纸机干燥部开式供热系统中喷射式热泵的结构分析

借助PHOENICS软件平台，通过求解二维N-S方程，模拟分析了喷射式热泵内部复杂的流动情况。从机理上解释了激波形成的条件，及其对喷射式热泵性能的影响。通过调整喷射式热泵结构，避免了吸收室内回流区的形成，从而将喷射系数提高4％。     

Influence of Pressure and Temperature on the Velocity of a Turbulent Jet Flow 3D

To investigate the influence of pressure and temperature on the jet velocity of a three-dimensional flow was the main goal of this study. Using a precipitation chamber with approximate capacity of 600 mL, it was studied the thermodynamic behavior of supercritical carbon dioxide mixture, dichloromethane and grape seed extract via SAS （supercritical antisolvent process）. For the numerical solution, the Navier-Stokes equations were used along with the model of turbulence k-ε and Peng-Robinson equation of state with quadratic mixing rules of Van der Waals. The method of Chung was employed to determine the viscosity, thermal conductivity and mass diffusivity of the flow numerically solved through commercial code based on CFD （computational fluid dynamics）. Simulations for pressures between 80 bar and 160 bar and temperatures between 308.15 K and 318.15 K showed large variations in the jet velocity, an important property in the dynamic mixing process that involves the size, size distribution and particle morphology.     

基于CFD的液固两相流冲刷腐蚀预测研究

为了分析液固两相流中固体颗粒对设备的冲刷腐蚀现象,基于湍动能和耗散率方程,利用RNGk-ε湍流模型,对整个喷嘴冲击模型区域进行了全三维粘性流动模拟,采用FLUENT软件中随机轨道模型对喷嘴,中击模型中的离散相颗粒进行追踪,模拟分析了液固两相流中固体颗粒对样本平面的水平冲刷速度和冲刷角度的分布规律。将模拟数据代入腐蚀率函数得到模拟腐蚀率,与实验数据进行对比,预测结果与实验结果吻合,为液固两相流冲刷腐蚀预测提供理论基础。     

De- and rehydration of Ca(OH)2 in a reactor with direct heat transfer for thermo-chemical heat storage. Part B: Validation of model

Heat storage technologies are used to improve energy efficiency of power plants and recovery of process heat. Storing thermal energy by reversible thermo-chemical reactions offers a promising option for high storage capacities especially at high temperatures. Due to its low material cost the use of the gas–solid reaction Ca(OH)₂ ? CaO + H₂O has been suggested. In Part A of this work the thermal behavior of a reactor with direct heat transfer was experimentally investigated. In this part a two-dimensional model is applied for the specified system. The experimental and simulated results during the exothermic hydration are discussed in order to confirm the validity of the model. The model is validated regarding heat transfer, integral reaction rate and maximum temperatures. In addition, an adaptation of the kinetic equation is proposed in order to take into account rate-limiting effects due to agglomeration in the powder bed.     

Experimental Study and CFD Modeling of Wall Deposition in a Spray Dryer

The wall deposition phenomenon in a pilot-scale spray dryer was investigated based on mathematical modeling and experimental trials. For this purpose, the governing equations were obtained and solved numerically by applying a mathematical modeling technique and an open-source computational fluid dynamics (CFD) software. The wall deposition, velocity distribution of the existing phases, and droplet trajectory in the drying chamber were determined. The effect of the operating parameters including the feed flow rate, inlet concentration of dissolved solid, and initial droplet diameter on the air flow pattern, droplet trajectory, and wall deposition was investigated. Through the experiments, the wall deposition of powder product in different positions of the drying chamber was measured. In modeling part of this study, we attempted to determine the effect of particle diameter on the percentage of wall deposition and the position where it occurred.

The model results obtained for wall deposition were compared with collected experimental data and good agreement was observed.     

Study on Drying Organic Sludges by Thermal Jet Dryer—Part 2: Characteristics of Air-Particle Multiphase Flow in Thermal Jet Dryer

The authors are developing a thermal jet dryer (TJD) with a vertical disc-shaped drying tank for the purpose of reducing the volume of solid wastes with high water content, such as organic sludges. In order to obtain the characteristics of air-particle multiphase flow in a TJD, cold model experiments and computational fluid dynamics (CFD) simulations were conducted. The following results were obtained: (1) A combined eddy was generated in the tank, such as in a cyclone separator. (2) “Cascading” phenomena occurred in the particle discharging mechanism. (3) In the TJD, particles maintained consistent drying conditions throughout the drying process.     

Numerical analysis of transport phenomena for designing of ejector in PEM forklift system

In the present study, Computational Fluid Dynamics (CFD) technique is used to design an ejector for anode recirculation in an automotive PEMFC system. A CFD model is firstly established and tested against well-documented and relevant solutions from the literature, and then used for different ejector geometries under different operating conditions. Results showed that a single ejector with optimized geometry cannot cover the required recirculation in the entire range of the fuel cell current. Having two ejectors for different ranges of currents is thus proposed as an alternative solution in which the system can better take the advantage of ejectors for recirculation purpose. In addition, the operating mode of one variable nozzle ejector has been investigated and compared with aforementioned cases. The results showed that the variable nozzle ejector can work in the same operational mode as in the case with two ejectors. However, in practice, the latter one needs a more complicated control system and it is more difficult to manufacture.     

Numerical analysis of a 20-kWe biogas steam reformer in PEMFC applications

This study supports the development of a 20-kW_e biogas reformer for PEMFC applications. Biogas contains a high concentration of carbon dioxide (CO₂) in the feedstock, which can act as a reforming agent but increases the carbon monoxide (CO) concentration in the product. The feedstock composition and the external heat supply impact both the methane (CH₄) conversion and the CO concentration in the product; thus, a numerical model is developed to investigate these impacts. As the CO₂ content in the feedstock or the external heat supply increases, both the CH₄ conversion and the CO concentration in the product increase. A high CO₂ concentration or a high operating temperature stimulates the reforming reactions but also shifts the equilibrium to favor CO production. However, the performance can be improved by controlling the heat supply method. Using a more uniform temperature distribution at approximately 650 °C, the CO concentration decreases while the CH₄ conversion increases. This finding suggests the importance of temperature control in biogas steam reforming.     

循环流化床锅炉选择性非催化还原脱硝工艺喷氨流场数值模拟研究

针对具体的工程项目,采用流场分析软件FLUENT,研究了喷嘴各参数对喷射流型的影响,同时研究了各种喷嘴布置对氨在旋风分离器及其下游烟道中分布的影响。研究表明,如果选择合适的喷嘴,优化喷氨点布置,使氨在锅炉炉内分布得更均匀,充分地与氮氧化物接触,可得到较高的系统脱硝率。