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Statistical uncertainty quantification to augment CDI electrode design and operation optimization

CHEMICAL engineering JOURNAL 2023年第1期469卷

作者： Mao, Yunfeng Long, Shunnan Kuai, Xingyu Xu, Longqian Zhang, Hua Wu, Weidong Wu, Deli Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Tongji Univ Coll Environm Sci & Engn State Key Lab Pollut Control & Resources Reuse Shanghai 200092 Peoples R China Shanghai Inst Pollut Control & Ecol Secur Shanghai 200092 Peoples R China

Capacitive deionization (CDI) is considered to be one of the most promising technologies to deionize water with low/medium concentration. Great attention has been paid to improve its performance by optimizing electrode architectures and operation conditions. However, no guidelines are built for developing such strategies due to the nonlinear impact of the parameters concerning electrodes and operations. Therefore, our work quantitatively reveals the influence of some key parameters involving electrode characteristics, operation conditions and ion properties using the statistical analysis based on uncertainty quantification. We find the porosity solely has a small influence on all the performance metrics. But the pore might play a significant role by the pore size distribution and connectivity that greatly determine the effective diffusion coefficient of salt ions. The high diffusion coefficient obviously raises the salt adsorption by facilitating ion transport, which also reduces the energy consumption while most of the consumed energy could even be recovered. The current exerts an opposite influence by shortening the charging period in the constant current (CC) mode. The salt concentration in the inflow water increases the adsorption capacity but decreases the removal efficiency. The decreased removal efficiency requires less external energy, enabling the usage of CDI as an economic pre-treatment unit. We highlight the ion transport resistance and its influence on CDI performance by acting upon charging time in the CC mode. We also suggest the application of the constant voltage mode to the low-salinity wastewater instead of the CC mode due to the high resistance. Our work addressed the importance of proper electrode and operation condition for high desalination performance and energy efficiency.

关键词： Capacitive deionization CDI electrode Energy efficiency Uncertainty quantification Mass transfer model

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Performance Prediction and Geometry Optimization of Ejector in Pemfc System Using Coupled Cfd-Bpnn and Genetic Algorithm

SSRN

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SSRN 2024年

作者： Pang, Zihui Han, Jiquan Feng, Jianmei Diao, Anna Yao, Yanchen Peng, Xueyuan School of Energy and Power Engineering Xi’an Jiaotong University Shaanxi Xi’an710049 China Shanghai Marine Diesel Engine Research Institute Shanghai Shanghai201108 China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Shaanxi Xi’an710049 China

The ejector is a promising hydrogen recirculation device in proton exchange membrane fuel cell (PEMFC) systems. However, the limited entrainment performance of the ejector at wide operating conditions hinders its development and widespread application in PEMFC systems. To address this challenge and design a high-performance ejector adapted to the wide power range of PEMFC systems, a backpropagation artificial neural network (BPNN) model with computational fluid dynamics (CFD) simulation data is developed. The sensitivity analysis of geometric parameters based on the CFD model reveals that the nozzle throat diameter (Dt) and the mixing chamber diameter (Dm) exert the most pronounced impact on the entrainment performance, with average influence rates of 24% and 57%, respectively. Furthermore, two advanced multi-objective genetic algorithms (LWGA and NSGA-II methods) are applied to improve ejector performance. The LWGA method proves effective in elevating the overall ejector performance, achieving a remarkable enhancement in entrainment performance of up to 7.9%. On the other hand, the NSGA-II method is favorable for expanding the operational power range of the ejector by 30%, as well as a 4.5% increase in overall ejector performance. This work provides a robust framework for designing and optimizing high-performance ejectors in high power PEMFC systems. © 2024, The Authors. All rights reserved.

关键词： Sensitivity analysis

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Experimental investigation on flow boiling instability of R1233zd(E) in a parallel mini-channel heat sink for the application of battery thermal management

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INTERNATIONAL JOURNAL OF heat AND MASS transfer 2022年 188卷 122585-122585页

作者： Xu, Dan Fang, Yidong Zhang, Zhao Wang, Yuchen Huang, Yuqi Su, Lin Univ Shanghai Sci & Technol Coll Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China Zhejiang Univ Coll Energy Engn Hangzhou 310058 Peoples R China

The present study focused on the flow boiling instability of R1233zd(E) in a 21 parallel mini-channel heat sink designed for the application on battery thermal management. Experiments were conducted under different conditions, including inlet subcoolings (2.5-8 K), mass fluxes (111-276 kg/m(2) s), and heat fluxes (up to 12 W/cm(2)). A high speed camera with the frequency of 2000 fps was used to capture the unstable flow pattern. The results showed that the period and the initial position of reverse flow were shortened with the increase of heat flux, meanwhile four typical reverse flow patterns in the parallel channel were captured. The Parallel Channel Instability (PCI) featured by large inlet pressure oscillation was suppressed when the inlet subcooling was increased, while mass flux had limited influence on the suppression of PCI. The standard deviation of inlet pressure Sigma(p(in)) was increased obviously under the inlet subcooling of 5 K. Beside, faster elevation of Sigma(p(in)) was observed under 111 kg/m(2) s when the heat flux was higher than 3.8 W/cm(2). Finally, the flow instability maps were established based on heat flux, mass flux and dimensionless parameters of subcooling number Nsub and phase change number Npch. The stable, transition and instability regions were divided on the maps based on the operating conditions and the flow patterns captured during the experiment. (c) 2022 Elsevier Ltd. All rights reserved.

关键词： flow boiling instability Parallel mini channel flow pattern Reverse flow Pressure oscillation

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Experimental study on low temperature heating performance of different vapor injection heat pump systems equipped with a flash tank and economizers for electric vehicle

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APPLIED THERMAL engineering 2023年第1期227卷

作者： Li, Kang Ma, Jingru Zhang, Bin Su, Lin Liu, Ni Zhang, Hua Dou, Binlin He, Qize Zhou, Xuejin Tu, Ran Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Univ Shanghai Sci & Technol Key Lab Multiphase Flow & Heat Transfer Shanghai P Shanghai 200093 Peoples R China Huaqiao Univ Coll Mech Engn & Automat Xiamen 361021 Fujian Peoples R China Shanghai Fire Res Inst MEM Shanghai 200032 Peoples R China

One of the most promising solutions is applying vapor injection technology to improve the heating performance of air conditioning heat pump systems in electric vehicles operating at extremely low temperatures. This study examined the effects of employing flash tank vapor injection (FVI) and economizer vapor injection (EVI) with both upstream injection (UI) path and downstream injection (DI) path configurations on a vapor injection heat pump system with a small ratio vapor injection scroll compressor. Experiments were conducted to record the system performance at low temperatures, and typical heat transfer characteristics were obtained with different expansion valve opening degrees and compressor speeds. The influence of the injection pressure on the system performance was also investigated, and the optimal injection pressure was determined. The results for the up-stream injection, downstream injection and flash tank vapor injection systems indicated maximum increases in the system's heating capacity of 19.7 %, 22.6 %, and 92.3 %, and in its coefficient of performance (COP) of 24.2 %, 16.9 %, and 118 %, respectively;the corresponding discharge temperatures decreased by 12.4 degrees C, 18.99 degrees C, and 16.95 degrees C, respectively. In addition, the optimal injection pressure was determined according to the maximum value of COP, and the optimal injection pressure range for the system is 0.16-0.37 MPa. Hence, a vapor injection system using an economizer with a downstream path could achieve better heating performance at relatively low temperatures. In contrast, a flash tank would offer some heating capacity advantages at temperatures below-15 degrees C.

关键词： Vapor injection Electric vehicle Flash tank Economizer Upstream and downstream injection

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Performance Analysis of Sco2 Tube with High Non-Uniform heat Flux: Thermal-Fluid-Structural Evaluation and Optimization

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SSRN 2023年

作者： Gao, Shuo Wang, Yanjuan Li, Yi Liu, Qibin Xu, Jinliang The Beijing Key Laboratory of Multiphase Flow and Heat Transfer North China Electric Power University Beijing102206 China Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing100190 China University of Chinese Academy of Sciences Beijing100190 China

Supercritical carbon dioxide (sCO2) has been a promising alternative working medium in coal-fired power plants, high-temperature solar power systems, and fuel cells. In these cases, sCO2 is in a round tube under high temperature and pressure with high non-uniform heat flux (NUH). In this study, a novel structure tube is proposed to match high NUH with thermal resistance by changing tube eccentricity. A three-dimensional (3D) multiphysical coupling model was constructed to compare the novel structure with a conventional tube. The properties of fluid dynamics, thermal stress, and coupled heat transfer were analyzed. The key working parameters were discussed. The maximum temperature of the novel structure was reduced by 13–36 K, and the maximum thermal stress was reduced by approximately 25–33% under all the simulated working conditions when the eccentricity changed from 0 to 0.4. The proposed structure can reduce the maximum temperature and thermal stress effectively under high NUH. Consequently, a novel insight is presented for the design and optimization of sCO2 tube under high NUH. © 2023, The Authors. All rights reserved.

关键词： heat transfer

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Optimal Control Strategies for Demand Response in Buildings under Penetration of Renewable Energy

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BUILDINGS 2022年第3期12卷 371页

作者： Chen, Yongbao Chen, Zhe Yuan, Xiaolei Su, Lin Li, Kang Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China Tongji Univ Sch Mech & Energy Engn Shanghai 201804 Peoples R China

The penetration rates of intermittent renewable energies such as wind and solar energy have been increasing in power grids, often leading to a massive peak-to-valley difference in the net load demand, known as a "duck curve". The power demand and supply should remain balanced in real-time, however, traditional power plants generally cannot output a large range of variable loads to balance the demand and supply, resulting in the overgeneration of solar and wind energy in the grid. Meanwhile, the power generation hours of the plant are forced to be curtailed, leading to a decrease in energy efficiency. Building demand response (DR) is considered as a promising technology for the collaborative control of energy supply and demand. Conventionally, building control approaches usually consider the minimization of total energy consumption as the optimization objective function;relatively few control methods have considered the balance of energy supply and demand under high renewable energy penetration. Thus, this paper proposes an innovative DR control approach that considers the energy flexibility of buildings. First, based on an energy flexibility quantification framework, the energy flexibility capacity of a typical office building is quantified;second, according to energy flexibility and a predictive net load demand curve of the grid, two DR control strategies are designed: rule-based and prediction-based DR control strategies. These two proposed control strategies are validated based on scenarios of heating, ventilation, and air conditioning (HVAC) systems with and without an energy storage tank. The results show that 24-55% of the building's total load can be shifted from the peak load time to the valley load time, and that the duration is over 2 h, owing to the utilization of energy flexibility and the implementation of the proposed DR controls. The findings of this work are beneficial for smoothing the net load demand curve of a grid and improving the ability of a g

关键词： building energy conservation energy flexibility demand response grid-integrated buildings supply-demand coordinated control

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A New Structure Tube for Supercritical Co 2 Turbulent flow with High Non-Uniform heat Flux

SSRN

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SSRN 2023年

作者： Wang, Yanjuan Gao, Shuo Shi, Weijie Liu, Qibin Xu, Jinliang The Beijing Key Laboratory of Multiphase Flow and Heat Transfer North China Electric Power University Beijing102206 China Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing100190 China University of Chinese Academy of Sciences Beijing100190 China

Supercritical carbon dioxide (sCO2) has been a promising alternative working medium in coal-fired power plants, high-temperature solar power systems, and fuel cells. In these cases, sCO2 is in a round tube under high temperature and pressure with high non-uniform heat flux (NUH). In this study, a novel structure tube is proposed to match high NUH with thermal resistance by changing tube eccentricity. A three-dimensional (3D) multiphysical coupling model was constructed. The novel structure can reduce Tmax and T effectively for the half-cycle uniform heat flux (HUH) and NUH cases. The maximum thermal stress decreased by 23 and 29% and Tmax decreased by 29.6 K and 24.8 K for HUH and NUH cases when Ec increased from 0 to 0.4. A comparison was made between the proposed structure, thin-walled tube, and traditional tube. Results showed that the performance of the proposed tube is the best. Tmax decreases by approximately 55 K compared with the traditional and thin-walled tubes. σeq,max of the eccentric tube is the smallest. Furthermore, the structure will facilitate the safety and economics of the tube. Consequently, a novel insight is presented for the design and optimization of sCO2 tube under high NUH. © 2023, The Authors. All rights reserved.

关键词： heat transfer

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Experimental study on optimal heating cycle characteristics of CO2 secondary throttling heat pump system for electric vehicles

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ENERGY CONVERSION AND MANAGEMENT 2023年第1期295卷

作者： Wang, Fengxian Wu, Weidong Huang, Yichen Zhang, Hua Yu, Qiangyuan Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Shanghai MAHLE Thermal Syst Co Ltd Shanghai 201206 Peoples R China Univ Shanghai Sci & Technol Inst Refrigerat & Cryogen Engn 516 Jungong Rd Shanghai 200093 Peoples R China

As HFC refrigerants widely employed in electric vehicle heat pump systems face stringent restrictions due to environmental concerns, CO2 has attracted significant attention as a highly promising alternative refrigerant. This paper presents a novel CO2 heat pump air conditioning system with a single-stage compression secondary throttling series gas cooler for electric vehicles. The heating cycle characteristics of the system at the maximum coefficient of performance (COP) are investigated for different combinations of dual electronic expansion valves (EEV 1 and EEV 2) openings, ambient temperature, indoor air volume, and compressor speed. Additionally, the relationship between the intermediate pressure and the discharge pressure is discussed. The results indicate that utilizing dual EEVs allows for graded regulation of system pressure, enabling effective control of the compression ratio, and achieving the objectives of reducing the system energy consumption and improving the performance. When the system achieves its maximum COP, a certain proportional relationship exists between the intermediate pressure and discharge pressure, and this proportionality is almost independent of factors such as ambient temperature, indoor air volume, and compressor speed. The outlet refrigerant temperature of the indoor gas cooler (IGC) exhibits a negative correlation with the COP. For each 1 degrees C reduction in the temperature difference between the outlet refrigerant of the IGC and the ambient air, there is an average increase of 4% in the COP. Based on the experimental data, a linear correlation between the optimal intermediate pressure and discharge pressure is established with a high degree of confidence. Additionally, a corresponding control logic is proposed and validated. The results can provide guidance for enhancing performance and developing control strategies for CO2 heat pump systems in electric vehicles.

关键词： CO 2 heat pump Secondary throttling Series gas cooler Control strategy Electric vehicles

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Development of a loop heat pipe with the 3D printed stainless steel wick in the application of thermal management

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INTERNATIONAL JOURNAL OF heat AND MASS transfer 2020年 161卷 120258-120258页

作者： Hu, Zhuohuan Wang, Dongcheng Xu, Jiayin Zhang, Li Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China East China Univ Sci & Technol Sch Mech & Power Engn Shanghai 200237 Peoples R China

The 3D printed wicks, whose structural parameters could be controlled by changing the distance between neighboring structural cylinders, were manufactured to experimentally investigate the effect of pore size (d) on the heat performance of the loop heat pipe (LHP). With the help of the 3D printing technique, the order 3D printed wicks with all pores interconnected were fabricated to avoid high randomness and appearance of closed pores in the traditional sintered wicks. In addition, high porosity, suitable pore radius, low effective thermal conductivity and high permeability were also realized in the same wick. A flat LHP with a transparent evaporator and vapor line was fabricated to observe the flow motion in the evaporator and the vapor line. It was indicated that the LHP with a 3D printed wick (d = 200 mu m) made of stainless steel could start successfully in about 100 s at a low heat load of 20 W (2.83 W/cm(2)). And a stable operation in a wide heat load range from 20 W to 160 W (22.63 W/cm(2)) was achieved with the allowable evaporator wall temperature of 100 degrees C. The minimum evaporator thermal resistance of the 3D printed wick was 0.031 K/W at a heat load of 140 W with a corresponding maximum heat transfer coefficient of 44,379 W/m(2)K. The minimum LHP thermal resistance was 0.181 K/W at a heat load of 160 W. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： 3D printed Wick Loop heat pipe heat leak Temperature oscillation

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Upgrading the wood vinegar prepared from the pyrolysis of biomass wastes by hydrothermal pretreatment

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ENERGY 2022年第PartA期244卷 122631-122631页

作者： Xu, Jiaqing Zhang, Shouyu Shi, Yue Zhang, Peizheng Huang, Dongdong Lin, Chunyu Wu, Yuxin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China Tsinghua Univ Dept Thermal Engn Beijing 100084 Peoples R China

Hydrothermal pretreatment (HT) is an effective method to upgrade biochar pellets, while little attention is paid to wood vinegar (WV), the byproduct of biochar pellets production. Therefore, Chinese fir sawdust (FS) and cotton stalk (CS) were hydrothermally pretreated first at 180e280 degrees C and then pyrolyzed at 350 degrees C in the study. The effect of hydrothermal pretreatment on the properties of biomass was evaluated by the Van Soest method and thermogravimetric method. The yield, pH, density, and composition of WV were analyzed. The results showed that hemicellulose and cellulose were completely decomposed at HT temperatures of 230 degrees C and 280 degrees C respectively. The removal of hemicellulose and the enrichment of cellulose and lignin in the samples pretreated before 230 degrees C result in a higher density and lower pH of WV, while the yield only increases before 200 degrees C. Compared with CS samples, the higher content and reactivity of cellulose, especially amorphous cellulose, and lignin in FS samples results in the higher yield of the organic compounds in FSWV. With HT temperature increasing to 230 degrees C, the content and yield of acids in FSWV/CSWV shows a declining trend, and the content and yield of phenols, ketones, and aldehydes increase. HT pretreatment below 230 degrees C can upgrade WV. (C)& nbsp;2021 Elsevier Ltd. All rights reserved.

关键词： Biomass wastes Hydrothermal pretreatment Pyrolysis Wood vinegar Chemical components

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