制冷空调系统冷凝器分布参数模型及数学仿真

冷凝器是制冷空凋系统的主要部件，建立冷凝器性能仿真模型，不仅是冷凝器自身优化设计的需要，也是开发制冷空凋仿真系统的一项重要工作。该文基于过程物理机理，建立了制冷空调系统冷凝器分布参数动态数学模型，并结合冷凝器的工作特点确定了具体的仿真算法。利用所建立的仿真模型，可以预测不同运行工况下冷凝器热力参数的瞬态分布状况，对冷凝器的动／静态特性进行较为全面的仿真分析，同时还可以十分方便地确定出制冷剂单／双相区域分界点的瞬态位置。文中通过一个仿真算例说明了所建立的仿真模型可用性。     

HAT循环中饱和器的动态仿真

该文从热力学、传热传质学、流体力学的基本原理出发,对饱和器内水滴侧和湿空气侧分别建立沿流动方向的一维动态数学模型;该模型在仿真平台EASY5上调试通过,通过计算得到饱和器稳态运行时的数据,然后完成了一组动态响应下的仿真实验;结论认为饱和器在稳态运行时,沿气体流动方向,气体质量流量增加,密度减小,速度增加;沿水滴流动方向,水滴的温度和速度降低,水滴浓度增加,水滴直径变小,但是水滴侧与空气侧的接触总面积却依然增加;对饱和器的动态响应而言,如果进水量出现扰动,饱和器内空气侧能够很快地响应水回路的变化。     

某飞机辅冷系统IMA应用实时验证模型研究

某飞机环控增加蒸发制冷式辅助冷却系统（简称辅冷系统）,对多个厨房、大功率电子设备以及设备舱进行冷却。为了对综合模块化航空电子系统(IMA)驻留应用进行硬件在环（HIL）测试验证,开展辅冷系统实时仿真模型研究。在对辅冷系统冷凝器等关键部件的建模原理进行数学描述后,利用MATLAB/Simulink进行部件建模与仿真分析,并根据建模框架对辅冷系统模型进行集成与仿真,最后将模型下载到实时机对IMA应用进行HIL测试。仿真与测试结果表明,制冷剂工作压焓曲线满足要求,辅冷系统模型仿真误差满足要求,可以对IMA应用进行实时的仿真验证。首次利用模型开展制冷剂在关键部件的工作压焓曲线以及飞机辅冷全系统的HIL测试研究,该研究对制冷领域的系统级实时仿真验证具有参考意义。     

唇形油封动态散热仿真研究

研究优化油封结构,提高散热效果,由于唇形油封在工作时与轴摩擦生热导致温度升高,容易造成材料破坏而引起油封的失效.在汽车实际运动过程中,由于封抱轴力太大,使部件温度升高,造成部件磨损.目前对于油封的散热机理还没有确切的认识.针对油封的高温失效问题,为优化油封的散热结构,提出建立了描述其固液传热的二维轴对称模型,利用Fluent软件的RNG k-ε湍流模型对油封的散热进行仿真.结果显示随着轴速的增加,摩擦而上的温度逐渐增加,摩擦面上温度最高点位于中心位置靠近空气侧,温度最低点位于润滑油侧的端点上,空气侧的温度分布整体高于润滑油侧的温度分布.油封唇口与轴之间产生的热量主要通过润滑油、轴被带走,通过空气带走的热量较少.通过研究或为油封有效散热提供了科学依据.     

基于狭缝文丘里管的气液两相流测量

提出了一种新的气液两相流测量系统-狭缝文丘里气液两相流测量系统.理论分析表明,狭缝文丘里管利用对称结构可以减小或消除摩阻压降的影响,中间狭缝处垂直于水平流向的重位压降的测量同样避免了沿程摩擦阻力的影响.提出了基于狭缝文丘里测量系统的气液两相流非分离测量方案,并进行了实验研究.利用狭缝文丘里重位压降信号在三类流动下的特性,可以直接识别流型,在不同的流型下用相应的测量模型求解气液两相的流量.结果表明该方法是可行的.     

风扇矩阵对冷却模块空气侧流场的影响

基于传统乘用车的单风扇系统,提出5种风扇矩阵形式,利用数值模拟技术分析不同矩阵形式对冷却模块空气侧流场的影响,结果表明：随着风扇数目的增加,冷却模块表面的速度均匀度皆表现出先减小后增大的变化趋势;N=4的风扇矩阵的速度分布均匀性最差,对应通过散热器的空气流量亦最小; N=15的风扇矩阵能够显著提升通过散热器的空气流量,相比原单风扇系统,空气流量提升15.6%。因此,在不降低散热器空气侧换热能力的前提下,采用该风扇矩阵形式能够使冷却系统的能耗降低,提高整车燃油经济性。采用风扇矩阵形式能够减少冷凝器前端的热回流区域,从而降低冷凝器迎风面的平均温度。     

人字形波纹板式换热器性能数值模拟的研究

基于简化模型的计算结果难以准确描述换热器内完整的流体流动和换热特性.为此,本文建立与人字形波纹板片完全相同的,含分配区和传热区冷热双流道换热的计算模型,用计算流体力学软件Fluent 6.3,数值模拟4组不同名义速度下流体的流动和换热情况.分析流道内速度场和温度场发现,进口分配区对流体流动分布和换热都有显著影响,还将流体在流道内的流动情况详细描述.两侧流体的压降和进出口温差的计算值与实验值的误差小于6%,较准确地反映了换热器内整体的流动和换热特性,可直接用于研究板式换热器的性能,具有一定的工程实际意义.     

受流股分流限制的石化工艺装置换热网络分析

石化工艺装置在工艺和流程优化的基础上,通过夹点分析可以确定换热网络的最小热、冷公用工程量;同时,为增加装置热能回收利用效率,通常利用夹点之下的余热生产相应压力等级的蒸汽。但是,在工程实践中,由于石化装置冷物流的分流限制,导致夹点之上的热量并不能全部用于加热冷物流,不可避免的引起热量穿越夹点换热。基于夹点技术,建立流股受分流约束的换热网络混合整数线性规划模型。将建立的模型应用于某延迟焦化装置,通过模型求解,获取不可避免的穿越夹点的换热量,指出在夹点附近处冷、热流股的合理匹配方案,并对比分析受流股分流限制和不受流股分流限制的冷、热公用工程,结果表明建立的模型能够为石化工艺装置换热网络设计或改造提供技术支持。     

建筑室内边界对流换热量的反向计算模型

针对目前反向计算模型还无法实现对建筑室内边界对流换热量进行反向计算这一制约性差距,采用温度贡献率方法,将边界对流换热量与室内测点温度之间表示成因果关系的温度贡献因子矩阵,基于计算流体力学,将最小二乘与Tikhonov正则化方法相结合,建立依据室内数个测点的离散温度求解边界对流换热量的反问题数学模型。应用三维通风空腔和某建筑内一间办公室进行实验验证,模型求解值与实测值的均方根差均小于80%,结果表明反向计算模型可以准确对室内边界对流换热量进行求解。     

采用不同制冷剂的汽车空调蒸发器性能仿真

运用制冷系统热动力学观点和动态分布参数方法建立起汽车空调蒸发器动态分布参数模型,用一种基于制冷剂质点追踪思想的解析-数值混合仿真方法进行求解,并对汽车空调蒸发器使用制冷剂R12、R22和R134a的热力性能进行了仿真.得出在相同的初始状态下,使用R22的蒸发器出口空气温度最低,出口过热度最小,制冷量最大,使用R134a的蒸发器热力性能略次于R22,而使用R12的蒸发器制冷效果是最差的.考虑到R22对环境的破坏作用,R134a是较理想的制冷剂替代物.     

Local heat transfer process and pressure drop in a micro-channel integrated with arrays of temperature and pressure sensors

One of the most important components in micro-fluidic system is the micro-channel which involves complicated flow and transport process. This study presents micro-scale thermal fluid transport process inside a micro-channel with a height of 37 μm. The channel can be heated on the bottom wall and is integrated with arrays of pressure and temperature sensors which can be used to measure and determine the local heat transfer and pressure drop. A more simplified model with modification of Young’s Modulus from the experimental test is used to design and fabricate the arrays of pressure sensors. Both the pressure sensors and the channel wall use polymer materials which greatly simplify the fabrication process. In addition, the polymer materials have a very low thermal conductivity which significantly reduces the heat loss from the channel to the ambient that the local heat transfer can be accurately measured. The air flow in the micro-channel can readily become compressible even at a very low Reynolds number condition. Therefore, simultaneous measurement of both the local pressure drop and the temperature on the heated wall is required to determine the local heat transfer. Comparison of the local heat transfer for a compressible air flow in micro-channel is made with the theoretical prediction based on incompressible air flow in large-scale channel. The comparison has clarified many of the conflicting results among different works.     

螺旋缠绕管式换热器传热性能优化与计算程序开发

螺旋缠绕管式换热器作为新型换热设备,与传统换热器相比,更为紧凑的管排列方式,增大了设备单位体积内的传热面积,且流体流动过程更易多流股化,从而提升传热综合效率;对设备的传热特性进行研究并与计算机技术相结合实现性能优化与计算方法改善,对于实际设备设计生产与使用具有重要意义;通过计算流体力学（CFD）方式,对螺旋缠绕管式换热器进行简化计算模型结构工作并开展数值模拟,研究不同管排列方式,相邻管层间距,壳程流速,换热管使用材料在设备换热性能方面的影响情况,得到设备优化结构,实现设备性能提升;选定管内径,管缠绕圈数,壳程流速以及管缠绕半径四个因素及其相对应水平参数开展正交试验,并分析单因素对于绕管式换热器综合传热性能PEC的影响情况及各因素的主次程度;运用Visual Basic语言进行计算程序开发,通过对流体物性参数,管内径,管缠绕圈数,管程数等进行输入并自动计算,实现压降,传热系数,综合性能指数等结果的可视化,提高后期设计工艺计算精度。     

A Microfabricated Flow Controller for Refrigerant Expansion

A flow controller for refrigerant expansion is reported. Devices are fabricated using a micromolding technique that is developed for thick nickel electrodeposition. The device consists of a short-tube restrictor with an integrated normally open valve, which, when actuated, presents a controllable blockage into the flow passage to obstruct the flow. Fabricated devices are evaluated with compressed air, with up to 22% reduction in mass flow rate at maximum actuation of the restrictor. The devices are also evaluated in an R134a vapor compression system of 1.5-2 kW, with the ability to control mass flow that is found to be greatly influenced by the vapor compression cycle's operational parameters. After the inlet pressure, the level of subcooling proved to be the most important parameter. For a cycle operating between 29 deg C and 4 deg C , saturation temperatures in the condenser and evaporator, respectively, actuation of the device reduced the refrigerant mass flow rate by 3.5% with 0.6 ^oC subcooling and up to 10.8 % with 5 deg C subcooling.     

多效蒸发系统优化设计目标函数的建立与求解

建立了带有冷凝水闪蒸的并流多效蒸发系统优化设计新模型。该模型以整个蒸发系统的年总费用（包括加热蒸汽年费用、真空系统年费用以及蒸发器和各辅助设备的年折旧维修费用等）最小为优化目标,以生蒸汽压力、冷凝器真空度及各效有效传热温度痉为决策变量,提出一种新算法——复合形法嵌套拉格朗日乘子法和矩阵法求最优解。算例表明,生蒸汽压力、冷凝器真空度、价格参数和冷凝水闪蒸对优化结果影响显著,按新模型优化设计比常规设计可节省年费用16％左右。新算法对初值要求不高、收敛稳定性好、收敛速度快。     

Design and fabrication of a cross flow micro heat exchanger

A cross flow micro heat exchanger was designed to maximize heat transfer from a liquid (water-glycol) to a gas (air) for a given frontal area while holding pressure drop across the heat exchanger of each fluid to values characteristic of conventional scale heat exchangers. The predicted performance for these plastic, ceramic, and aluminum micro heat exchangers are compared with each other and to current innovative car radiators. The cross flow micro heat exchanger can transfer more heat/volume or mass than existing heat exchangers within the context of the design constraints specified. This can be important in a wide range of applications (automotive, home heating, and aerospace). The heat exchanger was fabricated by aligning and then bonding together two identical plastic parts that had been molded using the LIGA process. After the heat exchanger was assembled, liquid was pumped through the heat exchanger, and minimal leakage was observed     

MPTL板翅式换热器性能的数值分析

研究机械泵驱动的两相冷却回路(MPTL)换热器传热效能优化问题,由于换热器的应用环境极为复杂,目前的实验数据极度匮乏,而且结构特殊,现有的标准叉流板式换热器的设计方法并不适用。为了提出可行的设计优化方法,针对某典型MPTL板翅式换热器,建立一种简化的三维物理数学模型,采用有限体积法及流固耦合方法深入研究该换热器在典型结构及设计工况下的流场特性,随后研究其在不同翅高及进口雷诺数时的换热性能变化规律。数值仿真结果表明,换热器换热效率较高,压力损失较小,且随着翅高的降低、进口雷诺数的增加,换热性能逐渐提高。结果证明,可为换热器的进一步设计与优化提供有益的参考。     

Investigation on pressure drop characteristic and mass transfer performance of gas–liquid flow in micro-channels

Pressure drop characteristics and mass transfer performance of gas–liquid two-phase flow in micro-channels with different surface wettabilities were experimentally investigated. Side-entry T micro-channel mixers made of glass and polydimethylsiloxane were tested. Frictional pressure drop was found to decrease as the hydrophobicity of the channel surface increased. The flow patterns observed in the experiment were classified as slug flow and continuous gas phase flows. The modified Hagen–Poiseuille equation and Lockhart–Martinelli model were developed to predict the pressure drop for these two types of flow, respectively. The effect of surface wettability was heuristically incorporated in the present models which can correlate well the experimental results. Mass transfer performance was studied by the physical absorption of oxygen into de-ionized water. The results show that the volumetric mass transfer coefficients in hydrophobic micro-channels are generally higher than those in hydrophilic ones. The empirical correlations of overall volumetric mass transfer coefficients were proposed.     

密封对汽车冷却模块性能影响的数值分析

为优化汽车前端设计,提高发动机舱散热性能,针对某乘用车发动机舱冷却性能提出冷却模块空气流量、格栅进气利用率和散热器实际散热量等3个评价参数,通过CFD软件对4种汽车前端进气冷却模块密封方案进行三维仿真计算,研究冷凝器、散热器与风扇罩之间的不同密封情况对3个评价参数的影响.研究结果表明,双密封方案是提高冷却模块性能的最佳方案.     

MODELING AND SIMULATION FOR INTELLIGENT CONTROL OF EXPANSION VALVE IN VAPOUR COMPRESSION REFRIGERATION SYSTEM

Conventional control techniques are not able to accomplish the stable cooling in VCRS (vapour compression refrigeration system) of air conditioning system. This article describes the fuzzy modeling and simulation for intelligent control to regulate the opening area of expansion valve for better and stable refrigerant flow even in the presence of operating condition change. Fuzzy logic control of expansion valve can make a quick response to the abrupt changes of operating parameters in VCRS. The expansion valve opening trend depending upon differential pressure across it (delP) and refrigerant mass flow rate is analyzed with fuzzy modeling using ANFIS. Differential pressures in the range of 3–7 bar are sustained across the valve. Flow rates up to 0.15 kg/sec for the refrigerant R-134a have been demonstrated. The performance of the model is evaluated by comparing the predicted results with the standard mathematical model.     

Modular simulation and thermodynamic analysis of absorption heat pumps

A modular simulation program of absorption heat pumps, refrigerators and air conditioners is developed under Mathematica ^®. The modular approach is an easier way to simulate various complex configurations. A comparative study between the simulator’s results—temperatures, pressures, refrigerant concentrations, heat duties, flow rates, overall heat transfer parameters and coefficient of performance (COP)—and experimental measurements shows a favorable agreement. The usefulness of the present program in performance analysis of thermodynamic cycles is thus established.