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Effects of non-uniform temperature of the ice nucleus on heterogeneous ice nucleation

INTERNATIONAL JOURNAL OF heat AND MASS transfer 2020年 163卷 120404-120404页

作者： Guo, Q. Cheng, P. Shanghai Jiao Tong Univ Sch Mech Engn DOE Key Lab Power Machinery & Engn Shanghai 200240 Peoples R China Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China

In this paper, effects of non-uniform temperature in the ice nucleus on heterogeneous ice nucleation are investigated via two approaches: changes in Gibbs free energy function and availability function. Analytical expressions for non-uniform temperature distribution inside the ice nucleus and heat transfer from the nucleus to the supercooled wall are obtained in terms of the contact angle and supercooled wall temperature based on the consideration that thermal conductivity resistance of the nucleus, interfacial resistance and thermal resistance due to curvature of ice/water interface are in series. With non-uniform temperature in the nucleus taken into consideration, it is found that the critical radius of the ice nucleation obtained based on availability analysis is slightly larger than those obtained based on Gibbs free energy analysis. Both heterogeneous critical radius and nucleation energy barrier are found to be increasing with surface contact angle. On an ice-phobic surface at small supercooling degrees, the critical radius and the nucleation energy barrier obtained with or without heat transfer taken into consideration differ greatly with the increase of the contact angle. However, at large supercooling degrees and small contact angles, differences in the critical radius and nucleation energy barrier by availability analysis are negligible with or without heat transfer effects. Thus, heterogeneous nucleation behaviors on ice-philic surfaces can be estimated based on the assumption of uniform temperature in the ice nucleus when degree of wall supercooling is large. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Availability analysis Gibbs function analysis Heterogeneous nucleation Ice nucleation theory Non-uniform temperature distribution in the ice nucleus

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Fates of the components in cotton stalk during the hydrothermal oxidative pretreatment and its relationship with the upgrading of biochar pellets and wood vinegar

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FUEL 2022年 320卷 123881-123881页

作者： Xu, Jiaqing Zhang, Shouyu Zhang, Peizheng Shi, Yue 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

In the present study, biochar pellets and wood vinegar are prepared from the cotton stalk (CS) through the densification and pyrolysis, and hydrothermal oxidative (HO) pretreatment (160-260 degrees C) is conducted to CS to upgrade the quality of biochar pellet and wood vinegar (WV). The results show that HO pretreatment can decompose the hemicellulose, amorphous cellulose, crystalline cellulose, and lignin at 160-230 degrees C, 160-200 degrees C, 200-260 degrees C, and < 200 degrees C, respectively. Therefore, the hemicellulose and cellulose (especially the crystalline cellulose) in CS are enriched at 160-180 degrees C and 160-200 degrees C respectively. Due to the enrichment of hemicellulose and cellulose, the organic compounds in WV increase dramatically after HO pretreatment, resulting in a significant increase in the density and acidity of WV. Furthermore, due to the enrichment of hemicellulose and cellulose, the biochar pellets exhibit more densified internal structures after HO pretreatment, contributing to a higher relaxation density, energy density, and compressive strength. Moreover, the biochar pellets exhibit better combustion performance and lower ash content after HO pretreatment at 160-180 degrees C. The CS sample pretreated at 180 degrees C is the best material for the production of biochar pellets and WV.

关键词： Cotton stalk Hydrothermal oxidative pretreatment Pyrolysis Biochar pellets Wood vinegar

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Solar and wind power data from the Chinese State Grid Renewable Energy Generation Forecasting Competition

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SCIENTIFIC DATA 2022年第1期9卷 577页

作者： Chen, Yongbao Xu, Junjie 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

Accurate solar and wind generation forecasting along with high renewable energy penetration in power grids throughout the world are crucial to the days-ahead power scheduling of energy systems. It is difficult to precisely forecast on-site power generation due to the intermittency and fluctuation characteristics of solar and wind energy. Solar and wind generation data from on-site sources are beneficial for the development of data-driven forecasting models. In this paper, an open dataset consisting of data collected from on-site renewable energy stations, including six wind farms and eight solar stations in China, is provided. Over two years (2019-2020), power generation and weather-related data were collected at 15-minute intervals. The dataset was used in the Renewable Energy Generation Forecasting Competition hosted by the Chinese State Grid in 2021. The process of data collection, data processing, and potential applications are described. The use of this dataset is promising for the development of data-driven forecasting models for renewable energy generation and the optimization of electricity demand response (DR) programs for the power grid.

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Saturated flow boiling heat transfer of R1233zd(E) in parallel mini-channels: Experimental study and flow-pattern-based prediction

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INTERNATIONAL JOURNAL OF heat AND MASS transfer 2023年第1期216卷

作者： Fang, Yidong Lu, Di Yang, Wenliang Yang, Huinan Huang, Yuqi 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 Pan Asia Tech Automot Ctr Co Ltd SAIC Motor Shanghai 201208 Peoples R China Zhejiang Univ Qingshanhu Energy Res Ctr Hangzhou 310027 Peoples R China

The parallel channel is widely used in the two-phase flow boiling heat transfer due to its simple structure, but the existence of multiple flow patterns causes a complex and non-unified explanation of the heat transfer mechanisms. In this study, a saturated flow boiling experiment was designed in a parallel mini channel heat sink with R1233zd(E) as the working fluid. By controlling the vapor quality difference at the inlet and outlet to around 0.1-0.2, each single flow pattern was isolated and presented in the test section, and the corresponding variations of heat transfer coefficient (HTC) were discussed. The results showed that the flow pattern during the saturated flow boiling included bubbly flow, slug flow, wavy-annular flow and local dry-out. The transition boundaries between bubbly flow, slug flow and wavy-annular flow showed good agreement with the present criteria, while a modification was made on the transition from wavy-annular flow to local dry-out. The HTC showed a fast increase under low vapor qualities, then became stable and decreased with the increase of vapor quality. In addition, 6 correlations were selected to compare with the measured HTC classified according to the flow patterns. The comparison showed that the present correlations had different prediction accuracies on the HTC data under each flow pattern. The best prediction on the heat transfer during bubbly and slug flow was achieved by Liu and Winterton's model with the MAE of 16.4% and 12.9%, while Li and Wu's model showed the best agreement with the HTC data during wavy-annular flow with the MAE of 9.1%.

关键词： Saturated flow boiling Parallel mini channel flow pattern heat transfer mechanism

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A review of recent literature on icing phenomena: Transport mechanisms, their modulations and controls

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INTERNATIONAL JOURNAL OF heat AND MASS transfer 2020年 159卷 120074-120074页

作者： Zhao, Y. Guo, Q. Lin, T. Cheng, P. Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China Shanghai Jiao Tong Univ Sch Mech Engn DOE Key Lab Power Machinery & Engn Shanghai 200240 Peoples R China

Icing is one of the most fascinating phenomena occurring ubiquitously in nature and multiple industrial applications. In spite of a century of research work on this topic, an in-depth physical description of icing process is still missing due to the unorthodox behaviors of water during solidification. In recent years, many important features pertaining to some ultrafast and microscale phenomena in icing have been revealed using latest experimental techniques and newly developed numerical simulation methods. This work aims to present a comprehensive up-to-date review on the subject of icing. Fundamentals of icing nucleation dynamics are introduced, followed by discussion on propagations of freezing phase fronts. Different forms of icing, including freezing of droplets, desublimation/sublimation, and condensation frosting, are presented sequentially. Emphasis is placed on a few recently revealed phenomena, such as dendritic ice growth through desublimation, kinetic behaviors of droplets upon freezing, frost spreading by building icing bridges, etc. A summary of recent progress in the application of anti-/deicing methods is also presented. The results of these studies not only improve our understanding of physical mechanisms on icing, but also benefit the understanding of solidification processes in other disciplines with different applications. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Icing Frosting Nucleation Phase propagation

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Study on the influence of distributed Joule-Thomson effect on the performance of microchannel cryocooler

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APPLIED THERMAL engineering 2022年 213卷

作者： She, Hailong Cui, Xiaoyu Weng, Jianhua Chang, Zhihao Univ Shanghai Sci & Technol Sch Energy & Power Engn 516 Jungong Rd Shanghai 200093 Peoples R China Key Lab Multiphase Flow & Heat Transfer Shanghai P Shanghai 200093 Peoples R China Shanghai Univ Elect Power Sch Energy & Mech Engn Shanghai 200090 Peoples R China

At present, the pros and cons of distributed Joule-Thomson (J-T) effect in throttling refrigeration systems have been controversial. In this paper, a microchannel J-T cryocooler is used as the prototype. The distributed J-T effect is produced by the friction loss in the throttling channel. The refrigeration performance of the cryocooler at 6.0 MPa is analyzed. Then, according to the dependence of the J-T coefficient on pressure and temperature, a fully distributed J-T effect microchannel is designed to replace the separate counterflow heat exchanger and throttling device on the high-pressure side. The characteristics are simulated and compared with the prototype. The results show that the refrigeration ability of the fully distributed J-T cryocooler is slightly inferior to that of the prototype under the same pressure drop, and excessively increasing or reducing the cross-sectional size of the channel is not conducive to cooling. However, the fully distributed J-T effect structure can effectively delay the occurrence of choked flow due to the low velocity of the fluid. Under 6.0 MPa inlet pressure, the limited massflow rate of fully distributed cryocooler is 7.51 g/s, and the lowest temperature can reach 147.7 K, which is significantly lower than 163.3 K that the prototype can reach in the choked state. In addition, this paper also explores the influence of distributed J-T effect on the low-pressure side, which is beneficial to precooling the high-pressure fluid more efficiently using a little distributed J-T effect. A proper part of the friction loss in the low-pressure channel helps improve the refrigeration ability. At 6.0 MPa inlet pressure, the best cooling effect is obtained when the pressure drops in the low-pressure channel account for 15.85 % of the total pressure drop.

关键词： Distributed J-T effect Microchannel heat exchange and throttling Choked flow

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Effect of copper metal foam proportion on heat transfer enhancement in the melting process of phase change materials

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APPLIED THERMAL engineering 2022年第PartB期201卷 117778-117778页

作者： Wang, Zilong Zhang, Hua Dou, Binlin Zhang, Guanhua Wu, Weidong Zhou, Xiang Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China Tongji Univ Sch Mech Engn 204 Jiyang Bldg1239 Siping Rd Shanghai 200092 Peoples R China

Phase change materials can overcome the low energy density and utilisation efficiency of solar energy. However, the low thermal conductivity of phase change materials significantly affects the thermal efficiency of solar devices;thus, improving the thermal conductivity of phase change materials has been the focus of many recent studies. Using paraffin wax and copper metal foam, copper metal foam composite phase change materials were prepared in this study. The effect of the copper metal foam proportion on heat transfer enhancement in the melting process of phase change materials was analysed using visualisation heat storage experimental equipment. The integrated heat transfer coefficient of the copper metal foam composite phase change materials was obtained. The experimental results showed that as the copper metal foam proportion increased from 0% to 2.13%, the melting time of the copper metal foam composite phase change materials decreased from 901 s to 791 s, and the heat storage rate and integrated heat transfer coefficient increased from 21.81 J/s to 25.08 J/s and 1.26 W/(m K) to 4.16 W/(m K), respectively. The heat storage capacity first increased and then decreased. The minimum temperature gradient of 5.2 K was reached when the copper metal foam proportion was 2.13%. More important, natural convection is the major heat transfer mechanism in the melting process of composite phase change materials with a low copper metal foam proportion;heat conduction plays a primary role in the melting process of composite phase change materials with a high copper metal foam proportion. The best heat storage and heat storage rate for copper metal foam composite phase change materials were 20260.49 J and 24.38 J/s, respectively, achieved with a copper metal foam proportion of 1.28%.

关键词： Copper metal foam Phase change materials heat transfer enhancement Integrated heat transfer coefficient heat storage property

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Three-dimensional shaping strategy via solidifying polygonal nanofluid drops

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CELL REPORTS PHYSICAL SCIENCE 2024年第4期5卷

作者： Jiang, Yupeng Zhao, Yugang Zhang, Hua Yang, Chun Cheng, Ping Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China China Aerodynam Res & Dev Ctr Key Lab Icing & Anti Deicing Mianyang 621000 Sichuan Peoples R China Nanyang Technol Univ Sch Mech & Aerosp Engn Singapore 639798 Singapore Shanghai Jiao Tong Univ Sch Mech Engn MOE Key Lab Power Machinery & Engn Shanghai 200240 Peoples R China

Manufacturing fine three-dimensional (3D) structures from mesoscale down to nanoscale is of considerable importance in multiple application backgrounds. Here, we investigate the freezing of a nanofluid drop whose contact line is pinned by a 2D wettability base pattern. A surprisingly rich variety of shape choices for the top plateau can be obtained for basic polygonal patterns, allowing us to control the out -of -plane shape of the frozen drop. To understand the morphology of such an edge -confined drop and its shape change during solidification, we assume that the drop is an assembly of multiple slices with varying contact radii and a shared axial. Each contact radius yields a corresponding top plateau size at a certain drop height, engendering a specific plateau shape. The ability to control the plateau of a frozen drop and the fundamental understanding of its formation shed light on an alternative 3D fabrication method.

关键词： out-of-plane shape control nanofluid wettability pattern 3D fabrication

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Simultaneous measurement of near-water-film air temperature and humidity fields based on dual-wavelength digital holographic interferometry

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OPTICS EXPRESS 2022年第10期30卷 17278-17289页

作者： Zhang, Mengmeng Liu, Jingnan Dou, Jiazhen Zhang, Jiwei Zhang, Lixin Di, Jianglei Zhao, Jianlin Northwestern Polytech Univ Sch Phys Sci & Technol MOE Key Lab Mat Phys & Chem Extraordinary Condit Xian 710129 Shaanxi Peoples R China Northwestern Polytech Univ Sch Phys Sci & Technol Shaanxi Key Lab Opt Informat Technol Xian 710129 Shaanxi Peoples R China Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China Guangdong Univ Technol Sch Informat Engn Adv Inst Photon Technol Guangzhou 51006 Peoples R China Guangdong Univ Technol Guangdong Prov Key Lab Informat Photon Technol Guangzhou 51006 Peoples R China

We present a method to reconstruct the near-water-film air temperature and humidity distributions synchronously by measuring the phase delays based on dual-wavelength digital holographic interferometry. A falling water film device was used to create a water film evaporation environment and generate axially uniform temperature and humidity fields. The relationship between air temperature, humidity and phase delay is derived from the Edlen equations. With such relationship, the temperature and humidity distributions can be solved directly according to phase delays of two different wavelengths. An edge phase enhancement method and an error elimination method with PSO are presented to improve the measurement accuracy. The temperature and humidity fields in the falling water film model were experimentally reconstructed with temperature deviation of 0.06% and relative humidity deviation of 2.61%. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Holographic interferometry Image sharpening Laser sources Phase measurement Spatial filtering Three dimensional measurement

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Analysis of thermal deviations in L-shape platen superheaters of a supercritical 600 MW circulating fluidized bed boiler

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APPLIED THERMAL engineering 2020年第0期166卷 114752-000页

作者： Ma, Youfu Jin, Xin Lyu, Junfu Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer Shanghai 200093 Peoples R China Tsinghua Univ Dept Energy & Power Engn Key Lab Thermal Sci & Power Engn Minist Educ Beijing 100084 Peoples R China

In circulating fluidized bed (CFB) boilers, L-shape platen superheaters often suffer from poor working conditions with a high risk of tube wall overtemperature. Thermal deviations of an L-shape platen superheater were studied by using a supercritical 600 MW CFB boiler as reference. Based on the prediction model of thermal deviations and a self-developed software, thermal deviations of the platen superheater were calculated and analyzed under three kinds of heat load distributions. The results show that the heat absorption deviations for steam are related to the heat load and heating area distribution, wherein the heat load is more effective than the heating area. The mass flow rate deviations for steam mainly depend on the header effect and the nonuniform tube length, while the mass flow rate deviations induced by thermal effects are negligible. The mass flow rates of each tube are nearly identical because the header effect offsets the effect of the nonuniform tube length. Therefore, the heat absorption deviations determine the final thermal deviations of the platen superheater. It is suggested to make complete use of the header effect on the mass flow rate distribution;thus, achieving good control of the thermal deviation of platen superheaters.

关键词： CFB boiler Platen superheater Thermal deviation Mass flow rate distribution

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