探针移动速度对等离子体射流热流密度测量结果的影响

采用自行研制的中心嵌有铜柱感应件的小尺寸杆状热流探针,在低扰动条件下,对射入大气环境的纯氩层流等离子体射流传向铜探头表面的热流密度进行了动态测量。结果表明,在射流最高温度16500 K、最大轴向速度850 m/s、探针垂直于射流流动方向的移动速度130～260 mm/s的实验参数范围内,随着探针移动速度的提高,测得的热流密度值减小;射流温度和速度越高,探针移动速度对热流密度测量值的影响越大。

高超声速飞行器测热试验研究

在JF-8脉冲风洞中,来流马赫数Ma＝8.0,来流单位长度雷诺数Re/L=1.47×107和2.52×107(1/m)两种试验条件下,对高超声速飞行器1/20缩尺模型进行了表面气动热的测量.模型攻角α=0°,10°,15°,20°,25°和30°.试验给出机身对称面、翼前缘、立尾前缘等处的热流率分布.机头部分最大热流率与由Fay-Riddell公式计算的驻点热流Q0率接近,翼前缘最大热流率在全机身中最大,约为Q0的2倍,因此翼前缘的热环境是最严酷的.

Subcooled Pool Boiling at Microgravity: Preliminary Ground-Based Experimental Results

A temperature-controlled pool boiling (TCPB) device was developed to perform pool boiling heat transfer studies at both normal gravity on Earth and microgravity in the drop tower Beijing and aboard a Chinese recovery satellite. Two platinum wires of 60 ?m in diameter were simultaneously used as heaters and thermometers. The lengths were 30 mm and 40 mm, respectively. The ends of wires were soldered with copper poles to provide low resistance paths for the electric current. The heater resistance, and thus the heater temperature, was kept constant by a feedback circuit similar to that used in constant-temperature hot-wire anemometry. The fluid was R113 at 0.1 Mpa and subcooled by 30 ?C nominally for all cases. The results of the experiments at normal gravity were presented. Four modes, namely single-phase convection, nucleate boiling, transition two-mode boiling, and film boiling were observed. A few data obtained from several preliminary experiments at microgravity in the drop tower Beijing were also presented. A slight increase of the heat flux was obtained.

Experimental Study on Subcooled Pool Boiling in Microgravity Utilizing

Pool Boiling in Microgravity: Recent Results and Perspectives for the Project DEPA-SJ10

Two research projects on pool boiling in microgravity have been conducted aboard the Chinese recoverable satellites. Ground-based experiments have also been performed both in normal gravity and in short-term microgravity in the Drop Tower Beijing. Steady boiling of R113 on thin platinum wires was studied with a temperature-controlled heating method, while quasi-steady boiling of FC-72 on a plane plate was investigated with an exponentially increasing heating voltage. In the first case, slight enhancement of heat transfer is observed in microgravity, while diminution is evident for high heat flux in the second one. Lateral motions of bubbles on the heaters are observed before their departure in microgravity. The surface oscillation of the merged bubbles due to lateral coalescence between adjacent bubbles drives it to detach from the heaters. The Marangoni effect on the bubble behavior is also discussed. The perspectives for a new project DEPA-SJ10, which has been planned to be flown aboard the Chinese recoverable satellite SJ-10 in the future, are also presented.

丝状加热面池沸腾临界热流尺度效应研究

本文以丝状加热表面上的池沸腾传热现象为主要研究对象，利用地面常重力实验，研究了不同热丝直径、不同过冷度下（(0～40℃）的丝状加热片面FC-72液体和丙酮液体的池沸腾传热特性。 本文利用自主研发的一套可控过冷度池沸腾实验设备，使用纯度为99.99%的铂丝同时作为加热元件和测温元件，加热丝直径分别为0.06mm、0.025mm、0.1mm，长度为30mm。实验采用控制加热电压按阶梯形式增长或下降（时间常数约20s）的稳态加热方式。 实验所得单相自然对流传热数据同Kuehn-Goldstein（1976）换热公式预测结果具有较高的一致性，说明实验设备可靠、实验数据可信。 实验过程中发现，在相同压力条件下，随着过冷度的增加，沸腾传热强化；CHF值在低过冷度时呈线性增加，然后增加趋势变缓。丙酮实验中，0.06mm热丝和0.1mm热丝在低过冷度(2.5～10℃)情况下都出现了从自然对流直接进入双膜态现象，不过，当降低加热电压时，膜态沸腾仍转化为核态沸腾，此时继续增高加热电压，沸腾曲线仍沿常规核态沸腾曲线上升至CHF后，再转换为膜态沸腾。对于同等直径热丝，无论核态沸腾或双膜态沸腾，在丙酮中所产生汽泡尺寸明显偏大。 过冷沸腾中，临界热流随过冷度的增加呈现出非线性依赖关系。在低过冷度线性区，FC-72中实验结果与几种低过冷度线性模型较一致；丙酮中实验结果 随 变化斜率明显高于几种低过冷度线性模型的预测，显示出对尺度的依赖关系。这说明在小Bond数时存在尺度效应对过冷度的影响，即对于小Bond数情况过冷度和尺度效应的耦合作用是非常重要的。 饱和沸腾中，FC-72和丙酮的CHF值随热丝直径的减小而不断增加，其中，FC-72的CHF数值尽管比LD模型预测结果略低，但定性地依然可用LD模型进行描述，尽管相比于LD模型原始的适用范围 已扩大了1~2个数量级；但丙酮的实验数据却远小于LD模型预测结果。综合分析表明，尽管热丝直径相同，但物性的差异使得FC-72和丙酮实验中的数据点分别处于不同的尺度特征区域，反映了小Bond数情形下分区准则的物性依赖性。

Kinetic Study Of The Rayleigh-Benard Flows

The present paper employs the direct simulation Monte Carlo (DSMC) method to study the Rayleigh-Benard flows, where the temperature ratio of the upper to lower plate is fixed to 0.1. For a Knudsen number (Kn) of 0.01, as the Rayleigh number (Ra) increases, the flow changes from the thermal conductive state to the convective state at about Ra=1700, and the calculated relation of heat flux through the lower plate versus Ra is in good agreement with classical experimental and theoretical results. For Kn=0.05, the thermal conductive state remains stable, and the increase of Ra cannot trigger thermal instability.

Modeling of a coal-fired slagging combustor: Development of a slag submodel

In a slagging combustor or furnace, the high combustion temperature makes the molten slag layer cover the wall and capture the particles. If these particles contain combustible matter, they will continue to burn on the running slag. As a result, the total amount of ash deposition will be much greater than that in dry-wall combustors and the total heat flux through the deposition surface will change greatly. Considering the limitations of existing simulation methods for slagging combustion, this paper introduces a new wall burning model and slag flow model from the analysis; of particle deposition phenomena. Combined with a conventional combustion simulation program, the total computational frame is introduced. From comparisons of simulation results from several kinds of methods with experimental data, the conclusion is drawn that the conventional simulation methods are not very suitable for slagging combustion and the wall burning mechanism should be considered more thoroughly.

Estimation of Transverse Thermal Conductivity of Doubly-periodic Fiber Reinforced Composites

For steady-state heat conduction a new variational functional for a unit cell of composites with periodic microstructures is constructed by considering the quasi-periodicity of the temperature field and in the periodicity of the heat flux fields. Then by combining with the eigenfunction expansion of complex potential which satisfies the fiber-matrix interface conditions, an eigenfunction expansion-variational method (EEVM) based on a unit cell is developed. The effective transverse thermal conductivities of doubly-periodic fiber reinforced composites are calculated, and the first-order approximation formula for the square and hexagonal arrays is presented,which is convenient for engineering application. The numerical results show a good convergency of the presented method, even through the fiber volume fraction is relatively high. Comparisons with the existing analytical and experimental results are made to demonstrate the accuracy and validity of the first-order approximation formula for the hexagonal array.

Evaporation of Ethanol Drops on a Heated Substrate Under Microgravity Conditions

We present in this paper results obtained from a parabolic flight campaign regarding ethanol sessile drop evaporation under reduced gravity conditions. Drops are created using a syringe pump by means of injection through a PTFE (polytetrafluoroethylene) substrate. The drops are recorded using a video camera and an infrared camera to observe the thermal motion inside the drop and on the heating substrate. The experimental set-up presented in this paper enables the simultaneous visualization and access to the heat flux density that is transferred to the drop using a heat flux meter placed between the heating block and the PTFE substrate. We evidence original thermal spreading phenomena during the ethanol drop creation on a heated PTFE substrate. The drop exhibits specific behaviour which is discussed here. This work is performed in the frame of a French-Chinese collaboration (project IMPACHT) for future experiments in a Chinese scientific satellite.

Neural network retrieval of ocean surface parameters from SSM/I data

A new algorithm based on the multiparameter neural network is proposed to retrieve wind speed (WS), sea surface temperature (SST), sea surface air temperature, and relative humidity ( RH) simultaneously over the global oceans from Special Sensor Microwave Imager (SSM/I) observations. The retrieved geophysical parameters are used to estimate the surface latent heat flux and sensible heat flux using a bulk method over the global oceans. The neural network is trained and validated with the matchups of SSM/I overpasses and National Data Buoy Center buoys under both clear and cloudy weather conditions. In addition, the data acquired by the 85.5-GHz channels of SSM/I are used as the input variables of the neural network to improve its performance. The root-mean-square (rms) errors between the estimated WS, SST, sea surface air temperature, and RH from SSM/I observations and the buoy measurements are 1.48 m s(-1), 1.54 degrees C, 1.47 degrees C, and 7.85, respectively. The rms errors between the estimated latent and sensible heat fluxes from SSM/I observations and the Xisha Island ( in the South China Sea) measurements are 3.21 and 30.54 W m(-2), whereas those between the SSM/ I estimates and the buoy data are 4.9 and 37.85 W m(-2), respectively. Both of these errors ( those for WS, SST, and sea surface air temperature, in particular) are smaller than those by previous retrieval algorithms of SSM/ I observations over the global oceans. Unlike previous methods, the present algorithm is capable of producing near-real-time estimates of surface latent and sensible heat fluxes for the global oceans from SSM/I data.

The Obduction of Equatorial 13 degrees C Water in the Pacific Identified by a Simulated Passive Tracer

The obduction of equatorial 13 degrees C Water in the Pacific is investigated using a simulated passive tracer of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO). The result shows that the 13 degrees C Water initialized in the region 8 degrees N-8 degrees S, 130 degrees-90 degrees W enters the surface mixed layer in the eastern tropical Pacific, mainly through upwelling near the equator, in the Costa Rica Dome, and along the coast of Peru. Approximately two-thirds of this obduction occurs within 10 years after the 13 degrees C Water being initialized, with the upper portion of the water mass reaching the surface mixed layer in only about a month. The obduction of the 13 degrees C Water helps to maintain a cool sea surface temperature year-round, equivalent to a surface heat flux of about -6.0 W m(-2) averaged over the eastern tropical Pacific (15 degrees S-15 degrees N, 130 degrees W-eastern boundary) for the period of integration (1993-2006). During El Nino years, when the thermocline deepens as a consequence of the easterly wind weakening, the obduction of the 13 degrees C Water is suppressed, and the reduced vertical entrainment generates a warming anomaly of up to 10 W m(-2) in the eastern tropical Pacific and in particular along the coast of Peru, providing explanations for the warming of sea surface temperature that cannot be accounted for by local winds alone. The situation is reversed during La Nina years.

Subtropical dipole mode in the Southern Hemisphere: A global view

A global wavenumber-3 dipole SST mode is showed to exist in the Southern Hemisphere subtropical climate variability in austral summer. A positive (negative) phase of the mode is characterized by cool (warm) SST anomalies in the east and warm (cool) SST anomalies in the southwest of the south Indian, Pacific, and Atlantic Oceans, respectively. This coherent dipole structure is largely a response of ocean mixed layer to the atmospheric forcing characterized by migration and modulation of the subtropical high-pressures, in which the latent heat flux play a leading role through wind-induced evaporation, although ocean dynamics may also be crucial in forming SST anomalies attached to the continents. Exploratory analyses suggest that this mode is strongly damped by the negative heat flux feedback, with a persistence time about three months and no spectral peak at interannual to decadal time scales. As the subtropical dipole mode is linearly independent of ENSO and SAM, whether it represents an additional source of climate predictability should be further studied. Citation: Wang, F. (2010), Subtropical dipole mode in the Southern Hemisphere: A global view, Geophys. Res. Lett., 37, L10702, doi: 10.1029/2010GL042750.

Long-Wave Dynamics of Sea Level Variations during Indian Ocean Dipole Events

Long-wave dynamics of the interannual variations of the equatorial Indian Ocean circulation are studied using an ocean general circulation model forced by the assimilated surface winds and heat flux of the European Centre for Medium-Range Weather Forecasts. The simulation has reproduced the sea level anomalies of the Ocean Topography Experiment (TOPEX)/Poseidon altimeter observations well. The equatorial Kelvin and Rossby waves decomposed from the model simulation show that western boundary reflections provide important negative feedbacks to the evolution of the upwelling currents off the Java coast during Indian Ocean dipole (IOD) events. Two downwelling Kelvin wave pulses are generated at the western boundary during IOD events: the first is reflected from the equatorial Rossby waves and the second from the off-equatorial Rossby waves in the southern Indian Ocean. The upwelling in the eastern basin during the 1997-98 IOD event is weakened by the first Kelvin wave pulse and terminated by the second. In comparison, the upwelling during the 1994 IOD event is terminated by the first Kelvin wave pulse because the southeasterly winds off the Java coast are weak at the end of 1994. The atmospheric intraseasonal forcing, which plays an important role in inducing Java upwelling during the early stage of an IOD event, is found to play a minor role in terminating the upwelling off the Java coast because the intraseasonal winds are either weak or absent during the IOD mature phase. The equatorial wave analyses suggest that the upwelling off the Java coast during IOD events is terminated primarily by western boundary reflections.

Ship-board measurements and estimations of air-sea fluxes in the western tropical Pacific during TOGA COARE

Direct air-sea flux measurements were made on RN Kexue #1 at 40 degrees S, 156 degrees E during the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean-Atmospheric Response Experiment (COARE) Intensive Observation Period (IOP). An array of six accelerometers was used to measure the motion of the anchored ship, and a sonic anemometer and Lyman-alpha hygrometer were used to measure the turbulent wind vector and specific humidity. The contamination of the turbulent wind components by ship motion was largely removed by an improvement of a procedure due to Shao based on the acceleration signals. The scheme of the wind correction for ship motion is briefly outlined. Results are presented from data for the best wind direction relative to the ship to minimize flow distortion effects. Both the time series and the power spectra of the sonic-measured wind components show swell-induced ship motion contamination, which is largely removed by the accelerometer correction scheme, There was less contamination in the longitudinal wind component than in the vertical and transverse components. The spectral characteristics of the surface-layer turbulence properties are compared with those from previous land and ocean results, Momentum and latent heat fluxes were calculated by eddy correlation and compared to those estimated by the inertial dissipation method and the TOGA COARE bulk formula. The estimations of wind stress determined by eddy correlation are smaller than those from the TOGA COARE bulk formula, especially for higher wind speeds, while those from the bulk formula and inertial dissipation technique are generally in agreement. The estimations of latent heal flux from the three different methods are in reasonable agreement. The effect of the correction for ship motion on latent heat fluxes is not as large as on momentum fluxes.