CO2不同螺纹管管外强化换热的实验研究

通过对CO2的物理特性及水平光管与不同螺纹管管外沸腾换热进行实验研究,得出了换热系数随蒸发压力和热流密度的变化关系。拟合得出CO2在蒸发压力的范围为2.6~3.6MPa、热流密度为10~50 kW.m-2的换热关联式h=A.qn。与Cooper预测值的偏差在±15%之内,与Ribatski关联式预测值的偏差在±7%之内,与Ye实验关联式预测值的偏差在±9%之内。在CO2在光管管外沸腾换热的基础上进一步研究其在螺纹管管外沸腾对换热的强化效果,为CO2强化换热进一步发展提供依据,具有一定工程实践意义。     

纳米尺度固体悬浮颗粒强化池沸腾换热的实验研究

文中对纳米尺度的固体悬浮颗粒对泡状池沸腾换热的影响进行了实验研究，固体颗粒为粒径0.0016mm的黄沙和28nm的三氧化二铝粉末。实验分析了悬浮颗粒的沸腾特性，并讨论了颗粒大小、颗粒浓度对换热的影响。实验结果表明，在池沸腾条件下加入纳米尺度的固体颗粒能够有效的强化换热，强化效果与固体颗粒的大小及颗粒密度有关。     

细微通道内低温CO_2流动沸腾换热特性研究

用CO2作为制冷剂,对内径为0.6和1.5 mm的细微通道内的低温流体流动沸腾换热特性进行了实验研究,定量分析了实验测试工况下低温流体流经管路时不同工况参数对换热系数的影响。研究表明:参考文献[7]中提出的流动沸腾换热模型具有较高的预测精度,且将误差控制在30%的范围时,流体发生干涸前的换热系数理论预测精度比(实验数据与模型数据之比)可达79.8%,平均偏差可达21.8%;流体发生干涸后的换热系数理论预测精度比为18.4%,平均偏差为59.9%。     

一个水基SiO2纳米流体核态池沸腾数学模型

基于水基SiO_2纳米流体沸腾实验研究结果,在双流体多相流模型和热流分区模型(RPI模型)的基础上建立了一个水基SiO_2纳米流体核态池沸腾数学模型。结果表明:汽化核心密度、气泡脱离直径和纳米流体润湿角是纳米流体换热性能提升的主要原因,所建立的新的汽化核心密度、气泡脱离直径模型预测结果与实验数据吻合非常好,证明该模型的可靠性,给精确预测水基SiO_2纳米流体核态沸腾换热特性提供了重要参考。     

微细通道CO_2流动沸腾换热临界热流密度研究

CO2在微细通道内流动沸腾换热过程所具有的临界热流密度(CHF)对于其换热系数有着重要影响。根据国内外现有发表的公开文献的实验数据分析了质量流量、饱和温度、管径等对临界热流密度的影响,并对理论模型与试验数据进行误差分析。发现Bowring预测关联式对小于3 mm管径内临界热流密度预测精度较高,在30%误差范围内可以达到70%预测精度,Wojtan预测关联式具有较小的平均绝对误差。提出了今后CO2在微细通道内沸腾换热CHF的研究方向。     

电场作用下肋表面电对流现象的可视化研究

电场可强化池态沸腾换热已经得到研究者的普遍认可.以往研究者主要针对光滑表面、加热管或加热线表面的电场强化换热进行研究.在光滑表面增加肋结构可以改变加热面附近的电场分布,从而影响加热面的换热效果.以R113作为实验工质,搭建了可视化的池沸腾实验台,采用高速摄像机记录了肋高为2 mm的加热面在电场作用下的电对流现象.实验发现,电对流随着施加电压的升高而增强,电对流加速了加热面附近流体的混合,破坏了热边界层,使得加热面温度降低从而强化了换热.     

石墨烯纳米制冷剂核态池沸腾换热的实验研究

为分析单层石墨烯纳米片对核态池沸腾换热的影响机理,对基液为R141b、分散相为单层石墨烯纳米片的纳米制冷剂的核态池沸腾换热特征进行了测定,采用Hot Disk热物性分析仪和铂金板法分别测定了石墨烯纳米制冷剂的热导率和表面张力,采用接触角测量仪和扫描电子显微镜（SEM）观测了沸腾后加热表面的润湿性和形貌特征。实验中,单层石墨烯纳米片的质量百分含量（ω）为0.02%~0.50%,实验压力为一个标准大气压,热流密度为20~200 kW/m2。实验结果表明：单层石墨烯纳米片的加入,使制冷剂R141b的核态池沸腾换热得到强化;当ω=0.2%时,换热系数提高比例出现峰值,为57.7%。伴随ω的增加,石墨烯纳米制冷剂的热导率增大、表面张力减小,沸腾表面润湿性增强且微腔数先增后减,综合作用的结果导致存在一个最佳的单层石墨烯纳米片浓度（即ω=0.2%）使换热系数最高。     

换热表面直接与间接测温的对比性实验研究

进行了沸腾换热表面的间接测温与直接测温的对比性实验研究。以水和乙醇作工质,对大气压力下的池沸腾换热平表面,用间接测温法和直接测温法同时测量壁面过热度,对两种测温方法的结果进行了比较研究。同时,用直接测温法进行三种不同管径的光管沸腾试验,并把实验结果与Rohsenow公式进行了比较。大量实验结果表明,在一定操作条件下,直接测温法测量沸腾换热表面过热度误差较小,是一种简便而又行之有效的方法。     

国内能源环保文献索引

02 0 40 1　赵言冰 ,施明恒 .纳米尺度固体悬浮颗粒强化池沸腾换热的实验研究 [Ｊ] .能源研究与利用 ,2 0 0 2 ,(3 ) :18-2 0 .实验分析了悬浮颗粒的沸腾特性 ,并讨论了颗粒大小、颗粒浓度对换热的影响。实验结果表明 ,在池沸腾条件下加入纳米尺度的固体颗粒能够有效的强化换热 ,强化效果与固体颗粒的大小及颗粒密度有关。0 2 0 40 2　施慧琴 .冷凝水回收系统改造 [Ｊ] .能源研究与利用 ,2 0 0 2 ,(3 ) :2 6-2 8.分析了扬子石化公司工艺外管网蒸汽伴热系统存在的问题 ,介绍了冷凝水回收系统改造情况以及改造后取得的经济效益 ,并对尚存问题…     

垂直矩形窄缝内的过冷流动沸腾换热性能

用高速摄像等方法研究了有压模化介质在单一垂直矩形窄缝流道内的气泡形态和传热情况 ,发现窄缝流动沸腾换热强化的原因在于流道尺寸较小 ,气泡的形状发生变化 ,增加了界面体积浓度 ,并强化了对加热面附近的扰动 ,使换热有所强化。通过与实际测量的壁温数据进行比较 ,发现用于计算大流道和池过冷沸腾换热的 Rohsenow关系式预测窄流道内高热流密度下的过冷流动沸腾换热的误差不大 ,但对于较低热流密度下的过冷流动沸腾时误差较大 ;通过最小二乘法对 Rohsenow关系式进行修正后 ,误差低于± 2 5 %。     

超临界碳氢燃料流动换热的仿真研究

建立了适用于温度、压力大范围变化的超临界碳氢燃料换热特性研究的一维模型,试验验证了模型的可靠性,基于该模型分析了质量流率、换热状态转换和压力等因素对超临界碳氢燃料的换热特性的影响。结果表明:4.0 MPa的低压力工况下,在超临界碳氢燃料的拟临界温度附近存在传热强化现象,而7.0 MPa的高压力工况下,该传热强化现象消失;不论质量流率的大小,4.0 MPa工况下的传热系数始终高于7.0 MPa工况下的传热系数,压力的高低在超临界碳氢燃料的汽相换热区对传热性能的影响更为显著;40kg/(m2.s)的低质量流率条件下,由液相换热区向汽相换热区的换热状态转换将导致转换区附近的传热恶化,而增大质量流率则可避免该问题的发生。     

内表面烧结型多孔管的流动沸腾换热

采用流动沸腾传热试验平台,研究了2 m长铁基烧结型内表面多孔管竖直管内流动沸腾传热特性,利用流动沸腾传热学基本原理及公式计算了传热过程中的热通量、沸腾传热系数及相关参数,并考察了过热度和流速对多孔管流动沸腾传热性能的影响.结果表明:烧结型表面多孔管的流动沸腾传热能力优于同条件下的光滑管,内表面沸腾传热系数是同尺寸光滑管...     

真空条件下珠状凝结传热特性的理论分析与试验研究

从理论分析和试验研究两个方面研究了真空状态下珠状凝结的传热特性.首先从蒸汽流场、气膜热阻和表面能3个角度进行理论分析,分析结果表明,珠状凝结的换热系数K值随着真空的提高而增大.然后进行真空条件下的珠状凝结试验,经过数据分析表明,试验结果与理论分析相吻合,即在真空条件下,凝结换热系数K值随着真空度的提高而增大,在较大Re数时(Re＝34755),真空度每提高0.01 MPa,换热系数可提高10%左右.     

干煤粉加压气流床气化试验研究

介绍了36t/d加压气流床气化中试装置主要设备、工艺流程及工艺条件的选择,并给出试验研究中多个煤种在气化压力3.0MPa、投干粉煤量1t/h条件下取得的主要试验数据。从试验数据看出,干法气化指标明显优于水煤浆气化,主要是CO2含量低,有效成分(CO H2)含量高(均大于89%),证明了干煤粉气化的优越性。试验结果基本达到预期目的,积累了干粉煤气流床气化数据。     

Experimental study on saturated flow boiling heat transfer of R290/R152a binary mixtures in a horizontal tube

An experimental study on the saturated flow boiling heat transfer for a binary mixture of R290/R152a at various compositions is conducted at pressures ranging from 0.2 to 0.4 MPa. The heat transfer coefficients are experimentally measured over mass fluxes ranging from 74.1 to 146.5 kg/(m²·s) and heat fluxes ranging from 13.1 to 65.5 kW/m². The influences of different parameters such as quality, saturation pressure, heat flux, and mass flux on the local heat transfer coefficient are discussed. Existing correlations are analyzed. The Gungor-Winterton correlation shows the best fit among experimental data for the two pure refrigerants. A modified correlation for the binary mixture is proposed based on the authors’ previous work on pool boiling heat transfer and the database obtained from this study. The result shows that the total mean deviation is 10.41% for R290/R152a mixtures, with 97.6% of the predictions falling within ±30%.     

Effects of pool subcooling on boiling heat transfer in a vertical annulus with closed bottom

Effects of inlet subcooling on pool boiling heat transfer in a vertical annulus with closed bottom have been studied experimentally. For the test, a tube of 19.1 mm diameter and the water at atmospheric pressure have been used. Up to 50 K of pool subcooling has been tested and results of the annulus are compared with the data of a single unrestricted tube. The increase in pool subcooling results in much change in heat transfer coefficients. As the heat flux increases and the subcooling decreases, a deterioration of heat transfer coefficients is observed. The governing mechanisms are suggested as single-phase heat transfer and liquid agitation for the single tube while liquid agitation and bubble coalescence are the major factors at the bottom closed annulus.     

Complete condensation in a vertical tube passive condenser

An experimental study is performed for the steam condensation in a vertical tube where steam is completely condensed. A condenser tube is submerged in a water pool where the heat from the condenser tube is removed through boiling heat transfer. The experiment data showed that the operating pressure is uniquely determined by inlet steam flow rate for the complete condensation. The condensation heat transfer rate increases and the condensation heat transfer coefficient decreases with the system pressure. For the condenser submerged in a saturated water pool, strong primary pressure dependency was observed on the condensation heat transfer.     

An Experimental Study of Carbon Dioxide Condensation in Mini Channels

In this study, the local characteristics of pressure drop and heat transfer were investigated experimentally for carbon dioxide condensation in a multi-port extruded aluminum test section, which had 10 circular channels each with 1.31 mm inner diameter. The CO2 was cooled with cooling water flow inside the copper blocks that were attached at both sides of the test section. The temperatures at the outer surface of the test section were measured with 24 K-type thermocouples embedded in the upper and lower surfaces along the length. Local heat fluxes were measured with 12 heat flux sensors to estimate the local enthalpies, temperatures and heat transfer coefficients. Bulk mean temperatures of CO2 at the inlet and outlet of the test section were measured with 2 K-type thermocouples. The measurements were performed for the pressure ranged from 6.48 to 7.3 MPa, inlet temperature of CO2 from 21.63 to 31.33℃, heat flux from 1.10 to 8.12 kW/m2, mass velocity from 123.2 to 315.2 kg/m2s, and vapor quality from 0 to 1. The results indicate that pressure drop is very small along the test section, heat transfer coefficient in the two-phase region is higher than that in the single-phase, and mass velocity has important effect on condensation heat transfer characteristics. In addition, experimental data were compared with previous correlations and large discrepancies were observed.