Jet Impingement Cooling of a Hot Moving Steel Plate: An Experimental Study

In the current study, a hot moving steel plate of 6 mm thickness with an initial temperature of 900°C has been considered for jet impingement cooling. The experiment has been designed with the help of Design of Expert software to optimize the process parameters based on the highest cooling rate. The various subsurface transient temperature histories have been measured during the cooling process. The surface heat flux and surface temperature were calculated with the help of a commercial inverse heat transfer solver called INTEMP. The experimental result has been presented in terms of cooling rate and critical heat flux.     

Pressure effect on the electromotive force of the type R thermocouple

ABSTRACT

The pressure effect on the electromotive force (EMF) of a Pt13Rh–Pt (type R) thermocouple was examined to determine the temperature measurement accuracy of solid pressure medium apparatuses in high-pressure experiments. Single-wire EMFs were measured up to pressure of 13?GPa and temperature of 1173?K with a Kawai-type multi-anvil apparatus for Pt13Rh and Pt based on the single-wire method. The pressure conditions along the wires were evaluated by in situ X-ray diffraction using synchrotron X-ray radiation. The pressure effect of the Seebeck coefficients of Pt13Rh and Pt were determined by the analysis of the single-wire EMFs and pressure–temperature profiles along the wires and was virtually consistent with those determined in previous studies at lower pressures and temperatures. For type R thermocouple, the difference between the nominal and real temperatures was determined to be as large as –75?K at 13?GPa and 873?K.     

高温壁面液体射流冲击瞬态沸腾传热的实验研究

以水作为冷却介质,对高温壁面在射流冲击淬冷时的瞬态换热特性进行了实验研究,获得了介质在不同过冷度、不同射流速度下的完整沸腾曲线。实验结果表明。无论是增大工质过冷度还是提高射流速度,总会使得热壁面的冷却速率加大。在一定的过冷度和射流速度下壁温变化呈现快－慢－快的特点。临界热流密度随平均壁温变化率的增大而增大,二者之间存在线性关系．     

Effect of Nozzle Geometry on the Rewetting of Hot Surface During Jet Impingement Cooling

An investigation has been carried out to investigate the effect of nozzle geometry on hot horizontal surface rewetting during water jet impingement cooling. The test surface of 800 ± 10°C initial surface temperature is cooled by water jet of 22 ± 1°C temperature. The water flow is varied to maintain the jet Reynolds number in a range of 5,000 to 24,000. The rewetting phenomena with sharp-edged and tube-type nozzles are compared on the basis of rewetting temperature, wetting delay, rewetting velocity, and maximum surface heat flux. The rewetting performance with tube-type nozzle is better than the sharp-edged nozzle particularly for the downstream spatial locations; however, maximum surface heat flux at the stagnation region is higher with the sharp-edged nozzle.     

Effect of impingement jet on the full-coverage film cooling system with double layered wall

The present study was conducted to evaluate the total cooling effectiveness in combined full-coverage film cooling and impingement jet using an infrared thermographic technique. The effect of film cooling hole angle, blowing ratio, and height to diameter ratio between the film cooling and impingement jet plates was discussed. The total cooling effectiveness increased as impingement jet cooling was added. The angled film cooling holes had approximately 4.6% higher total cooling effectiveness than the normal film cooling holes. The total cooling effectiveness was almost constant regardless of height to diameter ratio, but enhanced as the blowing ratio was increased.     

阵列射流冲击冷却局部对流换热特性的数值计算与试验验证

本文运用数值计算的方法对具有初始横流的阵列射流在不同的排列方式、冲击间距和横流/射流质量流量比下 的流动换热进行了三维数值研究,并采用热色液晶测试技术对阵列射流冲击的冷却表面温度分布进行了试验研究。获得了 每一股射流的冲击冷却局部对流换热系数分布的特征,研究结果表明本文的计算结果与实验特征是基本吻合的。     

Influence of Streamwise Pitch on Local Heat Transfer Distribution for In-Line Arrays of Circular Jets with Spent Air Flow in Two Opposite Directions

Abstract

The effect of streamwise jet-to-jet spacing on local heat transfer distribution due to an in-line rectangular array of confined multiple circular air jets impinging on a surface parallel to the jet plate are experimentally studied. The length-to-diameter ratio of nozzles of the jet plate is 1.0. The flow, after impingement, is constrained to exit in two opposite directions from the confined passage formed between the jet plate and target plate. Mean jet Reynolds numbers based on the nozzle exit diameter (d) covered are 3,000, 5,000, 7,500, and 10,000; jet-to-plate distances studied are d, 2d, and 3d. Streamwise jet-to-jet distances of 3d, 4d, and 5d, and a constant spanwise pitch of 4d, are considered. The jet plates have ten spanwise rows in the streamwise direction and six jets in each spanwise row. The flat heat transfer surface is made of thin stainless-steel metal foil. Local temperature distribution on a target plate is measured using a thermal infrared camera. Wall static pressures in the streamwise direction are measured midway between the spanwise jets to estimate cross-flow velocities and individual jet velocities. The streamwise distribution of the jet flow and the cross flow is found to be least influenced by the streamwise pitch variation for the range of parameters considered during the present study. Heat transfer characteristics are explained partially on the basis of flow distribution. The cooling performance, based on the strip-averaged Nusselt number per unit mass flow rate of coolant per unit area of cooled surface, indicates deterioration for lower streamwise pitch and higher jet-to-plate distance.     

莫尔偏折法及其在燃气射流冲击场中的应用

用傅里叶光学方法从理论上分析了带有滤波器的相干性莫尔偏折法的测量原理,把这种方法用于真实火箭燃气射流冲击场的实验研究.获得了真实火箭燃气射流冲击流场莫尔偏折图.解决了长期以来无法拍摄到高温、高速、强振动冲击、强火焰光的火箭射流流场图像问题.     

高效微射流阵列冷却热沉传热特性

微射流阵列冷却热沉是利用射流冲击在驻点区能产生很薄的边界层来提高换热效率,本次研究设计的热沉是5层结构的模块式铜微射流阵列冷却热沉,以去离子水为工质对传热特性进行了实验研究.结果表明,采用微射流阵列冷却不仅能通过增加驻点数目来强化换热,而且能有效地降低换热表面的温差.热沉的热阻会随着泵功的增加而降低;随着泵功的不断提高,热阻变化趋于平缓.     

Experimental Design and Methodology for Estimation of Local Heat Transfer Coefficient in Jet Impingement Using Transient Inverse Heat Conduction Problem

Abstract

This article aims to employ a two-dimensional inverse heat conduction technique in designing an experiment for accurately estimating the local convective heat transfer coefficient in slot jet impingement, given temperature measurements at some interior locations in the target plate. The method uses a sequential procedure together with the Beck function specification approach. Solution accuracy and experimental errors are examined using simulated temperature data. It is concluded that a good estimation of the space variable heat transfer coefficient can be made from the knowledge of the transient temperature recordings. The technique is used in a series of numerical experiments to provide the optimum experimental design for a slot jet impingement heat transfer investigation.     

涡轮叶片前缘阵列冲击冷却流动及传热特性数值研究

本文采用SST湍流模型模拟了类前缘通道内蒸汽射流阵列冲击冷却的流动与传热特性,分析了雷诺数(Re=10000~50000)、孔径比(d/H=0.5~0.9)和孔间距比(S/H=2~6)对流动及传热性能的影响规律,得到了相应的传热和摩擦关联式。结果表明:在不同雷诺数下,d/H从0.5到0.9变化时,通道压力损失系数降低了76%~79%,靶面平均努塞尔数降低了45%~49%;S/H从2增至6时,通道压力损失系数增加了1.64~1.92倍,靶面平均努塞尔数增加了54%~64%;增大d/H、减小S/H可有效提高类前缘通道蒸汽冲击冷却的综合热力系数。本文研究结果可为未来先进燃气轮机高温涡轮叶片蒸汽冷却结构的设计提供参考和借鉴。     

An Experimental Investigation of Liquid Jet Impingement and Single-Phase Spray Cooling Using Polyalphaolefin

Experiments on triangular and rectangular array jet impingement and single-phase spray cooling have been performed to determine the effect of both cooling techniques on heat transfer coefficient (h) and the coolant mass flux required for a given cooling load. Experiments were performed with circular orifices and nozzles for different H/D values from 1.5 to 26 and Reynolds number range of 219 to 837, which is quite lower than the ranges employed in widely used correlations. The coolant used was polyalphaolefin. The experiments simulated the boundary condition produced at the surface of the stator of a high power low-density generator or motor. For the custom fabricated orifices, commercial nozzles, and conditions used in this study, both cooling configurations showed enhancement of heat transfer coefficient as H/D increases to a certain limit after which it starts to decrease. The heat transfer coefficient always increases with Reynolds number. In keeping with previous studies, single-phase spray cooling technique can provide the same heat transfer coefficient as jets at a slightly lower mass flux, but with much higher-pressure head. Special Nu_d correlations that account for the range of parameters and coolant studied in this work are derived.     

高效微射流阵列冷却热沉的阻力特性

微射流阵列冷却热沉是利用射流冲击在驻点区能产生很薄的边界层来提高换热效率,合理的布置射流孔,可以极大的提高被冷却表面温度分布的均匀性。本次研究设计的热沉是5层结构的模块式铜微射流阵列冷却热沉(微射流孔直径d=0．15 mm),以氮气和去离子水为工质对阻力特性进行了实验研究,并与微射流阵列冷却热沉的理论计算进行了比较。结果表明,在微射流热沉中,热沉的实验压降值低于计算值,热沉总阻力主要是由局部阻力引起的,占到热沉总阻力的90％。     

Modèle correctif de la mesure de la température d'un gaz par couple thermoélectrique. Application à une zone à fort gradient thermique

Corrective model of the gas temperature thermocouple measure. Application to an important thermal gradient zone. The gas temperature measurement with a thermocouple in important thermal gradient zones requires a corrective model. For example, such zones exist for thermal boundary layers near active walls. We have calculated these thermocouple thermal exchanges where connection wires are considered as fins with a variable ambient gas temperature. The heat exchanges by convection and radiation on the thermocouple head are analytically calculated, then a numerical method is used for fins where the space increment is the same as for the experimental measure. The corrective model in steady state is semi-analytical. Its validation is made with experimental results from studies of flows along a non-isothermal vertical wall in a cavity filled with wet air. Several applications are offered for many thermal curves, for more important gradient zones corrections are larger than 1.5 K for a K type thermocouple of 0.08 mm wire diameter.     

Application of TiO2 nanofluid-based coolant for jet impingement quenching of a hot steel plate

Cooling rate in Run Out Table (ROT) in steel industries tailors microstructure which lead to improved mechanical properties. The current work aims to increase cooling performance of steel using TiO₂ nanofluid as coolant in jet impingement. Different concentrations of TiO₂ nanofluid have been used to study effect on jet cooling of a steel plate from 900°C. Thermal conductivity of nanofluid is found to significantly enhance at optimum concentration and this plays major role in increasing cooling rate of the steel plate. 19% enhancement in cooling rate is observed by using 40 ppm of TiO₂ nanofluid compared to water.     

Corona discharge as a temperature probe of atmospheric air microwave plasma jet

We developed and tested a new method for temperature measurements of near-LTE air plasmas at atmospheric pressure. This method is specifically suitable for plasmas at relatively low gas temperature (800–1700 K) with no appropriate radiation for direct spectroscopic temperature measurements. Corona discharge producing cold non-equilibrium plasma is employed as a source of excitation and is placed into the microwave plasma jet. The gas temperature of the microwave plasma jet is determined as the rotational temperature of N₂? produced in the corona discharge. The corona probe temperature measurement was tested by the use of a thermocouple. We found a fairly good agreement between the two methods after correcting the thermocouple measured temperatures for radiative losses. The corona probe method can be generally applied to determine the temperature of the near-LTE plasmas and contrary to the thermocouple it can be used for higher plasma temperatures and is not affected by radiative losses and problems of interaction with the microwave plasma and electromagnetic fields.     

Behavior of thermocouples under high pressure in a multi-anvil apparatus

We have conducted experiments to study the behavior of W5%Re–W26%Re (type C) and Pt10%Rh–Pt (type S) thermocouples under high pressure in a multi-anvil apparatus. The electromotive force (emf) between four different or three identical thermocouple wires was measured up to 15?GPa and 2100?°C. Mechanical and chemical stability of the thermocouples was examined during and after the experiments. Due to the effect of pressure on the emf/temperature relation, the temperature reading of the type C minus that of the type S thermocouple rises to +5?°C then falls to ?15?°C between room temperature and 1500?°C at 5?GPa, and to +25?°C and then ?35?°C between room temperature and 1800?°C at 15?GPa. In addition, we observed variations in the emf/temperature relation caused by uncertainties in the position and geometry of hot junctions in a steep temperature gradient, and by variable distribution of pressure gradient and non-hydrostatic stress on the thermocouple wires. These errors are estimated at 1.6% for the type S thermocouple up to 1700?°C, and 0.8% for the type C thermocouple up to 2100?°C. Self-diffusion and chemical contamination of the thermocouples by high-purity insulating ceramics appear negligible for the type S thermocouple at 1700?°C for one hour, and for the type C thermocouple at 2100?°C for half an hour. In contrast, large-scale displacement of the hot junction due to dislocation of the type C thermocouple wires and plastic deformation of the type S thermocouple wires may lead to large errors in temperature measurement (±200?°C).     

Flat Surface Heat Transfer Enhancement By An Impinging Circular Free Water Jet

Impinging a free water jet onto a heated flat plate was investigated with and without mesh screens. Increasing the jet velocity increased the surface cooling rate via turbulence increase. Lower temperature gradients existed due to the faster wetting front propagation for the water film to advance in shorter times. Decreasing the nozzle-to-block spacing slightly increased the cooling rates by counteracting effects of gravity acceleration and jet momentum dispersion. The turbulence role in the heat transfer enhancement was optimized via opposite changes in the strain rate and largest turbulence scale. Displacing the screens from the impingement zone increased the heat flux.     

迎风凹腔与逆向喷流组合热防护系统冷却效果研究

对迎风凹腔与逆向喷流组合热防护系统的冷却效果进行了分析, 研究了相同总压不同流速的逆向喷流对组合结构的流场、气动受力及壁面传热的影响. 通过与相关的实验结果对比, 验证了数值方法的可靠性. 研究发现:该结构能够有效地对飞行器鼻锥表面进行冷却, 引入很小总压的逆向喷流(逆喷总压比 PR=0.1), 组合结构的冷却效果就可以远远优于单一的迎风凹腔; 相同逆向喷流总压下, 逆喷速度越高, 逆喷流量越大, 外壁面的冷却效果越好; 随逆喷流速提高, 气动阻力也进一步减小. 本文研究的组合结构非常适用于远程、 需长时间飞行的高超声速飞行器的热防护.     

迎风凹腔与逆向喷流组合热防护系统冷却效果研究

对迎风凹腔与逆向喷流组合热防护系统的冷却效果进行了分析, 研究了相同总压不同流速的逆向喷流对组合结构的流场、气动受力及壁面传热的影响. 通过与相关的实验结果对比, 验证了数值方法的可靠性. 研究发现:该结构能够有效地对飞行器鼻锥表面进行冷却, 引入很小总压的逆向喷流(逆喷总压比 PR=0.1), 组合结构的冷却效果就可以远远优于单一的迎风凹腔; 相同逆向喷流总压下, 逆喷速度越高, 逆喷流量越大, 外壁面的冷却效果越好; 随逆喷流速提高, 气动阻力也进一步减小. 本文研究的组合结构非常适用于