Investigation of pool boiling of nanofluids using artificial neural networks and correlation development techniques

The nucleate pool boiling heat transfer characteristics of TiO₂ nanofluids are investigated to determine the important parameters' effects on the heat transfer coefficient and also to have reliable empirical correlations based on the neural network analysis. Nanofluids with various concentrations of 0.0001, 0.0005, 0.005, and 0.01 vol.% are employed. The horizontal circular test plate, made from copper with different roughness values of 0.2, 2.5 and 4 μm, is used as a heating surface. The artificial neural network (ANN) training sets have the experimental data of nucleate pool boiling tests, including temperature differences between the temperatures of the average heater surface and the liquid saturation from 5.8 to 25.21 K, heat fluxes from 28.14 to 948.03 kW m^− 2. The pool boiling heat transfer coefficient is calculated using the measured results such as current, voltage, and temperatures from the experiments. Input of the ANNs are the 8 numbers of dimensional and dimensionless values of the test section, such as thermal conductivity, particle size, physical properties of the fluid, surface roughness, concentration rate of nanoparticles and wall superheating, while the outputs of the ANNs are the heat flux and experimental pool boiling heat transfer coefficient from the analysis. The nucleate pool boiling heat transfer characteristics of TiO₂ nanofluids are modeled to decide the best approach, using several ANN methods such as multi-layer perceptron (MLP), generalized regression neural network (GRNN) and radial basis networks (RBF). Elimination process of the ANN methods is performed together with the copper and aluminum test sections by means of a 4-fold cross validation algorithm. The ANNs performances are measured by mean relative error criteria with the use of unknown test sets. The performance of the method of MLP with 10-20-1 architecture, GRNN with the spread coefficient 0.7 and RBFs with the spread coefficient of 1000 and a hidden layer neuron number of 80 are found to be in good agreement, predicting the experimental pool boiling heat transfer coefficient with deviations within the range of ± 5% for all tested conditions. Dependency of output of the ANNs from input values is investigated and new ANN based heat transfer coefficient correlations are developed, taking into account the input parameters of ANNs in the paper.     

A review of physics and correlations of pool fire behaviour in wind and future challenges

This paper reviews the physics and correlations for the burning behaviour of pool fires in wind, discussing also challenges for future research on this topic. In the past decades, the burning behaviour of pool fires in still air, which is solely buoyancy driven, has been extensively studied. These studies are primarily focused on scale, radiation, soot, pressure and gravity effects. However, these phenomena and physics change significantly with much more complexity in the presence of wind, with regard to heat feedback and burning rate; flame morphological characteristics; flame turbulence, soot and radiation emission. Remarkable progress has been made in understanding the behaviour of the heat feedback and burning rate, flame tilt, flame length and flame base drag of wind-blown pool fires. Several semi-empirical correlations have been proposed for these quantities, based on experimental data and the physically dimensional analysis. However, for wind-blown pool fires, the flame soot and radiation emission coupling with complex flow turbulence scales due to the interaction of buoyancy with wind still require more basic research. All these processes are more challenging especially for wind-blown large scale pool fires, which require knowledge and understanding of the physics, especially for establishing evaluation methodologies of their hazard and adverse impact.     

我国电子玻纤生产技术发展与产品开发方向

本文详细介绍了我国大陆玻纤工业电子玻纤的生产技术发展历程、生产现状,并讨论了其生产发展特点：池窑拉丝已成为我国玻纤工业生产技术升级换代及高速增长的强大动力并成为玻纤工业规模化生产的主导;全行业生产规模连年持续增长,产业集中度逐步提高;玻璃纤维深加工、高附加值产品逐年增多,玻纤制品出口连年持续增长;探讨了电子玻纤新产品开发方向：薄型系列电子布、低介电常数电子布、开纤电子布、混纺或混织电子布、新型后处理剂电子布,同时提出了几点建议。     

柯东1风险探井的突破及其战略意义

中国石油天然气股份有限公司重点风险探井柯东1井获工业油气流,这是继1977年柯克亚凝析气田发现后,塔里木盆地塔西南坳陷昆仑山前33年来首次重大突破。柯东1凝析气藏的发现,是转变思路、抓住关键难题锲而不舍,坚持石油地质研究和勘探技术攻关的结果,不仅深化了昆仑山前石油地质认识,而且展现了昆仑山前油气勘探的巨大潜力。为保障塔西南勘探开发公司发展,促进南疆三地州人民生活的改善、环境保护及社会稳定都有重要的意义。     

Pool boiling heat transfer enhancement on porous surface tube

The passive residual heat removal exchanger (PRHR HX),which is a key equipment of the passive residual heat removal system,is installed in an elevated pool.Its heat transfer performance affects security and economics of the reactor,and boiling heat transfer in the liquid surrounding the exchanger occurs when the liquid saturation temperature exceeded.The smooth tubes,which are widely used as heat transfer tubes in PRHR HX,can be replaced by some enhanced tubes to improve the boiling heat transfer capability.In this paper,the pool boiling heat transfer characteristics of smooth tube and a machined porous surface tube are investigated by using high-pressure steam condensing inside tube as heating source.Compared with smooth tube,the porous surface tube considerably enhances the boiling heat transfer,and shortens the time significantly before reaching the liquid saturation temperature.Its boiling heat transfer coefficient increases from 68% to 75%,and the wall superheat decreases by 1.5oC.Combining effect of condensation inside tube with boiling outside tube,the axial wall temperatures of heat transfer tube are neither uniform nor linear distribution.Based on these investigations,enhance mechanism of the porous surface tube is analyzed.     

Two phase natural convection: CFD simulations and PIV measurement

Buoyancy induced flow and heat transfer are important phenomena in a wide range of engineering systems e.g. electronics and photovoltaics cooling, thermosiphon heat exchangers, solar-thermal heat absorbers, passive decay heat removal systems, etc. Such systems are subject to thermal stratification. The objective of the present work is to study the single phase and two phase (boiling) natural convection accompanied by thermal stratification. We carried out velocity and temperature measurements in a rectangular tank (0.8×0.6×0.6 m³) fitted with (a) a central tube, and (b) a 10 tube assembly; which form the heat transfer surface. Flows were measured using Particle Image Velocimetry (PIV). Additionally, computational fluid dynamic (CFD) simulations of these systems were performed: first with an assumption of no-boiling (i.e. no phase change) near the heat transfer surfaces; for which we used the open source CFD code OpenFOAM-1.6. For two phase simulations, we used the boiling model of Ganguli et al. (2010) and carried out simulations using the commercial software FLUENT 6.3. The extent of stratification and mixing has been investigated for a range of Rayleigh numbers from 4.34×10¹¹ to 2.59×10¹⁴. The flow information obtained from PIV was analyzed for insights into the dynamics of turbulent flow structures. We used the signal processing technique of discrete wavelet transform (DWT) for this purpose. From the analysis, we were able to estimate the size, velocity and energy distribution of turbulent structures in our flows. This information was used to estimate wall heat transfer coefficients. A good agreement was observed between the predicted and the experimental values of heat transfer coefficients.     

LTE核心网MME Pool技术及组网规划研究

结合LTE核心网的技术现状以及发展趋势,介绍了MME Pool的发展背景与核心技术;在对MME Pool和SGSN Pool技术比较的基础上,阐述了MME/SGSN融合Pool的组网优势及技术要点,并对其组网规划进行了建议。     

添加剂对乙二醇—水溶液沸腾传热的强化

以乙二醇—水溶液及加入微量添加剂 (表面活性物质 )为工质进行池式沸腾传热实验。实验结果表明 ,十二烷基硫酸钠等表面活性物质对乙二醇—水溶液的沸腾传热有明显的强化作用。在此基础上 ,分析了表面活性物质强化乙二醇—水溶液沸腾传热的原因。     

Ozone Swimming Pool Water Treatment Under Tropical Conditions

This paper presents the first year operation report of an ozone swimming pool water treatment system under the severe conditions of tropical climate. The system installed in a 70 m³ pool with upflow hydraulics, comprises sand filtration and ozone/bromide ion treatment. Cupric sulfate was chosen as algaecide and pH was kept between 7.5 and 7.8 by adding adequate amounts of HC1. When required, a slight flocculation (aluminum sulfate, 5 mg/L) was applied weekly. Water physicochemical analyses performed twice a week throughout the year, including microbiological tests, clearly demonstrated the remarkable efficiency of the treatment, fulfilling all water quality standards, even at high bather loads and during the summer months (at water temperature higher than 31[ddot]C and an intense sunlight) being economically feasible as well. This experience will allow the extension of ozone water treatment to larger swimming pools in similar circumstances.     

Enhancement of R123 pool boiling by the addition of hydrocarbonsAmélioration de l'ébullition libre du R123 par l'ajout d'hydrocarbures

This paper presents pool boiling heat transfer data for 10 different R123/hydrocarbon mixtures. The data consisted of pool boiling performance of a GEWA-T^™ surface for pure R123 and for 10 dilute solutions of five different hydrocarbons: (1) pentane, (2) isopentane, (3) hexane, (4) cyclohexane, and (5) heptane with R123. The heat flux and the wall superheat were measured for each fluid at 277.6 K. A maximum (19±3.5)% increase over the pure R123 heat flux was achieved with the addition of 0.5% mass isopentane to R123. Other mixtures of isopentane, pentane, hexane, and cyclohexane with R123 exhibited smaller maximums than that of the R123/isopentane (99.5/0.5) mixture. Presumably, a layer enriched in hydrocarbon at the heat transfer surface caused the heat transfer enhancement. Conversely, an R123/heptane (99.5/0.5) mixture and an R123/cylcohexane (99.5/0.5) mixture exhibited only degradations with respect to the pure component performance for all test conditions. Several characteristics of the hydrocarbons were examined to determine their influence on the boiling heat transfer performance: molecular weight, molecular structure, composition, surface tension, and vapor pressure.