Characteristics of heat transfer coefficients during nucleate pool boiling of binary mixtures

Experimental studies were made on heat transfer on a horizontal platinum wire during nucleate pool boiling in nonazeotropic refrigerant binary mixtures at pressures of 0.25 to 0.7 MPa and at heat fluxes up to CHF. The boiling features of the mixtures and the single-component substances were observed by photography. The relationship between the boiling behavior and the reduction of heat transfer coefficients in binary mixtures is discussed in order to propose a correlation useful for predicting the present experimental data over a wide range of low to high heat fluxes. It is shown that the correlation is applicable to alcoholic mixtures. The physical meaning of k, which was introduced to evaluate the effect of heat flux on the reduction of a heat transfer coefficient, is clarified based on measured nucleate pool boiling heat transfer data and visual observations of the boiling features. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(7): 535–549, 1998     

高性能工业余热利用方式的CPL技术

在分析工业能源利用系统能源损耗与节能的特点基础上,提出一种新型能量转换和利用的技术－－ＣＰＬ,对其运行特性进行了可行性实验研究,提出对其应用前景的展望。     

具有凝结的混合气体传热理论研究

采用理论分析研究方法研究了含湿混合气体在竖向管内对流凝结换热，讨论了含有少量水蒸汽（8%～20%）的混合气体中水蒸汽凝结对换热的影响，利用修正的膜模型与Nusselt凝结理论得到了理论解。研究结果表明，对于含有少量水蒸汽的混合气体的凝结换热，其换强度与混合气体的单相对流换热处于同一数量级，换热方式均不能忽略，壁面温度与水蒸汽质量成份对凝结换热的影响十分显。     

Study of vapor concentration during boiling process of binary liquid mixtures

The object of the study is to clarify experimentally the variation of the vapor concentration of binary mixtures generated during nucleate boiling in a saturated pool under various boiling conditions. The generated vapor concentrations in the bulk vapor layer were measured for binary mixtures of water‐ethanol and ethanol‐acetone under various liquid concentrations, heat fluxes, and liquid layer heights from heated thin wires at atmospheric pressure. Two methods of measuring concentration, namely, the dew point method and the laser absorption method, were used. The dew point measurement utilized a copper heat transfer block installed in the center of the vapor layer in the boiling vessel. The commencement of condensation on the surface was observed directly via a microscope used for determining the dew point by controlling its temperature. A laser light having a wavelength of 3.39 µm was used for the laser light absorption method utilizing its absorptive property against ethanol vapor. The measurement of the concentrations of the bulk vapor was carried out for various superheats of heated wires, the depth of liquid mixture layer, and the liquid concentrations. They were almost independent of those parameters and were almost in equilibrium with bulk liquid conditions even under higher surface superheats and lower liquid heights. Also, the measured results using both methods were in close agreement. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(8): 595–605, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10060     

有限热源的有限时间可用性

本文指出,有限时间可用性的概念比传统可用性的概念更为重要和有用,它能更精确地反映出能源的实际作功本领。文中对有限热源的有限时间可用性作了分析,得到一些具有普遍意义的结论。     

Pool boiling heat transfer in binary mixtures of ammonia/water: Effect of heat of dilution and dissolution on heat transfer coefficient

Nucleate boiling heat transfer coefficients were measured on a horizontal heated wire during the pool boiling of non‐azeotropic mixtures of ammonia/water. The experiment was carried out at pressures of 0.4 and 0.7 MPa, at heat fluxes below 2.0 × 10⁶ W/m², and over a range of mass fraction. The heat transfer coefficients in the mixtures were smaller than those in single‐component substances. No existing correlation is found to predict boiling heat transfer coefficients over the range of mass fraction of interest. In the mixtures of the ammonia/water, the heats of dilution and dissolution were generated near a liquid surface while vapor with a rich concentration of ammonia was condensed and then was diffused into the bulk liquid; while in most other mixtures, little heat was generated during any dilution and dissolution. In relation to the heat generated, the effect of the heats of dilution and dissolution on pressure and temperature in a system (pressure vessel) is shown herein. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(4): 272–283, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10034     

Bubble behavior and heat transfer during pool boiling of binary mixtures

Heat transfer coefficients were measured during pool boiling of binary mixtures on a heated wire hung horizontally and bubble behavior was simultaneously captured with a high‐speed video camera. The experiment was carried out at a pressure of 0.4 and 0.7 MPa for the whole range of mass fractions in a binary mixture of R22/R11. We clarified the change in bubble behavior and heat transfer by measuring the bubble departure diameter, frequency and growth rate on the basis of the video images. Furthermore, we discussed the relationship between the bubble behavior and the boiling heat transfer coefficient in the binary mixtures. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(7): 449–459, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20087     

热漏对热机最佳功率与最佳效率特性的影响

对于有限时间热力学,以往文献对于卡诺热机最佳效率与最佳功率间关系的分析大多只考虑了热阻和装置热漏(本文称为外热漏),而没有考虑到工质热漏(本文称为内热漏)的影响。将热漏分为外热漏和内热漏两种方式,经过分析得出了由于内热漏损失使热机存在最佳功率和最佳效率两种不同工作状态,指出了内热漏的影响不同于外热漏,也不可将内热漏简单归结于内不可逆的重要结论。     

混合气体管内对流凝结传热研究

研究了混合气体在垂直圆管内的对流凝结传热。利用修正的膜模型与Nusselt凝结理论建立了换热数学模型，预测了壁面温度对膜厚度和界面温度的影响，计算了凝结液膜厚度，并与报相热阻法进行比较，研究结果表明该模型更接近实验果，提出了混合气体对流凝结换热与Nusselt凝结的不同。     

热力循环温差传热不可避免损失研究

~~热力循环温差传热不可避免损失研究@张晓晖$上海理工大学动力工程学院!上海200093 @杨茉$上海理工大学动力工程学院!上海200093 @章立新$上海理工大学动力工程学院!上海200093 @卢玫$上海理工大学动力工程学院!上海200093~~~~~~     

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。     

Zero‐flux zone model analysis of a single bubble in boiling liquid

We start from a bubble, the basic unit of boiling, to explore liquid boiling. Research indicates that the heat and mass transfer between liquid and vapor is the determinant factor of boiling heat transfer. We have analyzed interfacial vaporization and condensation of a single bubble in boiling liquid based on a zero‐flux zone model. We have deduced the expression of zero‐flux angle and discussed the relationship between zero‐flux zone and the other parameters in order to comprehend the mechanism of boiling heat transfer. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(4): 249–256, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10026     

热漏对热机功率效率特性的影响分析

在以往文献的基础上,对定常态流不可逆卡诺热机的热漏模型进行了改进,将热机热漏分为外热漏和内热漏两种方式,分析两种热漏方式对不可逆热机最优性能的影响。分析得出内热漏对热机功率效率特性的影响不同于外热漏,也与摩擦,涡流和非平衡等各种不可逆效应不同,内热漏应单独作为影响热机特性的一种因素。并导出存在热阻和两种热漏损失的热机存在最佳功率和最佳效率两种工作状态,两种工作状态分别对应不同的面积比。所得结果对热机设计具有一定指导意义。     

考虑空气量影响时蒸汽凝结放热系数的计算方法分析

空气量对蒸汽凝结放热系数影响的计算，目前还没有一个人们普遍公认的计算方法。文中首先对空气对轻微流动蒸汽、受迫流动蒸汽以及抽气器运行时蒸汽凝结放热系数影响进行了综述分析，然后对目前常用的几种计算空气量对蒸汽凝结放热系数影响的计算方法进行了计算分析，指出各种计算方法的特点及其存在的问题，为进一步研究空气对蒸汽凝结放热系数的影响奠定了一定的基础。     

水平单管外混合气体对流冷凝换热的理论研究

采用修正的膜模型与Nusselt凝结理论结合的方法,对含湿混合气体自上而下横掠水平管外时的对流冷凝换热机理进行研究,建立了液膜流动和传热模型,进行数值求解并分析了雷诺数、壁面温度及水蒸汽浓度等因素对混合气体冷凝换热的影响。计算结果表明:水管外壁液膜厚度分布很大程度上受气体边界层对液膜剪切力的影响。而局部努谢尔数不同于纯蒸气的的冷凝换热,它受气相热阻的影响很大,其分布状况类似于单相气体管外的对流换热。     

Recent developments in EHD Enhanced Heat Transfer

This paper considers that the case for using electrohydrodynamic (EHD) enhancement of heat transfer has been established, especially in thermodynamic renewable energy applications where temperature levels are relatively low. It goes on to establish the basis on which nucleate boiling heat transfer is enhanced by EHD forces at surfaces designed to improve condensation, giving experimental results for a six-tube, shell/tube heat exchanger boiling R12 at “Io-fin” surfaces as well as for single-tube tests using “Thermoexcel” and “Gewa-T” surfaces.     

热漏对热机功率效率特性的影响

本研究热漏对热机最优性能的影响,导出存在热阻和热漏损失的定常态流不可逆热机的最佳功率、效率关系,所得结果不同于仅存在热阻损失的内可逆热机的功率效率特性关系,且与实际热机特性较为一致,由此指出了一些献的“不可逆循环”模型的不完备之处。     

Flow boiling and condensation of tetrary refrigerant mixtures inside water/refrigerant enhanced surface tubing

This work presents the results of an experimental study concerning the heat transfer characteristics of two-phase flow condensation and boiling of tetrary (R-32/R-125/R143a/R134a) refrigerant mixtures inside water/refrigerant horizontal enhanced surface tubing. Heat transfer characteristics such as average heat transfer coefficients, as well as pressure drops of the tetrary refrigerant mixtures, have been predicted and compared with other mixtures during flow condensation and boiling inside enhanced surface tubing. It was found that the tetrary refrigerant blend has higher transfer coefficients than R-502, and the lowest pressure drop among the refrigerants studied. © 1997 by John Wiley & Sons, Ltd.     

流速对非等温凝结表面Marangoni凝结换热特性的影响

在具有温度梯度的凝结表面上进行了水-酒精混合蒸气的Marangoni凝结的实验。研究了3种流速(V=2、4和6 m/s)对凝结表面上不同位置热流密度的影响。研究发现:流速对纯水蒸气和混合蒸气凝结时的表面温差和热流密度的影响是不同的。对纯水蒸气而言,流速增大后,表面温差和热流密度是增加的,并加剧了热流密度的分布不均(热流密度的相对差值在压力为31.2 kPa,流速2 m/s时为0.538,流速4 m/s时为0.6,流速6 m/s时为0.625)。对于混合蒸气,表面温差随流速的增加而减小,而热流密度增大很少(压力31.2 kPa,流速2 m/s时为0.186,4 m/s时为0.182,6m/s时为0.098)。