共查询到19条相似文献,搜索用时 203 毫秒
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给水加热器作为热力发电系统中重要的辅助设备,其性能的提高可以有效提高机组运行效率。基于计算流体力学商用软件Fluent,参照厂家提供的某型号给水加热器的过热段的结构参数,进行建模与数值模拟。将模拟结果与厂家提供的热平衡图中的热力参数及推算结果进行比对,误差在10%以内,满足工程应用的需求。验证了数值模拟所使用的计算模型的正确性,为给水加热器的结构优化和强化换热提供了一定的基础。 相似文献
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为了及时发现并处理高压加热器运行经济性失常,采用传热系数直观地反映高压加热器的运行效率,提出基于时序数据分析方法得到传热系数的在线动态模型。首先通过热动力学机理分析得到影响高压加热器传热系数的主要特征参数并建立基于特征参数的动态模型;其次,通过蜻蜓算法改进的密度聚类方法构建具有最优邻域参数的优化聚类模型,得到可信端差区间。通过一段时间的某电厂的计算结果比较表明,基于改进密度聚类法的传热系数在线动态模型在计算高压加热器传热系数时均方误差MSE低至0.030 5%,说明该模型有效、可行。 相似文献
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该文建立了锅炉蒸发系统热力过程动、静态特性的一体化模型。利用该一体化计算模型既可进行锅炉蒸发系统的动态过程分析,又能够完成锅炉蒸发系统的静态校核计算,同时还可以确定出锅炉蒸发受热面中热力参数的动态、静态分布情况。 相似文献
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为了分析某660 MW超超临界二次再热燃煤机组快速响应动态特性,基于Modelica/Dymola平台建立了高精度二次再热机组动态仿真模型。为了验证模型的可靠性和精确性,将仿真结果与不同负荷下设计数据进行比较发现,模型在不同负荷下的静态误差均在±5%以内。针对目前灵活性运行对电网负荷快速响应要求,模拟机组在分别切除4个高压加热器后负荷的瞬态响应特性,并具体分析了切除1号高压加热器对汽轮机抽汽以及锅炉主要受热面烟气侧与蒸汽侧动态特性的影响,获得了切除高压加热器后汽轮机抽汽变化动态过程和发电功率快速响应情况,以及锅炉烟气侧与蒸汽侧的参数变化动态过程。模拟结果表明:切除4个高压加热器均可以有效增加机组瞬时电负荷,分别可以达到29.8,15.6,8和6 MW,快速发电功率增加持续时间达到1 100,100,130和250 s,说明切除高压加热器可以改善二次再热燃煤机组对电网自动发电控制(AGC)的快速响应特性。 相似文献
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Jun Ho Bae Jae Min Hyun Jae Won Kim 《Numerical Heat Transfer, Part A: Applications》2013,63(9):891-908
This study is made of an enhancement of a mixed-convection heat transfer in a channel containing multiple porous blocks heated from below. The heat flux from the most upstream heater varies in a sinusoidal form, while other heaters have a constant heat flux. The Brinkman-Forchheimer-extended Darcy model and two-equation energy model are adopted to characterize the flow and temperature fields inside porous regions. The explicit effect of thermal modulation at the upstream heater is examined by acquiring comprehensive numerical solutions. The heat transfer enhancement is pronounced at the far downstream heaters when resonance is realized. The resonance frequency is close to the characteristic frequency of the system, which scales with the time for the main stream to travel from a heater to a neighboring heater. The evolutions of flow and temperature fields are exemplified to provide physical interpretations. The effects of pore density and of porous block height are reported. The benefit of heat transfer augmentation, as opposed to the increased friction factor, is assessed to justify the use of thermal modulation in the upstream heater. 相似文献
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《Applied Thermal Engineering》2002,22(4):449-457
The performance of a proposed porous electric heater is investigated. The porous heater exchanges heat with the working fluid through its large volumetric surface area. As a result, it produces lower surface temperature as compared with the conventional heater for the same imposed heating power. Two mathematical models are presented to describe the thermal behavior of both heaters. Axial diffusion is included in the governing equation of the solid conventional heater. The predictions of both models are compared at different operating conditions where it is found that porous heaters have much better thermal performance than the conventional heaters. 相似文献
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A recently developed infrared (IR) local heating method is fairly effective to reduce springback of advanced high strength steel in manufacturing processes of car chassis. Although parabolic heaters, consisting of an IR lamp located on the focus of a parabolic reflector, can reduce springback in stamping processes, non-negligible temperature changes are generated in the heated area. For this reason, an improved heater has been required for the IR heating method. In this work, an overlapping heater array is designed to solve the problem of the parabolic heater for the IR local heating method. The overlapping heater array can reduce the temperature change in the heated area. In the overlapping heater array, the parabolic heaters are connected in series. The connected parabolic heaters are then placed on both sides of a thin sheet metal and intersected to reduce the temperature change. In order to design a more efficient overlapping heater array, a simple design parameter was employed. The numerical and experimental verifications have shown that the overlapping heater array drastically reduces the temperature change in the heated area. 相似文献
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Three-dimensional natural convection in a horizontal channel with an array of discrete flush-mounted heaters on one of its vertical walls is numerically studied. Effects of thermal conductivities of substrate and heaters and convection on outer sides of the channel walls on heat transfer are examined. The substrate affects heat transfer in a wider range of thermal conductivities than do the heaters. At lower heater thermal conductivities a higher heat portion is transferred by direct convection from the heaters to the adjacent coolant. However, higher substrate conductivity is associated with higher heat portion transferred through the substrate. The innermost heater column is found to become the hottest heater column due to the lower coolant accessibility. The heat transfer in the channel is strongly influenced by convection on the outer sides of the channel walls. Correlations are presented for dimensionless temperature maximum and average Nusselt number. 相似文献
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A three-dimensional (3-D) numerical model is developed to investigate the effects of inclination on the heat transport processes in a liquid-filled rectangular enclosure of finite size. The interactions of flows tangential and normal to the heater surfaces in an inclined enclosure cause a slight oscillation in Nusselt number. Inclination has little effects on the average heat transfer characteristics except configurations close to the conduction case with heaters on top leading to a sharp decrease in Nusselt number. The critical Rayleigh number of 1708 is also observed in the present study regardless of inclinations. Heat transfer from discrete heaters is non-uniform. Maximum Nusselt number occurs at the heater leading edge and decreases towards the trailing edge. Correlations for the row average Nusselt number vs. Rayleigh number at various inclination angles are presented. By taking the average of the discrete heater array, the numerical results compared well with the empirical correlations obtained from a single heater plate in literature. 相似文献
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Yemeli Wenceslas Koholé 《国际可持续能源杂志》2017,36(5):430-449
The paper presents a comparative study of three solar water heaters made of flat-plate collectors with different absorber configurations. The performance of the three solar water heaters is assessed under the same conditions. The collectors have the same surface area and are glazed. The theoretical model for each collector type, with the transient effects taken into account, is based on a control volume. By considering a small element of the collector in each case and the storage tank, six partial differential equations were developed for each solar water heater and were solved numerically for a cloudy day. This study shows that the thermal performance obtained with the solar water heater using the absorber-pipe lower bond configuration in the solar collector is always greater than the two others. These results showed that the solar water heater made of the absorber-pipe lower bond configuration is more efficient than the other systems. 相似文献
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In the present investigation the performance behaviour of thermosyphonic circulation solar water heaters using packed bed collectors has been analysed. Iron chips, gravels and stones have been used as packing materials. Average tank water temperature, collector as well as system efficiency and mony pay-back for these packed bed solar water heaters are compared with those for solar water heater using a plane collector. Experimental results reveal that the performance of solar water heater improves appreciably by packing its collector with packing material. Among the packed-bed solar water heaters tested the iron chips packed-bed solar water heater gives the overall best performance. 相似文献
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《Energy》1986,11(8):797-804
A methodology is outlined that has been used to study the sensitivity of the performance of portable electric and kerosene space heaters to several parameters, including: the price of fuel for the conventional central heating system, the price of portable heater fuel, the thermal integrity of the structure, the size of the room that the portable heater is used to heat, the setback temperature for the central heating system, the duration of use, rates of air exchange with other spaces, and geographic location. Results are used to identify the conditions for which portable heaters are most beneficial and to which parameters the savings are most sensitive. The results show that savings are most sensitive to the thermal integrity of the structure, the price of fuel for the conventional heater, the thermostat setting during setback, and the duration of use of the portable heater. Payback periods for portable heaters are found to range from several months to more than six years. 相似文献