百叶窗板翅式换热器换热与阻力性能数值模拟研究

为了解决百叶窗板翅式换热器的内部性能优化问题,通过对层流稳态下换热器燃气侧的典型流动换热单元进行建模及流动换热分析,得到了单元体内部速度、流线及温度的分布特性,并通过对换热系数、科尔本传热因子、进出口单位压降、范宁摩擦系数的比较,获得了不同燃气入口速度下翅片间距及翅片角度对换热器换热性能及流动阻力的影响。结果表明:在百叶窗翅片角度及其他尺寸参数不变时,当百叶窗间距为0. 7 mm时其换热性能最优,阻力随间距增大而减小;在翅片间距等参数不变而角度变化时,换热性能与阻力均随角度增大而增大,当百叶窗角度从15°增加至30°时,换热性能的增加幅度较为明显。     

百叶窗翅片管换热器空气侧传热和流动特性数值模拟

采用数值模拟方法对百叶窗翅片管换热器空气侧传热和流动特性进行研究,分析管排数、开窗角度和翅片间距对百叶窗翅片管换热器空气侧性能的影响.结果 表明:空气侧传热系数随管排数增多而降低,最大降幅约12.5％,压降随管排数增多而增大;低雷诺数下百叶窗角度为20°时换热器具有较好的综合性能,较大雷诺数下25°为最佳百叶窗角度;随...     

低气压下翅片管换热器空气侧换热特性的实验研究

为研究低气压环境下翅片管换热器空气侧的换热特性,对不同气压环境下空气侧流速和翅片间距对平翅片管换热器空气侧换热特性的影响进行了实验分析。实验环境气压范围为40～100 kPa,换热器迎面风速为1.0～3.5 m/s,翅片间距2～3 mm。研究表明:实验工况下环境气压40 kPa时空气侧传热因子仅为常压下的30.42%～46.41%;低气压环境空气侧流速和翅片间距对空气侧换热的影响趋势与常压数据基本保持一致;不改变换热器结构,环境气压的变化仅影响空气物性,而对空气的流动状态的影响不大;翅片间距影响随Re的减小和环境气压的降低而减弱,两种翅片间距模型空气侧传热因子平均差异在环境气压为100 kPa时为12.07%,40 kPa时缩小为3.00%。     

椭圆管翅式换热器空气侧传热和流动特性的数值模拟

建立了椭圆管百叶窗翅片换热器三维模型,对椭圆管翅式换热器空气侧传热和流动特性进行了数值模拟,分析管径、管排数、翅片间距对椭圆管翅式换热器空气侧传热流动的影响。结果表明:管排数为1～3时,椭圆管百叶窗翅片换热器空气侧换热系数随换热器管排数的增加而降低,最大降幅达17.1%;椭圆率为2:3的椭圆管翅式换热器综合性能最好,与同周长圆管管翅式换热器相比,换热性能提高了10.1%,降阻幅度达32.3%;随着风速的提高,翅间距对管翅式换热器换热性能及阻力影响逐渐降低。     

百叶窗结构参数对管带式散热器流动传热特性影响的研究

本文利用CFD计算软件star ccm＋,建立了管带式散热器空气侧的三维热固耦合模型,分析了不同空气流速和百叶窗结构参数对散热器流动和传热特性的影响,发现阻力损失主要集中在空气进入百叶窗的入口区域,百叶窗的前端传热效果较好,同时计算区域后半部分存在滞止区域;随着百叶窗倾角的增大,传热j因子先增后减,摩擦f因子一直增加,24°时传热j因子达到最大值;随着百叶窗厚度的增大,传热效果变差,摩擦f因子先增后减;百叶窗间距增加到一定程度,传热j因子和摩擦f因子增加缓慢,甚至减小。     

空压机内置冷却器的热力性能优化

为了提升空压机内置冷却器的热力性能,选取冷却器的最小结构单元,基于k-ε湍流模型建立百叶窗翅片流动传热的数值模型,分析百叶窗翅片结构参数对冷却器内部流动传热特性的影响。结果表明：增大百叶窗倾角、翅片厚度,气流与翅片之间的对流传热能力增强,流动阻力增加;增加百叶窗间距,冷却器传热效果增强,流动阻力减小。百叶窗倾角为29°、间距为1.6 mm、翅片厚度为0.08 mm时,翅片的综合热力性能最佳。     

基于VB和MATLAB的同心圆热管传热分析与结构优化

建立同心圆热管结构参数计算模型,运用VB和MATLAB软件,并与自编程序相结合,分析同心圆热管传热特性。研究结果表明:单根热管外壁换热系数随着翅片间距的增大而增加,但翅片间距越大,其翅片传热面积越小,翅片间距须大于相邻两翅表面间流体的流动边界厚度之和。凝结换热系数随内管径的增大而减小。经计算,模拟同心圆热管的最佳充液率为43.2%。     

汽车水散热器设计软件开发

为了降低散热器的设计成本并提高计算精度,利用PowerBuilder开发了汽车水散热器设计软件,其计算功能包括校核计算、翅片间距优化计算、翅片高度优化计算、管长优化计算及管排数优化计算。对比分析试验表明:计算结果具有较高的精度。计算分析翅片间距、开窗角度、风速及冷却液中乙二醇百分比对散热器性能的影响。研究表明:减小翅片间距及增大风速可提高换热性能;减小开窗角度可降低风侧阻力;增大乙二醇百分比可降低冷却液出口温度。     

百叶窗翅片传热与流动的三维数值模拟

本文对空气在百叶窗翅片内部流动和传热建立了三维数值计算模型.计算结果与文献所提供的实验数据进行了对比,在整个计算范围内,Re=0～1500,j和f的平均偏差分别为1.96%和10.5%.在深入揭示百叶窗翅片流动机理的基础上,进一步比较了百叶窗翅片开窗角度La和换向区长度S对其传热和流动阻力的影响,分析结果为百叶窗翅片的模具制作及其优化设计提供了依据.     

管间距对开缝翅片管换热器传热与阻力特性的影响

为了获得管间距对开缝翅片管换热器传热与阻力特性的影响规律,对5种不同翅片管换热器进行了数值模拟研究,并进行了模化试验验证。结果表明:开缝翅片管束的传热和阻力特性与翅片侧气体的Re数有关,随着Re数增大,翅片侧Nu数增大,摩擦因子f逐渐减小;纵向间距S2对开缝翅片管换热器的综合流动传热性能的影响较大。数值模拟与试验结果偏差较小,采用数值模拟方法能够比较准确地分析开缝翅片管换热器的传热与阻力特性。     

Numerical study on air-side performance of an integrated fin and micro-channel heat exchanger

A new type of aluminum heat exchanger with integrated fin and micro-channel has been proposed. The air-side heat transfer and flow characteristics of the integrated fin and micro-channel heat exchanger are systematically analyzed by a 3D numerical simulation. The effect of flow depth, fin height, fin pitch and fin thickness at different Reynolds number is evaluated by calculating Colburn factor j and Fanning friction factor f. A parametric study method is used to analyze the fin designed parameters affecting the performance of the heat exchanger. The results show that the contribution ratio of the fin geometries in descending order is flow depth, fin pitch, fin height and fin thickness. The air-side performance of the integrated fin and micro-channel heat exchanger is compared with that of the multi-louver fin micro-channel heat exchanger and the wavy fin micro-channel heat exchanger.     

百叶窗翅片的传热和阻力性能试验研究

风洞试验台上对8种不同结构参数的百叶窗翅片进行传热和流动阻力的性能试验。分析比较了翅片长度、翅片间距、翅片高度对其传热和阻力性能的影响，其中翅片长度和翅片间距对无量纲传热j因子和摩擦阻力f因子影响较大，翅片高度影响较小。同时采用3√j/f因子综合评价了8种翅片的强化传热效果。结果表明，翅片长度对强化传热影响最为显著。     

Heat transfer and pressure drop correlations for compact heat exchangers with multi-region louver fins

An experimental study on the air-side heat transfer and pressure drop characteristics for brazed aluminum heat exchangers with multi-region louver fins and flat tubes was conducted. A series of tests were conducted for heat exchangers with different numbers of louver regions at the air-side Reynolds numbers of 400–1600 based on the louver pitch. The air-side thermal performance data were analyzed by using the effectiveness-NTU method. The characteristics of the heat transfer and pressure drop for heat exchangers with different geometry parameters were presented in terms of the Colburn j factor and Fanning friction f factor as function of the Reynolds number.     

Parametric and design optimization investigation of a wavy fin and tube air heat exchanger using the T-G technique

The focus of this paper is to optimize the air-side performance of a wavy fin and tube heat exchanger at different design parameters on an individual target response using the Taguchi method. However, a statistical concept, gray relational analysis, is also studied for combined optimization, considering all target responses at a time. Based on the heat exchanger requirement, parametric study for the air-side is regarded as a more significant heat transfer and lower frictional factor. Experimental correlations were available and used for the 27 orthogonal runs. Investigation revealed the highest 47.06% fin pitch, 37.24% fin pitch, 25.46% air velocity, and 23.9% fin thickness contribution ratio for the target response of friction factor (TPF), heat transfer coefficient, and Colburn factor, respectively, with the application of the Taguchi method in a heat exchanger. GRG gives an optimum set of design parameters, A3B3C2D1E3F2G1, for wavy fin and tube of fin pitch of 6 mm, tube row number of 6, waffle height 1.8 mm, fin thickness 0.12 mm, and air velocity 5 m/s. Also, longitudinal tube pitch is 27.5 mm, and transverse tube pitch of 24.8 mm, at which TPF is maximum while the friction factor is minimal. The Colburn factor is the most significant, minor friction factor, and the heat transfer coefficient and TPF are the most considerable in GRG. Hence, an improved heat transfer performance design of a wavy fin and tube heat exchanger is achieved using the above techniques.     

Numerical investigation of fluid flow and heat transfer over louvered fins in compact heat exchanger

Numerical investigation of fluid flow and heat transfer characteristics over louvered fins and flat tube in compact heat exchangers is presented in this study. Three-dimensional simulations of single and double row tubes with louvered fins have been conducted. Simulations are performed for different geometries with varying louver pitch, louver angle, fin pitch and tube pitch and for different Reynolds number. Conjugate heat transfer and conduction through the fins are considered. The air-side performance of heat exchanger is evaluated by calculating Stanton number and friction factor. The results are compared with experiment and a good agreement is observed. The local Nusselt number variation along the top surface of the louver is calculated and effects of geometrical parameters on the average heat transfer coefficient is computed. Design curves are obtained which can used to predict the heat transfer and the pressure drop for a given louver geometry.     

Numerical Investigation of the Air-Side Thermal Hydraulic Performance of a Louvered-Fin and Flat-Tube Heat Exchanger at Low Reynolds Numbers

In this study, the air-side heat transfer and fluid flow characteristics of a louvered-fin and flat-tube type heat exchanger used in the household refrigerators were investigated numerically. Louver angles of 20°, 24°, 28°, and 32° and fin pitches of 1.50, 2.00, and 2.50 mm were tested. To represent domestic refrigeration systems, the simulations were conducted for low Reynolds numbers, between 223 and 573. The results were evaluated using the volume goodness factor for the air side. The best performance was obtained with louver angle of 20° and fin pitch of 1.50 mm at Reynolds number of 229 over the investigated cases. It was demonstrated that the Colburn j-factor, friction factor, Stanton number, and volume goodness factor did not change linearly with respect to the parameters considered.     

Three-dimensional performance analysis of plain fin tube heat exchangers in transitional regime

Three-dimensional CFD simulations are carried out to investigate heat transfer and fluid flow characteristics of a four-row plain fin-and-tube heat exchanger using the Commercial Computational Fluid Dynamics Code ANSYS CFX 12.0. Heat transfer and pressure drop characteristics of the heat exchanger are investigated for Reynolds numbers ranging from 400 to 2000. Fluid flow and heat transfer are simulated and results compared using both laminar and turbulent flow models (k-ω) with steady and incompressible fluid flow. Model validation is carried out by comparing the simulated case friction factor (f) and Colburn factor (j) with the experimental data of Wang et al. [1]. Reasonable agreement is found between the simulations and experimental data. In this study the effect of geometrical parameters such as fin pitch, longitudinal pitch and transverse pitch of tube spacing are studied. Results are presented in the form of friction factor (f) and Colburn factor (j). For both laminar and transitional flow conditions heat transfer and friction factor decrease with the increase of longitudinal and transverse pitches of tube spacing whereas they increase with fin pitches for both in-line and staggered configurations. Efficiency index increases with the increase of longitudinal and transverse pitches of tube spacing but decreases with increase of fin pitches. For a particular Reynolds number, the efficiency index is higher in in-line arrangement than the staggered case.     

Effect of inclination on the air-side performance of a brazed aluminum heat exchanger under dry and wet conditions

This study presents the effect of an inclination angle from the vertical position on the air-side thermal hydraulic performance for a multi-louvered fin and flat tube heat exchanger. For a heat exchanger with a louver angle of 27°, fin pitch of 1.4 mm and flow depth of 20 mm, a series of tests for dry and wet surface conditions were conducted for the air-side Reynolds numbers of 100–300. The inclination angles from the vertical position were 0°, ±30°, ±45°, and ±60° clockwise. The heat transfer performance for both dry and wet conditions was neither influenced significantly by the inclination angle (−60°<θ<60°), nor by the presence or absence of an upstream duct, while the pressure drops increased consistently with the inclination angle. The heat transfer coefficients and the pressure drops for the wet conditions revealed the importance of the role of condensate drainage.     

Thermal-hydraulic performance of novel louvered fin using flat tube cross-flow heat exchanger

Experimental studies were conducted to investigate the air-side heat transfer and pressure drop characteristics of a novel louvered fins and flat tube heat exchangers. A series of tests were conducted for 9 heat exchangers with different fin space and fin length, at a constant tube-side water flow rate of 2.8 m³/h. The air side thermal performance data were analyzed using the effectiveness-NTU method. Results were presented as plot of Colburn j factor and friction factor f against the Reynolds number in the range of 500–6500. The characteristics of the heat transfer and pressure drop of different fin space and fin length were analyzed and compared. In addition, the curves of the heat transfer coefficients vs. pumping power per unit heat transfer area were plotted. Finally, the area optimization factor was used to evaluate the thermal hydraulic performance of the louvered fins with differential geometries. The results showed that the j and f factors increase with the decrease of the fin space and fin length, and the fin space has more obvious effect on the thermal hydraulic characteristics of the novel louvered fins.