R134a闭式喷雾冷却传热性能实验研究

本文搭建了以R134a为工质的闭式喷雾冷却系统实验台,通过实验分析了稳态下制冷剂流量、过冷度和充注量对传热性能的作用规律,其中制冷剂流量范围为0.20～0.25 L/min、过冷度范围为5～8℃、充注量范围为0.95～1.25 kg.研究表明:在制冷剂流量为0.184 L/min、充注量为0.95 kg条件下,实验获得...     

R134a喷雾冷却系统换热性能研究

本文建立了以R134a为冷却工质的封闭式喷雾冷却系统,研究了工质过冷度、质量流量和热流密度对喷雾冷却系统换热性能的影响。其中,工质过冷度由喷嘴入口前的过冷段控制,质量流量通过变频齿轮泵调节,热流密度通过改变加热电源电压和电流控制。实验结果表明,在热流密度和质量流量保持不变时,改变过冷度对热源表面温度和换热系数的影响并不明显;在热流密度和过冷度保持不变的条件下,系统存在一个临界质量流量值,在质量流量达到临界值之前,热源表面温度随质量流量的增大而降低,当质量流量高于临界值时,热源表面温度随质量流量的增大而升高;当质量流量和过冷度保持不变时,存在一个热流密度使液滴的蒸发量等于补充量,在此热流密度下热源表面系数能达到最大。     

压电微孔雾化器的冷却性能研究

为了研究微孔雾化器的喷雾冷却性能,搭建了微孔雾化器的喷雾冷却试验台,研究了雾化量、喷雾高度、雾化器驱动频率等参数对冷却性能的影响。研究发现微孔雾化器的具有较好的冷却效果,雾化量对对冷却性能的影响基本呈线性关系;雾化性能随着喷雾高度的增加而降低;雾化器的驱动频率对冷却性能基本没有影响。研究结果可以为微孔雾化器的冷却应用提供参考。     

喷雾冷却系统中雾化特性影响因素研究

为研究喷雾式蒸发冷却超级计算机中喷射压力和喷嘴口径对喷雾雾化质量的影响,采用相位多普勒粒子分析仪(PDPA)对成雾状况做了精确测量,分析了雾化参数——雾滴速度、雾滴粒径与喷雾压力、喷嘴口径之间的关系。研究发现:喷雾的粒径分布呈现中间小、两边大的趋势,喷雾速度呈现中间大,两边小的趋势。随着喷雾压力的增加,喷雾的Sauter平均直径(SMD)逐渐变小,雾滴粒径分布趋向均匀,同时喷雾的平均速度变大。随着喷嘴口径的减小,雾滴粒径逐渐变大,速度则先增大后减小。平均SMD与喷雾压力P之间呈指数减小,平均速度V与喷雾压力P之间呈线性关系。平均SMD与喷嘴口径和压力有很好的二元线性关系。     

喷雾参数对喷雾冷却换热特性影响的实验研究

搭建了一套封闭式喷雾冷却实验系统(水为工质),利用高速摄像仪对实验进行了可视化研究,分析对比了喷雾高度和喷雾压力在光滑表面及微结构表面对喷雾冷却换热特性的影响。结果发现:相比于光滑表面,在微结构表面上,喷雾高度和喷雾压力对喷雾冷却换热的影响更加明显。当喷雾高度较高时,降低喷雾高度可明显提高热流密度,直至喷雾高度较低且喷雾底圆与换热面内接时,继续降低喷雾高度,热流密度也略有上升;反之,提高喷雾高度则会降低热流密度,减小工质的有效流量,使换热表面过早出现干涸,表面温度均匀性变差。但大幅降低喷雾高度会延迟喷雾冷却进入两相区换热,降低喷雾冷却效率,并不利于换热。所以,喷雾高度对喷雾冷却换热特性的影响具有两面性,而喷雾压力的影响则趋于单一性,增大喷雾压力能提高喷雾冷却热流密度,增强表面温度均匀性,尤其在单相区,随着喷雾压力的增大,热流密度明显增大,最后趋近于一个固定值。     

基于激光粒度仪测量油品喷雾粒径的方法研究

为了测量油品喷雾过程的雾化性能,通过对喷嘴雾化粒径的指标和雾化粒径测定方法的分析,利用激光粒度仪及粒径发生装置设计喷嘴雾化实验系统,并对实验系统的工作原理进行描述;在不同喷雾压力下测定煤基柴油特征平均粒径dv10、dv50、dv90、d[3,2]、d[4,3]数据。结果表明:柴油雾化过程分为形成阶段、扩散阶段、稳定阶段;喷雾压力越大,雾滴特征平均粒径dv10、dv50、dv90、d[3,2]、d[4,3]参数值越小,雾化效果越好,并且随着喷雾压力的增大,液滴雾化粒径减小的趋势变缓。     

气-水雾化喷嘴特性实验研究

为解决冷却器换热效率低的问题,提出将气一水雾化喷嘴应用于间接蒸发冷却,实验研究间接蒸发冷却器专用扇形气-水两相雾化喷嘴的特性,获得不同压力时喷嘴的雾化角和气水流量值及其变化规律,确定出最佳的喷雾气水比和雾化角等特性参数。     

制冷剂充注量对冷藏车用制冷机组性能的影响

为了研究制冷剂充注量对冷藏车用制冷机组性能的影响,在数值模拟得到的制冷剂标准充注量的基础上,试验研究制冷剂充注量对压缩机吸/排气压力、吸/排气温度、蒸发器出口过热度、冷凝器出口过冷度及制冷能力的影响。研究表明,数值模拟方法得到的制冷剂标准充注量适用于实际制冷机组。     

气-水雾化喷嘴特性实验研究

为解决冷却器换热效率低的问题,提出将气-水雾化喷嘴应用于间接蒸发冷却,实验研究间接蒸发冷却器专用扇形气-水两相雾化喷嘴的特性,获得不同压力时喷嘴的雾化角和气水流量值及其变化规律,确定出最佳的喷雾气水比和雾化角等特性参数。     

低压环境下喷雾特征实验研究

对蒸馏水分别通过压力雾化喷嘴和直流喷嘴喷射到低压环境的喷雾过程进行了实验研究,分析了环境压力、工质温度、工质流量对压力雾化喷嘴喷雾锥角和直流喷嘴喷雾瞬态特征的影响。实验结果显示,当采用压力雾化喷嘴时,环境压力越低,工质初始温度越高,喷雾锥角越大;工质流量越大,工质冲转旋转叶片速度越快,喷雾锥角也越大。当采用直流喷嘴时,环境压力越低,工质温度越高,工质流量越大,液柱出现破碎所用的时间越短。直流喷嘴的喷雾现象表现为随时间生长的过程,喷雾形态经历了液柱—液柱破碎—液柱完全雾化的过程。工质温度、环境压力直接影响工质的过热度,来影响闪蒸的剧烈程度,从而改变喷雾形态。     

Effects of injection pressure difference on droplet size distribution and spray cone angle in spray cooling of liquid nitrogen

Spray cooling with liquid nitrogen as the working fluid has been widely employed in a plenty of fields requiring cooling at cryogenic temperature, such as the cryogenic wind tunnels and cooling super-conducting magnets. In this study, we built a liquid nitrogen spray system and experimentally investigated the influence of injection pressure difference on the droplet size distribution and the spray cone angle. The measurements using particle size analyser show increasing the injection pressure difference improves the atomization, as indicated by the homogenization and reduction of the droplet size. The initial spray cone angle is insensitive to the injection pressure difference. However, the far-field spray cone angle decreases dramatically with increasing the injection pressure difference. The results could enrich our knowledge of spray cooling of cryogenic fluids and benefit the design of cryogenic spray cooling systems.     

双介质喷嘴雾化特性数值模拟研究

目的 双介质喷嘴雾化效果直接影响烟卷加料工艺的进一步提升，通过对雾化过程进行数值模拟，方便对雾化特性进行透彻的分析，提升雾化效果。方法 采用数值模拟方法构建两相流连续相流场与DPM离散态双向耦合的数值模型，研究蒸汽压力、液体流量以及双介质喷嘴结构对喷嘴雾化特性的影响。结果 适当增加蒸汽压力，可以在不影响最大流速、颗粒粒径均匀度及颗粒中值粒径的情况下，减小雾化扩散角，小幅度地增加喷射距离，雾化细度变好，进而提高雾化效果。随着有机液流量的增加，雾化扩散角增大，喷射距离增加，雾化粒径均匀度变好，从而使雾化效果变好。液体路通流面积越大喷雾的贯穿距离越小，气路通流面积越大喷雾的雾化扩散角度越大。若需要得到较好的雾化效果，需要保证较小的蒸汽路通流面积，与此同时液路侧保持正常开度。结论 适当地提高有机液流量或者蒸汽压力，以及采用较小蒸汽路通流面积，同时液路侧保持正常开度的结构，有利于提高料液喷洒的均匀性，减少了料液的浪费，提高了烟丝制备的工艺水平。     

The influence of cavitation on the flow characteristics of liquid nitrogen through spray nozzles: A CFD study

Spray cooling with cryogen could achieve lower temperature level than refrigerant spray. The internal flow conditions within spray nozzles have crucial impacts on the mass flow rate, particle size, spray angle and spray penetration, thereby influencing the cooling performance. In this paper, CFD simulations based on mixture model are performed to study the cavitating flow of liquid nitrogen in spray nozzles. The cavitation model is verified using the experimental results of liquid nitrogen flow over hydrofoil. The numerical models of spray nozzle are validated against the experimental data of the mass flow rate of liquid nitrogen flow through different types of nozzles including the pressure swirl nozzle and the simple convergent nozzle. The numerical studies are performed under a wide range of pressure difference and inflow temperature, and the vapor volume fraction distribution, outlet vapor quality, mass flow rate and discharge coefficient are obtained. The results show that the outlet diameter, the pressure difference, and the inflow temperature significantly influence the mass flow rate of spray nozzles. The increase of the inflow temperature leads to higher saturation pressure, higher cavitation intensity, and more vapor at nozzle outlet, which can significantly reduce mass flow rate. While the discharge coefficient is mainly determined by the inflow temperature and has little dependence on the pressure difference and outlet diameter. Based on the numerical results, correlations of discharge coefficient are proposed for pressure swirl nozzle and simple convergent nozzles, respectively, and the deviation is less than 20% for 93% of data.     

Numerical study of liquid nitrogen cavitating flow through nozzles of various shapes

The cavitating flow of cryogenic liquid through a spray nozzle is influenced by many factors, such as unique thermophysical properties of cryogenic liquid, the inflow temperature and the complicated geometrical structure of the spray nozzle. The geometrical parameters of liquid nitrogen spray nozzles have a profound impact on cavitating flow which in turn affects spray atomization characteristics and cooling performance. In present study, CFD simulations are performed to investigate influence of the nozzle geometry on the liquid nitrogen cavitating flow. The mixture model is used to describe the liquid-vapor two phase flow, and both the cavitation and evaporation are considered for the phase change. The predictions of mass flow of liquid nitrogen spray are validated against experimental results. The effects of geometric parameters, including the outlet orifice diameter and the length of nozzle, the inlet edge angle of orifice, the inlet corner radius of orifice, the orifice shape and different positions of swirl vanes, are investigated under a wide range of pressure difference and inflow temperature. The results show that the effects of geometric parameters on cavitating flow show different trends under subcooled conditions compared with saturated temperature conditions. The flow characteristics are more affected by the changes of the inlet edge angle, the inlet corner radius, and the orifice shape. The insert of swirl vanes has an effect on the distribution of the cavitated vapor within the orifice, but it has little influence on flow characteristics. The results could enrich our knowledge of liquid nitrogen cavitating flow in spray nozzles of various shapes.     

多层喷射共沉积制备 SiCP/Al-8.5Fe-1.3V-1.7Si复合材料

采用多层喷射沉积工艺制备SiC_P/Al-8.5Fe-1.3V-1.7Si复合材料, 研究了雾化及沉积工艺参数对沉积坯状态及SiC颗粒捕获的影响。结果表明, 液流直径大、雾化气体压力小、喷射高度小会导致沉积坯组织恶化, 反之则造成收得率低、致密度低。雾化器扫描不均匀则会造成沉积坯形状不均匀, 而且会由于热量集中导致显微组织恶化。SiC颗粒输送压力的提高有利于SiC颗粒的捕获以及颗粒的均匀分布。多层喷射沉积制备SiC_P/Al-8.5Fe-1.3V-1.7Si的优化工艺参数为: 液流直径3.6 mm, 雾化气体压力0.8 MPa, 喷射高度200 mm, SiC 颗粒输送压力0.5 MPa。 沉积坯存在两种SiC-Al界面: 晶态Si界面层与非晶态SiO₂界面层。     

Investigation on the atomization characteristics of a solid-cone spray for dust reduction at low and medium pressures

Water spray is the most widely used means of wet dust reduction, and its atomization parameters are directly related to the effect of dust reduction. In order to obtain the atomization properties of solid-cone spray for dust reduction, the paper used droplet velocity and particle size to characterize its atomization characteristics. The Phase Doppler Particle Analyzer (PDPA) was used to precisely measure droplet sizes and velocities of a solid-cone spray at distances of 15?cm, 25?cm and 45?cm horizontally from the nozzle outlet, using low and medium spray pressures. The results show that the droplet size was fluctuant before spray pressure increasing to 2.0?MPa and then decreased gradually with the increasing of spray pressure. The droplet velocity increased with the raising spray pressure and the velocity at 45?cm is the minimum. The droplet size measurements taken 45?cm from the nozzle exhibited more complex slope changes in particle size curve that were not existed at the closer distances spray of 15?cm or 25?cm, which implies that the near-field spray is more stable than far-field spray. This study is of important significance for further understanding the characteristics of solid-cone spray and guiding its application in dust reduction.     

大豆蛋白喷涂液雾化粒子场实验

目的研究大豆蛋白喷涂液雾化场的粒度分布,及喷涂过程中喷涂参数对大豆蛋白液雾化液滴粒径的影响,从而在蔬菜复合纸覆膜成型过程中选择最优喷涂参数。方法利用激光粒度仪测量不同喷涂参数下大豆蛋白液喷涂雾化场的粒度分布,并通过数据分析软件Origin研究喷涂参数对大豆蛋白液喷涂雾化粒度的影响。结果喷涂参数相同时,喷涂雾化场中随着轴向距离的增加,大豆蛋白液液滴粒径先显著减小后趋于稳定;喷涂雾化场中同一轴向位置随着径向距离的增加,大豆蛋白液液滴粒径呈减小趋势。在喷涂雾化场同一测量点,随着喷涂气压的增大,大豆蛋白液液滴粒径逐渐减小;喷涂液压对大豆蛋白液液滴粒径没有显著影响。结论喷涂气压为0.2 MPa,喷涂液压为0.16 MPa,喷涂雾化场轴向30 cm平面内,大豆蛋白液雾化液滴粒径较小且均匀。     

多功能超音速火焰喷涂雾化喷嘴的设计

对多功能超音速火焰喷涂系统的雾化原理与影响因素进行了分析，采用专门设计的射流雾化喷嘴，加工安装方便、雾化效果好。雾化的影响因素有：喷口大小、喷嘴压降、雾化介质的理化性质和燃烧室的压力与温度等。点火阶段为低速射流雾化，喷涂阶段为高速射流雾化。