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中压废热锅炉换热装置受换热面积裕度、换热面积等因素的影响,导致其换热能耗较高,为此以管壳式相变储能换热器为研究对象,提出了其节能控制技术,并探究该技术的应用效果。以管壳式相变储能换热器的蓄放热特性为基础,将管壳式相变储能换热器的储能材料和管材作为约束条件,构建节能控制优化目标函数。利用粒子群算法求解构建的目标函数,实现管壳式相变储能变换器的节能控制。实验结果表明,所提技术应用后可有效降低管壳式相变储能换热器的换热面积裕度、实际换热面积,具有较强的节能控制性能,同时减少了换热器费用,提高了其成本效益。 相似文献
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催化器性能评价试验中,起燃特性和温度特性是两个重要性能,这两个特性的研究都需要对催化器入口温度进行稳定连续的调节。本文设计了冷轧翅片管、整体轧制式、U型管壳式换热器和单程管壳式换热器,通过比较,选定冷轧翅片管换热器进行温度特性和起燃特性试验,试验结果表明该换热器能够达到设计要求,对温度的控制也比较稳定。 相似文献
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针对国内某北方核电厂的设备冷却水系统热回流式换热器,分析了不同热负荷下热回流式换热系统的稳态特性及负荷阶跃变化下热回流式换热系统缺陷机理,提出了热回流式换热器系统优化方法。研究表明:在不同热负荷下热回流式换热器系统切换的关键是与不同热负荷对应的具有特定温度的伴流的形成;热负荷阶跃变化下状态转换瞬态过程中存在系统缺陷,其根本原因在于单纯采取调节热回流率的方法,具有较大的时间滞后性;调节换热器冷介质侧的流体流量,改变换热器传热系数,强化了对状态改变的快速响应;采取热回流叠加换热器旁流方法,可以解决原有系统状态转换瞬态过程中存在的缺陷。 相似文献
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基于计算流体力学方法对板壳式换热器内部流场进行模拟,建立了板壳式换热器流动及换热计算的模型,模拟了换热器内部流动和换热情况,分析了流道内温度场和压力场及流线的分布情况,对流体的流动和传热进行了详细的描述,分析了换热器内流体流动和传热特性,对实际工程具有一定的指导意义。 相似文献
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建立了可进行壳管式换热器动态特性试验研究系统,通过试验研究的方法对水-油为换热工质的连续螺旋折流板管壳式换热器动态特性进行了试验研究,进口流量扰动为等百分比流量特性,研究了4种流量扰动方式下水和油出口温度的动态响应。同时研究了在一定Re数下,不同的流体扰动量对换热器进出口温升的影响,得到了换热器进出口温升与流体扰动量之间的关联式。实验表明,液液换热系统温度的动态响应时间比较长,研究发现在正负的流量扰动下,换热器进出口温度变化呈现线性变化,进出口温升在正负流量扰动下其变化曲线具有对称特征。分别建立了有限差分数值预测模型及人工神经网络模型对换热器油侧的出口温度进行了动态预测,预测结果与试验值符合良好,人工神经网络的预测结果要好于数值模拟预测,其偏差绝对值在1.3%以内,表明人工神经网络在进行复杂的系统辨识时具有一定的参考及应用价值。 相似文献
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为探究相变温度对相变材料回填地埋管换热器传热性能的影响,建立管内流体换热、回填区域相变换热及土壤换热的三维耦合传热数值模型,利用焓-多孔介质模型对相变区域相变问题进行处理,研究夏季间歇运行工况下不同相变温度回填材料对埋管换热器传热性能的影响。结果表明:添加PCM,可有效提高换热量,短期内缓解埋管周围热积聚,利用相变温度18℃的PCM回填,单位井深换热量至少比普通材料回填提高49.54%;在间歇运行初期,换热量随相变温度的升高逐渐减小,低相变温度的PCM可明显改善埋管换热量,但随着时间的进行,较高相变温度PCM回填对换热器换热量的改善效果优于前期低相变温度。此外,在运行期间,不同相变温度的PCM表现出不同的熔化、凝固特性,当PCM的熔化、凝固过程交替进行时,可减缓土壤温度在运行期间内波动幅度。 相似文献
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针对日益严重的环境问题,“煤改电”已经成为实现北方清洁供暖的有效手段。此外,我国每年在余热利用,尤其是在中低温品质热能利用上还相当不充分。在此大背景下,以相变储热供热技术为切入点,着重对目前相变储热换热器进行了比较,定性分析了板式、管壳式、热管式及其他异形(储热砖/球)换热器的优缺点。并通过数值模拟的方式,定量比较了相同换热面积及边界条件下,管壳式和板式相变换热的二维相变材料熔化模型,管壳式换热器需6 h完全熔化,板式换热器需8.5 h完全熔化,主要原因在于二者在换热管/板在排布上差异导致。但考虑到相较于管壳式换热器,板式换热器结构紧凑、加工工艺简单、拆卸方便,未来可形成通过制成储热砖的方式实现模块化运行,为后期维护提供了很大便利,因此具有巨大发展潜力。 相似文献
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This paper presents a theoretical analysis and an experimental test on a shell‐and‐tube latent heat storage exchanger. The heat exchanger is used to recover high‐temperature waste heat from industrial furnaces and off‐peak electricity. It can also be integrated into a renewable energy system as an energy storage component. A mathematical model describing the unsteady freezing problem coupled with forced convection is solved numerically to predict the performance of the heat exchanger. It provides the basis for an optimum design of the heat exchanger. The experimental study on the heat exchanger is carried out under various operating conditions. Effects of various parameters, such as the inlet temperature, the mass flow rate, the thickness of the phase‐change material and the length of the pipes, on the heat transfer performance of the unit are discussed combined with theoretical prediction. The criterion for analyzing and evaluating the performance of heat exchanger is also proposed. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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This article presents design analysis of a fuel oil preheater. The preheater is a concentric tube heat exchanger where the fuel oil is on the tube-side and the heating medium flows in the annular space. Two situations were addressed in this study. In the first case, an analytical model was developed where the required heat exchanger length, diameter and the fluid velocity were determined for a given heat transfer duty and for an allowable pressure loss. A detailed study was conducted by individually varying parameters such as pressure loss, preheater discharge temperature, and mass flow rate of the fuel oil. In each instance their influence on the predicted design of the heat exchanger was investigated. In the second case, an optimization strategy was proposed for a certain heat transfer duty. The heat exchanger dimensions and the fluid flow rate were selected such that the annual operating cost of the heat exchanger was minimized. In addition, a detailed study was conducted to understand the total annual operating cost as a function of the fuel oil outlet temperature and the fuel oil mass flow rate. 相似文献
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Z. S. Abdel-Rehim 《Energy Sources, Part A: Recovery, Utilization, and Environmental Effects》2013,35(12):1081-1096
Abstract Thermal analysis of heat transfer through different storing media using oil as working fluid is presented. The storing medium is solid material in spherical shape. Steel, glass, and pebbles are selected as storing media and oil is selected as working fluid. The physical model is a heat exchanger in cylindrical shape, which is packed with each of the selected storing medium. The heat transfer through the heat exchanger is assumed to be one dimensional along its height. The flow of the working fluid is an axial direction from the top to downward. The problem is governed by two partial differential equations for the working fluid (oil) and the storing medium. Finite difference method and Thomas algorithm solver are used to solve the couple of the two partial differential equations along with their associated initial and boundary conditions. The modified computer program is used to obtain the solution of transient temperature distribution of the storing medium and the working fluid. The amount of absorbed heat inside each of the storing medium is obtained. The effect of special operating parameters on the amount of absorbed heat inside the storing medium, such as aspect ratio (the ratio between diameter and length of the heat exchanger), storing media, mass velocity, the number of charging cycles, and void fraction, is discussed. Therefore, the dimensionless heat transfer coefficient parameter (Nusselt number, Nu) provides a measure of the convection and conduction heat transfer at the surface of storing medium when the working fluid (oil) flows over a solid surface of the medium. The numerical results of transient temperature profiles and the amount of absorbed heat inside the storing medium for each system with respect to the operating parameters and the heat exchanger characteristics are illustrated. The results show that steel storing medium is charging by four cycles while the pebble storing medium is charging by two cycles only, this due to the thermal and physical properties of these materials. The absorbed heat inside storing medium, which has aspect ratio equals one (diameter of the heat exchanger equals its length) is higher than others. Increasing mass velocity increases absorbed heat inside the storing medium and decreasing the charging time. Increasing void fraction decreases absorbed heat inside the storing media due to the smaller volume of absorbing medium. The amount of absorbed heat (at certain time) inside the steel > glass > pebble is due to the thermal conductivity of these materials. 相似文献
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Optimization for a heat exchanger couple based on the minimum thermal resistance principle 总被引:1,自引:0,他引:1
Lin Chen Qun Chen Zhen Li Zeng-Yuan Guo 《International Journal of Heat and Mass Transfer》2009,52(21-22):4778-4784
Following the brief introduction to the concept of a physical quantity, entransy, the equivalent thermal resistance of a heat exchanger couple is defined based on the entransy dissipation. The minimum thermal resistance principle is applied to obtain the optimal heat capacity rate of the medium fluid and the optimal allocation of heat exchangers thermal conductance, which correspond to the maximum heat transfer rate in the heat exchanger couple. In addition, analytical expression for the optimal heat capacity rate of the medium fluid is derived, whose reciprocal equals the sum of the reciprocal of the individual heat capacity rate of the hot and cold fluids, just like the case of two electrical capacitors in series. Numerical results in the variation of the thermal resistance and the heat transfer rate with the medium fluid heat capacity rate or the thermal conductance allocation agree with the theoretical analyses. Finally, for comparison, the entropy generation rate is also calculated to obtain its relation with the thermal performance of the heat exchanger couple. The results show that there is no one-to-one correspondence of the minimum entropy generation rate and the maximum heat transfer rate. This indicates that the minimum entropy generation principle cannot be used for optimizing the heat exchanger couple. 相似文献
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The present study aims to develop an approach to define the optimal dimensions of a phase change material (PCM) packed bed heat exchanger used as a cold thermal energy storage system in a conventional refrigerator. The heat exchanger is used to extend the daily refrigerator downtime and to ensure effective temperature control to contribute to the improved performance of the refrigerator. The mathematical model has been developed according to the technical characteristics and operating conditions of the refrigerator, the technical characteristics of the ventilator, and the thermo‐physical properties of the PCM. The model parameters that have been analyzed are the PCM melting time, air velocity range for tolerable efficient operating conditions, and the pressure drop through the PCM heat exchanger. As a case study, the approach was applied to a 600‐L conventional refrigerator equipped with a 63‐W ventilator. It has been found that over the tolerated velocity range of [2.5‐3.7 m/s], the optimal dimensions of the PCM heat exchanger are defined for an optimal velocity of 3.495 m/s. This is equivalent to an optimum sphere diameter of 0.071 m, a PCM heat exchanger length of 0.213 m, and a width of 0.148 m. The PCM heat exchanger ensures an extended compressor downtime of 12.6 hours for an ice‐PCM mass of 7.15 kg and occupies only 1.2% of the useful volume of the refrigerator. 相似文献
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列管式换热器具有结构牢固、传热面积大、材料使用适应性强等优点,是相变储热领域应用较为广泛的一种换热器。但由于大部分相变材料热导率偏低,导致换热器的换热性能较差,因此提高相变储热器的储热效率,是目前国内外研究的热点。本工作对列管式相变储热单元进行了二维非稳态模拟优化,研究了换热器结构、翅片数目及中心距3种参数对储热性能的影响,并探讨了熔化过程中相变材料的温度和液相率变化趋势。研究结果表明,与圆形换热器结构相比,正方形换热器储热性能更优;相比于无翅片的储热换热器,添加翅片后储热性能得到显著提升,相变材料熔化时间缩短66%;对中心距而言,在一定范围内,随中心距减小进出口降压增大,但储热性能相应提高。 相似文献
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This article investigates the effectiveness of embedded vortex generators in enhancing the heat transfer performance of a plate-fin heat exchanger with a four-row staggered oval tube bundle. Two different types of vortex generator are considered, namely annular and inclined block. Numerical simulations are performed to analyze the effects of the three-dimensional turbulence induced by the vortex generators on the heat transfer and fluid flow characteristics of the heat exchanger. The results indicate that compared to a plate-fin heat exchanger with circular tubes, the use of oval tube fins and vortex generators increases the heat transfer rate by 3 to 16% and reduces the pressure drop by 17 to 35% for inlet velocities in the range of 1 to 8 m/s. Furthermore, the vortex generators make possible an average area reduction ratio of 14 to 18%. Overall, the results show that the inclined block shape vortex generators yield the greatest improvement in the heat transfer performance at medium to high inlet velocities. 相似文献