Numerical approach to film cooling effectiveness over a plate surface with coolant impingement

The aim of the present study is conducting the numerical approach to a combination of internal jet impingement and external film cooling over a flat plate. A multi-block three-dimensional Navier-Stokes code, CFX 4.4, with k-e turbulence model is used to simulate this complicated thermal-flow structure induced by the interaction of coolant jet and hot cross mainstream. By assuming the adiabatic wall boundary condition on the tested film-cooled plate, both the local and the spanwise-averaged adiabatic film cooling effectiveness are evaluated for comparison of the cooling performance at blowing ratios of Br=0.5, 1.0, and 1.5. Film flow data were obtained from a row of five cylindrical film cooling holes, inclined in angle of 35?and 0?in direction of streamwise and spanwise, respectively. The film cooling hole spacing between adjacent holes is 15 mm for all the holes. Before the coolant flow being injected through individual cooling hole then encountered with the mainstream, an impingement chamber containing an impingement plate with 43 holes is located on the path of coolant flow. Present study also focused on the effect of impingement spacing, 10mm, 20mm, and 30mm. Compare the results, we find the impingement jet has a significant effect on the adiabatic film cooling effectiveness. As the coolant impingement spacing is fixed, results indicated that higher blowing ratio would enhance the local and the spanwise-averaged adiabatic film cooling effectiveness. Moreover, neither uniform nor parabolic distribution of pressure distribution are observed within the coolant hole-pipe.     

Forced air cooling for CPU modules with high heat dissipation

We describe forced air cooling, based on two new concepts, for CPU modules with high heat dissipation. The first concept is a slit jet flow system, and the second is an impingement duct flow system. These systems are designed for electronic equipment with multiple circuit boards (CPU modules), on which the CPUs have high heat dissipation and the SRAMs have low heat dissipation, loaded in three dimensions and in parallel. The slit jet flow system is very simple compared with the impingement jet flow system, which has a complicated comb‐style impingement jet. The slit jet system includes an air duct with slit orifices and an axial fan upstream from the circuit boards. The impingement duct system consists of an air duct and a heat sink with a fan, which is attached to the CPU. This system also has slit orifices and an axial fan upstream or downstream from the circuit boards. For electronic equipment with each of these flow systems installed, the increases in external thermal resistance for the CPU and SRAMs were measured after stopping one of the cooling fans or the CPU's micro cooling fan. The results showed that the slit jet and impingement duct flow systems provide good cooling performance and redundancy. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(3): 226–236, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10031     

Experimental investigations of a double‐decker jet impingement/film structure's cooling effectiveness

Experiments were carried out to investigate the cooling coefficient of a laminar double‐decker jet impingement/film structure. Blowing rate M, the ratio of the jet impingement distance to the diameter of the jet hole H/D, the ratio of the distance between the jet hole and film hole to the diameter of the jet hole P/D were changed to study the rules of local cooling coefficient varying with these parameters. All the results show that a higher cooling coefficient was achieved under larger blowing rate conditions. There exists a proper range of H/D and P/D, which can result in a maximum cooling coefficient. It is verified that when H/D=0.5 and P/D=4, the maximum cooling coefficient can be achieved. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(4): 232–239, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20199     

具有新型双层壁结构的透平叶片流热耦合研究

多通道壁面射流冷却结构是一种新型的燃气透平动叶内部冷却结构,具有消耗冷气少、压力损失小等优点.本文构建了简化的壁面射流冷却叶片与GE-E3冷却结构叶片模型,采用流热耦合方法对比研究了其流动与换热特性.结果表明,壁面射流冷却通道内的狭小空间抑制了横流的产生,冷气在冷却通道中形成了流向涡;前缘冷气流道中的大量冷气流经吸力侧冷却区,并从出口压力更小、面积更大的尾缘排出,使得前缘气膜孔出流的冷气流量和动量较小,冷气在叶片外表面的气膜覆盖特性更好;离心力的影响导致前缘冷气流道中叶根处的压力较低,叶根附近的气膜孔出现燃气主流入侵现象.相比于GE-E3叶片,壁面射流冷却叶片的前缘温度和温度梯度都较小,因此多通道壁面射流冷却在前缘具有更优异的冷却特性.     

Heat Transfer and Thermal Characteristics Effects on Moving Plate Impinging from Cu-Water Nanofluid Jet

The present article is focused on modelling of flow and heat transfer behaviour of Cu-water nanofluid in a confined slot jet impingement on hot moving plate. Different parameters such as various moving plate velocities, nanoparticles at various concentrations, variation in turbulent Reynolds number and jet nozzle to plate distance have been considered to study the flow field and convective heat transfer performance of the system. Results of distribution of local and average Nusselt number and sk...     

溴化锂蒸汽制冷在宝钢应用的可行性研究

针对宝钢低压蒸汽系统夏季余热蒸汽大量放散的问题,对增加夏季蒸汽负荷进行了可行性方案的研究。通过比较采用澳化锂蒸汽制冷取代电制冷的相关热力参数,可发现发展澳化锂蒸汽制冷实现热电冷三联产,不仅可以提高宝钢热电系统的热经济性,也可以降低宝钢夏季蒸汽放散量和电网的峰谷差,从而达到节电、节能、减少环境污染的目的。     

The effect of flow field and turbulence on heat transfer characteristics of confined circular and elliptic impinging jets

The flow field of confined circular and elliptic jets was studied experimentally with a Laser Doppler Anemometry (LDA) system. In addition, heat transfer characteristics were numerically investigated. Experiments were conducted with a circular jet and an elliptic jet of aspect ratio four, jet to target spacings of 2 and 6 jet diameters, and Reynolds number 10 000. The toroidal recirculation pattern was observed in the outflow region for both geometries at dimensionless jet to plate distance 2. Higher spreading rates in the minor axis direction of the elliptic jet have also been mapped. Along the target plate, different boundary layer profiles were obtained for circular and elliptic jets at H/d=2, but profiles became similar when dimensionless jet to plate distance was increased to 6. Positions of maximum radial and axial velocities and turbulence intensities have been determined for both geometries. For the confined circular and elliptic jet geometries, analysis of flow field measurements and numerical heat transfer results showed that inner peaks in local heat transfer closely relate to turbulence intensities in the jet and radial flow acceleration along the wall. Differences between the circular and elliptic jet, in terms of flow field and heat transfer characteristics, reduced with increase in the jet to plate distance.     

Time resolved numerical modeling of oil jet cooling of a medium duty diesel engine piston

In medium to heavy duty diesel engines, ever increasing power densities are threatening piston's structural integrity at high engine loads and speeds. This investigation presents the computational results of the heat transfer between piston and an impinging oil jet, typically used to keep the pistons cool. Appropriate boundary conditions are applied and using numerical modeling, heat transfer coefficient (h) at the underside of the piston is predicted. This predicted value of heat transfer coefficient significantly helps in selecting right oil (essentially right oil grade), oil jet velocity, nozzle diameter (essentially nozzle design) and distance of the nozzle from the underside of the piston. It also predicts whether the selected grade of oil will contribute to oil fumes/mist generation. Using numerical simulation (finite element method), transient temperature profiles are evaluated for varying heat flux (simulating varying engine loads) to demonstrate the effect of oil jet cooling. The model, after experimental validation, has been used to understand the transient temperature behavior of the piston and the time taken in achieving steady state. High speed CCD camera is used to investigate the oil jet breakup, localized pool boiling and mist generation due to impinging jet on the piston's underside.     

The Impingement Heat Transfer Data of Inclined Jet in Cooling Applications: A Review

On the impingement heat transfer data, the experimental studies of air and liquid jets impingement to the flat surfaces were collected and critically reviewed. The oblique impingements of both single circular and planar slot jets were considered in particular. The review focused on the surface where the jet impingement cooling technique was utilized. The nozzle exit Reynolds numbers based on the hydraulic diameter varied in the range of 1,500–52,000. The oblique angles relative to the plane surf...     

The effect of jet array arrangement on the flow characteristics of the outlet hole in short confined channels

This experimental study is part of the research program related to the aerodynamic characteristics of impingement in a confined channel. Experimental research on better understanding flow structure in confined channel with impingement cooling is rarely found in open literature. The main purposes of this project are (1) gaining greater insight into the structure of the impingement jet flow and flow in the outlet hole; (2) understanding the effect of impingement hole arrangement build up on the flow structure and aerodynamic parameters within holes and channels with different aspect ratios. The test models are two confined channels with three staggered circular jet holes, and a single large size outlet hole placed downstream of the jet plate. The structure parameters of these orifices are different. In this paper, detailed flow field in the outlet hole was measured with a straight five‐hole probe, and the discharge coefficient of outlet holes with different aspect ratios was also studied in each channel. Experimental data shows that the jet arrangement has little influence on the flow behavior of the outlet hole when the aspect ratio of the passage was 1, but it played an important role on the discharge coefficient. Distinctively different flow patterns were found in two models with the aspect ratios of 3 and 5, while the variation of the discharge coefficient showed a slight influence on impingement hole arrangement. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(1): 20–28, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20188     

新型高效空气冷却燃气轮机系统热力性能分析

为改善空气冷却重型燃气轮机热力性能,提出了一种能够高效利用抽气能量的新型空气冷却燃气轮机系统并研究了其热力性能的变化.以传统典型F级燃气轮机不同环境温度下的性能数据作为对比基础,通过数值仿真分析了新型高效空气冷却燃气轮机中冷却系统设计参数变更条件下的系统性能指标变化,计算对比了3种运行模式下的热力性能.结果表明:新型高效空气冷却燃气轮机能够有效降低压气机抽气温度,进而改善燃气轮机热力性能.在夏季工况下,进口温度分别被冷却到30、20、15 ℃时,燃气轮机功率分别升高了25.92、40.49、48.22 MW,燃气轮机效率分别提升了0.78、1.19、1.40个百分点.     

基于压缩空气储能的新型冷热电联供系统性能研究

为了解决用户负荷需求在时间上的变动和传统冷热电联供(Combine Cooling,Heating&Power,CCHP)系统大部分时间处于非设计工况下运行导致系统的能源利用效率较低的问题,提出了一种耦合压缩空气储能系统(Compressed Air Energy Storage system,CAES)和蓄热装置的新型 CCHP 系统(CAES based CCHP system,CAES-CCHP),建立系统的热力学模型,在给定的充、放电工作条件下对CAES-CCHP系统的热力学性能进行分析,并对影响该系统性能的CAES压气机压缩比、透平进气口压力、流经CAES的烟气质量流量3 个关键参数进行敏感性分析.研究结果表明:CAES-CCHP系统能实现冷热电灵活调控,且系统的CAES功转换效率为57.41%,一次能源利用率、一次节能率及火用效率分别为76.22%,24.84%和31.97%,比传统的CCHP系统分别提高10.97%,18.15%和7.58%.     

涡轮叶片前缘泄流孔抽吸对回流式冲击流动和换热特性影响

面对涡轮入口温度不断提升造成的日益增长的冷却需要,本文针对涡轮叶片前缘,提出了一种抑制积聚横流对射流冷却消极影响的回流式冲击冷却结构。采用CFD数值计算方法,通过对多种泄流孔排布形式的数值计算结果进行对比与分析,探究基于此回流式冷却结构下泄流孔的抽吸作用对冷却结构流动和换热特性的影响。研究发现:泄流孔的加入对射流冲击流场产生重构,一定程度抑制了壁面射流的发展,对冲击靶面的换热表现起到削弱作用;相较于三排泄流孔的布置形式,双排泄流孔对靶面换热水平影响更小;相比于泄流孔与冲击孔在流向位置错列排布,二者位置保持一致时,泄流孔的抽吸作用对换热效果削弱最为严重。     

Prediction algorithm of thermal resistance for impingement cooling of heat sinks for LSI packages with pin-fin arrays

This paper is a semi-empirical report on an algorithm for the prediction of thermal resistance for impingement cooling of pin-fin heat sinks for LSI packages when the inlet orifice is relatively large and is located over the center of the sink. We present a physical model suitable for these types of heat sinks, based on flow visualization results. The model divides the flow region into five parts: I) the top surfaces of the fins where they are directly under the inlet orifice, II) the portions of the vertical surfaces of the pin-fin cylinders, where those surfaces are directly below the inlet port, III) the surface of the base to which the fins are attached, excluding the areas occupied by the feet of the fins themselves, IV) the portions of the vertical surfaces of the fin-cylinders excluding those portions of the surfaces that are directly below the inlet port (complementary to region II), V) the portions of the top surfaces of the pins, excluding those portions directly below the inlet port (complementary to region I). We predicted thermal resistance values for heat sinks with pin-fin arrays, for a variety of orifice diameters, gaps, pin-fin diameters, and heights, and number of fins. These values agreed with experimental data within ±30%. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 25(7): 434–448, 1996     

蒸汽喷射式热泵变工况性能分析

采用数值模拟的方法对低压蒸汽增压利用系统中的蒸汽喷射式热泵在非设计工况下的操作性能进行研究,计算并分析了工作蒸汽压力和温度、引射流体压力及混合流体压力等热力参数对热泵操作性能的影响。数值结果表明：当混合流体的压力低于一定的数值时,喷射系数维持一定值;而热泵对引射流体压力的变化极为敏感,引射压力的微小变化可能导致热泵操作性能的急剧下降;提高工作蒸汽的压力并不一定能改善喷射泵的工作性能,这是因为提高工作蒸汽压力会增加额外的蒸汽量所致;喷射系数随工作蒸汽温度的升高而略有增大,并近似呈线性率。     

正弦波形填料基底上液膜的研究及热经济性分析

为研究正弦波形填料基底上液膜的流动、传热特性及不同结构该基底的冷却效果对电厂热经济性的影响,通过建立合理的物理模型,运用Fluent软件对不同振幅、波长和倾斜角度条件下正弦波形填料基底上的冷却液膜进行了数值模拟.以数值模拟的出口水温为计算依据,通过热力计算分析了不同正弦波基底结构对全厂热经济性指标的影响.结果表明:倾斜角度、振幅不变时,随着波长的增加,基底上液膜的厚度变薄,出口水温升高;波长、振幅不变时,倾斜角度的增大使得基底上液膜的厚度增加,出口水温降低;倾斜角度、波长不变时,随着振幅的增大,基底上液膜的厚度变厚,出口水温降低.