Performance Optimization of Co-current Gas-to-Gas Micro Heat Exchanger Considering Radiation

Optimization of a parallel flow gas-to-gas tubular micro heat exchanger with hot core and cold annulus fluid is numerically analyzed, considering the beneficial role of surface radiation. Operating and geometric parameters are varied for fixed overall mass flow rate and temperature of cold core fluid, to study the effects on the following performance parameters: heat transferred to annulus fluid, logarithmic mean temperature difference, effectiveness, and volumetric heat transfer coefficient. The micro heat exchanger is optimized for high heat transfer to annulus fluid and volumetric heat transfer coefficient, for different operating and geometric conditions. Optimization for high volumetric heat transfer coefficient maximizes the micro heat exchanger effectiveness, heat transferred and improves logarithmic mean temperature difference.     

Mean Temperature Difference for Shell-and Tube Heat Exchangers with Condensing on the Shell Side

Shetl-and-tube heat exchangers with condensing on the shell side usually have a nonlinear heat release curve and a variable shell-side heat transfer coefficient. Using an effective average coolant temperature, it is possible to separate the calculation of the mean temperature difference from the heat transfer coefficient. Thus, it is possible to calculate the weighted mean temperature difference before the heat transfer coefficients are calculated. As a result, the complexity of the calculations is greatly reduced from present incremental procedures. When compared to a detailed incremental calculation of the mean temperature difference, tht maximum error is about 2%. A manual incremental method is also presented, which requires only moderately more work than industrial methods that use average heat transfer coefficients.     

基于温差均匀性因子协进化的双层算法同步优化换热网络

针对同时存在整型变量和连续型变量的换热网络综合问题,提出一种双层优化方法。外层以换热网络的温差均匀性因子作为网络结构性能的评价指标,通过蒙特卡洛随机抽样技术产生试探结构,采用整型优化算法逐步进化外层结构;内层以最小年综合费用作为优化指标,采用动态更新子群的改进粒子群算法优化连续变量。优化结果表明,温差均匀性因子可以有效评价换热网络的结构性能,从而指导结构的进化;改进的粒子群算法具有更强的全局搜索能力,相关算例均找到了更优的网络设计,应用于工业生产实际,可以有效节约成本。     

南平市年平均气温变化趋势分析

采用Kendall秩次相关检验与重标极差R/S相结合的分析方法对闽江上游南平市年平均气温变化趋势进行了研究.结果表明,南平市年平均气温近50 a来总体呈上升趋势,尤其近年较显著,未来几年仍有上升趋势.该方法能较好地揭示气温变化的趋势特征,且可用于分析其他水文时间序列变化趋势,为流域防汛备汛提供科学依据.     

Temperature Difference Error Determination for Heat Meter Validation

A method to calculate the maximum value of temperature difference error in heat meters is presented. It is designed for heat meters used for measuring the volume of heat provided to buildings by heating systems using hot water. Validation offices generally use computer-based numerical methods for the calculation of the error over the full temperature range and temperature difference range. Use of these methods is time-consuming due to taking in succession the temperature and temperature difference with a constant gradient as well as selecting the maximum value of error. The author has developed a method that allows the practicing engineer to calculate the maximum error in a short time with his or her own program. This method can also be used for heat meters not conforming to any standard or pairs of temperature sensors not dedicated for heat meters.     

多股流板翅式换热器温度交叉的数值分析

以平行多股流板翅式换热器为研究对象,给出了考虑翅片旁通作用的多股流板翅式换热器流体和翅片的能量方程。在改变多股流板翅式换热器各通道的流体参数、流动方式及换热器的结构参数等情况下,对能量方程进行数值求解,获得了各通道的流体温度分布情况及相邻通道的流体温度差,并分析了流体参数、流动方式和结构参数的变化对相邻通道流体温度交叉的影响。     

4.2 MW燃煤热风炉换热器壁温计算方法研究

推导了烟气在管内流动、均匀受热管壁的壁温计算公式,分析得出,影响壁温的主要因素是烟气温度和表面传热系数。降低管壁温度的有效方法是降低烟气温度,即在受热面前的高温烟气中混入冷烟气或冷空气,对降低壁温的两种方法进行了比较。研究了热风炉计算中过量空气系数、再循环系数的确定方法及热风炉对风温变化的适应性。     

较大规模换热器网络的一种综合优化方法

基于分级超结构换热器网络模型的特点，改进了计算温度分布的通用解方法，以遗传算法和模拟退火算法为主，以瞎子爬山优化算法以及一些特殊优化策略为辅，设计了相应的计算程序，它需要的计算机内存要比现有的其他方法小。实例证明，该方法可成功地应用于较大规模的换热器网络的优化，并得到比现有各种方法更优的结果。     

一种监测换热器污垢的新方法

在考虑污垢对换热器传热性能影响的基础上,提出换热器当量总污垢热阻和污垢函数的概念,并给出换热器当量总污垢热阻的监测方法,讨论了换热流型、传热有效度ε和冷热流体热容量率比R对换热器当量总污垢热阻的影响。     

热网加热器运行经济性的定量诊断方法

针对影响热网加热器运行性能的主要因素－运行端差和抽汽压损偏离标准值对供的热机组经济性影响的研究,提出了其经济性定量诊断数学模型,并利用实例对数学模型的计算结果进行分析,得出了可以满足工程实际要求的等效热降理论诊断方法。     

循环流化床锅炉外置式换热器设计方法的探讨

简要介绍了循环流化术锅炉置式换热器的工作原理,特点及其应用情况,并在冷,热态试验基础上,给出了外置式换热器的设计原则和方法,利用该原则和方法对１台４２０ｔ／ｈ循环流化床锅炉的外置式换器进行了设计。     

The RODbaffle Heat Exchanger

The RODbaffle exchanger offers a solution to the vexing problem of tube failures in shell-and-tube exchangers resulting from tube vibration. Additional benefits are good heat transfer rates, low pressure drop, and lower fouling rates. The ratio of heat transfer rate to pressure drop can be more than double that of the conventional plate-type baffle in a comparable application.     

基于效率分析的换热器计算新方法

文中根据换热器效率的概念,即冷流体获得的能量与热流体放出的能量之比,提出换热器效率-单元数设计方法,得出顺流和逆流状态两种基本流型下的效率坐标图,并利用该方法进行实际算例计算。     

换热器最佳温度差的研究

在设计和选择换热器时,冷、热流体之间的温度差是首先要确定的参数。本研究表明：在高温换热器中,提高流体间的换热温差,可以减少换热器的面积;而在低温换热器中,较低的流体换热温差有助于热交换品质的改善。通过技术经济对比分析可以得到最佳的换热温差。分析研究了换热器设计中,如其对数平均温差不变,则换热器的热交换性能也不变这个普遍认可的观点。发现：即使当时数平均温差相同时,热交换过程的ｙｉｎｇ的损失也和流体进、出换热器两端的温度差之比有关。在相向流动的换热器中,热流体进口处的最佳温差值应该比其在冷流体进口处的值要大,热流体的比热容应该比冷流体的比热容要小。对于一个给定的热交换过程,可以应用本文所得的热论确定换热器两端的流体温差的最佳关系式或冷、热流体比热的最佳比率。     

平均温压变化对吸热偏差的影响及在锅炉改造中的应用

改造前后平均温压变化剧烈则会对系统吸热量产生较大影响,到目前为止,该问题未受到充分关注。本文研究了温压变化对吸热偏差的影响,引入了温压修正系数概念,考虑平均温压变化对吸热偏差的影响,对吸热偏差系数进行修正,并应用于江苏利港电力有限公司2号锅炉热偏差超温实炉改造,较好地解决了该炉热偏差超温难题,获得了良好的社会和经济效益。图8参4     

换热器效能评价的新方法

在用热力学第一、第二定律及物质能值分析换热器制造使用中的能量流向后,就确立衡量换热效果的新尺度,如何用最小的材料、能量投入获得最大的转换效果,做出研究。     

Hybrid Spline Difference Method for Steady-State Heat Conduction

This work proposes a simple and high-precision hybrid spline difference method, and finds that the computing method of spline difference is as simple as that of the finite-difference method. It also discusses steady-state heat conduction problems to overcome the complex computation and time-consuming problems of the previous spline method. In addition, due to the concept of hybrid parameters, the truncation error of numerical solutions is enhanced to o(h⁴). This method is expected to be a simple and high-precision numerical method that can replace the finite-difference method.     

间接蒸发冷却板式换热器的(火用)效率分析

在考虑壁面两侧空气温度实际变化的前提下,对间接蒸发冷却传热过程中影响yong效率的主要因素,如一次空气进口温度、一、二次空气流速之比,二次空气相对湿度,一、二次通道宽度之比以及壁面润湿率进行了分析研究,为实际换热器设计提供理论依据。     

On-Line Fuzzy-Logic-Based Temperature Control of a Concentric-Tube Heat Exchanger Facility

We have developed a fuzzy-rule-based controller to perform on-line temperature control of a concentric-tube heat exchanger facility. The rules for the controller were derived from dynamical values of the mass flow rates and fluid temperatures in the heat exchanger. The fuzzy controller was embedded in a closed-loop, single-input single-output system to control the outlet temperature of the cold fluid. The development of the controller was done in two phases, the difference between the phases being the information about the system that was used to build the corresponding control scheme. To validate this fuzzy controller, a series of experiments, corresponding to regulation and tracking of a setpoint, was carried out for maintaining specific values of the outlet temperature under different perturbations. Results from this investigation demonstrate that the fuzzy-rule-based controller is able to effect control of the system, and that the amount of information about the plant provided to it is important in terms of accuracy and efficiency.     

New Characterization of Fluid Temperature Profiles in a Heat Exchanger

Although the determination of heat exchanger performance based on the log-mean-temperature-difference approach or the temperature effectiveness approach had been well established, the understanding of the fluid temperature variation along the heat exchanger was still essential in some situations in which the fluid properties were expected to vary substantially across the heat exchanger. In this study, two normalized temperature surpluses were employed to predict the temperature profiles of the hot and cold fluid streams. With specified capacitance rates for the hot and cold fluid streams and the overall heat transfer value of the heat exchanger, unified profiles for the normalized temperature surplus along the heat exchanger could be formulated irrespective of the actual fluid entering temperature. The differences between the mean normalized temperature surplus and that based on the arithmetic mean between the fluid inlet and outlet increased when the capacitance rates of the two fluid streams departed more. By comparing the simulated performances of a sample waste heat recuperator based on both mean-temperature approaches to evaluate the respective average fluid properties with those using a detailed numerical approach over a range of entering fluid temperatures, it was found that the mean normalized temperature surplus was better.