共查询到20条相似文献,搜索用时 86 毫秒
1.
利用Fluent软件对壳体和中心管均为椭圆的管壳式换热器的融化过程进行了模拟分析。研究壳体和中心管的不同长短半轴之比以及热源温度对石蜡融化过程的影响,得到了石蜡融化过程液相分数及热流密度的变化规律。结果表明:内外椭圆管长短半轴比均为1.7的结构融化时间最短,结构最优。相比于内管,外管对融化过程的影响更大。斯蒂芬数对融化有较大影响,斯蒂芬数越大,初期融化速率越快。 相似文献
2.
以赤藻糖醇为相变材料,采用Fluent软件对同心套管式相变蓄热单元的熔化和凝固过程进行了三维非稳态数值研究。在考虑自然对流的前提下,对比了水平入射式、顶部入射式及底部入射式相变蓄热单元的传热特性,得到了固液界面分布图和温度云图随时间的变化特性,对比了各自的蓄放热速率。研究表明:自然对流在熔化过程中起主要作用,而在凝固过程中起的作用很小;蓄热速率从大到小排列,依次是水平入射式、顶部入射式和底部入射式,相比于底部入射式,水平入射式的总熔化时间可减少27.2%,而顶部入射式的总熔化时间仅减少3.7%;放热速率从大到小排列,依次是顶部入射式、水平入射式和底部入射式,相比于底部入射式,顶部入射式的总凝固时间可减少9.2%,而水平入射式的总凝固时间仅减少0.6%;水平入射式蓄热单元是满足蓄放热速率快这一要求的首选型式。 相似文献
3.
数值模拟研究了内管和外管之间的圆心距离(偏心率)对石蜡在水平相变蓄热单元中熔化过程的影响。利用焓-多孔模型得到内管加热温度为60、65、70℃和偏心率为0.20、0.40、0.60、0.80、0.93工况下蓄热单元内的速度场,温度分布,液相率分布和综合传热系数。模拟研究结果表明:加热温度为65℃,偏心率为0.20、0.40、0.60、0.80、0.93时总熔化时间分别减少了31.6%、57.4%、76.4%、86.7%、86.7%,偏心率大于0.80,增大偏心率对减少熔化时间没有明显效果;加热温度为60℃,偏心率从0.80增加至0.93,Fo增加了7.5%,总熔化时间增加,熔化过程中综合传热系数总体上逐渐减小,偏心率为0.60和0.80时,综合传热系数先增大后减小,熔化过程中,综合传热系数最大为329.72 J/(m2·K)。 相似文献
4.
板式石蜡储热器传热的数值模拟 总被引:1,自引:0,他引:1
在相变储热器中采用强化传热技术,克服相变材料的低导热性能,是目前国内外研究的热点。应用FLUENT软件数值模拟了翅片强化板式石蜡储热器的凝固传热过程,得到随时间变化的相界面位置、总凝固时间、壁面热流、翅片温度分布等,并进一步分析了翅片对不同长宽比叫的储热器的强化传热效果。模拟结果表明,只有当ω≥1时,翅片才能对储热器起到明显的强化传热作用,研究结果可为相变储热器的优化设计提供可靠的依据。 相似文献
5.
对椭圆芯管矩形翅片和大功率晶闸管用热管散热器偏心圆芯管矩形翅片的传热进行了分析和数值模拟,获得了相应的肋效率曲线,并与已有的近似解作了比较。初步考查了偏心度、材料变物性和翅基温度的不均匀性对偏心圆芯管矩形翅片传热的影响。 相似文献
6.
7.
8.
蒸汽蓄热器是一种高效的储存蒸汽热能的设备。从传热传质的角度,推导出蒸汽蓄热过程中单个高温蒸汽泡在低温连续液相中的汽泡半径比k和努赛尔数Nu的数学表达式。通过Mat Lab模拟出汽泡半径比k和努赛尔数Nu与汽泡上升速度U、汽泡初始半径R0和汽液两相温度差ΔT随时间的变化规律。研究表明,汽泡半径比k随着汽泡的上升逐渐减小。努赛尔数Nu随着汽泡的上升先减小后增大。在汽泡初始半径R0和汽泡上升速度U相同的工况下,存在一个最优汽液两相温度差ΔT,使得汽泡半径比k和努赛尔数Nu曲线下降最快。加快汽泡上升速度U、减小汽泡初始半径R0以及选择合适的汽液两相温度差ΔT,可以提高蒸汽蓄热过程的传热效率。 相似文献
9.
利用FLUENT软件对矩形单元内石蜡的熔化过程进行了数值模拟,分别研究不同的矩形单元上部尺寸、不同壁面温度对单元内石蜡熔化过程的影响,通过非线性拟合获得了单元内液相分数β与无量纲数Fo、Ste、Ra的准则关系式,为优化矩形单元内PCM总体熔化速率提供了方案与依据。研究结果表明:在石蜡熔化过程中,自然对流作为主导传热方式的时间比例随矩形单元上部尺寸的增加先增大后减小;自然对流对传热的强化作用随矩形单元内上部尺寸增加而增大,但平均储热速率随单元内上部尺寸的增加先增大后减小直至趋于平稳,存在最优值;温差是影响PCM熔化的关键因素之一,将温差从43℃提高至53℃,再从53℃提高至63℃熔化时间分别缩短14.63%、24.26%不等。 相似文献
10.
11.
12.
针对不同形状管道对蓄热状况影响不同,建立了圆形管道与方形管道的石蜡蓄热模型,运用FLUENT软件对其熔化过程进行了仿真,讨论了自然对流及石蜡厚度对石蜡蓄热的影响。计算结果表明:熔化初期,方形装置内的固液界面呈“脚丫”状,而圆形装置内的固液界面近似呈椭圆状。自然对流对熔化结果影响较大,对流的存在加速了石蜡的熔化;在自然对流的作用下石蜡的熔化速率先快后慢,而熔化总时间与石蜡厚度成正相关。在蓄热单元面积保持不变的情况下,当内管周长相等时,方管内石蜡熔化总时间大于圆管内石蜡熔化总时间;当内管面积相同时,方管内石蜡熔化总时间小于圆管内石蜡熔化总时间。 相似文献
13.
The latent thermal energy storage system of the shell-and-tube type during charging and discharging has been analysed in this paper. An experimental and numerical investigation of transient forced convective heat transfer between the heat transfer fluid (HTF) with moderate Prandtl numbers and the tube wall, heat conduction through the wall and solid–liquid phase change of the phase change material (PCM), based on the enthalpy formulation, has been presented. A fully implicit two-dimensional control volume Fortran computer code, with algorithm for non-isothermal phase transition, has been developed for the solution of the corresponding mathematical model. The comparison between numerical predictions and experimental data shows good agreement for both paraffin non-isothermal melting and isothermal solidification. In order to provide guidelines for system performance and design optimisation, unsteady temperature distributions of the HTF, tube wall and the PCM have been obtained by a series of numerical calculations for various HTF working conditions and various geometric parameters, and the thermal behaviour of the latent thermal energy storage unit during charging and discharging has been simulated. 相似文献
14.
15.
Both numerical and experimental investigations were conducted to understand convective heat transfer from a single round pipe coiled in rectangular pattern. The studied heat exchangers are composed with inner and outer coils so that the exterior flow is very similar to flow within tube-bundles. The inner and outer coils of the heat exchangers are in turn composed of bends and straight portions. Calculations and experiments were done for two cases with different outside flow arrangements. The results showed the effects of geometric arrangement with better heat transfer for the case 1 of staggered arrangement due mainly to its more tortuous flow characteristics and better mixing of the exterior fluid. The numerical and experimental results qualitatively agree well with each other. The numerical and experimental results showed that coiling a pipe so that an exterior fluid flows over or in tube bundle can help to induce the turbulence without increasing the velocity. 相似文献
16.
17.
The asymmetric plate heat exchanger (APHE) has the possibility of achieving balanced pressure drops on both hot and cold sides for situations with unbalanced flow, which may in turn enhance the heat transfer. In this paper, the single-phase water flow and heat transfer of an APHE consisted of two types of plates are numerically (400≤Re≤12000) and experimentally (400≤Re≤ 3400) investigated. The numerical model is verified by the experimental results. Simulations are conducted to study the effects of N, an asymmetric index proposed to describe the geometry of APHEs. The correlations of the Nusselt number and friction factor in the APHEs are determined by taking N and working fluids into account. It is found that an optimal N exists where the pressure drops are balanced and the heat transfer area reaches the minimum. The comparison between heat transfer and flow characteristics of the APHEs and the conventional plate heat exchanger (CPHE) is made under various flow rate ratios of the hot side and the cold side and different allowable pressure drops. The situations under which APHE may perform better are identified based on a comprehensive index Nu/f1/3. 相似文献
18.
《International Journal of Heat and Mass Transfer》1986,29(2):183-192
Melting heat transfer in an inclined rectangular enclosure is investigated experimentally. The effect of enclosure inclination is to establish three-dimensional natural convective motion which intensifies as the inclination angle from the vertical is increased. The three-dimensionality of the flow field results in nonuniform melting of the solid. The interface morphology is used to infer flow structure and the extent of three-dimensional energy transport. These flow patterns are found to be dependent on the angle of inclination and the initial solid subcooling. A correlation is presented describing the effect of inclination angle on the timewise variation of the melt fraction. A one-dimensional theoretical model is outlined and predictions are compared to experimental data. 相似文献
19.
20.
M. Lacroix 《Solar Energy》1993,50(4)
A theoretical model was developed to predict the transient behavior of a shell-and-tube storage unit with the phase change material (PCM) on the shell side and the heat transfer fluid (HTF) circulating inside the tubes. The multidimensional phase change problem is tackled with an enthalpy-based method coupled to the convective heat transfer from the HTF. The numerical predictions are validated with experimental data. A series of numerical experiments are then undertaken to assess the effects of various thermal and geometric parameters on the heat transfer process and on the behavior of the system. Results show that the shell radius, the mass flow rate, and the inlet temperature of the HTF must be chosen carefully in order to optimize the performance of the unit. 相似文献