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Study of Variable Turbulent Prandtl Number Model for Heat Transfer to Supercritical Fluids in Vertical Tubes

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Journal of Thermal Science 2018年第3期27卷 213-222页

作者： TIAN Ran dai Xiaoye WANG Dabiao shi Lin Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Energy and Power Engineering Tsinghua University Department of Chemical Engineering Tsinghua University

In order to improve the prediction performance of the numerical simulations for heat transfer of supercritical pressure fluids, a variable turbulent Prandtl number(Pr_t) model for vertical upward flow at supercritical pressures was developed in this study. The effects of Pr_t on the numerical simulation were analyzed, especially for the heat transfer deterioration conditions. Based on the analyses, the turbulent Prandtl number was modeled as a function of the turbulent viscosity ratio and molecular Prandtl number. The model was evaluated using experimental heat transfer data of CO_2, water and Freon. The wall temperatures, including the heat transfer deterioration cases, were more accurately predicted by this model than by traditional numerical calculations with a constant Pr_t. By analyzing the predicted results with and without the variable Pr_t model, it was found that the predicted velocity distribution and turbulent mixing characteristics with the variable Pr_t model are quite different from that predicted by a constant Pr_t. When heat transfer deterioration occurs, the radial velocity profile deviates from the log-law profile and the restrained turbulent mixing then leads to the deteriorated heat transfer.

关键词： Turbulent Prandtl Number Supercritical Fluid Heat Transfer

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Improved model for defect detection in photovoltaic cells based on Yolov5

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Optoelectronics Letters 2025年

作者： BAI Xinfeng XUE Yuming dai Hongli WANG Luoxin BAI Xin HU Xiaofeng Institute of New Energy Intelligence Equipment， School of Integrated Circuit Science and Engineering， Tianjin University of Technology

In order to meet the requirements of recognition speed and accuracy for complex photovoltaic (PV) cell defect detection tasks， this paper proposed an improvement strategy based on the Yolov5 network model. First， the model's ability to localize defects was enhanced by adding shallow feature inputs to strengthen the model's fusion of shallow feature information; second， the Squeeze-and-excitation (SE) attention mechanism was introduced to expand the receptive field and strengthen the dependency between feature channels; finally， a smoothing downsampling module was constructed to replace the convolutional sampling， which reduced the loss of information while retaining the important features. The experimental results show that the Yolov5 model based on this improved strategy achieved an average accuracy of 92.06% in the multiclassification defect detection task， and the average recognition speed reached 25.31 frames per second (FPS)， which took into account the requirements of performance and real-time performance， and can satisfy the needs of PV cell defect detection in industrial scenarios.

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The effects of selenization conditions on the microstructure and optoelectronic properties of CZTSSe absorber layers prepared by the sol-gel method

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Optoelectronics Letters 2025年

作者： BAI Xin XUE Yuming dai Hongli WANG Luoxin BAI Xinfeng HU Xiaofeng Institute of New Energy Intelligence Equipment， School of Integrated Circuit Science and Engineering， Tianjin University of Technology

Cu2ZnSnSSe4（CZTSSe） thin film solar cells， with adjustable bandgap and rich elemental content， hold promise in next-gen photovoltaics. Crystalline quality is pivotal for efficient light absorption and carrier transport. During the post-selenization process， understanding crystal growth mechanisms， and improving layer quality are essential. We explored the effects of ramp rate and annealing temperature on CZTSSe films， using XRD， Raman， SEM， and UV-Vis. The optimal performance occurred at 25.25 ℃/min ramp rate and 530℃ annealing. This led to smoother surfaces， higher density， and larger grains. This condition produced a single-layer structure with large grains， no secondary phases， and a 1.14 eV bandgap， making it promising for photovoltaic applications. The study has highlighted the effect of selenization conditions on the characteristics of the CZTSSe absorber layer and has provided valuable information for developing CZTSSe thin film solar cells.

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A Detection-Switching-Assisted DCF Mechanism for Simulcast WLAN-over-Fiber Based Distributed Antenna Systems

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Chinese Journal of Electronics 2017年第4期26卷 837-841页

作者： fan Yuting LI Jianqiang XU Kun dai Yitang State Key Laboratory of Information Photonics and Optical Communications Beijing University of Posts and Telecommunications

Distributed antenna systems(DASs) using Radio-over-fiber(Ro F) links is a promising candidate to provide flexible coverage and high data rates. For simulcast Wireless local-area network(WLAN) use in Ro F systems, the stations covered by different Remote antenna units(RAUs) contend for the wireless medium using Media access control(MAC) mechanism. Severe inter-RAU hidden nodes problem will happen due to the stations in different RAUs cannot detect each other very well. In order to alleviate this inter-RAU collision problem, a promising detection-switching-assisted Distributed coordination function(DCF) mechanism is presented using in the uplink. The control delay issues of the proposed mechanism are also discussed in this paper.

关键词： Radio-over-fiber(RoF) Distributed an tenna system IEEE 802.11.Detection-switch mechanism

Enhancing the performance of the absorber of Cu2ZnSn（S， Se）4 photovoltaic materials by doping Cd2+

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Optoelectronics Letters 2025年

作者： YANG Shuqi XUE Yuming dai Hongli WANG Luoxin ZHANG Haiwei BAI Xin Institute of New Energy Intelligence Equipment， School of Integrated Circuit Science and Engineering， Tianjin University of Technology

Cationic doping is considered to be an effective way to improve the efficiency of Cu2ZnSn（S，Se）4（CZTSSe） photovoltaic materials. To improve the quality of the absorption layer of the crystal film， CZTSSe film was doped with some Cd to change the ratio of Cd and Zn in the precursor solution. XRD， Raman， SEM， UV-Vis spectroscopy， and other results showed that Cd successfully replaced Zn in the crystal lattice during post-selenization. The formation of harmful Zn-related defects was reduced， the grain size and crystallinity of the films were significantly increased， and the photoelectric properties of the films such as crystal quality and structural morphology were improved. As the Cd/（Cd+Zn） ratio increased from 0 to 0.35， the band gap of CZCTSSe decreased to 1.02eV. When Cd/（Cd+Zn）=0.25， the crystallinity and grain size reached the best value， and the film surface was smooth and dense， which inhibited the formation of the second phase on the surface of *** theoretical basis and experimental results showed that proper Cd doping can promote the growth of grain， so that compact CZCTSSe films with larger grain sizes and fewer holes could be prepared.

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Influence of band gap and different defects on the performance of Cu（In， Ga）Se2 solar cells

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Optoelectronics Letters 2025年

作者： LU Yahan XUE Yuming dai Hongli WANG Luoxin LI Weiwei JI Licui Institute of New Energy Intelligence Equipment， School of Integrated Circuit Science and Engineering， Tianjin University of Technology

The SCAPS-1D simulator， a one-dimensional solar cell capacitance simulator is utilized for simulating CIGS solar cells. It has been observed that the performance of solar cells can be enhanced by uniformly adjusting the band gap value of the CIGS absorption layer. Upon doing so， the solar cell's conversion efficiency reaches 22.13% when the band gap of the CIGS absorption layer is 1.3eV. Subsequently， the influence of defect type and density on photoelectric properties is analyzed by using the improved absorption band gap. The findings indicate that to heighten the photovoltaic efficiency， it is imperative to minimize the defect concentration in the absorption layer， as high-density defects significantly impact the efficiency， and can even render the conversion efficiency to zero. This study underscores the pivotal influence of band gap adjustments and defect charge types on the photoelectric properties of thin film solar cells.

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Optimization of CZTSSe thin film solar cell performance using PbS back surface field layer

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Optoelectronics Letters 2025年

作者： WENJING LUO ZHIJIAN BAI YUMING XUE LUOXIN WANG YANHONG DING HONGLI dai Tianjin Key Laboratory of Film Electronic & Communication Devices， School of Electronics Information Engineering， Tianjin University of Technology School of Materials Science and Engineering ，Jilin University

CZTSSe is an Earth-abundant， environmentally friendly， and low-cost material， with a current record power conversion efficiency of 14.9%， This result is well below the prediction of the Shockley-Queisser limit. To improve the performance of solar cells， a layer of PbS (BSF) was added to the CZTSSe， which was simulated using the SCAPS-1D software. The optimal photovoltaic performance of AZO/ZnO/CdS/CZTSSe/PbS/Mo was studied by changing the parameters of the CZTSSe absorption layer and PbS layer. Studies have shown that the efficiency can be increased to 20.86% after using PbS.

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Effect of ammonia concentration of complexing agent on CdxZn1-xS buffer layer by chemical bath deposition and performance of CIGS cell

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Optoelectronics Letters 2025年

作者： LU Yahan XUE Yuming dai Hongli WANG Luoxin ZHOU Liwei TAN Zhiyuan Institute of New Energy Intelligence Equipment， School of Integrated Circuit Science and Engineering， Tianjin University of Technology

In this paper， CdxZn1-xS thin films were deposited on glass substrates by chemical bath deposition （CBD），and the effects of different concentrations of ammonia water on the morphology， structure and optical properties of the films were studied. CdxZn1-xS thin films have hexagonal crystal structure， the transmittance is above 75% in the visible range， and the optical band gap is between 2.6 eV and 2.9 eV. The influence of the experimental group of deposited thin films on the performance parameters of the CIGS battery was studied by simulation with SCAPS-1D software and the cell efficiency reached 22.42%. It is introduced that the buffer layer prepared in this experiment is feasible in CIGS solar cells.

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Phosphorus-doping-tuned PtNi concave nanocubes with high-index facets for enhanced methanol oxidation reaction

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Nano Research 2022年第8期15卷 6961-6968页

作者： Aixin fan Congli Qin Ruxia Zhao Haixiao Sun Hui Sun Xiaoping dai Jin-Yu Ye shi-Gang Sun Yanhong Lu Xin Zhang School of Chemistry&Material Science Langfang Normal UniversityLangfang 065000China ShanDong Drug and Food Vacational Colleage Weihai 255000China State Key Laboratory of Heavy Oil Processing College of Chemical EngineeringChina University of PetroleumBeijing 102249China State Key Laboratory of Physical Chemistry of Solid Surfaces Department of ChemistryCollege of Chemistry and Chemical EngineeringXiamen UniversityXiamen 361005China

Surface engineering has been found to be an efficient strategy to boost the catalytic performance of noble-metal-based *** this work,a small amount of P was doped to the surface of PtNi concave cube(P-PtNi CNC).Interestingly,the P-PtNi CNC nanocatalyst shows an enhanced methanol oxidation reaction(MOR)performance with achieving 8.19 times of specific activity than that of comercial Pt/*** electrochemical in situ Fourier transform infrared spectroscopy(FTIR)results reveal that the surface P doping promotes the adsorption energy of OH,enhancing the resistance against CO ***,the intermediate adsorbed CO(COads)reacted with adsorbed OH(OHads)through the Langmuir–Hinshelwood(LH)mechanism to generate CO_(2)and release surface active sites for further *** work provides a promising strategy via the incorporation of non-metallic elements into the PtNi alloys bounded with high-index facets(HIFs)as efficient fuel cell catalysts.

关键词： P doping high-index facets methanol oxidation reaction in situ Fourier transform infrared spectroscopy