Development and validation of a micro-fin tubes evaporator model using R134a and R1234yf as working fluids

This paper presents a model of shell and tube evaporator with micro-fin tubes using R1234yf and R134a. The model developed for this evaporator uses the ε-NTU method to predict the evaporating pressure, the refrigerant outlet enthalpy and the outlet temperature of the secondary fluid. The model accuracy is evaluated using different two-phase flow boiling correlations for micro-fin tubes and comparing predicted and experimental data. The experimental tests were carried out for a wide range of operating conditions using R134a and R1234yf as working fluids. The predicted parameter with maximum deviations, between the predicted and experimental data, is the evaporating pressure. The correlation of Akhavan– Behabadi et al. was used to predict flow boiling heat transfer, with an error on cooling capacity prediction below 5%. Simulations, carried out with this validated model, show that the overall heat transfer coefficient of R1234yf has a maximum decrease of 10% compared with R134a.     

Augmentation of boiling heat transfer from horizontal cylinder to liquid by movable particles

This paper presents a series of experimental results on a passive augmentation technique of boiling heat transfer by supplying solid particles in liquid. A cylindrical heater 0.88 mm in diameter is placed in saturated water, in which a lot of mobile particles exist, and the nucleate and film boiling heat transfer characteristics are measured. Particle materials used were alumina, glass, and porous alumina, and the diameter ranged from 0.3 mm to 2.5 mm. Particles are fluidized by the occurrence of boiling without any additive power, and the heat transfer is augmented. The maximum augmentation ratio obtained in this experiment reaches about ten times the heat transfer coefficient obtained in liquid alone. The augmentation ratio is mainly affected by the particle material, diameter, and the height of the particle bed set at no boiling condition. The augmentation mechanism is discussed on the basis of the experimental results. © 2001 Scripta Technica, Heat Trans Asian Res, 31(1): 28–41, 2002     

复合乳化沥青的粘附性试验方法研究

鉴于目前使用的阳离子乳化沥青粘附性试验方法难以有效评价复合乳化沥青粘附性，通过试验研究并综合考虑乳化沥青施工和路用实际情况，提出了乳化沥青水煮法试验方法和采用该方法检验复合乳化沥青粘附性时的评定标准。     

核反应堆加热流道含汽量计算研究

指出了加热流道内含汽量传统算法中存在的问题 ,并提出了新的算法     

Boiling: Size Distribution of Bubbles as Demanded by the Principle of Maximum Information

The principle of maximum informational entropy is used to find the probability density function for the departure radius of a bubble in boiling on a solid surface. A general relation is derived, which leads to particular expressions.     

Pool boiling on a superhydrophilic surface

Titanium Dioxide, TiO₂, is a photocatalyst with a unique characteristic. A surface coated with TiO₂ exhibits an extremely high affinity for water when exposed to UV light and the contact angle decreases nearly to zero. Inversely, the contact angle increases when the surface is shielded from UV. This superhydrophilic nature gives a self-cleaning effect to the coated surface and has already been applied to some construction materials, car coatings and so on. We applied this property to the enhancement of boiling heat transfer. An experiment involving the pool boiling of pure water has been performed to make clear the effect of high wettability on heat transfer characteristics. The heat transfer surface is a vertical copper cylinder of 17 mm in diameter and the measurement has been done at saturated temperature and in a steady state. Both TiO₂-coated and non-coated surfaces were used for comparison. In the case of the TiO₂-coated surface, it is exposed to UV light for a few hours before experiment and it is found that the maximum heat flux (CHF) is about two times larger than that of the uncoated surface. The temperature at minimum heat flux (MHF) for the superhydrophilic surface is higher by 100 K than that for the normal one. The superhydrophilic surface can be an ideal heat transfer surface. Copyright © 2002 John Wiley & Sons, Ltd.     

Nucleate Pool Boiling of Pure Liquids and Binary Mixtures：PartI－Analytical Model for Boiling Heat Transfer of Pure Liquids on Smooth Tubes

ＮｕｃｌｅａｔｅＰｏｏｌＢｏｉｌｉｎｇｏｆＰｕｒｅＬｉｑｕｉｄｓａｎｄＢｉｎａｒｙＭｉｘｔｕｒｅｓ：ＰａｒｔＩ－ＡｎａｌｙｔｉｃａｌＭｏｄｅｌｆｏｒＢｏｉｌｉｎｇＨｅａｔＴｒａｎｓｆｅｒｏｆＰｕｒｅＬｉｑｕｉｄｓｏｎＳｍｏｏｔｈＴｕｂｅｓＧｕｏｑｉｎ...     

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。     

Forced convection subcooled boiling of binary mixtures

A mode based on an additive mechanism of heat transfer is proposed for forced convection subcooled boiling of binary mixtures. The contributing modes of heat transfer are: (i) the heat transferred as latent heat by the rising bubbles, (ii) the heat transferred as the heat contained in the superheated thermal layer that is removed from the surface in the wake of the rising bubbles and (iii) the single phase forced convection heat transfer from the heating surface not influenced by the bubbles. Experimental data from the literature on binary systems show good agreement with the model, validating the postulated mechanism.     

不同品位高钛渣对沸腾氯化工艺的影响

分别以94％品位高钛渣和90％品位高钛渣为原料，采用沸腾氯化工艺制备粗TiCl4，分析了两种品位高钛渣对沸腾氯化工艺的影响。结果表明：94％品位高钛渣由于其活性低而对沸腾氯化工艺的影响较大。