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Conduction-convection coupled heat transfer around a hollow cylinder under different buoyancy forces

Chinese Journal of Aeronautics 2024年第4期37卷 216-228页

作者： Wanyu ZHANG Jingyi WU Guang YANG institute of refrigeration and cryogenics Shanghai Jiao Tong UniversityShanghai 200240China

In order to clarify the effect of a buoyancy force on conduction–convection coupled heat transfer in a hollow cylinder, the flow and thermal characteristics were analyzed using an RNG k-ε turbulence model. The Reynolds number was fixed at 1.014 × 10^(6), and the Rayleigh number varied from 1.122 × 10^(10)to 1.088 × 10^(11). Results have shown that, when considering the effect of an opposed buoyancy force, increasing the Rayleigh number has a positive impact on the rate of change and uniformity of the cylinder temperature. The temperature distributions along the axial and circumferential directions are similar for different Rayleigh numbers, but extreme values *** the axial direction, the maximum temperature is obtained at the interface between the variable-diameter part and the constant-diameter part. The maximum dimensionless temperature value decreases to 0.12 when the Rayleigh number increases to 1.088 × 10^(11). Along the circumferential direction, the temperature distribution is affected by the buoyancy force, which results in the temperature of the upper part being higher than that of the lower part. After nondimensionalization of the temperature and time, a correlation was proposed to illustrate the transient heat transfer process quantitatively. The standard deviation of the maximum relative temperature, representing the temperature uniformity, was also calculated. It was found that the difference in the direction of the buoyancy force made a huge difference. Compared with the opposed buoyancy force, the maximum dimensionless temperature is almost two times higher with an assisted buoyancy force. Similarly, the heat transfer coefficient with an assisted buoyancy force is half of that with an opposed buoyancy force. Overall, an assisted buoyancy force plays a negative role in terms of thermal characteristics. The flow field around the hollow cylinder was also illustrated to reveal the mechanism of the buoyancy force on magnitude and direction aspects

关键词： Buoyancy Conduction-convection heat transfer Transient analysis Hollow cylinder Non-dimensionalization

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A New Excess Free Energy Mixing Rule for Representing Vapor-Liquid Equilibria of Mixed Refrigerants

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Journal of Thermal Science 2024年第3期33卷 1161-1173页

作者： YE Gongran FANG Yibo YAN Yuhao LIU Ying OUYANG Hongsheng GUO Zhikai HAN Xiaohong Key Laboratory of refrigeration and Cryogenic Technology of zhejiang Province Institute of Refrigeration and CryogenicsZhejiang UniversityHangzhou310027China State Key Lab for Fluorine Greenhouse Gases Replacement and Control Treatment Zhejiang Research Institute of Chemical IndustryHangzhou310014China zhejiang Key Laboratory of Clean Energy and Carbon Neutrality Zhejiang UniversityHangzhou310027China

A suitable mixing rule is important for vapor liquid equilibrium(VLE)investigations for mixed *** this work,a new excess free energy mixing rule(MRv)was proposed at zero pressure based on the linear relationship between dimensionless parameter 1/(u-1)and *** mixing rule was explicit adopted variable liquid molar *** applicable temperature range of MRv could be extended by means of an empirical method to estimate the liquid molar volume for components at high *** mixing rules modified Huron-Vidal mixing rule(MHV1),Wong-Sandler mixing rule(WS),and MRv at two reference pressures were used to compare the VLE data in the calculation of 37 mixed *** demonstrated that MRv had a relatively similar accuracy to MHV1 and WS for component and pressure ***,the average excess Gibbs free energy using the MRv mixing rule for the 37 selected mixed refrigerants(0.0013)was much lower than those using the MHV1(0.0078)and WS(0.0809)mixing rules,which was very valuable for the design and optimization of thermodynamic systems using mixed refrigerants.

关键词： mixed refrigerant vapor liquid equilibrium(VLE) mixing rule reproducibility

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Flow Boiling Heat Transfer Characteristics and Delayed Dry-Out Ability of Non-Azeotropic Mixtures R245fa/R134a in Microchannels

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Journal of Thermal Science 2024年第3期33卷 1174-1188页

作者： LU Yongjie LING Yongjun ZHUANG Yuan LI Chenyang OUYANG Hongsheng HAN Xiaohong Key Laboratory of refrigeration and Cryogenic Technology of zhejiang Province Institute of Refrigeration and CryogenicsZhejiang UniversityHangzhou310007China zhejiang Zhongguang Electrical Co. Ltd.Lishui323000China State Key Lab for Fluorine Greenhouse Gases Replacement and Control Treatment Zhejiang Research Institute of Chemical IndustryHangzhou310014China

Microchannel flow boiling heat transfer has the advantages of strong heat dissipation capacity,good temperature uniformity,and compact *** is an excellent way to thermally manage electronic devices,but when the heat flux exceeds CHF(Critical Heat Flux),the heat transfer performance deteriorates as the working fluid dries ***-azeotropic mixtures have the potential to effectively delay or avoid dry-out during the boiling process due to their temperature slide characteristics which causes the mass transfer *** understand the influence of non-azeotropic mixtures on microchannel flow boiling,using the phase-change microchannel heat sink as the research object,the experiments on the flow boiling heat transfer performance of R245fa/R134a mixtures under different working conditions were carried out,and the characteristics of flow boiling heat transfer were obtained under the different working conditions,and comparison was developed with those of pure substance *** results demonstrated that a small amount of low-boiling-point components in the high-boiling-point working fluid inhibited boiling heat transfer to some extent,and lowered the average heat transfer coefficient under the non-dryout condition slightly lower than that of the pure substance;however,it also effectively delayed the onset of local dry-out and prevented significant deterioration in thermal transfer performance under the lower mass flow rate and higher heat flux,which could enhance the heat sink's stability.

关键词： microchannel flow boiling non-azeotropic mixture heat transfer characteristics dry-out

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Generative pre-trained transformers(GPT)-based automated data mining for building energy management:Advantages,limitations and the future

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Energy and Built Environment 2024年第1期5卷 143-169页

作者： Chaobo Zhang Jie Lu Yang Zhao institute of refrigeration and cryogenics Zhejiang UniversityHangzhouChina Department of the Built Environment Eindhoven University of TechnologyEindhovenThe Netherlands Key Laboratory of Clean Energy and Carbon Neutrality of zhejiang Province Jiaxing Research InstituteZhejiang UniversityJiaxingChina

Advanced data mining methods have shown a promising capacity in building energy ***,in the past decade,such methods are rarely applied in practice,since they highly rely on users to customize solutions according to the characteristics of target building energy ***,the major barrier is that the practical applications of such methods remain *** is necessary to enable computers to have the human-like ability to solve data mining *** pre-trained transformers(GPT)might be capable of addressing this issue,as some GPT models such as GPT-3.5 and GPT-4 have shown powerful abilities on interaction with humans,code generation,and inference with common sense and domain *** study explores the potential of the most advanced GPT model(GPT-4)in three data mining scenarios of building energy management,i.e.,energy load prediction,fault diagnosis,and anomaly detection.A performance evaluation framework is proposed to verify the capabilities of GPT-4 on generating energy load prediction codes,diagnosing device faults,and detecting abnormal system operation *** is demonstrated that GPT-4 can automatically solve most of the data mining tasks in this domain,which overcomes the barrier of practical applications of data mining methods in this *** the exploration of GPT-4,its advantages and limitations are also discussed comprehensively for revealing future research directions in this domain.

关键词： ChatGPT GPT-4 Artificial general intelligence Data mining Building energy management

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End-to-end data-driven modeling framework for automated and trustworthy short-term building energy load forecasting

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Building Simulation 2024年第8期17卷 1419-1437页

作者： Chaobo Zhang Jie Lu Jiahua Huang Yang Zhao Department of the Built Environment Eindhoven University of TechnologyEindhovenThe Netherlands Energy Efficient Cities Initiative Department of EngineeringUniversity of CambridgeCambridgeUK institute of refrigeration and cryogenics Zhejiang UniversityHangzhouChina institute of Green Building and Engineering Design Zhejiang Province Institute of Architectural Design and Research Co.Ltd.HangzhouChina Key Laboratory of Clean Energy and Carbon Neutrality of zhejiang Province Jiaxing Research InstituteZhejiang UniversityJiaxingChina

Conventional automated machine learning(AutoML)technologies fall short in preprocessing low-quality raw data and adapting to varying indoor and outdoor environments,leading to accuracy reduction in forecasting short-term building energy ***,their predictions are not transparent because of their black box ***,the building field currently lacks an AutoML framework capable of data quality enhancement,environment self-adaptation,and model *** address this research gap,an improved AutoML-based end-to-end data-driven modeling framework is *** optimization is applied by this framework to find an optimal data preprocessing process for quality improvement of raw *** bridges the gap where conventional AutoML technologies cannot automatically handle missing data and outliers.A sliding window-based model retraining strategy is utilized to achieve environment self-adaptation,contributing to the accuracy enhancement of AutoML ***,a local interpretable model-agnostic explanations-based approach is developed to interpret predictions made by the improved *** overcomes the poor interpretability of conventional AutoML *** performance of the improved framework in forecasting one-hour ahead cooling loads is evaluated using two-year operational data from a real *** is discovered that the accuracy of the improved framework increases by 4.24%–8.79%compared with four conventional frameworks for buildings with not only high-quality but also low-quality operational ***,it is demonstrated that the developed model interpretation approach can effectively explain the predictions of the improved *** improved framework offers a novel perspective on creating accurate and reliable AutoML frameworks tailored to building energy load prediction tasks and other similar tasks.

关键词： building energy load forecasting end-to-end data-driven modeling automated machine learning Bayesian optimization model retraining model interpretation

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一种基于“最优捕集窗口”设计的全球化空气取水系统

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Science Bulletin 2024年第10期69卷 1437-1447页

作者：李乾邵昭邹启宏潘权稳赵曜冯耀辉王雯雯王如竹葛天舒 institute of refrigeration and cryogenics Shanghai Jiao Tong UniversityShanghai 200240China

Atmospheric water harvesting(AWH)is a promising solution to the water shortage *** sorption-based AWH(SAWH)systems seldom obtain both wide climatic adaptability and high energy efficiency due to the lack of thermodynamic *** achieve the ideal harvesting circulation in SAWH systems,the“optimal harvesting window”(OHW)design based on thermodynamic analysis was first proposed and validated by our ***“OHW”theory indicates the water production rate and energy efficiency could be improved by properly reducing the adsorption *** the humidity increases,the optimal adsorption temperature should be closer to the dew point of the *** results revealed that,loaded with 3 kg widely adopted silica gel,the daily water production could reach 5.76-17.64 L/d with ultrahigh energy efficiency of 0.46-1.5 L/*** prototype could also achieve optimal performance in wide climatic conditions in terms of 13-35℃and 18%-72%***,the performance of photovoltaic(PV)-driven SAWH was *** showed that a 1 m^(2)PV panel could generate 0.66-2 L water per day in Shanghai throughout the year,the highest in opening ***,this work introduces a promising concept that can help achieve large-scale,ultra-fast,energyefficient AWH worldwide.

关键词： Atmospheric water harvesting Thermodynamic optimization Optimal harvesting window Large-scale and worldwide water production

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A comprehensive review of the modeling of transport phenomenon in the flow channels of polymer electrolyte membrane fuel cells

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Frontiers of Chemical Science and Engineering 2024年第8期18卷 123-161页

作者： Niyi Olukayode Shenrong Ye Mingruo Hu Yanjun Dai Rui Chen Sheng Sui institute of Fuel Cell Shanghai Jiao Tong UniversityShanghai 200240China institute of refrigeration and cryogenics Shanghai Jiao Tong UniversityShanghai 200240China Low Carbon Engineering Loughborough UniversityLoughborough Leicestershire LE113TUUK

Reactant gas and liquid water transport phenomena in the flow channels are complex and critical to the performance and durability of polymer electrolyte membrane fuel *** polymer membrane needs water at an optimum level for proton *** management involves the prevention of dehydration,waterlogging,and the cell’s subsequent performance decline and *** process requires the study and understanding of internal two-phase *** experimental visualization techniques are used to study two-phase flows in polymer electrolyte membrane fuel ***,the experiments have limitations in in situ measurements;they are also expensive and time *** contrast,numerical modeling is cheaper and faster,providing insights into the complex multiscale processes occurring across the components of the polymer electrolyte membrane fuel *** paper introduces the recent design of flow *** reviews the numerical modeling techniques adopted for the transport phenomena therein:the two-fluid,multiphase mixture,volume of fluid,lattice Boltzmann,and pressure drop ***,this work describes,compares,and analyses the models’approaches and reviews the representative results of some selected ***,the paper summarizes the modeling perspectives,emphasizing future directions with some recommendations.

关键词： two-phase flows numerical model flow channel polymer electrolyte membrane fuel cells water management

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Review on Anti-Frost Technology Based on Microchannel Heat Exchanger

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Journal of Shanghai Jiaotong university(Science) 2024年第2期29卷 161-178页

作者：叶振鸿王炜李新华陈江平 institute of refrigeration and cryogenics Shanghai Jiao Tong UniversityShanghai 200240China Shanghai High Eficient Cooling System Research Center Shanghai 200240China

Frosting is an inevitable adverse phenomenon in many fields such as industrial refrigeration,cryo-genics,and heat pump air conditioning,which may influence the efficiency of the equipment and increase the energy consumption of the *** complicated louvered-fin structure and fuid-channels arrangements of the microchannel heat exchanger(HEX)will affect the heat transfer performance and frosting ***,this article analyzes different factors such as refrigerant distribution,refrigerant fow pattern,and HEX surface temperature ***,combined with the features of the microchannel HEX,the existing anti-frosting technologies and various methods of surface treatment for anti-frosting are *** review focuses on the preparation of superhydrophobic surfaces and their superior ***,the internal mechanism is analyzed in conjunction with the relevant research of our *** character has excellent anti-frosting performance and heat transfer performance,which is of great significance for improving energy-saving and system ***,the future development of superhydrophobic surface technology is analyzed and prospected.

关键词： anti-frost technology microchannel heat exchanger(HEX) superhydrophobic surface

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Solid Desiccant Heat Pump Fresh Air Unit using Composite Silica Gel

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Journal of Thermal Science 2024年第4期33卷 1286-1300页

作者： YANG Tianyu GUO Defang GE Tianshu institute of refrigeration and cryogenics Shanghai Jiao Tong UniversityKey Laboratory of Power Mechanical EngineeringMOE ChinaShanghai200240China Qingdao Haier A/C Electronic Co. LtdQingdao266101China

The introduction of fresh air into the indoor space leads to a significant increase in cooling or heating *** desiccant heat pump fresh air unit which can handle the latent and sensible load of fresh air efficiently have been proposed *** improve the performance of the solid desiccant heat pump fresh air unit in the fresh air handling process,in this paper,the application of composite silica gel in a heat pump fresh air unit was *** comparison between silica gel coating(SGC)and composite silica gel coating(CSGC)shows that the adsorption rate and water uptake capacity of CSGC are more than two times higher than those of *** experimental setup for the solid desiccant heat pump fresh air unit was *** performance of SGC and CSGC was tested in the setup *** show that under summer conditions,compared with the solid desiccant heat pump fresh air unit using silica gel(SGFU),the average moisture removal and COP of the one using composite silica gel(CSGFU)increased by 15%and 30%,*** winter conditions,compared with SGFU,the average humidification and COP of CSGFU increased by 42%and 17%.With optimal operation conditions of 3 min switchover time and 40 r/s compressor frequency,the COP of CSGFU under summer conditions can reach *** also show that the CSGFU and SGFU have higher COP and dehumidification rate under higher outdoor temperature and humidity ratio.

关键词： fresh air system desiccant coated heat exchanger humidification dehumidification experimental comparison

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Working Fluid Distribution and Charge Regulation Control in Organic Rankine Cycle

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Journal of Shanghai Jiaotong university(Science) 2024年第2期29卷 188-201页

作者：叶振鸿李新华王炜陈江平 institute of refrigeration and cryogenics Shanghai Jiao Tong UniversityShanghai 200240China Shanghai High Efficient Cooling System Research Center Shanghai 200240China

Charge-based studies,in particular investigations of mass distribution,are still almost absent,although the efficiency of the organic Rankine cycle(ORC)has attracted a great deal of scholarly *** paper aims to provide a new perspective on the intrinsic relationship among the mass distribution,phase-zone distribution in the heat exchanger(HEX),charge of working fuid(WF),rotation speed of the pump(RSP),and system performance.A comprehensive ORC simulation model is presented by linking each component's sub-models,including the independent models for HEX,pump,and expander in an object-oriented *** visualization study of mass distribution of the WF in the system is investigated under different working ***,the volume and mass of the gas phase,two-phase and liquid phase of WF in the HEX and their variation rules are analyzed ***,the strategies of charge reduction considering HEX areas and pipe sizes are *** results show that the model based on the interior-point method provides high levels of accuracy and *** mass ratio of the WF is concentrated in the liquid receiver,especially in the regenerator,which is 32.9%and 21.9%of the total mass,***,2.4 kg(6.9%)WF in the system gradually migrates to the high-temperature side as the RSP increases while 6.1 kg(17.4%)WF migrates to the low-temperature side,especially to the condenser,as the charge in the system *** power and efficiency both decrease gradually after the peak due to changes in RSP and ***,reducing heat transfer areas of the condenser and regenerator is the most effective way to reduce WF charge.

关键词： simulation organic Rankine cycle(ORC) working fuid charge mass distribution

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