蓄热体余热回收换热器强化传热实验研究

利用蓄热式热热交换理论和高温空气燃烧技术的原理,在热态实验基础上建立了蜂窝陶瓷蓄热体的性能研究实验.结果表明,热效率及温度效率随换向时间的增加均呈现先上升后下降的趋势,存在一个最佳换向时间,即热效率和温度效率随着长度的增加而增大,但阻力损失也随之增大;同时存在一个最佳气体流速使蓄热体效率与经济效益达到最佳值;蓄热体的平均温度与气体出口温度均随着换向周期数的增加而升高;对于给定几何外形尺寸的蓄热体,四边形孔格结构的蓄热体具有较大的比表面积,流动性更好,具有更高的温度效率和热效率.     

蜂窝体蓄热室结构优化及软件开发

以蜂窝体蓄热室的结构优化为研究目标,模型采用的多目标优化以蜂窝蓄热体的温度效率和热回收率作为目标函数.,以空气流速,换向时间和蜂窝蓄热体的高度为优化变量,模型的计算采用线性加权法,对蜂窝体蓄热室的主要结构参数进行了优化设计,以保证气体在满足换热强度条件下,尽量减小阻力损失。并开发了蜂窝体蓄热室结构优化的软件。     

高效蓄热室阻力及传热特性

根据蓄热室结构特性，建立了高效蓄热室阻力特性和传热特性的数学模型．通过实验分析了单位球层上的无因次阻力（单位阻力系数）与流体速度、温度的依变关系；分析了蓄热体、换向时间等对烟气的排放温度和空气的预热温度的影响，得出了高效蓄热室温度效率和热效率．采用刚玉质小球的适宜换向时间为60s，高效蓄热室的温度效率为83．6％，热效率为72．8％．     

陶瓷蓄热体的流动与传热特性模拟研究

为了选用合适的蓄热陶瓷体填充乏风氧化装置氧化床,首先对方形、圆管形和六边形蓄热陶瓷体的几何结构进行理论分析,得出特征长度对蓄热陶瓷体孔隙率和比表面积的影响规律。然后利用FLUENT软件对方形、圆管形和六边形蓄热陶瓷体进行模拟,得出在相同孔密度和开孔率条件下,选用方形孔可以获得较好的蓄热能力,选用圆管形、六边形孔可以降低其压强损失。在同孔隙率、比表面积和当量直径条件下,方形陶瓷体的阻力损失较低,六边形陶瓷体的传热效率较高。     

散堆拉西环蓄热室热工特性的数值模拟

提出将拉西环作为蓄热元件用于蓄热室的技术构想,并建立数学模型对散堆拉西环蓄热室的热工特性进行模拟.结果表明:不同时刻蓄热体及气体的温度分布大致呈对数曲线;随换向时间及气体流速的减小、蓄热室长度的增加,温度效率、热效率逐渐升高;空气的出口平均温度取决于空气出口最低温度,烟气的出口平均温度取决于烟气出口最高温度,要达到较高...     

蜂窝型陶瓷蓄热体换热器的热动态特性实验研究

对高温空气燃烧技术中的关键设备——蜂窝型陶瓷蓄热体换热器的热动态特性进行了实验测试。结果表明:蜂窝型陶瓷蓄热体换热器的压力损失随着空气流速以及蓄热体长度的不同而变化,但总体上说,其压力损失并不大;四通换向阀的换向周期和蜂窝陶瓷蓄热体换热器的体积等是影响其温度效率和热回收率等热性能的重要因素。     

蜂窝蓄热式空气单预热烧嘴换热特性的热态试验研究

采用热态模拟方法对蜂窝蓄热式空气单预热烧嘴的换热特性进行了试验研究，通过对试验数据的分析，得出了蓄热式烧嘴换热性能与空气流量、换向时间的关系及蓄热室内温度的分布特点等，确定了最佳换向时间、单位蓄热体体积的合适流量和蓄热室的适宜长度等。     

新型蓄热体结构蓄热过程分析北大核心CSCD

为提高工程实际应用中固体蓄热器蓄热体的蓄热能力,以碱性耐火材料MgO砖作为蓄热介质,设计一种新型蓄热体结构,基于物理参数非定值的热分析方法,对新型蓄热体结构的蓄热性能及温度分布情况进行分析。结果表明:目标蓄热时间下,传统蓄热体温度分布梯度较大,温度分布以蓄热体中心点为核心呈面性递减,整体温差值为227.0 K,新型蓄热体温度分布以横向轴线呈线性递减,整体温差值为107.8 K,较传统蓄热体整体温差值减小119.2 K,监测点温度偏差率降低5.7%;目标蓄热时间下,传统蓄热体网格节点温度在设计蓄热温度873 K温度段占比仅为8.7%,而在高温段占比达到70.1%,整体温度分布不均,新型蓄热体网格节点温度在设计蓄热温度873 K温度段占比达60.4%,未形成明显高温段,整体温度分布更优;目标蓄热温度下,新型蓄热体结构的实际蓄热容量达到理论蓄热容量的96%,较传统蓄热体提升16%,同时相同蓄热容量下体积仅有传统蓄热体的83%,能有效提高蓄热体蓄热能力,相应降低蓄热成本,有利于市场推广。     

蜂窝蓄热体内单向流及往复流阻力特性试验研究

试验研究蜂窝蓄热体内单向流及往复流阻力特性.单向流动中研究蓄热体长度、结构参数对阻力特性影响,并分析得到热态条件下蓄热体阻力计算公式;往复流动中研究换向半周期、总阻力对阻力波动特性的影响.实验结果表明,蓄热体阻力并非与其长度成绝对正比关系;热态时蓄热体阻力与流体温度和速度有关;往复流动时蓄热体阻力波动幅值、最小稳定时间受总阻力及空截面流速影响.     

换向时间对蓄热式均热炉能耗的影响和分析

通过数值模拟和实验方法,重点研究了换向时间对蓄热式均热炉能耗的影响。结果表明:蓄热式均热炉存在最佳换向时间,蓄热式均热炉在最佳换向时间下工作时可以显著降低能耗;换向时间影响换向盲区的煤气损失量;如根据均热炉实时烟气流量和排烟温度动态调节换向时间,可进一步降低均热炉的能耗。     

Thermal performance analysis on a two composite material honeycomb heat regenerators used for HiTAC burners

Honeycomb heat regenerators do not only reduce the fuel consumption in a high temperature air combustion (HiTAC) burning system but also provide the necessary high temperature of combustion air. A two-dimensional simulation model was developed to numerically determine the dynamic temperature and velocity profiles of gases and solid heat-storing materials in a composite material honeycomb regenerator. Consequently, the energy storage and the pressure drop are calculated and the thermal performance of honeycomb heat regenerator is evaluated at different switching times and loading. The model takes into account the thermal conductivity parallel and perpendicular to flow direction of solid and flowing gases. It considers the variation of all thermal properties of solid material and gases with temperature. Moreover, the radiation from combustion flue gases to the storage materials was considered in the analysis. The results are presented in a non-dimensional form in order to be a design tool as well. These analyses were applied on a regenerator made of two layers of ceramic materials, one is pure alumina and other is cordierite. This regenerator is contained in a 100 kW twin-type regenerative-burning system used for HiTAC. The effectiveness and the energy recovery rate were 88% and 72% respectively at nominal operating range of the regenerator and the pressure drop across the twin regenerator system was 1.16 kPa. The periodic steady state condition is reached after about 11 min and it takes only 2 min of operation until the temperature of combustion air remains above the self-ignition temperature that is required for HiTAC. Furthermore, these mathematical analyses show good agreement with experiments made on the same regenerator. In the experiments, the dynamic behavior of the heat regenerator operation was considered in order to compensate measurement readings for this effect.     

Study the Heat Recovery Performance of Micro and Nano Metfoam Regenerators in Alpha Type Stirling Engine Conditions

This paper experimentally investigates the performance of micro and nano metfoam regenerators in alpha-type Stirling engine conditions. The thermal efficiency of this engine depends on performance of regenerator. Therefore, increase the heat recovery of regenerator raises the total efficiency. Accordingly, two types of regenerators from porous media are designed and simulated with different materials. Three-dimensional regenerator CFD simulation shows that randomize porous open cell metfoam made of silver as high conductivity and high heat capacity material is the best structure to fabricate metfoam regenerator. The porosity and matrix element diameter are optimized. The nano coating methodology enhances the activated surface. The regenerators are fabricated using casting polymer mold layer deposition. The nano silver particles are coated on the metfoam by sol-gel coating method. Experimental results show the improvement in regenerator percentage of heat recovery by 3.40% and 5.93% for micro metfoam and nano metfoam, respectively. The maximum improvement is achieved up to 8.65% in case of using the nano metfoam regenerator at 543 K.     

Model validation and case study on internally cooled/heated dehumidifier/regenerator of liquid desiccant systems

Traditional dehumidifiers and regenerators of liquid desiccant systems often use packed columns supporting adiabatic heat and mass transfer between air and liquid desiccant. As new-style equipment, internally-cooled dehumidifiers can improve dehumidification performance due to restraining temperature increase of the desiccant. Similar to internally-cooled dehumidifiers, an idea of internally heating is imitated to put forward internally-heated regenerators. The uniform mathematical model for an internally cooled dehumidifier and internally heated regenerator was presented and validated by comparison of computation results with experimental data in this study. The case study focused on the parameters distribution comparisons of the internally cooled/heated dehumidifier/regenerator with adiabatic ones and demonstrated coupled heat and mass transfer behavior. The results show that the internally-heated regenerator can produce higher regeneration efficiency than the adiabatic one to produce better energy efficiency and eliminate the dehumidification possibility which would happen in adiabatic regenerators. The internally-cooled dehumidifier can also provide better dehumidification performance comparing with the adiabatic one; however its benefit would be not as good as the internally-heated regenerator. In addition, effect of the width of the air channel on internally cooled/heated dehumidifier/regenerator was discussed and the results can help the optimal design of this kind of dehumidifiers and regenerators.     

Comparison of performance of heat regenerators: Relation between heat transfer efficiency and pressure drop

Heat regenerators transfer heat from one gas to another, with an intermediate storage in solids. The heat transfer surface for gas flow application should provide at the same time high surface area and low friction factor. Three geometries of heat transfer surface, monolith, stack of woven screens and bed of spheres, have been compared. Their performance was evaluated from the pressure drop of the heat regenerator working at a given heat transfer efficiency. The comparison was performed using numerical simulation and published measurements of heat transfer and flow friction characteristics. By adjusting the length and the period of the exchanger, it is possible to obtain the same heat transfer efficiency with the three geometries. Beds of spheres give very short and compact heat regenerators, working at high pressure drop. At the opposite, monoliths form long regenerators working at low pressure drop. Stacks of woven screens cover a wide range of performance: low porosity woven screens give high heat transfer efficiency and high pressure drop, while high porosity woven screens offer performance similar to that of the monoliths. Copyright © 2001 John Wiley & Sons, Ltd.     

Analysis of single blow effectiveness in non-uniform parallel plate regenerators

Non-uniform distributions of plate spacings in parallel plate regenerators have been found to induce loss of performance. In this paper, it has been investigated how variations of three geometric parameters (the aspect ratio, the porosity, and the standard deviation of the plate spacing) affects this loss in a single blow model of a parallel-plate regenerator. Simple analytical functions for the magnitude and the time scale of the reduction of performance are presented and compared to numerical results.     

梭式窑烟气废热利用的模拟研究

采用商用CFD软件,通过数值模拟和正交实验分析了蜂窝陶瓷的结构参数及各工况条件对换热性能和压力损失的影响,优化了工况参数。数值模拟结果为：进入稳定工作期后,加热期温度效率为94．6％,冷却期温度效率为93．7％,压力损失为457．7Pa。在此基础上,设计了梭式窑高温空气燃烧（HTAC）系统,构建实体模型进行实验,研究余热回收系统的温度效率及烟气在蜂窝陶瓷内压力损失。研究结果表明,加热期与冷却期的温度效率分别为：92．0％,93．2％,测量热烟气和预热空气的压力损失分别为126．3,107．8Pa。     

回热器孔隙率对VM循环热泵性能的影响分析

孔隙率是表征回热器结构和效率的重要参数,影响整个系统的流动和传热特性。以热驱动斯特林循环的VM(Vuilleumier,维勒米尔)循环热泵为研究对象,建立了其内部回热器的模型,研究了在不同的热源温度、系统压力、转速、容积比和工质的情况下,孔隙率对整个热泵系统性能的影响。结果表明：随着孔隙率的增加,系统性能系数先增加后减小,在0.6左右达到最佳。在相同孔隙率的情况下,系统性能系数随着热源温度、系统平均压力、容积比、转速的增加而分别增大,并且增加的幅度是越来越小的。对于工质而言,氦气和氢气的性能较优,而氮气的性能较差。综合考虑安全等因素,宜选氦气作为工质。     

Explicit Design of Balanced Regenerators

An explicit procedure for the design and sizing of balanced regenerators has been developed. A set of performance curves relating the thermal ratio, harmonic mean reduced length and period, and minimum cold fluid outlet temperature is presented. The specific characteristics of the regenerator's matrix including the heat transfer and pressure drop correlations are used to develop interrelations, represented by a set of three design curves, between these quantitites and the operating characteristics of the regenerator. The performance and design curves are used in the design procedure to determine the dimensions of the regenerator for the specified operating conditions.     

A thermoacoustic engine capable of utilizing multi-temperature heat sources

Low-grade energy is widespread. However, it cannot be utilized with high thermal efficiency directly. Following the principle of thermal energy cascade utilization, a thermoacoustic engine (TE) with a new regenerator that can be driven by multiple heat sources at different temperature levels is proposed. Taking a regenerator that utilizes heat sources at two temperatures as an example, theoretical research has been conducted on a traveling-wave TE with the new regenerator to predict its performance. Experimental verification is also done to demonstrate the benefits of the new regenerator. Results indicate that a TE with the new regenerator utilizing additional heat at a lower temperature experiences an increase in pressure ratio, acoustic power, efficiency, and exergy efficiency with proper heat input at an appropriate temperature at the mid-heater. A regenerator that uses multi-temperature heat sources can provide a means of recovering lower grade heat.     

新型档位蓄热器的开发与研究

研究开发了一种可应用在高温空气燃烧（HTAC）技术中的新型蓄热器--档位蓄热器.档位蓄热器吸收了回转式蓄热器的思想,结合了切换式蓄热器的特点,将二者的优势融合在一起,其外观类似于回转式蓄热器,但运动型式却由回转式蓄热器的连续运动变为间歇转动,且具有了新型的密封结构.对档位蓄热器的基本工作原理、具体设计方案、实验研究及应用前景进行了详细介绍.研究结果表明档位蓄热器具有以下特点：可实现对炉窑的连续供气,保证了炉内火焰的稳定性,从而使炉内工况不易波动;另外系统的漏风率较低,阻力损失也较低,并且设备紧凑、操作安全可靠,易于实现标准化生产.实验研究的结果证明该蓄热器的温度效率可达88%,热效率可达77%.