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为了分析结构形式和流动状态等因素对换热器换热效果的影响,首先,以单根圆管换热器为研究对象验证了SolidWorks Flow Simulation软件进行仿真分析的可行性。然后,基于该软件分析了流动形式和扁管厚度对扁管换热器换热性能的影响,并拟合了扁管沿程摩擦阻力系数计算公式。研究结果表明,本文所提数值模拟方法是有效地,所得扁管沿程摩擦阻力系数计算公式具有一定的参考价值。 相似文献
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太阳热水器技术讲座(五)太阳热水器的生产 总被引:2,自引:0,他引:2
1平板太阳集热器的生产平板太阳集热器是平板太阳热水器的关键部件,它的产品质量直接影响热水器的性能,其生产成本约占热水器总成本的1/2。根据吸热板的断面结构形状来看,平板集热器有管板式、翼管式、扁盒式、扁方式、塑料圆管式、铜铝复合式等(图1),还有蛇形管式和热管式。集热器吸热板的长宽尺寸应按照国家标准GB/T6424—1997的规定加以选择。吸热板的进水口和出水口的设置基本可分为4出口(外循环)和3出口(内循环)2类,如图2所示。(1)吸热板的生产吸热板的生产要根据吸热板的材料及其工质通道与板的结合方式确定加工工艺。例如:不锈钢扁… 相似文献
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为了研究不可凝气体(non-condensable gases, NCG)对火电与光热发电机组上广泛使用的大扁管空冷凝汽器性能的影响,以工程机组凝汽器上普遍应用的通流面积220 mm×20 mm的大扁管为研究对象,针对汽轮机典型工况下的实际蒸汽流量,基于Lee相变方程、VOF方法以及组分扩散模型,对蒸汽与NCG混合气体管内两相流凝结换热进行数学建模与数值计算。结果表明:由于大扁管的狭窄通流几何结构与高蒸汽流量,NCG对管内蒸汽凝结的抑制效果要远低于预期;当入口空气质量分数按2%增加时,凝结管凝结换热系数仅下降2%左右,这与NCG导致低流量圆管凝结性能急剧下降的结论不同;空气正常泄漏不会导致空冷凝汽器性能下降而影响发电机组效率。 相似文献
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圆管内流动水发生结冰的影响因素研究 总被引:6,自引:3,他引:3
该文测量了不同运行状态下圆管内流动水发生结冰的时间,研究了水的流速不变时圆管内表面温度对结冰发生的影响,研究了水的流动状态对结冰发生的影响,提出了防止圆管内流动的水发生结冰的条件,并从理论上对流动状态对结冰发生的影响进行了分析。 相似文献
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含加热圆管方腔内自然对流的数值研究 总被引:2,自引:0,他引:2
采用数值计算方法对含不同直径圆管以及相同直径圆管位置不同方腔内的层流自然对流进行了研究。以冷热壁面温度差为基准的瑞利数Rn为10^6,以圆管壁面热流密度为基准的Ra为10^8。计算结果表明,当圆管处于方腔中间位置时,随着圆管直径的增大,圆管表面局部努塞尔数呈减小趋势。当圆管直径不变时,由于在不同位置处浮力作用的强弱不同,随着圆管在方腔内位置的改变,方腔内流场结构和温度场分布也会发生变化。整个计算结果可为工程设计提供参考。 相似文献
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John C Chai T.M TsaiJi Jinn Foo Vincent Chan 《International Journal of Heat and Mass Transfer》2002,45(4):785-792
The formations of Factor Xa and thrombin, two intermediate chemicals leading to the formation of blood clots in damaged blood vessels are predicted in this paper using a finite-volume method. The steady-state forms of the continuity, momentum and concentration equations are solved. The surface reactions are modeled using the classical Michaelis-Menten reaction kinetics. The results are compared with three sets of experimental data. These experiments were conducted using circular tubes and parallel flat plates. The present computational model is able to predict experimental results very well over a range of shear rates and inlet concentrations. 相似文献
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Ravi Kumar H.K VarmaBikash Mohanty K.N Agrawal 《International Journal of Heat and Mass Transfer》2002,45(1):201-211
An experimental investigation has been carried out to augment the heat transfer rate by enhancing the heat transfer coefficient during the condensation of pure vapours of steam and R-134a over horizontal finned tubes. The study was conducted for plain tubes, circular integral-fin tubes (CIFTs), spine integral-fin tubes (SIFTs) and parially spined circular integral-fin tubes (PCIFTs). The SIFT out performed the CIFT for the condensation of R-134a by approximately 16%. However, the spines were found most effective in the bottom side of the CIFT. The PCIFTs with the spines only in the bottom side of the tube augmented the heat transfer coefficient by 20% and 11% for the condensation of steam and R-134a, respectively, in comparison to the CIFT. 相似文献
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For the purpose of disclosing the hydrodynamic flow characteristics, under the low mass velocity conditions of the 600-MW supercritical circular fluidized beds boilers, experimental studies on instability of two-phase flow in parallel vertical internally ribbed tubes were conducted. Two kinds of oscillations, pressure-drop oscillation and density-wave oscillation, have been observed. In the range of test parameters the effects of pressure, mass flux, inlet subcooling, compressible volume, exit throttle, and asymmetric heat flux to the two-phase instability were explored and analyzed. Indications from experiment data are: To increase system pressure, mass flux and inlet subcooling will intensify the stability of water wall tubes. To increase exit throttle will intensify the instability of water wall tubes. The bounding pressure and bounding mass flux of density-wave oscillations and the bounding pressure of pressure-drop oscillation have been obtained. Based on the results of testing and using a homogeneous model, the threshold relational expressions of instability were obtained. The results may be used for the design and safe operation of parallel vertical rifled water wall tubes of supercritical circular fluidized beds boilers. 相似文献
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A set of vertical flat tubes cooled by natural convection and placed in a finite size space is designed based on the constructal law. The constraint in this design is the size of the space where the tubes are placed. The freedom inside the space is the distance between the tubes. When the constructal law is applied, the optimal distance between the tubes is determined. Rayleigh numbers are taken as (Ra = 103, 104, and 105). The dimensionless tube diameter (tube diameter/tube height) is changed from (D* = 0.2) to (D* = 1) (circular tube). All the tubes are heated to the same wall temperature. The air used to cool the tubes has a Prandtl number (Pr = 0.72). The equations of conservation of mass, momentum, and energy for steady, two-dimensional, and incompressible flow are solved by the finite volume method. The result showed that the best or optimal distance at a given Rayleigh number remains constant for all tube diameters. The result also showed that the number of the small diameter tubes must be more than the number of the large-diameter tubes for the same Rayleigh number and the same size of the space to make the heat flow from the tubes to the coolant easier. 相似文献
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Enhancement of condensation heat transfer using a nonuniform electric field was experimentally investigated for horizontal smooth and low‐finned tubes. In the experiments, a wire electrode parallel to the tube was placed beneath the tube. The experimental parameters were the distance and voltage between the wire electrode and the tube, and the condensation heat flux. Results of the present experiment for the low‐finned tube indicate that, as the applied voltage increases, the enhancement ratio increases steeply at a certain voltage and it reaches 2.4. It was observed that the condensate flow pattern falling down from the bottom of the tube changed from a flat film to circular columns at a critical voltage. © 2000 Scripta Technica, Heat Trans Asian Res, 29(4): 269–279, 2000 相似文献
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An experimental study on the air-side heat transfer and pressure drop characteristics for brazed aluminum heat exchangers with multi-region louver fins and flat tubes was conducted. A series of tests were conducted for heat exchangers with different numbers of louver regions at the air-side Reynolds numbers of 400–1600 based on the louver pitch. The air-side thermal performance data were analyzed by using the effectiveness-NTU method. The characteristics of the heat transfer and pressure drop for heat exchangers with different geometry parameters were presented in terms of the Colburn j factor and Fanning friction f factor as function of the Reynolds number. 相似文献
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Stationary solar collector such as flat-plate collector is a thermal device, which traps solar energy and converts it into heat that can be used in industrial and domestic applications such as water heating. Flat-plate collector thermal performance enhancement is investigated in this research paper. Two cross-sectional geometries of the tube in the heat exchanger were investigated; a normal circular tube and a twisted tube were used in the experiment. The aim of the twisted tube exchanger is to enhance the performance of heat transfer of the tubes and to reduce the shell pressure drop; flat-plate solar collector is the used application to study the heat exchanger performance. Both twisted tubes heat exchanger and normal circular tubes heat exchanger were examined in the same location and conditions with the same solar collector, both were used in the heat exchanger to study their effect, with two different working fluids, which are distilled water and multiwalled carbon nanotube (MWCNT)/water nanofluid. The system shows an increase in the performance when twisted tubes were used in the system compared with the circular tubes in both distilled water and MWCNT/water nanofluid by 12.8% and 12.5%, respectively, with an improvement by 34% for twisted tubes with MWCNT compared with normal circular tubes with distilled water. 相似文献
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Md. Ashraful Islam Masanori Monde Peter Lloyd Woodfield Yuichi Mitsutake 《International Journal of Heat and Mass Transfer》2008,51(5-6):1226-1237
Experiments were conducted to understand the phenomena that happen just after a subcooled free-surface circular water jet impinges on a high temperature surface. A 2 mm-water-jet of 5–80 K subcooling and 3–15 m/s velocity was impinged on the flat surface of a cylindrical steel/brass block that was preheated to 500–600 °C. The transient temperature data were recorded and used to predict the surface temperature by an inverse heat conduction technique. A high-speed video camera was also employed to capture the flow condition. It is found that for a certain period of time the surface temperature remains well above the thermodynamic limiting temperature that allows stable solid–liquid contact. What happens during this period and what makes the surface temperature drop to the limiting temperature are important questions whose possible answers are given in this article. The cooling curves at the center of the impinging surface for different experimental conditions are also explained in relation with the limiting temperature and three characteristic regions having different types of flow patterns are identified. 相似文献