Icing is a multiphase/multiscale/multiparameter physical process, and is of frequent occurrence when suitable conditions with temperature, pressure and humidity are met. In the present work, we ...prepared a series of PDMS-matrix nanocomposite films with different SWCNT contents, which were endowed with hydrophobicity based on the low-surface-energy PDMS matrix and the conductivity on the SWCNT filler. Furthermore, by etching the pillar-textured structure on its surface, the nanocomposite with 5.0 wt% SWCNT was given the superhydrophobicity. These nanocomposites can be easily switched from a hydrophobic anti-icing mode to an electro-thermal deicing mode by supplying a low voltage. Using non-contact infrared thermometry, we presented an analysis of the freezing phase transition process of a single water droplet on cooling surfaces with different wettability, and investigated their ice nucleation rate and macroscopic growth velocity on these surfaces. The ice-retarding capability of superhydrophobic nanocomposite surface subjected to lots of condensed droplets was also confirmed, and understanding in light of weak contact interaction with droplets. Also under consideration is the icephobicity after freezing in terms of ice shear strength. In addition, we performed a statistical analysis about the Joule heat distribution on nanocomposite surface, the results of which demonstrated that the nanocomposite could supply a suitable heating function for active deicing, demonstrating with an energy-input deicing experiment subsequently.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•First experimental study of effusion and transpiration cooling on the single blade.•Quantitative investigation of the overall cooling effectiveness on the blade.•Qualitative investigation of flow ...structure via smoke-laser sheet visualization.•Transpiration cooling achieves superior cooling than effusion and internal cooling.
A great number of studies have been conducted on a film cooling for turbine blades, which is to prevent thermal damage on blades originated from high turbine inlet temperature. However, film cooling with several rows of cooling-holes results in lifting-off of coolant film and limited cooling on a restricted area due to flow reattachment. In this study, effusion and transpiration cooling were applied to the single C3X blade. A multiple hole-array with a diameter of 0.5 mm was fabricated by the electric discharging machining, and a porous structure with an equivalent pore diameter of 40 μm was manufactured by the 3-D metal additive manufacturing. Experiments were performed in the high-temperature subsonic wind tunnel, which has a freestream temperature of 100 °C and a velocity of 20 m/s. The surface temperature of blades was measured using infrared thermometry with a specially designed protocol to eliminate background radiation errors from the surroundings. Also, the outflow of coolant from blades was investigated with smoke-laser sheet visualization. The overall cooling effectiveness was quantitatively analyzed on the pressure-side, suction-side, and leading-edge of blades. Due to the enhancement of convective cooling through porous media, transpiration cooling achieves 34% and 25% higher cooling effectiveness than effusion and internal cooling each.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
► In this study we demonstrate how an empirical crop water stress index was related to in situ stress measurements. ► Average seasonal empirical CWSI values were inversely related to crop water use ...and crop yield. ► Contour plots of the average seasonal CWSI can be used to map spatial variability of within-field crop water stress.
The use of digital infrared thermography and thermometry to investigate early crop water stress offers a producer improved management tools to avoid yield declines or to deal with variability in crop water status. This study used canopy temperature data to investigate whether an empirical crop water stress index could be used to monitor spatial and temporal crop water stress. Different irrigation treatment amounts (100%, 67%, 33%, and 0% of full replenishment of soil water to field capacity to a depth of 1.5
m) were applied by a center pivot system to soybean (
Glycine max L.) in 2004 and 2005, and to cotton (
Gossypium hirsutum L.) in 2007 and 2008. Canopy temperature data from infrared thermography were used to benchmark the relationship between an empirical crop water stress index (CWSI
e) and leaf water potential (
Ψ
L) across a block of eight treatment plots (of two replications). There was a significant negative linear correlation between midday
Ψ
L measurements and the CWSI
e after soil water differences due to irrigation treatments were well established and during the absence of heavy rainfall. Average seasonal CWSI
e values calculated for each plot from temperature measurements made by infrared thermometer thermocouples mounted on a center pivot lateral were inversely related to crop water use with
r
2 values >0.89 and 0.55 for soybean and cotton, respectively. There was also a significant inverse relationship between the CWSI
e and soybean yields in 2004 (
r
2
=
0.88) and 2005 (
r
2
=
0.83), and cotton in 2007 (
r
2
=
0.78). The correlations were not significant in 2008 for cotton. Contour plots of the CWSI
e may be used as maps to indicate the spatial variability of within-field crop water stress. These maps may be useful for irrigation scheduling or identifying areas within a field where water stress may impact crop water use and yield.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The turbine inlet temperature keeps increasing as high-efficient gas turbines have been developed for the last decades. The increase of turbine inlet temperature makes the turbine blades being ...exposed in thermally severe conditions, leading to thermal damage. The thermal management with advanced cooling techniques is thus necessary to protect turbine blades from thermal deformations. For properly evaluating the air-cooling effects on turbine blades, the more accurate surface temperature measurement must be preceded. Infrared thermometry has often been employed for high-temperature turbine blades due to its convenience. However, background radiation must be carefully considered if the surrounding environment is at a higher temperature than the surface to be measured, as in the case of a gas turbine blade. In addition, the spectral emittance of an object should also be known a priori. In this study, we propose an accurate measurement scheme of infrared thermometry by properly considering the background radiation from the high-temperature environment as well as the spectral emittance of an object. The accuracy of infrared thermometry was examined for two exemplary surfaces with low and high emittance in a high-temperature wind tunnel. The proposed measurement scheme was found to be in good agreement with the thermocouple measurements within 5% for both surfaces.
•An advanced methodology of IR thermometry is developed considering background radiation.•The test section is specially designed to minimize the background radiation.•The measured normal hemispherical emittance is applied to the temperature conversion method with wavelength.•The transpiration cooling shows better cooling performance than the internal cooling.•The differential conversion method can be a unique solution that is used in actual gas turbine applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•High-speed infrared thermometry allows to obtain time and space-resolved surface temperature distribution.•Local surface heat flux is obtained using the measured surface temperatures.•The ...mechanistic parameters relevant in analyzing collision heat transfer are measured.•The effectiveness for a single-droplet/wall collision is determined.
This study experimentally investigated the heat transfer characteristics during the collision of a single droplet with a plate heated to temperatures ranging from 176 to 375°C. The heated plate was made of infrared (IR)-transparent sapphire with a very thin IR-opaque platinum film on top, which allowed the top-surface temperature to be measured from below using an IR camera. The dynamics of the droplets and the corresponding top-surface temperature distribution of the heated plate during collision were acquired using synchronized high-speed video and IR cameras. The three-dimensional transient conduction equation for the heated plate was solved numerically using the measured surface temperatures as boundary conditions, and the time- and space-resolved surface heat flux was obtained. Various physical characteristics associated with the heat transfer during the collision of a single droplet with a heated plate were analyzed, including the local heat flux distribution, effective heat transfer area, instantaneous heat transfer rate, total heat transfer, and vapor film thickness. In addition, the crucial surface temperature at which the total heat transfer from a single-droplet collision is significantly degraded, known as the dynamic Leidenfrost point, was detected.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•We studied pool boiling of water at ambient pressure under exponential heat inputs.•We used synchronized infrared thermometry and high-speed video.•Single phase heat transfer is governed by ...transient conduction.•Transient boiling mechanisms depend on subcooling and period of the heat escalation.
This paper presents an investigation of transient pool boiling heat transfer phenomena in water at atmospheric pressure under exponentially escalating heat fluxes on plate-type heaters. Exponential power escalations with periods ranging from 5 to 100ms, and subcooling of 0, 25 and 75K were explored. What makes this study unique is the use of synchronized state-of-the-art diagnostics such as infrared (IR) thermometry and high-speed video HSV, which enabled accurate measurements and provided new and unique insight into the transient boiling heat transfer phenomena. The onset of nucleate boiling (ONB) conditions were identified. The experimental data suggest that ONB temperature and heat flux increase monotonically with decreasing period and increasing subcooling, in accordance with the predictions of a model based on transient conduction and a nucleation site activation criterion. Various boiling regimes were observed during the transition from ONB to fully developed nucleate boiling (FDNB). Onset of the boiling driven (OBD) heat transfer regime and overshoot (OV) conditions were identified, depending on the period of the power escalation and the subcooling. Forced convection effects have also been investigated and are discussed in the companion paper (Part II).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•We develop a machine learning methodology to analyze boiling experiments.•It is as accurate as image processing algorithms but much faster.•It can be used online and quasi-real-time.•Its ...capabilities are independent of the operating heat flux and surface morphology.
We present a machine learning methodology that can be used online and quasi-real-time (i.e., as fast as we can practically run an experiment) to accelerate the analysis of infrared, boiling heat transfer investigations. Precisely, we use feed-forward artificial neural networks with one layer of hidden neurons to measure bubble growth time, bubble period, and nucleation site density directly from the radiation recorded by the high-speed infrared camera. We test and validate the methodology against saturated pool boiling experiments with water, run on both plain and nanoengineered surfaces. Using such a technique, we have measurements of the quantities above within a few seconds from the moment the camera records the boiling surface radiation, with a regression coefficient of 0.95 or higher compared to reference measurements obtained by conventional, time-consuming, image processing techniques.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Grapevine leaves have diverse shapes and sizes which are influenced by many factors including genetics, vine phytosanitary status, environment, leaf and vine age, and node position on the shoot. To ...determine the relationship between grapevine leaf shape or size and leaf canopy temperature, we examined five seedling populations grown in a vineyard in California, USA. The populations had one parent with compound leaves of the Vitis piasezkii type and a different second parent with non-compound leaves. In previous work, we had measured the shape and size of the leaves collected from these populations using 21 homologous landmarks. Here, we paired these morphological data with canopy temperature measurements made using a handheld infrared thermometer. After recording time of sampling and canopy temperature, we used a linear model between time of sampling and canopy temperature to estimate temperature residuals. Based on these residuals, we determined if the canopy temperature of each vine was cooler or warmer than expected, based on the time of sampling. We established a relationship between leaf size and canopy temperature: vines with larger leaves were cooler than expected. By contrast, leaf shape was not strongly correlated with variation in canopy temperature. Ultimately, these findings indicate that vines with larger leaves may contribute to the reduction of overall canopy temperature; however, further work is needed to determine whether this is due to variation in leaf size, differences in the openness of the canopy or other related traits.
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