Quantitative temperature imaging in gas-phase turbulent thermal convection by laser-induced fluorescence of acetone

In this paper, an acetone planar laser-induced fluorescence (PLIF) technique for nonintrusive temperature imaging is demonstrated in gas-phase (Pr = 0.72) turbulent Rayleigh-Bénard convection at Rayleigh number Ra = 1.3᎒⁵. The PLIF technique provides quantitative spatially correlated temperature data without the flow intrusion or time lag associated with physical probes, and without the significant path averaging that plagues most optical heat-transfer diagnostic tools, such as the Mach-Zehnder interferometer, thus making PLIF an attractive choice for quantitative thermal imaging in easily perturbed, complex three-dimensional flow fields. The "instantaneous" (20-ns integration time) thermal images presented have a spatial resolution of 176쐀아 µm and a single-pulse temperature measurement precision of - 2.5 K, or 2.5% of the total temperature difference. These images represent a two-dimensional slice through a complex three-dimensional flow, allowing for thermal structure of the turbulence to be quantified. Statistics such as the horizontally averaged temperature profile, root-mean square (rms) temperature fluctuation, two-point spatial correlations, and conditionally averaged plume structures are computed from an ensemble of 100 temperature images. The profiles of the mean temperature and rms temperature fluctuation are in good agreement with previously published data, and the results obtained from the two-point spatial correlations and conditionally averaged temperature fields show the importance of large-scale coherent structures in this turbulent flow.     

Dust entrainment in a shock-induced,turbulent air flow

Dust from a layer on the floor of a shock tube is entrained by the air flow behind the unsteady shock wave. The development of the dust mass concentration profiles is measured by means of an optical extinction method. The concentration profiles which can be described by an exponential law approach a stationary limit consistent with the results of pneumatic transport theory. A theoretical model simulating the dust entrainment by a diffusion process is evaluated numerically and compared with the experimental results.     

A laser-induced fluorescence measurement for aqueous fluid flows with improved temperature sensitivity

This paper presents temperature-sensitive laser-induced fluorescence measurements of Fluorescein 27 dissolved in aqueous solutions. We show that Fluorescein 27, dissolved in water and excited by a 532-nm Nd:YAG laser pulse, yields improved temperature sensitivity over traditional organic dyes such as Rhodamine B. The high temperature sensitivity of Fluorescein 27 when excited at 532 nm is due primarily to a temperature-dependent shift of the absorption spectrum to longer wavelengths for increased temperatures. The linearity of the fluorescence signal with respect to the incident laser intensity and dye concentration is reported. In addition, Fluorescein 27 dissolved in an aqueous solution remains photo-stable for >10⁵ laser pulses at both ambient and high temperatures (T > 60°C) when excited with low-irradiance laser pulses. Finally, we demonstrate that using a dual tracer (or ratiometric) technique in which the fluorescence from Fluorescein 27 and another dye (e.g., Rhodamine B or Kiton Red 620) are detected following the 532 nm excitation results in a significantly enhanced temperature sensitivity over a single tracer measurement and previously reported dual tracer methods. Such temperature sensitivity is useful in multi-dimensional temperature imaging and temporally resolved measurements.

---

Limited-view optical tomography technique and its application to temperature field measurement in flow of hot air

In this paper, a limited-view optical tomography technique is presented, which contains an orthographic holography system, an image processing system and the simultaneous algebraic reconstruction technique (SART). Using this technique, the temperature field of a cross section in the flow of hot air from a nozzle is measured. The measured results are satisfactory. The project supported by the National Natural Science Foundation and the State Science and Technology Commission of China     

Speckle photographic measurement of turbulence in an air stream with fluctuating temperature

The deflection of laser light passing through the mildy heated, turbulent air stream in a lowspeed wind tunnel is measured by means of speckle photography. This optical wholefield method provides a dense distribution of data values of the deflection angle in the field of view. When isotropic turbulence is assumed, it becomes possible to calculate the correlation function of the three-dimensional, turbulent temperature (or density) field from the correlation function of the plane distribution of measured deflection angles. Spectra and characteristic length scales are determined and compared with cold-wire data reported in the literature.A version of this paper was presented at the 10th Symposium on Turbulence, University of Missouri-Rolla, Sept. 22–24, 1986To Professor R. J. Emrich on the occasion of his 70th birthday     

Local film thickness and temperature distribution measurement in wavy liquid films with a laser-induced luminescence technique

Heat transfer in falling liquid film systems is enhanced by waviness. Comprehension of the underlying kinetic phenomena requires experimental data of the temperature field with high spatiotemporal resolution. Therefore a non-invasive measuring method based on luminescence indicators is developed. It is used to determine the temperature distribution and the local film thickness simultaneously. Results are presented for the temperature distribution measurement in a laminar-wavy water film with a liquid side Reynolds number of 126 flowing down a heated plane with an inclination angle of 2° at two positions in flow direction. The measured temperature distributions are used to calculate the local heat transfer coefficient for solitary waves at two positions in flow direction.     

A laser interferometric measurement of the temperature distribution in convective thermal transfer boundary layers

By means of a double mirror interferometry a two-dimensional temperature distribution measurement in convective thermal boundary layers is presented. When the cold air flows along a hot plate model, the interferometric fringe inside the boundary layer will bend. According to the displacement of the fringe and the relation between temperature and index of refraction, a two-dimensional temperature profile is obtained. All is accomplished by optical device with the help of micro-computer without any contact with the flow field. The project supported by the National Natural Science Foundation of China     

比色测温技术在瞬态爆炸温度场测量中的应用研究

为了研究瞬态爆炸温度场分布规律,基于高速相机、黑体辐射理论、图像传感器的拜尔阵列和自编python代码,构建了依据比色测温原理的高速二维温度测试系统,并对添加不同含量TiH₂的乳化炸药、TiH₂粉尘以及C₂H₂气体的爆炸温度场进行了测量。实验结果表明：TiH₂的加入可以显著提高炸药的爆炸温度和火球持续时间,当乳化炸药中的TiH₂质量分数为6%时,爆炸平均温度最大值为3048 K,相比纯乳化炸药提高了41.5%;此外,TiH₂粉尘云火焰平均温度呈现先增大,再稳定,最后减小的趋势,浓度为500 g/m³的粉尘云火焰平均温度高于浓度为833 g/m³的平均温度,其最高平均温度分别为2231 和 2192 K;10%C₂H₂/90%空气预混气体（即体积分数为10%的C₂H₂和90%空气组成）的早期火焰温度均匀,内部略低于边缘温度,随着火焰膨胀,火焰边缘温度逐渐升高,火焰平均温度开始降低。与传统爆炸测温手段相比,比色测温方法可以准确测量某区域的瞬态爆炸温度,获得温度分布云图,为研究瞬态爆轰温度规律及影响因素提供了一种新的技术手段。

     

TiNi合金冲击相变过程中温度变化规律的实验研究

针对初始SME(shape memory effect)和PE(pseudo-elastic)状态TiNi合金试样,采用带有红外测温系统的SHPB冲击压缩装置,实时测量了冲击相变过程中两种材料试样表面瞬态温度,并根据实验结果计算了相应的温度变化。实验结果表明,冲击加载相变过程中,温度随相变应变的增大而升高,当应变最大时,温度最高;卸载过程中,对初始PE状态试样,温度降低,对初始SME状态试样,温度保持最高温度不变或降低,这同加载最高温度有关;卸载完成后,两种试样温度均高于其初始温度。计算温度结果表明,相变耗散功对加、卸载相变过程中温度变化的作用不可忽略。     

Composition measurement of bicomponent droplets using laser-induced fluorescence of acetone

Commercial fuels are complex mixtures, the evaporation of which remains particularly difficult to model. Experimental characterization of the differential vaporization of the components is a problem that is seldom addressed. In this paper, the evaporation of binary droplets made of ethyl-alcohol and acetone is investigated using a technique of measurement of the droplet composition developed in purpose. This technique exploits the laser induced fluorescence of acetone which acts as a fluorescent tracer as well as the more volatile component of the fuel associated with an accurate measurement of the droplet diameter by forward scattering interferometry. A model of the fluorescence intensity of the binary mixture, taking into account the absorption of the acetone molecules, is proposed and validated. The sensitivity of the technique is discussed. Finally, the reliability of the technique is demonstrated on binary combusting droplets in linear stream.     

Reducing thermal shock-induced vibration of an axially moving beam via a nonlinear energy sink

Nonlinear Dynamics - Thermal shock-induced vibration suppression of an axially moving beam with a nonlinear energy sink (NES) is investigated. Owing to thermal shock on the beam, the beam is...     

Laser absorption density direct measurements with limitation of temperature variation field in shock-induced gaseous mixing

We describe a laser absorption technique to obtain reasonably accurate density profiles within a shock-induced Richtmyer-Meshkov mixing zone. Assuming a small temperature variation through the probed region, a single wavelength absorption experiment only is needed. When this criterium is satisfied, the technique described represents a considerable simplification over the more generally required dual wavelength experiments. Received 4 May 1996 / Accepted 7 October 1996     

Application of underwater shock wave and laser-induced liquid jet to neurosurgery

Paper deals with applications of underwater shock waves to medicine. A historical development of underwater shock wave generation by using pulsed Ho:YAG laser beam irradiation in water is briefly described and an overview is given regarding potential applications of shock waves to neuro-surgery. The laser beam irradiation in a liquid-filled catheter produces water vapor bubble and shock waves intermittently produces micro-liquid jets in a controlled fashion from the exit of the catheter. Correlations between shock dynamics and bubble dynamics are emphasized. To optimize the jet motion, results of basic parametric studies are briefly presented. The liquid jet discharged from the catheter exit has an impulse high enough to clearly exhibit effectiveness for various medical purposes. In liquid jets we observed reasonably strong shock waves and hence invented a compact shock generator aiming to apply to microsurgery. We applied it to a rat's bone window and developed an effective method of brain protection against shock loading. The insertion of Gore-Tex® sheet is found to attenuate shock waves drastically even for very short stand off distance and its physical mechanism is clarified. The laser-induced liquid jet (LILJ) is successfully applied to soft tissue dissection. Animal experiments were performed and results of histological observations are presented in details. Results of animal experiments revealed that LILJ can sharply dissect soft tissue with a minimum amount of liquid consumption, while blood vessels larger than 0.2 mm in diameter are preserved. Shock waves and LILJ have a potential to be indispensable tools in neuro-surgery.This paper was based on work that was presented at the 2nd International Symposium on Interdisciplinary Shock Wave Research, Sendai, Japan, March 1–3, 2005.Communicated by K. Takayama PACS 42.62.Be, 47.40.-x, 42.62.-b     

Seeding of high temperature air flow

Seeding of high temperature air flows is problematic because common seeding materials can ignite and may pose a threat for human health in case of inhalation. Sodium chloride is proposed as a seeding material to avoid these problems. The generation of crystals using an ultrasonic atomizer is described and the measured particle size distribution is presented. The described method has the additional advantage that the particle size can easily be adjusted. This allows the operator to comply with the experimental requirements in terms of resolvable frequencies. The described method has been successfully applied to LDA measurements in a 500°C air flow.     

PVDF在动态应变测量中的应用

研究了用PVDF压电薄膜进行动态应变测量的原理和方法,在单向应变块上对两种PVDF应变片的应变电荷常数进行了标定,并对一维应力杆中的应变波形进行了测量。实验给出了较好的测量精度。研究结果表明,PVDF应变片在动态应变测量中具有很好的应用潜力。     

Measurements of mean and fluctuating temperature in an underexpanded jet using electrostrictive laser-induced gratings

Instantaneous temperature measurements were obtained in an underexpanded jet using electrostrictive laser-induced gratings. Evaluation of the technique under static, low-pressure conditions provided a baseline uncertainty or precision for single-shot temperature measurements of 4.4% of the local mean temperature, which represents the minimum detectable temperature fluctuation. The underexpanded jet was operated at a nozzle pressure ratio of 2.39 and a fully expanded jet Mach number of 1.19. Data were acquired along the centerline and over two radial traverses through the shear layer. Mean temperature data agree well with expectations, describing the shock-cell structure and the compressible shear layer. The growth in shear-layer width with downstream distance can be identified in the mean and fluctuating temperature measurements. Temperature fluctuations are near the baseline detection limit in the jet core and surrounding ambient air, and reach a maximum in the shear layer. The temperature fluctuation measurements compare well with previous computational and experimental work, confirming the application of the technique to a turbulent, supersonic flow.     

Simultaneous imaging of temperature and mole fraction using acetone planar laser-induced fluorescence

Imaging of concentration with acetone PLIF has become popular in mixing investigations. More recently, studies of the temperature dependences of acetone fluorescence have enabled quantitative imaging of temperature using single- or dual-wavelength excitation strategies. We present here the first demonstration of simultaneous imaging of temperature and mole fraction with acetone PLIF. Laser excitation is at 248 and 308 nm; the resulting fluorescence images are captured by an interline transfer CCD camera capable of acquiring two frames with a separation in time of as little as 500 ns. In addition to adding temperature imaging capability, this dual-wavelength approach enables mole fraction to be accurately measured in non-isothermal flows. Tests in a heated turbulent jet demonstrate the ability to record instantaneous mole fraction and temperature structure. The expected correspondence of the temperature and concentration fields is observed, and mean values of these quantities derived from image averaging show the expected radial and centerline profiles as the jet becomes fully developed. Received: 13 January 1999/Accepted 10 February 2000     

Heat conduction in a plane wall subject to periodic temperature changes

Analytical solutions for the heat conduction in a plane wall with periodic temperature variations at the wall surface are presented. Series and asymptotic developments of these solutions are deduced. The results are important for the calculation of the heat transfer in rotary kilns or other rotaring units.

---

Die Wärmeleitung in einer ebenen Wand mit periodischen Temperaturänderungen

Zusammenfassung Es werden analytische Lösungen für die Wärmeleitung in einer ebenen Wand mit periodischen Temperaturänderungen an ihrer Oberfläche mitgeteilt. Reihen- und asymptotische Entwicklungen dieser Lösungen werden abgeleitet. Die Ergebnisse sind wichtig für die Berechnung des Wärmetransportes in Drehrohröfen oder ähnlichen Maschinen.

---

Nomenclature a ² =/ C m²/s thermal diffusivity, Eq. (1) - C J/kg K specific heat - F K initial temperature of the wall, Eq. (4) - F m² surface of the wall - G Green's function, Eq. (10) - G₁ Green's function, Eq. (12) - h m thickness of the wall - H Heaviside function, Eq. (5) - k constant, Eq. (25) - k _x constant, Eq. (25) - Q J total energy, Eq. (17) - Q ^u J total energy from temperatureU, Eq. (18) - Q ^v J total energy from temperatureV, Eq. (19) - s s^–1 Laplace variable - t s time - t ₁ s heating time, Eq. (5) - t ₂ s period, Eq. (5) - T K temperature of the wall - T _i K surface temperature of the wall - T ₁ K surface temperature of the wall during the heating time - T ₂ K surface temperature of the wall during the cooling time - U K temperature of the wall defined in problem 1 - V, K temperature of the wall defined in problem 2 - x m coordinate - ₀ W/m²K overall heat transfer coefficient, Eq. (31) - ₁₀ W/m² K overall heat transfer coefficient, Eq. (32) - ₂₀ W/m² K overall heat transfer coefficient, Eq. (33) - Dirac Delta function - s^–1/2 parameter, Eq. (6) - W/mK thermal conductivity - kg/m³ specific mass - dimensionless time, Eq. (34) - Riemann Zeta function surfix Laplace transformed variable