风力机叶片气热除冰系统研究

针对风力机叶片结冰问题,提出了一种基于气热法原理设计的叶片除冰系统。首先对气热除冰系统进行设计,并借助地面试验来分析气热加热系统的可行性,然后通过对已装机运行的风电机组进行现场改造的方式来对气热除冰系统的可靠性进行分析。试验结果表明所设计的气热除冰系统方案可行,对环境温度为-10~0℃范围的叶片除冰效果显著,试验运行稳固可靠无异常。     

大型风力机叶片气弹稳定分析

本文采用铰接刚性叶片模型对大型风力机叶片进行了气弹稳定分析,建立了叶片动力学方程。即把质量和刚度非均匀分布的弹性叶片简化为与其具有相同一阶频率的铰接刚性叶片。气动力采用准定常叶素理论计算,轴向诱导速度通过动量定理求出。叶片的稳定分析采用多变量Floquet理论。最后按照本文方法对"十五"科技攻关项目,1.5MW风力机叶片进行了稳定计算。     

立式热虹吸再沸器设计

本文对热虹吸式再沸器的计算问题进行了研究,首先考虑到液体在再沸器加热器中上升时的闪蒸,并且将Sarma法(即在传热计算回路中用平均热强度代替逐段热强度以及将传热与流体力学分两个回路计算的方法)改进为将流体力学计算和传热计算合并在同一个回路中进行,沿加热管逐段做热量平衡,当分段数足够多时,则避免了试差不易收敛的问题,加快了计算速度。     

风电叶片气热抗冰系统理论设计及工程应用

针对MW级风电叶片气热抗冰技术建立了加热融冰过程中的热力学模型,对复合材料叶片表面融冰时间进行了计算,其结果与有限元仿真计算结果误差小于7%。对风场服役的2 MW机型叶片进行融冰实验,结果表明,气热抗冰系统在环境温度为-10℃的条件下可以有效融冰/防冰。     

电热元件-疏水涂层复合除冰系统的实验研究

针对当今风电叶片面临的电热除冰能耗巨大及疏水涂层除冰效果欠佳的问题,提出了一种结合电热元件除冰与疏水涂层除冰共同优势的复合除冰系统。借助涂层疏水性表征手段和冰层粘结强度测试实验,分析了疏水性对冰层剪切附着力的影响,最后通过特定环境下的除冰模拟实验对复合除冰系统的可行性与可靠性进行了评估。该除冰系统不但满足风电叶片的除冰要求,而且可降低除冰能耗,起到节能作用,可应用于降低冰脊对叶片造成的损害。     

基于CATIA二次开发的风力机叶片建模技术

针对风力机叶片三维模型,利用VB平台建立与EXCEL的接口,方便叶片模型参数从EXCEL读入.为精确建模,计算过渡翼型以及叶片空间离散数据点坐标,再基于VB平台建立CATIA应用软件的二次开发,输出CATIA几何图形集.此软件的开发意义在于能够快速、高效、精确、智能化建立风力机叶片三雏模型,从而可进行气动分析、结构有限元分析、动态仿真以及为制造叶片模具提供数控加工模型.     

基于Qblade和Matlab的风力机叶片设计与气动性能分析

首先使用Qblade计算翼型的气动参数,将数据进行处理后,利用Wilson设计模型,结合Matlab编程软件对某小型风力机叶片进行设计。再基于叶素动量理论,利用Qblade对所设计的叶片进行气动性能计算,并根据weibull风速分布模型计算风力机的性能。计算结果表明:编写的程序正确,Qblade风力机性能计算软件能正确反映叶片气动模型,并在保证计算结果准确的同时节省风力机叶片设计前期计算的时间。     

水平轴风力机叶片自振频率计算方法研究

本文应用商业有限元软件,通过选取不同的单元类型(梁单元和壳体单元)对国内200kW风力机叶片进行模态分析。结果表明,两种方法精确相符,从而证明在计算叶片自振基频时可把复杂叶片结构简化为一悬臂梁来进行分析。鉴于把叶片简化为一悬臂梁进行结构动力有限元计算易于实现计算的程序化,基频计算具有足够的精度且计算效率高,因此其对于叶片的初步结构设计具有一定意义,在分析叶片基频时不必建立复杂的三维叶片有限元模型。     

基于ANSYS建模的风力机叶片模态分析及稳定性分析

以1MW水平轴风力机叶片为例,应用ANSYS有限元软件,通过APDL参数化语言实现风力机叶片的有限元建模。模型建好后可以直接设置单元类型、材料参数、剖分网格,进行有限元计算。本文主要利用ANSYS建模技术对风力机叶片进行模态分析及稳定性分析。     

风力机叶片结构强度复合材料力学分析方法研究

截面结构强度分析校核方法是风力机叶片设计优化的关键问题。针对现有的叶片工程力学计算方法精度不高、有限元分析方法计算开销较大的问题,在研究风力机复合材料叶片结构设计模型的基础上,基于复合材料力学理论,推导出计算叶片截面周向各处拉伸和剪切应变的计算公式;在叶片生命周期内的极限载荷下,对某1.5 MW叶片进行了结构强度计算和分析,通过与该叶片在当量极限载荷下的测试结果对比,验证了所述方法的有效性。     

Eulerian–Eulerian simulation of heat transfer between a gas–solid fluidized bed and an immersed tube-bank with horizontal tubes

A two dimensional Eulerian–Eulerian simulation of tube-to-bed heat transfer is carried out for a cold gas fluidized bed with immersed horizontal tubes. The horizontal tubes are modelled as obstacles with square cross section in the numerical model. Simulations are performed for two gas velocities exceeding the minimum fluidisation velocity by 0.2 and 0.6 m/s and two operating pressures of 0.1 and 1.6 MPa. Local instantaneous and time averaged heat transfer coefficients are monitored at four different positions around the tube and compared against experimental data reported in literature. The effect of constitutive equations for the solid phase thermal conductivity on heat transfer is investigated and a fundamental approach to modelling the solid phase thermal conductivity is implemented in the present work. Significant improvements in the agreement between the predicted and measured local instantaneous heat transfer coefficients are observed in the present study as compared to the previous works in which the local instantaneous heat transfer coefficients were overpredicted. The local time averaged heat transfer coefficients are within 20% of the measured values at the atmospheric pressure. In contrast, underprediction of the time averaged heat transfer coefficient is observed at the higher pressure.     

空气-石蜡直接接触换热特性实验研究

在间壁式换热器中石蜡因为其热导率低影响了蓄热系统的换热速率,采用石蜡与空气直接接触换热可大幅提高蓄热系统的换热速率。把常温的空气通过气体分布器注入熔融状态的石蜡（100~150℃）中,具体考察了表观气速、静液位高度和传热温差等参数对石蜡-空气鼓泡换热中体积传热系数与气含率的影响。实验结果表明,随着表观气速的增大,体积传热系数与气含率随之增大,并且对于气含率,在较低的表观气速下的增长速率更快;在实验条件下,增加静液位高度都只会导致体积传热系数与气含率的降低,而改变气液温差对体积传热系数的影响不甚明显。根据实验结果获得了石蜡与空气直接接触换热的体积Nusselt数经验关联式。     

气体流动条件下钴基催化剂固定床的传热

在气体流量4~8 Nm3/h、气体分布器进口温度190~210℃、加热管壁温约240℃的条件下,对气体流动时活性组分呈蛋壳型分布的钴基催化剂固定床的传热进行了实验研究,建立了二维拟均相传热模型,利用正交配置法和Levenberg-Marquardt法对其求解,得到了钴基催化剂床层径向有效导热系数及壁给热系数的关联式,并将传热参数与由气体处于静态时固定床的有效导热系数计算而得的固定床传热参数值进行了比较,在气体入口温度范围内考察了其对固定床传热参数的影响. 结果表明,实验所得传热参数与文献值的最大偏差绝对值均在15%以内.     

Determination of heat transfer formulas for gas flow in fin-and-tube heat exchanger with oval tubes using CFD simulations

Plate fin-and-tube heat exchangers operate in a cross-flow arrangement with the complex path of gas flow, hence in order to determine the velocity field and heat transfer characteristics, the numerical methods must be used. The CFD codes allow obtaining local values of the heat transfer coefficient, however it is impossible to incorporate these values into the analytical formulas for the overall heat transfer coefficient, that is fundamental for the designing procedure of the cross-flow heat exchangers. Therefore this paper presents a method for determination of the average heat transfer coefficient for gas flow in a plate fin-and-tube heat exchanger using the CFD simulations. The values of the heat transfer coefficient obtained using the heat transfer formulas for the Nusselt number, determined with the CFD simulations, can be directly implemented in the thermal designing procedure of the cross-flow heat exchangers. The results of the numerical computations are validated experimentally.     

In situ measurement and simulation of temperature and stress gradients during sintering of large ceramic components

A special thermooptical measuring system was used to determine mechanical, thermal and sintering properties during firing simultaneously. Combining customary and novel in situ measuring methods, a complete dataset was obtained which includes elastic and viscous moduli, thermal conductivity and coefficients of heat transfer, specific heat, reaction and sintering data and gas permeability. Using finite element methods (FEM) the temperature fields in large components were simulated for various time temperature cycles. From the temperature field local reaction and shrinkage rates were calculated. The corresponding stresses were obtained using FEM again. The time temperature cycle was optimized taking into account both a sufficient safety margin to the respective strength of the sintering material and the economic requirement for a short firing cycle. The use of the methods was demonstrated considering as example a large high voltage porcelain insulator, which undergoes a number of phase transformations during firing.     

Investigation into gas-solid heat transfer in a cryogenic vibrated fluidised bed

Experiments were carried out in a cryogenic vibrated fluidised bed to investigate the heat transfer between gas and rubber particles obtained from discarded tyres. The effects of parameters such as bed layer thickness and gas flow rate on the gas-solid heat transfer were investigated, and a heat transfer correlation obtained by regressing the experimental data. Theoretical analysis based on radial thermal conductivity indicated that higher heat transfer efficiency could be obtained by the use of a fluidised bed rather than a fixed bed or a moving bed, especially for rubber particles having low thermal conductivity under cryogenic conditions. A numerical modelling was developed, based on assumptions of the movement of the particles and the vibrating bed plate, using a unique method of regarding particles as the source term in the energy equation. Computational results from the modelling showed good agreement with the experimental data.     

Four stages of the simultaneous mass and heat transfer during bubble formation and rise in a bubbly absorber

We studied nonisothermal absorption of a solvable gas from growing at an orifice and rising bubble when the concentration level of the absorbate in the absorbent is finite (finite dilution of absorbate approximation). It is shown that simultaneous heat and mass transfer at all stages of bubble growth and rise in a bubbly absorber can be described by a system of generalized equations of nonstationary convective diffusion and energy balance. Solutions of diffusion and energy balance equations are obtained in the exact analytical form. Coupled thermal effects during absorption and absorbate concentration level effect on the rate of mass transfer are investigated. It is found that the rate of mass transfer between a bubble and a fluid increases with the increase of the absorbate concentration level. The suggested approach is valid for high Peclet, Prandtl and Schmidt numbers. It is shown that for the positive dimensionless heat of absorption K thermal effects cause the increase of the mass transfer rate in comparison with the isothermal case. On the contrary, for negative K thermal effects cause the decrease of the mass transfer rate in comparison with the isothermal case. The latter effect becomes more pronounced with the increase of the concentration level of the absorbate in the absorbent. Theoretical results are consistent with the experiments of Kang et al. (Int. J. Refrigeration 25 (2002) 127) for absorption from ammonia gas bubbles rising in water and aqueous ammonia solutions.     

Analysis of local heat transfer and hydrodynamics in a bubble column using fast response probes

A fast response probe is used to measure local heat transfer in a bubble column. It captured the variations in local heat transfer coefficients due to changes in local hydrodynamic conditions in radial and axial directions. These measurements have been used to identify flow regime transitions, variations in flow patterns and local hydrodynamic structure as obtained with different gas distributors and varying gas velocity. Standard deviations of pressure measurements obtained with a fast response probe have been compared with heat transfer coefficient fluctuations for the first time and the similarities and differences have been pointed out. Variations in average heat transfer coefficients and standard deviations in radial and axial directions point to different hydrodynamic conditions and are compared with literature studies. Relationships between local heat transfer measurements and hydrodynamic conditions are shown.     

加热方式对管壳式相变蓄热单元强化传热的可视化及数值模拟

为了提高相变蓄热系统在实际应用中的蓄热速率,本文建立了管壳式相变蓄热单元可视化实验平台,提出了一种外部加热法的强化传热方式,讨论了相变蓄热单元在外部加热法时的熔化特性和传热机理。通过Fluent软件模拟对比了外部加热法和内部加热法在熔化过程中的液相分数、熔化速率和均匀性等方面的差异。研究结果表明：外部加热法的使用能大幅提升蓄热单元的蓄热效率。与内部加热法相比,外部加热法在熔化过程中的传热和相变更加均匀。相比于内部加热法,由于外部加热法传热面积较大,熔化时间缩短了69.1%;在消除传热面积的影响后,外加热方法依靠广泛而强烈的自然对流使熔化时间减少了23.2%。