Airside fin efficiencies for finned-tube heat exchangers with forced convection

The heat transfer and mass transfer fin efficiencies were analyzed numerically to show that popular models for heat transfer fin efficiency for circular fins are not always reasonable.The numerical results show that the effective heat transfer area of a circular fin increases several times faster than that of a straight fin for the same tube radius.Then,a simple but accurate heat transfer fin efficiency model was developed and verified by numerical results for a wide range of fin designs.This model predicts...     

A pin fin microheat sink for cooling macroscale conformal surfacesunder the influence of thrust and frictional forces

Conventional microheat sink design primarily focuses on the use of continuous fin arrays to optimally dissipate thermal energy from electronic components. By contrast, this paper experimentally measures the thermal and structural performance of two micro pin fin heat sinks designed for use in load bearing applications such as mechanical seals and thrust bearings. One pin fin array is of low porosity, which is more optimal for load bearing capacity, and the other is of high porosity, which is more optimal for heat dissipation. By using these two extreme cases, the thermal-structural tradeoff found in load bearing microheat sinks is demonstrated. The heat sinks are constructed of nickel, electrodeposited onto a stainless steel thrust ring using a modified LIGA technique. Under forced air cooling, the thermal performance of each is compared to a simple model based on a combination of macroscale pin fin heat sink results and classical correlations for fins in cross flow. The low porosity design is also tested under the application of a 44.5 N thrust load at 2500 rpm and found to be structurally sound. Experimental temperature profiles demonstrate a substantial benefit of the microheat sink in cooling the load bearing surface     

一种相控阵天线强迫风冷热设计方法

阵面温度控制是相控阵天线结构设计的关键技术之一。文中针对某相控阵天线的热设计要求,设计了一种用于相控阵天线散热的强迫风冷系统,并采用数值分析方法,对该系统作用下的相控阵天线阵面热性能进行了分析。对不同流道参数、散热器参数和冷却气体流速下的阵面温度和流体压力进行了仿真。仿真结果表明：冷却气体温度和速度对散热效果影响显著,增加散热片的肋片数量和高度能够提高散热性能。以仿真结果为依据,对相控阵天线的结构参数进行了优选。进行了对比实验,验证了仿真计算的有效性。     

压电风扇与散热器组合系统的散热性能及其改进

为提高散热器的散热性能,将压电风扇分别与直肋和针肋式散热器组合进行散热,利用FLUENT软件仿真其散热流场并计算其协同角,分析2种散热器的散热性能特点。考虑压电风扇的振动特性,将直肋式散热器的肋片改为扇形布置,并根据仿真结果进一步将该散热器扇形肋片的后端改为针肋,设计新型散热器。根据散热器温度和协同角分布对散热器的散热性能进行评价分析,结果表明：自然散热时,针肋散热器的散热性能最好,且协同角相对较小;当压电风扇工作时,新型散热器散热性能最好,可比原直肋散热器组合温度降低4 K,比原针肋散热器组合温度降低2 K。新型散热器仅通过改变散热器的肋片布置即可明显改善散热器的散热性能。     

CFD simulation and optimization of ICEs exhaust heat recovery using different coolants and fin dimensions in heat exchanger

In this paper, finned type heat exchangers with different fin dimensions in the exhaust of a gasoline engine are modeled numerically for improving the exhaust energy recovery. RNG k-ε viscous model is used and the results are compared with available experimental data presented by Lee and Bae (Int J Therm Sci 47:468–478, 2008) where a good agreement is observed. Also, the effect of fin numbers, fin length and three water-based nanofluid coolants (TiO₂, Fe₂O₃ and CuO) on the heat recovery efficiency are investigated in different engine loads. As a main outcome, results show that increasing the fin numbers and using TiO₂-water as cold fluid are the most effective methods for heat recover. Furthermore, an optimization analysis is performed to find the best fins dimensions using response surface methodology.     

Using bulk micromachined structures to enhance pool boiling heat transfer

This paper presents the important results of enhancing the boiling heat transfer of the pressurized water reactors (PWRs) by using LIGA or LIGA-like techniques to add microstructures on the surface of heater elements. The heater elements were made of 10 mm × 80 mm silicon strips with different in-line square micro-pin-fin configurations of 200 μm fin width, 35 μm fin height, and different inter-fin spacing values of 200, 400, 600, 800, 1000 μm and infinity. The experiments were conducted in de-ionized water at the atmospheric pressure. The input power, heater temperature, steam generation rate and video images of boiling phenomena were continuously recorded. Their relationships was studied and used to evaluate the total boiling heat transfer performance. The optimized microstructures can then be mass-fabricated on PWR tubes by using LIGA or LIGA-like technology. The experimental results suggest that by adding micro-sized in-line pin-fin arrays on heater surface and modifying heater surface morphology, the boiling process can be greatly enhanced through the improvements of vapor nucleation and vapor evolution processes at heater surface, which yields a low wall superheat and achieves a higher boiling heat transfer efficiency. The video images showed that the bubble nucleation sites are located immediately on top of each micro-pin fins. At current experimental setup, the 200 μm-spacing heater has the highest steam generation efficiency.     

核电厂最终热阱冷却塔内填料装置的抗震分析和评价

本文采用有限元分析方法对核电厂最终热阱冷却塔内的填料装置结构进行了自重载荷下的静态分析及地震载荷下的动态反应分析,介绍了填料装置的分析方法,各种工况下的载荷组合,建模过程中对模型进行合理简化的方法和评定准则,并给出了按照ASME规范对计算结果进行应力评定的方法。     

整车环境下加装散热翅片对轮毂电机散热性能的影响

为提高电动车轮毂电机散热性能,在整车环境下采用CFD数值计算方法,对不同车速下轮毂电机的散热性能进行数值计算并分析;研究加装散热翅片对轮毂电机散热性能的影响,得到轮毂电机的温度场、空气质量流量、外流场和表面对流传热系数.结果表明：电机的最高温度位于定子上,外表面最高温度区域分布在电机的侧面外壳上;在电机侧面外壳上加装散热翅片可以对电机起到较好的降温效果,当翅片长度方向与电机轴中心线成30°夹角时,更加有利于电机的散热.     

Computational fluid dynamics for effects of coolants on on-chip cooling capability with carbon nanotube micro-fin architectures

Carbon nanotubes (CNTs) have shown a broad promising application in high mechanical strength and electronic structure. In this work, the effects of coolants on heat transfer capability of on-chip cooling with CNTs Micro-fin Architectures was studied, and the two-dimensional computational fluid dynamics (CFD) simulations have been done for a series of material parameters of coolants in this paper. The influences of thermal conductivity, density, specific heat and viscosity on cooling have been obtained in the case studies. The results demonstrate that pressure drop between the inlet and outlet of the cooling device is dependent on coolant’s density and viscosity. Consequently, it will be necessary to find out a good balance between heat transfer capability and pressure drop. The simulation results also indicate that the heat sink capability will be better if there are more fin rows in the microchannel.     

Laminar convection in the annulus of a double-pipe with triangular fins

A steady and laminar convective flow has been numerically simulated in the fully-developed annular region of a finned double-pipe subjected to the constant heat flux boundary condition imposed at the inner-pipe wall. Finite element method has been employed in this study. Friction factor and Nusselt number have been studied as flow characteristics against variations in the ratio of radii of the inner and the outer pipes, the fin height, the fin half angle and the number of fins. The results show significant enhancement in the heat transfer rate in both the cases when sufficient pumping power is available and when it is not. The minimum and maximum increase in the product of friction factor and Reynolds number relative to the finless geometry is more than one time and more than 40 times respectively while gain in the relative value of Nusselt number lies in the range 1–177. This provides an evidence of more than four times enhancement in the heat transfer coefficient relative to that in the pressure loss as a result of extended fin surfaces.     

A microchannel heat exchanger design for microelectronics cooling correlating the heat transfer rate in terms of Brinkman number

Microchannel heat exchangers are a well known device in the application of microelectronics cooling. In this paper, liquid microchannel heat exchangers were designed and investigated with varying channel width in order to find the maximum cooling efficiency when combined with pumping performance. A recently developed correlation of heat transfer rate in terms of Nusselt number and Brinkman number was adopted to predict cooling efficiency of the microchannel heat exchanger and was compared with the experimental results. Conventional heat transfer theories and numerical commercial code were also used to predict the cooling efficiency. The measured minimum thermal resistance of the microchannel heat exchanger showed a good agreement with the prediction from the new correlation, whereas calculation results from conventional theories and numerical code showed large divergence. It can be seen that the microchannel heat exchanger can be optimized when combined with pumping performance. In addition, the new correlation of heat transfer rate in terms of Brinkman number can be quite a useful tool in design of microchannel heat exchanger.     

Experimental study of heat sink performance using copper foams fabricated by electroforming

In this study, performance of heat sinks using the copper foams as heat-sinking material is investigated experimentally. The copper foam is fabricated by electroforming technique using polymer foam with pre-coated silver film as the precursors. The manufactured copper foams have the porosity, pore density (pore per inch, PPI), permeability and inertial coefficient in the ranges of 0.5–0.8, 10–40, 0.6–2 × 10⁻⁹ m² and 1.5–3, respectively. Besides the copper-foam heat sink, performances of single-channel, plate-fin and pin-fin heat sinks are also investigated and compared with copper-foam heat sinks. The experimentally measured results show that the thermal resistances of copper-foam heat sinks are better than the single-channel, plate-fin and pin-fin heat sinks because of special flow features inside the porous media, enlarged heat-transfer area and enhanced heat transfer coefficient. Detail comparisons between the results of copper-foam heat sinks indicate that the thermal resistance of copper-foam heat sink decreases with the decrease in porosity and increase in pore density. The pressure drop crossing the copper-foam heat sink increases with the increase in pore density and decrease in porosity.     

Microelectronic chip cooling: an experimental assessment of a liquid-passing heat sink,a microchannel heat rejection module,and a microchannel-based recirculating-liquid cooling system

Results of heat transfer testing of heat absorption modules (HAM), heat rejection modules (HRM), and a recirculating-liquid cooling system are reported. Low-profile, Cu-based, microchannel heat exchangers (MHEs) were fabricated and used as the HAM as well as components for assembly of a microchannel HRM. Detailed experimental assessment of two different liquid-passing HRMs and a microchannel-based recirculating-liquid cooling system was carried out, and benchmarked against all-solid devices of the same geometric dimensions. Incorporating microchannel liquid flow through each fin, the device-level heat transfer performance of the microchannel HRM was improved by up to ~50%. Detailed testing of a microchannel-based recirculating-liquid cooling system indicate that low-profile Cu MHEs are highly effective in heat flux removal while having a small area/volume footprint, and that enhancing the HRM performance is critical to boosting the overall performance of such recirculating-liquid cooling systems.     

Heat transfer enhancement using flow-induced vibration of a microfin array

Advanced computers are facing thermal engineering challenges from both high heat generation due to rapid performance improvement and the reduction of an available heat removal surface due to large packaging density. Efficient cooling technology is desired to provide reliable operation of microelectronic devices. This paper investigates the feasibility of heat transfer enhancement in laminar flow using the flow-induced vibration of a microfin array. The microfins are initially bent due to the residual stress difference. In order to characterize the dynamics of the microfin flow-induced vibration, a microfin sensor is fabricated. Increase in air velocity provides larger vibrating deflection, while the vibrating frequency of the microfin is independent of the air velocity. The thermal resistances are measured to evaluate the thermal performance of the microfin heat sink and compared with those of a plain-wall heat sink. For a fluid velocity of 4.4 m/s, the thermal resistance of the microfin array heat sink is measured to be 4.45°C/W and that of the plain-wall heat sink to be 4.69°C/W, which indicates a 5.5% cooling enhancement. At a flow velocity of 5.5 m/s, the thermal resistance of the microfin array heat sink is decreased by 11.5%. From the experimental investigations, it is concluded that the vibrating deflection plays a key role in enhancing the heat transfer rate.     

Numerical analysis of heat transfer in a manifold microchannel heat sink with high efficient copper heat spreader

A manifold microchannel heat sink integrated with a high efficient copper heat spreader is presented. A series analysis of three-dimensional fluid flow and heat transfer performance in this mirochannel heat sink and conventional structure are performed by CFX commercial software package. The temperature difference along the flow direction in the new microchannel heat sink is less than that of the conventional microchannel heat sink due to effect of the transverse channel arrays. The maximum heat flux input of the new microchannel heat sink increases 75% more than the conventional structure with the flow rate of 1 m/s. The new design has better heat transfer characteristics than conventional one for the full range of flow rates considered.     

高热流微冷却器的换热性能研究

对以水为换热介质的微通道冷却器对模拟发热电子芯片进行冷却的换热性能进行了实验研究.通过测量流体的流量、进出口温度、发热片表面热流密度,获得了不同几何结构微通道冷却器在不同加热功率、不同Re数条件下的换热特性和冷却效果.结果表明,微通道冷却器可以有效地对表面热流密度高达5.34×105 W/m2的发热电子芯片进行冷却;微通道冷却器的换热性能随Re数的增大而提高,所提高的幅度随加热功率的增大而增大;微通道的几何结构对换热性能有显著影响,平均Nu数随微通道的宽深比增大而增大.     

Model based control of compact heat exchangers independent of the heat transfer behavior

Compact heat exchangers have a wide range of applications where standard control strategies typically rely on the knowledge of the heat transfer model and thus on the overall heat transfer coefficient. In particular for compact plate heat exchangers, the overall heat transfer coefficient strongly varies with the manufacturer's plate design and has to be identified by means of extensive measurements. This paper presents an alternative approach for the control of compact heat exchangers which can be implemented without the knowledge of the heat transfer behavior and is robust against changes in the coolant supply system. For this, a model based control strategy is presented which relies on the total thermal energy stored in the fluids of the heat exchanger as control variable instead of the outlet temperature. Furthermore, two methods are developed in order to estimate the total thermal energy, one based on a Kalman Filter and the other one on quasi-static considerations. Finally, the proposed control and estimation strategies are validated by means of simulation and measurement results on an industrial plate heat exchanger.     

采用多齿肋片的电机控制器散热器设计分析

电机控制器作为纯电动汽车的控制核心,其散热性能直接影响到驱动系统的可靠性。以某MOS多管并联的电机控制器样机为研究对象,将原设计的光滑肋片替换为多齿肋片结构,以MOS管芯片温升和肋片散热器重量为评价指标,对原散热器结构进行改进设计,并进行CFD数值分析。结果表明,相对于原设计的光滑肋片,多齿肋片结构增加了对流散热的表面积和换热系数,使得肋片的散热能力得到了提升。通过改变肋片数量、小齿的几何尺寸及位置分布,在不高于原设计的芯片温升的前提下,最优设计方案的肋片散热器重量轻化了6.41%。     

Simulation of a high-power LED lamp for the evaluation and design of heat dissipation mechanisms

High-power LED lamps have been under intense development in recent years. However, issues related to heat dissipation on the LED chip continue to plague research efforts. Heat generation increases with the power of the LED chip and heat accumulation is exacerbated by the plastic casinge of the lamp. Accumulated heat can seriously shorten the lifespan of an LED device. Consequently, manufacturers are constantly seeking ways to improve heat dissipation via heat transfer mechanisms. Little analysis has been performed on coupling the fluid field and heat dissipation inside LED lamps. Using FLUENT software, this study developed a simulation method for LED lamps in order to investigate thermal and fluid fields inside a lamp. The simulation results of an 8 W LED lamp predicted a chip temperature of 75.1 °C and maximum air velocity of 97.3 mm/s within the lamp with two sets of air circulation. The proposed model facilitates new fin designs and the determination of the optimal inner-shell thickness with the proposed design of a LED lamp having 36 fins and an inner-shell thickness of 1 mm for increased heat dissipation.     

Estimation of critical dimensions for a trapezoidal-shaped steel fin using hybrid differential evolution algorithm

This paper deals with the inverse prediction of parameters in a trapezoidal fin with temperature-dependent thermal conductivity and heat transfer coefficient. Three critical dimensions along with the relevant heat transfer coefficient at the fin base have been simultaneously predicted for satisfying a given temperature distribution on the surface of the trapezoidal fin. The inverse problem is solved by a hybrid differential evolution-nonlinear programming (DE-NLP) optimization method. For a given fin material which is considered to be stainless steel, it is found from the present study that many feasible dimensions exist which satisfy a given temperature distribution, thereby providing flexibility in selecting any dimensions from the available alternatives by appropriately regulating the base heat transfer coefficient. A very good estimation of the unknown parameters has been obtained even for temperature distribution involving random measurement errors which is confirmed by the comparisons of the reconstructed distributions. It is concluded that for a given fin material, the hybrid DE-NLP algorithm satisfactorily estimates feasible dimensions of a trapezoidal fin even with random measurement error of 11 %.