扭曲管蒸发式冷凝器的性能与工业应用

提出了扭曲管强化蒸发式冷凝器性能,实验测试了螺距、管径、冷却水喷淋密度和风速对传热与功耗性能的影响.实验结果表明,扭曲管比圆管的性能好,螺距和管径越小、水喷淋密度和风速越大,传热系数越高,但流动阻力同时增大,存在合适的螺距、管径、水喷淋密度和风速使蒸发式冷凝器综合性能最佳.以实验结果为基础,将蒸发式冷凝器在工业中应用,起到良好的节能节水效果.     

板式蒸发式冷凝器传热性能试验研究

搭建了板式蒸发式冷凝器传热性能试验平台,对影响板式蒸发式冷凝器传热性能的主要因素———喷淋水流量、风速、汽液流向以及工艺流体进出口位置进行试验研究。结果表明:空气与水并流时传热效果最好、逆流次之、错流最差;板内冷凝压力随冷却循环水喷淋密度、风速的增大而减小;在各自最佳风速,不同汽液流向操作下,蒸汽对角进出时的热流密度均比蒸汽同侧进出时大。     

水膜式蒸发冷凝器管外液膜分布的三维数值模拟

利用Fluent软件对水膜式蒸发冷凝器管外成膜情况进行了三维数值模拟,将模拟结果与文献中的试验值进行了比较,变化趋势总体吻合较好,计算并分析了椭圆管在不同迎面风速和倾斜角度下的管外水膜厚度及分布情况。结果表明:液膜厚度波动随着风速的增大而增大,且波动区主要集中在周向130°~160°附近;随着倾斜角度的增大,水膜厚度波动区向下偏移;迎面风速一定时,管外周向液膜厚度呈先减小至周向65°位置后开始增加的趋势。     

蒸发式冷凝器雨区气温水温测量方法的研究

对蒸发式冷凝器雨区中空气与喷淋水滴进行传热试验研究的困难主要在于雨区中的空气温度难以准确测量.针对蒸发式冷凝器雨区空气与水逆向流动的特点,设计了可以同时测量雨区气温和水温的装置.试验测量了不同喷淋量和不同风速下的雨区气温值,根据传热学和热力学理论分析了雨区气温测量值的变化规律.试验和分析表明,该装置能有效分离水和空气,准确测出气温和水温.本测量方法对气液两相逆向流动的深入实验研究有积极作用.     

蒸发式冷却器热质传递性能研究

喷淋水量和迎面风速等参数对蒸发式冷却器的换热性能有重要影响,对此进行了实验研究。结果表明：在同一喷淋密度下,空气进出口焓差随迎面风速的增加而降低,传热系数K₀和传质系数K_m随迎面风速的增加而增加,但增加的趋势越来越平缓。在实验工况下喷淋密度为0.046～0.1389kg·m^-1·s^-1和迎面风速为0.85～2.29m/s范围内,传热系数K₀和传质系数K_m呈现出随喷淋密度先增大后减小的趋势,随着迎面风速增大到1.87m/s,K₀增长到最大值的喷淋密度逐渐后移到0.0926kg·m^-1·s^-1。     

立式蒸发式冷凝器水膜流动特性试验研究

对立式蒸发式冷凝器的水膜流动特性进行了试验研究,分析了喷淋水量、进口空气流速和螺旋线插入物对水膜流态的影响,并探讨了管内的液泛现象和得到液泛的经验公式,为立式蒸发式冷凝器的设计和优化提供参考依据.     

平行流冷凝器空气侧传热性能探讨

根据Devonport关联式,利用数值模拟的方法,针对某平行流冷凝器,分析了迎面风速变化时空气侧主要结构参数(翅片间距、翅片高度、百叶窗间距和角度)对空气侧传热系数及压降的影响规律。为平行流冷凝器空气侧的结构优化提供了理论研究。     

扁管空冷器翅片结构优化研究

基于带翅片的扁管空冷器的传热过程,对带翅片的扁管建立模型,并利用该模型在不同的翅片长度及不同风速下进行数值模拟,分析了翅片长度的选择与迎面风速的关系。分析结果表明,当翅片长度增加到一定值后,通过增加翅片长度的手段来强化换热性能收效很小;在低迎面风速下,翅片长度不要过长;在高迎面风速下,仍存在较大的传热温差,空气出口温度的增加只能通过增加翅片长度来完成。     

蒸发式冷凝器的设计选型及在氨制冷系统中的应用

介绍了用温降计算法进行蒸发式冷凝器的选型计算,分析了影响蒸发式冷凝器传热效率的因素,指出设置洗涤式油分离器对于氨制冷系统的有利作用。同时结合工程实例对蒸发式冷凝器的管路进行了设计,并对其结构提出了改进意见。     

蒸发式冷凝器在离心式冷水机组中的应用研究

介绍了蒸发式冷凝器在离心式冷水机组中的应用原理,分析了蒸发式冷凝器应用于离心式冷水机组中的相应优势,以及应用中可能存在的相应问题,即影响蒸发式冷凝器传热性能的几个制约因素。针对以上优势和问题因素提出蒸发式冷凝器在离心式冷水机组中应用的相关研究思路和设想,实现离心式冷水机组的高效节能。     

Cooling characteristics on the forced convection of an array of flat-form electronic components in channel flow

Present study is concerned with forced convective heat transfer of the channel flow with line arrays of heated electronic components mounted on a printed circuit board. For the assessment of thermal performance in channel flows, three separate variables are used:channel spacing, row number of the component, and inlet air velocity. The thermal characteristics of a component due to own power and upstream air heated by components were studied. The experimental results were compared with those of numerical solution for various conditions: surface temperature of the components, adiabatic temperature rise, and heat transfer coefficient. The experimental results agree well with the numerical solutions. The study shows that the adiabatic heat transfer coefficient is significantly affected by the inlet velocity in channel flow and less dependent on the channel spacing and row number, except for the case ofH/B=3.3. While reviewing the previous literatures, it is found that a little difference in the correlation between Nu and Re is due to the different geometric ratio of the packaged components.     

Thermal performance analysis of heat exchanger for closed wet cooling tower using heat and mass transfer analogy

In closed wet cooling towers, the heat transfer between the air and external tube surfaces can be composed of the sensible heat transfer and the latent heat transfer. The heat transfer coefficient can be obtained from the equation for external heat transfer of tube banks. According to experimental data, the mass transfer coefficient was affected by the air velocity and spray water flow rate. This study provides the correlation equation for mass transfer coefficient based on the analogy of the heat and mass transfer and the experimental data. The results from this correlation equation showed fairly good agreement with experimental data. The cooling capacity and thermal efficiency of the closed wet cooling tower were calculated from the correlation equation to analyze the performance of heat exchanger for the tower.     

Experimental measurement and numerical computation of the air side convective heat transfer coefficients in a plate fin-tube heat exchanger

The air-side forced convective heat transfer of a plate fin-tube heat exchanger is investigated by experimental measurement and numerical computation. The heat exchanger consists of a staggered arrangement of refrigerant pipes with a diameter of 10.2 mm and a fin pitch of 3.5 mm. In the experimental study, the forced convective heat transfer was measured at Reynolds numbers of 1082, 1397, 1486, 1591 and 1649 based on the diameter of the refrigerant piping and on the maximum velocity. The average Nusselt number for the convective heat transfer coefficient was also computed for the same Reynolds number by using the commercial software STAR-CD with the standard k - ɛ turbulent model. It was found that the relative errors of the average Nusselt numbers between the experimental and numerical data were less than 6 percent in a Reynolds number range of 1082∼1649. The errors between the experiment and other correlations from literature ranged from 7% to 32.4%. However, the literature correlation of Kim et al. is closest to the experimental data within a relative error of 7%. This paper was recommended for publication in revised form by Associate Editor Man-Yeong Ha Jin-Gi Paeng recieved a bachelor’s degree in Aero Mechanical Engineering from Gyeong-sang National University in 2000. He then went on to recieve his M.S. degrees from Changwon National University in 2004. Currently, he completed the doc-tor’s course and a doctoral dissertation in 2007 and 2008, respectively. He will take a doctorate in 2008.     

基于正交试验的等弦波形管热工性能分析

基于模拟正交试验法并通过Fluent软件分析,开发出新型等弦波形强化换热管（D＝10 mm, L＝45 mm,R＝50 mm）,分析得出了较大的法向分速度冲刷壁面是影响其对流换热的主要因素;利用场协同理论分析了等弦波形管的强化换热原理,计算出协同角,通过与直管对比发现,协同角有明显减小,局部达10°以上;最后从泵功耗指标出发,计算得出与直管相比,换热效率提高47．6％,验证了新型等弦波形强化换热管具有较优越的热工性能。     

An experimental apparatus measuring convective heat transfer coefficient from a heated fine wire traversing in nanofluids

Most of the previous convection experiments for nanofluids have been performed for internal tube flow with constant heat flux boundary condition. In contrast, a simple experimental apparatus measuring convective heat transfer coefficient from a heated wire to external nanofluids is proposed and its working principles are explained in detail. The convective heat transfer coefficient provided by the present system might be used as a useful indication justifying the adoption of prepared nanofluids as new efficient heat transfer fluids. Validation experiments by comparing convective heat transfer coefficients between the conventional correlation and measured values are carried out for base fluids. Also the effect of increased thermal conductivity of nano lubrication oil on the enhancement of convective heat transfer coefficient is investigated.     

内冷型降膜除湿过程的数值模拟与实验研究

以内冷型竖直板降膜除湿器为对象,考虑实际对流换热边界条件,建立相应的除湿过程数学模型并求解.设计加工了除湿器实验平台,实验结果与模拟计算值的比较证明了模型的有效性,测试了溶液和被处理空气的进口参数对除湿器性能的影响,为系统的设计和运行提供了依据.     

环状与蜂窝蓄热体传热与阻力特性试验研究

蓄热换热器具有结构简单、造价低、效率高等优点,在余热回收方面有着广阔的应用前景。蓄热体作为蓄热换热器的关键部分,其形状、大小及材质等各项性能参数都会对蓄热系统的余热回收效果产生重要的影响。对环状和蜂窝这两种蓄热体的传热与阻力特性进行了试验研究,通过对试验结果分析,得出了热空气进口温度和速度对蓄热体冷热空气出口温度、传热速率、温度效率、热效率及阻力损失的影响规律,并从温度效率、热效率和阻力损失几方面比较了两蓄热体的传热与阻力性能,发现在低进口速度时环状蓄热体的综合性能更好。     

凹槽微通道铜-水纳米流体传热与流动分析

对铜-水纳米流体在圆弧型凹槽微通道中的传热与流动特性进行了分析。比较了不同体积分数的铜-水纳米流体在深宽比分别为0.3和0.5的凹槽微通道中的温度和速度分布,分析了体积分数和凹槽深宽比对凹槽微通道中铜-水纳米流体的传热系数和流体输运动力因子的影响。凹槽强化了微通道对流传热,与平板型微通道相比,铜-水纳米流体在圆弧型凹槽微通通内呈现出不同的传热特性。纳米流体体积分数、流体输运动力因子和凹槽深宽比对凹槽强化微通道传热影响较大。分析结果与已有的实验结果符合较好。     

Convective heat transfer in ventilated space with various partitions

The laminar convective heat transfer in ventilated space with various horizontal partitions was studied numerically and experimentally. For the numerical study, the governing equations were solved by using a finite volume method for various numbers Re, Gr, Pr and partition numbers. The experimental study was conducted by using a holographic interferometer. The isotherms and velocity vectors have been presented for various parameters. As the number and length of partition ncreased, convective heat transfer decreased. Based on the numerical data, correlation equations were obtained for the mean Nusselt number in term of Gr/Re². In the region ofGr/Re²<-1, the mean Nusselt number was small, but in the region ofGr/Re²>1, the mean Nusselt number was constant.     

The effects of design and operating factors on the frost growth and thermal performance of a flat plate fin-tube heat exchanger under the frosting condition

An experimental study of the effects of various factors (fin pitch, fin arrangement, air temperature, air humidity, and air velocity) on the frost growth and thermal performance of a fin-tube heat exchanger has been conducted under the frosting condition. It is found that the thermal performance of a heat exchanger is closely related to the blockage ratio of the air flow passages due to the frost growth. The maximum allowable blockage ratio is used to determine the criteria for the optimal operating conditions of a fin-tube heat exchanger. It is also shown that heat transfer rate of heat exchanger with staggered fin arrangement increases about 17% and the time required for heat transfer rate to reach a maximum value becomes longer, compared with those of an inline fin-tube heat exchanger under the frosting condition. The energy transfer resistance between the air and coolant decreases with the increase of inlet air temperature and velocity and with decreasing inlet air humidity.