Numerical simulation of the two-dimensional flow in high pressure catalytic combustor for gas turbine

The objective of this paper is modeling the mechanism of high pressure and high temperature catalytic oxidation of natural gas, or methane. The model is two-dimensional steady-state, and includes axial and radial convection and diffusion of mass, momentum and energy, as well as homogeneous (gas phase) and heterogeneous (gas surface) single step irreversible chemical reactions within a catalyst channel. Experimental investigations were also made of natural gas, or methane combustion in the presence of Mn-substituted hexaaluminate catalysts. Axial profiles of catalyst wall temperature, and gas temperature and gas composition for a range of gas turbine combustor operating conditions have been obtained for comparison with and development of a computer model of catalytic combustion. Numerical calculation results for atmospheric pressure agree well with experimental data. The calculations have been extended for high pressure (10 atm) operating conditions of gas turbine.     

Aluminum nitride as an alternative ceramic for fabrication of microchannel heat exchangers: A numerical study

Advances in micro electro mechanical systems (MEMS) necessitate utilizing efficient types of materials which are capable of dissipating high heat transfer rates. Aluminum nitride (AlN) as a member of advanced ceramics family, offers remarkable thermal conductivity which makes it suitable candidate in manufacturing of special and high-tech heat exchangers. The present work aims to investigate the application of a micro-sized heat exchanger made of AlN. According to the performed numerical simulations using Comsol Multiphysics, AlN made heat exchanger showed remarkable heat transfer enhancement of 59%, compared to the Al₂O₃ made one. Such a considerable improvement can be attributed to the higher thermal conductivity of AlN in comparison with Al₂O₃. The effectiveness of the heat exchangers were calculated for both AlN and Al₂O₃ made heat exchangers, and a 26% improvement was observed using aluminum nitride.     

A numerical approach to the heat transfer in monolithic and SiC reinforced HfB2, ZrB2 and TiB2 ceramic cutting tools

Cutting tools are widely used in industry and must be hard enough for machining processes, which should work appropriately at low temperatures to improve cutting speed and productivity. In this research, a numerical method was employed to calculate the temperature distribution in the cutting tools made of different diborides. Monolithic and SiC reinforced HfB₂, ZrB₂ and TiB₂ ceramics were selected for investigation and comparison studies. In this regard, 3-dimensional heat conduction equation was solved in a cutting tool with radiative, convective and heat flux boundary conditions by finite element method using COMSOL Multiphysics. This study clarifies that the maximum temperature in the tools made of ZrB₂ and TiB₂ among the monolithic ceramics is lower than that of HfB₂. Moreover, the temperature variation slope versus time is the highest in HfB₂. All composite materials reinforced with SiC showed lower maximum temperature than the monolithic ones. The thermal performance of TiB₂–SiC and ZrB₂–SiC composites was acquired to be better than that of the other investigated materials. The dominant heat transfer mechanism in the cutting tools was conduction.     

Experimental study on high temperature performances of silica-based ceramic core for single crystal turbine blades

Silica-based ceramic cores are widely utilized for shaping the internal cooling canals of single crystal superalloy turbine blades. The thermal expansion behavior, creep resistance, and high temperature flexural strength are critical for the quality of turbine blades. In this study, the influence of zircon, particle size distribution, and sintering temperature on the high-temperature performance of silica-based ceramic cores were investigated. The results show that zircon is beneficial for narrowing the contraction temperature range and reducing the shrinkage, improving the creep resistance and high-temperature flexural strength significantly. Mixing coarse, medium and fine fused silica powders in a ratio of 5:3:2, not only reduced high temperature contraction, but effectively improved the creep resistance. Properly increasing the sintering temperature can slightly reduce the thermal deformation and improve the high-temperature flexural strength of the silica-based core, but excessively high sintering temperature negatively impacts the creep resistance and high-temperature flexural strength.     

裂解气压缩机蒸汽透平管道的热应力分析

以1996年中国石化齐鲁石化公司烯烃厂450kt／a乙烯装置改造裂解气压缩机蒸汽透平进出口管道为例，探讨了复杂管道系统热应力分析的基本方法、力学模型模拟计算和应力校核基准，并就该系统管道设计进行了较为详尽的热应力分析；分析并总结了减小透平管口受力的方法，为项目的实施提供可行性方案。     

Pore-level numerical simulation of methane-air combustion in a simplified two-layer porous burner

A simplified two-dimensional model of two-layer porous burner based on pore level is developed.The heat transfer of solid phase in porous burner is seen as the synergistic effects of conduction through con-necting bridges and surface radiation between the solid particles in the model.A numerical simulation study on the characteristics of flow,combustion and heat transfer in the two-layer porous burner is car-ried out using the pore level model,and the effects of the control parameters such as the inlet velocity and solid thermal conductivity on thermal non-equilibrium are investigated.The results show that the flame structure is highly two-dimensional based on pore level.Obvious thermal non-equilibrium in the burner for the two phases and solid phase are observed,the largest temperature difference between the gas and solid phases is observed in combustion zone,while the temperature difference inside the solid particles is largest near the flame front.The results also reveal that thermal non-equilibrium of por-ous burner is much affected by the inlet velocity and solid thermal conductivity.     

Industrial gas turbine combustion performance test of DME to use as an alternative fuel for power generation

DME (dimethyl ether, CH₃OCH₃) is both a good alternative fuel for transportation and power generation and an LPG substitute owing to its cleanliness, multi-source productivity and the ease with which it is transported. This study was conducted to verify whether DME is a good fuel for gas turbines and to identify potential problems in fuelling a commercial gas turbine with DME. In this study, the GE7EA gas turbine of the Pyong-tak power plant in Korea was selected as the target of DME application. Combustion performance tests were conducted by comparing DME with methane, which is a major component of natural gas. Most results of the combustion performance tests show that DME is very clean and efficient fuel for gas turbines. However, other results have shown that it is necessary to retrofit a fuel nozzle to the combustor in consideration of the combustion properties of DME in order to enhance the availability and reliability of DME fired gas turbines.     

Microstructure dependent ablation behaviour of precursor derived SiOC ceramic foam for high temperature applications

Ablation behaviour of poly(hydridomethylsiloxane) derived open and closed porous structured SiOC ceramic foams was evaluated using oxy-acetylene flame at 1500 °C for various time durations. X-ray diffraction and scanning electron microscopy analyses of ablated SiOC ceramic foams revealed the formation of a thin protective SiO₂ layer inhibiting further oxidation. The closed porous structured SiOC ceramic foams exhibited very low mass ablation rate in contrast to open porous structured SiOC ceramic foams owing to the differences in thermal energy dissipation mechanism. The feasibility of the plausible foam reduction reactions pertaining to the ablation mechanism was further investigated by computing the Gibbs energy and HR-TEM analysis. The study corroborated the significance of tailoring the microporous structured SiOC ceramic foams as potential thermal protection material for high temperature applications.     

Controlling heat radiation for development of high-temperature insulating materials

Conventional industrial insulating materials have a porous structure, and provide good resistance to conduction. However, at high temperatures greater than 1000 °C, this structure permits heat transfer through radiation. In recent years, many high-performance insulating materials have been developed that consist of nanosized particles and pores. Such materials have a thermal conductivity less than 0.1 W/(m K) up to 800 °C. However, it has very less heat resistance over 1000 °C.In this study, we have developed an insulating material which has a great suppress radiation and its thermal conductivity was less than 0.3 W/(m K) at 1500 °C. The insulating material was considered to be porous magnesium aluminate spinel of two different pore sizes, 0.05–1 and 1–5 μm, with a porosity of 78%. Among the two pores, the 1–5 μm pores were more efficient to restrain heat transfer through radiation.     

Theoretical prediction of temperature-dependent fracture strength for ultra-high temperature ceramic composites considering the evolution of damage and thermal residual stress

Based on the maximum storage energy density criterion of material fracture, a model of temperature-dependent fracture strength for ultra-high temperature ceramic composites is established. The combined impacts of the evolution of damage and thermal residual stress with temperature are considered. The model predictions are highly consistent with available experimental values. Besides, the critical crack sizes of ZrB₂–30 vol%SiC in air from 1400 to 1600 °C are predicted using the proposed model, which agree well with the total oxidation thickness of the reported literature at 1400 and 1500 °C, and a more reasonable definition of critical crack size at 1600 °C are given. Moreover, the quantitative effect of crack size on the fracture strength is analyzed under different environment temperature, and a useful conclusion is obtained that decreasing crack size is more effective to improve the fracture strength of the composites at low temperatures. This study not only provides a feasible and convenient method to predict the fracture strengths at different temperatures, but also offers a theoretical support for the design of ultra-high temperature ceramic composites.     

Development of a slurry injection technique for continuous fibre ultra-high temperature ceramic matrix composites

A simple and effective slurry injection method for producing dense and uniform ultra-high ceramic matrix composites from preforms of high fibre density was developed. As this method is based on slurry injection the homogeneity is not constrained to small preform sizes; dense components of high fibre volume can be produced in theoretically any size and shape. Samples produced by this method demonstrated high and consistent densities, with the injection method obtaining densities an average 27% higher and 87% lower in variability when compared to conventional vacuum impregnation. Tomography demonstrated no bias in the ceramic powder distribution for samples produced by injection, whereas samples produced by vacuum impregnation alone displayed poor powder penetration to the centre of large samples. The new approach yielded composites that were as strong and/or more consistent in strength compared to vacuum impregnation. Thermo-ablative testing demonstrated significant improvements in protective capability for materials produced by this route.     

螺旋扭曲管用于燃气轮机进气温度调节换热器的可行性研究

对将螺旋扭曲管用于燃机进气温度调节换热器进行可行性分析,模拟燃机进气加热器实际运行的工况条件进行综合传热性能实验研究,得到了传热与流阻准则关系式;引入综合评价因子概念并与传统钢铝翅片管换热器进行对比发现,螺旋扭曲管换热器是钢铝翅片管换热器的1.31~1.52倍。以某建设项目采用的E级PG9171E型机组为例,对采用螺旋扭曲管和钢铝翅片管的两种进气温度调节换热器进行对比发现：当采用螺旋扭曲管换热器时,在同样换热能力下,换热器风侧阻力增大了14.7%;在同等质量下,换热器换热能力提高9.9%左右。     

单颗粒褐煤高温烟气干燥过程数值模拟

褐煤干燥对于提高其品质具有重要意义。为了模拟高温烟气干燥这一高温差、变温差非稳态传热传质过程中褐煤内水分蒸发过程,采用有限体积法建立了一维球坐标系下蒸发界面向内迁移的单颗粒褐煤干燥数学模型,并利用该模型分析了初始烟气温度和颗粒粒径对单个褐煤颗粒干燥特性的影响。模型模拟结果与实验结果对比表明二者变化趋势一致,所建模型能较好地反映出高温烟气干燥过程中褐煤内水分蒸发过程。结果表明,初始烟气温度越高,颗粒粒径越小,蒸发界面向内迁移速度越快,水分脱除越快,干燥时间越短;蒸发界面平均迁移速度均与初始烟气温度和颗粒粒径呈线性关系;在初始烟气温度700℃下,较短的停留时间使得颗粒表面温度未达到挥发分析出温度,本研究中不同粒径褐煤颗粒在干燥过程中基本没有挥发分的析出。     

Analysis of purge gas temperature in cyclic TSA process

This study analyzes the effect of an operating parameter on the dynamic behavior by performing dynamic simulations of cyclic thermal swing adsorption (TSA) system, in fixed beds packed with activated carbon as an adsorbent. This TSA process purifies and regenerates the ternary mixtures consisted of benzene, toluene and p-xylene. A mathematical model, considering the dynamic variation and spatial distribution of properties within the bed, has been formulated and described by a set of partial differential algebraic equations. The models are based on non-equilibrium, non-isothermal and non-adiabatic conditions. The breakthrough curves of our simulation model are compared with those of Yun's experiments (1999). The cyclic steady-state (CSS) cycles are obtained for the various cases by cyclic simulation. The influences of the purge gas temperature on breakthrough curves, CSS convergence time, cyclic operating step time, purge gas consumed, regeneration energy requirement and adsorption ability at CSS are also discussed.     

轻质油藏空气驱低温氧化数值模拟研究

通过注空气的室内实验和数值模拟方法研究油层温度场分布特征、含氧剖面、原油性质变化、产出气体组成、采收率等进一步分析低渗油藏注空气驱油机理。研究表明:低温氧化过程热效应相当明显,形成稳定的高温剖面,最高温度达到460℃;氧气被逐渐消耗,氧气浓度由21%逐渐降到0,含氧剖面由注入井逐渐向生产井推进;产生的N2、CO2和CO含量高达97%,气体突破前原油中重质组分和中间组分的含量逐渐减少,轻质组分的含量逐渐增加,部分原油轻质组分被气体所抽提,表现出烟道气驱的特征;当注入1.8PV空气时,采收率可达到47.23%,再进行注空气,增产效果已不明显,可以考虑气水交替或空气泡沫驱油。