIC) method in temperature control of solar cells in high concentrating photovoltaic (CPV) systems, electrical characteristics of GaInP/GaInAs/Ge triple-junction solar cells immersed in dimethyl silicon oil of 1.0–30.0 mm thickness were studied experimentally under 500 suns and 25 °C. Theoretical photocurrent losses caused by spectrum transmittance decrease from spectral absorption of silicon oil were estimated for three series sub-cells, and an in-depth analysis of the electrical performances changes of the operated cell in silicon oil was performed. Compared with cell performances without liquid-immersion, the conversion efficiency and the maximum output power of the immersed solar cell in silicon oil of 1.0 mm thickness has increased from 39.567% and 19.556 W to 40.572% and 20.083 W respectively. However, the cell electrical performances decrease with increasing silicon oil thickness in the range of 1.0–30.0 mm, and the efficiency and the maximum output power of the cell have become less than those without liquid-immersion when the silicon oil thickness exceeds 6.3 mm
[en] Highlights: • Atmospheric plate thermosyphon (APT) cooling solar cells was first proposed. • APT can reduce the temperature of PV panels without parasitic energy consumption. • The maximum temperature difference was less than 6 °C. • The heat transfer resistance at the evaporator is between 0.00486 and 0.02368 K/W. - Abstract: Since the heat pipe has no parasitic energy consumption, it is an important method for cooling the photovoltaic. In this paper, a novel type of atmospheric plate thermosyphon (APT) cooling system has been designed, which can be used for the heat dissipation of the single or low concentrated solar cells. In the experiments, the non-condensable gas (NCG) was collected by a gas reservoir. The coolant, ethanol, formed a liquid film on the porous medium and directly cooled the photovoltaic panel. The effect of various parameters such as heat flux density, tilt angle and inlet temperature have been studied. The results demonstrated that APT cooling system could effectively reduce the temperature of PV cells, and the higher heat flux density was, the shorter start-up time. The temperature of evaporator was uniform, and the larger inclined angle was, the greater surface temperature difference which maximumly was 5.6 °C. The thermal resistance at the evaporator was between 0.00486 and 0.02368 K/W.
[en] Better performance can be achieved when the bare silicon solar cells are immersed into liquids for the enhanced heat removing. In this study, the performance of solar cells immersed in liquids was examined under simulated sunlight. To distinguish the effects of the liquid optic and electric properties on the solar cells, a comparison between immersion of the solar module and the bare solar cells was carried out. It was found that the optic properties of the liquids can cause minor efficiency changes on the solar cells, while the electric properties of the liquids, the molecular polarizable and ions, are responsible for the most of the changes. The bare solar cells immersed in the non-polar silicon oil have the best performance. The accelerated life tests were carried out at 150 deg. C high temperature and under 200 W/m2 ultraviolet light irradiation, respectively. It was found that the silicon oil has good stability. This study can give support on the cooling of the concentrated photovoltaic systems by immersing the solar cells in the liquids directly
[en] Highlights: • Thermal performances of ethanol phase-change immersion and active water cooling are compared. • Effects of operation parameters on ethanol phase-change immersion are studied. • Optimum filling ratio is 30% for ethanol phase-change immersion cooling system. • Exergy efficiency of ethanol phase-change immersion method increases by 57%. - Abstract: This paper presents an optimized ethanol phase-change immersion cooling method to obtain lower temperature of dense-array solar cells in high concentrating photovoltaic system. The thermal performances of this system were compared with a conventional active water cooling system with minichannels from the perspectives of start-up characteristic, temperature uniformity, thermal resistance and heat transfer coefficient. This paper also explored the influences of liquid filling ratio, absolute pressure and water flow rate on thermal performances. Dense-array LEDs were used to simulate heat power of solar cells worked under high concentration ratios. It can be observed that the optimal filling ratio was 30% in which the thermal resistance was 0.479 °C/W and the heat transfer coefficient was 9726.21 W/(m2·°C). To quantify the quality of energy output of two cooling systems, exergy analysis are conducted and maximum exergy efficiencies were 17.70% and 11.27%, respectively. The experimental results represent an improvement towards thermal performances of ethanol phase-change immersion cooling system due to the reduction in contact thermal resistance. This study improves the operation control and applications for ethanol phase-change immersion cooling technology.
[en] Highlights: • Direct-contact liquid film cooling dense-array solar cells was first proposed. • Average temperature was controlled well below 80 °C. • The maximum temperature difference was less than 10 °C. • The heat transfer coefficient reached up to 11.91 kW/(m"2·K) under 589X. - Abstract: This paper presented a new method of cooling dense-array solar cells in high concentrating photovoltaic system by direct-contact liquid film, and water was used as working fluid. An electric heating plate was designed to simulate the dense-array solar cells in high concentrating photovoltaic system. The input power of electric heating plate simulated the concentration ratios. By heat transfer experiments, the effect of water temperatures and flow rates on heat transfer performance was investigated. The results indicated that: the average temperature of simulated solar cells was controlled well below 80 °C under water temperature of 30 °C and flow rate of 300 L/h when concentration ratio ranged between 300X and 600X. The maximum temperature difference among temperature measurement points was less than 10 °C, which showed the temperature distribution was well uniform. The heat transfer coefficient reached up to 11.91 kW/(m"2·K) under concentration ratio of 589X. To improve heat transfer performance and obtain low average temperature of dense-array solar cells, lower water temperature and suitable water flow rate are preferred.
[en] Co-pyrolysis behaviors of different plastics (high density polyethylene, low density polyethylene and polypropylene), low volatile coal (LVC) and their mixtures were investigated by TGA. Experiments were conducted under N2 atmosphere at heating rate of 20 deg. C/min from room temperature to 750 deg. C. The results showed that the thermal degradation temperature range of plastic was 438-521 deg. C, while that of coal (LVC) was 174-710 deg. C. Plastics showed similar pyrolysis characteristics due to similar chemical bonds in their molecular structures. The overlapping degradation temperature interval between coal and plastic provide an opportunity for free radicals from coal pyrolysis to participate in the reactions of plastic decomposition. The difference of weight loss percent (ΔW) between experimental and theoretical ones, calculated as an algebraic sum of those from each separated component, ΔW is 2.0-2.7% at the pyrolysis temperature higher than 530 deg. C, which indicates that the synergistic effect during pyrolysis occurs mainly in the high temperature region. The kinetic studies were performed according to Coats and Redfern method for first-order reaction. It was found that for plastics (HDPE, LDPE and PP), the pyrolysis process can be described by one first-order reaction. However, for LVC and LVC/plastic blends, this process can be described by three and four consecutive first-order reactions, respectively. The estimated kinetic parameters viz., activation energies and pre-exponential factors for coal, plastic and their blends, were found to be in the range of 35.7-572.8 kJ/mol and 27-1.7 x 1038 min-1, respectively
[en] Highlights: • The direct-contact liquid film cooling is experimentally and numerically investigated. • The temperature of simulated dense-array solar cells is well controlled and the temperature distribution is uniform. • The flow characteristic of liquid film and heat transfer performance is analyzed. • The effects of various inlet parameters are obtained and the best optimizing combination of inlet parameters is achieved. • The calculated cooling capacity is so prominent that the heat transfer coefficient is above 5000 W/m2·K. - Abstract: Thermal management is a critical issue for normal operation of dense-array solar cells in high concentration photovoltaic system. A cooling method of direct-contact liquid film was experimentally and numerically investigated. In the experiments, deionized water was adopted as coolant and an electric heating plate was optimal designed to simulate dense-array solar cells. A two-dimension model was derived to present the temperature distribution on the surface of the simulated solar cells and flow characteristic of liquid film. The effect of various inlet parameters such as water temperature, inlet width and velocity had been numerical studied. The experiment results suggest that the surface temperature is well controlled under 120 °C at corresponding conditions, with concentration ratios ranging from 300 to 500X. The numerical results show that inlet width has a crucial effect on the liquid film thickness. The subcooled boiling state is a necessary condition to ensure cooling effect. High water inlet temperature is preferable for better heat transfer performance and temperature uniformity. The best optimizing inlet velocity, width and temperature are 1.06 m/s, 0.75 mm and 75 °C, respectively.
[en] Highlights: • A fixed photovoltaic-SODIS (solar water disinfection) system was constructed. • The system could generate electricity and produce clean water simultaneously. • The daily solar generated electricity was much more than the system consumption. • The system can be used for about 90% of whole year in Lhasa and Chennai. • Temperature enhanced the SODIS process for about 60% days of whole year in Chennai. - Abstract: The objective of the study is to construct and evaluate a fixed PV (photovoltaic) cell integrated with SODIS (solar water disinfection) system to treat drinking water and generate electricity under different climate through experimental and simulation methods. The photovoltaic and disinfection performances of the hybrid system were studied by the disinfection of Escherichia coli. The applicability of the system in Lhasa and Chennai was evaluated by analyzing the daily radiation and predicting the daily water temperature and the system electricity output. The results confirm that the temperature would dramatically enhance the SODIS process and shorten the disinfection time, when the water temperature was above 45 °C. The PV cell in the hybrid system could work under low temperature because of the water layer and the generated electricity was much more than the system consumption. The simulation results show that the days with maximum water temperature above 45 °C were more than 60% of whole year in Chennai. The generated electricity of the hybrid system was 49682.3 W h and 45615.9 W h a year in Lhasa and Chennai respectively. It was sufficient to drive the system of whole year. The number of days which realized drinking water treatment was 324 days in Lhasa and 315 days in Chennai a year.