冷氦换热器数值建模及性能仿真研究

采用基于集总参数法的AMESim仿真软件对某型号运载火箭冷氦换热器进行建模,模型考虑了管外的高温燃气凝结换热、管内的强制对流换热及换热管沿轴向、径向的导热。在此基础上,开展了冷氦换热器的单元无关性分析、换热器性能仿真及参数影响性分析。仿真模型有效性通过搭载发动机地面试车试验数据进行验证。计算结果表明:仿真模型能较好地模拟冷氦换热器的性能,且随着冷氦进口温度升高,出口温度也基本线性递增;随着冷氦流量增大,出口温度逐渐降低,而工作压力对换热器性能影响较小。     

筒型翅片管换热器空气侧换热模型分析与实验

本文对筒型翅片管换热器的空气侧流动特点进行了理论分析,基于现有换热模型提出了一种能够反映筒型翅片管换热器结构特点的集中参数形式的换热因子关联式。通过实验对比了筒型和普通型的换热因子,对理论分析进行验证,结果表明:现有换热模型对筒型翅片管换热器的预测误差较大,平均相对误差达到81.16%;对传统换热器预测较准,平均误差为7.53%;使用本文实验数据拟合后的新关联式对筒型换热器平均相对误差仅为8.86%,对传统换热器平均误差为8.80%,且误差分布均匀,大幅提高了关联式对筒型翅片管换热器的预测精度,也保持了对传统换热器的预测精度。     

不同环境参数对SK型翅片管式换热器结霜换热性能的影响

以SK型翅片管式换热器为研究对象,在循环式风洞中对其结霜工况下的性能进行试验研究,研究了入口空气流速和相对湿度等环境参数对SK型翅片管式换热器性能的影响。研究结果表明：结霜工况下,翅片表面未覆盖满霜层时,在雷诺数Re=3602～5509,进口相对湿度？=60%～80%范围内,空气侧对流换热系数随迎面风速的增大而增大,随相对湿度的增加而增加;换热器表面阻力降随着流速的增加而增大,随着相对湿度的增大而增大。实验结果表明,空气相对湿度对SK型翅片管式换热器性能的影响远大于空气流速的影响。     

圆柱型翅片管换热器变工况传热性能模拟与分析

基于分排参数模型,本文建立了圆柱型翅片管换热器的性能仿真计算模型,对换热器的传热性能进行计算,并进行实验验证。结果表明:换热量的平均相对误差最大,为6.31%;出风干球温度的平均相对误差最小,为0.61%。计算所得各性能参数与实验值吻合良好。根据仿真模型,对不同制冷工况下的换热器进行计算,研究了循环风量、水质量流量、进风干球温度以及进水温度的变化对换热性能的影响。分析换热器的变工况特性可预测其非设计工况下的换热性能,并为换热器的运行工况调节提供依据。     

进口35000m~3/h空分设备更换国产可逆式换热器

鞍钢进口35000m~3/h原配切换式换热器两次发生泄漏,文章介绍了更换国产切换式换热器的情况;通过更换前后工艺参数的对比,分析了更换后的运行效果及国产切换式换热器存在的问题。     

受限空间中翅片管换热器的性能分析

受限空间翅片管换热器,是指由于总体框架尺寸的限制,部分结构参数被限定的换热器。为研究此类翅片管换热器的在换热传质时的不同特性,基于空调箱中的有限空间结构模型,建立适用于此类换热器计算的集总参数模型。利用二分迭代法求解的结果表明模型可高效精准地计算出翅片管换热器沿气流方向的排数,并且当任意工况参数或者结构参数发生变化时,此模型也可分析预测翅片管换热器的性能变化规律。利用实验数据对模型计算结果进行了对比验证:模型计算所得的各性能参数值与实验值吻合良好,其平均相对误差均小于2%,最大相对误差均小于8%。通过焓差实验台测定和分析翅片管换热器的制冷量和压降随工况参数和结构参数的变化规律,不仅优化换热器的设计,并为换热器运行调节方法的选取提供依据。     

氢低温套管式换热器模拟及实验验证

建立了考虑外管壁轴向导热与辐射漏热的套管式换热器数值模型,对搭建的预冷型液氢温区JT制冷机中套管式换热器出口温度进行模拟,结果表明:考虑外管壁的模型与实验结果更加吻合.利用该模型计算不同压比与流量情况下换热效率变化,流量由10 mg/s升高至30 mg/s,效率降低2.70％;压比由6升高至10,效率升高0.25％.     

喷流式换热器Ｙou效率分析

本文建立了喷流式换热器的Ｙou效率计算模型，并通过实例计算，分析了各运行参数，对喷流式换热器Ｙou效率的影响。     

绕管换热器壳侧气相流动实验与数值模拟

搭建了绕管换热器壳侧流动实验平台,并对一个竖直布置的4层绕管式换热器进行了壳侧空气流动实验。与关联式进行对比,包含换热器结构参数的Messa压降关联式,平均绝对偏差12.82%。同时,针对绕管式换热器壳侧几何结构的周期性,利用周期性边界条件,简化了绕管换热器壳侧的几何模型。并应用简化后的三维微元结构对绕管壳侧的传热和压降特性进行了数值模拟。模拟结果与实验较为吻合,压降的平均绝对偏差为16.81%。     

基于CFD原理的V形换热器流场分析

针对一款美式风管机上面的V形翅片管式换热器,利用Fluent软件中的多孔介质模型,模拟了V形翅片管式换热器中空气流动的不均匀性分布情况。经过对比分析,表明该模型能够较准确的计算出V形翅片管式换热器空气侧风速的不均匀分布情况。结合翅片管式换热器设计软件EVAP-COND和Coil Designer软件,计算换热器换热及制冷剂出口状态,合理安排管路布置。     

State-space model for dynamic behavior of vapor compression liquid chiller

A state-space model has been developed to investigate the dynamic behaviors of refrigeration system. By using vector-matrix notation and linearization, the ordinary differential equations describing the chiller's dynamic thermal behaviors are transformed into a representation form of the state space. The model has been validated by a series of dynamic response experiments of a chiller with the refrigerant R-134a. The average errors of the model results compared with the experimental data are all less than 10% in the experimental cases. Afterward, the model is used to investigate the transient behaviors of the exit cold carrier temperature of evaporator under different A disturbances. The state-space model developed in this study helps us have a good idea of the dynamic performance of a refrigeration system under transient conditions and design optimized control strategies for a high-energy-efficiency HVAC system.     

A control chart based approach to monitoring supply network dynamics using Kalman filtering

In today's global market, a critical issue for companies to survive the increasing competition is how to handle uncertainty in their supply network. In this paper, we explore the application of Kalman filtering to estimate the dynamic states in a supply network. Two state-space models are developed. The first one focuses on processing each individual order which includes both waiting time and value-added processing time. Considering the correlation of consecutive orders, the second one enhances the state-space model by employing autoregressive model of waiting time. To signal potential abnormal events, the estimates from the models are further used in control charts with control limits being updated at each monitoring stage according to the related estimation error. A supply network case example is studied and we conclude in the benchmark model (without using Kalman filtering) and the first state-space model, the data collected from the bottleneck stage turns out to be most valuable for increased accuracy in detecting tardy orders. The second state-space model consistently outperforms both the benchmark model and the first state-space model for robustly early detection of abnormalities at all stages, especially the stages before the bottleneck stage, of the system.     

A state-space dynamic model for vapor compression refrigeration system based on moving-boundary formulation

A transient response model for vapor compression refrigeration system has been developed in the paper. The system model contains four sub-models representing condenser, evaporator, compressor and electronic expansion valve (EEV). The condenser and the evaporator are developed based on the moving-boundary formulation. Through linearization, these dynamic models are transformed into state-space representation which is expressed in the form of matrix. The compressor and EEV adopt steady models because their thermal inertia is much smaller compared with the heat exchangers (i.e., condenser and the evaporator). The system model has been validated by experiment in terms of step change of EEV opening degree and heat load as well as ramp increase of inlet temperature of coolant oil of condenser. The results show that the model simulations have a good agreement with the experimental data. The simulation errors compared with the experimental data are mostly less than 10%. Since the model proposed in this study is expressed in the form of state-space matrix, they are featured by strong portability and high computation efficiency. It allows us to investigate the thermal dynamic characteristics of a refrigeration system under any complicated conditions and develop excellent control schemes.     

能源地铁车站板式热交换构件瞬态传热问题的理论解

能源地铁车站技术是一种利用地球地温能的新型建筑节能技术,对其传热计算方法进行的研究是推动该项技术前进的重点与难点。根据能源地铁车站板式热交换构件实际瞬态传热的特点,对该传热问题的理论解进行了研究与探讨。首先根据有足够埋深、有足够的换热面积两个作为热交换构件的前提条件,探讨了地铁车站中可用作热交换构件的地下结构构件,并根据其外形特点将其分为板式热交换构件和桩柱式热交换构件两大类;其次通过分析板式热交换构件实际瞬态传热特点,利用傅立叶变换对其热流边界条件进行变换,推导出能源地铁车站板式热交换构件实际瞬态传热问题的理论解;最后,分别用理论解和数值解对某具体工况进行了计算,理论解和数值解得到的两条曲线基本重合,可见,该理论解推导正确。     

Multivariable control-oriented modeling of a direct expansion (DX) air conditioning (A/C) system

A dynamic mathematical model for a DX A/C system has been developed. The dynamic model, written in state-space representation which was suitable for designing multivariable control, was linearized at steady state operating points. The linearized model has been validated by comparing the model simulation results with the experimental data obtained from an experimental DX A/C system. The simulated results agreed well with the experimental data, suggesting that the model developed was able to capture the transient characteristics of the DX A/C system modeled. It is expected that the model developed can be useful in designing a multi-input multi-output (MIMO) controller to simultaneously control indoor air temperature and humidity in a space served by a DX A/C system.     

风冷式热交换器传热强化的试验分析研究

本文对风冷式热交换器传热强化的几种典型方法进行试验研究， 并建立和利用电子计算机辅助试验程序，对风冷式热交换器传热强化特性进行分析计算，并绘制热交换器的工况图， 对风冷式热交换器的特性进行了分析。     

A State-Space Model of Fatigue Crack Growth

This paper proposes a nonlinear dynamic model of fatigue crack growth in the state-space setting based on the crack closure concept under cyclic stress excitation of variable amplitude and random loading. The model state variables are the crack length and the crack opening stress. The state-space model is capable of capturing the effects of stress overload and underload on crack retardation and acceleration, and the model predictions are in fair agreement with experimental data on the 7075-T6 aluminum alloy. Furthermore, the state-space model recursively computes the crack opening stress via a simple functional relationship and does not require a stacked array of peaks and valleys of stress history for its execution; therefore, savings in both computation time and memory requirement are significant. As such, the state space model is suitable for real-time damage monitoring and control in operating machinery. This revised version was published online in July 2006 with corrections to the Cover Date.     

制冷剂流量控制法在风冷热泵除霜中的应用

根据热泵空调系统中制冷工况和制热工况时制冷剂流量的差别,采用制冷剂流量控制法对热泵空调系统中的制冷剂流量进行控制,并将制冷剂流量控制法与热气旁通法除霜相结合应用于热泵除霜过程中。结果表明,在控制制冷剂流量的热泵空调系统中,系统正常运行时,该循环系统能抑制或减缓室外换热器表面的结霜;当室外换热器表面结霜时,则可加速除霜,缩短除霜时间。     

Diffraction of Elastic Waves by a Spherical Inclusion with an Anisotropic Graded Interfacial Layer and Dynamic Stress Concentrations

Scattering of compressional waves in multiphase metal matrix composites containing spherical particles with spherically isotropic graded interfacial layers is investigated using a state-space approach. A continuous transition from the particle to the matrix with the change of volume fraction of one of the constituents is assumed to exist across the thickness of the interphase zone. A simplified multilayer model for the interphase complications including both anisotropy and inhomogeneity is considered. Taylor’s expansion theorem is employed to solve a modal state equation leading to a global transfer matrix that directly links the boundary conditions at the outer surface of the interface layer to those at the inner surface. Numerical calculations reveal the important effects of interphase anisotropy and inhomogeneity on the total scattering cross section and dynamic stress concentrations for a moderately wide range of frequencies and interface layer thicknesses.     

弹性支承输流管道固有频率计算

本文建立了两端弹性支承输流管模型,导出该模型管道随内流体流速变化的固有振动特性方程,并对上游铰支加扭簧支承,下游铰支的模型进行了计算和实验,计算结果和实验数据吻合较好.结果表明,输流管各阶固有频率随内定常流的流速增加而降低。