基于表面及迎风面改性的锯齿翅片强化传热研究

为了在提高锯齿型翅片散热器换热性能的同时尽量控制压降损失的增大，本文采用数值模拟的方法对锯齿型翅片性能进行研究，分析了不同翅片表面、迎风面结构及尺寸参数对传热Nu、流动压降损失Δp以及综合性能η的影响规律。结果表明：无论翅片表面设置何种形状凹槽和凸起对传热的影响差异较小，但圆形凹槽和凸起对压降损失的增加最少，综合性能最优。在翅片表面设置圆形凹槽和凸起的基础上继续将翅片两端迎风面改为圆形，可使传热提高的同时减小压降损失，综合性能最多提高12.2%。圆形凹槽和凸起尺寸R=0.15 mm时，传热和压降损失的平衡达到最佳，与传统锯齿型翅片相比，平均压降损失基本不变，传热和综合性能平均提高均为8.7%。     

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...     

百叶窗翅片的传热与阻力性能试验关联式

在风洞试验台上对20种不同结构参数的扁管百叶窗翅片进行了传热和流动阻力性能试验,分析比较了翅片间距和翅片高度对其表面对流换热系数和空气阻力性能的影响。同时通过对20种不同结构参数百叶窗翅片的336个试验数据点进行多元回归和F显著性检验,获得了j因子和f因子的经验关联式。在ReLp=200～3000范围内,j和f因子经验关联式拟合的最大误差范围分别为±10％和±12％,绝对平均偏差分别为4．1％和5．6％。     

冷凝器翅片表面流体流动及换热过程的三维数值模拟

本文应用CFD软件FLUENT对冷凝器常用的平翅片和波纹翅片表面的流体流动及换热过程进行了数值模拟,获得了翅片表面流体的流场图、温度场图、压力场图以及翅片换热量、平均表面换热系数等重要数据,并通过这些图形、数据对两种翅片的流体流动特性和传热性能进行了比较.     

锯齿型翅片内不同温区氦气流动与传热性能对比及节距对翅片性能影响的研究

为分析板翅式换热器在低温工况下的流动换热性能与常温工况下的差异和翅片节距对其性能影响,建立氦气在锯齿翅片通道内流动与传热的数值模型,开展数值模拟分析。结果表明：低温氦气在锯齿型翅片通道内的传热性能优于常温氦气。在氦气入口温度为20 K时,j因子比300 K时提升1.1%～55.9%,比77 K时提升0.41%～13.01%;在氦气入口温度为77 K时,j因子比300 K时提升0.53%～38.47%。低温氦气在锯齿型翅片通道内的流动性能比常温氦气差。在氦气入口温度为20 K时,f因子比300 K时高16.84%～28.87%,比77 K时高3.98%～23.19%。翅片节距大小在不同温区下对翅片流动与传热性能均有显著影响。在不同温区下,j因子随着翅片节距增大而减小,f因子随着翅片节距减小而增大。低雷诺数时,JF因子随着翅片节距减小而增大,而高雷诺数时则出现相反的趋势。     

换热器翅片表面空气流动热力过程的三维数值模拟

本文利用软件FLUENT模拟了发生在双排(叉排)波纹翅片表面空气流动和传热过程,获得了有代表性的翅片表面温度分布、换热系数等值线图,表面气流速度矢量图和相关计算结果.分析了翅片入口风速对翅片表面的温度、气流流动、换热系数、换热量的影响.     

多孔式翅片传热与流阻特性分析

采用CFD数值模拟技术,研究了多孔式翅片传热与流阻特性,重点分析了不同孔口因素对多孔式翅片传热与流阻的影响.研究结果表明:随着孔隙率增加,多孔式翅片流阻增大,但其传热并未明显提升.同一孔隙率下,翅片传热与流阻随孔径减少而提升.开孔方式呈错列布置的流阻与传热性能高于孔口呈并行布置的情况.开孔结构对多孔式翅片传热性能影响较...     

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。     

计算机CPU热管散热器换热性能研究

电子计算机的集成化发展对CPU散热器传热性能提出了新的要求,散热器表面最高温度和表面均温性是保证CPU正常运行的重要参数。本文运用ANSYS软件对CPU热管式散热器和普通翅片散热器进行计算,对二者稳态温度场分布和不同功率下散热器中心点温度变化进行了分析比较,计算结果表明,在稳定状态时,热管式散热器比普通翅片散热器具有更好的热传导性能和表面均温性;在CPU高功率工作（50W）时,普通翅片散热器无法满足换热要求,而热管式散热器仍可达到良好换热效果。搭建实验台对热管式散热器表面温度进行了测定,实验测试数据与模拟计算数据基本吻合,证明了数值模型的正确性和可行性。本研究对于计算机CPU散热器传热性能分析及其优化设计具有一定指导意义。     

新型无接触热阻空调换热器性能研究

将不同形状的波纹翅片与无接触热阻技术结合研制了波纹型无接触热阻换热器,并利用CFD仿真软件进行对比分析尖角波纹翅片和圆角波纹翅片空气侧换热性能及阻力特性,寻找较好的翅片形状。按照仿真结果生产无接触热阻尖角波纹翅片空调换热器实验样件,进行实验测试,实验结果表明:翅片表面换热系数仿真结果与实验结果较为一致,整体误差在10%以内,仿真结果能基本反映翅片表面的实际换热情况。引入强化传热指标,通过仿真结果计算可知,在不同风速下强化传热指标DEC均大于1,说明尖角波纹翅片的传热效果优于圆角波纹翅片。     

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.     

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.     

Air-side thermal hydraulic performance of multi-louvered fin aluminum heat exchangers

An experimental study on the air-side heat transfer and pressure drop characteristics for multi-louvered fin and flat tube heat exchangers has been performed. For 45 heat exchangers with different louver angles (15–29°), fin pitches (1.0, 1.2, 1.4 mm) and flow depths (16, 20, 24 mm), a series of tests were conducted for the air-side Reynolds numbers of 100–600, at a constant tube-side water flow rate of 0.32 m³/h. The inlet temperatures of the air and water for heat exchangers were 21 and 45°C, respectively. The air-side thermal performance data were analyzed using effectiveness-NTU method for cross-flow heat exchanger with both fluid unmixed conditions. The heat transfer coefficient and pressure drop data for heat exchangers with different geometrical configurations were reported in terms of Colburn j-factor and Fanning friction factor f, as functions of Reynolds number based on louver pitch. The general correlations for j and f factors are developed and compared to other correlations. The f correlation indicates that the flow depth is one of the important parameters for the pressure drop.     

Heat transfer characteristics of flat plate finned-tube heat exchangers with large fin pitch

The objective of this study is to provide experimental data that can be used in the optimal design of flat plate finned-tube heat exchangers with large fin pitch. In this study, 22 heat exchangers were tested with a variation of fin pitch, number of tube row, and tube alignment. The air-side heat transfer coefficient decreased with a reduction of the fin pitch and an increase of the number of tube row. The reduction in the heat transfer coefficient of the four-row heat exchanger coil was approximately 10% as the fin pitch decreased from 15.0 to 7.5 mm over the Reynolds number range of 500–900 that was calculated based on the tube diameter. For all fin pitches, the heat transfer coefficient decreased as the number of tube row increased from 1 to 4. The staggered tube alignment improved heat transfer performance more than 10% compared to the inline tube alignment. A heat transfer correlation was developed from the measured data for flat plate finned-tubes with large fin pitch. The correlation yielded good predictions of the measured data with mean deviations of 3.8 and 6.2% for the inline and staggered tube alignment, respectively.     

Experimental Study of Heat Transfer Enhancement in Solar Tower Receiver Using Internal Fins

The receiver is an important element in solar energy plants. The principal receiver’s tubes in power plants are devised to work under extremely severe conditions, including excessive heat fluxes. Half of the tube’s circumference is heated whilst the other half is insulated. This study aims to improve the heat transfer process and reinforce the tubes’ structure by designing a new receiver; by including longitudinal fins of triangular, circular and square shapes. The research is conducted experimentally using Reynolds numbers ranging from 28,000 to 78,000. Triangular fins have demonstrated the best improvement for heat transfer. For Reynolds number value near 43,000 Nusselt number (Nu) is higher by 3.5% and 7.5%, sequentially, compared to circular and square tube fins, but varies up to 6.5% near Re = 61000. The lowest friction factor is seen in a triangular fin receiver; where it deviates from circular fins by 4.6%, and square fin tubes by 3.2%. Adding fins makes the temperature decrease gradually, and in the case of no fins, the temperature gradient between the hot tube and water drops sharply in the planed tube by 7%.     

翅片结构对换热器结霜特性影响的实验研究

本文对空气源热泵的翅片管换热器表面霜层生长特性进行实验研究,通过红外热像仪对霜层表面温度进行测量,并用热电偶直接测量装置进行校核.分析了平片、波纹片、条缝片3种翅片类型及翅片节距对霜层厚度、结霜量、换热量的影响,并用霜层-湿空气界面条件等作为传热及传质驱动力分析了霜层生长规律.实验结果表明,波纹片及条缝片翅片换热器界面...     

Heat transfer characteristics of spirally-coiled circular fin-tube heat exchangers operating under frosting conditions

The objective of this study is to investigate the heat transfer characteristics of spirally-coiled circular fin-tube heat exchangers under frosting conditions. The heat transfer rate, pressure drop, frost thickness, and Nusselt number of the heat exchanger were measured and analyzed by varying the fin pitch and number of tube rows under frosting conditions. In addition, the Nusselt number of the spirally-coiled circular fin-tube exchanger was compared with those of flat plate fin-tube heat exchangers with discrete fins. An empirical correlation of the Nusselt number was developed as a function of the Reynolds number, dimensionless fin pitch normalized by the hydraulic diameter, i.e., D_h/F_p, Fourier number, and number of tube rows. The measured Nusselt number was consistent with the predicted value with mean and average deviations of 3.5% and 0.3%, respectively.     

圆孔和半圆孔交叉翅片管的传热与流阻性能研究

本文提出一类可用于结霜和灰尘较多场合的新型翅片——圆孔和半圆孔交叉翅片。为了考察这类翅片的性能特征,对9种不同几何参数的单排肋管式换热器样件在吸风式直流热风洞内进行了实验。这些几何参数包括圆孔、半圆孔的直径和位置。通过多元线性回归法将实验数据整理为以雷诺数和换热器几何参数为自变量的j和f关联式。结果表明开孔参数对换热性能有明显影响,而对阻力影响不显著。与平片相比,样片3的平均当量换热系数提高18.3％,节约金属耗材12％。