板翅式回热器传热性能的试验研究

采用等流量,变流量两种试验方法对板翅式回热器进行传热性能试验,并进行传热数据分析,获得有工程应用价值的Nu-Re准则关系式。通过数值模拟的方法,分析流道的温度场和流场分布情况,得出了此回热器可通过改变流道表面粗糙度或结构来提高其换热性能。图6表2参6     

回热器对HAT循环影响的分析

目前对HAT循环中回热器的理论分析大多采用传热温差法和表征回热器特性的回热度分析的方法。针对这两种不同的分析方法分别进行了计算，比较分析了它们对HAT循环的影响，结果表明，传热温差法更加适合于对HAT循环进行理论分析，但应当注意传热温差的选取。而回热度法更多应用于回热器的设计。     

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。     

一次表面回热器的流动和传热研究

对一次表面回热器的流动和传热特性进行了试验研究和理论评价，获得了有工程价值的k-u和f-u试验曲线以及经验计算公式。指出对于当量直径为lmm左右的一次表面回热器不宜采用工业级通道而应使用微小通道的准则式，才能较为准确地评估其热性能。对比分析一次表面回热器的明显优点：质量轻，紧凑性好，传热效率高，占地面积和占用空间小以及热响应快，具有管壳式、板翅式等传统换热器无法比拟的性能和价格优势。图7表2参7     

通道形面对PSR性能影响的分析

针对一种新型的紧凑式换热器－－一次表面换热器（PSR），分析了分别由椭圆、正弦曲线和抛物线构成板片波纹对芯体性能的影响。结合一台用于燃气轮机回热器的一次表面换热器样机的设计，给出了三种板片波纹形式的PSR芯体的主要性能，并通过与相应的板翅式芯体的对比，表明这种换热器的优越性。     

低雷诺数流动错位翅片传热和压降特性的实验研究

通过对油水板翅式换热器进行的性能试验，得到了低雷诺数流动下板翅式换热器翅片侧传热与阻力特性的数据，在此基础上获得了错位翅片传热因子与摩擦系数的准则关系式，传热因子和摩擦系数的最大计算误差分别为0．62％和1．44％。根据这些准则关系式提出了一个衡量翅片质量的经济系数。     

新型回热器结构设计及换热特性研究

回热器作为斯特林热机的关键部件,对于太阳能斯特林热机整机性能有着重要影响。为克服传统金属丝网回热器结构存在的填料单一,制造成本较高,工艺复杂问题,采用实用等温分析法,以回热器的长径比、通流面积、填料种类以及孔隙率各项回热器参数为基础,设计了一种新型斯特林热机回热器,该回热器具有轴向压降小,换热性能高,结构稳定,加工制造简单的特点。开展了新型回热器和传统金属丝网回热器的换热性能对比研究,采用振荡条件下的局部热平衡方法研究回热器的传热过程,对比传统金属丝网回热器和新型回热器的温度变化,速度变化以及压力变化。结果表明:在整体孔隙率相同的条件下,新型回热器和传统金属丝网回热器相比,整体启动速率相似,但新型回热器压降减少0.04 MPa,速度出现分段式变化,有利于回热器的换热和结构稳定。因此,新型回热器不但在结构上优于传统金属丝网回热器,在换热特性上也优于传统金属丝网回热器。     

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.     

高温熔盐吸热器的传热研究和系统设计

本文对非均匀辐射热流密度太阳能熔盐吸热器传热过程进行了模拟研究,得到了熔盐吸热器内部的温度、传热性能等特征参数。结果表明在轴向和径向上熔盐流体温度和管壁的温度都非常不均匀,同时其综合传热性能要高于按照Sieder-Tate公式的计算值。并对10 MW塔式太阳能热发电的熔盐吸热器进行了设计和分析。     

逆流板翅式换热器动态性能的建模与仿真

对间冷回热燃气轮机关键部件逆流板翅式换热器进行了动态性能的仿真研究。在考虑气体工质压缩性的基础上，根据换热器内部冷、热流体的压力、流量和温度的变化和冷热流道间隔板的热平衡，建立了逆流板翅式换热器的动态数学模型，在EASY5平台上搭建了逆流板翅式换热器的分布参数模型，并进行了动态的仿真试验计算。分析结果表明该逆流板翅式换热器模型较好地实现了对换热器内部流体流动和换热的模拟，可以作为部件模块，用来时间冷回热燃气轮机系统性能的仿真研究。     

Thermal design and model analysis of the Swiss-roll recuperator for an innovative micro gas turbine

For the advanced power systems based on the use of microturbines, the major considerations are higher power density as well as higher efficiency for energy-saving. In order to achieve higher efficiency, recuperated systems which recover the exhaust heat then become mandatory and the paramount requirements for the recuperator are high effectiveness and low pressure loss. Here, the thermal design and model analysis of a proposed Swiss-roll recuperator for future higher efficiency microturbines were made with both theoretical approach and numerical simulation. The proposed Swiss-roll recuperator is basically the primary surface type. It is composed of two flat plates that are wrapped around each other, creating two concentric channels of rectangular cross-section. The characteristics of Swiss-roll recuperator resemble the counter-flow spiral plate heat exchanger and have the excellent performance in effectiveness and pressure-loss. From a theoretical analysis, the thermal characteristics of the Swiss-roll recuperator were investigated and its preliminary designs at a given effectiveness for an innovative micro gas turbine were also demonstrated, including the determination of the number of turns, the corresponding channel widths and the required number of transfer unit (NTU). The consequent pressure loss through the recuperator was also predicted. For a given design of the recuperator, the model simulation was then made to provide the insights and needs for further improving the performance of the Swiss-roll recuperator.     

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.     

微型燃气轮机圆筒原表面回热器的性能试验研究

对微型燃气轮机圆筒形原表面式回热器的传热与流动性能进行了试验研究.利用计算机控制检测传热性能试验台对该回热器在①两侧流量相等、改变两侧温度及②固定两侧温度,改变系统质量流量的情况下进行了传热性能和阻力性能试验.结果表明:随着质量流量的增加,回热器的传热系数增大,传热量逐渐增加,回热器的两侧压降也增大;在等流量时,回热器两侧的压降有所不同,高压低温侧压降比低压高温侧压降大,但低压高温侧压降增加较快,因此在设计回热器时必须重视两侧压降的变化情况,根据试验结果得出了传热和阻力随工况改变的变化趋势.     

Recuperator considerations for future higher efficiency microturbines

First-generation microturbines are based on the use of existing materials and proven technology, and with low levels of compressor pressure ratio and modest turbine inlet temperatures, have thermal efficiencies approaching 30% for turbogenerators rated up to 100 kW. For such small machines the goal of advancing beyond this level of performance is unlikely to include more complex thermodynamic cycles, but rather will be realised with higher turbine inlet temperatures. Advancing engine performance in this manner has a significant impact on recuperator technology and cost. In the compact heat exchanger field very efficient heat transfer surface geometries have been developed over the last few decades but further improvements perhaps using CFD methods will likely be only incremental. Automated fabrication processes for the manufacture of microturbine recuperators are in place, and on-going developments to facilitate efficient higher temperature operation are primarily focused in the materials area. Based on the assumptions made in this paper it is postulated that in the 100 kW size the maximum thermal efficiency attainable for an all-metallic engine is 35%. To achieve this the recuperator cannot be designed in an isolated manner, and must be addressed in an integrated approach as part of the overall power conversion system. In this regard, temperature limitations as they impact the recuperator and turbine are put into perspective. In this paper there is strong focus on recuperator material selection and cost, including a proposed bi-metallic approach to establish a cost-effective counterflow primary surface recuperator for higher temperature service. If indeed there is a long-term goal to achieve an efficiency of 40% for small microturbines, it can only be projected based on the utilisation of ceramic hot end components. Alas, the high temperature component that has had the minimum development in recent years to realise this goal is the ceramic recuperator, and efforts to remedy this situation need to be undertaken in the near future.     

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.     

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.     

Performance analysis of metallic concentric tube recuperator in parallel flow arrangement

A performance model for parallel flow arrangement in metallic concentric tube recuperator that can be used to utilize the waste heat in the temperature range of 1100–1800 K is presented. The arrangement consists of metallic concentric shells wherein flue gases pass through the inner shell and air to be preheated passes through annular gap in the same direction. The recuperator height is divided into small elements and an energy balance is performed on each element. Necessary information about axial shell-surface, gas and air temperature distribution, and the influence of operating conditions on recuperator performance is obtained. The recuperative effectiveness is found to be increased with increasing inlet gas temperature and with decreasing fuel flow rate. The present model provides a valuable tool for metallic concentric tube recuperator performance considerations in parallel flow arrangement.     

利用金属辐射网强化换热器烟气侧传热的研究

提出了用金属辐射网来强化高温烟气／空气换热器传热的方法，并通过实验研究了金属辐射网对其传热特性的影响。得出了烟气温度越高、流速越低、空气侧传热系数越大，则辐射网的效果越好等结论，为换热器传热的强化提供了一个新的途径。     

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.