新型强化换热方法的换热性能研究

通过分析设置翼涡发生器、扰流柱 ,采用多头螺旋槽管等几种新型强化换热方法的换热性能 ,得出不同涡发生器强化换热程度不同及换热增强与压力损失的最佳强化效果有别。并指出大容量设备即紧凑式换热器的研究为强化换热、节能降耗提供了可能 ,发展前景广阔。

基于扩散近似法和双通量法耦合的多孔介质内燃烧辐射换热计算方法

将Rosseland辐射模型和双通量法结合,对瓦斯气体在泡沫陶瓷中预混燃烧辐射换热计算方法进行研究.数值模拟的结果与试验结果吻合比较好,证明提出的辐射换热计算方法是有效的.

气候实验室高传热比换热器的设计与验证方法

针对大型气候实验室的宽温域大流量空气循环加热与冷却问题,基于空气处理系统需求和换热器原理,采用“正设计法”确定特征参数,开展不同实验条件下的定片距与变片距翅片管换热器的设计研究,并针对已设计的换热器开展低温工况换热特性试验验证,探究换热器传热系数、压降随时间的变化规律,对比两种换热器在低温工况下的响应特征,通过分析特征参数来表征所设计的换热器构型满足气候试验需求。研究表明,两种换热器所有工况换热系数的实验值与计算值误差在6.8%以内,换热器压降误差都在45 Pa以内,满足设计要求;相比于定片距换热器,变片距换热器换热系数增加、压降减少。

强化对流换热场协同唯象理论

根据现代热力学流与力的热力学线性唯象关系 ,导出了对流换热强度与流体中存在的各种内场及外场的关系 ,从唯象上阐明了降低热边界层厚度、增加流体扰动和增加近壁面速度梯度的强化对流换热方法的物理机制。结果表明 ,强化对流换热的本质是控制内场和外场方向的协同 ,并以此可指导发展强化对流换热的新方法。

换热器单侧换热系数分离方法研究

因环境保护、工艺要求、能源危机和市场需求,各种新型换热器层出不穷,这些新型换热器在内部宏观和微观结构、换热介质以及设备材质方面与传统管壳式换热器均存在较大差异,原热工设计方法均已不再适用,需要设计新的热工试验来测定其实际换热性能,拟合验证新的热工设计方法。目前现有的换热器单侧换热器系数的分离方法均有各自的适用范围和优缺点。鉴于此,提出了一种适用于该种情况的新型单侧换热器系数的分离方法,可以更精确快速地拟合出符合要求的单侧换热系数计算关联式。

考虑压降的换热网络合成的研究进展

文章对文献中提出的考虑压降的换热网络合成方法的内容和方法进行评述 ,分析各自的优缺点 。

板式换热器在船舶轮机中的应用

伴随社会经济的持续、稳健化发展,科学技术水平的不断提升,许多先进技术、理念被应用在船舶的设计、生产当中,强有力推动着此领域的发展与完善;轮机乃是船舶运作的关键性设备,保障其运作正常、高效,十分必要且关键;而要想强化船舶轮机运作质量,板式换热器的应用必不可少。本文结合当前实况,首先对板式换热器的基本构造及特点进行改善,总结其换热计算方法,且就其在船舶轮机中的应用及所需注意事项作剖析,望能为此领域应用研究提供一些参考。

Simulated Annealing Approach to the Optimal Synthesis of Distillation Column with Intermediate Heat Exchangers

This article presents a simulated annealing-based approach to the optimal synthesis of distillation column considering intermediate heat exchangers arrangements. T-he number of intermediate condensers and/or intermediate reboilers, the placement locations, the.operating pressure of column, and the heat duties of intermediate heat exchangers are treated as optimization variables. A novel coding procedure making use of an integer number series is proposed to represent and manipulate the structure of system and a stage-to-stage method is used for column design and cost calculation. With the representation procedure, the synthesis problem is formulated as a mixed integer nonlinear programming （MINLP） problem, which can then be solved with an improved simulated annealing algorithm. Two examples are illustrated to show the effectiveness of the suggested approach.

A Two-step Design Method for Shaft Work Targeting on Low-temperature Process

In low-temperature processes, there are interactions between heat exchanger network(HEN) and refrigeration system. The modification on HEN of the chilling train for increasing energy recovery does not always coordinate with the minimum shaft work consumption of the corresponding refrigeration system. In this paper, a systematic approach for optimizing low-temperature system is presented through mathematical method and exergy analysis. The possibility of "pockets", which appears as right nose section in the grand composite curve(EGCC) of the process, is first optimized. The EGCC with the pockets cutting down is designed as a separate part. A case study is used to illustrate the application of the approach for a HEN of a chilling train with propylene and ethylene refrigerant system in an ethylene production process.

Calculation of optimal current density of double side permanent magnet linear synchronous motor

The use of design method considering a coil temperature to maximize the thrust density of a double side coreless permanent magnet linear synchronous motor(PMLSM) was presented.The optimal current density where the coil temperature reaches an allowable temperature with heat analysis was applied to a magnetic circuit design.Changing optimal current density is verified whenever the design parameters of the motor are altered.The design parameters of the motor were applied to thrust calculation.In this way,the optimal model,which is a reversal of the existing design method,is deduced.The results were compared with the experimental data to verify their validity.When the convection heat transfer coefficient is applied to other models,the results of the analysis and test values show good concordance.The method proposed has some limitations.

Study on the Stability of Ion-exchange Resin Catalysts:Ⅰ. TGA as a Rapid Evaluating Method

The thermal stability of five commercial ion-exchange resin catalysts was studied by means of thermal gravimetric analysis （TGA） at elevated temperatures of up to 600℃ and isothermal temperatures in the range of 150℃ and 200 ℃. Resin samples with different initial water contents were also investigated. The study indicated that TGA, as a complementary evaluating method for the plug flow reactor system approach, could be used as a fast analyzing means for study on the thermal stability of ion-exchange resin catalysts. The stoichiometric calculation of the isothermally treated resin catalysts based on the FTIR analysis and acid capacity confirmed that the weight loss of the resins at 150℃ and 200℃ was caused by the desulfonation process and that desulfonation occurred mainly at the para-position of the benzene ring in the resins. H＋ ions and moisture played an important role in the desulfonation process.

Compact Thermosyphon Heat Exchanger for Power Electronics Cooling

The heat losses density in power electronics products follows an ever increasing trend. Nowadays they reach 200 W/cmz at chip level and 50 W/cm2 at heatsink base level. Water cooling is the most effective cooling method but unfortunately water is often undesired due to high voltages or costumer requirements. Two-phase cooling is a promising technology for electronics cooling. It allows using dielectric fluids in passive systems and still benefits from very high heat transfer coefficients. Thermosyphons are a particularly interesting technology in the field of power electronics because it is entirely passive and a simple equipment. ABB has developed a compact thermosyphon heat exchanger based on automotive technology, which uses numerous multi-port extruded tubes with capillary sized channels disposed in parallel and brazed to a heated base plate in order to achieve the desired compactness. The experimental performances of this novel power electronics cooling system are presented with R134a as a working fluid. The influence of several parameters on the performances was studied experimentally： coolant flow rate, coolant temperature, heat load and fluid filling.

强化换热结构的工业应用

据《Теплознергетика》2012年1月刊报道，热能动力装置的技术经济指标在很大程度上取决于热交换器的参数，这些热交换器的质量和尺寸都很大。随着动力装置单机功率的提高，其中热交换器的绝对质量和尺寸越来越大，相应提高了热交换器性能。借助于有效的强化换热方法，可以减少其尺寸和质量并降低泵栽热体通过热交换器所消耗的功率。

Comparative study on constructal optimizations of T-shaped fin based on entransy dissipation rate minimization and maximum thermal resistance minimization

The constructal optimizations of T-shaped fin with two-dimensional heat transfer model are carried out by finite element method and taking the minimization of equivalent thermal resistance based on entransy dissipation and the minimization of maximum thermal resistance as optimization objectives, respectively. The effects of the global parameter a (integrating the coefficient of convective heat transfer, the overall area occupied by fin and its thermal conductivity) and the volume fraction ? of fin on the minimums of equivalent thermal resistance and maximum thermal resistance as well as their corresponding optimal configurations are analyzed. The comparison of the results based on the above two optimization objectives is conducted. The results show that the optimal structures based on the two optimization objectives are obviously different from each other. Compared with the optimization result by taking the minimization of maximum thermal resistance as the objective, the optimization result by taking the equivalent thermal resistance minimization as the objective can reduce the average temperature difference in the fin obviously. The increases of a and ? can all improve the working status of local hot spot and the global heat transfer performance of the system. But the improvement effects of the increases of a and ? on the minimization of equivalent thermal resistance are different from those on the minimization of maximum thermal resistance. For either objective, the effect of a is different from that of ?. The T-shaped fin with minimum equivalent thermal resistance is much taller than that with minimum maximum thermal resistance; for either optimization objective, the stem of fin is thicker than the branches of fin, and the stem thickness is relatively close to branch thickness when the minimization of equivalent thermal resistance is taken as the optimization objective. The T-shaped fin with flat stem and slender branches can benefit the reduction of the maximum thermal resistance.

ZnO hierarchical aggregates： Solvothermal synthesis and application in dye-sensitized solar cells

ZnO hierarchical aggregates have been successfully synthesized by solvothermal methods through reaction of zinc acetate and potassium hydroxide in methanol solution. The shapes of the aggregates were controlled by varying the ratio of Zn2~ and OH- ions in the reaction system, while the size can be tuned from 2μm to 100 nm. Oriented attachment was found to be the main mechanism of the three-dimensional assembly of small ZnO nanocrystallites into large aggregates. The performance of these aggregates in dye-sensitized solar cells （DSCs） indicated that hierarchical structured photoelectrodes can increase energy conversion efficiency of DSCs effectively when the sizes of aggregates match the wavelengths of visible light.

Pattern Formations in Heat Convection Problems

After Bénard＇s experiment in 1900, Rayleigh formulated heat convection problems by the Oberbeck-Boussinesq approximation in the horizontal strip domain in 1916. The pattern formations have been investigated by the bifurcation theory, weakly nonlinear theories and computational approaches. The boundary conditions for the velocity on the upper and lower boundaries are usually assumed as stress-free or no-slip. In the first part of this paper, some bifurcation pictures for the case of the stress-free on the upper boundary and the no-slip on the lower boundary are obtained. In the second part of this paper, the bifurcation pictures for the case of the stress-free on both boundaries by a computer assisted proof are verified. At last., Bénard-Marangoni heat convections for the ease of the free surface of the upper boundary are considered.

Uniform Deterministic Discrete Method for Three Dimensional Systems

For radiative direct exchange areas in three dimensional system, the Uniform Deterministic Discrete Method (UDDM) was adopted. The spherical surface dividing method for sending area element and the regular icosahedron for sending volume element can meet with the direct exchange area computation of any kind of zone pairs. The numerical examples of direct exchange area in three dimensional system with nonhomogeneous attenuation coefficients indicated that the UDDM can give very high numerical accuracy.

Integral Transform Methods for Inverse Problem of Heat Conduction with Known Boundary of a Thin Rectangular Object and its Stresses

The three-dimensional inverse transient thermoelastic problem for a thin rectangular object is considered within the context of the theory of generalized thermoelasticity. The upper surface of the rectangular object occupying the space D： -a〈xSa; -b〈_y〈b; 0〈z〈h; with the known boundary conditions. Laplace and Finite Marchi-Fasulo transform techniques are used to determine the unknown temperature, temperature distribution, displacement and thermal stresses on upper plane surface of a thin rectangular object. The distributions of the considered physical variables are obtained and represented graphically.

Thermal performances of non-equidistant helical-coil phase change accumulator for latent heat storage

Helical-coil is a common structure of heat exchanger unit in phase change heat accumulator and usually has the equal coil pitch between adjacent coils. Its thermal performances could be improved by improving the uniformity of the phase change material （PCM） temperature distribution. Thus, a novel non-equidistant helical-coil structure was proposed in this study. Its coil pitch decreased along the flow direction of heat transfer fluid, which made the heat exchange area in unit volume increase to match the decreasing temperature difference between the heat transfer fluid and PCM. The structure was optimized using numerical simulation. An experimental system was developed and the experiment results indicated that the proposed non-equidistant helical-coil heat accumulator was more effective than equidistant helical-coil for latent heat storage. The uniformity of the temperaalre distribution was also confirmed by simulation results.