强化传热管束狭窄空间内R_11的沸腾换热特性

对紧凑型滚压面传热管管束狭窄空间内R－11的沸腾强化换热进行了实验研究,确认了由紧凑型滚压强化管束组成的满液式蒸发换热器具有良好的换热性能。其原理是利用强化传热管管束狭窄空间提前从自然对流换热转换为旺盛核沸腾换热,实验结果确认了管束形成的狭窄空间和强化传热面两种强化技术对沸腾换热的强化效果不能简单叠加。     

紧凑满液型叉排管束蒸发换热器内水的沸腾强化换热特性

采用紧凑满液型蒸发换热器,利用水平传热管叉排管束狭窄空间内早期沸腾强化换热机理将中小热负 荷条件下的自然对流换热转化为旺盛核沸腾换热,换热性能大大优于传统的降膜式蒸发换热器。对水平传热管 管束在受限空间内沸腾强化换热进行实验研究,确认了紧凑满液式水平管蒸发换热器具有良好的换热性能,传 热管在管束中的位置对换热特性已经没有明显影响,随着压力增加,受限空间内沸腾强化换热强化效果显著增 加。     

满液型海水淡化蒸发器的换热特性研究

海水淡化装置，太阳能或余热吸收式制冷机中的蒸发换热器目前使用管排外降膜式蒸发方式。如将传热管束紧凑排列置于饱和状态液体中则变为满液式蒸发换热器，利用传热管束间受限空间内早期沸腾强化换热机理，将中小热负荷条件下的自然对流换热转化为核沸腾换热，在间隙尺寸适宜时，其换热性能可能优于降膜式蒸发换热器。该研究以盐水为实验工质，对紧凑传热管束受限空间的沸腾换热进行了实验研究，确认了满液式蒸发换热器也具有很好的换热性能，在中小热负荷条件下甚至超过降膜式蒸发换热器。     

紧凑传热管束受限空间内沸腾强化换热特性

海水淡化装置以及太阳能或余热吸收式制冷机中的蒸发换热器,采用管排外降膜式蒸发方式,它具有很多优点,但管间距离较大,以致尺寸较大,供液方式较复杂。将传热管束紧凑排列置于饱和状态液体中,将其变为满液式蒸发换热器,利用传热管束间受限空间内早期沸腾强化机理,将中小热负荷条件下的自然对流换热转化为核沸腾换热,在间隙尺寸适宜时,其换热性能可能优于降膜式蒸发换热器。对紧凑传热管束在受限空间内沸腾强化换热进行实验研究,确认了满液式蒸发换热器具有良好的换热性能,在中小热负荷条件下甚至超过降膜式蒸发换热器。     

紧凑传热管束爱限空间内沸腾强化换热特性

海水淡化装置以及太阳能或余热吸收式制冷机中的蒸发换热器,采用管排我降膜式蒸发方式,它具有很多优点,但管间距离较大,以致尺寸较大,供液方式较复杂。将传热管束紧凑排列置于饱和状态液体中,将其变为满液式蒸发换热器,利用传热管束间受限空间内早期沸腾强化机理,将中小热负荷条件下的自然对流换热转化为核沸腾换热,在间隙尺寸适宜时,其换热性能可能优于降膜式蒸发换热器。     

低压条件下紧凑式顺排管束满液型蒸发换热器的强化换热特性研究

提出了一种新型紧凑式顺排光滑管束组成的满液式蒸发换热器。在低压条件下对水平光滑顺排管束的小空间内沸腾强化换热特性进行了实验研究,确认了管距、管位置和运行压力对强化换热性能的影响。实验表明存在一个能得到最大强化换热效果的最佳管距,这一最佳管距接近沸腾气泡的脱离直径。压力对强化换热效果也有重要影响:随着压力降低,强化换热效果也逐步减弱。实验结果对高效节能型蒸发换热器设计提供了设计基础。     

紧凑高效型水平管束降膜蒸发换热器的实验研究

在大气压条件下使用单列和3列叉排光滑管和滚压强化换热管紧凑管束进行了水降膜蒸发换热实验,确认了滚压管在中,低热负荷范围内能够增强换热系数3～4倍,有很好的沸腾强化换热性能。管间距及液膜溅射损失对蒸发换热特性影响很小。同时也考察了单列和3列管束换热特性闯的差异。实验发现这种差异在低雷诺数区域时更加明显。     

R134a在水平高效强化蒸发管内流动沸腾传热特性的实验研究

本文阐述了新型替代工质HFC—134a在内螺旋微翅片强化蒸发管内水平流动沸腾换热实验研究。归纳总结了大量沸腾换热性能曲线，揭示了壁面温度沿轴向变化的规律以及沸腾换热系数与热流密度及质量流量等的因变关系，并获得了强化管的换热强化倍率。     

空调用液 气式换热器的强化换热分析与主要节能强化措施

<正> 本文回顾了暖通空调用液——气式换热器的基本原理,对强化换热的机理作了分析,并探讨了几种主要的强化换热手段。对设计换热器有一定的参考价值。     

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。     

Enhancement of boiling heat transfer in restricted spaces in compact horizontal tube bundles

ln desalinization devices and some heat exchangers making use of low‐quality heat energy, both wall temperatures and heat fluxes of heated tubes are quite low and generally cannot cause boiling in flooded‐type tube bundle evaporators with a large tube spacing. But when the tube spacing is very small, boiling in restricted spaces can occur and induce a higher heat transfer than that of a falling film or pool boiling at the same heat flux. This study investigated experimentally the effects of tube spacing, positions of tubes, and heating status of tubes as well as surface status (smooth and roll‐worked) on boiling in restricted spaces in compact horizontal tube bundle evaporators under atmospheric pressure. The experimental results provide a restricted space boiling database for water in smooth and enhanced surface tube bundles. Of particular importance is information concerning the influence of tube spacing of flooded‐type tube bundle evaporators, especially for the case of zero pitch, when the neighboring tubes are contacting each other. © 2001 Scripta Technica, Heat Trans Asian Res, 30(5): 394–401, 2001     

Enhanced Boiling Heat Transfer of Water/Salt Mixtures in the Restricted Space of the Compact Tube Bundle

In desalinization devices and some heat exchangers making use of low-quality heat energy, both the wall temperature and the heat flux of the heated tubes are generally quite low, hence cannot cause boiling in flooded-type tube bundle evaporators with a large tube spacing. But when the tube spacing is quite small, incipient boiling can occur in the restricted space and results in higher heat transfer than that in a falling-film evaporator or during pool boiling at the same heat flux. This study experimentally investigates the effects of the tube spacing, the positions of tubes, and the salt-water concentration on bundle boiling heat transfer of salt water in the restricted space of the compact tube bundle evaporator under atmospheric pressure. The experimental results provide a restricted space boiling database for salt water in the compact tube bundle. Of particular importance is information concerning the influences of the tube spacing of the tube bundle and the concentration of salt water in desalination evaporators.     

Enhanced boiling heat transfer in restricted spaces of a compact tube bundle with enhanced tubes

In flooded-type tube bundle evaporators with smooth tubes and general tube gaps, both wall superheat and heat flux are generally quite low and boiling cannot occur on the heated tubes. But when the tube gap is quite small or the enhanced heat transfer tubes are employed, the incipient boiling can occur at low heat flux levels and results in a significant heat transfer enhancement effect. This study investigates experimentally enhancement effects by the restricted space comprising the compact tube bundle and the enhanced tubes for boiling heat transfer of pure water and salt-water mixtures under atmospheric pressure. The experimental results show that the small tube gaps can greatly enhance boiling heat transfer for the compact enhanced tube bundle.     

Enhanced Boiling Outside 8 × 3 Plain and Coated Tube Bundles

Experiments were conducted for pool boiling on the outside of 8 × 3 (eight rows and three columns) plain and coated tube (surface roughness = 8.279 μm) bundles for three different pitch distances with the distinct objective to study the behavior and the enhancement of boiling heat transfer in horizontal staggered tube bundles (of plain and coated tubes for different equilateral triangular arrangements) with heat flux values ranging from ～12 to 45 kW/m². At higher heat fluxes, coated and plain tube bundles had almost similar bundle average heat transfer coefficients at a given pitch distance, while at lower heat fluxes, the coated tube bundles have higher bundle average heat transfer coefficients as compared to that of the plain tube bundle. The coated tube bundles with the minimum pitch to diameter ratio of 1.4 exhibited the maximum bundle average heat transfer coefficients. The present study concludes that the bundle factor needs to be considered in the design of flooded evaporators.     

Enhanced Boiling Heat Transfer of the Compact Staggered Tube Bundles under Sub-Atmospheric Pressures

An experimental investigation was carried out on the boiling heat transfer enhancement of water on plain tubes in compact staggered tube-bundle evaporators under atmospheric and sub-atmospheric pressures. The experiment investigated the effects of the tube spacing and positioning and the test pressure on the boiling heat transfer characteristics in restricted spaces of compact tube bundles. The experimental results indicated that for compact tube bundles, the effect of the tube spacing is very significant on the boiling heat transfer. The boiling heat transfer has a maximum enhancement when the tube spacing is so selected as to take an optimum value. The enhanced heat transfer efficiency for the compact bundles would gradually decrease as the test pressure was reduced.     

Enhancement of boiling heat transfer in a 5 × 3 tube bundle

The results of an experimental investigation on nucleate boiling heat transfer in an electrically heated 5 × 3 in-line horizontal tube bundle under pool and low cross-flow conditions of saturated water near atmospheric pressure are presented here. It is observed that the heat transfer coefficient is minimum on bottom row tubes and increases in the upward direction with maximum values on top row tubes. Also, heat transfer coefficient on central column tubes was found to be slightly higher than those on the corresponding side tubes. Further, a Chen-type relation has been used to determine the local boiling heat transfer coefficient on a tube in a heated tube bundle.