共查询到20条相似文献,搜索用时 0 毫秒
1.
On the Performance of Ag/Oil Nanofluids in Heat Transfer Enhancement in a Sinusoidal Tube: Constant Heat Flux Boundary Condition
下载免费PDF全文
![点击此处可从《亚洲传热研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The present work provides an empirical investigation on the thermal characteristics of Ag/oil nanofluids flow inside a sinusoidal tube under a constant heat flux boundary condition. Ag/oil nanofluids have been prepared in low‐volume concentrations of 0.011%, 0.044%, and 0.171%. The average size of the nanoparticles was 20 nm. A heated coil was attached to the upper and lower surface of the tube that satisfied the constant thermal boundary condition of 204 W. The experiment has been pursued at low Reynolds numbers less than 160. A loop was designed to keep the flow hydrodynamically fully developed during the experiment. The test case was a sinusoidal tube. Upper and lower surfaces of the tube have been designed sinusoidally. Moreover, the width of the plates was long enough, so the problem was not considerably affected by the three‐dimensional releasing effect. Convective heat transfer coefficient and Nusselt number were calculated. It has been observed that based on the acquired data of the present work, convective heat transfer coefficient increased up to 23% for the best case (nanofluid with a volume concentration of 0.171%) compared to the base fluid. This happened while the rise of the friction factor was very low. In addition, a comparison between the new results and the previous work by authors showed the positive performance of sinusoidal tubes in increasing the convective heat transfer coefficient (the average increase was calculated to be about 82%) compared to the annular tube. 相似文献
2.
3.
基于热力学第一、二定律,在恒热流工况下分析了污垢对管内对流换热过程热力学性能的影响,提出了一项在恒热流工况下反映污垢对管内流换热过程热力学性能影响的指标-无因次熵产相对增加数;讨论了管内流体雷诺数(无污垢时)和无因次热流密度等参数对无因次熵产相对增加数的影响。研究结果表明,该指标不仅能反映污垢对管内传热过程的影响,而且能反映污垢对管内流动过程的影响,而由污垢层导热所引起的熵产在管内传热过程总的熵产中占有重要的地位,同时,还把结果与恒壁温时的有关结果进行了比较。 相似文献
4.
基于扭曲椭圆管的换热器是一种新型的新风系统换热器,针对扭曲椭圆管及其应用特点,设计了两种不同结构参数的新风系统换热器。应用FLUENT软件,在夏季工况下对两种不同结构参数的新风系统换热器壳程进行模拟分析,并通过与实验数据的对比,验证计算模型的可靠性。结果显示在相同体积流量下,随着壳程开孔面积的增大,对流换热系数h不断减小,压降Δp不断减小,综合性能系数h/Δp1/3变化不明显;随着螺距的减小,对流换热系数h不断增大,压降Δp不断增大,综合性能系数h/Δp1/3也不断增大;流场分析显示,扭曲椭圆管换热器壳程流道内,呈现出明显沿着扭曲椭圆管壁面的螺旋流,使得空气在流道内充分扰动,增强换热效果。 相似文献
5.
6.
Babak Lotfi 《传热工程》2020,41(13):1117-1142
AbstractAs a new type of fin structure in finned tube heat exchangers, dimple turbulators exhibit excellent potential for thermo-hydraulic performance enhancement. A three-dimensional numerical simulation study was conducted to investigate the influences of five kinds of innovative concave dimple turbulators (CDTs), namely – elliptical dimple, conical frustum dimple, trapezoidal prism dimple, leeward triangular dimple and upward triangular dimple (UwTD) on the thermo-hydraulic performance enhancement in a plate fin-and-elliptical tube (PFET) heat exchanger, where CDTs are textured on the fin surface transversely between the elliptical tubes. The computational results are analyzed by considering the performance evaluation criterion for the PFET heat exchangers with different types of CDT shapes. The present investigation demonstrates that the heat transfer enhancement is intimately pertained to ejection with longitudinal counter-rotating flow, strengthened secondary flow and vortex structures at the downstream rim of CDT. A parametric study on the CDTs indicated that the UwTD vortex turbulators give better thermo-hydraulic performance under the present conditions. The numerical simulation results illustrated different secondary flow structures and heat transfer characteristics of the CDTs with various shapes, which disclosed the influential mechanisms of differently shaped dimple turbulators on the heat transfer augmentation in PFET heat exchangers. 相似文献
7.
Different heat transfer enhancement techniques can be used successfully in the retrofit design of shell-and-tube heat exchangers that can lead to significant cost savings. Tube inserts are frequently used in such applications. Twisted tapes, wire coils, helically coiled ribbons (as tube inserts in smooth pipes), and rifled pipes have been evaluated as heat transfer enhancement techniques. To assess the benefit of using these kinds of techniques, extended performance evaluation criteria (PEC) have been implemented under different constraints. The decrease in entropy generation can be combined with the relative increase in the heat transfer rate or decrease of the heat transfer area to determine the geometrical parameters of the tubes for optimal thermodynamics performance. 相似文献
8.
变热流条件下木材点燃的实验研究 总被引:1,自引:0,他引:1
为研究木材在变化的热流条件下的点燃性能,对泡桐、榆木、红椿木和刺槐等4种木材进行了小尺寸的实验研究.测量了木块表面接受到的热辐射强度、点燃时间、质量损失和木块的内部温度等参数.在实验数据的基础上,得出木材点燃的临界热流增长率约为0.07kW/(m~2·s),临界质量损失速率约为20~30g/(m~2·s).利用PDE模型计算出木块温度变化情况,并与实验数据进行了比较.计算结果表明,在自然着火情况下,木块点燃时的表面温度约为500℃左右. 相似文献
9.
为研究脉动流体对强化换热的影响,设计Helmholtz共振腔并分别在加装和不加装共振腔的情况下进行对比试验,发现水流经共振腔后变成了脉动流体,脉动的水经过单管换热器后强化了换热,在一定的共振腔参数的配合下,换热系数提高约10%~40%。 相似文献
10.
多孔表面管沸腾传热试验研究 总被引:6,自引:0,他引:6
针对烧制成多孔表面管,进行了传热性能研究,试验表明:多孔管可以显著地强化多孔侧沸腾传热,民同规格光滑管传热性能试验对比,其沸腾给热系数比光滑管提高5-6倍。 相似文献
11.
12.
管内插物强化换热性能分析及应用 总被引:4,自引:0,他引:4
管内插物的种类很多,扭带、螺旋线圈以及绕花丝是三种较常用的管内插物强化换热技术,对它们的强化换热性能以及应用进行分析比较,是非常有必要的。从综合强化性能来看,螺旋线圈内插物比扭带内插物效果好;绕花丝内插物是一种新型综合强化换热技术,它优于前两种内插物的特点是:可使流体在流动方向上做复杂的三维混合流动,并且所产生的阻力降非常小,所以综合强化换热性能最好。图7表1参10 相似文献
13.
14.
15.
16.
This study provides an experimental analysis on the heat transfer performance of a flat aluminum tube microchannel heat exchanger with spray cooling. The effects of water spraying rate, airflow rate, and relative humidity were investigated. The test results show that the heat transfer performance increased with increasing the water spraying rate but without the penalty of increased flow resistance at low spray conditions. This effect is further enhanced by increasing the water spraying rate. However, when the spraying rate is high, part of the nonevaporated drops attached to the fin surface and formed a liquid film, which caused the flow passage to become narrower. Further increase in the spraying rate resulted in part of the flow passages being blocked by the nonevaporated water drops and caused a region of poor heat transfer. The friction coefficient jumped drastically at this condition. This phenomenon deceased gradually with increasing airflow rate. High inlet air humidity resulted in the water accumulation phenomenon appearing at lower water spraying rates. The evaporative cooling effect decreased and flow friction increased. The test results just described show that the water spray is able to significantly improve the air-side heat transfer performance. The optimum spray rate for each airflow rate must be carefully determined. 相似文献
17.
全玻璃真空集热管的使用寿命 总被引:1,自引:0,他引:1
使用寿命是全玻璃真空集热管最重要的指标之一。本文从应用角度分析了真空度、内璧导热能力、抗冻能力等对使用寿命的影响,并探讨了相应的对策。 相似文献
18.
The present work deals with the numerical and experimental analyses to study the detailed behavior of the thermally induced flow of water in an open vertical annulus, circulating through a cold leg forming a closed loop thermo-siphon. Spatio-temporal behavior of fluid flow is also studied for variety of heat fluxes. The annuli in the present study have a radius ratio of 1.184 and aspect ratio (length to annular gap) equal to 352. The objective of the present work is to quantify the effect of heating on design parameters such as liquid and wall temperatures, mass flow rate, and heat transfer coefficient. Experiments have also been conducted on a similar system with water at constant heat flux of 1 kW/m2, 2.5 kW/m2, 5 kW/m2, 7.5 kW/m2, 10 kW/m2, 12.5 kW/m2 and 15 kW/m2. For numerical purpose, a two-dimentional solver has been developed for direct numerical simulation of the essential thermally induced flow dynamics The numerical solution was thus performed for Rayleigh numbers ranging between, 4.4 × 103 and 6.61 × 104 which correspond to the given heat flux, respectively. 相似文献
19.
本文采用试验研究的方法研究了流体动力学不稳定性对强化换热的影响。水流经Helmholtz共振腔时被转变为脉动流体,脉动的水经单管换热器时被加热,测量了不同条件下加装共振腔和不加共振腔时的换热系数。研究发现,加装了Helmholtz共振腔时换热系数明显提高约10%~40%。 相似文献
20.
采用试验研究的方法研究了流体力学不稳定性对强化换热的影响。水流经Helmholtz共振腔时被转变为脉动流体,脉动的水经单管换热器时被加热,测量不同条件下加装共振腔和不加共振腔时的换热系数。研究发现,加装了Helmholtz共振腔时换热系数明显提高约10%~40%。 相似文献