•We evaluated canopy temperature on six deficit irrigation treatments of corn.•Corn canopy temperature was highly correlated with midday leaf water potential.•Three previously used and three new ...water stress indices were evaluated.•All indices showed linear relationship with soil water deficit at high temperatures.•Indices that require canopy temperature only are highly correlated with CWSI.
Infrared thermal radiometers (IRTs) are an affordable tool for researchers to monitor canopy temperature. In this maize experiment, six treatments of regulated deficit irrigation levels were evaluated. The main objective was to evaluate these six treatments in terms of six indices (three previously proposed and three introduced in this study) used to quantify water stress. Three are point-in-time indices where one daily reading is assumed representative of the day (Crop Water Stress Index – CWSI, Degrees Above Non-Stressed – DANS, Degrees Above Canopy Threshold – DACT) and three integrate the cumulative impact of water stress over time (Time Temperature Threshold – TTT, Integrated Degrees Above Non-Stressed – IDANS, Integrated Degrees Above Canopy Threshold – IDACT). Canopy temperature was highly correlated with leaf water potential (R2=0.895). To avoid potential bias, the lowest observation from the non-stressed treatment was chosen as the baseline for DANS and IDANS indices. Early afternoon temperatures showed the most divergence and thus this is the ideal time to obtain spot index values. Canopy temperatures and stress indices were responsive to evapotranspiration-based irrigation treatments. DANS and DACT were highly correlated with CWSI above the corn threshold 28°C used in the TTT method, and all indices showed linear relationship with soil water deficit at high temperatures. Recommendations are given to consider soils with high water-holding capacity when choosing a site for non-stressed reference crops used in the DANS method. The DACT may be the most convenient index, as all it requires is a single canopy temperature measurement yet has strong relationships with other indices and crop water measurements.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Drought stress is a major limiting factor for banana production and the incidence of drought spells is expected to increase with climate change. Climate smart practices and varieties are needed, but ...evaluation in the field is hampered by a lack of reliable physiological drought stress indicators. We investigated the potential of using stable carbon isotope ratios (δ13C) and leaf temperature and its derived DANS (Degrees above Non-Stressed Canopy) index as proxies for drought stress in banana. Leaf samples were taken for δ13C analysis and leaf temperature was monitored throughout the day in a field trial with different banana plant stages (mother and daughter plants) under two irrigation treatments (rainfed and irrigated) during the dry season in Arusha, Tanzania. We found that δ13C, leaf temperature and DANS were highly sensitive proxies for drought stress in banana. Soil volumetric water content had a significant effect on both δ13C values and DANS. There was a significant difference in δ13C (1.5 ± 0.1‰, p < 0.01) and afternoon leaf temperature (7 ± 1 °C, p < 0.01) between the rainfed and irrigated treatment. To deal with variability in δ13C within the leaf, we developed a banana tailored sampling method. This study also revealed the complexity of carbon isotope dynamics in the intertwined system of mother and daughter plants. Daughter plants had more negative δ13C values (−1.9 ± 0.1‰, p < 0.01) and lower temperatures (4 ± 1 °C) than mother plants. This indicates less stress, but interpretation of the δ13C ratio is complicated by the potential carbon flux from mother to daughter plant. Once we have a full understanding of these complexities within the plant, the δ13C and leaf temperature based methods we developed, can be directly implemented for both mother and daughter plants under various field conditions.
•Large differences in δ13C ratios and leaf temperature between drought stressed and optimally irrigated banana plants.•δ13C ratio and leaf temperature significantly correlated.•Daughter plants less stressed than mother plants.•Developed banana-tailored sampling approach for δ13C analysis.•Carbon allocation in banana proves to be complex and complicates interpretation of δ13C ratio as a stress proxy.
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·The wall temperature distribution was visualized at 3000 fps using a high-speed infrared camera.·Artificial nucleation sites are formed by ink-jet printing of superhydrophobic agent.·Liquid-phase ...heat transfer enhanced by bubble motion and evaporation dominated wall heat transfer.·Contribution of microlayer evaporation to wall heat transfer was less than 35% because of its small area coverage ratio.·Macrolayer was observed under large coalesced bubble.
In this study, the heat transfer mechanisms in pool saturated boiling of water on a sapphire heat transfer surface with a controlled nucleation site density (NSD) were observed using a high-speed infrared camera. Artificial nucleation sites were arranged on the wall surface by ink-jet printing of a superhydrophobic agent, and NSD was varied between 24 and 318 sites/cm2. The heat transfer characteristics of each fundamental heat transfer process and its contribution to the total wall heat transfer were evaluated through the heat flux partitioning analysis. There was an upper limit to the heat transfer enhancement by increasing the NSD. The boiling heat transfer coefficient (HTC) did not increase monotonically with increasing NSD but had a maximum value at an NSD between 89 and 130 sites/cm2. When NSD was increased excessively, the microlayer formation was inhibited by bubble–bubble interaction. The contribution of the microlayer evaporation to the wall heat transfer also decreased, resulting in a decrease in the boiling HTC. At all tested NSDs, liquid-phase heat transfer dominated the wall heat transfer, as in the case of the bare surface. The contribution of the microlayer evaporation that occupies a small area to the total wall heat transfer was less than 35%. In the high heat flux region, the macrolayer, a liquid layer with suppressed liquid motion, was successfully observed at the bottom of the coalesced bubble.
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The measurement of turbine outlet temperature is challenging because of an intense swirl and high speed at this position. However, accurate measurement of the turbine outlet temperature is ...fundamental for characterizing the turbine performance. The paper proposed an infrared thermometry method based on the temperature sensing net (TSN) to measure the temperature distribution at the turbine outlet. First, this article describes the design and operation of the measurement procedure through infrared technology to accomplish this difficult task. Then, the temperature and velocity distribution at the turbine outlet and the adiabatic efficiency of the turbine are obtained using the CFD (Computational Fluid Dynamics) method to verify the feasibility of the proposed scheme. And the CHT (Conjugate Heat Transfer) simulation results for the TSN show that the incoming flow mass rate has a great influence on TSN temperature. In contrast, the influence of the incoming flow temperature gradient on it is almost negligible. Moreover, the fluid flow behavior and static temperature distribution around the temperature-sensing wire (TSW) at different Mach numbers are analyzed, and the heat transfer mechanism between the TSW and the fluid is revealed. The results show that the temperature of the TSN is lower than that of the incoming flow, but the distribution law is similar. The main factor affecting the temperature difference between the TSW and the fluid is the incoming flow velocity.
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•Convective forced film boiling heat transfer of water flow over a hot moving solid was studied.•Effects of varying the velocity, temperature of solid, and water temperature were investigated.•Heat ...flux profile was compared to the theoretical solutions.•A correlation for predicting the surface heat flux was built.
The film boiling of free-surface water flow over a moving hot steel sheet is a common occurrence in the run-out table (ROT) cooling process used in hot rolling mills in the steel industry. Engineers seek to optimize cooling operations, necessitating the comprehension of forced convective heat transfer characteristics between cooling water and hot steel sheets in the film-boiling regime. In this study, we developed an experimental methodology using an infrared camera to evaluate the heat flux distribution along a moving solid with a high spatial resolution. Specifically, a 0.5-mm-thick test sheet made of stainless steel was subjected to cooling by a water film flowing at 0.72 m/s. The surface heat flux was measured while varying the velocity of the test sheet (0.5, 1.0, and 1.5 m/s), temperature of the test sheet (450–590 °C), and water temperature (30–60 °C). The study revealed that the heat flux was highest in the region where the water first contacted with the moving solid and then decreased downstream. The peak values of the surface heat flux depended on the water temperature, but were almost independent of the moving velocity. We compared the results with the similarity solutions for single- and two-phase boundary layer theories to gain insights into the heat transfer mechanism and to discuss the effects of varying the examined parameters. In addition, we developed a correlation formula to predict the heat flux profile in the first contact region.
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•We develop a heater to study boiling on rough surfaces using infrared thermometry.•A stochastic heat partitioning model captures the boiling curve.•The boiling crisis is a critical transition in the ...near-wall bubble coalescence process.•The boiling crisis is captured by a continuum percolation model.
We design and build a special heater to enable infrared investigations of boiling heat transfer on surfaces featuring the typical roughness and scratch pattern of commercial-grade heat transfer surfaces (in this case a zirconium alloy typically used as fuel cladding material in nuclear reactors). We use high-speed infrared thermometry to investigate surface effects on the boiling process for both the rough infrared heater and a reference more conventional, nano-smooth infrared heater. Compared to the nano-smooth surface, the rough surface has larger nucleation sites, which require a lower nucleation temperature. The rough surface has a much smaller bubble departure volume. However, it has a much higher nucleation site density, and, overall, a higher heat transfer coefficient. We capture this behavior with a stochastic heat flux partitioning model. Notably, while the two surfaces have very different boiling dynamics, the boiling crisis has a common “signature”. For both surfaces, the probability density functions of bubble footprint areas follow a power law with a negative exponent smaller than 3, also known as a scale-free distribution. We predict these observations and the onset of the boiling crisis using a continuum percolation model. These results corroborate the hypothesis of the boiling crisis as a percolative critical phase transition of the bubble interaction process.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ
•We study nucleate boiling on substrates of small thermal capacity using IR camera.•Microlayer does not fully evaporate due to limited thermal capacity of the heater.•Microlayer evaporation and ...rewetting are less important compared to thick heaters.•Most energy is removed by convective effects created by bubble growth and departure.•We re-derived heat flux partitioning model to quantify each heat transfer mechanism.
In this work, we studied the wall heat flux partitioning during the pool boiling of water on thin metallic surfaces. We conducted boiling experiments on surfaces where we engineered nucleation sites by nanosecond-fiber-laser texturing. These nucleation sites form triangular lattice patterns with different pitches. We measured the time-dependent temperature and heat flux distributions on the boiling surface using an infrared camera. We developed post-processing algorithms to measure, based on these distributions, all the fundamental boiling parameters used in heat flux partitioning models (e.g., nucleation site density, bubble wait and growth time, and bubble footprint radius) and the actual partitioning of the heat flux, i.e., how much heat is transferred by evaporation of the microlayer, rewetting of the surface, and convective effects.
This work reveals that the mechanisms of heat transfer on substrates of small thermal capacity are very different compared to substrates of large thermal capacity. With water, the bubble microlayer typically does not dry out and the surface temperature at rewetting is practically the same as the rewetting fluid temperature. These effects limit the efficiency of microlayer evaporation and rewetting heat transfer. Instead, convective effects generated by the bubble growth process remove most of the energy from the heated surface. This behavior is captured by a heat flux partitioning model that we re-derived from first principles to describe the heat transfer mechanisms on substrate of small thermal capacity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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
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