蜂窝板换热器内部流动传热特性研究

建立了蜂窝板换热器湍流流动的物理数学模型,并应用数值分析方法模拟了蜂窝板换热器的三维流动传热过程;分析了不同雷诺数下通道内流动阻力和换热性能及其随雷诺数的变化规律,并与相同当量直径的平行平板通道的流动换热性能进行了对比.结果表明,蜂窝板换热器在换热系数提高的同时流动阻力也增大了,在雷诺数Re=3000~15000的范围内,其传热努塞尔数比平行平板增大了0.93~2.12倍,阻力系数增大了2.24~2.35倍.最后从场协同理论的角度分析了蜂窝板强化传热的机理.     

点波板式换热器内流体流动换热及压降特性的实验研究

介绍了丹佛斯提出并开发的点波板式换热器。分别通过单相水-水换热测试和制冷剂(R410A)-水蒸发换热测试,实验研究了点波板式换热器与传统人字波板式换热器的传热及流动性能。结果表明,新型点波钎焊板式换热器,作为单相换热装置,具有较好的传热和流动性能。与传统的人字波板式换热器相比,较大雷诺数下,点波板式换热器强化传热20%以上,沿程阻力因子降低为传统结构的1/4左右。同时,作为蒸发器,在相似的制冷剂流动特征下,点波板式换热器比人字波板式换热器具有更好的流动和传热性能,这些性能优势,随着制冷剂流动特征的加强将变得更为明显。     

扇叶型折流板换热器壳程性能及传热机理的数值模拟

利用数值模拟方法比较分析了扇叶型折流板换热器及螺旋折流板换热器流动传热性能及传热机理。结果表明:两种换热器壳程流动状态相近,流体倾斜于管束流动;扇叶型折流板换热器壳程传热系数和压降大于螺旋折流板换热器;雷诺数2 500—5 500时扇叶型折流板换热器综合性能低于螺旋折流板换热器,当雷诺数大于6 500时扇叶型折流板换热器综合性能略高于螺旋折流板换热器;扇叶型折流板换热器内壳程流体要比螺旋折流板换热器中的壳程流体更早的进入充分发展阶段,导致扇叶型折流板换热性能较高;扇叶型折流板换热器壳程流体流场和温度场协同性优于螺旋折流板换热器,因此前者具有更好的对流传热性能。     

蜂窝换热板研究进展

本文介绍了两种典型蜂窝换热板的结构特征、热工特性及传热机理,并讨论了结构形式、蜂窝尺寸、排列方式等参数对其性能的影响,分析了蜂窝换热板的工程应用情况,对其未来发展做了展望。相对于平滑通道,蜂窝板结构能够有效增强综合换热性能。     

整体翅片式微通道换热器的数值模拟

采用CFD数值模拟的方法,对整体翅片式微通道换热器空气侧的流动与传热特性进行研究,用场协同的原理分析翅片参数(长度、高度、间距)对换热器性能的影响,并与传统微通道换热器空气侧性能进行对比。结果表明:在考查的翅片尺寸范围内,随着翅片长度的缩短、高度的增加、间距的减小,温度场和速度场的协同性随之改善,有利于换热效果的提高;与传统的微通道换热器相比,整体翅片式微通道换热器空气侧换热性能变差,但是阻力大大降低,总体性能有所改善。     

负压低温板翅式换热器锯齿翅片性能的数值模拟研究

换热器在低温工况下的流动换热性能与常温工况下有明显差异.为分析负压低温工况下板翅式换热器关键结构参数对流动换热性能的影响,构建并完善了锯齿翅片通道内流动换热性能的数值模型.采用中心复合设计方法得到实验点并结合Kriging响应面方法,拟合得到了负压低温氦气在锯齿翅片通道内的流动传热关联式.研究结果表明:j因子与间距、厚...     

大热流背景下蜂窝板内流动传热的数值模拟

为研究蜂窝板内流体在大热流背景下的流动与传热规律，优化板件结构，建立了多种结构参数及流道形式的蜂窝板几何模型，并利用Fluent软件进行数值模拟。结果表明：流体与蜂窝板焊点碰撞生成的射流和小漩涡使湍流强度加剧、边界层被破坏；矩形和菱形两种焊点排布方式的传热与阻力性能差异不显著；焊点直径D和鼓胀高度H对蜂窝板性能的影响较大，焊点间距L对其影响较小，应根据具体情况选取合适的结构参数；折流焊缝能有效提升蜂窝板的换热效率，而交错式与螺旋式两种流道形式的传热与阻力性能较为接近。     

泡沫金属换热器内流动与换热性能的研究进展

基于泡沫金属三维结构的复杂性,从理论分析、实验研究和数值模拟三个方面论述了近年来泡沫金属换热器内流动与换热性能的研究进展。基于多孔介质的流体动力学和传热传质理论,简述了提高泡沫金属换热器换热性能的研究进展、阻力特性和传热特性及其对换热器换热性能的影响,并结合泡沫金属模型,分析了泡沫金属强化换热的机理及其对流动和换热性能的影响,提出精细化处理泡沫金属的微孔尺寸和完善泡沫金属模型,研究了泡沫金属用于换热器方面的发展趋势。     

凹陷阵列印刷电路板式换热器里超临界甲烷换热和流动特性模拟研究

为了强化液化甲烷在印刷电路板式微通道换热器中的换热能力,提出了一种凹陷阵列的微小通道换热器整体性能提高的被动式强化技术并进行了数值模拟验证。研究了流体温度范围125—265 K范围内的超临界甲烷在凹陷阵列结构微通道内的换热和流动特性,考察了凹陷阵列微通道和光滑微通道下,流体温度、质量流量、雷诺数和进口压力对传热系数、努塞尔数、摩擦因子和综合效益系数(PEC)的影响。此外,通过凹陷结构的局部流动特性分析强化换热机理,数值模拟结果表明相较于光滑微通道,凹陷阵列微通道的换热特性得到大大强化,且随雷诺数(由质量流量或者流体温度改变)的增大而增强,而摩擦因子只是有较弱的劣化。     

翅片管换热器与微通道换热器腐蚀对比分析

通过对铜铝翅片管换热器和微通道换热器进行腐蚀研究,本文对比分析了腐蚀对换热器形貌、传热、空气流通阻力方面的影响。结果表明,经过1 250 h腐蚀试验后,翅片管换热器主体完好,但边板处的翅片腐蚀严重并出现脱落,而微通道换热器局部区域的翅片脱离扁管,出现翅片粉化现象。腐蚀引起换热器的传热性能下降,720 h时,两种换热器的换热量衰减程度接近;1 250 h时,微通道换热量衰减程度明显大于翅片管换热器。腐蚀引起换热器的空气流通阻力增大,微通道换热器的风阻增幅明显高于翅片管换热器。     

Heat transfer and pressure drop characteristics of nanofluids in a plate heat exchanger

In this paper, the heat transfer characteristics and pressure drop of the ZnO and Al2O3 nanofluids in a plate heat exchanger were studied. The experimental conditions were 100-500 Reynolds number and the respective volumetric flow rates. The working temperature of the heat exchanger was within 20-40 degrees C. The measured thermophysical properties, such as thermal conductivity and kinematic viscosity, were applied to the calculation of the convective heat transfer coefficient of the plate heat exchanger employing the ZnO and Al2O3 nanofluids made through a two-step method. According to the Reynolds number, the overall heat transfer coefficient for 6 vol% Al2O3 increased to 30% because at the given viscosity and density of the nanofluids, they did not have the same flow rates. At a given volumetric flow rate, however, the performance did not improve. After the nanofluids were placed in the plate heat exchanger, the experimental results pertaining to nanofluid efficiency seemed inauspicious.     

Impact of plate design on the performance of welded type plate heat exchangers for sorption cycles

Numerical and experimental analysis was carried out to examine the heat transfer and pressure drop characteristics of welded type plate heat exchangers for absorption application using Computational Fluid Dynamics (CFD) technique. The simulation results based on CFD are compared with experimental results. A commercial CFD software package (FLUENT) has been used to predict the characteristics of heat transfer, pressure drop and flow distribution within the plate heat exchangers. In this paper, a welded plate heat exchanger with a plate of chevron embossing type was tested by controlling mass flow rate, solution concentration, and inlet/outlet temperatures. The working fluid is H₂O/LiBr solution with the LiBr concentration of 54–62% in mass. The numerical simulation examines the internal flow patterns, temperature distribution and the pressure distribution within the channel of the plate heat exchanger. Three plates of embossing types; chevron embossing, elliptic and round, are proposed and simulated in this paper. The simulation results show reasonably good agreement with the experimental results. Also, the numerical results show that the plate with the elliptical shape gives better performance than the plate of the chevron shape from the viewpoints of heat transfer and pressure drop.     

板式蒸发冷却空冷器的阻力和传热特性实验研究

通过改变风量、水量和增湿供水量,对板式蒸发空冷器阻力及传热特性进行实验研究,得到干工况下空气侧和热水侧的阻力及对流换热系数关联式.实验结果表明,增湿工况下,空气侧阻力几乎不受影响,换热系数随增湿供水量增加而增大,约为干工况时的6倍.     

Heat transfer analysis of fin-and-tube heat exchangers with flat and louvered fin geometries

This paper analyzes the fluid flow and heat exchange on the air side of a multi-row fin-and-tube heat exchanger. A comparison is given between fin-and-tube heat exchanger characteristics with flat and louvered fins in a wider range of operating conditions defined by Reynolds number (based on fin spacing and air frontal velocities). The detailed representation of calculated data for the louvered heat exchanger shows significantly better heat transfer characteristics and a slightly higher pressure drop. The CFD procedure was validated by comparing the numerical simulation results with the experimental results showing the minimal average Nusselt number deviation and an almost perfectly corresponding pressure drop.     

多元平行流冷凝器传热流动性能研究

平行流冷凝器空气侧采用间断型扩展表面的波纹型百叶窗翅片,制冷剂侧采用小水力直径的非圆截面微通道多孔铝制扁管,选用适合于该微尺度强化换热结构的传热和压降关联式,对某规格的平行流冷凝器建立数学模型并在一定工况下进行数值模拟.结果分析表明,制冷剂在非圆截面微通道内的冷凝过程中,表面张力对表面传热系数的强化效果明显;通过改变流程数和各流程管数来改变冷凝过程中的流通截面而达到调整流速的作用,从而可以保持较高的冷凝换热系数和较低的流动压降,与常规换热器相比具有显著的优越性.     

Pressure drop and heat transfer characteristics of clathrate hydrate slurry in a plate heat exchanger

Pressure drop and heat transfer characteristics of 0-17.5 vol% tetrabutylammonium bromide (TBAB) clathrate hydrate slurry (CHS) as a secondary refrigerant flowing through a plate heat exchanger (PHE) were investigated in the present research. It was found that the pressure drop of TBAB CHS was about 3.0-50.0 kPa which was about 1.2-2 times of that of the chilled water at the flow rate of 2.5-13.0 L min⁻¹. The pressure drop increased with the increase of the volume fraction. Variation of the pressure drop with the modified Reynolds number was discussed and compared with that of the ice slurry. Flow friction factor correlation and local heat transfer correlation for TBAB CHS flowing through PHE were both proposed based on the experimental data. In addition, the influential factors, such as the inlet water temperature and inlet CHS volume fraction, on the overall heat transfer coefficient were discussed.     

板式蒸发器换热性能的数值模拟1：数学模型

采用分布参数法对波纹型多通道单流程板式蒸发器建立数学模型，通过计算局部蒸发换热系数和摩擦压降可以简化板式蒸发器内复杂三维流动的换热关系。总结了文献已有的各种换热和压降关联式，并添加到模型控制方程组中。基于此模型，可对目前应用较广的R134a和R410A制冷剂的板式蒸发器在小换热温差下的换热性能进行研究。     

射流冲击凸台时传热与流动的数值模拟研究

针对冲击射流应用中经常会遇到不平整表面的情况(如各种电子元件),采用RNG的κ-ε模型,对处在半封闭板内凸台的冲击传热和流动进行了数值模拟.研究了冲击凸台表面、侧面及平板上的传热特性,分析了冲击高度H/D、流动Re数等参数对传热和流动的影响.结果表明,冲击高度较小时凸台上表面的传热Nu数沿径向的分布有一个先抑后扬的特征,在凸台边缘处达到最大.数值模拟还较好地给出了射流冲击凸台后流体分离、再次冲击平板等复杂的流动特征.     

旋转射流冲击凸台换热特性的数值模拟

运用重整化(RNG)的κ-ε模型对半封闭板内带旋流的射流冲击凸台的传热及流动进行仿真,研究了旋转射流冲击凸台时的流场特性以及凸台表面、侧壁和平板上的传热特性.分析了旋流强度(旋转数)、流动Re数、冲击高度H/D对传热与流动的影响.结果表明,不同Re数下旋流会削弱驻点处的冲击作用,从而使得驻点处的传热Nu数减小.在雷诺数Re=25 000时,在旋转数0相似文献   

Numerical comparison for thermo-hydraulic performance of pin fin heat sink with micro channel pin fin heat sink

Cooling of miniature size electronic components has become a challenge for designer in the development of integrated circuits. Micro pin fin heat sink and Micro channel pin fin heat sink are thermal management techniques for effective cooling. The paper presents comparison of fluid flow and heat transfer characteristics for micro pin fin heat sink and micro channel pin fin heat sink with unfinned micro channel heat sink. A three-dimensional heat sink with water as coolant subjected to constant heat flux 10 W/cm², for Reynolds number ranging between 100 and 900 was considered for the study. Extended surfaces of different shapes namely, square and circular with staggered arrangement was considered for both micro pin fin heat sink and micro channel pin fin heat sink. Two non-dimensional parameters namely Nusselt number and thermal performance index were employed to access the performance of heat sink. Results indicate that the microchannel pin fin heat sink has highest nusselt number and friction factor over the whole Reynolds number range. Results also revealed that formation of secondary vortices enhances heat transfer in micro channel heat sink with square pin fin compared to micro channel heat sink with circular pin fin. However, pin fin heat sink has better thermal performance index compared to Micro channel pin fin heat sink and is more preferable when heat dissipation is compared with pressure drop penalty. The Governing equations for fluid and solid domain were solved using FLUENT to study flow and heat transfer characteristics.