大型燃气轮机透平第一级静叶表面温度分布的计算方法

利用附加源项法计算叶片外表面换热系数及温度分布,编制叶片内部冷却计算程序及壁面导热程序,应用该程序计算了某大型燃气轮机第一级静叶表面温度分布,对燃气涡轮叶片先进的内外部冷却系统设计方法的消化吸收奠定了基础。     

The effect of start-up cycle in ceramic coating used as thermal barrier for a gas turbine bucket

The unsteady aerodynamic and aero-thermal performance of a first stage gas turbine bucket with thermal barrier coating (TBC) and internal cooling configuration were investigated by application of a three dimensional Navier–Stokes commercial turbomachinery oriented CFD-code. Convection and conduction were modeled for a super alloy blade with TBC.The CFD simulations were configured with a mesh domain including the nozzle and bucket interstage in order to accurately predict the fluid parameters at inlet and outlet of bucket. Comparisons to the gas turbine manufacturer data have permitted validation of the flow conditions at the inlet of the rotor.The effects of blade TBC surface temperature changes during a start-up cycle were simulated by means of an unsteady simulation, with unsteady inlet/outlet boundary conditions specified according to test data. The calculations include not only the fluid but also the solving of conduction within the blade, allowing for a correct modeling of the large difference of thermal inertia between the fluid and solid.The role of thermal barrier coatings (TBC) is, as their name suggests, to provide thermal insulation of the blade. A coating of about 100–400 μm can reduce the temperature by up to 200 °C. A TBC can be used either to reduce the need for blade cooling (by about 36%) increasing the turbine efficiency, while maintaining identical creep life of the substrate; or to increase considerably the creep life of the blade while maintaining level of blade cooling (and therefore allowing the blade to operate at a lower temperature for an identical turbine inlet temperature).     

石墨烯-PFA复合材料换热器与金属换热器的传热性能对比

氟塑料换热器以其耐腐蚀、耐磨损等优点而备受关注,但氟塑料热导率较低,换热能力差,限制了其广泛应用。石墨烯-PFA复合材料兼具石墨烯优异的导热性和可熔性聚四氟乙烯(PFA)良好的耐酸碱腐蚀性,是新一代的换热器材料。搭建了余热回收测试实验台,对石墨烯-PFA复合材料换热器和金属换热器的传热性能进行对比。研究了不同烟气流速、不同进口烟气温度以及不同石墨烯配比对复合材料传热性能的影响。结果表明:对于金属换热器和复合材料换热器,当烟气流速从2.0增加到4.0 m/s时,传热系数分别增加到原来的1.19和1.34倍;随着进口烟温的升高,两种材质的传热系数分别降低了15.6%和14.7%;随着石墨烯含量增加,复合材料的导热系数以及传热系数均增加。     

柴油机冷却水套中无水冷却液的数值模拟分析

运用FLUENT软件对某型号柴油机冷却水套三种无水冷却液在不同温度下的冷却效果进行数值模拟分析.模拟结果表明:由于冷却液表面换热系数的变化受冷却液粘度及导热率的影响,而这两个因素随温度的变化而变化;温度较低时,冷却液的导热率的影响占主导地位,表面换热系数随温度的增大而减小;温度较高时,冷却液粘度的影响占主导地位,表面换热系数随温度的升高而增大.     

Conjugate heat transfer investigation on the cooling performance of air cooled turbine blade with thermal barrier coating

A hot wind tunnel of annular cascade test rig is established for measuring temperature distribution on a real gas turbine blade surface with infrared camera. Besides, conjugate heat transfer numerical simulation is performed to obtain cooling efficiency distribution on both blade substrate surface and coating surface for comparison. The effect of thermal barrier coating on the overall cooling performance for blades is compared under varied mass flow rate of coolant, and spatial difference is also discussed. Results indicate that the cooling efficiency in the leading edge and trailing edge areas of the blade is the lowest. The cooling performance is not only influenced by the internal cooling structures layout inside the blade but also by the flow condition of the mainstream in the external cascade path. Thermal barrier effects of the coating vary at different regions of the blade surface, where higher internal cooling performance exists, more effective the thermal barrier will be, which means the thermal protection effect of coatings is remarkable in these regions. At the designed mass flow ratio condition, the cooling efficiency on the pressure side varies by 0.13 for the coating surface and substrate surface, while this value is 0.09 on the suction side.     

凹坑深度对透平叶片前缘换热的影响

涡轮叶片前缘由于受到燃气的冲击,热负荷较高,其冷却和换热情况极大的影响了燃机的性能,因此是涡轮叶片上最关键的传热区,在对涡轮进行传热设计和计算时必须对该区域予以考虑。设计冲击靶面,对凹坑结构进行冲击,建立模型,通过数值计算分析其冷却效果。通过对凹坑的温度场进行对比分析,给出凹坑深度的变化对冲击靶面换热的影响。对于带凹坑结构,通过凹坑深度分析叶片前缘换热效果,当凹坑深度不太大时,凹坑深度的增加会增强冲击靶面的换热;当凹坑深度增加得较大时,则会明显降低冲击靶面的换热。     

Overall Thermal Performances of Double-Wall Effusion Cooling Covered by Simulated Thermal Barrier Coatings

A coupling configuration of double-wall cooling and exterior surface thermal barrier coating(TBC)is one of the most promising thermal protection methods of hot components of modem gas turbine.The combined influences of coating thickness,impingement layout,and cooling air flowrate on the overall thermal performances of such configuration were discussed deeply,to provide the valuable guidance of design.Overall effectiveness measurements were implemented under engine-matched Biot numbers and mainstream-to-coolant temperature ratio.Conjugate heat transfer simulations provided the additional information difficult to be acquired by the measurements.The results indicated that the contribution of TBC is much larger than that of increasing the cooling air amount.The thicker TBC can produce the stronger insulation,while the higher risk of thermal damage of itself.The larger coolant flowrate enlarges the benefit of TBC,while the trend is suppressed by the thick TBC.The constant coating thickness cannot bring to the uniform metal temperature,which can be solved through properly adjusting the backside impingement.The trends in overall effectiveness with TBC’s thickness are independent on the change of internal impingement.     

Heat transfer coefficient of wheel rim of large capacity steam turbines

A way of calculating the overall equivalent heat transfer coefficient of wheel rims of large capacity steam turbines is presented. The method and formula to calculate the mean forced convection heat-transfer coefficient of the surface of the blade and for the bottom wall of the blade passage, are introduced. The heat transmission from the blade to the rim was simplified by analogy to heat transmission in the fins. A fin heat transfer model was then used to calculate the equivalent heat transfer coefficient of the blade passage. The overall equivalent heat transfer coefficient of the wheel rim was then calculated using a cylindrical surface model. A practical calculation example was presented. The proposed method helps determine the heat transfer boundary conditions in finite element analyses of temperature and thermal stress fields of steam turbine rotors.     

大功率汽轮机叶轮轮缘传热系数的研究

提出了大功率汽轮机叶轮轮缘总传热系数的计算方法.介绍了汽轮机动叶片叶身平均对流换热表面传热系数和叶片流道下壁面对流换热表面传热系数的计算方法和计算公式.把汽轮机叶片对叶轮的传热简化为肋片传热,使用肋片传热模型计算汽轮机叶片流道的等效传热系数,采用圆筒壁模型计算汽轮机叶轮轮缘的总传热系数,并给出了应用实例.在汽轮机转子的温度场与热应力场有限元分析中,该计算方法为确定叶轮轮缘的传热边界条件提供了依据.     

不同冷气/燃气温比下高温涡轮叶片旋流冷却流固耦合特性研究

采用流固耦合方法对燃气轮机高温涡轮叶片旋流冷却结构进行数值模拟分析。探究了不同冷气/燃气温度比条件下旋流冷却的流动与传热特性、叶片前缘区域固体温度、热应力以及热应变分布。研究表明：在进气腔入口雷诺数固定的条件下,随着温度比升高,冷气密度降低,冷气流速逐渐提升,同时湍动能升高,靶面努塞尔数逐渐升高;当温度比较低时冷气的流速较低、单位时间冷气带走的热量较少,当温度比较高时冷气温度较高、单位质量冷气所能吸收的热量有限,靶面处热流密度先升高后降低。受靶面热流密度分布影响,随着温度比升高,叶片前缘固体的温度、热应力以及热应变先降低后升高。     

Thermal performance of an architectural window with chemically deposited SnS---CuxS solar control coating

A mathematical model enabling the prediction of the thermal performance of solar control glazings employing chemically deposited solar control coatings with or without a transparent protective polymer coating is presented. Differential energy balance for the glazing is set up assuming one-dimensional steady state case for normal incidence of air mass 2 solar radiation and by considering conductive heat transfer within the glazing and convective and radiative heat transfer into the interior and exterior of the building. Using the specific example of the optical properties of the already reported SnS---Cu_xS solar control coatings, the redistribution of the absorbed component of the solar radiation is evaluated for constant convective heat transfer coefficient and temperature in the interior and for exterior temperatures in the 0–50°C range. The results yield shading coefficient versus exterior temperature curves for two specific SnS---Cu_xS coatings without and with a protective transparent varnish and offering transmittance in the visible region of 27 and 21%.     

Heat Transfer in a Horizontal Cylinder With Eccentric Surfaces

Heat transfer in horizontal cylinders exposed to free convection and radiation is of importance in many industries. Usually this problem is treated by adopting a concentric geometry, disregarding that the external surface temperature is not uniform. If an eccentric geometry is used, the external surface temperature should have a larger variation, changing the flow around the cylinder and the heat transfer coefficient, either improving or reducing the heat transfer. A numerical analysis is presented of the heat transfer in a horizontal cylinder with an internal isothermal surface eccentric to the external surface that is exposed to air free convection and radiation. The conduction problem was solved analytically and integrated numerically, while the free convection was solved by the PHOENICS software. The parameters analyzed were the ratio of radius, the ratio between the material and air thermal conductivities, the Rayleigh number, the emissivity of the outer surface, and the eccentricity between the external and inner surfaces. The parameters of a proposed equation to estimate the total heat of an eccentric arrangement in terms of the total heat of the corresponding concentric arrangement and the ratio between the convective and conductive thermal resistances were determined for given ratios of radius and eccentricities.     

Natural convection heat transfer of high temperature gas in an annulus between two vertical concentric cylinders

Water cooling panels have been adopted as the vessel cooling system of the High Temperature Engineering Test Reactor (HTTR) to cool the reactor core indirectly by natural convection and thermal radiation. In order to investigate the heat transfer characteristics of high temperature gas in a vertical annular space between the reactor pressure vessel and cooling panels of the HTTR, we carried out experiments and numerical analyses on natural convection heat transfer coupled with thermal radiation heat transfer in an annulus between two vertical concentric cylinders with the inner cylinder heated and the outer cylinder cooled. In the present experiments, Rayleigh number based on the height of the annulus ranged from 2.0 × 10⁷ to 5.4 × 10⁷ for helium gas and from 1.2 × 10⁹ to 3.5 × 10⁹ for nitrogen gas. The numerical results were in good agreement with the experimental ones regarding the surface temperatures of the heating and cooling walls. As a result of the experiments and the numerical analyses, the heat transfer coefficient of natural convection coupled with thermal radiation was obtained as functions of Rayleigh number, radius ratio, and the temperatures and emissivities of the heating and cooling wall surfaces. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(5): 293–308, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20070     

Radiative heat transfer by flowing multiphase medium-part I. An analysis on heat transfer of laminar flow between parallel flat plates

The multiphase flow of gaseous suspensions of fine particles furnishes high heat transfer characteristics at high and/or extremely high temperatures and at high heat fluxes due to the radiative transfer from heat source to suspensions. The phaseshift of particulate medium improves the overall heat transfer remarkably and from the practical viewpoint there exists important relevance pertinent to the industrial applications.

It is worth having a closer look at the behaviors of the suspensions and the heat transfer mechanism in flowing multiphase media so that the discussions are held concerning the foregoing media in some details.

An analysis is carried out on the laminar flow between parallel plates by taking into account of thermal radiation and the results illustrate the temperature profiles of fluid and dispersed phase, respectively, and the heat transfer characteristics for the wide ranges of dimensionless parameters such as conduction y, and radiation interaction parameter, loading ratio of particles, optical depth of duct, heat transfer between the two phases and so forth. Reference to the temperature profiles reveals the facts that while the temperature gradient in the vicinity of the heating surface increases due to the presence of particulate phase, the cupmixing mean temperature is raised appreciably by thermal radiation through the dispersed medium. In consequence, the contributions of suspensions on heat transfer are drastic, particularly in high temperature cases. Alternatively the correlations between the foregoing dimensionless parameters are also examined in current study.     

Heat transfer coefficient of wheel rim of large capacity steam turbines

A way of calculating the overall equivalent heat transfer coefficient of wheel rims of large capacity steam turbines is presented. The method and formula to calculate the mean forced convection heat-transfer coefficient of the surface of the blade and for the bottom wall of the blade passage, are introduced. The heat transmission from the blade to the rim was simplified by analogy to heat transmission in the fins. A fin heat transfer model was then used to calculate the equivalent heat transfer coefficient of the blade passage. The overall equivalent heat transfer coefficient of the wheel rim was then calculated using a cylindrical surface model. A practical calculation example was presented. The proposed method helps determine the heat transfer boundary conditions in finite element analyses of temperature and thermal stress fields of steam turbine rotors. __________ Translated from Journal of Power Engineering, 2007, 27(2): 153–156 [틫自: 뚯솦릤돌]     

Analysis of a metal hydride reactor for hydrogen storage

In this paper a two-dimensional model of an annular cylindrical reactor filled with metal hydride suitable for hydrogen storage is presented. Comparison of the computed bed temperatures with published experimental data shows a reasonably good agreement except for the initial period. Effects of hydrogen pressure and external fluid temperatures on heat transfer and entropy generation are obtained. Results show that the time required for hydrogen charging and discharging is higher when the thermal capacity of the reactor wall is considered. The time required for absorption and desorption can be reduced significantly by varying the hydrogen gas pressure and external fluid temperatures. However, along with reduction in time the entropy generated during hydrogen storage and discharge increases significantly. Results also show that for the given input conditions, heat transfer between the external fluid and hydride bed is the main source of entropy generation.     

Analysis of Natural Convection in Horizontal Concentric Annuli of Varying Inner Shape

An investigation is presented of free convection in horizontal concentric annuli of varying with inner shape where the inner and outer surfaces are kept at a constant temperature. The simulation is categorized into four groups based on the shape of the inner entity, which is either cylindrical, elliptical, square, or triangular. Flow and thermal fields are exhibited by means of streamlines and isotherms. Overall heat transfer correlations incorporating thermal radiation are established and presented in terms of the Nusselt number. It is observed that the surface radiation and presence of corners and larger top space enhances the heat transfer rate. As the reference temperature increases, surface radiation plays a more prominent role in the overall heat transfer performance.     

Effects of heat absorption and thermal radiation on heat transfer in a fluid–particle flow past a surface in the presence of a gravity field

A continuum two-phase fluid–particle model accounting for fluid-phase heat generation or absorption and thermal radiation is developed and applied to the problem of heat transfer in a particulate suspension flow over a horizontal heated surface in the presence of a gravity field. Analytical solutions for the temperature distributions and the wall heat fluxes for both phases are obtained. Two cases of wall thermal conditions corresponding to stationary and periodic temperature distributions are considered. Numerical evaluations of the analytical solutions are performed and the results are reported graphically to elucidate special features of the solutions. The effects of heat absorption and thermal radiation are illustrated through representative results for the temperature distributions and heat fluxes of both phases for various fluid–particle suspensions. It is found that heat absorption increases the total heat transfer rate for various particulate volume fraction levels while thermal radiation decreases it.     

Study of the steady and transient temperature field and heat flow in the combustion chamber components of a medium speed diesel engine using finite element analyses

The present work describes the development of a model for the calculation of the temperature field and heat flow in the combustion chamber components of internal combustion piston engines, which occur both under steady and transient engine operating conditions. Two and three-dimensional finite-element analyses were implemented for the representation of the complex geometry metal components (piston, liner and cylinder head). The model is applied for the piston and liner of a medium speed diesel engine, for which relevant experimental data exist in the literature. Special care is given for accurately specifying the thermal boundary conditions (temperatures and heat transfer coefficients). Gas side boundary conditions are calculated using a thermodynamic cycle simulation code, including spatial variation of the gas side heat transfer coefficient. Coolant sides (water on the external liner surface and oil on the piston undercrown surface) boundary conditions are calculated using correlations pertaining to real engine conditions. Also an effort is made to model the piston-ring belt-liner complex thermal paths using equivalent thermal circuits. A satisfactory degree of agreement is found between theoretical predictions and experimental measurements, revealing that the finite-element methods presented are successful in formulating this kind of problem, giving accurate results with reasonable computational cost. The utilization of the model reveals very clearly the essential role of engine operating transients (sudden changes in speed and/or load) in the generation of sharp temperature excursions in the metal components until a new steady state is reached. The phenomenon should be taken into account for correct engine design and safe operation (i.e. the avoidance of high local stresses).     

Numerical predictions of augmented heat transfer of an internal blade tip-wall by hemispherical dimples

The heat transferred to the turbine blade is substantially increased as the turbine inlet temperature is increased. Improved cooling methods are therefore needed for the turbine blades to ensure a long durability and safe operation. The blade tip region is exposed to very hot gas flow, and suffers high local thermal loads due to the external tip leakage flow. A common way to cool the tip is to design serpentine passages with 180° turn under the blade tip-cap taking advantage of the three-dimensional turning effect and impingement. Increased internal convective cooling is therefore required to increase the blade tip lifetime. In this paper, augmented heat transfer of a blade tip with internal hemispherical dimples has been investigated numerically. The computational models consist of two-pass channels with 180° turn and arrays of dimples depressed on the internal tip-cap. Turbulent convective heat transfer between the fluid and dimples, and heat conduction within dimples and tip are simultaneously computed. The inlet Reynolds number is ranging from 100,000 to 600,000. Details of the 3D fluid flow and heat transfer over the tip-walls are presented. Comparisons of the overall performance of the models are presented. It is found that due to the combination of turning impingement and dimple-induced advection flow, the heat transfer coefficient of the dimpled tip is up to two times higher than that of a smooth tip with less than 5% pressure drop penalty. It is suggested that the use of dimples is suitable for augmenting blade tip cooling to achieve an optimal balance between thermal and mechanical design requirements.