R123水平强化单管外池沸腾换热实验研究

对替代工质R123在光管、机加工多孔表面强化管水平单管外池沸腾换热进行了实验研究.在沸腾温度分别为5℃、8℃和10℃时,光管外沸腾换热系数的实验数值较Cooper公式的预测值最大偏低10%;同时得到了强化管外沸腾换热系数随热流密度、沸腾压力的变化规律以及强化管的强化效果,强化管的强化倍率在4.56～4.18之间.对R11也进行了同样实验,并把二者沸腾换热特性进行比较,强化管外R123比R11沸腾换热系数要低8%左右.     

蒸发温度对强化换热管管外核态池沸腾换热性能的影响

对R134a在水平强化管(Φ25 mm)外核态池沸腾进行了实验研究。通过Wilson图解法求得管内换热准则关系式,通过改变蒸发温度(5.6℃,0℃,-2℃,-4℃,-6℃,-8℃)和热流密度(4~55 k W/m2),得到了管外沸腾换热系数随热流密度和蒸发温度变化的规律。实验表明,管外沸腾换热系数随着热流密度和蒸发温度的升高而增加。结合实验数据,提出了一个新的管外池沸腾换热关联式,该关联式与实验数据点的偏差显示,95%的数据点的相对误差在±20%以内。     

R14池内核态沸腾换热特性研究

开展了全氟甲烷(R14)纯质池内核态沸腾换热特性的实验研究,测量了不同热流密度和不同系统压力下的R14纯质池内核态沸腾换热数据,分析了热流密度和压力对沸腾换热特性的影响。实验结果同现有的经验关联式的计算结果进行了比较,对不同压力下R14沸腾换热提出了不同的关联式,为混合工质节流制冷等相关领域提供基础数据。     

R32在水平管内流动沸腾换热特性的试验研究

对R32在水平光滑管和微肋管(外径均为7mm)内的沸腾换热特性展开试验研究,测试的制冷剂质量流速为100~250 kg/(m~2·s),饱和蒸发温度为7~11℃,热流密度为3~8 kW/m~2,测试管内制冷工质平均干度值为0~0.7。试验结果表明:热流密度是影响R32沸腾换热系数的主导因素之一,质量流速的增大、饱和蒸发温度的升高、热流密度的增大均有利于提高R32的沸腾换热系数;微肋管有强化传热的效果,其平均沸腾换热系数比光管增大11.8%~33.2%;干度对R32沸腾换热系数的影响比较复杂,R32的沸腾换热系数随干度的增加先增大后减小,这是由于出现了干涸值,本文试验测得的干涸值范围为0.41~0.57,制冷剂质量流速的降低和热流密度的增大均有利于干涸值的增大。     

含油制冷剂在泡沫金属圆管内流动沸腾的换热特性

实验研究了填充泡沫金属的圆管内制冷剂与润滑油混合物流动沸腾换热特性。实验对象为两根分别填充5PPI、90%孔隙率与10PPI、90%孔隙率泡沫铜的圆管,以及相同管径的光管。实验工况为蒸发压力995kPa,质流密度为10~30 kg/(m2.s),热流密度为3.1~9.3kW/m2,入口干度0.175~0.775,油浓度为0~5%。实验结果表明:纯制冷剂工况下,泡沫金属的存在强化流动沸腾换热,换热系数最多提高185%;含油工况下,泡沫金属强化换热的效果弱化;相同工况下,更小的孔径可以提高流动沸腾换热系数,相比5PPI泡沫金属的实验数据,10PPI的泡沫金属可以使换热系数最多提高0.6倍。基于流型建立了填充泡沫金属的圆管内制冷剂与润滑油流动沸腾换热系数的预测模型,预测模型与98%的实验数据误差在±30%以内。     

纯工质及混合工质管外沸腾换热特性研究

对水平管外纯工质R22、R134a,R125浓度分别为6%,12%,18%的R134a/R125混合工质以及三元混合工质R417A(R134a/R125/R600浓度分别为50%/46.6%/3.4%)池沸腾换热性能进行了试验研究。通过对不同工质在光管和强化管外的沸腾换热性能进行比较与分析表明:强化管外沸腾换热系数明显高于光管,在热流密度为60k W/m2时,纯工质R22在强化管外沸腾换热系数是光管的3.10倍;纯工质R134a在强化管外沸腾换热系数是光管的2.85倍;在分别含6%、12%、18%R125的R134a/R125混合工质中,强化管外的沸腾传热系数是相对于同条件下光管的2.49、2.42、2.28倍;在R417A中,强化管外沸腾换热系数是光管的2.10倍。不同质量浓度的R125对光管沸腾换热系数影响相对较小,而对强化管外沸腾换热系数影响较大。     

R290与R404A在水平管内沸腾换热的压降研究

将R22的两种新型替代工质R290和R404A在光管和内螺纹管中的沸腾换热压降实验结果与Lockhart ＆ Martinelli压降计算关联式预测结果进行了比较，并依据工质R290和R404A在内螺纹管中的实验压降值对Lockhart ＆ Marlinelli压降计算关联式进行了修正。结果表明Lockhart ＆ Martinelli关联式对R404A在光管和内螺纹管的沸腾换热摩擦压降，均有良好的预测精度，平均偏差分别为-11．52％和-17．86％。Lockhart ＆ Martinelli关联式可以较好的预测R290在光管内的沸腾换热摩擦压降，平均偏差为-21．68％；经修正后的Lockhart ＆ Martinelli关联式可以较好的预测R290在在内螺纹管中的沸腾换热摩擦压降，Lockhart ＆ Martinelli关联式乘上修正系数2．06后的修正值与实验值偏差较小，平均偏差为2．37％。研究结果对R290和R404A蒸发器的工程设计及优化具有一定参考意义。     

降膜式蒸发器用高效传热管换热性能试验研究

通过试验对降膜式蒸发器用高效传热管的换热性能进行研究,并将其与之相对应的池沸腾换热性能进行比较.由比较数据可知:样管池沸腾换热性能均随热流密度的增大而增强,降膜蒸发性能在一定热流密度下随喷淋流量的增大而增强;在恒定热流密度和恒定喷淋流量下,光管降膜燕发性能低于池沸腾性能,强化管降膜蒸发性能高于池沸腾性能;池沸腾性能高的强化管降膜蒸发性能也强.     

两种池沸腾强化换热管的传热性能实验研究

对两种用于池沸腾换热的强化管在蒸发温度为5℃的工况下进行了水平管外传热性能的实验研究.两种管子为管内外双侧强化管,管外表面同属于TURBO-B类的强化换热管,但表面形状有区别.利用威尔逊图解法确定这两种管型的管内外换热系数的关联式,同时,根据实验测得的数据对这两种管型的换热性能进行比较.结合金相显微镜拍摄的外观形状,分析尺寸结构对强化换热管的换热性能的影响.结果得出:在相同工况下,准三角形形状的管内螺纹换热性能要比梯形好,且管内螺纹数越多,换热性能越好;在一定热流密度范围内,管外换热系数随着热流密度的增加而变大,这主要与管子外表面结构的凹穴半径、凹穴开口尺寸、次级表面通道的宽度和形状等因素有关,且翅顶表面刻画的浅槽有利于池沸腾换热.     

CFC_S替代工质R134a、R142b在水平管外池沸腾传热与强化

研究了Ｒ１３４ａ、Ｒ１４２ｂ在光滑管和机械加工表面多孔管水平管外的池沸腾换热性能，分析了工质在水平管外的沸腾传热机理，实验的对比压力Ｐ／Ｐｃ＝０．２０。实验结果表明，光滑管外沸腾实验结果与取平均表面粗糙度为２μｍ的Ｇｏｒｅｎｆｌｏ公式预测结果吻合较好，与光滑管相比，机械加工表面多孔管能显著地强化沸腾传热，且随着热流密度的增加，强化倍率减小。通过数据拟合，得到了沸腾换热系数的经验关系式。     

Pool boiling heat transfer from a horizontal tube coated with oxide ceramics

Pool boiling heat transfer from a horizontal copper tube coated with 0.2 mm of aluminum oxide-titanium oxide ceramics has been investigated for several pure fluids (refrigerants and hydrocarbons) and three propane/n-butane mixtures. The heat transfer coefficient shows a similar dependence on heat flux and normalized saturation pressure as with a metallic heating tube. At normalized saturation pressures p/p_c0.1, the absolute values of the heat transfer coefficient are just as high as for a sandblasted copper tube of similar surface roughness and at lower saturation pressures even higher. The negative influence of the low thermal conductivity of the ceramics is completely compensated or even overcompensated by the positive influence of the microstructure which results in a higher nucleation site density. This is especially effective in pool boiling of mixtures.     

竖直狭缝通道中液氮沸腾强化换热的实验研究

实验表明，狭缝间隙对液氮自然对流核态沸腾换热有明显的影响，在低热流密度下，间隙小的狭缝沸腾换热比间隙大的狭缝明显增强，当狭缝间隙小于实验压力下气泡的脱离直径时，对于同样的热流密度，传热温差减小一个数量级以上，沸腾换热系数提高十几倍到二十倍以上，当热流密度增加一定程度（＞4W/cm^2)时，间隙小的狭缝沸腾换热比间隙大的狭缝有所减弱。     

Nucleate boiling heat transfer coefficients of pure halogenated refrigerants

Nuclate pool boiling heat transfer coefficients (HTCs) of HCFC123, CFC11, HCFC142b, HFC134a, CFC12, HCFC22, HFC125 and HFC32 on a horizontal smooth tube of 19.0 mm outside diameter have been measured. The experimental apparatus was specially designed to accomodate high vapor pressure refrigerants such as HFC32 and HFC125 with a sight glass. A cartridge heater was used to generate uniform heat flux on the tube. Data were taken in the order of decreasing heat flux from 80 to 10 kW m⁻² with an interval of 10 kW m⁻² in the pool of 7 °C. Test results showed that HTCs of HFC125 and HFC32 were 50–70% higher than those of HCFC22 while HTCs of HCFC123 and HFC134a were similar to those of CFC11 and CFC12 respectively. It was also found that nucleate boiling heat transfer correlations available in the literature were not good for certain alternative refrigerants such as HFC32 and HCFC142b. Hence, a new correlation was developed by a regression analysis taking into account the variation of the exponent to the heat flux term as a function of reduced pressure and some other properties. The new correlation showed a good agreement with all measured data including those of new refrigerants of significantly varying vapor pressures with a mean deviation of less than 7%.     

Influence of the heat flux in mixture boiling: experiments and correlations

Heat transfer at nucleate pool boiling of the binary and ternary refrigerant mixtures R404A, R407C and R507 at the outside of a horizontal tube with emery ground surface has been investigated in a wide range of pressures and heat fluxes. Together with experimental data of Bednar and Bier for wide boiling ethane/n-butane mixtures, the results of these comparatively narrow boiling mixtures are used to investigate the influence of heat flux q on the heat transfer coefficient as predicted by various correlations for nucleate boiling of mixtures. At comparatively high saturation pressures with experimental -values markedly smaller than the molar average of the pure components, the ,q-relationships predicted differ significantly from the experimental, particularly for wide boiling mixtures.     

The influence of a low viscosity oil on the pool boiling heat transfer of the refrigerant R507Influence d'une huile à faible viscosité sur le transfert de chaleur lors de l'ébullition libre du frigorigène R507

This paper describes the influence of a low viscosity polyolester based lubricating oil on the pool boiling heat transfer of the refrigerant R507. The pool boiling heat transfer coefficients for this refrigerant–oil mixture are measured on a smooth tube and on an enhanced tube. The investigation is made for oil mass fractions up to 10% and for saturation temperatures between −28.6°C and +20.1°C. For the smooth tube the heat transfer increases for increasing oil mass fractions up to 3% at lower saturation temperatures. At higher saturation temperatures the heat transfer decreases for increasing oil mass fractions for both tubes. For oil mass fractions greater than 1% at the higher saturation temperatures a range of decreasing heat transfer coefficient is found for increasing heat flux. The effect is caused by the different miscibility of the oil and the components of the refrigerant mixture.     

R717在小管径水平光管内流动沸腾换热及压降特性

氨制冷剂存在可燃性和毒性,因此减少其在制冷系统中的充注量极为重要。小管径换热管通常可以提供更高的表面传热系数,这可以作为提升换热器紧凑性同时减少系统中充注量的有效方法。本文搭建了氨制冷剂管内流动沸腾换热及压降测试实验装置,测试了氨制冷剂在4 mm水平光管内的流动沸腾换热及压降,并分析了干度、质量流速及热流密度对换热及压降特性的影响。结果表明:流动沸腾换热表面传热系数随着干度的增加而增大,同时质量流速和热流密度越高,流动沸腾换热表面传热系数越大。此外,氨制冷剂在管内的两相摩擦压降也随着干度的增加而增大,在固定干度下,质量流速的升高导致压降增大。     

Experimental investigation of forced flow boiling of nitrogen in a horizontal corrugated stainless steel tube

Experimental investigation is performed on the heat transfer characteristics of forced flow boiling of saturated liquid nitrogen (LN₂) in a horizontal corrugated stainless steel tube with a 17.6 mm maximum inner diameter. The local heat transfer coefficients (HTCs) are measured at two mass flow rates with a wide range of wall heat fluxes. The effects of the heat flux, mass flow flux and vapor quality on the two-phase heat transfer characteristics are discussed. The results reveal that the local HTCs increase with the heat flux and mass flow flux. The measured local HTCs present a strong dependence on the heat flux. The circumferential averages of the HTCs for the present corrugated tube are compared with the empirical correlations proposed for the smooth tubes, and the results show that the heat transfer is enhanced due to the area augmentation.     

Heat transfer and pressure drop for boiling nitrogen flowing in a horizontal tube: 1. Saturated flow boiling

Forced convection boiling of liquid nitrogen in a smooth horizontal copper tube with 14 mm id has been studied experimentally. The measured local heat transfer coefficients in nucleate boiling depend on the heat flux as well as on the mass flow rate. Furthermore, the influence of the vapour quality cannot be neglected.Our own experimental heat transfer data were correlated by an empirical equation. Mass flow rate, pressure, and diameter dependence of para-hydrogen data of other authors can also be correlated with this equation. A relationship for the critical heat flux is also given.