超微玉米秸秆的沉降稳定性及产氢能力研究

以红螺菌科光合细菌为实验菌种,以超微玉米秸秆为产氢底物,研究超微玉米秸秆的沉降稳定性及产氢能力,结果表明超微粉碎时间越长,颗粒度越小,超微玉米秸秆的比重和沉降速度越大,且超微粉碎技术可增大光合细菌和玉米秸秆的接触面积,提高光合细菌的产氢能力,但粉碎粒度太小,超微秸秆内部具有较强的凝聚作用,玉米秸秆的稳定性降低,超微玉米秸秆沉积于反应器底部,难以及时被分解利用,最佳粉碎时间60~80 min。     

复合微生物预处理玉米秸秆产沼气的试验研究

利用白腐菌、木霉菌以及白腐菌和木霉菌复合菌在相同的条件下对玉米秸秆进行预处理,对预处理后的秸秆进行厌氧发酵制取沼气。结果表明,利用微生物进行秸秆预处理能促进秸秆厌氧发酵产沼气的进程,提高产气量和产气效率,其中以混合菌预处理效果最好,产气量比未经预处理秸秆的产气量提高11.95%、产气时间提前6 d、产气高峰期提前16 d,容积产气率达到1.196 mL/(mL.d),原料产气率达到518.33 mL/g。仅利用白腐菌进行秸秆预处理也具有良好的效果,而利用木霉进行秸秆预处理对厌氧发酵的促进作用效果较差。说明利用木质素降解菌株进行秸秆预处理对提高秸秆的厌氧发酵效率具有重要的作用。     

玉米秸秆鼓泡床内快速热解过程数值模拟研究

采用数值模拟对鼓泡床内玉米秸秆快速热解过程进行描述并对产物分布进行预测,深入了解高温热解反应器内气固流动特性及传热传质过程,进而对系统运行参数进行优化设计。模拟结果表明,流化风风速决定秸秆颗粒在反应器内的运动轨迹;床内平均空隙度的变化可影响床内换热过程,形成热解产物产率分布的差异。实验结果对比表明数值模拟在定量分析准确度上仍需进一步提高。     

相变蓄热装置内温度场的模拟与实验研究

对螺旋盘管相变蓄热装置性能和相变材料(PCM)的传热特性开展模拟和实验研究,建立相变蓄热装置物理和数学模型,对蓄热温度场进行了数值模拟和实验测试。结果表明:自然对流换热对PCM的熔化过程影响很大,当考虑自然对流时,相变蓄热速率加快,相变分层现象明显;实验实测温度与模拟温度相近,说明所建立的模型适用于相变装置内部温度场的模拟。     

化学气相沉积制备多壁碳纳米管反应器内流场的数值模拟

建立制备多壁碳纳米管CVD反应器的二维几何模型,将参与反应物的材料参数拟合为随温度变化的非线性多项式方程,采用计算流体力学软件对反应器内部的温度场及速度场进行模拟研究。研究结果表明:反应器内温度场及速度场分布并不均匀,在反应器中部温度较为均匀温度基本维持在1 100 K左右,这样有助于多壁碳纳米管的合成,同时对于速度场的研究发现合理的控制气体进口速度有助于碳纳米管在均匀流场中稳定生长。     

相变蓄热装置内部温度场的理论与实验研究

对螺旋盘管相变蓄热装置性能和相变材料 (PCM)的传热特性开展理论和试验研究,建立相变蓄热装置物理和数学模型,对蓄热温度场进行了数值模拟和实验测试。结果表明 ：自然对流换热对PCM的熔化过程影响很大,当考虑自然对流时,相变蓄热速率加快,相变分层现象明显;实验实测温度与模拟温度相近,说明所建立的模型适用于相变装置内部温度场的模拟。     

高温铝水反应器内反应与传热过程建模及计算

对一种典型的高温熔融铝水反应器内部反应和传热过程进行建模研究,以分析反应器内部的热特性。建立了铝液与水的反应过程和传热过程物理及数学模型,设计了水滴蒸发和反应以及传热过程的程序算法和耦合算法,并利用Visual Basic语言编制了模拟计算软件,应用该软件对反应器的关键运行参数进行了模拟计算。结果表明:反应进水质量流量与反应器的壁面最高温度呈正相关,而冷却水质量流量与壁面最高温度呈负相关;计算结果与实验结果吻合较好。     

利用Fluent软件建立蓄热体数学模型的研究

利用Fluent软件建立通用性较佳的蓄热体的数学模型,所得到的模拟数据通过可视化处理可清晰直观地显示出蓄热体与流体传热过程中的温度场及流场的变化,弥补了实验手段的不足。     

生物质及其热裂解产物生物油的特性分析

以红松、白松、落叶松、玉米秸秆等不同生物质为原料,对流化床反应器热裂解制取的生物油进行了研究试验,通过对生物油的物理特性及其成分的分析,得出的实验结果表明:红松制取的生物油品质最好,热值高,含水率低,更适合进一步改性研究和应用,并利用现代精密仪器GC-MS对生物油进行了组分分析,解释了生物油高含氧和高含水特性。     

采用热重与红外光谱联用研究玉米秸秆热解

采用热重与红外光谱联用技术(TG—FTIR),在升温速率为20℃/min下,对玉米秸秆各部分(秸秆皮、秸秆瓤、叶子及苞叶)的热解产物及析出过程进行了实验研究。实验结果表明,玉米秸秆各部分的热解产物主要为CO2、CO、CH4、H2O,同时含有少量的丙酸类物质;秸秆皮和秸秆瓤热解气体的析出呈单峰形状,而叶子和苞叶热解气体的析出呈双峰形状;玉米秸秆各部分的热解最大失重率对应的热解温度约为360～371℃,相差较小;对玉米秸秆的同一部分,主要热解产物的最大失重率对应的热解温度基本相同。     

Removal of K and Cl by leaching of straw char

A pretreatment process to remove potassium from straw fuel may be based on pyrolysis followed by char wash. The straw is pyrolysed at moderate temperatures at which the potassium is retained in the char. Potassium and residual chlorine are extracted from the residual char by water. Char and pyrolysis gases may then be used in a conventional boiler without problems due to the high straw potassium content. To evaluate this pretreatment process knowledge about the char wash process is needed. In this study wheat straw chars were experimentally investigated in the laboratory to determine the extraction time of potassium and chlorine during char wash with water. The influence of particle size, water temperature, straw type, potassium content in water and pyrolysis conditions were investigated. Based on the experimental data a mathematical model describing the extraction, was developed. The laboratory experiments showed that three fractions of potassium in the straw reacted differently: 35–58% of the char potassium was dissolved very fast, followed by a secondary slow potassium release that was strongly influenced by particle sizes, water temperature, char type and water KCl content. The residual 5–10% of the char potassium remains in the char and could not be removed with pure water.     

Self-heating in a bioreactor: Coupling of heat and mass transfer with turbulent convection

A tridimensional mathematical model that considers the turbulent flow inside a bioreactor of municipal waste material (MWM) is studied. The MWM is self-heating by the biological activity of micro-organisms. The model includes the unsteady solution of the turbulent flow field inside the reactor, the energy transport in the flow and the ensuing heat and mass transfer by convection over the MWM load. The MWM is treated as a porous medium and the oxygen depletion and heat generation produced by aerobic bacteria are also included. Turbulence treatment is done with the κ–ε model. The numerical simulation shows good agreement with experimental measurements available. The results also shed light over some design criteria that can be explored in order to increase the efficiency of the process.     

Ground heat exchanger temperature distribution analysis and experimental verification

The underground two-dimensional symmetry temperature field of a vertical double spiral coil ground heat exchanger (GHX) designed by the authors for a ground source heat pump (GSHP) system was simulated using the volume-control method. A heat transfer model of underground coil is made, and the underground temperature distribution of the coil was solved numerically. Experimental temperature data are measured. The analytical results are compared thoroughly with the experimental data. The mathematical mode presented herein may provide design guidance for the design of GHX for GSHP systems.     

熔融碳酸盐燃料电池动态性能数值模拟

建立了正确描述带有热量生成、质量迁移以及电化学反应特性的三维变参数燃料电池动态数学模型,并采用数值模拟方法,对燃料电池温度、速度分布等性能进行预报。通过实验研究,获取燃料电池发电系统输出性能以及温度分布等实验数据,并将数值计算结果与实验结果进行对比分析,验证了数值模拟的准确性,证明了采用的数学模型具有较高的可靠性。     

Three-dimensional model for numerical analysis of thermal phenomena in laser–arc hybrid welding process

This paper describes mathematical and numerical models of thermal phenomena developed for computational analysis of the laser–arc hybrid welding process. The mathematical and numerical models were established to estimate temperature field and velocity field of melted material in the welding pool. Different heat source power distribution models for electric arc and laser beam, latent heat of fusion and latent heat of evaporation as well as buoyancy and liquid material flow through a porous medium were taken into consideration in the computational model. The results of computer simulation of laser–arc hybrid welding process, including temperature field and melted material velocity field, are presented in this study. The correctness of elaborated models is verified by experimental results.     

Analysis of heat and mass transport characteristics in anode-supported solid oxide fuel cells at various operating conditions

In this study, the heat and mass transport characteristics of anode-supported solid oxide fuel cells (SOFCs) are numerically investigated by using a two-dimensional model. The mathematical model is validated by comparing the numerical results with experimental data found in the open literature. The species and temperature distributions of SOFCs at different cell voltages are presented and compared. Effects of operating temperature, flow direction arrangement, and flow velocity on the overall cell performance and local temperature distribution are also analyzed. It is concluded that the local temperature is increased with decreasing operating cell voltage, increasing operating temperature, and decreasing cathode flow velocity. The temperature distribution is significantly changed when counter-flow arrangement is used instead of coflow arrangement. In addition, the effect of anode flow velocity on temperature distribution is negligible.     

Thermofluidynamic modelling of hydrogen absorption in metal hydride beds by using multiphysics software

In this study, a performance analysis of metal hydride reactors (MHRs) based hydrogen storage during absorption process is presented. The study shows the effect of using heat pipe and fins for enhancing heat transfer inside MHRs at various hydrogen supply pressures. Three different cylindrical MHR configurations using LaNi₅ as a storage media were adopted including: i) reactor cooled by means of natural convection, ii) reactor equipped with a heat pipe along its central axis, iii) reactor equipped with finned heat pipe. A 3-D mathematical model is developed and utilized to simulate the thermofluidynamic behaviour of a metal hydride bed. The simulation study is conducted by solving simultaneously the energy, mass, momentum, and kinetic differential equations of conservation by using COMSOL multiphysics 5.2a software. Parameters such as hydrogen stored capacity, internal temperature distribution for the reactor, and their duration have been optimized. The model was validated against experimental result which have been previously published by the authors. The obtained results confirmed that the simulation and experimental results reasonably match where the maximum error vlaue was less than 8% at 10-bar hydrogen supply pressure, which proves that the model has efficiently captured the key experimental trends. On the other hand, the MHR design, which is equipped with a finned heat pipe is shown a superior performance as compared to all the other tested configurations in terms of charging time and storage capacity. Therefore, the model can be used as a helpful tool in the optimization of the MHR designs and performance.     

Heating and Flow Analysis in Hot‐Rolled Stainless Strip Continuous Annealing Furnace Based on CFD Modeling

A three‐dimensional mathematical model was found for a continuous annealing furnace, the temperature field, and flow field of the furnace and the temperature of the stainless strip could be calculated by using this model. The simulation results were compared with measured data and the accuracy of the model was proved by the predicted temperature distribution. By using this model, the convective heat transfer coefficient and equivalent radiation heat transfer coefficient of the strip surface were also analyzed.     

Mathematical modelling of a hydrocracking reactor for triglyceride conversion to biofuel: model establishment and validation

In the study, a 2D, non‐isothermal, heterogeneous model of a triglyceride hydrocracking reactor is investigated. The internal heat and mass transfer within the phases in the reactor were considered using the film theory. The conservation equations for energy and mass were solved simultaneously using appropriate numerical techniques whose reliability was assessed by comparison of the results with previously reported experimental data. The modelling was performed with consideration of two proposed hydrocracking kinetic models. The model predictions showed reasonable correlation with published experimental data and conversion rates. The calculations indicated that at feed temperature of 380 °C, liquid hourly space velocity of 8 h^?1 and hydrogen : feed ratio of 1500:1, the total triglyceride conversion was 82.54% for four major classes of hydrocarbons (light, middle, heavy and oligomerised). In addition, the concentration distribution and temperature profile along the reactor were investigated. The product concentrations along the reactor show that higher rates of production at the beginning of the reactor were achieved because of high concentration of triglyceride due to the exothermic hydrocracking reactions and counter‐current flow modes of triglyceride and hydrogen; a jump of 90 °C was shown at the beginning of the reactor temperature profile. Copyright © 2014 John Wiley & Sons, Ltd.