纯环路型和混合型行波热声发动机的对比实验

研制了以陶瓷为板叠的行波热声发动机实验装置,进行了纯环路型与混合型行波热声发动机热力性能的对比实验研究,分析了系统的起振和消振过程及机理,研究了加热端温度、冷却端温度和回热器对系统性能的影响。结果表明,混合型行波热声发动机比纯环路型行波热声发动机具有更低的起振温度;且随着冷却端温度的升高,系统的起振温度也随着升高;回热器孔径对系统的性能有较大的影响,本实验中回热器孔径为0.8mm时系统起振温度最低;实验过程中还发现了"二次起振"现象。     

外加扰动对热声发动机起振特性的影响

热声发动机利用热声效应将热能转化为声功，系统中没有任何运动部件，具有结构简单、效率高、环境友好等突出优点。为了充分发挥热声发动机可利用低品位热能的优势，进一步降低系统的起振温度对热声热机的应用具有重要意义。该文首次提出利用外加扰动降低系统起振温度的设想，并在自行研制的多功能行波热声发动机实验台上进行了实验验证。初步实验结果表明，外加扰动可以大幅降低热声发动机的起振温度。实验以氮气为工质，当系统充气压力为0．9MPa时，通过加入压力扰动使系统的起振温度由原来的219℃降低到193℃。系统研究了外加扰动对热声发动机整个起振和消振过程的影响，获得的结果对加深热声系统起振机理的认识及热声发动机的实用化研究具有重要的指导意义。     

以氦气为工质的行波热声发动机研究

随着对热声热机研究的深入，特别是行波热声发动机概念的提出，热声发动机效率得到了质的提高。为了实现热声发动机与制冷机的良好匹配，以氦气为工质时热声发动机需具有较低的起振温度、较大的压力波强度、较好的单频率特性。本文对自行研制的新型热声发动机进行了深入研究，以氦气为工质，在充气压力为2．0MPa时获得了1．19的压比，系统频率稳定在约73Hz，为利用新型热声发动机驱动脉管制冷机或其它热声制冷机创造了有利条件。此外，该热声发动机起振温度较低，初步具备了利用工业废热等低品位能源驱动的条件。     

新世纪的发动机——没有运动件的发动机热声斯特林发动机简介

1979年Ceperley首先提出热声斯特林发动机的设想,但是他做的模型未能运转。其后的热声发动机(又称热声热机)采用不可逆驻波热声循环,热效率较低。1999年5月,“NATURE”刊载美国能源部LosAlamos国家试验室科学家S.Backhaus和G.Swift的文章:“热声斯特林热发动机(AthermoacousticStirlingHeatEngine)”,采用可逆斯特林循环热声热机,使热效率大大提高。热声斯特林发动机被认为是21世纪的发动机,将有可能替代传统的发动机——内燃机。国外许多刊物的“未来的发动机”、“没有运动件的发动机”、“无活塞热气机——热声发展的方向”等为题…     

回热器热功转换特性的实验研究

搭建一个实验测试平台,对回热器热声转换特性进行实验研究。实验系统由分别充当压缩机和发电机的多台直线电机及被测的回热器、换热器、热缓冲管等组成。实验对不同加热温度与声场条件下回热器的热声转换特性进行系统的研究。在平均压力为4 MPa时,实验获得的最大净输出声功为688 W,最大热声效率为34.2%。实验结果表明,在同等条件下,回热器加热温度越高,其输出声功越大,同时热声转换效率越高;回热器工作存在最优的声场条件,使其净输出声功与热声效率分别达到最大。     

安装倾角对热声发动机性能影响的试验研究

为充分利用太阳能作为驱动热源,开展了驻波型热声发动机在不同安装倾角下热力性能的试验研究.试验结果表明,热声发动机的安装倾角对热声系统的起振温度、消振温度以及起振时板叠中的温度梯度等参数有着显著的影响,当系统中氮气压力为1.3MPa时,在试验的7种角度下.最高起振温度484℃,最低起振温度428℃,该特性为选择合适角度以降低系统起振温度提供了试验依据;而当系统稳定振荡时,安装倾角的变化对系统的压比和压力振幅等热力特性的影响较小,该特性为利用自动跟踪太阳能集热器在不同角度下驱动稳定振荡的热声发动机创造了有利条件.试验结果为设计太阳能驱动的热声发动机提供了试验依据.     

热声热机的热力学分析

回顾了热声现象的研究历史,介绍了热声热机的结构和分类,基于气体微团的热力学循环和能量转换,分析了热与声功的转换原理、转换条件以及热声热机的工作机理,并指出了该研究领域的工业应用前景。     

换热管周围声流强化对流传热的数值模拟

为研究稳态声流成分对换热管对流换热特性的影响,建立了行波场中单换热管外声流强化传热的数值计算模型.采用分离时间尺度的数值方法模拟了声流和非均匀温度场的耦合作用,分析了换热管局部努塞尔数和平均努塞尔数在不同激励频率(10～1500 Hz)和声压级(103～127 dB)作用下的变化规律.结果 表明:平均努塞尔数随着激励频...     

热声网络的辛矩阵分析北大核心CSCD

对热声分布参数网络模型的传输矩阵进行了辛对称分析。在辛对称的基础上,将传输矩阵转化为阻抗矩阵,利用瑞利商式分析了热声系统各部件的最小本征阻抗,结果表明,阻抗矩阵的最小本征阻抗反映了最小网络损耗。数值计算了回热器和谐振管的结构对最小本征阻抗的影响,并根据计算结果提出了降低最小网络损耗的方法。     

热声发电之直线发电机的理论研究

针对热声发动机驱动直线发电机的热声发电技术中的直线发电机的特性进行了理论研究,考察了驱动频率、负载电阻和活塞直径对发电机性能的影响.研究表明,电路谐振可以提高直线发电机的效率,但机械谐振与否对效率没有影响,并且效率对负载电阻存在最大值.当电路和机械均共振时,输出电功对负载电阻实部存在最大值,此时,增加活塞面积可以增加电功输出.     

Thermo-acoustic velocity coupling in a swirl stabilized gas turbine model combustor

Limit-cycle thermo-acoustic velocity coupling mechanisms are studied in a perfectly-premixed swirl-stabilized combustor using data from 10 kHz repetition-rate stereoscopic particle image velocimetry (S-PIV) and OH planar laser induced fluorescence (PLIF). Five cases over a range of thermal powers and equivalence ratios were investigated, each of which underwent different amplitude limit-cycle oscillations. Proper orthogonal decomposition (POD) of the velocity data showed that each case contained a dynamic helical vortex core (HVC) that rotated around the combustor and greatly affected the flame behavior. Flow and flame statistics were compiled as a function of both the phase in the thermo-acoustic cycle and a phase representing the azimuthal position of the HVC relative to the measurement plane. These data were used to determine the thermo-acoustic energy transfer field at each HVC azimuthal angle, as described by the Rayleigh integral. It was found that periodic deformations of the HVC caused large-scale flame motions, resulting in regions of positive and negative energy transfer. The deformation of the HVC was linked to a swirl number wave that propagated from the burner nozzle. While the mechanism of thermo-acoustic coupling was the same for all cases, the phase between heat release and pressure oscillations varied significantly. This phase relationship was determined by the interaction of the pressure field, swirl wave, HVC deformation, and flame response. It was shown that these can be described by the combination of a Helmholtz resonator and a convective disturbance.     

Multi-field coupling thermo-acoustic radiation using free-standing nano-thin films in a static magnetic field

Abstract

Thermo-acoustic radiation from nano-thin film has been widely reported these years. In this paper, a static magnetic field is introduced to enhance the acoustic power in the multi-field thermo-acoustic generation. The coupled thermo-acoustic system in a static magnetic field shares the same acoustical unit with very few additional components. In the presence of a static magnetic field, thin-film vibration is excited instead of being still in the classical thermo-acoustic system. Not surprisingly, a steady magnetic field has very little impact on the thermo-acoustic generation system when a constant amplitude sinusoidal current is introduced. The oscillation perpendicular to the nano-thin film is driven by the electromagnetic force. The system response of thermo-acoustics and magneto-acoustics can be generally matched when suitable parameters are introduced. The acoustical pressure output can be significantly improved in the presence of a static magnetic field although more electrical input power should be provided in the multi-field thermo-acoustic system. Evidently, the coupled multi-field acoustical system is able to handle more electrical power input and the power input can be more easily dissipated relatively. The results show that the acoustic response of this new multi-filed coupled system can be significantly improved as compared to the classical system without magnetic effects.     

一次表面回热器动态特性的数值模拟与实验研究

对一次表面回热器(Primary Surface Recuperator,PSR)流量阶跃变化时的动态特性进行了数值分析和实验研究.根据能量守恒原理和一次表面回热器(PSR)的结构特点,导出回热器冷热流体和固体间壁非稳态温度变化的微分方程式,研究流体流量发生阶跃变化时PSR的响应时间.在冷热空气进口参数和换热量相同的条件下,当冷热侧流量分别增加为原来3倍的情况下,PSR的响应时间只有管壳式换热器的1/8,板翅式的1/3.数值分析结果与实验结果相符.由于PSR的固体壁面时间常数远小于板翅式和管壳式回热器,因此这种轻重量结构的先进回热器响应特性明显优于常规回热器.     

Steady-State and Transient Investigation of the Primary Surface Recuperator for Microturbines

The aim of this work is to study numerically and experimentally the thermal performance of the primary surface recuperator (PSR) operating under steady and transient conditions. Numerical simulations are carried out to investigate the heat transfer characteristics in the corrugated passages of the primary surface recuperator. The effects of velocity, intersection angle, and pitch-to-height ratio are considered. Numerical simulation of the transient behavior of the PSR is performed as its mass flow rate or hot inlet temperature is subject to a sudden change, which is based on the conservation theorem of energy and its structural characteristics. One prototype of a PSR for experimental purposes has been designed and manufactured, and is used in an experimental setup to carry out the experimental studies. The comparative results show that the low-weight PSR has much more advantages in transient response because its time constant of the solid wall is much less than that of a shell-and-tube recuperator or plate-fin recuperator. The PSR is quite fit for application to the marine or vehicle gas turbine engine that works under changeable conditions.     

微型燃气轮机CW原表面回热器芯体内传热及阻力特性分析

建立微型燃气轮机CW(交叉波浪型,Cross Wavy)原表面回热器三维周期性充分发展数值计算模型,对芯体内传热和阻力特性进行了分析,确定了质量流量和温度水平对换热量及压降的影响,给出了CW原表面芯体板内阻力、传热因子以及努塞尔数与雷诺数之间的经验关联式。传热及阻力性能分析结果表明:随着雷诺数的增大,回热器芯体单元传热系数增大,传热量逐渐增加,并且随着低压高温烟气侧的进口温度升高,传热量增加幅度增大;回热器芯体单元回热度随雷诺数的增大而减小,随燃气进口温度升高而减小。     

Flow-flame interactions causing acoustically coupled heat release fluctuations in a thermo-acoustically unstable gas turbine model combustor

A detailed analysis of the flow-flame interactions associated with acoustically coupled heat-release rate fluctuations was performed for a 10 kW, CH₄/air, swirl stabilized flame in a gas turbine model combustor exhibiting self-excited thermo-acoustic oscillations at 308 Hz. High-speed stereoscopic particle image velocimetry, OH planar laser induced fluorescence, and OH∗ chemiluminescence measurements were performed at a sustained repetition rate of 5 kHz, which was sufficient to resolve the relevant combustor dynamics. Using spatio-temporal proper orthogonal decomposition, it was found that the flow-field contained several simultaneous periodic motions: the reactant flux into the combustion chamber periodically oscillated at the thermo-acoustic frequency (308 Hz), a helical precessing vortex core (PVC) circumscribed the burner nozzle at 515 Hz, and the PVC underwent axial contraction and extension at the thermo-acoustic frequency. The global heat release rate fluctuated at the thermo-acoustic frequency, while the heat release centroid circumscribed the combustor at the difference between the thermo-acoustic and PVC frequencies. Hence, the three-dimensional location of the heat release fluctuations depended on the interaction of the PVC with the flame surface. This motivated the compilation of doubly phase resolved statistics based on the phase of both the acoustic and PVC cycles, which showed highly repeatable periodic flow-flame configurations. These include flames stabilized between the inflow and inner recirculation zone, large-scale flame wrap-up by the PVC, radial deflection of the inflow by the PVC, and combustion in the outer recirculation zones. Large oscillations in the flame surface area were observed at the thermo-accoustic frequency that significantly affected the total heat-release oscillations. By filtering the instantaneous reaction layers at different scales, the importance of the various flow-flame interactions affecting the flame area was determined. The greatest contributor was large-scale elongation of the reaction layers associated with the fluctuating reactant flow rate, which accounted for approximately 50% of the fluctuations. The remaining 50% was distributed between fine scale stochastic corrugation and large-scale corrugation due to the PVC.     

Low-cost compact primary surface recuperator concept for microturbines

By the year 2000, microturbines in the 25–75 kW power range are projected to find acceptance in large quantities in the distributed power generation field, their major attributes include low emissions, multifuel capability, compact size, high reliability and low maintenance. For this type of small turbogenerator, an exhaust heat recovery recuperator is mandatory in order to realize a thermal efficiency of 30% or higher. The paramount requirements for the recuperator are low cost and high effectiveness. These characteristics must be accomplished with a heat exchanger that has good reliability, high performance potential, compact size, light weight, proven structural integrity, and adaptability to automated high volume production methods. In this paper, a recuperator concept is discussed that meets the demanding requirements for microturbines. The proposed stamped and folded metal foil primary surface recuperator concept has as its genesis, a prototype heat exchanger module that was fabricated as part of an energy research program in Germany over two decades ago. This novel heat exchanger approach was clearly ahead of its time, and lacking an application in the late 1970s was, alas, not pursued and commercialized. Based on this earlier work, a further evolution of the basic concept is proposed, with emphasis placed on the following: (1) minimization of the number of parts, (2) use of a continuous fabrication process, (3) matrix overall shape and envelope flexibility (annular or platular geometry), (4) ease of turbogenerator/recuperator integration, and (5) a later embodiment of a bi-metallic approach, towards the goal of establishing a compact and cost-effective recuperator for the new class of very small gas turbines that are close to entering service. For a representative microturbine, an annular recuperator would have only five basic parts. The matrix cartridge would be essentially a plug-in component, analogous to an automobile oil filter element. In this paper, the important role that the recuperator has on turbogenerator performance is discussed, together with a summary of the early prototype heat exchanger development. The major requirements, features and cost goals for a compact primary surface recuperator for microturbine service, are also covered.     

A novel Swiss-Roll recuperator for the microturbine engine

The design and analysis of a Swiss-Roll recuperator are investigated using a theoretical approach, numerical simulation and an experimental approach. The novel Swiss-Roll recuperator is a primary surface-type heat exchanger for micro gas turbine engines. The preliminary design of the Swiss-Roll recuperator, which is based on theoretical analysis, provides the required channel width, number of turns and number of transfer units (NTUs) for a given effectiveness. Friction causing a pressure loss is also predicted. For a given recuperator design, model simulation was performed to provide insights and improve model performance. Comparison of numerical results and theoretical predictions for efficiency of heat recovery shows a 10% error; however, pressure drop predictions were consistent. Test results show that the engine with a recuperator has a thermal efficiency of 27%. Fuel consumption rate is 600 ml/min. Conversely, a microturbine without a recuperator has a thermal efficiency of 12%, and fuel consumption rate is 800 ml/min. This experimental result indicates the engine with a recuperator use at least 1.5 times less fuel than an engine without a recuperator. This experimental result is consistent with predictions from analytical and numerical solutions. An engine with a recuperator saves energy, is economical and produces low amounts of emissions.     

4E Multi‐objective Optimization of Cogeneration Plant with Details Modeling of Recuperator

There are many works on improving the performance of a cogeneration plant such as the implementation of a recuperator. In previous works, the authors modelled a gas turbine cycle considering the recuperator as a black box. In this paper, a cogeneration plant is modeled and optimized with details of recuperator parameters. For this purpose, 13 design variables for a plant as well as a recuperator are selected. Then, a genetic algorithm is applied to optimize exergy efficiency and total cost rate, simultaneously. This work included Energy, Economy, and Environmental factors which with Exergy provided 4E analysis. A 36% decrease in total cost and a 33% increase in exergy efficiency in comparison with a simple gas turbine system were found. The above results for a gas turbine with a preheater and inlet cooling system reveal a 36% decrease in total cost and 35% increases in exergy efficiency. In addition, the optimum recuperator design parameters reveal that, higher effectiveness is more important than the investment cost. Moreover, a plant with higher exergy efficiency needs a recuperator with a lower pressure drop. Finally sensitivity analysis for variation of objectives functions with a change in fuel cost and interest rate are performed.     

Operating conditions of an open and direct solar thermal Brayton cycle with optimised cavity receiver and recuperator

The small-scale open and direct solar thermal Brayton cycle with recuperator has several advantages, including low cost, low operation and maintenance costs and it is highly recommended. The main disadvantages of this cycle are the pressure losses in the recuperator and receiver, turbomachine efficiencies and recuperator effectiveness, which limit the net power output of such a system. The irreversibilities of the solar thermal Brayton cycle are mainly due to heat transfer across a finite temperature difference and fluid friction. In this paper, thermodynamic optimisation is applied to concentrate on these disadvantages in order to optimise the receiver and recuperator and to maximise the net power output of the system at various steady-state conditions, limited to various constraints. The effects of wind, receiver inclination, rim angle, atmospheric temperature and pressure, recuperator height, solar irradiance and concentration ratio on the optimum geometries and performance were investigated. The dynamic trajectory optimisation method was applied. Operating points of a standard micro-turbine operating at its highest compressor efficiency and a parabolic dish concentrator diameter of 16 m were considered. The optimum geometries, minimum irreversibility rates and maximum receiver surface temperatures of the optimised systems are shown. For an environment with specific conditions and constraints, there exists an optimum receiver and recuperator geometry so that the system produces maximum net power output.