Effective conductivity bounds by inserting adiabatic or isothermal surfaces

Structure-dependent bounds of the effective thermal conductivity ETC in polyphasic materials, with a regular inclusion array, are proposed. The bounds account for the contact resistance and are based on the enhancement of the ETC by insertion of any isothermal surface (for the upper bounds) and on the decrease of the ETC by insertion of any adiabatic surface (for the lower bounds). The method is above all able to introduce bounds for the high contrast filled composite polymers, whose inclusions are much more conductive than the polymer matrix. Computations for the ETC of a simple cubic array of spheres, which simulate well the heat conduction features in filled polymers, show that two such lower bounds and an upper one are easily computable. For all ETC higher than 3 or 4 times the matrix thermal conductivity, the bounds by insertion of isothermal or adiabatic surfaces are tighter than the other known structure-dependent bounds which account for the imperfection of the perfect contact – the 3rd order variational bounds of Torquato and Rintoul [S. Torquato, M. Rintoul, Effect of the interface on the properties of composite media, Phys. Rev. Lett. 75 (1995) 4067–4070].     

Development of effective thermal conductivity models for Reserve Shutdown Control fuel block of prismatic HTGR for hydrogen production

A hydrogen production system coupled to High Temperature Gas-cooled nuclear Reactor (HTGR) is considered to be one of the most promising ways for massive hydrogen production. For the reliability of the coupled system, the safety analysis on the HTGR is to be conducted by a system-scale analysis code. The system-scale analysis code adopts an effective thermal conductivity (ETC) model for a fuel block due to its complex geometry containing large number of coolant holes and nuclear fuel rods. The ETC of the fuel block is crucial to calculate the heat transfer inside the reactor core and prediction of thermal distribution over the reactor core is the most significant for the safety analysis of HTGR. Therefore, the verification of the ETC model that contributes to the prediction is essential. This ETC model based on Maxwell's theory shows an inaccurate prediction when the configuration of the composite materials is not homogeneous. Since the geometry of Reserve Shutdown Control (RSC) fuel block of HTGR is not homogeneous due to a large RSC hole, the ETC model for RSC fuel block should be developed to improve the accuracy and reliability of the reactor system analysis code. In this study, the two ETC models for the RSC fuel block have been developed by the thermal network modeling. Computational fluid dynamic simulations with a real geometry were performed to evaluate the accuracy of the ETC models for the RSC fuel block. The comparative result between CFD analysis and the ETC model shows that the newly developed model predicts the effective thermal conductivity of RSC fuel block more accurately than the previous model.     

The temperature dependence of effective thermal conductivity of the samples of glass wool reinforced with aluminium foil

In this study, the temperature dependence of effective thermal conductivity (ETC) for samples of binary, ternary, and quadruple glass wools reinforced with aluminium foil was examined. The experiments were realized by the guarded hot plate in temperature differences of 5, 10 and 15 °C and the temperatures of 25 and 40 °C. The results revealed that in the case of reinforcing the aluminium foil, ETC increased with increasing the temperature or changing of temperature difference (5, and 15 °C). Also, an increase of additional layers decrease its' influence on low temperature. Consequently, reflectivity materials may increase or reduce ETC.     

Performance optimization of evacuated tube collector for solar cooling of a house in hot climate

Evacuating the space connecting cover and absorber significantly improves evacuated tube collector (ETC) performance. So, ETCs are progressively utilised all over the world. The main goal of current study is to explore ETC thermal efficiency in hot and severe climate like Kuwait weather conditions. A collector test facility was installed to record ETC thermal performance for one-year period. An extensively developed model for ETCs is presented, employing complete optical and thermal assessment. This study analyses separately optics and heat transfer in the evacuated tubes, allowing the analysis to be extended to different configurations. The predictions obtained are in agreement with experimental. The optimum collector parameters (collector tube length and diameter, mass flow rate and collector tilt angle) are determined. The present results indicate that the optimum tube length is 1.5 m, as at this length a significant improvement is achieved in efficiency for different tube diameters studied. Finally, the heat generated from ETCs is used for solar cooling of a house. Results of the simulation of cooling system indicate that an ETC of area 54 m², tilt angle of 25° and storage tank volume of 2.1 m³ provides 80% of air-conditioning demand in a house located in Kuwait.     

Analysis of effective thermal conductivity for circular tubes made with porous media based on fractal theory

Accurately evaluating the relation between heat transfer performance and the complex structure of porous media is still a difficult task. Most previous fractal models of effective thermal conductivity (ETC) are developed to describe the heat-conducting characteristics of a unit cell or a representative elementary volume in porous media, and few models have paid attentions to the ETC for practical circular tubes made with a porous structure based on fractal theory. This paper proposes a new ETC model for a circular tube made with porous media based on fractals, and the validity of the present model is proved by previous models and testing data in the literature, then the effects of intrinsic thermo-physical properties of each component and pore structures on the ETC are discussed. The analysis results indicate that a circular tube made with porous media can improve its heat-insulating performance by about 25% compared with a common parallel circular tube. This can supply an alternative scheme for pipe insulation design in cold/hot fluid supplying systems or air conditioning systems.     

Numerical simulation of concrete hollow bricks by the finite volume method

Numerical thermal analysis has become a powerful tool for hollow brick design concerning energy saving issue. In the present paper it was employed to understand the heat transfer performance of 240 × 115 × 90 concrete hollow bricks with 71 different configurations. The general commercial computational fluid dynamics (CFD) soft FLUENT^® was used in the research. A comprehensive investigation on the effect of enclosure configurations with the same void volume fraction on equivalent thermal conductivity (ETC) was conducted. The enclosure numbers in parallel and vertical directions of heat transfer were investigated in details. The effect of enclosure staggered form is also discussed carefully. In the research, ETC data was compared with radiation and nature convection and without them. In addition, temperature and velocity vector distributions were also illustrated in order to clarify heat transfer mechanism. It can be concluded from this research that ETC values are dependent on the combining effect of heat conduction in all domains, natural convection within enclosure and radiation on inner surface. ETC values decrease with the increasing enclosure numbers in the parallel direction of heat transfer and increase in the vertical direction of heat transfer, vise versa. Therefore, increasing enclosure numbers in the parallel direction becomes more favorable to decrease ETC than that in the vertical direction of heat transfer. Secondly, the relative enhancement of radiation heat transfer on ETC ranged from 7.41% to 25.39%, and the nature convection from near zero to 22.50%, depending on the enclosure numbers and their arrangement configurations. Finally, the increasing enclosures in the parallel direction can decrease ETC values from 11.59% to 20.94% for enclosure vertical aligned bricks. Under the given conditions the smallest ETC is 0.32619 W/(m K) for enclosure staggered form with three enclosures in length direction and eight in width direction, which is only 23.30% of the solid concrete brick in the present research.     

Effective media formation and conduction through unsaturated granular materials

A theory for the effective thermal conductivity (ETC) of an unsaturated and saturated medium containing three phases is presented using the effective continuous media (ECM) approximation. The boundary condition for ECM through a successive dispersion technique is first derived. Small dispersions are then allowed in the proposed ECM. The method is an analytical one and shows the validity and emergence of ECM for large dispersions. The theory is applicable for all saturating fluids including gas and is useful for determining the content of petroleum products in underground soil. A comparison of calculated values of ETC with experimental ones when the saturating fluids are air and water shows a good agreement.     

Calculation Model of Effective Thermal Conductivity of a Spiral-wound Lithium Ion Battery

This paper proposed an analytical model which can calculate the effective thermal conductivity (ETC) of a spiral-wound Lithium-ion battery (Li-ion battery). It bases on a two-dimensional energy balance with both radial and spiral heat transfer, as well as internal thermal contact resistance (TCR) considered simultaneously and studies the influence of winding layers and winding tension on the ETC. Results show that the analytical data are in good agreement with the numerical results. With the winding layers decreased and the winding tension enhanced, the ETC of Li-ion battery increases gradually. The radial temperature in Li-ion battery is also investigated which demonstrates a relatively higher temperature when considering the internal TCR.     

Productivity amelioration of stepped solar still using phase change material and evacuated tube collector

This study investigates the individual and cumulative effects of phase change material (PCM) and evacuated tube collector (ETC) on the performance of a stepped solar still (SSS). Experiments have been performed on SSS, SSS loaded with PCM (SSS-PCM), SSS coupled with ETC (SSS-ETC), and SSS loaded with PCM and coupled with ETC (SSS-PCM-ETC). An innovative way of loading paraffin wax as PCM is introduced to utilize solar energy efficiently for the distillation process during off-sunshine hours. ETC is used to provide pre-heated RO wastewater to the distillation unit. The distillate output was observed maximum for SSS-PCM-ETC (4.97 kg/m² day) which is 99% more than that of the SSS unit. The PCM and ETC individually with SSS unit increases the distillate output by 31% and 24%, respectively. The working time of the distillation unit was observed to be increased by 3 h by the use of PCM. The total heat transfer coefficient was evaluated at the maximum for SSS-PCM-ETC and was observed in the range of 16.94–167.04 W/m² °C. The thermal energy efficiencies of SSS, SSS-ETC, SSS-PCM, and SSS-PCM-ETC were evaluated as 28.65%, 35.59%, 43.88%, and 44.04%, respectively. SSS-PCM-ETC is found to be the most economic with the best environmental conservation having maximum values of daily productive cost ($0.69) and carbon credits earned ($184.8).     

Optimization of concrete hollow brick using hybrid genetic algorithm combining with artificial neural networks

A structure optimization of concrete hollow brick with four rectangle enclosures is carried out to minimize the equivalent thermal conductivity (ETC) in the constraint of variable shape and position parameters. During the optimization hybrid genetic algorithm (HGA) is developed combining with artificial neural networks (ANN). The modified Latin hypercube sampling (i.e. the maximum minimum distance criterion) is employed to make a robust decision. The ETC of the samples is computed using the finite volume method (FVM) on the basis of 3D multi-mode heat transfer simulation. It indicates that the well-trained ANN can accurately predict the ETC of the concrete hollow brick which matches very well with data obtained from the FVM simulation. The optimization obtains 21.69% improvement on the ETC for the given range of design parameters. The optimized concrete hollow brick owns the largest void volume fraction, the minimum rid and wall thickness, same width of the enclosure, and the optimum staggered arrangement with two same large enclosures and two same small enclosures, which is resulted by the multi-mode heat transfer characteristic of the concrete hollow brick. A novel method of the optimum concrete hollow is proposed to construct new concrete hollow brick with many rows of enclosures. Relative Staggered Ratio (RSR) is used to discuss the effect of the staggered form. By combining two or more rows of the optimized enclosures to one brick with the same size the efficiency to block heat transfer is evidently improved. It is concluded by the present work that the combination of ANN and HGA and the popularizing method are powerful to the optimization of the concrete hollow brick.     

电子节气门控制系统的构建

分析了电子节气门系统的构成,将电子节气门系统软、硬件集成到了自行开发的基于16位单片机的发动机控制系统中,对控制参数进行了标定,利用变参数PID策略实现了节气门系统的住置控制,构建了电子节气门系统在发动机控制系统中的应用框架,为通过对发动机进气量进行智能化的控制从而提高其动力性、经济性、排放性打下了基础。     

增压柴油机瞬态排放仿真平台

提出了针对于欧洲瞬态测试循环(ETC)的典型工况建模思想,并引入复合瞬变率作为输入变量建立了瞬态排放神经网络模型,建立了增压柴油机瞬态工况全程仿真平台.通过对不同EGR率下十三工况排放和不同瞬变率变负荷工况排放的模拟,验证了该仿真平台的准确性和泛化能力,其稳、瞬态排放验证性模拟差异率分别低于3%和4%,瞬态排放泛化性模拟趋势相同,峰值差异率在8%以内.该平台完全适用于以控制策略开发为目的 ETC典型工况的瞬态模拟.     

Durability of polymeric glazing materials for solar applications

The economic viability of solar collector systems for domestic hot water (DHW) generation is strongly linked to the cost of such systems. Installation and hardware costs must be reduced by 50% to allow significant market penetration. An attractive approach to cost reduction is to replace glass and metal parts with less expensive, lighter weight polymeric components. Weight reduction decreases the cost of shipping, handling, and installation. The use of polymeric materials also allows the benefits and cost savings associated with well established manufacturing processes, along with savings associated with improved fastening, reduced part count, and overall assembly refinements. A key challenge is to maintain adequate system performance and assure requisite durability for extended lifetimes. Results of preliminary and ongoing screening tests for a large number of candidate polymeric glazing materials are presented. Based on these results, two specific glazings with moderate and poor weathering stability are selected to demonstrate how a service lifetime methodology can be applied to accurately predict the optical performance of these materials during in-service use. A summary is given for data obtained by outdoor exposure and indoor testing of polyvinyl chloride (PVC) and high temperature modified polycarbonate copolymer (coPC) materials, and an initial risk analysis is given for the two materials. Screening tests and analyses for service lifetime prediction are discussed. A methodology that provides a way to derive correlations between degradation experienced by materials exposed to controlled accelerated laboratory exposure conditions and materials exposed to in-service conditions is given, and a validation is presented for the methodology based upon durability test results for PVC and coPC.     

微孔硅酸钙的有效导热系数和最佳使用密度

利用等效热阻模型,考虑辐射传热影响,对硬硅钙石型微孔硅酸钙绝热材料的有效导热系数进行了预测,给出了计算公式,探讨了不同使用温度下微孔硅酸钙绝热材料的最佳使用密度.分析表明,模型计算值与实验值吻合好,有效导热系数预测模型可精确预测其绝热性能并指导绝热设计施工.     

安装SCR系统的国Ⅳ发动机排放特性研究

试验采用50×10-6和350×10-6两种不同硫含量的燃油,对装有SCR系统的发动机进行ETC和ESC测试,研究了SCR开启/关闭情形下的排放;并采用ELPI分析了在不同条件下颗粒排放差异的原因以及细颗粒的排放特性。试验结果表明:在使用不同硫含量的燃油条件下,NOx排放降低率均可以达到60%以上;SCR开启时,ETC下硫含量350×10-6比50×10-6的颗粒排放增加18%,ETC下颗粒排放均比ESC下增加30%~50%。在50%~70%负荷时,颗粒数目排放较低,低负荷和全负荷时颗粒排放较高,全负荷时最高;在负荷一定时,转速越高,颗粒排放浓度越高;使用低硫燃油,颗粒物质量排放较低,而数目排放却增多;多出的部分主要是粒径小于100 nm的超细颗粒。     

Intelligent optimization methodology of battery pack for electric vehicles: A multidisciplinary perspective

Past studies focused on proposing new materials for batteries components, state of health (SOH) prediction, thermal design, equivalent circuit modeling, and so on. Those studies have been implemented on individual basis on a single battery or battery pack. However, there is hardly any research found that encompasses all the multidisciplinary aspects (such as materials, SOH, intelligent configuration [assembly], thermal design, mechanical safety, and recycling of materials and pack) simultaneously for the battery pack design of electric vehicles. This research article proposes a synthetic methodology for an advanced design of battery pack and its components by incorporating optimal scenario of materials selection for battery electrodes, SOH estimation, configurations (assembly) of cells, thermal (air and liquid cooling) design, battery pack casing mechanical safety, and recycling aspects of battery and battery pack. The problem is divided into the several parts and methodology for each is proposed. Cumulative advantages of the methodology with six future critical directions are discussed in the end.     

Prediction of pressure drop in a packed bed dehumidifier operating with liquid desiccant

In this paper a more rigorous model, which is valid for both structured and random packing columns, is used for predicting the irrigated pressure drop in a desiccant–air contact system. Calcium chloride solution is considered as the desiccant. Four different random packing materials and three different structured packing materials are considered in the present study. The effects of random packing shape and the type of structured packing on the hydraulic performance are studied. The model has been validated for a wide range of operating values available in the literature. It is found that the structured packing has the lower pressure drop and higher capacity compared with random packings. Among the random packing materials considered in the present study, Intalox saddles can provide the least irrigated pressure drop and among the structured packing materials the sheet-type Mellapak 250 Y has the lowest pressure drop.     

电喷摩托车混合气的管理

本文介绍了电喷摩托车进气系统的组成以及电喷系统对空气进气量的计量和控制方式.同时就节气门体总成的结构和技术要点,特别是电子节气门ETC的控制技术进行了讨论.研究表明,混合气的管理对电喷摩托车的综合性能至关重要.     

Probabilistic estimation of remaining life of a pipeline in the presence of active corrosion defects

A methodology is presented for the assessment of remaining life of a pressurised pipeline containing active corrosion defects. A probabilistic approach is adopted to this methodology and the associated variables are represented by normal or non-normal probabilistic distributions. A failure pressure model based on fracture mechanics is adopted for the assessment of pipeline failure pressure and linear idealisation of the long-term corrosion growth rate is carried out. Because of the presence of nonlinearity in the limit state function and also of the presence of non-normal variables, the Level II advanced first order second moment iterative method is employed for carrying out reliability analyses. The methodology is applied to an example pipeline and the remaining useful life of this pipeline is assessed. Relative contribution of the random variables and the sensitivity of the reliability index to the change in variance of the random variables is also investigated.     

Modeling and Coupling Particle Scale Heat Transfer with DEM through Heat Transfer Mechanisms

The detailed heat transfer mechanisms particle interior, gas film around particles, gas gap between contact surfaces, and rough surface are considered to model heat transfer between particles. The validation of the heat transfer model is accomplished and the predicted results show good agreement with other experiments. From the quantitative comparison of four heat transfer paths, it is revealed that the heat transfer through gas gap and rough surface could be neglected for a particle diameter larger than 2 mm. Furthermore, the detailed heat transfer model is coupled with the discrete element method (DEM) to calculate macro effective thermal conductivity (ETC) of fixed beds, and the accuracy and applicability is verified by comparing with other estimated and experimental results. The influence of particle diameter, density, specific thermal capacity, and thermal conductivity on ETC is investigated. Results show that the proposed heat transfer model provides an effective and accurate way to couple with DEM in the particle system.