基于某百千瓦级微型燃气轮机的HAT循环热力系统设计与分析

为了研究基于微型燃气轮机的湿空气透平(humid air turbine, HAT)循环用于热电联供的热力性能,建立了某百千瓦级回热循环微型燃气轮机及其HAT循环的热力性能模型,优化了循环参数,分析了压损与换热温差对循环效率的影响,并对HAT循环热电联供效率与回热循环进行了比较分析。研究表明基于回热循环微型燃气轮机构建的HAT循环折合发电效率可以达到29.66%,比回热循环提高4.28个百分点。HAT循环的热电比范围为0～2.8,回热循环的热电比范围为0～2.4。当热电比为0～1.6时,HAT循环热电联供效率高于回热循环;当热电比为1.6～2.4时,回热循环效率高于HAT循环。本研究为HAT循环热电联供系统的设计与应用提供参考。     

超临界CO2布雷顿循环中换热器夹点判断方法

为了分析超临界CO_2布雷顿循环中换热器的夹点情况,建立了换热器传热单元模型,提出了一套系统性的夹点判断方法:夹点的简化判据和分段计算分析方法。结果表明:夹点简化判据简单易行,但是实用性较为局限;分段计算是一套准确有效的夹点分析方法,能用于换热器夹点存在性、夹点位置和夹点温差的判断分析;高温回热器内一般不存在夹点,最小温差出现在换热器冷端;低温回热器和冷却器中存在夹点的可能性较大。     

微型HAT循环过渡过程动态模拟

在建立压气机、燃烧室、透平、回热器、湿化器、气水换热器、转轴转动惯性模型、气道热惯性模型和燃料供给系统模型等单元部件动态模型的基础上,建立了恒转速微型HAT循环的系统动态模型及其控制系统模型。对其阶跃降负荷过渡过程进行了动态模拟,并与微燃机简单、回热循环进行了对比。结果表明,该动态模型能够有效地对系统的过渡过程进行模拟与分析,计算稳定可靠,可为微型HAT循环控制系统设计与分析提供模型基础;控制系统设计合理,能够满足调节负荷和转速的要求,保证循环系统安全运行;水路的热惯性对系统响应影响较小,而回热器的热惯性是影响微型HAT循环和回热循环过渡过程响应的主要因素。     

逆流式空气湿化器热力性能的效率分析

为了详细研究HAT循环关键部件湿化器的热力学性能,用分析的方法定义了湿化器的效率的概念,并结合实验得出了不同进口参数,如湿空气含湿量、水气比和进口水温(水气温差)对效率的影响规律,为提高湿化器性能和确定合理的运行工作状态提供了依据。图4参13     

板翅式回热器传热性能研究

对板翅式回热器的传热性能进行了实验和数值模拟,对板翅式回热器的传热性能以及其温度场和速度场的情况进行了分析,为今后的此种换热器的设计与改进提供了一定的理论依据。并且为研究板翅式气-气回热器在高温下的传热规律,分析参与换热两侧流体的传热特性,做出了初步探讨。     

泡沫陶瓷填料湿化器加湿性能实验研究

温化器是湿空气透平(HAT)循环的关键部件,其性能优劣对于循环的性能有着重要的影响.对采用新型SiC泡沫陶瓷填料的湿化器在加压条件下的湿化性能进行了实验研究,分析了水气比、进口水温、操作压力以及进口空气温度对湿化过程的影响,研究表明,提高水气比或进口水温会使进出口空气温差、含湿量差相应增加,湿化器节点温差增大.操作压力...     

新型加压填料饱和器及其关键结构研究

为了进一步揭示HAT循环的集成和运行的规律,促进HAT循环的商业化,搭建了100kW级的HAT循环示范系统。本文主要工作是研制HAT循环的关键部件加压饱和器及其内部气体分布器、液体分布器、气液两相测量装置等。在前人工作基础上,设计了分布性能好、压力损失小的双向环流式气体分布器。利用FLU-ENT软件对其进行了数值分析,结果显示该气体分布器可以满足饱和器内气流分布均匀性的要求。     

航改燃气轮机的湿空气透平循环改型方案研究

航改燃气轮机具有压比高、效率高、可靠性高和结构紧凑等特点,它将航空发动机先进技术有效地应用于工业领域。以某型三轴航改燃气轮机为研究对象,对其不同的HAT循环改型方案进行了研究。建立了一种基于饱和曲线和工作线的饱和器模型,该模型避免使用难以准确获得的传热传质系数,利用饱和器实验数据对该模型进行了验证,结果表明:建立的饱和器模型具有较高的准确性,其中出口空气温度最大误差小于0.8%,出口湿度最大误差小于1.9%。此外,设计并仿真了3种不同结构形式的HAT循环方案,仿真结果表明:原始的压气机和透平特性不适合于改型后的HAT循环,它限制了HAT循环的效率和燃气轮机的输出功率(简称出功)。针对这一问题,提出了改进透平特性方案,该方案有效地解决了水蒸气的加入带来部件不匹配问题。在此基础上分析了3个HAT方案设计点的性能,结果表明方案2即在简单循环基础上加入了饱和器、经济器、回热器和中冷器是最佳的改型方案。     

航空发动机中回热器传热和阻力性能的数值模拟

航空发动机中的回热器是以椭圆形管结构为载体,即以椭圆管共同组成回热器,这是一种新型的紧凑式高温回热器,其在航空等相关工业领域备受青睐。但是,现阶段,我国并未明确回热器的传热性能以及强化机制,而相关准则和规范也不甚完善。对此,通过FLUENT数字化模拟回热器传热和阻力性能,可以在很大程度为实现回热器结构优化奠定良好的理论基础。主要对椭圆管回热器传热与阻力性能的影响因素进行了进一步分析,并以综合性能评价指标为基础,最优化了回热器结构综合性能,在此基础上,提出了平椭圆管结构的回热器,同时对其传热和阻力性能进行了计算分析,进而实现了平椭圆管回热器结构综合性能的最优化,最后还以场协同原理为基础,深入探究了椭圆形管回热器传热的强化机制。     

有无后冷器的微燃气轮机HAT循环性能比较

基于某80kW微燃气轮机回热循环改造工作,比较了有后冷器和无后冷器的HAT(Humid Air Turbine)循环性能和需要增加的换热器面积。研究结果表明,对于所研究的微燃气轮机,有、无后冷器的HAT循环系统折合效率和折合输出功相当,与有后冷器的HAT循环相比,无后冷器的HAT循环湿化器更高,体积更大,但是由于省掉了后冷器,其总换热面积(后冷器、湿化器、省煤器换热面积之和)更小,即意味着其投资更低,且无后冷器的HAT循环系统结构更简单,将使系统更加紧凑且控制更容易。     

能源岛回热技术的发展现状

利用燃气轮机循环实现热、电、冷三联供的能源岛系统是可持续发展能源利用的新技术，采用回热技术可显著提高燃气轮机循环效率。为此，综述了能源岛中回热技术的发展现状，对回热器材料、换热型面、回热器的制造情况进行了研究。发现采用不锈钢材料和耐热陶瓷作为回热器的材料还有一些问题有待解决；强化板式和板翅式换热型面是很有发展前途的回热器换热型面。通过分析，提出了新型回热器的构想，为进一步开展回热技术研究提出了方向。     

Optimization principles for convective heat transfer

Optimization for convective heat transfer plays a significant role in energy saving and high-efficiency utilizing. We compared two optimization principles for convective heat transfer, the minimum entropy generation principle and the entransy dissipation extremum principle, and analyzed their physical implications and applicability. We derived the optimization equation for each optimization principle. The theoretical analysis indicates that both principles can be used to optimize convective heat-transfer process, subject to different objectives of optimization. The minimum entropy generation principle, originally derived from the heat engine cycle process, optimizes the convective heat-transfer process with minimum usable energy dissipation focusing on the heat–work conversion. The entransy dissipation extremum principle however, originally for pure heat conduction process, optimizes the heat-transfer process with minimum heat-transfer ability dissipation, and therefore is more suitable for optimization of the processes not involving heat–work conversion. To validate the theoretical results, we simulated the convective heat-transfer process in a two-dimensional foursquare cavity with a uniform heat source and different temperature boundaries. Under the same constraints, the results indicate that the minimum entropy production principle leads to the highest heat–work conversion while the entransy dissipation extremum principle yields the maximum convective heat-transfer efficiency.     

湿度对HAT循环燃烧室旋流扩散燃烧特性的影响

为研究湿度对燃烧特性的影响,采用湍流雷诺应力模型和层流小火焰模型,对湿空气透平(HAT)循环燃气轮机带有旋流器的燃烧室内甲烷扩散燃烧过程进行了数值模拟对比了在4种不同空气含湿量(0、100、200、300g／kg(DA))情况下的燃烧室内部温度场、速度场以及NO组分分布的情况,分析了湿度对HAT循环燃烧室扩散燃烧特性的影响结果表明,加湿降低了整个燃烧室的温度,并使其内部温度分布更加均匀;加湿使燃烧室的NO浓度大大降低;加湿减小了回流区长度。     

Study of humid air turbine cycle with external heat source for air humidification

In this paper, through introducing an external heat source to the conventional humid air turbine (HAT) cycle, we have studied the performances of the improved humid air gas turbine cycle mainly by exergy analysis method. In order to attain the performance of the humid air gas turbine with external heat source, we compare it with the conventional HAT cycle in detail with different factors such as the pressure ratio, turbine inlet temperature (TIT) and the external circulating water mass flow. The results showed that the specific work of the new system and the humidity ratio of saturator are all increased in some degree. For example, in the same pressure ratio and TIT, when the ratio of the external circulating water mass flow rate with that of the internal water is 0.2, the specific work increases more than 15.2 kJ kg⁻¹a, and the humidity raises at least 2.0 percent points. By introducing the external circulating water into the system, though thermal efficiency of the new HAT cycle is lower than that of the conventional HAT cycle, the exergy efficiency exhibits different results. Generally, when the pressure ratio is over 8, the exergy efficiency for the proposed HAT cycle is higher than the conventional HAT cycle; while less than 8, whether or not the exergy efficiency increases will mainly depend on TIT. In addition, the exergy destructions of components in systems were investigated. Through the comparison of the new system with the conventional HAT cycle, it was found that the exergy loss proportion in combustion declines for the new system, and the proportion of exhaust loss increases. From the viewpoint of total energy system, the HAT cycle with utilization of external heat source is a beneficial way to improve the overall performances of energy utilization. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermodynamic studies of a HAT cycle and its components

The electric power grid contains more and more renewable power production such as wind and solar power. The use of renewable power sources increases the fluctuations in the power grid which increase the demand for highly efficient, fast-starting power-producing units that can cope with sudden production losses. One of the more innovative power plant cycles, that have the potential of competing with conventional combined power plants in efficiency but has a higher availability and faster start up time, is the Evaporative Gas Turbine (EvGT) or Humid Air Turbine (HAT). A thermodynamic evaluation of different HAT cycle layouts has been done in this paper. Each layout is evaluated separately which makes it possible to study different components individual contribution to the efficiency and specific power. The thermodynamic evaluation also shows that it is important to look at different cool-flow extracting positions. The effect of water temperature entering the cycle, called make-up water, and where it is introduced into the cycle has been evaluated. The make-up water temperature also affects the optimal pressure level for intercooling and it is shown that an optimal position can be decided considering design parameters of the compressor and the water circuit.     

A simple solution for transient heat transfer during heating of a slab product

A theoretical and experimental study of transient heat transfer in the heating of an individual slab product, subjected to an air flow at a temperature of 50°C and a velocity of 1 m/s, is presented. Experimental temperature measurements at the centre of the slab product were made, and the experimental heat-transfer rates were derived from the temperature data. A simplified analytical technique, using the boundary condition of the third kind in transient heat transfer, was used to predict the theoretical heat transfer rates for two cases, the first considering that the heat transfer coefficient is a convective heat transfer coefficient, and the second considering that heat transfer coefficient is the sum of the convective and radiative heat transfer coefficients. The experimental heat-transfer rates were compared with the predictions for two cases, and a very good agreement was obtained.     

Humid air turbine cycle blade cooling exergetic analysis

Starting from the first steam injection cycles (GE‐STIG; Cheng), the technique of increasing gas turbine performances by injecting water/steam somewhere before the combustion chamber, has shown very interesting results for power and efficiency increase and for NO_x emissions. Very interesting performances are achieved by evaporative cycles, such as the HAT (Humid Air Turbine), which is capable of achieving 50% conversion efficiency with lower investment costs compared to combined cycles. Other advantages of the steam injected cycle include the power modulation that is possible by varying the injected steam flow rate, keeping the maximum temperature constant. In particular, for the HAT cycle, it is possible to choose different temperature, pressure and compositions for the blade cooling fluid, depending on the bleed point. In this paper, a second law analysis of the HAT cycle and its components, has been performed. In particular, the exergetic analysis of blade cooling has been carefully analysed. Copyright © 1999 John Wiley & Sons, Ltd.     

An iterative regularization method in simultaneously estimating the inlet temperature and heat-transfer rate in a forced-convection pipe

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown space- and time-dependent inlet temperature and heat-transfer rate on the external wall of a pipe system using temperature measurements at two different locations. It is assumed that no prior information is available on the functional form of the unknown inlet temperature and heat-transfer rate; hence the procedure is classified as the function estimation in inverse calculation. The temperature data obtained from the direct problem are used to simulate the temperature measurements. The accuracy of the inverse analysis is examined by using simulated exact and inexact temperature measurements. Results show that an excellent estimation on the space- and time-dependent inlet temperature and heat-transfer rate can be obtained for the test case considered in this study.     

Marangoni condensation of steam–ethanol mixtures on a horizontal tube

For condensation of binary mixtures where the less volatile constituent has the higher surface tension the condensate film is potentially unstable and various “modes” of condensation are seen depending primarily on composition and vapour-to-surface temperature difference. Of particular interest is the so-called “pseudo-dropwise” mode of condensation where the appearance of the condensate closely resembles that of dropwise condensation of a pure fluid on a hydrophobic surface. In recent years the so-called Marangoni condensation problem has been studied experimentally in great detail by Utaka and co-workers [4], [5], [6], [7], [8], [11] for condensation of steam–ethanol mixtures on small vertical plane surfaces. It has been found that very small concentrations of ethanol in the liquid phase can give rise to significantly larger heat-transfer coefficients than found with pure steam.In the present investigation the problem has been studied using a horizontal condenser tube. Heat flux and vapour-to-surface temperature difference have been measured for steam–ethanol mixtures over a wide range of composition at atmospheric pressure. The results show the same trends as those found by Utaka for vertical surfaces. Differences in detail can be explained by geometry considerations and strong dependence of heat-transfer coefficient on vapour-to-surface temperature difference and vapour velocity, both of which vary around the perimeter of the horizontal tube.     

Conjugated heat transfer in double-pass laminar counterflow concentric-tube heat exchangers with sinusoidal wall fluxes

An analytical method is proposed to predict the temperature distribution and local Nusselt number for laminar flow in a double-pass countercurrent heat exchanger with sinusoidal heat flux distribution. A design of inserting in parallel an impermeable barrier to divide an open conduit into two subchannels for conducting double-pass operations, resulting in substantially improved the heat transfer rate, has been evaluated theoretically in the fully developed region. Comparison with the theoretical results shows that the heat-transfer efficiency improvement for double-pass concentric circular heat exchangers is generally higher than those in the single-pass operations without an impermeable barrier inserted. The influences of the impermeable-barrier location on the heat-transfer efficiency improvement and power consumption increment, as indicated from theoretical predictions, can be used to determine the economical feasibility in operating double-pass devices.