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Experimental Study on Frost Crystal Morphologies and Frosting Characteristics Under Different Working Pressures

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SSRN 2022年

作者： Lai, Tianwei Liu, Xue Dong, Xiaojun Qiang, Mingchen Yan, Shaohang Hou, Yu State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Frost usually grows on the cooling surface of heat transfer equipment which often operates under different working pressures. In such conditions, one of the fundamental influencing factors of frosting, the diffusion coefficient of water vapor around the cooling surface is different from that in the normal atmosphere pressure. In order to investigate the pressure effect on frosting, a test rig for frosting visualization is designed. The role of working pressure around the cooling surface on the frost crystal morphologies and frost layer characteristics are evaluated under different air parameters and temperatures of cooling surface. The vertical growth and lateral distribution of frost crystals are related strongly to working pressure around the cooling surface. More frost crystal morphologies and faster growth rate of frost layer are presented at a lower pressure. The frost thickness, frost accumulation and density reduce with higher pressure. The dimensionless correlation of frost thickness is proposed considering working pressure around the cooling surface, humid air parameters, and temperature of cooling surface. © 2022, The Authors. All rights reserved.

关键词： Working pressure

Enhancing Heat Transfer in Immersion Cooling Via Guest Non-Condensable Gas Microbubbles

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SSRN 2024年

作者： Luo, Peng Tong, Wei Wei, Lichuan Zhao, Yugang Zhang, Hua Cheng, Ping Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering School of Energy and Power Engineering University of Shanghai for Science and Technology Shanghai200093 China Shenzhen Envicool Technology Co. Ltd. Shenzhen518129 China MOE Key Laboratory of Power Machinery and Engineering School of Mechanical Engineering Shanghai Jiaotong University Shanghai200240 China

Electronic systems produce increasingly high density of heat along with their performance elevated to meet the booming needs from industrials and human activities, and therefore more effective cooling methods are always in demand. Liquid immersion, both single-phase and dual-phase, is one of the most popular cooling methods developed, due to its simplicity, energy efficiency and operational feasibility. However, the heat dissipation capacity of single-phase immersion cooling is relatively low, while multi-phase only occurs above the boiling point of refrigerants. We here introduce a brand-new immersion cooling method with the injection of cold guest non-condensable gas (NCG) microbubbles. Experimental results show that the heat transfer rate is drastically enhanced, and in particular surface superheating is suppressed or even eliminated which is the key to maintaining the safety performance of micro-electronic chips. As bubbles approach the heating surface, they disturb the thermal boundary layer on the surface when their size is comparable with the layer thickness, attach to the surface serving as evaporation/boiling nuclei, and collide with existing bubbles to facilitate their departure. Also, the effects of bubble size distribution and pool subcooling are evaluated. The present cooling method performs better at a larger degree of pool subcooling while the effect of bubble size is relatively minor. This work demonstrates that guest NCG bubbles can drastically promote heat transfer in immersion cooling unlike others reported in the literature. The fundamental understanding of bubble dynamics upon impinging with the heating surface in subcooled liquid has promising applications in thermal management systems, such as electronic chips, nuclear reactors, heat exchangers, steam generators, and among others. © 2024, The Authors. All rights reserved.

关键词： Steam generators

Numerical Investigation on the Radiation Performance of a Crisscross Liquid Droplet Radiator in Space Under Different Operating Conditions

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SSRN 2022年

作者： Zhu, Maoguo Sha, Zhaoyang Zhao, Quanbin Chong, Daotong Chen, Weixiong Yan, Junjie State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'An710049 China

Crisscross liquid droplet radiator (LDR) is a promising solution for the heat dissipation of large-power space structures. In this study, a three-dimensional steady numerical simulation of the radiation performance of crisscross LDR in space under different operating conditions was conducted. Significantly, the radiation interaction between adjacent droplet planes was introduced into the radiation model to accurately compute the energy radiated by the crisscross droplet sheet. Simulation results indicated the radiation performance of crisscross droplet sheet deteriorated with an increase in the nonuniformity of droplet planes arrangement and hence droplet planes uniformly arranged were required for a good crisscross LDR. Moreover, there existed a critical droplet sheet angle of 72° where the pressure disturbance frequency almost had no influence on the radiation performance of crisscross LDR. For certain pressure disturbance frequency, decreasing the droplet sheet angle can expand the available operational pressure difference range. The radiation performance of crisscross LDR with high initial droplet temperature was more sensitive to the changes in droplet sheet angle than that with low initial droplet temperature. Finally, the optimal working medium collocation scheme and droplet sheet configuration for crisscross liquid metal LDR were proposed. Given the lightweight and efficiency of crisscross liquid metal LDR, the collocation scheme of working medium including tin and lithium can be adopted and the droplet sheet angle should be designed as 15°. The present work can provide significant guidance for selecting suitable operating conditions for droplet generators to optimize the thermal design of a crisscross LDR. © 2022, The Authors. All rights reserved.

关键词： Drops

Improving sampling depth of laser speckle imaging by topical optical clearing:A theoretical and in vivo study

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Journal of Innovative Optical Health Sciences 2020年第2期13卷 33-43页

作者： D.Li Y.Zhang B.Chen State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an Shaanxi 710049P.R.China

The effect of optical cleaning method combined with laser speckle imaging(LSI)was discussed to improve the detection depth of LSI due to high scattering characteristics of skin,which limit its clinical application.A double-layer skin tissue model embedded with a single blood vessel was established,and the Monte Carlo method was used to simulate photon propagation under the action of light-permeating agent.808 nm semiconductor and 632.8 nm He–Ne lasers were selected to study the e®ect of optical clearing agents(OCAs)on photon deposition in *** show that the photon energy deposition density in the epidermis increases with the amount of tissue°uid replaced by *** with glucose solution,polyethylene glycol 400(PEG 400)and glycerol can considerably increase the average penetration depth of photons in the skin tissue,thereby raising the sampling depth of the *** the action of glycerol,PEG 400,and glucose,the average photon penetration depth is increased by 51.78%,51.06%,and 21.51%for 808nm,68.93%,67.94%,and 26.67%for 632.8 nm lasers,*** vivo experiment by dorsal skin chamber proves that glycerol can cause a substantial decrease in blood°ow rate,whereas PEG 400 can signicantly improve the capability of light penetration without a®ecting blood velocity,which exhibits considerable potential in the monitoring of blood°ow in skin tissues.

关键词： Laser speckle image topical optical clearing imaging depth Monte-Carlo simulation dorsal skin experiment

Experimental Investigation on Separation Characteristics of Gas-Liquid Two-Phase flow Around the Perforated Tube

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SSRN 2022年

作者： Wang, Jinzhi Xie, Xiangdong Wang, Yechun Xu, Qiang Wang, Jiang Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

The flow around cylinder is widely used in industrial applications. In this study, the separation characteristics of gas-liquid two-phase flow around a perforated tube are investigated experimentally. The interface fluctuation process of the gas pocket and liquid slug periodic separation around the perforated tube is presented intuitively using a high-speed camera. The mean value and standard deviation of the void fraction in the wake region are independent of the inlet liquid flow rate. When the flow pattern is plug flow, the air separation efficiency first decreases and then increases with an increase in the inlet void fraction;the separation efficiency increases monotonically when the flow pattern is slug flow. The separation purity and total pressure drop increase with increasing inlet void fraction. Based on the principle of minimum kinetic energy, methods for predicting the void fraction in the wake region, separation purity, air separation efficiency and pressure drop have been developed. The new correlations are based on the Weber number and liquid-phase Reynolds number that are also controlling dimensionless group in determining the void fraction, separation efficiency and pressure drop. The prediction accuracies of the void fraction and separation purity are within ±10% and the prediction accuracies of the separation efficiency and pressure drop are within ±20%, which provides an accurate prediction of the separated flow around the perforated tube. © 2022, The Authors. All rights reserved.

关键词： Void fraction

Numerical Investigation on Combustion Characteristics and NOx Emission of Double-Reheat Tower Boiler at Different Loads 9th

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Numerical Investigation on Combustion Characteristics and NO...

9th International Symposium on Coal Combustion, ISCC 2019

作者： Zhang, Yan Ma, Shihao Guo, Jin Li, Yuesheng Zhu, Zhengrong He, Jiaqi Deng, Lei Che, Defu State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi’an Jiaotong University Xi’an 710049 China Guangdong Institue of Special Equpiment and Research Foshan528251 China Guangdong Institue of Special Equipment Inspection and Research Shunde Institue of Inspection Foshan528300 China

ISBN: (纸本)9789811616563

In this study, a three-dimensional numerical investigation using a finite volume method is presented to obtain the velocity, temperature, and species distributions in a 660 MW double-reheat tower boiler fed with bituminous coal. The refined oxidation model of HCN and NO-char reaction model were used to substitute the default model by the user-defined functions (UDFs). The effects of different loads and excess air ratios on combustion characteristics and NOx emission were studied numerically. The results show that temperature distribution is more uneven at the upper part of the furnace and the NOx emission increases as the load decreases. The temperature distributions in the furnace have little differences under three different excess air ratios. That the oxygen concentration increases significantly as the increase of excess air ratios leads to an increase of NOx emission at the furnace outlet. The minimum NOx concentration at the furnace outlet, 308 ppm, appears under 100% THA with excess air ratio of 1.15. The simulation results in this study can provide reference for optimization of combustion characteristics in double-reheat tower boiler and illustrate a method to reduce NOx emission. © 2022, Tsinghua University Press.

关键词： Furnaces

Numerical Investigation on the Thermal-Hydraulic Performance of a Cryogenic Printed Circuit Heat Exchanger for Liquid Air Energy Storage

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SSRN 2022年

作者： Yu, Pengfei Liu, Hu Xue, Jingwen Zhang, Yankang Che, Defu State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University Xi'An710049 China

The liquid air energy storage integrated with liquefied natural gas regasification is a promising large-scale storage method, but its development is limited by the lack of the thermal-hydraulic data of the cryogenic printed circuit heat exchanger. In this paper, a reduced numerical model for conjugate heat transfer was established, and the effect of the inclined angle (0°, 15°, 30°, 45°, and 60°) was investigated. The minimum internal temperature approach for optimal system operation is approximately 6 K, located in the middle of the heat exchanger. The nature of local flow and heat transfer was analyzed by quantifying the vortex strength and visualizing the vortex core. Results indicate that the evolution of Dean vortices plays a crucial role in heat transfer augmentation. The secondary flow caused by the elbow forces the velocity and temperature cores to strike the windward side periodically, which disturbs the boundary layer and enhances the fluid mixing. Entropy production analysis shows that the thermal entropy generation has a dominant share of the irreversibility. The zigzag channel with an inclined angle of 45° yields the best comprehensive performance since the irreversibility is reduced by augmenting the heat transfer. © 2022, The Authors. All rights reserved.

关键词： Air

Investigation on the Parallel Computing Technique Using on the Numerical Simulation of Carbon Free Fuel

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Investigation on the Parallel Computing Technique Using on t...

Information Science, Parallel and Distributed Systems (ISPDS), International Conference on

作者： Weibin Wang Xutao Wei Department of Computer Science Xi'an Fanyi University Xi'an China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an China

The numerical simulation of the turbulent combustion is identified as one of the most promising methods on the designs of the combustion devices, for example: the internal combustion engine and gas turbine. This mainly depends on the development of parallel computing technique. However, the computational efficiency for different cases on different compute nodes and number of cores still needs to be studied. On the other hand, due to the requirements from the aim of peaking carbon dioxide emissions before 2030 and achieving carbon neutrality before 2060, modern energy system is requesting low carbon or carbon free fuels, such as ammonia (NH3). Therefore, the simulations of ammonia/air flame were performed in present investigation. The comparison between simulation cases on different compute nodes and number of cores illustrates that different cases requires different number of cores to achieve the best computational efficiency. The computational efficiency of each compute nodes are dissimilar, which can decrease the efficiency. Meanwhile, the methods in present study can predict the ammonia/air flames. The initial condition of velocity fluctuation is necessary for simulating turbulent flame. The wrinkles of the flames can be well predicted by the velocity fluctuation initial boundary condition.

关键词：

Water Washing of Biomass and Biochar

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SSRN 2022年

作者： Huang, Xiaole Tie, Yuan Jiang, Jiahao Deng, Lei Che, Defu State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi’an Jiaotong University Xi’an710049 China

To investigate the differences of organics composition between leachates of biomass and biochar, four biomass materials and the corresponding biochar are water washed. The distributions of organic compounds in leachates are characterized by GC-MS. Raw and washed biomass, and biomass leachates dried at 333 K are sent for TG/DTG analysis. The results show that considering the content of aromatic hydrocarbons, corn and sorghum stalk are referred to be washed after high-temperature pyrolysis at 303 K, with the value of 11% and 29.95% respectively. Wheat straw and rice husk are proposed to wash directly. Considering the alkanes, cycloalkanes and heterocyclic hydrocarbons contents in leachates, it is proposed to washing low-temperature pyrolyzed biochar. It is recommended to wash biomass directly to inhibit acidic organics release. Washed and raw biomass have similar DTG curves. The combustion stage of dried leachate is more complicated, with one or two peaks during the third stage. The activation energy follows an order of washed biomass > raw biomass > biomass leachate. © 2022, The Authors. All rights reserved.

关键词： Biomass