共查询到18条相似文献,搜索用时 171 毫秒
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高温空气燃烧系统中陶瓷蓄热体传热特性分析研究 总被引:15,自引:0,他引:15
针对小球、圆孔、方格孔、三角孔和正六边形孔蜂窝体等不同几何结构下的陶瓷蓄热体对高温空气燃烧系统的非稳态交替加热和冷却的传热过程的影响进行了理论分析,得出了正方形蜂窝体具有最佳的比表面积和开孔率的结论。建立了陶瓷蓄热体和气体的温度变化微分方程和数值计算的离散方程,并选取实例进行了数值计算,得出了温度变化和传热变化的特性曲线,其与实验测试结果变化规律基本一致。研究结果可以为高温空气燃烧过程中合理有效地控制蓄热体中交替换热过程提供理论依据。 相似文献
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蜂窝蓄热体对于改善空气燃烧过程,降低NOx起着至关重要的作用。通过Pointwise和FLUENT软件建立了蜂窝蓄热体三维数值模型,从不同的换向时间、孔型、边长、材料的角度对比了蜂窝蓄热体的换热特性,并对实际工作中节能效率进行了理论计算。结果显示:当换向时间从15增长到45 s时,正方形蓄热体的温度效率从78.5%降低到63.1%;当边长、壁厚相同时,圆形蓄热体的温度效率最高,压降也最大,六边形蓄热体的温度效率最低,但压降最小。总结发现,孔隙率的减小可以有效地提高温度效率,但是同时会增大流动的压力损失,在实际应用中可据此选择合适的孔隙率。同时得到,在实际运行中,当a=2.00 mm时,圆形蓄热体的节能效率最高(26.9%),六边形节能效率最低(24.4%)。 相似文献
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为了解多孔介质蓄热材料热动态条件下的蓄热特性,得到表征蓄热材料的动态蓄热特性参数,在120 kW多孔介质热动态蓄热系统中,对不同孔径(2.9、4、5.5 mm)、长度(100~400 mm)的蜂窝多孔陶瓷蓄热体在不同热烟气条件下的动态蓄热特性包括蓄热速率、蓄热效率、蓄存单位热量所要克服的蓄热阻力进行了试验研究。结果表明:蓄热速率与时间的关系呈"抛物线"状,蓄热效率随蓄热时间的进行逐渐降低。相同时间下蓄热速率及单位蓄热阻损随蓄热体比表面积的增大或孔径的减小而增大,蓄热效率随蓄热体长度的增加而增大。根据试验研究和分析,采用蓄热速率、蓄热效率及单位蓄热阻损可以用来表征多孔蓄热体的动态蓄热特性。 相似文献
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蜂窝蓄热体易损原因分析及其解决措施 总被引:5,自引:1,他引:4
针对加热炉采用的蜂窝蓄热体出现的问题,从材质性能、炉内实际情况、结构等方面分析出其破损原因。并设计一种新型的蓄热式烧嘴,通过热态试验对其换热性能与普通蓄热烧嘴进行了比较,表明采用这种新型烧嘴是解决蓄热体破损的有效措施之一。 相似文献
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介绍了高温空气燃烧过程中蜂窝陶瓷蓄热体的工作原理和损毁原因,采用代数雷诺应力模型和修正的速度-压力耦合算法SIMPLEC,耦合蓄热体内流体的流动和换热过程,运用有限元分析方法,对蜂窝陶瓷蓄热体格孔壁面上的应力变化规律进行数值研究,并根据计算结果对操作参数进行了改进。结果表明,频繁的蓄热和释热过程变换,使得蓄热体格孔壁面交替地受到拉应力和挤压应力的作用。流体的流速越大,应力变化越大;换向时间越短,应力交替作用的影响越大。适当地调低烧嘴负荷,延长四通阀的换向时间,有利于提高蓄热体的使用寿命,计算结果为蓄热体结构设计和操作参数的优化提供了依据。 相似文献
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《International Journal of Heat and Mass Transfer》2006,49(3-4):671-681
In this paper, an experimental investigation was performed to study the heat transfer performance of metal foam heat sinks of different pore densities subjected to oscillating flow under various oscillatory frequencies. The variations of pressure drop and flow velocity along the kinetic Reynolds number of oscillating flow through aluminum foams were compared. The measured pressure drops, velocities and surface temperatures of oscillating flow through aluminum 10, 20 and 40 PPI foams were presented in detail. The calculated cycle-averaged local temperature and Nusselt number for different kinetic Reynolds numbers were analyzed and compared with finned heat sinks. The results of length-averaged Nusselt number for both oscillating and steady flows indicate that higher heat transfer rates can be obtained in metal foams subjected to oscillating flow. For the purpose of designing a novel heat sink using metal foam, the characteristics of the pumping power of the cooling system for aluminum foam with different pore densities were also analyzed. 相似文献
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Deterioration in heat transfer of endothermal hydrocarbon fuel 总被引:5,自引:0,他引:5
Numerical studies under supercritical pressure are carried out to study the heat transfer characteristics in a single-root coolant channel of the active regenerative cooling system of the scramjet engine, using actual physical properties of pentane. The relationships between wall temperature and inlet temperature, mass flow rate, wall heat flux, inlet pressure, as well as center stream temperature are obtained. The results suggest that the heat transfer deterioration occurs when the fuel temperature approaches the pseudo-critical temperature, and the wall temperature increases rapidly and heat transfer coefficient decreases sharply. The decrease of wall heat flux, as well as the increase of mass flow rate and inlet pressure makes the starting point of the heat transfer deterioration and the peak point of the wall temperature move backward. The wall temperature increment induced by heat transfer deterioration decreases, which could reduce the severity of the heat transfer deterioration. The relational expression of the heat transfer deterioration critical heat flux derives from the relationship of the mass flow rate and the inlet pressure. 相似文献
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In this paper, heat transfer of the ceramic honeycomb regenerator was numerically simulated based on the computational fluid dynamics numerical analysis software CFX5. The longitudinal temperature distribution of regenerator and gas were obtained. The variation of temperature with time was discussed. In addition, the effects of some parameters such as switching time, gas temperature at the inlet of regenerator, height of regenerator and specific heat of the regenerative materials on heat saturating time were discussed. It provided primarily theoretic basis for further study of regenerative heat transfer mechanism. 相似文献
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建立微型燃气轮机CW(交叉波浪型,Cross Wavy)原表面回热器三维周期性充分发展数值计算模型,对芯体内传热和阻力特性进行了分析,确定了质量流量和温度水平对换热量及压降的影响,给出了CW原表面芯体板内阻力、传热因子以及努塞尔数与雷诺数之间的经验关联式。传热及阻力性能分析结果表明:随着雷诺数的增大,回热器芯体单元传热系数增大,传热量逐渐增加,并且随着低压高温烟气侧的进口温度升高,传热量增加幅度增大;回热器芯体单元回热度随雷诺数的增大而减小,随燃气进口温度升高而减小。 相似文献