喷射火焰环境下液化气容器的热响应

利用ＰＬＧＳ数值模拟程序,引入喷射火焰环境下的容器外部边界条件,对盛有丙烷的水平圆柱体在喷射火焰环境下的热响应进行了数值模拟。模拟结果与实验结果吻合良好,为有效防止液化气泄漏、容器爆炸及火灾事故提供必要的理论依据。     

热冲击下LPG储罐力学响应研究

液化石油气(LPG)储罐在遭受火焰侵袭时通常会面临较为恶劣的环境.在高温和内压作用下,金属材料强度下降,罐体将会出现局部屈服变形,严重时可能会发生破裂甚至爆炸.对储罐在喷射火焰下其壁面的力学响应规律进行了研究,在分析壁面应力产生机理的同时,利用有限元分析ANSYS软件对该物理过程进行了数值模拟,得出了壁面不同位置的应力分布.结果表明:在喷射火焰情形下,LPG储罐的力学响应与火焰的喷射方向有关,面向火焰一侧的壁面由于温度上升更快,材料强度下降的速度也较快,故较之背向火焰一侧的壁面发生破坏的可能性增大;另外,储罐壁面顶部附近由于温度最高,材料的强度下降最明显,因此发生破坏的可能性最大.     

燃油喷射特性数值模拟与实验验证

基于STAR-CD对燃油喷射进行三维两相流数值模拟,利用高速摄影对定容室内喷雾过程进行了研究分析.比较了喷雾特性的模拟计算结果和实验图片,验证了模型的正确性.分析了喷射压力、缸内温度和喷孔直径对喷雾特性的影响.通过研究,获得了喷雾贯穿距和索特平均直径随喷射、环境条件和喷嘴几何参数变化的一般规律.     

蒸汽喷射压缩器性能的三维数值模拟

通过对蒸汽喷射压缩器内流场进行三维数值模拟,对初步设计的蒸汽喷射压缩器进行结构优化,并研究了结构参数、工况参数和调节锥对喷射器工作性能的影响.结果 表明:混合室直径和喷嘴出口到混合室入口间距是影响喷射器性能的两个关键参数;降低工作蒸汽压力、提高引射蒸汽压力和降低背压都能够使喷射系数升高;使用调节锥能够在一定程度上提高喷...     

汽油缸内喷射喷雾特性的三维数值模拟

用三维计算流体力学软件模拟了汽油缸内喷射的静态喷雾特性 ,研究了燃烧室压力、初始液滴直径和喷雾锥角对喷雾特性的影响 ,并与试验结果进行了比较。研究结果表明 :燃烧室压力、初始液滴直径和喷雾锥角对喷雾特性有较大影响     

135型四气门直喷式柴油机二次喷射燃烧数值模拟计算

以KIVA-3V为计算平台,对135型四气门直喷式柴油机二次喷射燃烧做了数值模拟计算.结果表明：燃油气基本上是由中心向外扩散并消耗掉,而氧气则是由中心向外被消耗掉,氧气的分布与燃油气有很大的联系,截面的不同会产生一些差异,在分析的过程中进行了对照.     

二甲醚发动机燃油喷射过程的数值模拟及其试验研究

针对采用普通油泵—油管—油嘴燃油系统的二甲醚发动机,建立了燃油喷射过程的数学模型,通过对不同工况下燃用DME和柴油的燃油喷射过程的数值模拟与计算结果的试验验证,揭示了二甲醚发动机燃油喷射过程的物理本质及其特性参数的变化规律。研究表明,由于DME具有较高的可压缩性,致使其泵端与嘴端压力上升及下降都较柴油缓慢,压力上升始点延迟,实际喷油始点滞后,嘴端油管压力峰值较低,高压油管中的残余压力较高,较易出现二次喷射现象。     

液化石油气发动机燃油喷射过程的数值模拟及其试验研究

针对采用普通泵-管-嘴燃油系统的液化石油气(LPG)直喷式发动机,建立了考虑高压油泵柱塞偶件燃油泄漏量影响的燃油系统数学模型,并对燃油喷射过程进行了模拟计算及其计算结果的试验验证,揭示了LPG发动机燃油喷射过程的基本规律与工作特征。研究表明:由于LPG具有较高的饱和蒸汽压和可压缩性,致使其压力上升和下降都比较缓慢,供油持续期加长,油管内燃油残余压力较高,压力波动较大,容易发生二次喷射;通过增大出油阀卸载容积的办法,可以消除LPG的二次喷射等异常喷射现象。     

圆柱形内肋强化换热数值模拟与火积耗散分析

对内肋管内部流体的湍流换热过程进行了数值模拟,讨论了肋高和肋的轴向夹角对换热的影响。相比于普通圆管,内肋圆管内的传热性能明显得到提高。无量纲肋高度和角度分别为0.8°和40°时传热效果最佳,而在0.1°和40°时换热与阻力的比值(Performance Evaluation Criteria,PEC)最大,综合换热性能最佳,可用于强化地源热泵地埋管换热。此外,本研究从火积耗散与传热效率的角度分析了内肋强化传热机理,得到管壁冷却管内流体的火积传递效率计算式,为内肋管强化换热的深入分析提供了依据。     

柴油机多脉冲喷射预混燃烧过程多维数值模拟

建立了三维CFD耦合化学反应动力学模型,对柴油机缸内多脉冲喷射形成的预混燃烧过程进行了模拟,结果表明:该模型能够较准确地预测缸压曲线、着火时刻、NOx和CO2排放,能够预测着火位置、燃烧中间产物和有害排放物的生成历程.多脉冲喷射预混燃烧产生的NOx、CO和未燃HC排放主要来源于靠近缸壁余隙内,要提高这种燃烧方式的效率和降低排放,关键是要减少燃油附壁.     

Numerical simulation on liquid jet behavior issued into still air

Numerical simulations have been conducted to clarify the effects of turbulence, in the onset of protrusions on liquid jet surfaces. The turbulences in the liquid jet were simulated by the Rankin vortices. The liquid jet surface was tracked numerically by the VOF method. From numerical simulations, the protrusions on the liquid jet surface are induced by the vortices in the liquid, whose rotational direction decelerates the jet surface. Despite the distance between vortices, the displacement of the liquid jet surface from the initial surface location increases linearly, in time, at almost the same growth rate. In the initial region, the growth rate of the displacement increases as the major semiaxis‐to‐minor semiaxis ratio of the ellipsoidal vortex increases. The initial growth rate of displacement is almost proportional to the vortex intensity. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(2): 141–152, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10078     

室内燃气火灾的数值模拟研究

通过采用FLUENT软件进行数值模拟计算的方法,将实际房间进行简化和抽象,建立模型用丙烷代替液化石油气作为燃料,来研究室内燃气火灾火焰蔓延过程。运用通用有限速率燃烧模型和大涡模拟模型来模拟750mm×500mm×50mm与750mm×500mm×250mm的箱体,研究了反应热、化学反应速率、火焰面分布以及箱体内各组分质量分数的分布,发现化学反应速率与反应热的变化趋势是一致的,大箱体的火焰面发展较小箱体快并且燃烧充分。     

Numerical simulation on the behavior of a liquid jet into an air flow

A numerical simulation has been performed to clarify the effects of turbulence in a liquid on the deformation of the liquid jet surface into an air flow. The turbulences in the liquid jet were simulated by the Rankin vortices, and the liquid jet surface was tracked numerically by the volume of fluid method. By numerical simulations, the onset of the protrusions on the liquid jet surface is caused by the vortices in the liquid, and the surrounding air flow plays an important role in the amplification of the protrusions. The amplification rate of the trough displacement is proportional to the air‐to‐liquid velocity ratio. At large imposed vortex intensities, the trough displacement increases with the vortex intensity. On the other hand, at small imposed vortex intensities, the amplification of the trough displacement is also affected by factors other than vortex intensity. © 2001 Scripta Technica, Heat Trans Asian Res, 30(6): 473–484, 2001     

汽油发动机燃用LPG的燃烧性能数值模拟及试验研究

应用GT-POWER软件和化学动力学软件CHEMKIN建立了汽油发动机工作过程计算模型,并用试验结果进行了验证。在此基础上对汽油发动机燃烧LPG时的动力性能及经济性能进行了变参数研究。模拟结果表明,在相同工况条件下,随着压缩比的增大,燃用LPG发动机的经济性和动力性能都有所提高,但同时爆震指数也相应增加。随着空燃比的增加,发动机的经济性能和动力性能均先提高后降低,空燃比对缸内层流燃烧速度和绝热火焰温度影响较大。     

LPG碰壁喷雾的试验及数值模拟研究

基于离散液滴模型(DDM),并结合柴油机实际工作情况,建立了喷雾碰壁的数学模型.将该模型与KIVA程序耦合,对多种形态的喷雾碰壁进行了模拟计算.在压力定容室内,利用PIV高速摄影技术对液化石油气(LPG)和柴油的碰壁喷雾过程进行了试验研究.将模拟与试验结果进行了对比分析,并着重考察了碰壁角度对燃料碰壁过程的影响,获得了LPG喷雾碰壁特性的一般规律.与柴油相比,在同样条件下,LPG能在壁面上溅起较厚的液滴雾层,且溅起的液滴尺寸较小,在壁面上附着的油膜厚度较薄,说明LPG比柴油蒸发速度快,雾化质量好;随着碰壁喷雾倾斜角的增大,2种燃料在碰撞点壁面附近所产生的液滴数显著减少.     

机械式搅拌锌浸出槽内流场和停留时间的数值模拟

采用标准的k-ε湍流模型、多重参考系稳态流动方法,对锌浸出槽内流动过程进行了数值模拟研究,并且采用示踪剂法,研究了流体在槽内停留时间的分布。模拟结果表明:浸出槽无阻尼板时槽内流体主要以周向流动为主,桨叶承受的压力较大,流体在槽内有局部"短路"现象出现。增加阻尼板后,流体在槽内由原来的周向流动为主转变为轴向流动为主,加速了槽内矿浆的混合,桨叶承受的压力明显降低,其最大压力降低15%,平均压力降低57%,流体在槽内停留时间分布与无阻尼板基本相同,但平均停留时间略有增大,有利于浸出过程的进行。     

Experimental and numerical investigations of hydrogen jet fire in a vented compartment

Hydrogen fires may pose serious safety issues in vented compartments of nuclear reactor containment and fuel cell systems under hypothetical accidents. Experimental studies on vented hydrogen fires have been performed with the HYKA test facility at Karlsruhe Institute of Technology (KIT) within Work Package 4 (WP4) - hydrogen jet fire in a confined space of the European HyIndoor project. It has been observed that heat losses of the combustion products can significantly affect the combustion regimes of hydrogen fire as well as the pressure and thermal loads on the confinement structures. Dynamics of turbulent hydrogen jet fire in a vented enclosure was investigated using the CFD code GASFLOW-MPI. Effects of heat losses, including convective heat transfer, steam condensation and thermal radiation, have been studied. The unsteady characteristics of hydrogen jet fires can be successfully captured when the heat transfer mechanisms are considered. Both initial pressure peak and pressure decay were very well predicted compared to the experimental data. A pulsating process of flame extinction due to the consumption of oxygen and then self-ignition due to the inflow of fresh air was captured as well. However, in the adiabatic case without considering the heat loss effects, the pressure and temperature were considerably over-predicted and the major physical phenomena occurring in the combustion enclosure were not able to be reproduced while showing large discrepancies from the experimental observations. The effect of sustained hydrogen release on the jet fire dynamics was also investigated. It indicates that heat losses can have important implications and should be considered in hydrogen combustion simulations.     

Numerical simulation of the effect of LPG blending on the characteristics of a diesel engine

The present work aims to investigate numerically the effect of LPG blending on the characteristics of diesel engines subjected to variable compression ratio, injection timing, and engine speed. Three blends of LPG are used, which are 10% LPG + 90% diesel, 20% LPG + 80% diesel, and 30% LPG + 70% diesel. The numerical investigation is carried out using the simulation software Diesel-RK. Increasing the percentage of LPG in diesel starts combustion early where the lowest delay period is recorded for a blend of 30% LPG + 70% diesel 6.36 deg. The combustion pressure and heat release are decreased due to the difference in the heating values of blended fuels. Although the peak energy release for diesel is 0.05458 (1/deg.) at 375 deg. BTDC, it was 0.0542, 0.05424, and 0.0537 (1/deg.) at 375 deg. BTDC for 10%, 20%, 30% LPG, respectively. Diesel with 30% LPG has a higher spray penetration followed by 20% LPG then 10% LPG and diesel come last. The diesel with 10% LPG gives a 5.35% reduction in NOx, while diesel with 20% and 30% LPG emit less NOx emission by 9.05% and 16.5%, respectively. Increasing the percentage of LPG in diesel yields to reduce soot concentration because LPG has lower carbon to hydrogen ratio. The lowest ability to emit smoke is detected for fuel with 30% LPG where a 7.4% reduction is obtained. It is worth noting that blending LPG with diesel can fight the trade-off relation between Soot-NOx as a reduction in both of them is obtained. Based on the results obtained, the blending ratio is 30% LPG. The obtained results are validated with the results of other researchers.     

Numerical simulation of three-dimensional flow dynamics in a hot water storage tank

A hot water storage device is one of the most common household appliances yet it is also one of the biggest sources of energy consumption. With natural resources fading, it is imperative that typical high-energy users such as hot water systems are made as energy efficient as possible. Research has shown that the thermal performance of a hot water system can be increased by maximising the level of thermal stratification within the storage tank, which could lead to huge energy saving. To analyse the effects of tank geometry and operating conditions on the thermal stratification within a storage tank, seven three-dimensional models have been numerically simulated by using the computational fluid dynamics program Fluent with realistic boundary and initial conditions applied. The level of thermal stratification in each model has been quantified using exergy analyses. The results show that increasing the tanks height/diameter aspect ratio, decreasing inlet/outlet flow rates and moving the inlet/outlet to the outer extremities of the tank all result in increasing levels of thermal stratification.