螺旋翅片管束空气侧流动与换热特性研究

采用数值模拟与模化试验相结合的方法研究螺旋翅片管空冷器空气侧的流动与换热特性。分析翅片螺距、翅片高度、横向管间距、纵向管间距对换热与阻力的综合性能影响;基于正交试验原理,以Q_v,Nu,Δp,f为指标,分析翅片螺距、翅片高度、横向管间距、纵向管间距对不同指标的影响程度差异,并获得各指标均较优的翅片螺距、翅片高度、横向管间距、纵向管间距的优化组合。结果表明:当其他结构参数一定时,PEC最优的翅片螺距、翅片高度、横向管间距、纵向管间距分别为3.5,6.5,67,53.69 mm;Q_v,Nu,Δp,f较优的结构参数组合为翅片螺距3.5 mm、翅片高度15.5 mm、横向管间距67 mm、纵向管间距53.69 mm;与国标推荐结构相比,相同Q_v时优化结构的Δp明显较小。研究成果可为空冷器螺旋翅片管束优化提供依据。     

柱形涡发生器强化撞击流反应器流场特性的数值模拟

利用数值模拟方法分析设有柱形涡发生器的撞击流反应器的流场特性,优化了柱形涡发生器的尺寸与位置参数,考察了柱形涡发生器尺寸与位置参数对撞击流反应器流场结构、速度分布、湍流尺度和混合性能的影响。结果表明,柱形涡发生器直径D=10 mm时,反应器内旋涡数量最多,涡系影响范围最广;D<10 mm时,旋涡数量减少;D>10 mm时,涡系影响范围减小。柱形涡发生器横向间距的增加使反应器内旋涡数量减小,涡系影响范围增大。随着柱形涡发生器横向间距、纵向间距的增加,撞击流反应器径向流速、湍流尺度和混合强度均先增大后减小。当柱形涡发生器横向间距K=5 mm、纵向间距J=70 mm时,撞击流反应器混合效果最佳。     

螺旋翅片管空冷器换热与阻力性能研究及优化

为了获得翅片螺距t、翅片高度h、横向管间距S1和纵向管间距S2对螺旋翅片管束换热与阻力性能的影响,并优化翅片结构,对12组螺旋翅片管束进行数值模拟,并通过模化试验验证.结果表明:t为2.3-2.6 mm时,增大翅片螺距,Nu与Eu都减小;h为9.5-15.5 mm时,增大翅片高度,Nu与Eu都增大;S,为62-72 m...     

气流横向冲刷管束湍流换热的场协同分析

推导出了气流横向冲刷管束湍流换热时的传热Nu数与场参数的关系表达式,用数值模拟的方法对湍流时场协同原理进行了分析与验证。结果表明,换热随管排方式和管间距的改变而有所不同,是因为速度场与热流场的协同作用的不同,速度场与热流场的协同性好,则传热性能好。场协同原理同样适合于气流横向冲刷管束湍流流动与换热。对湍流换热时场协同作用特点进行了分析,指出湍流时速度场与热流场的协同作用对换热的影响主要表现在粘性底层以外的壁面附近。     

气液两相流中顺列管束涡街特性实验研究

对受气液两相流横向冲刷的顺列管束旋涡脱离特性进行了实验研究。实验中通过测量顺列管束所受升力的频谱特性来确定涡街的脱离频率。实验中来流雷诺数的范围为 1.6× 10 4～ 8× 10 4,截面含气率的范围为 0～ 0 .30 ,横向管间距比 T/ D=1.5、 2 .0、 3.0 ,纵向管间距比 P/ D=2 .0、 3.0、 4.0。实验结果揭示了顺列管束涡街特性和斯特罗哈数随含气率、管间距、两相雷诺数的变化规律     

管束结构对开缝翅片椭圆管换热器性能的影响

在模化试验验证的基础上,对不同横向管间距S_1、纵向管间距S_2和椭圆管长短轴比a/b的开缝翅片椭圆管换热器进行了数值模拟,分析了管束结构的差异对开缝翅片椭圆管换热器性能的影响。结果表明:横向管间距在60.55~70.55 mm范围内,空气侧N_u和E_u均随S_1减小而增大,S_1为60.55 mm时换热器综合流动传热性能最好;纵向管间距在65~75 mm范围内,空气侧N_u随S_2减小而增大,E_u变化不明显,S_2为65 mm时换热器综合流动传热性能最好;横向管间距对开缝翅片椭圆管换热器传热、流动性能的影响较纵向管间距更为明显;在等周长条件下,椭圆管长短轴比a/b在1.5~2.5范围内,a/b为1.8时换热器综合流动传热性能最好。研究成果可为此类换热器在工程实际中的应用与进一步优化提供依据。     

管束结构对开缝翅片椭圆管换热器性能的影响

在模化试验验证的基础上,对不同横向管间距S₁、纵向管间距S₂和椭圆管长短轴比a/b的开缝翅片椭圆管换热器进行了数值模拟,分析了管束结构的差异对开缝翅片椭圆管换热器性能的影响。结果表明：横向管间距在60.55～70.55 mm范围内,空气侧Nu和Eu均随S₁减小而增大,S₁为60.55 mm时换热器综合流动传热性能最好;纵向管间距在65～75 mm范围内,空气侧Nu随S₂减小而增大,Eu变化不明显,S₂为65 mm时换热器综合流动传热性能最好;横向管间距对开缝翅片椭圆管换热器传热、流动性能的影响较纵向管间距更为明显;在等周长条件下,椭圆管长短轴比a/b在1.5～2.5范围内,a/b为1.8时换热器综合流动传热性能最好。研究成果可为此类换热器在工程实际中的应用与进一步优化提供依据。     

蒸发式冷凝器在空气流动下优化设计数值模拟

利用FLUENT软件对3种常用的管形蒸发式冷凝器在空气流动状态下进行了优化设计的数值模拟,比较分析了在不同入口风速下的压降变化规律;对来流速度大小与来流角进行了优化设计,得到最适宜的来流速度在2.4—3.3 m/s,入口来流角θ范围为-15°—15°;在不同空气流量下管排的纵向间距与横向间距之比(S/L)模拟结果表明,在一定空气流量下,不同管形管排的S/L存在着一个最佳值,使得单位压降下换热盘管的平均表面传热系数最大,而且随着流量的增加,最佳的比值呈减小趋势。为蒸发式冷凝器的优化设计提供了重要依据。     

纵肋管束换热器特性研究

对纵肋管束换热器的传热、阻力特性进行了试验研究,得出其实验关系式.以此分析管束节距的影响,指出横向节距是决定纵肋管束流阻的首要因素,增加横向节距将大幅度减小流胆;而横向节距和纵向节距对换热的影响程度基本相同.对于1组节距为S_t/D=3.29、S_l/D=1.6的纵肋管束,其实际换热系数可增加9%～12.5%,流阻系数可降低15%～65%.结果表明,纵助管束具有低流阻特性和较强的传热强化作用.     

立式花瓣管外空气螺旋流动传热及流阻性能研究

螺旋隔板花瓣管换热器具有优异的换热性能,但由于目前基础数据不足,螺旋隔板花瓣管换热器的应用还未能普及,研究花瓣管几何结构参数对换热过程的影响规律及传热机理,可为该类型换热器提供设计依据.今在实验中通过采用空气在缠绕金属螺旋片的换热管外套管环隙中的换热来模拟螺旋隔板换热器的换热过程,研究了空气在缠绕螺旋片的立式光滑管和不同翅片高度与间距的立式花瓣管外螺旋流动的传热与流阻性能,分析了花瓣管翅片高度和间距等主要几何结构参数以及管外空气流速对传热与流阻性能的影响.实验结果表明:翅片高1.5mm、间距1.0mm的花瓣管具有最佳的传热性能,花瓣管外空气对流换热系数是光滑管的1.48～3.24倍;在实验范围内,随着空气流速的增加,花瓣管外空气对流换热系数与流动阻力也相应增加,但综合换热性能下降并在空气流速为36.0～42.2m·s-1时达到最低值.     

空气在立式花瓣管外螺旋流动传热与流阻性能研究

试验研究了空气在5种管径相同、不同翅片高度和翅片间距的立式花瓣管外螺旋流动的传热和流阻性能,分析出在试验范围内:花瓣管翅片高度相同时存在一最适宜翅片间距,使其传热性能最优;花瓣管翅片间距相同,翅片越高,其传热性能越好,而流动阻力损失也越大;管外系统压力越高,换热效果越好,且不会增加其流动阻力,这可为设计高效立式螺旋隔板花瓣管换热器提供参考依据。     

V型导液槽对HFC245fa水平管束外冷凝换热影响

试验研究了HFC245fa在水平光管与强化管管束外的冷凝换热特性,提出在管束中加装V型导液槽来消除管束效应的方法,并通过试验研究了V型导液槽对管束冷凝换热特性的影响。试验管束由4列排深为5排的列管构成,带导液槽管束的前4排管下方加装了两段长度为450 mm的导液槽;试验换热管公称外径为19.05 mm、换热长度为1000 mm。试验中,以Wilson描点法获得强化换热管水侧对流传热系数,以对比试验方法研究了V型导液槽对水平管束外冷凝换热性能的影响。结果表明：传统的管束效应模型仅在较小的热通量范围适用;凝液在管间的迁移形态与流态随管上作用凝液量的系列变化是导致管束效应变化的主要因素;加装导液槽可有效控制凝液在管间的迁移,控制管束效应;加装导液槽使光管单管冷凝传热能力下降10%左右,使光管管束总体换热能力提升4.5%相似文献   

氟里昂R-113在水平管束管外池沸腾实验研究

通过对氟里昂R-113在水平管束管外地沸腾的实验研究,分析了管束沸腾的滞后现象及沸腾换热系数的管束效应.得出了管束沸腾换热系数的经验关系式,并讨论了关系式中系数和指数与换热机理的内在联系.     

氟里昂R-113在水平管束管外池沸腾实验研究

通过对氟里昂R-113在水平管束管外地沸腾的实验研究,分析了管束沸腾的滞后现象及沸腾换热系数的管束效应.得出了管束沸腾换热系数的经验关系式,并讨论了关系式中系数和指数与换热机理的内在联系.     

水平管束沸腾传热的对流与薄层蒸发贡献

引言目前,卧式再沸器的热设计仍沿用Palen等人60年代初基于单管池沸腾传热机理所提出的方法．近十几年来,大量实验研究结果表明,在相同条件下管束的沸腾传热系数高于单管．人们逐渐认识到管束沸腾传热为核沸腾、对流和薄层蒸发传热机理所控制．由此可见,在卧式再沸器的设计中,基于单一的池沸腾传热机理所得关联式进行卧式再沸器的热设计,造成传热面积裕度偏大、设备体积庞大、浪费材料、设备效率低,显得十分保守．因此,深入研究水平管束的沸腾传热机理,进而发展更为合理的卧式再沸器的设计模型,对于改进这类设备的设计、改善设备…     

The effect of vapour shear and condensate drainage in condensers using roped tubes

It is well known that the heat transfer performance of a condensing heat exchanger can be improved by using roped or spirally indented tubes. Most of the published work refers to experiments carried out on single tubes in closely controlled laboratory experiments. If such tubes are to be used in practical situations the designer must know how they will perform in tube bundles. One of the main problems in condensers is the effect of condensate drainage (inundation) and vapour shear on the performance of that condenser. A series of experimentals have been carried out in three different tube bundles of 21 tubes in order to investigate the above phenomenon. One of the bundles was of plain tubes the other two were of roped tubes of the same diameter, groove pitch and groove depth but of differing helix angle. These values were 11mm., 0.2mm. and 6.4mm. respectively. The tubes were all 0.69.m long. The main experimental variables were cooling water velocity and logarithmic mean temperature difference.The results show that, as would be expected, condensate inundation reduces heat transfer in condensers. In addition, the flow pattern of the vapour in the condenser has a significant effect on the heat transfer performance of tubes in the bundle. Experiments with the roped tubes show that their performance is not as adversely affected by condensate drainage as is the plain tube bundle.     

Boiling Heat Transfer Enhancement of Water/Salt Mixtures on Roll‐Worked Enhanced Tubes in Compact Staggered Tube Bundles

An experimental study was performed for the boiling heat transfer enhancement of water/salt mixtures on both plane and roll‐worked enhanced tubes in compact staggered tube‐bundle evaporators under atmospheric and increased pressure conditions. The effects of tube spacing, position of tubes, test pressure and salt‐water concentration on the boiling heat transfer characteristics in restricted spaces of compact tube bundles consisting of plane and roll‐worked tubes were investigated. The experimental results indicate that the single roll‐worked tubes in a bulk liquid have a greater boiling heat transfer promotion than the single plane tubes. For the plane tubes in compact tube bundles, the effect of tube spacing on the boiling heat transfer is very significant. The boiling heat transfer has a maximum enhancement when the optimum tube spacing is selected. For the roll‐worked tubes in compact bundles, the effect of tube spacing on the boiling heat transfer is also significant as the tube spacing is small. The boiling heat transfer still has a maximum value and a compound enhancement effect of the boiling heat transfer from both the optimum tube spacing and the surface treatment is observed for the enhanced tube bundles.     

U形圆管中超临界压力RP-3航空煤油换热数值研究

基于航空发动机空-油换热器的冷却换热问题,开展了竖直U形圆管内超临界压力RP-3航空煤油换热的数值研究。探究了进口竖直段、弯管段、出口竖直段的换热特征和换热机理,阐述了运行压力和热质比对换热的影响机制。结果表明：进口竖直段呈现均匀换热的特征。弯管段离心力作用致使流体温度出现异常分层,周向密度不均匀,横向不平衡动能诱发强二次流问题,最大二次流速度达到0.45 m·s^-1。固体热传导过程也受到影响,出现固体温度异常分层。两者综合作用下导致管壁温度和热通量的周向差别。出口竖直段的周向换热差别依然存在,二次流被削弱。提高运行压力或降低热质比,管截面热物性变化趋缓,周向换热差别减弱。     

Enhancement Boiling Heat Transfer Study of a Newly Compact In‐line Bundle Evaporator under Reduced Pressure Conditions

For common flooded‐type evaporators, nucleate boiling heat transfer cannot occur on the heated tubes since heat fluxes and wall superheats of heated tubes are generally quite low. However, when the tube spacing is very small, nucleate boiling in restricted spaces can occur easily under low heat flux or low wall superheat conditions. The generation of nucleate boiling can effectively enhance the heat transfer performance of bundle evaporators. This study investigated experimentally the boiling heat transfer enhancement effects of the restricted space in compact in‐line tube bundles with smooth tubes under various reduced pressures. The experimental results show that the compact in‐line tube bundles have a significantly enhanced heat transfer compared to those of the common tube bundles, and there is an optimum tube spacing that provides the greatest heat transfer enhancement effect. The test pressures have a marked influence on the boiling heat transfer enhancement in the compact bundles. The heat transfer enhancement effect decreases with decreasing test pressure. In addition, the heat transfer enhancement effects of the in‐line tube bundles are also compared with those of the staggered bundles. Under reduced pressure, there is no significant difference between the heat transfer enhancement effects for the two types of bundles.     

水平管外降膜蒸发的传热实验

为了提高水平管降膜蒸发的传热性能,提出了在水平管间增加肋板结构来强化传热。研究了以蒸馏水为介质的水平管外降膜蒸发的传热性能,结果表明,管外降膜蒸发传热系数随传热喷淋密度、传热温差和管间肋板宽度的增大而增大,随管径的增大而减小。