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This study presents new data on nucleate boiling heat transfer obtained in compact horizontal tube bundles with small tube gaps. The experiment investigates the heat transfer enhancement effects by the restricted spaces comprising the compact tube bundles and the enhanced heat transfer tubes for nucleate boiling heat transfer of R-11 at atmospheric pressure. A roll-worked tube was used as a new type of enhanced heat transfer tube. The experimental results show that the small tube gaps can greatly enhance boiling heat transfer in a smooth tube bundle, while enhancement effects of small gaps were not quite significant for the enhanced tube bundle. There is a compound effect from the enhanced surface and the restricted space only for the enhanced tube bundle with the tube gap of 0.5 mm. The effects of the tube positions within both compact tube bundles on the boiling heat transfer were minor. 相似文献
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本文对含Solest-120冷冻油的R134a,在饱和温度为5℃和10℃工况下,在水平高效强化管(管E21.为C3型管,管E22为A1型管)管外池沸腾换热进行了实验研究。实验结果表明:与相同管径的光管的换热性能相比,强化管E21、E22的管内传热系数强化倍率分别为3.703和3.035。随着含油浓度的增加,管外池沸腾换热效果得到优化,含油率为1.0×10~(-4)时的管外传热系数比含油5.0×10~(-5)时更高,在实验研究的水流速范围内,在蒸发温度为5℃时增加了3.7%~7.2%,而在蒸发温度为10℃时增加了0.8%~10.9%。从含油R134a的黏度、表面张力等的角度,对含油率高时换热系数大的结论进行了必要的物理解释。研究对开发设计蒸发器有一定实际的指导意义。 相似文献
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The effect of thermal environment on boiling heat transfer performance in a section of a horizontal tube bundle was investigated using R-113 as the working fluid. The in-line tube bundle has five columns and 27 rows with a pitch-to-diameter ratio of 1.3. Heal transfer coefficients obtained from the instrumented tube in the tube bundle with only one tube heated while the other tubes remained unhealed and with all the lubes in the bundle heated are reported for a range of heat flux, pressure, mass flow rate, and quality. The results showed that heat transfer coefficient of a tube in a heated bundle is slightly higher than that in an unhealed bundle, with the variation of heat transfer coefficient decreasing as heat flux, mass flow rate, or pressure increased. It was also found that higher quality would tend to improve the heat transfer. However, the effect of quality disappeared as heat flux, mass flow rate, and pressure increased. Based on the experimental data, the mechanism of the heat transfer augment due to thermal environment was analyzed. It was proposed that fluid agitation and thin liquid film formation are two main factors for a heated bundle to have better transfer performance than an unhealed bundle, 相似文献
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采用实验的方法,研究了在较宽的不凝气体含量范围内,煤油蒸汽在不同几何结构的螺旋扁管管束外的冷凝换热现象,得出了螺旋扁管的几何结构对冷凝换热的影响规律,并与同样条件下的光管管束的冷凝换热进行了分析比较。 相似文献
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微结构表面上FC-72的强化沸腾换热研究 总被引:1,自引:1,他引:0
针对电子器件的高效冷却问题,对表面加工有微结构的硅片上FC-72的池沸腾换热性能进行了实验研究。测试了四种表面微结构,采用化学蒸汽沉积法在芯片表面生成-SiO2薄层所形成的亚微米粗糙面(Chip CVD),采用溅射方法在芯片表面生成-SiO2薄层,然后再对SiO2层进行湿式腐蚀技术处理形成的亚微米粗糙面(Chip E),采用一系列微电子加工技术生成的微米级双重入口洞穴(Chip CAVITY)以及采用干式腐蚀方法生成的方柱微结构(Chip PF)。实验所得的沸腾曲线表明,所有微结构表面与光滑面(Chip S)相比都显示出较大的强化沸腾换热效果,临界热流密度按芯片 S、E、CVD、CAVITY和PF的顺序增大。对于芯片PF来说,随着壁面过热度的增加,热流量呈剧烈的增加趋势且临界热流密度时芯片的表面温度低于芯片回路正常工作的临界上限温度85℃,最大临界热流密度可达80 W/cm2。 相似文献
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R410A和R22在水平强化管内的蒸发和冷凝性能 总被引:1,自引:0,他引:1
空调器高效节能、环保及小型化发展的要求,促进了高效换热管及新型冷媒应用的发展。本文建立了无润滑油的实验台,并比较了混合工质R410A和单一工质R22在两种9.52.mm外径水平强化管:新型铜管Turbo-DWT和常规应用的内螺纹铜管Turbo-A中蒸发和冷凝的换热性能。在蒸发100-400 kg/m2·s和冷凝209-800 kg/m2·s的实验范围内,对比综合性能可知:新管型Turbo-DWT冷凝性能优于Turbo-A,效率高63%(R410A),而蒸发性能却略弱;无论是蒸发还是冷凝工况,R410A的综合性能均高于R22在57%以上(DWT)。 相似文献
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Abstract A test rig and measurement techniques for horizontal flow boiling of pure and mixed refrigerants are described. Local heat transfer coefficients were measured for R22/R114 and R12/R152a mixtures as well as the corresponding pure components. The test section consists of an S-m-long, 9.1-mm-i.d., electrically heated stainless steel tube and has the distinctive feature of variable heated length. Details of pressure, composition, and fluid and wall temperature measurements are discussed. The composition of subcooled liquid entering test section varied from test to test, and it is recommended that it be measured for each test. For the R22/R114 mixture, local composition measurements in the annular liquid film revealed a composition variation of up to 0.07 mole fraction around the circumference of the heated tube. 相似文献
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