The steady-state and dynamic simulation of cascade distillation system for the production of oxygen-18 isotope from water

Accurate simulation of water distillation system for oxygen-18(18O) isotope separation is necessary to guide industrial practice, since both deuterium(D) and oxygen-18 isotope get enriched and interfere with each other. In the present work, steady-state and dynamic distillation models are established based on a classic method and a cascade distillation system with 5 towers is introduced to test the models. The theoretical expressions of separation factor αH/Dfor protium/deuterium and separation factor α^(16)O/^(18) O.for oxygen-16/oxygen-18 were derived,with the existence of deuterium and oxygen-18, respectively. The results of the steady-state simulation by the classical method proposed in the present work agreed well with the results of the lumping method. The dynamic process could be divided into 5 stages. Impressively, a peak value of product withdraw was observed before the final steady state, which was resulted from the change of ^(16)O/^(18) O separation factor and isotope distribution. An interesting low concentration zone in the towers of T2–T5 existed at the beginning of the dynamic process and it required industrial evidence.

Numerical Study of Methane Dry Reforming Reaction in a Disk Reactor with Focused Solar Simulator

Heat transfer and thermochemical energy storage process of methane dry reforming in a disk reactor with focused solar simulator was modeled and analyzed. The results showed that thermochemical energy storage efficiency of disk reactor can reach 28.4%, and that is higher than that of tubular reactor.?The maximum reaction rate occurs at catalyst bed corner near the baffle, because the corner has high temperature and high reactant molar fraction. As reactant flow increases, methane conversion and thermochemical energy storage efficiency decrease as catalyst bed temperature and heat loss decrease.?The?thermochemical energy storage efficiency increased first and then decreased with methane molar ratio increasing, while?methane conversion?and the?thermochemical energy storage efficiency increased with reactant temperature increasing.?As catalyst bed porosity rises,?methane conversion?and?thermochemical energy storage efficiency increased first and then decreased, and optimum porosity is 0.31.

Simulation of Steady-State and Dynamic Behaviour of a Plate Heat Exchanger

The present paper deals with both the steady-state and dynamic simulation of a plate heat exchanger, in counter-flow arrangement. A CFD （computational fluid dynamics） program FLUENT has been used to predict the temperature distribution in steady-state conditions in plate heat exchanger as well as fluid temperatures at exit of flow channels in transient condition. The results are presented for the heat exchanger, which is simulated according to the configuration of the plate heat exchanger used in the experiment. The simulated results obtained by the CFD model have been compared with the experimental data from the literature, which shows that the CFD model developed in this study is capable of predicting the steady-state and transient performance of the plate heat exchangers satisfactorily.

Development and Experimental Evaluation of a Steady-state Model for the Step-feed Biological Nitrogen Removal Process

In this article,a steady-state mathematical model was developed and experimentally evaluated to inves- tigate the effect of influent flow distribution and volume ratios of anoxic and aerobic zones in each stage on the to- tal nitrogen concentration of the effluent in the step-feed biological nitrogen removal process.Unlike the previous modeling methods,this model can be used to calculate the removal rates of ammonia and nitrate in each stage and thereby predict the concentrations of ammonia,nitrate,and total nitrogen in the effluent.To verify the simulation results,pilot-scale experimental studies were carried out in a four-stage step feed process.Good correlations were achieved between the measured data and the simulation results,which proved the validity of the developed model. The sensitivity of the model predictions was analyzed.After verification of the validity,the step feed process was optimally operated for five months using the model and the criteria developed for the design and operation.During the pilot-scale experimental period,the effluent total nitrogen concentrations were all below 5mg·L -1 ,with more than 90%removal efficiency.

Device simulation of lead-free CH_3NH_3SnI_3 perovskite solar cells with high efficiency

The lead-free perovskite solar cells(PSCs) have drawn a great deal of research interest due to the Pb toxicity of the lead halide perovskite.CHNHSnIis a viable alternative to CHNHPbX,because it has a narrower band gap of 1.3 eV and a wider visible absorption spectrum than the lead halide perovskite.The progress of fabricating tin iodide PSCs with good stability has stimulated the studies of these CHNHSnIbased cells greatly.In the paper,we study the influences of various parameters on the solar cell performance through theoretical analysis and device simulation.It is found in the simulation that the solar cell performance can be improved to some extent by adjusting the doping concentration of the perovskite absorption layer and the electron affinity of the buffer and HTM,while the reduction of the defect density of the perovskite absorption layer significantly improves the cell performance.By further optimizing the parameters of the doping concentration(1.3 × 10cm~3) and the defect density(1 × 10cm~3) of perovskite absorption layer,and the electron affinity of buffer(4.0 eV) and HTM(2.6 eV),we finally obtain some encouraging results of the Jof 31.59 mA/cm~2,Vof 0.92 V,FF of 79.99%,and PCE of 23.36%.The results show that the lead-free CHNHSnIPSC is a potential environmentally friendly solar cell with high efficiency.Improving the Snstability and reducing the defect density of CHNHSnIare key issues for the future research,which can be solved by improving the fabrication and encapsulation process of the cell.

Numerical Simulation of Sensitivities of Snow Melting to Spectral Composition of the Incoming Solar Radiation

Snow albedo is an important factor influencing the snow surface energy budget and snow melting, yet uncertainties remain in the calculation of spectrally resolved snow surface albedo because the spectral composition （visible versus near infrared） of the incident solar radiation is seldom available. The influence of the spectral composition of the incoming solar radiation on the snow surface albedo, snow surface energy budget, and final snow ablation is investigated through sensitivity experiments of four snow seasons at two open sites in the Alps by using a multi-layer Snow-Atmosphere-Soil-Transfer scheme （SAST）. Since the snow albedo in the near infrared （NIR） spectral band is significantly lower than that in the visible （VIS） band, and almost the entire NIR part of the solar radiation is absorbed in the top layer of the snow pack, given a fixed amount of incoming solar radiation, a lower VIS/NIR ratio implies that more NIR radiation is reaching the ground surface and more is absorbed by the top layer of the snow pack, therefore, speeding up the snow melting and increasing the surface runoff, although a lesser part of the solar radiation in the visible band is transmitted into and trapped by the sub-layer of the snow pack. The above VIS/NIR ratio effect of the incoming solar radiation can result in a couple of days difference in the timing of snow ablation and it becomes more significant in late spring when the total solar radiation is intensified with seasonal evolution. Snow aging also slightly intensifies this VIS/NIR ratio effect.

Simulation and Analysis of Flexible Solar Panels' Deployment and Locking Processes

To predict the attitude of satellite during the whole deployment process and evaluate the locking impact, a numerical flexible model of a certain satellite associated with four flexible honeycomb solar panels was established. The flexible solar panel was modeled by the finite element analysis (FEA), and the motion equations were derived by Lagrangian formulation. The locking process was based on the method of Hertzian contact, which enables one to predict the locking impact on the satellite and the subsequent oscillation of solar panels. The results reveal that locking operation has great impact on the attitude of the satellite, and the angular acceleration of satellite reaches 22.03°/s2 at the locking moment; the flexible solar panels model is feasible to predict the accurate response of the satellite during deployment and the oscillation of solar panels; the instantly impulsive force occurred during locking process is about 1.5 kN and the changing time is nearly 0.32 s. It provides an effective approach to present the flexible solar panels' deployment process and evaluate the locking impact.

Numerical simulation of a triple-junction thin-film solar cell based on μc-Si_(1-x)Ge_x :H

In this paper, a-Si：H/a-SiGe：H/μc-SiGe：H triple-junction solar cell structure is proposed. By the analyses of mi- croelectronic and photonic structures （AMPS-1D） and our TRJ-F/TRJ-M/TRJ-B tunneling-recombination junction （TRJ） model, the most preferably combined bandgap for this structure is found to be 1.85 eV/1.50 eV/1.0 eV. Using more realistic material properties, optimized thickness combination is investigated. Along this direction, a-Si：H/a-SiGe：H/μc-SiGe：H triple cell with an initial efficiency of 12.09% （Voc = 2.03 V, FF = 0.69, Jsc = 8.63 mA/cm^2, area = 1 cm^2） is achieved in our laboratory.

Studies on the polycrystalline silicon/SiO2 stack as front surface field for IBC solar cells by two-dimensional simulations

Interdigitated back contact（IBC） solar cells can achieve a very high efficiency due to its less optical losses. But IBC solar cells demand for high quality passivation of the front surface. In this paper, a polycrystalline silicon/SiO_2 stack structure as front surface field to passivate the front surface of IBC solar cells is proposed. The passivation quality of this structure is investigated by two dimensional simulations. Polycrystalline silicon layer and SiO_2 layer are optimized to get the best passivation quality of the IBC solar cell. Simulation results indicate that the doping level of polycrystalline silicon should be high enough to allow a very thin polycrystalline silicon layer to ensure an effective passivation and small optical losses at the same time. The thickness of SiO_2 should be neither too thin nor too thick, and the optimal thickness is 1.2 nm.Furthermore, the lateral transport properties of electrons are investigated, and the simulation results indicate that a high doping level and conductivity of polycrystalline silicon can improve the lateral transportation of electrons and then the cell performance.

Simulation of embedded heat exchangers of solar aided ground source heat pump system

Aimed at unbalance of soil temperature field of ground source heat pump system, solar aided energy storage system was established. In solar assisted ground-source heat pump (SAGSHP) system with soil storage, solar energy collected in three seasons was stored in the soil by vertical U type soil exchangers. The heat abstracted by the ground-source heat pump and collected by the solar collector was employed to heating. Some of the soil heat exchangers were used to store solar energy in the soil so as to be used in next winter after this heating period; and the others were used to extract cooling energy directly in the soil by circulation pump for air conditioning in summer. After that solar energy began to be stored in the soil and ended before heating period. Three dimensional dynamic numerical simulations were built for soil and soil heat exchanger through finite element method. Simulation was done in different strata month by month. Variation and restoration of soil temperature were studied. Economy and reliability of long term SAGSHP system were revealed. It can be seen that soil temperature is about 3 ℃ higher than the original one after one year's running. It is beneficial for the system to operate for long period.

Optical simulation of CsPbI_(3)/TOPCon tandem solar cells with advanced light management

Monolithic perovskite/Si tandem solar cells(TSCs)have experienced rapid development in recent years,demonstrating its potential to exceed the Shockley-Queisser limit of single junction Si solar cells.Unlike typical organic-inorganic hybrid perovskite/silicon heterojunction TSCs,here we propose CsPbI_(3)/TOPCon TSC,which is a promising architecture in consideration of its pleasurable thermal stability and good compatibility with current PERC production lines.The optical performance of CsPbI_(3)/TOPCon TSCs is simulated by the combination of ray-tracing method and transfer matrix method.The light management of the CsPbI_(3)/TOPCon TSC begins with the optimization of the surface texture on Si subcell,indicating that a bifacial inverted pyramid with a small bottom angle of rear-side enables a further minimization of the optical losses.Current matching between the subcells,as well as the parasitic absorption loss from the front transparent conductive oxide,is analyzed and discussed in detail.Finally,an optimized configuration of CsPbI_(3)/TOPCon TSC with a31.78%power conversion efficiency is proposed.This work provides a practical guidance for approaching high-efficiency perovskite/Si TSCs.

Simulation study of the losses and influences of geminate and bimolecular recombination on the performances of bulk heterojunction organic solar cells

We use the method of device simulation to study the losses and influences of geminate and bimolecular recombinations on the performances and properties of the bulk heterojunction organic solar cells. We find that a fraction of electrons（holes）in the device are collected by anode（cathode）. The direction of the corresponding current is opposite to the direction of photocurrent. And the current density increases with the bias increasing but decreases as bimolecular recombination（BR）or geminate recombination（GR） intensity increases. The maximum power, short circuit current, and fill factor display a stronger dependence on GR than on BR. While the influences of GR and BR on open circuit voltage are about the same.Our studies shed a new light on the loss mechanism and may provide a new way of improving the efficiency of bulk heterojunction organic solar cells.

Research on Reduction of Solar Power Curtailment with Grid Connected Energy Storage System Based on Time-Series Production Simulation

Due to the variable output of renewable energy (RE) generation, difficulties of dispatching RE for power system operators could not be avoided. One of possible solutions is the energy storage technology, especially the battery storage system. The large-scale energy storage system is available to support power system reliable flexibility for load following and system frequency regulation. In this paper, the bottlenecks of large-scale solar power generation dispatching and operation in Qinghai grid are discussed, and a new PV-energy storage coordinated dispatching method is proposed for reduction of PV curtailment in Qinghai. Moreover, the validation based on the time-series production simulation is provided using real data from Qinghai. The results indicate that the proposed method can effectively decrease the curtailment of solar power and future vision of large-scale solar power coordinated operation with energy storage system is also presented.

Numerical Simulation of a P^(+) a-SiC:H/N^(+) Poly-Si Solar Cell with High Efficiency and Fill Factor

The P^(+)a-SiC:H/N^(+)poly-Si solar cell is simulated by an AMPS-1D device simulator to characterize the new thin film polycrystalline-silicon solar cell.In order to analyze the characteristics of the device,the thickness,working temperature,and impurity concentration for the N^(+)polysilicon layer are considered.The results show that the performance of the cells shows little change when the thickness of N^(+)polysilicon varies from 10 to 30μm.It is concluded that the P^(+)a-SiC:H/N^(+)poly-Si solar cell has the highest performance with high open circuit voltages(V_(oc))of 1.31 V,high conversion efficiency of 17.363%and high fill factor of 0.884.Therefore,the P^(+)a-SiC:H/N^(+)poly-Si solar cell has promising future applications.

Simulation design of P–I–N-type all-perovskite solar cells with high efficiency

According to the good charge transporting property of perovskite, we design and simulate a p–i–n-type all-perovskite solar cell by using one-dimensional device simulator. The perovskite charge transporting layers and the perovskite absorber constitute the all-perovskite cell. By modulating the cell parameters, such as layer thickness values, doping concentrations and energy bands of n-, i-, and p-type perovskite layers, the all-perovskite solar cell obtains a high power conversion efficiency of 25.84%. The band matched cell shows appreciably improved performance with widen absorption spectrum and lowered recombination rate, so weobtain a high J_（sc） of 32.47 m A/cm^2. The small series resistance of the all-perovskite solar cell also benefits the high J_（sc）. The simulation provides a novel thought of designing perovskite solar cells with simple producing process, low production cost and high efficient structure to solve the energy problem.

An integrated simulation system for operating solar sail spacecraft

An integrated simulation system for solar sail spacecraft with individually controllable elements(SSICE)is investigated in this paper,including the modelling of power management,thermal control,attitude control,umbra prediction,and orbit prediction subsystems.Considering the self-control and reactivity subsystems,an agent based method is applied to develop the subsystem models.Each subsystem is an individual agent component,which manages itself autonomously and reacts to the requirements from other agents.To reduce computing burden on a specified computer and improve the suitability and flexibility of the integrated simulation system,a distributed framework is employed in the system by deploying agent components on different computers.The data transmission among agents is based on the transmission control protocol/Internet protocol(TCP/IP).A practical example of sun pointing is used to test the operating effect of the integrated system and the working condition of subsystems.The simulation results verify that the integrated system has higher sun pointing accuracy,quicker dynamical response to variations of the lighting,attitude and temperature and fewer computing resources with effective and accurate subsystems.The integrated system proposed in this paper can be applied to solar sail design,operation,and mission planning.

Results in Sizing and Simulation of PV Applications Based on Different Solar Cell Technologies

Modeling and simulation of photovoltaic (PV) systems represents an essential task for the integration of PV panels in current power applications. At the present time, there are sizing tools of photovoltaic systems available on the market, taking into account the proposed energy consumption, site localization and system cost. An advanced specialized program (PVSyst) was considered. The sizing and simulations of two PV important applications were developed using PV modules based on three different technologies: monocrystalline and polycrystalline silicon, as well as CIS. Our results showed how different types of solar cell technologies influenced the final power output and performances for a PV LED lighting, as well as for a PV water pumping system, in terms of overall yield, efficiency and system availability.

Research on Solar Simulation System for Test of Solar Radiation Measuring Instrument

Since traditional solar simulators are mainly applied to spacecraft and photovoltaic industry,they are not suitable for solar radiation measuring instrument test. Therefore,a deep research is carried out on solar simulators to test of solar radiation measuring instrument,so that obtain the requirements of performance test of solar radiation measuring instrument. With a combination of the requirements for national regulations of metrological verification and performance test of pyranometer and pyrheliometer,it lays emphasis on the research of design methods for improving radiation uniformity and stability of solar simulators; it also focuses on design methods of multidimensional detection workbench,which achieves different detection of solar radiation. After practical test,solar irradiation is within Φ60 mm; irradiation non-uniformity is better than ±0.8%; instability is better than ±0.72%;rotating angle precision is better than 0.09°. Then,solar simulator is used to carry out pyranometer sensitivity test,pyranometer directional response test,pyranometer tilt response test and non-linearity test for radiation instruments. Test results showthat the solar simulator meets the testing requirements of solar radiation measuring instruments.

Effect of Valence Band Tail Width on the Open Circuit Voltage of P3HT:PCBM Bulk Heterojunction Solar Cell:AMPS-1D Simulation Study

The effect of the valence band tail width on the open circuit voltage of P3HT：PCBM bulk heterojunction solar cell is investigated by using the AMPS-1D computer program. An effective medium model with exponential valence and conduction band tail states is used to simulate the photovoltaic cell. The simulation result shows that the open circuit voltage depends Iinearly on the logarithm of the generation rate and the slope depends on the width of the valence band tail. The open circuit voltage decreases with the increasing width of the band tail. The dark and light ideality factors increase with the width of the valence band tail.

Numerical Modeling and Simulation of CIGS-Based Solar Cells with ZnS Buffer Layer

Usually a buffer layer of cadmium sulphide is used in high efficiency solar cells based on Cu(In,Ga)Se2(CIGS). Because of cadmium toxicity, many in-vestigations have been conducted to use Cd-free buffer layers. Our work focuses on this type of CIGS-based solar cells where CdS is replaced by a ZnS buffer layer. In this contribution, AFORS-HET software is used to simulate n-ZnO: Al/i-ZnO/n-ZnS/p-CIGS/Mo polycrystalline thin-film solar cell where the key parts are p-CIGS absorber layer and n-ZnS buffer layer. The characteristics of these key parts: thickness and Ga-content of the absorber layer, thickness of the buffer layer and doping concentrations of absorber and buffer layers have been investigated to optimize the conversion efficiency. We find a maximum conversion efficiency of 26% with a short-circuit current of 36.9 mA/cm2, an open circuit voltage of 824 mV, and a fill factor of 85.5%.