Conjugate heat transfer analysis of a rotor blade with coolant channels

The present study deals with the conjugate heat transfer analysis of a cooled high-pressure turbine rotor blade consisting of eight cooling channels. Computational investigations are performed in a five-bladed cascade to determine characteristics of flow and heat transfer at different values of mainstream and coolant flow rate. Surface temperature measurements using infrared thermography are performed for validating the computational fluid dynamics results. The results show nonuniform variation of surface effectiveness: (a) higher average surface temperature on the pressure side than on the suction side, (b) peak surface temperature at the pressure side trailing edge region, (c) lowest temperature at midspan region of both pressure and suction sides, (d) intermediate values of temperature on the leading edge, and (e) these temperature patterns vary with the changes in mainstream Reynolds number and coolant flow rates, signifying the importance of carrying out conjugate heat transfer analysis. This study also emphasizes the importance of considering realistic coolant channel geometry over the idealized, an illustration showed that the maximum Nusselt number may vary up to 200% due to idealization.     

Conjugate heat transfer analysis of film cooling flows

The objective of this study is to evaluate the potential of various grids to satisfactorily simulate the development of a cooling film, using a coupled computation that takes into account the full geometry. Detailed computations of a single row of 30 degrees round holes on a flat plate are presented for blowing ratios of 0.764,1.01 and 1.54. The simulation results are compared well with experimental data. The two-layer model gave more accurate results but consumed much more computational time than the standard wall functions. The k-e turbulence model with wall functions with appropriate values of y is suitable for practical use. The results show the importance of the conjugate calculation for accurately describing the influence of the heat transfer within the cooling film.     

Heat transfer model with two heat transfer coefficients along a multiperforated plate — Application to combustion chamber wall cooling

Walls‘ cooling of aeronautic propeller combustion chamber is performed with the injection, through the combustion chamber wall, of a part of the air coming from compressors placed upstream. Measurements of the wall thermal fields are made by infrared thermography along the injection wall. This injection wall is pierced by 9 rows of 8 holes (α=90°) in staggered configuration (p/D=s/D=6). We propose a model using two heat transfer coefficients to represent the convective exchanges. The results are non-dimensioned and presented in comparison with the case without holes. The use of this model allows us to define 4 zones. Those 4 zones exist for the 5 blowing rates.     

Conjugate heat transfer investigation on the cooling performance of air cooled turbine blade with thermal barrier coating

A hot wind tunnel of annular cascade test rig is established for measuring temperature distribution on a real gas turbine blade surface with infrared camera. Besides, conjugate heat transfer numerical simulation is performed to obtain cooling efficiency distribution on both blade substrate surface and coating surface for comparison. The effect of thermal barrier coating on the overall cooling performance for blades is compared under varied mass flow rate of coolant, and spatial difference is also discussed. Results indicate that the cooling efficiency in the leading edge and trailing edge areas of the blade is the lowest. The cooling performance is not only influenced by the internal cooling structures layout inside the blade but also by the flow condition of the mainstream in the external cascade path. Thermal barrier effects of the coating vary at different regions of the blade surface, where higher internal cooling performance exists, more effective the thermal barrier will be, which means the thermal protection effect of coatings is remarkable in these regions. At the designed mass flow ratio condition, the cooling efficiency on the pressure side varies by 0.13 for the coating surface and substrate surface, while this value is 0.09 on the suction side.     

Experimental study on heat transfer and flow resistance in improved latticework cooling channels

Characteristics of heat transfer and flow resistance of the latticework （vortex） cooling channel with ribs truncated at their two ends were theoretically and experimentally studied compared with regular and smooth channels of the same configuration. The results showed： the heat transfer efficiency of the latticework channel with two slots was better than those of regular and smooth channels of the same configuration, its flow resistance situation in the slotted channel becomes quite complex; The flow resistances of 2 mm- and 4 mm-slotted channels were obviously lower than that of the regular channel, but they are still much higher than that of the smooth channel; Compared with the regular channel, the total heat transfer efficiencies of the slotted channels were pretty improved, among them the 4-mm slotted channel has the biggest enhancement. From the experimental results, it is obvious that the latticework channel with proper slots has a great prospect in the design of the inner cooling channels of turbine blades.     

An experimental investigation of heat transfer characteristics for steam cooling in a rectangular channel with parallel ribs

An experimental study of heat transfer characteristics in superheated steam cooled rectangular channels with parallel ribs was conducted.The distribution of the heat transfer coefficient on the rib-roughed channel was measured by IR camera.The blockage ratio(e/Dh) of the tested channel is 0.078 and the aspect ratio(W/H) is fixed at3.0.Influences of the rib pitch-to-height ratio(P/e) and the rib angle on heat transfer for steam cooling were investigated.In this paper,the Reynolds number(Re) for steam ranges from 3070 to 14800,the rib pitch-to-height ratios were 8,10 and 12,and rib angles were 90°,75°,60°,and 45°.Based on results above,we have concluded that:In case of channels with 90° tranverse ribs,for larger rib pitch models(the rib pitch-to-height ratio=10 and12),areas with low heat transfer coefficient in front of rib is larger and its minimum is lower,while the position of the region with high heat transfer coefficient nearly remains the same,but its maximun of heat transfer coefficient becomes higher.In case of channels with inclined ribs,heat transfer coefficients on the surface decrease along the direction of each rib and show an apparent nonuniformity,consequently the regions with low Nusselt number values closely following each rib expand along the aforementioned direction and that of relative high Nusselt number values vary inversely.For a square channel with 90° ribs at Re= 14800,wider spacing rib configurations(the rib pitch-to-height ratio=10 and 12) give an area-averaged heat transfer on the rib-roughened surface about8.4%and 11.4%more than P/e=8 model,respectively;for inclined parallel ribs with different rib angles at Re=14800,the area-averaged heat transfer coefficients of 75°,60° and 45° ribbed surfaces increase by 20.1%,42.0%and 44.4%in comparison with 90° rib angle model.45° angle rib-roughened channel leads to a maximal augmentation of the area-averaged heat transfer coefficient in all research objects in this paper.     

New correlations for heat transfer coefficients during direct cooling of products

An analytical method for determining the heat transfer coefficients of food products being cooled in water and in air flows is presented. Food products are idealized as geometrical solid objects of regular shapes. New correlations between heat transfer coefficients and cooling coefficients are developed in simple forms for practical use in the refrigeration industry. These correlations are then used to determine the heat transfer coefficient for a cylindrical carrot cooled in air flow as an illustrative example. In addition, evaluating the heat transfer coefficients for several products using the available experimental cooling coefficient values from the literature, two new correlations between the heat transfer coefficient and the cooling coefficient are also obtained for water and air cooling applications. The results show that the correlations presented in this article can determine the heat transfer coefficients of food products forced-convection cooling in a simple and accurate manner.     

A simplified approach to solving conjugate heat transfer problems in annular and dissimilar parallel plate ducts

A simple perturbation technique is used to reformulate the energy equations which describe the treatment thermal behaviour of a radially lumped conjugate that transfer problem is annular and dissimilar parallel plate ducts of finite wall thickness. The simplified perturbation tecnique is used to eliminate the coupling between the fluid and the solid-wall energy equations when the temperature difference between the fluid and the solid-wall is a small perturbed quantity, which is true when the interface convective heat transfer coefficient between the fluid and the solid-wall is high. A mathematical criterion is derived to determine the conditions under which the fluid and the solid-wall are in thermal equilibrium. It is found that seven dimensionless parameters control the state of the thermal equilibrium between the fluid and the solid domains. © 1998 John Wiley & Sons, Ltd.     

Measurement of turbulent heat transfer using infrared thermography near ambient conditions and its quantitative error estimation

Infrared thermography was applied to measurement of turbulent heat transfer in order to investigate its applicability under near-ambient conditions. Natural convection along a vertical smooth flat plate and forced convection along a smooth flat plate were realized in a large darkroom, where individual heat transfer coefficients were quantitatively measured using infrared thermography in the laminar, transition, and turbulent regions. The measurement error was then estimated using ANSI/ASME PTC 19.1-1985 measurement uncertainty to confirm the accuracy. It is obvious from a series of application experiments and error analyses that the present technique is useful for estimating turbulent heat transfer quantitatively and dynamically. Infrared thermography is an appropriate measurement procedure for engineering applications because it can be applied to diagnose a two-dimensional and dynamical temperature field instantaneously and nondestructively. © 1999 Scripta Technica, Heat Trans Asian Res, 28(6): 442–455, 1999     

Endwall heat transfer and film cooling measurements in a turbine cascade with injection upstream of leading edge

Detailed heat transfer measurements were conducted on the endwall surface of a large‐scale low‐speed turbine cascade with single and double row injection on the endwall upstream of leading edge. Local film cooling effectiveness and the heat transfer coefficient with coolant injection were determined at blowing ratios 1.0, 2.0, and 3.0. In conjunction with the previously measured flow field data, the behaviors of endwall film cooling and heat transfer were studied. The results show that endwall film cooling is influenced to a great extent by the secondary flow and the coverage of coolant on the endwall is mainly determined by the blowing ratio. An uncovered triangle‐shaped area with low effectiveness close to pressure side could be observed at a low blowing ratio injection. The averaged effectiveness increases significantly when injecting at medium and high blowing ratios, and uniform coverage of coolant on the endwall could be achieved. The averaged effectiveness could be doubled in the case of double row injection. It was also observed that coolant injection made the overall averaged heat transfer coefficient increase remarkably with blowing ratio. It was proven that film cooling could reduce endwall heat flux markedly. The results illustrate the need to take such facts into account in the design process as the three‐dimensional flow patterns in the vicinity of the endwall, the interactions between the secondary flow and coolant, and the augmentation of heat transfer rate in the case of endwall injection. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(3): 141–152, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20007     

Fundamental Research on Convective Heat Transfer in Electronic Cooling Technology

During the past six years comprehensive research programs have been conducted at the Beijing PolytechnicUniversity to provide a better understanding of heat transfer characteristics of existing and condidate cool-ing techniques for electronic and microelectronic devices.This paper provides a review and summary of theprograms with emphasis on direct liquid cooling.Included in this review are the heat transfer investigationsrelated to the following cooling modes:liquid free,mixed and forced convection,liquid jet impingement,flowingliquid film cooling,pool boiling,spray cooling,foreign gas jet impingement in liquid pool,and forced convectionair-cooling.     

Conjugate natural convection heat transfer in an inclined square cavity containing a conducting block

The present work is concerned with computation of natural convection flow in a square enclosure with a centered internal conducting square block both of which are given an inclination angle. Finite volume method through the concepts of staggered grid and SIMPLE algorithm have been applied. Deferred QUICK scheme has been used to discretize the convective fluxes and central difference for diffusive fluxes. The problem of conjugate natural convection has been taken up for validating the code. The abrupt variation in the properties at the solid/fluid interface are taken care of with the harmonic mean formulation. Solution has been performed in the computational domain as a whole with proper treatment at the solid/fluid interface. Computations have been performed for Ra = 10³–10⁶, angle of inclination varying from 15° to 90° in steps of 15° and ratio of solid to fluid thermal conductivities of 0.2 and 5.0. Results are presented in terms of streamlines, isotherms, local and average Nusselt number.     

微尺度通道内流动沸腾研究综述

阐述了微尺度通道内传热问题出现的工程背景——高密度微电子器件的冷却。对当前国内外微尺度通道内流动沸腾换热特性的研究现状进行了归纳。突出分析了工质种类、微尺度通道的几何参数和工质的工况参数等对微尺度通道内流动沸腾换热特性的影响。同时分析了微尺度通道内流动沸腾换热的强化机理、流动阻力特性、压降关联式和沸腾换热关联式的理论和实验研究。最后根据分析对今后的工作提出了一些建议。     

The interior heat transfer characteristics of gas turbine blade due to sparse film cooling holes

The film cooling technique is one of the most useful cooling methods. At present, the midchord region of gas turbine blades in an aeroengine often adopt a sparse film cooling technique and impingement cooling technique at the same time. So the interior heat transfer characteristics on the inner side of blades due to the sparse film cooling holes have become a very complicated and interesting problem. In this paper, the heat transfer characteristics of impingement‐cooling have been investigated experimentally. Through lots of experimental data, the effect of flow parameters and geometric parameters on heat transfer characteristics has been studied. Correlation equations obtained show good agreement with experimental data. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(3): 197–207, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20052     

Forced Convective Air Cooling from Electronic Component Arrays in a Parallel

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Improvement of the heat transfer quality by air cooling of three-heated obstacles in a horizontal channel using the lattice Boltzmann method

This study focuses on the cooling of three heated obstacles with different heights mounted on the bottom of the channel wall using different aspects that influence the enhancement of the heat exchange, as is known in the concept of cooling electronic devices. The lattice Boltzmann method associated with multiple relaxation times (LBM-MRT) was adopted to simulate the physical configurations of the studied system. In this context, the D2Q9 and D2Q5 models are applied to describe the fluid flow behavior and conjugate heat transfer, respectively. The evaluation of heat exchange between the cold fluid and three-heated obstacles has been accurately analyzed under the effect of several parameters such as Reynolds number, obstacle spacing, and thermal conductivity ratio. In addition, the setting of two and three fluids flow inlets were also studied. The results are presented in terms of streamlines, isotherms, and local Nusselt curves. The heat transfer increases with increasing solid-fluid thermal conductivity. It is also more pronounced for large Reynolds numbers. Moreover, the heat transfer significantly enhances for the second and third obstacles when obstacle spacing increases. The improvement of the heat transfer is performed by the implementation of several jet flows in the studied system.     

Flow and heat transfer characteristics in fuel cooling channels of a recooling cycle

Developing fuel with higher heat sink is widely carried out to meet the cooling requirement for an air breathing hypersonic vehicle. Especially, a recooling cycle has been newly proposed for an actively cooled scramjet to reduce the fuel flow for cooling. Fuel heat sink (cooling capacity) is repeatedly used to indirectly increase the fuel heat sink in a recooling cycle. The variation of fuel thermal property related with heat transfer and flow as temperature and pressure is added to the one-dimensional analytical fin-type model for rectangular ducts. Heat transfer performance comparison between recooling cycle and regenerative cooling is carried out, and detailed discussion about the variation and influence of heat transfer and flow characteristics caused by the introduction of the recooling process are discussed. Performance comparison between a recooling cycle at supercritical pressure and it at subcritical condition is also investigated.     

Convective Heat and Mass Transfer in Water at Super—Critical Pressures under Heating or Cooling Conditions in Vertical Tubes

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Numerical investigation of heat transfer coefficient in a low speed 1.5-stage turbine

The paper numerically investigated the heat transfer coefficients over the rotating blades in a 1.5-stage turbine. The hexahedral structured grids and k-ε turbulence model were applied in the simulation. A film hole with diameter of 0.004 m, angled 36°and 28° tangentially to the suction side and pressure side in streamwise respectively, was set in the middle span of the rotor blade. Simulations are done at three different rotating numbers of 0.0239, 0.0265 and 0.0280 with the blowing ratio varying from 0.5 to 2.0. The effects of mainstream Reynolds number and density ratio are also compared. Results show that increasing blowing ratio can increase the heat transfer coefficient ratio on the pressure side, but the rule is parabola on the suction side. Besides, increasing rotating number and Reynolds number is positive while increasing density ratio is negative to the heat transfer on both the pressure side and the suction side.     

矩形冷却通道内超临界RP-3航空煤油对流传热数值研究

对超临界压力下RP-3航空煤油在内截面宽为4mm、高为4mm、固体壁面厚为1mm、加热段长度为500mm的水平矩形冷却通道内的对流传热特性进行了数值模拟研究。分析了通道内速度场的分布规律,讨论了热流密度、压力、进口温度对传热的影响。计算结果表明:当主流温度处于拟临界温度附近时,流体物性参数变化剧烈,导致传热系数降低,传热出现恶化。在超临界压力下,较低的热流密度、增大压力、降低进口流体温度或提高质量流速均有利于改善冷却通道内的传热性能。