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滑动轴承运行过程中油膜剪切和搅油产生的功耗约80%会转换成热量,导致油箱内润滑油温度升高,为将润滑油温度控制在设计值内,通常在油箱内安装油水冷却器带走热量,冷却器换热性能直接影响滑动轴承的运行温度和主机的正常工作。油水冷却器的散热能力主要由换热系数和流阻特性决定,对不同油流量条件下的油水冷却器进行试验测试,研究其换热和流阻特性,结果表明:在控制进油、进水温度及进水流量的前提下,油流速在一定范围内增加时,换热系数先增加后趋于稳定,压力损失增大,换热因子和阻力系数减小,冷却器可在一定油流速范围内获得最佳的换热和流阻特性;试验获得了对数坐标系下努赛尔数、欧拉数与雷诺数的拟合曲线,理论计算与试验拟合结果具有良好一致性,并在此基础上获得了油流速与换热系数及流阻的经验公式。 相似文献
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基于强化传热技术,以光滑椭圆管为基本研究对象,对比不同扁平度n及导程S的扁平螺旋管,通过合理的简化与假设,采用计算流体力学(CFD)的方法对扁平螺旋管进行数值模拟研究,以期为该换热设备结构优化设计及实际工程应用提供参考。研究证明:扁平螺旋管与光管对比,扁平螺旋管内产生了明显的旋流运动,促进了流体在垂直于轴向方向的混合,使得管内流体的轴向速度增大,且这种混合使得换热管边界层厚度变薄,保持了较高的温度梯度,达到了强化传热的目的;扁平螺旋换热管的旋转程度越大(即相同的截面尺寸,S越小),换热管的强化换热的性能越好,但换热管内流体介质的流动阻力也相应越大,所以导程S在84~150之间为扁平螺旋管导程的优选区间;扁平螺旋管的压扁程度不一定越扁越好,当换热管的扁平度过大时,会导致扁平螺旋管的努塞尔数Nu急剧下降,压降△P急剧增加,使得换热管的强化换热效果降低,而当换热管的扁平度过小时,努塞尔数Nu和压降△P变化缓慢,对换热管的强化换热影响较弱,所以扁平度n的最佳选择是0.7~1.4。 相似文献
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对制冷剂R134A在花柄管管内单向流动传热特性及温度场进行CFD数值模拟研究,结果表明:在同一质量流速下,螺旋花柄管的努塞尔数和阻力系数均随螺旋导程的增加而降低,在同一螺旋导程下,螺旋花柄管的努塞尔数和阻力系数均随质量流速的增加而增加,当PEC1时,螺旋花柄管的综合性能均高于花柄管,在螺旋花柄管内流体做旋流运动,有效增加了湍流程度,提高了换热效率,且螺旋流动可有效避免结垢。 相似文献
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为了解决芯片结温过高而导致的热失效问题,以某通信用的多芯片组件MCM-BGA为例,对MCM-BGA芯片温度场热分布和热量传递路径进行分析,确定了芯片的主要热传递路径,发现影响芯片结温的主要因素有环境对流换热系数、基板厚度、基板导热系数、焊料层厚度、封装外壳等;并基于响应面法试验设计,采用CCD(中心复合设计)选取并构建了自然对流系数、基板导热系数、基板厚度、焊料层厚度与多芯片组件的最高结温之间的数学模型,通过仿真验证了该模型的准确性和有效性;然后采用遗传算法对该数学模型进行优化设计,获得了芯片各参数优化的最佳组合。当自然对流换热系数为60 W/m2·k、基板导热系数为32 0W/m·k、基板厚度为1.4 mm、焊料厚度为0.16 mm时,MCM-BGA最高结温具有最小值,使多芯片组件MCM-BGA最高结温降低了7.375%。 相似文献
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对污水源热泵系统中污水换热器进行了现场测试,依据测试数据分析污水换热器换热量、传热系数的衰减规律。依据测试数据和理论计算分析了污水换热器内污水侧对流换热热阻和污垢热阻的变化规律,以及各热阻在总热阻中的所占比例。结果表明:洁净的污水换热器投入运行225h后,实际换热量为初始值的43.8%;实际传热系数为440W/(m2.℃),为初始值的46.3%;污水侧对流换热热阻占总热阻的60%,污垢热阻占总热阻的20%。提高污水换热器换热效率,保持污水换热器换热量的稳定应从降低污水侧对流换热热阻着手。 相似文献
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以水为传热介质,对温差驱动的二维方腔内自然对流换热过程进行了模拟分析。利用流体流动与热量传递的无因次控制方程,采用热线及流线可视化方法,取相同Ra=5×107值,倾斜角为控制参数,讨论分析了方腔中的温度、流动及对流换热传输结构。给出了倾斜角对于流型、分离点、对流换热传输结构及高低温壁面的传热性能的影响。分析结果表明:当Ra=5×107时,随着的θ增大,双涡结构越来越明显,倾斜角度对于方腔的流动的流型,具有较大的影响;分离点从低温壁面下部开始形成,随着倾斜角的增大分离点沿着低温壁面向上流动,接着到达绝热壁面,最终到达高温壁面;温度梯度受θ变化的影响较大,不同θ时,产生温度梯度最大值的地点不同;高低温壁面的平均Nu在60°最大,180°时最小。 相似文献
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Nae-Hyun Kim Do-Young Kim Jun-Hyun Hwang 《Journal of Mechanical Science and Technology》2008,22(12):2498-2508
The effect of inclination angle on the heat transfer and pressure drop characteristics of brazed aluminum heat exchangers
was experimentally investigated under wet conditions. Three samples having different fin pitches (1.25, 1.5 and 2.0 mm) were
tested. Results show that heat transfer coefficients are not affected by the inclination angle. However, friction factors
increase as the inclination angle increases with negligible difference between the forward and backward inclination. The effect
of fin pitch on the heat transfer coefficient and on the pressure drop is also discussed. Comparison of the dry and wet surface
heat transfer coefficients reveals that dry surface heat transfer coefficients are significantly larger than wet surface heat
transfer coefficients. Possible explanation is provided by considering the condensate drainage pattern. The data are also
compared with the existing correlation.
This paper was recommended for publication in revised form by Associate Editor Man-Yeong Ha
Nae-Hyun Kim is a Professor of Mechanical Engineering, University of Incheon. His area of interest spans boiling and condensation, heat
transfer enhancement and heat exchanger design. He has been active in heat transfer community, and was a Chairman of Thermal
Engineering Division of KSME. He holds several editorial position including Journal of Enhanced Heat Transfer. He is a recipient
of Asian Academic Award awarded by SAREK and JSRAE. 相似文献
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This study concerns the performance of the heat transfer of the thermosyphons having 60, 70, 80, 90 axial internal low-fins
in which boiling and condensation occurr. Water, HCFC-141b and CFC-11 have been used as the working fluids. The operating
temperature, the liquid charge ratio and the inclination angle of thermosyphons have been used as the experimental parameters.
The heat flux and heat transfer coefficient at the condenser are estimated from experimental results. The experimental results
have been assessed and compared with existing theories. As a result of the experimental investigation, it was found that the
maximum heat flow rate in the thermosyphons is dependent upon the liquid charge ratio and inclination angle. A relatively
high rate of heat transfer has been achieved by the thermosyphon with axial internal low-fins. The inclination of a thermosyphon
has a notable influence on the condensation. In addition, the overall heat transfer coefficients and the characteristics at
the operating temperature are obtained for the practical applications. 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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This study is focused on the comparison of heat transfer performance of two thermosyphons having 60 straight and helical internal grooves. Distilled water has been used as working fluid. Liquid fill charge ratio defined by the ratio of working fluid volume to total internal volume of thermosyphon, the inclination angle and operating temperature were used as experimental parameters. The heat flux and heat transfer coefficient are estimated from experimental results. The conclusions of this study may be summarized as follows; Liquid fill charge ratio, inclination angle and geometric shape of grooves were very important factors for the operation of thermosyphon. The optimum liquid fill charge ratio for the best heat flux were 30%. The heat transfer performance of helically grooved tube was higher than that of straight grooved tube in low inclination angle (less than 30°), but the results were opposite in high inclination angle (more than 30°). As far as optimum inclination angle concerns, range of 25°-30° for a helically grooved tube and about 40° for a straight grooved tube are suggested angles for the best results. 相似文献
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The heat transfer phenomenon occurring during stratified condensation inside an inclined tube is investigated theoretically
and numerically. Differential equations governing the kinematic, dynamic, and thermal aspects for vapor condensation inside
inclined tubes, which are derived from a thin film flow modeling, are solved simultaneously. These solutions are achieved
by applying an explicit finite difference numerical method to predict the condensation heat transfer coefficient variations
along the tangential and axial coordinates. The inclination angle is found to have a significant effect on condensation heat
transfer coefficient inside inclined tubes. In addition, in accordance with the given physical and thermal condition of working
fluids, there is a specific optimum inclination angle. In this study, the 30°–50° range from the horizontal position is found
to be the range of the optimum inclination angle for achieving the maximum condensation heat transfer coefficient, with R134a,
R141b, and R11 as the working fluids. The results of the present study are compared with experimental data, and a good agreement
is observed between them. 相似文献
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Shang Fumin Fan Shilong Yang Qingjing Liu Jianhong 《Journal of Mechanical Science and Technology》2020,34(1):425-433
Journal of Mechanical Science and Technology - Heat input and inclination angle are essential factors influencing heat transfer performance of a pulsating heat pipe (PHP). The heat transfer... 相似文献
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Kui-Soon Kim 《Journal of Mechanical Science and Technology》1993,7(3):258-271
The flow and heat transfer characteristics of an impinging jet is investigated in two major stages. The first stage is about the investigation of the three dimensional mean flow and the turbulent flow quantities in free jet, stagnation and wall jet region. After a complete documentation of the flow field, the convective heat transfer coefficient distributions on the impingement plate are presented, during the second stage of the study. Heat transfer experiments using the new hue-capturing technique result in high resolution wall heating rate distributions. The technique is fully automated using a true color image processing system. The present heat transfer results are discussed in detail in terms of the flow characteristics. The measurements from the new method are compared with conventional heat flux sensors located on the same model. These heat transfer distributions are also compared with other studies available from the literature. The new non-intrusive heat transfer method is highly effective in obtaining high resolution heat transfer maps with good accuracy. 相似文献
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The heat dissipation of a ventilated disc on high-speed trains during emergency braking is studied to improve heat dissipation performance. The conjugate heat transfer method is employed to understand the distribution and variation of convective heat transfer coefficients on the disc surfaces during braking. Finite element models of the ventilated disc and the complicated air flow field under the train are built. Boundary conditions are derived based on real working conditions. Heat transfer simulation is carried out using the FLUENT computer code. Simulation results, including temperature rise of the disc, convective heat transfer coefficient distribution, and heat transfer rate, are presented and analyzed. Using materials with high thermal conductivity coefficients and reducing the heat transfer wall thickness of the disc are proposed to improve the heat dissipation performance of the disc based on the simulation results. Both methods are effective in improving the heat transfer rate of the disc with a 10% improvement in the improved thermal conductivity case and a 30% improvement in the reduced wall thickness case. 相似文献