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1.
Michael A. Marr James S. Wallace Sanjeev Chandra Larry Pershin Javad Mostaghimi 《Experimental Thermal and Fluid Science》2010,34(2):183-189
A fast response thermocouple was developed for measuring surface temperatures of aluminum components in ICE combustion chambers. The key features of the design are the use of the aluminum substrate as one of the thermocouple metals and the use of a thick copper layer as the hot junction at the surface. The copper equalizes the hot junction temperature with the surrounding aluminum to correct for the differences in thermal properties between the two materials. FEA determined the optimum thickness of the copper layer to be between 100 and 125 μm. Under typical SI engine heat flux conditions, the thermocouple should be able to measure average surface temperatures within 0.19 °C and the magnitude of temperature swings within 6% of true values.Following the FEA, the optimized thermocouple was tested in a SI engine. Experimental results displayed the same trends as the FEA at measuring average temperatures and temperature swings, suggesting the thermocouple was performing as predicted. 相似文献
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为探究叠层复合装药的爆轰释能规律,采用爆速差为1.85 km/s的3,4-二硝基呋咱基氧化呋咱(DNTF)基高爆速炸药与高爆热炸药制备成等厚度的叠层复合装药,通过狭缝扫描试验和圆筒试验分别获得了装药内的爆速变化和产物的膨胀释能曲线,并结合2种炸药爆轰产物的相互作用过程,分析了叠层复合装药与单一装药释能过程的主要差异。结果表明:爆轰波交替传播时,2种炸药均能迅速进入稳定爆轰状态;产物膨胀时,2种炸药的相互作用使装药爆轰驱动能量的分布特征发生显著变化,高爆速炸药的加载区域扩大,导致铜管速度降低,比动能较单一装药下降了6.7%,而高爆热炸药的加载区域缩小,铜管速度升高,比动能较单一装药提升了14.1%;此外,高爆热炸药爆轰产物处于压缩状态,有利于提升铝粉的反应速率,有望进一步增强叠层复合装药的驱动做功能力。
相似文献3.
F. J. White 《Experimental Mechanics》1962,2(7):204-210
Results of an investigation of the accuracy of iron-constantan thermocouples in measuring transient surface temperatures produced by radiant heating on metallic specimens are given. The criterion of thermocouple accuracy was derived from the theory of heat conduction. The thermocouples were tested on metallic specimens of different thicknesses at varying heating rates. Comparison of these results with analytical criteria permitted quantitative determination of thermocouple errors. 相似文献
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Free convection from cubical air channel equipped with copper plate was taken into consideration in the presence of electrostatic field as the channel position was varied. The paper examines the artificial neural network capability in modeling and prediction of five output parameters for plate temperatures as affected with four input parameters of heat flux, applied voltage, the inclination angle of channel, and inlet ambient temperature. The proposed network’s performance was measured with increasing number of neurons in hidden layer. The best network structure was found 4-20-5 with Levenberg–Marquardt training algorithm and mean squared error of 0.06366. The mean relative error for all output cases were <2.9 %. The best coefficient of determination was resulted at 30 cm from channel entrance section to the amount of 0.9807. The discrepancies of the results are chiefly attributed to 90° channel inclination angle. The network was able to predict accurately temperature trend of airflow and plate with voltage, heat flux, and channel positions. 相似文献
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An extensive experimental campaign has been carried out for the measurement of saturated critical heat flux in a multi-microchannel copper heat sink. The heat sink was formed by 29 parallel channels that were 199 μm wide and 756 μm deep. In order to increase the critical heat flux and reduce the two-phase pressure drop, a split flow system was implemented with one central inlet at the middle of the channels and two outlets at either end. The base critical heat flux was measured using three HFC Refrigerants (R134a, R236fa and R245fa) for mass fluxes ranging from 250 to 1500 kg/m2 s, inlet subcoolings from ?25 to ?5 K and saturation temperatures from 20 to 50 °C. The parametric effects of mass velocity, saturation temperature and inlet subcooling were investigated. The analysis showed that significantly higher CHF was obtainable with the split flow system (one inlet–two outlets) compared to the single inlet–single outlet system, providing also a much lower pressure drop. Notably several existing predictive methods matched the experimental data quite well and quantitatively predicted the benefit of higher CHF of the split flow. 相似文献
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M. I. Podduev 《Fluid Dynamics》1980,15(1):53-58
The creation of an active medium by means of detonation has been investigated on a number of occasions. It was suggested that one could use the expansion of the detonation products of an acetylene-air mixture in vacuum [1] or the cooling of the detonation products of a mixture of hydrocarbons and air through a nozzle [2, 3]. In [4], the detonation of a solid high explosive was used to produce population inversion in the gas mixture CO2-N2-He(H2O). Stimulated emission from HF molecules was observed in [5] behind the front of an overdriven detonation wave propagating in an F2-H2-Ar mixture in a shock tube. Population inversion behind a detonation wave was studied in H2-F2-He mixtures in [6–8] and in H2-Cl2-He mixtures in [9] with energy release on a plane and on a straight line in a medium with constant density. Similar problems were solved for shock waves propagating in both a homogeneous gaseous medium [7, 10] and in the supersonic part of an expanding nozzle. In the present paper, we study theoretically population inversion behind an overdriven detonation wave propagating in a mixture (fine carbon particles + acetylene + air) which flows through a hypersonic nozzle. The propagation of detonation in media with variable density and initial velocity was considered, for example, in [11, 12]. Analysis of the gas parameters behind a detonation wave propagating in a medium with constant density (for a given fuel) showed that the temperature difference across the detonation front is insufficient to produce population inversion of the vibrational levels of the CO2 molecule.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 65–71, January–February, 1980.I am grateful to V. P. Korobeinikov for a helpful discussion of the results. 相似文献
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This paper reports an experimental investigation of the heat transfer performance of the new low-GWP refrigerants, R1234yf and R1234ze(E), during flow boiling heat transfer inside a horizontal high porosity copper foam with 5 Pores Per Inch (PPI). Metal foams are a class of cellular structured materials consisting of a stochastic distribution of interconnected pores; these materials have been proposed as effective solutions for heat transfer enhancement during both single and two-phase heat transfer. R1234yf and R1234ze(E) refrigerants are appealing alternatives of the more traditional R134a by virtue of their negligible values of GWP and normal boiling temperatures close to that of R134a, which make them suitable solution in several different applications, such as: refrigeration and air conditioning and electronic thermal management. This work compares the two-phase heat transfer behaviour of these new HFO refrigerants, studying the boiling process inside a porous medium and permitting to understand their effective heat transfer capabilities. The experimental measurements were carried out by imposing three different heat fluxes: 50, 75, and 100 kW m−2, at a constant saturation temperature of 30 °C; the refrigerant mass velocity was varied between 50 and 200 kg m−2 s−1, whilst the mean vapour quality varied from 0.2 to 0.95. The two-phase heat transfer and pressure drop performance of the two new HFO refrigerants is compared against that of the more traditional R134a. 相似文献
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飞板运动姿态的测定是爆炸焊接机理研究的基础,针对传统电测方法存在干扰因素多、易产生弯曲波等缺陷,设计了一种适用于野外大当量下爆炸焊接飞板姿态实验的连续电阻测试方法。研制了3种不同结构的梯形支架型连续电阻探针元件,利用有限元程序分析了探针的导通压力和响应时间,在此基础上,对3种探针实施了爆炸焊接实验,实验结果表明:金属丝网型探针元件具有最优的导通效果,各段测试曲线光滑无毛刺。以该探针数据计算获得了待测飞板的运动姿态曲线,并与Richter简化模型下的近似计算公式结果进行了对比,两者基本一致。所述测试方法实现了炸药爆速和飞板变形曲线的连续、可靠和快速测量,为滑移爆轰驱动问题、爆轰产物状态方程等的研究提供了测试方法补充。 相似文献
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J. Taler 《Heat and Mass Transfer》1990,25(2):77-83
This paper presents a procedure for determining the transient heat transfer coefficient in cylindrical, thick-walled pressure parts. From theoretical considerations, the temperatures can be predicted at discrete locations throughout the wall, when input data such as thermocouple responses are known at one or several interior locations.Special emphasis is placed on the dynamic response of the thermometer, which measures the temperature of the inside fluid, to enable exact determination of both heat transfer coefficient and fluid temperature. The transient response of a thermocouple in a convectional thermowell (pocket) is described by the first-order convective heat transfer model in which the rate of thermoelement temperature change is proportional to the instantaneous difference between the thermoelement and fluid temperatures. 相似文献
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在爆震室内快速形成稳定传播的爆轰波是脉冲爆震发动机的关键.本文利用有限速率化学反应模型,考虑粘性、热对流,基于N-S方程对氢气与空气/氧气为反应混合物的爆震发动机爆震室内流场进行计算.从流场压力、速度、涡量、湍流动能等方面研究爆震室壁面条件对燃烧爆轰性能的影响,分析流场爆轰波压力与流场湍动能的关系,讨论可燃气体燃烧转爆轰的机理.结果表明:爆震室内燃烧爆轰机理受到化学反应能量释放、壁面摩擦效应、壁面与外界热交换的影响.在文中讨论的范围内,相比于半圆形和三角形的爆震室装置,矩形的爆震室增强装置能在更短的时间内得到较高的爆轰波压力和湍动能峰值.壁面粗糙层高度(粗糙度)影响爆震室的燃烧爆轰性质.当壁面粗糙度为0.15mm时,粗糙度对爆轰的激励作用大于抑制作用,能较快形成稳定的爆轰波,且推力为35.5N;随着壁面对流换热系数的增大,爆震室壁面的散热加剧.当壁面对流换热系数大于临界值2.6W/(m2·K)时,爆震室内不能形成稳定的爆震波. 相似文献
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An experimental study was carried out to investigate flame acceleration and deflagration-to-detonation transition (DDT) in
fuel–air mixtures at initial temperatures up to 573 K and pressures up to 2 atm. The fuels investigated include hydrogen,
ethylene, acetylene and JP-10 aviation fuel. The experiments were performed in a 3.1-m long, 10-cm inner-diameter heated detonation
tube equipped with equally spaced orifice plates. Ionization probes were used to measure the flame time-of-arrival from which
the average flame velocity versus propagation distance could be obtained. The DDT composition limits and the distance required
for the flame to transition to detonation were obtained from this flame velocity data. The correlation developed by Veser
et al. (run-up distance to supersonic flames in obstacle-laden tubes. In the proceedings of the 4th International Symposium
on Hazards, Prevention and Mitigation of Industrial Explosions, France (2002)) for the flame choking distance proved to work
very well for correlating the detonation run-up distance measured in the present study. The only exception was for the hydrogen–air
data at elevated initial temperatures which tended to fall outside the scatter of the hydrocarbon mixture data. The DDT limits
obtained at room temperature were found to follow the classical d/λ = 1 correlation, where d is the orifice plate diameter and λ is the detonation cell size. Deviations found for the high-temperature data could be
attributed to the one-dimensional ZND detonation structure model used to predict the detonation cell size for the DDT limit
mixtures. This simple model was used in place of actual experimental data not currently available.
PACS 47.40.-x; 47.70.Fw
This paper was based on work that was presented at the 19th Interna-tional Colloquium on the Dynamics of Explosions and Reactive
Sys-tems, Hakone, Japan, July 27 - August 1, 2003 相似文献
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The problem is considered concerning the breakdown of an arbitrary discontinuity, due to the emergence of a detonation wave at the boundary of a condensed explosive charge. The real equation of state of the detonation products of Hexogen was used in the numerical calculations. A u vs p diagram is constructed, which allows graphical calculations to be carried out of the discontinuity breakdown for different media. A comparison is carried out of the calculated values of the initial shock-wave velocities with the experimental data obtained at a certain distance from the explosive charge. It is shown that an increase of the pressure of the gas in which dispersion of the explosion products occurs leads to a reduction of the initial shock wave velocity and to an enhancement of its attenuation during its further motion in the shock tube. 相似文献
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A combined experimental and theoretical study has been carried out to investigate mixed-convection heat transfer in a narrow, vertical cavity. The shear force is produced at the left side of a cavity by a belt moving upward that constitutes the sixth wall of the cavity. The left wall of the cavity was cooled and the opposite (right wall) was heated. Hence, the buoyancy force tries to bring the fluid down, and the shear force tends to induce upward fluid flow. The test cell was equipped with two heat exchangers and three thermocouple racks for measuring the temperature distributions at 12 different positions. The temperature field was scanned in the cavity for various flow and temperature boundary conditions. Three-and-two-dimensional laminar models were used to analyze the problem theoretically. The experimental measurements were found to be in good agreement with the numerical predictions. 相似文献
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本文介绍了一种用光电技术同时测定爆速和爆温、爆压和爆温的方法。用光电比色技术测定炸药爆轰温度的同时,用两个爆轰面上爆轰的时间差计算爆轰波速度;或用透明介质中冲击波速度来反算炸药中的爆轰压力。方法原理可靠,技术简便。 相似文献
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爆炸去磁脉冲功率发生器的实验和理论计算 总被引:2,自引:0,他引:2
设计了两种结构的爆炸去磁脉冲功率发生器:炸药透镜平面波冲击加载圆柱形磁体和中心装药冲击加载圆环形磁体,磁体材料都采用Nd2Fe14B永磁体。进行了爆炸冲击加载实验,测量了爆炸去磁脉冲发生器的输出电流、电压以及Nd2Fe14B永磁体中的冲击波速度。通过对爆炸去磁脉冲功率发生器基本原理的分析,建立了感生电动势的理论计算方法。用Maxwell 3D电磁场分析软件,对Nd2Fe14B永磁体进行了静磁场分析,给出了Nd2Fe14B永磁体的磁场强度分布规律。实验结果表明:爆炸去磁脉冲功率发生器每匝线圈能够产生约67 V的感生电动势,对于0.56 H的电感负载能够输出脉宽78.3 s、峰值1 212 A的脉冲电流。 相似文献
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Recent experimental results on detonation limits are reported in this paper. A parametric study was carried out to determine the minimum tube diameters for steady detonation propagation in five different hydrocarbon fuel–oxygen combustible mixtures and in five polycarbonate test tube diameters ranging from 50.8 mm down to a small scale of 1.5 mm. The wave propagation in the tube was monitored by optical fibers. By decreasing the initial pressure, hence the sensitivity of the mixture, the onset of limits is indicated by an abrupt drop in the steady detonation velocity after a short distance of travel. From the measured wave velocities inside the test tube, the critical pressure corresponding to the limit and the minimum tube diameters for the propagation of the detonation can be obtained. The present experimental results are in good agreement with previous studies and show that the measured minimum tube diameters can be reasonably estimated on the basis of the \(\lambda \) /3 rule over a wide range of conditions, where \(\lambda \) is the detonation cell size. These new data shall be useful for safety assessment in process industries and in developing and validating models for detonation limits. 相似文献