A comprehensive study on the dynamic mixing process of biomass particles and inert particles in a cylindrical fluidized bed is conducted. The particle mixing parameters at multipositions inside three-dimensional fluidized beds are obtained by a specially designed measurement system. The local particle mixing ratios and dispersion coefficients are analyzed. Particle mixing mechanisms, including the convection mechanism and diffusion mechanism, are analyzed based on variations of mixing ratios and dispersion coefficient at multipositions inside the beds. Results show that the averaged radial dispersion coefficient at half-radius ranges from 0.0038 to 0.026 m2/s, which is about 1.5 times of that near the wall. The averaged axial dispersion coefficient ranges from 0.004 to 0.056 m2/s, which is about 2.3 times the radial dispersion coefficient. The particle mixing at the center and top is mainly driven by a convection mechanism; meanwhile, particle mixing at the bottom and near the wall is mainly driven by a diffusion mechanism.

The distribution and fluctuation of particle concentration in a supercritical water fluidized bed (SCWFB) are studied using a specially-designed capacitance probe measurement system. The measurement error of capacitance probe system is 2.48%. Results show that the particle concentration at the axial line fluctuates largely with time and the fluctuation is weakened when increasing the distance from axial line or decreasing particle diameter. At Uf/Umb=1.5, the largest difference between particle concentrations is 0.026, 0.04, 0.082 when the particles with a diameter of 0.124mm, 0.198mm, 0.235mm are used, indicating a larger non-uniformity of larger particles. The probability density of local particle concentration mainly follows a unimodal distribution with the peak at right side. The main frequency of SCWFB ranges from 1.39Hz to 2.73Hz in this experiment and the main frequency decreases when larger particles are used.

This study introduces a combined heat and power (CHP) system primarily based on proton exchange membrane (PEM) fuel cells, which can provide electricity and heat for residential buildings in the East China region under two operating strategies. The analysis and discussion focus on the impact of parameters such as current density and gas inlet pressure on the system's output power and efficiency. The results indicate that excessively high current density decreases the system's electricity generation efficiency, while a moderate increase in hydrogen inlet pressure contributes to greater heat generation. Considering energy, economic, and environmental factors, the system operates with the thermal-led strategy in parallel with the grid, resulting in a substantial 73.3 % reduction in fuel costs. The annual greenhouse gas (GHG) emissions and the amount of emission reduction are lowered to 6.96 x 107 g and 3.39 x 107 g, respectively.

In order to promote the sustainable development of green energy, this study developed a hybrid combined cooling, heating and power system primarily consisting of proton exchange membrane fuel cells and an adsorption chiller. The system is designed to provide both power generation and heating, while also offering cooling capabilities. Initially, the models of the proton exchange membrane fuel cell stack and adsorption chiller were rigorously validated against experimental data, showcasing remarkable consistency with discrepancies below 3.5 %. Subsequently, the investigation delved into the influence of operational parameters for the proton exchange membrane fuel cell stack and adsorption chiller on various performance. These metrics encompassed energy efficiency, exergy efficiency, annual costs, and annual greenhouse gas reduction. Finally, the NSGA-II optimization algorithm was employed to perform multi-objective optimization on the system. The outcomes demonstrated that, in comparison to the initial configuration, the optimized system achieved a 22.51 % reduction in annual greenhouse gas emissions, while simultaneously enhancing energy efficiency by 14.72 %, exergy efficiency by 0.34%, cooling power by 3.14%, and heating power by 42.63 %. Moreover, the annual cost experienced a substantial decrease of 69.86 %.

A combined heat and power system (CHPs) using proton exchange membrane fuel cells (PEMFC) as its primary energy output device is an attractive option due to its high electrical generation efficiency and low heat-to-power ratio. A hybrid PEMFC-based CHPs (PEMFCCHPs) has been designed to provide both electricity and heat for a hydrogen high-speed service area. A comprehensive model of the system has been established and validated to analyze the impacts of key parameters such as PEMFC current density and anode hydrogen inlet pressure on the performance of hybrid PEMFC-CHPs. Evaluate and analyze the system from the perspectives of exergy, energy, and economy. The findings indicate that by fulfilling the service area's load demand, the thermal-led strategy can effectively prevent a waste of 670 kW of heat energy daily but exhibits a power shortage of 573.8 kW.& COPY; 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The immersion phase-change cooling technology utilizes the latent heat of the cooling liquid to dissipate heat by directly contacting the cooling liquid with the heat-generating electronic chip, which can meet the cooling requirements of current high heat flux density data centers. In this paper, the effect of different factors on the heat dissipation performance of immersion phase-change cooling technology was explored through numerical simulation. The results show that, under certain power conditions, the inlet temperature and flow rate of the cooling water in the condensation module, as well as the different arrangement of servers, have a significant impact on the heat dissipation performance of the entire system. The inlet water temperature mainly affects the chip temperature after stabilization. With the decrease in the inlet temperature, the chip surface temperature decreases significantly. The inlet water flow rate mainly affects the time required for the heat exchange to reach the desired temperature. With the increase in the inlet flow rate, the required cooling time is shortened. As the spacing between servers increases, the thermal safety and stability of the entire system increase. When the spacing between servers increases from 5 mm to 15 mm, the highest temperature and the temperature uniformity coefficient between the systems decrease significantly. When the spacing increases from 15 mm to 25 mm, the highest temperature and the temperature uniformity coefficient decrease slightly. These results can provide useful information for the designers of immersion phase-change cooling systems to improve the cooling efficiency of data centers, save energy, and ensure the safe operation of related computers, servers, and communication systems.

开发了一种基于电容探针的稠密气固两相流中异质颗粒混合特性测试新方法.研究了鼓泡流化床内异质颗粒混合过程中微观混合比的变化规律,分析了流化床一系列位置处对流与扩散机制对于混合过程的作用规律及其微观机理.结果表明:随着流化床床层高度的增加,对流机制对于颗粒混合的作用先增大后减小;壁面处微观混合比随着混合时间出现小幅波动,主要表现出扩散混合行为;不同高度处颗粒达到混合平衡所需时间无明显差异,而壁面处颗粒达到混合平衡所需时间是轴线处颗粒混合时间的2倍左右;混合平衡状态下最终微观混合指数相近.

A novel method for measuring the micro mixing ratio of binary solids in dense fluidizations is developed. The mixing process within a bubbling fluidized bed that can be assumed as one mixing cell is resolved. Dispersion co-efficient and mixing index methods are applied to characterize the mixing process. Results show that diffusion has an important effect on mixing at the bottom and top of the fluidized bed. Meanwhile, convection is the prin-cipal mechanism of mixing at the center. The lateral micro dispersion coefficient is between 0.005 m/s and 0.03 m/s. The vertical micro dispersion coefficient is approximately twice as that in the lateral direction. A new mixing index is proposed to evaluate the micro mixing quality of binary solids. The time required to reach uni-form mixing in the lateral direction is more than twice as that in the vertical direction.(c) 2022 Elsevier B.V. All rights reserved.

A novel measurement system for mixing property of binary mixtures in three-dimensional fluidized beds is developed based on capacitance probe method. The mixing processes at multi-positions of the bed are acquired simultaneously. A new dispersion coefficient is proposed to characterize the local dispersion of particles and a new mixing index is proposed to evaluate the local mixing quality in three-dimensional fluidized beds. The effect of convection and diffusion mechanism on particle mixing is discussed separately. Results show that the governing mechanism of particle mixing at the center and top of the beds is convection; meanwhile the governing mechanism for particle mixing at the bottom and near the wall is diffusion. The radial dispersion coefficient at the half-radius of the bed is mainly between 0.0038 and 0.026 m2/s, which is about 1.5 times that near the wall. The vertical dispersion coefficient is about 2.5 times that the radial dispersion coefficient.

A novel measurement system for radial particle mixing in annular fluidized beds is designed on the basis of the capacitance probe method. Mixing parameters at different radial positions are acquired. The effects of the convection/diffusion mechanism on radial mixing are analyzed individually. It is found that the governing mechanism of mixing at the axial line is convection; meanwhile, diffusion is the governing mechanism of mixing near the wall. The effect of convection on radial mixing at the upper part is more important than that at the lower part. The radial dispersion coefficient ranges from 0.006 to 0.072 m2/s. At the upper part, the radial dispersion coefficient at half-radius is between 0.016 and 0.072 m2/s and that near the wall is 0.006 and 0.028 m2/s, which is four times and twice that at the same radial position and at the lower part, respectively. The radial dispersion coefficient is about 1.5 times that in two-dimensional fluidized beds.

Measuring the particle mixing parameters at multi positions in three-dimensional fluidized beds continuously remains a challenging task. A novel measurement method for the mixing and segregation of particles inside three-dimensional fluidized beds is developed based on capacitance probe. The measurement error is generally below 7%. The particle mixing parameters and dispersion coefficients at multi-positions of the three-dimensional fluidized bed are acquired. The effect of convection and diffusion mechanism on particle mixing is discussed. Results show that the governing mechanism of particle mixing at center and top of the bed is convection; meanwhile the governing mechanism for particle mixing at bottom and near the wall is diffusion. The radial dispersion coefficient at half-radius of the bed is mainly between 0.0038 and 0.026 m2/s, which is about 1.5 times that near the wall. The axial dispersion coefficient is mainly between 0.004-0.056 m2/s, which is about 2.3 times that in radial direction.

基于显微粒子成像测速(Micro-PIV)技术,对微通道内单柱绕流特性展开实验研究,分析了10＜ Re＜ 350范围内不同高度流层的速度场、涡量场及旋涡特性.结果 表明:微尺度绕流现象相比宏观尺度存在滞后,首次出现旋涡的第一临界Re约为10.随着Re的增大,尾流区长度不断增加,旋涡尺度逐渐增大,旋涡中心位置向下游延伸.涡量强度随Re的增加而提高,涡量向下游扩散能力增强,高涡量区变窄.不同高度流层的速度场与涡量场存在差别,体现出三维效应.

A novel experimental method for the lateral mixing of binary solids in bubbling fluidized beds was developed based on the capacitance probe technique. The evolutions of local mixing ratios in a fluidized bed which can be assumed as one mixing cell were analyzed in detail. The solids mixing within one mixing cell was resolved and the effect of convection and diffusion mechanism on lateral mixing was evaluated individually. The results show that at lower part of the fluidized bed, convection plays a more important role in the mixing process near the wall; meanwhile, diffusion is very important for the mixing around the center line. This is opposite with that at the higher part. A lateral micro dispersion coefficient was proposed to characterize the lateral mixing within the mixing cell and the value is generally between 0.005 and 0.025 m/s. A new mixing index was proposed to evaluate the lateral mixing quality of binary solids. It was found that at the lower part of the fluidized bed, the best mixing is acquired at the half radius, whereas mixing at the center line is the worst. At the higher part, solid mixing is better when increasing the distance from the wall. The influences of gas velocity and static bed on the lateral mixing were also discussed from a microscopic perspective.

The supercritical-water fluidized bed (SCWFB) is a reactor for coal and biomass gasification without pollutant emission. We carried out a series of experiments in a SCWFB, and a dual-capacitance probe measurement system was applied to measure the hydrodynamics of slugs, such as the slug frequency, chord length, and rising velocity. Four groups of Geldart-B particles with different mean diameters were fluidized by supercritical water with a system pressure of 20-27 MPa and at 410-570 degrees C. The minimum slugging Reynolds number increases logarithmically with Archimedes number and a predicting correlation of the minimum slugging fluidization velocity in the SCWFB is presented: Re-ms = 32908.84 ln (Ar-0.(55) + 260376.65) - 410361.90. The relative error of the above correlation was within +/- 15% and the averaged relative error was 7.5%. The effect of operating conditions on the minimum slugging fluidization velocity is discussed. This research provides useful guidance for scaling-up design and for determining the optimum range of operating conditions in the SCWFB. (C) 2020 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

The treatment of dissimilar particles in a fluidized bed reactor is needed in many chemical industries, and detailed knowledge of mixing behavior of dissimilar particles is critical to design the reactor. Because dissimilar particles must be large enough to be differentiated in the bed frozen method, or to be clearly captured using an imaging system in the particle tracking method, former experimental research studies mainly concentrated on the mixing behavior of large particles (d(p) = 1.1-10 mm). For this problem, a novel research on particle mixing is carried out in this paper that emphasis is laid on the mixing behavior of small binary particles with the diameter being only 0.55 mm. The measurement problem is solved by developing a new measurement system of particle mixing based on the capacitance probe. Real-time mixing states at various positions of the fluidized bed from initially segregated to finally steady mixing are analyzed in detail and new phenomenon of small particle mixing is observed. The results show that the volumetric mixing ratio of jetsam particles decreases directly with fluidization time at the lower part of the fluidized bed, while significant fluctuations are found at the middle and upper part; final particle mixing is more uniform at the middle and upper part of fluidized bed than that at the lower part and near the wall; compared with coarse dissimilar particles, the mixing of small dissimilar particles is slower but more uniform in the end. Mixing behavior of small dissimilar particles is revealed by experiments for the first time. The findings may provide theoretical guidance for enhancing heat and mass transfer efficiency in fluidized bed reactors dealing with small particles and also enrich the fluidization theory.

Supercritical water fluidized bed (SCWFB) is a newly developed reactor for coal and biomass gasification without releasing pollutants. The knowledge of two-phase flow properties in SCWFB is still lacked so far in literatures due to the extreme operating condition of high-pressure and high-temperature supercritical water. In this paper, a special dual-capacitance probe measurement system is developed for the extreme flow environment in SCWFB. It is found that the linear relationship is more precise in converting the capacitance of the probe sensor into local volume fraction of solids in SCWFB than Bottcher relationship. With the help of the newly-developed dual-capacitance probe measurement system, an experimental study on the bubbling fluidization in a SCWFB is carried out when the system pressure is in the range of 20-27 MPa and the system temperature is in the range of 410-570 degrees C. Four groups of quartz sands with different mean diameters which belong to Geldart type B classification are fluidized. It is found that the bed expansion method which was used in literatures to identify the onset of bubbling fluidization in supercritical carbon dioxide fluidized bed doesn't have enough precision in a SCWFB. To solve this problem, a new method of identifying the onset of bubbling fluidization in SCWFB is proposed. The minimum bubbling Reynolds number increases with the Archimedes number in a logarithmic relationship in SCWFB. At last, a new predicting correlation of the minimum bubbling fluidization velocity in SCWFB is proposed: Re-mb = 26.7091n(Ar + 10253.88) - 247.339, 1900 < Ar < 180000 The relative error of the new predicting correlation is within +/- 20% and the averaged relative error is 7.5%. The research work in this paper provides useful guidance for the optimization and operation of SCWFB reactor. (C) 2019 Elsevier Ltd. All rights reserved.

A supercritical water-fluidized bed (SCWFB) is a very promising reactor for the clean utilization of biomass. In the present article, the flow structure in SCWFB is analyzed from a microscopic point of view via a special measurement system based on a capacitance probe. Five groups of particles are fluidized under a supercritical condition in a wide range of operating parameters: 20-27 MPa and 410-570 degrees C. Fluctuations and distributions of local voidage are analyzed in detail to shed some light on the special flow structure. The results show that bubbles tend to move toward the axial line of SCWFB and slugging fluidization is formed at a higher superficial velocity. In particular, a Core-Annulus Flow in SCWFB is found, which is enhanced by the increase of superficial velocity or decrease of the particle diameter. The results may be useful for the development of the SCWFB technique.

The supercritical water fluidized bed (SCWFB) is a new concept of reactor for coal and biomass gasification without releasing pollutants. In this paper, a special dual-capacitance probe measurement system is developed and a comprehensive study on bubble hydrodynamics in SCWFB is carried out. Four groups of particles with different mean diameters were fluidized by supercritical water with the pressure ranges from 20 to 27 MPa and temperature ranges from 410 to 570 °C. The effect of operating parameters on bubble size, frequency, and rising velocity is discussed in detail. Special rules of bubble hydrodynamics are observed, and the theoretical mechanisms are revealed. New predicting correlations of bubble diameter and bubble rising velocity are proposed. The results in this paper expand the research of fluidization under extreme operating conditions and also provide useful guidance for the optimization of the reactor.

Supercritical water fluidized bed (SCWFB) has been used to gasify biomass, coal and solid waste to produce gas fuel. Supercritical carbon dioxide fluidized bed (SCCO2FB) was applied in the coating industry. Both the two fluidized bed treats the supercritical fluids as fluidization medium. The fluidization behaviours of particles in the supercritical fluids are quite important issues for achieving the basic two phase flow pattern. Few research institutions have conducted experimental and numerical investigations on the fluidization in supercritical conditions. The authors try to establish a comprehensive insight of fluid dynamics of the supercritical fluidized bed. For the SCWFB, the fluidization transitions of fixed bed, homogeneous bed expansion and bubbling were demarcated by discrimination number Dn. A flow pattern map of Reynolds number vs. Archimedes number was available for describing the flow patterns and their boundaries of the SCCO2FB. Ergun equation was acceptable for calculating the fixed bed pressure drop for both SCWFB and SCCO2FB. Wei and Lu correlations of the minimum fluidization velocity, minimum bubbling velocity and homogeneous bed expansion rate are suggested to design the SCWFB. Wen and Yu equation of the minimum fluidization velocity, Vogt et al. correlation of the homogeneous bed expansion rate and their method for determining the minimum bubbling velocity, Nakajima et al. equation of transition velocity, and Bi and Fan correlation of turbulent velocity were recommended to calculate SSCO2FB.