共查询到19条相似文献,搜索用时 171 毫秒
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颗粒阻尼应用于平板叶片减振试验 总被引:3,自引:0,他引:3
以填充颗粒的平板叶片为研究对象,研究了结构阻尼与颗粒阻尼器各参数问的非线性变化关系;同时研究了颗粒参数和结构参数的变化对结构减振效果的影响规律.研究结果表明:填充颗粒密度越大,减振效果越好;在颗粒填充率为70%左右时系统的阻尼比最大. 相似文献
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通过在液冷式CPU散热器蛇形流道内填充不同粒径的不锈钢珠,使液冷式CPU散热器流道形成类似多孔介质的复杂流道以提高其散热性能。通过对改进前后液冷式CPU散热器的试验研究,分析了各因素对液冷式CPU散热器的传热和流阻性能的影响规律。结果表明:在本试验范围内,相同Re和Pr下,改进后散热器的对流换热系数为改进前的1.2~4.8倍,阻力系数f是改进前的1.4~4倍;散热器填充Φ4mm开孔不锈钢珠的强化传热效果最佳,芯片表面温度较填充前降低了33,°对流换热系数增大4.8倍,而流动阻力仅增加了1.4倍。 相似文献
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非圆截面小通道内R113的流动沸腾换热特性 总被引:1,自引:0,他引:1
针对非圆截面小通道流动沸腾换热研究报道较少的现状,以R113为工质,对4种不同水力直径的正方形、三角形截面小通道内的流动沸腾换热特性进行试验研究,试验参数范围:入口干度,过冷~1.0;质量流速400~ 3 300 kg/(m2?s);热流密度20~150 kW/m2,并将试验结果与相近水力直径的圆通道内流动沸腾试验结果进行了对比分析。试验结果表明:非圆小通道内饱和流动沸腾局部壁面温度与质量流速密切相关,并受热负荷与流动沸腾换热状况的影响;质量流速和壁面热负荷是非圆小通道内流动沸腾换热特性的主要影响因素;与相近水力直径的圆通道内流动沸腾试验数据对比显示,非圆截面小通道具有明显的强化传热作用。 相似文献
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随着机械电子设备的不断发展,热管理问题面临越来越严重的挑战,为解决此问题,根据仿生学原理,以天鹅绒竹芋表面微观凸起结构为设计依据,以纳米尺度铜粉为材料烧结制备锥形毛细芯,构造新型平板热管,并以去离子水为工质对其热性能进行研究。研究加热功率、平板热管放置角度及毛细芯氧化与未氧化等因素对平板热管传热特性的影响。结果表明,由于锥形毛细芯多尺度孔隙结构的存在,不仅实现蒸汽从大尺度孔隙逸出,液体从小孔隙吸入,而且缩短了液体流动路径,减小了流动阻力,同时扩大了换热面积,因此大大提高了平板热管的传热性能。锥形毛细芯平板热管具有较好的传热性能及抗重力特性。毛细芯经氧化处理后可显著减小平板热管的换热热阻,提高平板热管的传热性能,在热流密度为107.1 W/cm2时,其总热阻最小值为0.079 K/W。 相似文献
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建立单面加热垂直矩形窄通道流动沸腾换热试验装置,针对截面250mm×3.5mm的窄缝通道,对水流动沸腾换热特性进行试验研究。通过试验分析可知:(1)随着干度的增加,局部换热系数先增加后减小,有一个最大值,此时处于饱和核沸腾区域,其蒸汽干度也接近于0,同时也接近于沸腾起始点。相应地流体从单相流-泡状-块状流-搅拌-环状流转变。(2)在流动沸腾换热中,热流密度对核态沸腾换热有明显影响,而对流动沸腾液膜蒸发的影响甚小,所以可以认为由热流密度的变化而引起的换热变化,主要表现在核态沸腾。(3)入口温度的变化对单相流动的换热系数有影响,而沸腾换热系数与流型及汽泡的产生及扰动有极大关系,入口温度对流动沸腾局部换热系数基本没有影响。 相似文献
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Kwang Soo Kim Won Tae Kim Ki Baik Lee 《Journal of Mechanical Science and Technology》1998,12(1):132-142
Present study is concerned with forced convective heat transfer of the channel flow with line arrays of heated electronic
components mounted on a printed circuit board. For the assessment of thermal performance in channel flows, three separate
variables are used:channel spacing, row number of the component, and inlet air velocity. The thermal characteristics of a
component due to own power and upstream air heated by components were studied. The experimental results were compared with
those of numerical solution for various conditions: surface temperature of the components, adiabatic temperature rise, and
heat transfer coefficient. The experimental results agree well with the numerical solutions. The study shows that the adiabatic
heat transfer coefficient is significantly affected by the inlet velocity in channel flow and less dependent on the channel
spacing and row number, except for the case ofH/B=3.3. While reviewing the previous literatures, it is found that a little difference in the correlation between Nu and Re
is due to the different geometric ratio of the packaged components. 相似文献
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The boiling heat transfer characteristics of two-phase closed thermosyphons with internal grooves are studied experimentally
and a simple mathematical model is developed to predict the performance of such thermosyphons. The study focuses on the boiling
heat transfer characteristics of a two-phase closed thermosyphons with copper tubes having 50, 60, 70, 80, 90 internal grooves.
A two-phase closed thermosyphon with plain copper tube having the same inner and outer diameter as those of grooved tube is
also tested for comparison. Methanol is used as working fluid. The effects of the number of grooves, the operating temperature,
the heat flux are investigated experimentally. From these experimental results, a simple mathematical model is developed.
In the present model, boiling of liquid pool in the evaporator is considered for the heat transfer mechanism of the thermosyphon.
And also the effects of the number of grooves, the operating temperature, the heat flux are brought into consideration. A
good agreement between the boiling heat transfer coefficient of the thermosyphon estimated from experimental results and the
predictions from the present mathematical model is obtained. The experimental results show that the number of grooves and
the amount of the working fluid are very important factors for the operation of thermosyphons. The two-phase closed thermosyphon
with copper tubes having 60 internal grooves shows the best boiling heat transfer performance. 相似文献
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Boiling heat transfer characteristics of a two-phase closed thermosyphons with various helical grooves are studied experimentally
and a mathematical correlation is developed to predict the performance of such thermosyphons. The study focuses on the boiling
heat transfer characteristics of two-phase closed thermosyphons with copper tubes having 50, 60, 70, 80, 90 internal helical
grooves. A two-phase closed thermosyphon with plain copper tube having the same inner and outer diameter as those of grooved
tubes is also tested for comparison. Water, methanol and ethanol are used as working fluid. The effects of the number of grooves,
various working fluids, operating temperature and heat flux are investigated experimentally. From these experimental results,
a mathematical model is developed. In the present model, boiling of liquid pool in the evaporator is considered for the heat
transfer mechanism of the thermosyphons. And also the effects of the number of grooves, the various working fluids, the operating
temperature and the heat flux are brought into consideration. A good agreement between the boiling heat transfer coefficient
of the thermosyphon estimated from experimental results and the predictions from the present mathematical correlation is obtained.
The experimental results show that the number of grooves, the amount of the working fluid and the various working fluids are
very important factors for the operation of thermosyphons. Also, the thermosyphons with internal helical grooves can be used
to achieve some inexpensive and compact heat exchangers in low temperature. 相似文献
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An investigation is performed into the heat transfer performance of jet impingement flow boiling using Al2O3-water nanofluids with Al2O3 additions of 0, 0.0001, 0.001 and 0.01 vol%, respectively. It is shown that the heat transfer performance of jet impingement flow boiling using Al2O3-water nanofluid is poorer than that obtained when using de-ionized (DI) water as the working fluid. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS) observations reveal that the reduction in the heat transfer performance is due to the formation of a nano-sorption layer on the heated surface, which results in an increase in the thermal resistance. However, it is shown that by applying acoustic vibration to the heated surface, the formation of the nano-sorption layer is prevented; with the result that the heat transfer performance obtained using the Al2O3-water nanofluids is better than that obtained using pure DI water. 相似文献
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The study focuses on the heat transfer performance of two-phase closed thermosyphons with plain copper tube and tubes having
50, 60, 70, 80, 90 internal grooves. Three different working fluids (distilled water, methanol, ethanol) are used with various
volumetric liquid fill charge ratio from 10 to 40%. Additional experimental parameters such as operating temperature and inclination
angle of zero to 90 degrees are used for the comparison of heat transfer performance of the thermosyphon. Condensation and
boiling heat transfer coefficients, heat flux are obtained using experimental data for each case of specific parameter. The
experimental results are assessed and compared with existing correlations. The results show that working fluids, liquid fill
charge ratio, number of grooves and inclination angle are very important factors for the operation of thermosyphons. The relatively
high rate of heat transfer is achieved when the thermosyphon with internal grooves is used compared to that with plain tube.
The optimum liquid fill charge ratio for the best heat transfer performance lies between 25% and 30%. The range of the optimum
inclination angle for this study is 20°-30° from the horizontal position. 相似文献
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There are many parameters that have significant effects on forced convection heat transfer in packed beds, including Reynolds
and Prandtl numbers of flow, porosity, pebble geometry, local flow conditions, wall and end effects. In addition, there have
been many experimental investigations on forced convection heat transfer in packed beds and each have studied the effect of
some of these parameters. Yet, there is not a reliable correlation that includes the effect of main parameters; at the same
time, the prediction of precise correct limits for very low and high Reynolds numbers is off hand. In this article a general
well-known model of convection heat transfer from isothermal bodies, next to some previous reliable experimental data has
been used as a basis for a more comprehensive and accurate correlation to calculate the laminar constant temperature pebble-fluid
forced convection heat transfer in a homogeneous saturated bed with spherical pebbles. Finally, for corroboration, the present
results are compared with previous works and show a very good agreement for laminar flows at any Prandtl number and all porosities. 相似文献
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利用正交函数法对定热流密度加热、壁面温度在周向可任意变化条件下,气体在微矩形槽道内的热充分发展滑移流动的换热特性进行理论分析,获得相应条件下的Nu数计算方法及换热特性,并与大尺度槽道的换热特性进行比较,探讨了Kn数、槽道高宽比及不同加热条件对微矩形槽道内滑移流动换热性能的影响。结果表明,在任何加热条件下,微矩形槽道内的平均Nu数均低于相同加热条件下大尺度矩形槽道中的Nu数,且随Kn数的增加而减小。高宽比越小,平均Nu数下降越大。在相同的高宽比和Kn数下,单边加热条件下的换热性能相比相同加热条件的常规大槽道内的换热性能下降最小。 相似文献
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Shinpyo Lee 《Journal of Mechanical Science and Technology》2011,25(1):135-142
Most of the previous convection experiments for nanofluids have been performed for internal tube flow with constant heat flux
boundary condition. In contrast, a simple experimental apparatus measuring convective heat transfer coefficient from a heated
wire to external nanofluids is proposed and its working principles are explained in detail. The convective heat transfer coefficient
provided by the present system might be used as a useful indication justifying the adoption of prepared nanofluids as new
efficient heat transfer fluids. Validation experiments by comparing convective heat transfer coefficients between the conventional
correlation and measured values are carried out for base fluids. Also the effect of increased thermal conductivity of nano
lubrication oil on the enhancement of convective heat transfer coefficient is investigated. 相似文献