Temperature Measurements Of Droplets Research Articles

Measurements of deposition rate and droplet temperature in GMAW of aluminum alloys

This article explores the reason behind the higher deposition rate in Mg-containing aluminum alloys in gas metal arc welding (GMAW). Experiments performed on ER1100 (Mg-free alloy) and ER5183 (high Mg alloys) measured current, wire feed speed, and droplet temperature. A non-linear analysis of Joule heating at the electrode extension and an analysis of the power needed to heat the consumable to the droplet temperature were performed. Analysis revealed that Joule heating is two orders of magnitude smaller than what was necessary for the higher wire feed speed. The droplet temperature measurements were done for the first time for both consumables under identical conditions, which revealed that ER5183 had a lower droplet temperature than ER1100 by almost 350 K.

Droplet temperature measurement in GMAW

This work presents measurements of the droplet temperature for the Gas Metal Arc Welding process. Four different aluminium electrodes were used for experiments performed under the same conditions. The approach used yielded higher droplet temperatures than were obtained in previous experiments with the same raw data because the energy balance approach differed. However, trends were similar, with a minimum value close to the transition current and a tendency to increase with the current. Anode fall voltages behaved similarly, increasing with the current. Differences in temperature were found between the four electrodes. This can be explained by the different alloying elements present on the electrodes, which evaporate and take energy out of the droplet.

Theoretical investigation of global rainbow refractometry in spray combustion of polydisperse microdroplets

Global rainbow refractometry (GRR) is an important technique for temperature measurements of droplets and has been applied to a wide field of technical sprays. In this work, the application of GRR to sprays with droplets as small as m in diameter is investigated by means of Lorenz–Mie theory to evaluate the influence of varying droplet size distributions (DSD) and varying refractive indexes on the global rainbow. DSDs were found by fitting a Rosin–Rammler–Sperling–Bennett distribution to experimental data. Different DSDs, that are typical for flame spray pyrolysis applications were evaluated systematically with varying widths and mean diameters. A study of the angular rainbow maxima position with varying widths of DSDs shows a strong non-linearity. It is concluded that GRR experiments in polydisperse applications should be accompanied with an accurate sizing technique. Furthermore, possible droplet size-dependent distributions of refractive indexes within the samples may influence the results.

Droplet Temperature Measurement in Metal Inert Gas Welding Process by Using Two Color Temperature Measurement Method

Droplet Temperature Measurement in Metal Inert Gas Welding Process by Using Two Color Temperature Measurement Method

Comparative investigation on the spray characteristics and heat transfer dynamics of pulsed spray cooling with volatile cryogens

Cryogen spray cooling with R134a has been widely used in laser dermatology such as port wine stain to prevent unspecific thermal injury due to the absorption of laser energy by melanin in the epidermis. However, R134a spray cooling has shown poor efficacy for darkly-pigmented human skin. This paper presents an experimental study on the spray characteristics and heat transfer dynamics of pulsed spray cooling with three kinds of volatile cryogens (R134a, R407C and R404A), the latter two of which have potential to improve the cooling effect due to their lower saturation temperature. The spray patterns reveal that R404A generates the narrowest spray width and the smallest cooling spot on the cooling surface, which facilitates the accurate control of the cooling area. The R404A spray produces the smallest droplet diameter and the largest velocity, whereas the opposite applies to the R134a spray. The droplet temperature measurements show that R404A spray has the lowest temperature of spray, while the R134a spray has the highest. However, the non-dimensional temperature in the decrease period shows a similar pattern, independent of the cryogens. For the common spray distance in laser surgery (30mm), R404A spray leads to the lowest surface temperature and highest heat flux, and also removes the most heat from the cooling surface, indicating that R404A has the strongest cooling capacity. Furthermore, R404A spray has the least liquid film resistance time on the cooling surface, implying that it provides the best selectively spatial cooling effect. The results of spray and heat transfer all reveal that R404A possesses significant superiority with regard to pulsed spray cooling for epidermis protection, with the potential of substituting the current R134a in the application of laser dermatology, especially in the case of darkly-pigmented human skin.

Droplet temperature measurement based on 2-color laser-induced exciplex fluorescence

Measurements of liquid phase temperature distributions in liquid–vapor co-existing conditions (such as in evaporating sprays) are important to understand the physics of droplet evaporation. The techniques based on laser-induced fluorescence are not suitable for evaporating case since both liquid and vapor phases emit fluorescence with the same wavelength. In this study, the fluorescence from liquid and vapor phases was separated by use of laser-induced exciplex fluorescence (LIEF) technique. Two fluorescence bands from the liquid phase fluorescence spectra were detected simultaneously, and their intensity ratio was correlated to the liquid phase temperature. For the LIEF imaging system, FB-DEMA-n-hexane was selected as it was a typical LIEF system for the vapor concentration diagnostic, and thus easily to be extended to a simultaneous diagnostic on the vapor concentration and the droplet temperature. The fluorescence spectra were obtained in the temperature range from 303 to 423 K. The effects of liquid temperature, liquid pressure, dopant concentration and laser energy on the temperature measurement were investigated. The results show a good linear relationship between the fluorescence ratio and the temperature function. Increasing the dopant concentration can raise the signal-to-noise ratio but deteriorate temperature sensitivity. The optimal range of the dopant concentration was found between 0.1 % and 0.5 %. After calibration, the technique was applied to a monosized droplet stream, and the measurement results demonstrated excellent measurement accuracy with error below 1 % in the range of 303–423 K.

Study of the droplet size effect coupled with the laser light scattering in sprays for two-color LIF thermometry measurements

The present paper deals with a new optical diagnostic that aims to perform droplet temperature measurements based on the two-color laser-induced fluorescence (2cLIF). The 2cLIF requires a single tracer, and the fluorescence intensity is collected on two spectral bands. The ratio of both intensities measured in the case of single monodisperse droplets depends in principle only on the temperature. However, the application in the case of polydispere sprays failed. Indeed, a dependence of the droplet size correlated to the depth of field of the optics, used for fluorescence collection, induces a bias in the ratio value. This work analyses these coupled effects by using combined LIF and Phase Doppler Analyser measurements. This device allows achieving fluorescence ratio measurements per droplet size class. The study is conducted with two different sprays in terms of particles size and density. The use of a third spectral band of detection (3cLIF) and a long distance microscope leads to correct the size effect and reduce the depth of field effect, respectively. These investigations are then demonstrated by measuring temperatures in an overheated water spray.

Combined PDA and LIF applied to size–temperature correlations measurements in a heated spray

This paper aims to demonstrate the possibility to achieve droplet temperature measurements per droplet size class by combining two-color laser-induced fluorescence (LIF) and phase Doppler analyzer (PDA). For that purpose, PDA and LIF signal acquisitions are synchronized on the same time base. LIF signal is processed on each of the defined size classes in order to derive the droplet temperature. Since PDA is roughly sensitive to D 2 and LIF roughly to D 3, the detection range of the combination of the two techniques in term of droplet size is carefully analyzed. Finally, the technique is demonstrated on a spray of n-decane injected in a turbulent over-heated air flow. The influence of the droplet size and Stokes number on the heating process of the droplets is clearly highlighted.

New insight into two-color LIF thermometry applied to temperature measurements of droplets

When laser-induced fluorescence of droplets is used for measurements such as droplet temperature, a new dependence of the droplet size on the spectral distribution of fluorescence has been highlighted. The two-color laser-induced fluorescence technique applied to droplet temperature measurement requires a single fluorescent tracer and two spectral bands of detection for which the temperature sensitivity is different. Generally, the ratio of the intensities measured on each of the spectral bands of detection is assumed to be only temperature dependent. However, droplet dependence on diameter is also likely to influence the intensities ratio. This study provides some illustrations of the phenomenon, first on sprays with different mean statistical diameters and secondly on single droplets, for two temperature-sensitive fluorescent tracers in their solvents: sulforhodamine B dissolved in water and pyrromethene 597-8C9 dissolved in n-decane.

Measurements of multicomponent microdroplet evaporation by using Rainbow Refractometer and PDA

The evaporation process of a multi-component droplet has been studied utilizing optical diagnostic techniques. Investigation focused on the measurements of the different volatility mixtures and the variation of the mass fraction within a droplet of different components. The method for determining the temperature of a multicomponent droplet containing nonvolatile and volatile compositions has been proposed. For a droplet with two volatile compositions, such as water and ethanol mixture, the model of evaporation for droplet temperature measurements was also suggested based on the experimental data. Droplets with different mass fractions of each component under different temperature conditions were measured utilizing a primary rainbow refractometer and a recently improved phase-Doppler analyzer. It was also found that the droplet temperature could hardly reach its saturation temperature within the droplet unlike explained by previous researchers. The effects of temperature gradient within an evaporating microdroplet and the temperature discontinuity on the evaporating surface have been discussed.

Measurement of the temperature distribution within monodisperse combusting droplets in linear streams using two-color laser-induced fluorescence

Two-color laser-induced fluorescence can be use to perform space-averaged flying droplet temperature measurements. In this paper, the possibility to extend this technique to the measurement of the temperature distribution within a moving combusting droplet is considered and demonstrated. This technique may provide new experimental data related to the heat diffusion in liquid fuel droplets injected in high-temperature gas streams, for example, in combustion chambers. The main principles of the technique and the data reduction process are discussed, and a test on combusting a monodisperse ethanol droplets (200 μm in diameter) stream is presented.

Evaporating and combusting droplet temperature measurements using two-color laser-induced fluorescence

The paper presents a new technique based on laser-induced fluorescence, allowing droplet temperature measurement of evaporating and combusting droplets to be performed. The liquid spray is seeded with a low concentration of rhodamine B. The fluorescence, induced by the green line of an argon laser, is measured on two separated color bands. It is demonstrated that two color bands can be selected for their strong difference in the temperature sensitivity of the fluorescence quantum yield. The determination of the fluorescence ratio between the fluorescence intensity corresponding to each color band allows the tracer concentration and the droplet size dependences to be eliminated. The technique was applied on a monodisperse spray: the effect of a thermal impulse on the distribution of the droplet temperature is studied and, the temperature of combusting droplets is investigated.

LASER-INDUCED FLUORESCENCE TEMPERATURE SENSOR FOR IN-FLIGHT DROPLETS

Laser-induced fluorescence (LIF) is used to develop a noncontact temperature sensor. The noninvasive sensor is sensible, reversible, and reproducible to temperature changes, and can be used as a temperature indicator for in-flight droplets. A calibration curve relating fluorescence emission intensity to temperature of a solution was developed for a mixture of ethanol-pyrene at S mM concentration. The percentage by mass of the mixture is 99.9% ethanol and 0.1% pyrene. The calibration curve was used as a noninvasive sensor to measure temperature of in-flight droplets. The mixture of ethanolpyrene concentration at 5 mM was used as the base fluid to generate droplets of 215 μm. These droplets were atomized at a velocity of 10 m/s. Droplet temperature measurements were achieved at 1.9, 2.9, and 3.9 cm downward from the tip of the atomizer with the aid of the noncontact thermometer. The initial temperatures of the droplets were changed to 50, 40, and 33°C, and the resulting decrease in temperatures was attributed to heat and mass transfer between the droplets and the surrounding environment

Global rainbow thermometry for droplet-temperature measurement

Standard rainbow thermometry connects the scattering angle of the main rainbow maximum, generated by a single droplet, to the droplet's refractive index and thus to its temperature. Droplet nonsphericity influences the rainbow position and therefore degrades the quality of the droplet-temperature measurement. We propose global rainbow thermometry, which measures the average rainbow position that is created by multiple droplets and from which a mean temperature can be derived. The new technique aims at eliminating the nonsphericity effect. The principle of this method is presented, and a typical recorded image is discussed.