Severe Heat Load Research Articles

Large eddy simulation of boundary layer combustion of hydrogen and hydrocarbon fuel films in a modeled scramjet combustor

Supersonic fuel film cooling is a promising way to simultaneously reduce the severe wall heat and friction load of the internal passage in a scramjet engine when operating at hypersonic conditions. Large eddy simulations were performed to investigate the cooling and wall friction characteristics of hydrogen and hydrocarbon films under inert and reactive circumstances. The results show that the essential difference of the turbulent state in the mixing layer contributes to the totally different behaviors of the cooling and wall friction reduction performances of the two fuel films. The turbulent transport processes between the hydrogen film and the mainstream are much weaker as compared to the case of hydrocarbon film, making inert hydrogen rather superior in cooling and friction reduction applications. Besides, the increase of wall temperature for hydrogen film under the inert case is mainly driven by the loss of hydrogen with high heat capacity instead of by direct heat addition. However, the film cooling performance severely deteriorates when the hydrogen film burns due to presence of severe heat release sources near the wall. On the other hand, combustion of hydrocarbon film in the boundary layer can remarkably improve its originally barely-satisfactory cooling and friction reduction performance to the level comparable to that of hydrogen film, due to the suppression of turbulent transport processes in the mixing layer and presence of heat absorption sources near the wall. Overall, the hydrogen film is more advantageous in friction reduction, while the hydrocarbon film is more suitable for cooling.

The use of body surface temperatures in assessing thermal status of hutch-reared dairy calves in shaded and unshaded conditions.

The study was carried out in a Hungarian large-scale dairy farm during a 5-day period in hot August weather. Altogether 16 preweaning calves were chosen for the study. An agricultural mesh with 80% shielding was stretched over eight calf cages at 2 m from the ground to shield the cages in their entirety, while eight others were left unshaded. Ambient temperature and relative humidity were measured in 10 min intervals inside and outside one of the hutches in the shaded and unshaded groups during the total length of the study. The rectal temperature of the calves was measured by a digital thermometer every 4 h. Surface temperatures were measured on body parts, in the same intervals as rectal temperature with an infrared thermometer. Measuring sites included: the leg (metacarpus), muzzle, eye bulb, scapula, and ear. Statistical analyses were performed to assess the effects of shading on environmental and body temperatures and to also assess the strength of the association between core, skin and ambient temperatures; to estimate the temperature gradient between body shell and core; to compare the changes in heat dissipation capacity of the different body regions (as represented by temperatures of various sites) with increasing ambient temperature controlling for shaded or unshaded conditions; and to predict the risk of hyperthermia (rectal temperature not lower than 39.5°C) with the CART classification method. The average rectal temperatures suggest that the temperature conditions both in shaded and unshaded groups imposed a severe heat load on the calves. The temperature of the body shell, as represented by skin temperatures, shows a much more significant variation, similar to ambient temperature. As expected, areas that are closer to the core of the body (ear and eye) show less difference from rectal temperature and show a narrower range (lower variance), as more distal regions (leg, scapula) have a wider range. Body surface temperatures are more related to ambient temperature in calves than rectal temperature. The predictive value of infrared body surface temperatures for predicting heat stress or rectal temperature is low.

Experimental and computational assessment into the heat transfer for the blade multicavity tips

In the gas turbine, the tip region of the shroudless blade is under severe heat load, and thus is seriously ablated. Therefore, an in-depth understanding of the tip heat transfer distributions is of great significance for tip cooling design. In the present work, the heat transfer coefficient distributions of the multicavity tips were measured by a steady-state thermal-analysis method with Infrared camera. The measurements were conducted under two inlet Reynolds number conditions (1.10 × 105, 2.23 × 105) and two tip gaps (1.6 %, 3.5 % Chord length). In addition, the computational simulations verified by the experimental data were conducted to attain the detailed flow field near the tip, and to gain insight into the heat transfer characteristics. Measured results show that additional hot spots are detected behind the rib for the multicavity tips with three or four cavities owing to the leakage flow reattachment. The heat transfer at the suction-side corner is also enhanced by the multicavity tips, whereas a low heat transfer coefficient region is found in the corner in front of the rib. Increasing the inlet Reynolds number would not change the heat transfer patterns, but would evidently increase the heat transfer coefficient values. Adopting a larger tip gap also increases the heat transfer coefficient values, but the effect is not so obviously as the inlet Reynolds number. Compared with the conventional one-cavity tip, the multicavity tips can reduce the aerodynamic losses, and the loss values are reduced by about 2 %.

Experimental comparisons of film cooling performance for the multi-cavity tips at two different tip gaps

The unshrouded blade tip in a gas turbine needs to be cooled down due to the severe heat load. In this paper, multi-cavity tip structures were applied in the tip region to help enhance the cooling performance. Distributions of film cooling effectiveness (η) on multi-cavity tips were measured by pressure sensitive paint (PSP) approach under five different coolant blowing ratios. A turbulence-validated computational prediction was performed to help indicate the flow field of multi-cavity tips gap. Then, impact of tip gap on the multi-cavity tips film cooling performance was studied. Results show that multi-cavity tips mainly enhance the cooling performance at tip mid-portion compared with the classic one-cavity tip, but weaken it near the trailing edge (TE). Increasing the tip gap reduces cooling effectiveness values for most portion of the tip, but increases it near the TE. Lower aerodynamic losses were obtained in multi-cavity tips, especially for the leakage loss region.

The effect of hutch compass direction on primary heat stress responses in dairy calves in a continental region

AbstractHeat stress reduction in hutch-reared dairy calves is overlooked on most dairy farms. We hypothesised that during summer, the microclimate within hutches is directly affected by compass direction as a result of differences in exposure to solar radiation. On a bright, mid-August day a number of behavioural and physiological heat stress response measures (respiratory rate, body posture, being in the shade or sun) were recorded in 20-min intervals from 0720-1900h on calves housed in hutches with entrances facing all four points of the compass. In conjunction with this, dry bulb (ambient) and black globe temperatures, and wind speed were recorded both inside the plastic hutches and at one sunny site at the exterior. Data were compared in terms of distinct periods of the day (0720-1100, 1120-1500, 1520-1900h). Dry bulb temperatures were higher inside hutches compared to outside while for black globe temperatures the opposite was true. Daily average temperatures and respiratory rates did not differ between hutches facing different compass points. In the morning and afternoon, hutch temperature and calf respiratory rate differed relative to compass point. Calves in east- and north-facing hutches were seen more in the shade than those in south- and west-facing ones. Our conclusion was that in a continental region having hutch entrances face towards the east or north confers some advantages in mitigating severe solar heat load in summer.

Micro-drilling of straight and inclined holes on thermal barrier coated Inconel 718 for turbine blade cooling

ABSTRACT Thermal barrier coatings (TBC) are widely used on turbine blades working at high-temperature condition. Drilling different angled cooling holes on these blades is essential to minimize the severe heat load experienced and to improve their service life. In this study, mechanical micro-drilling is proposed to check the feasibility of the process and study the basic characteristics of thrust signal. The drilling experiments were performed on TBC Inconel 718 to drill micro-holes at different inclinations using 600-μm TiAlN-coated carbide drill under dry environment. Drilling performance is assessed in terms of the number of holes produced before drill breakage, drilling thrust, fluctuation of thrust signal, and tool wear. The longest tool life was observed while drilling at the combination of lower spindle speed and drill feed for both straight and inclined holes. However, the life of drill while drilling inclined holes was found to be lesser than that of the straight holes and spindle speed is found to be a statistically significant parameter affecting the drilling thrust. Two different drill wear mechanisms, namely, abrasion and adhesion were observed during drilling. Finally, during the drill failure phase, a large fluctuation in thrust signal was observed followed by the drill breakage.

Alleviation of heat-stress-related physiological perturbations in growing rabbits using natural antioxidants

The current study was performed to evaluate the effects of the dietary inclusion of extra virgin olive oil (EVOO), betaine (BET), lemongrass essential oil (LGEO), gallic acid (GA), vitamin C (VC) and vitamin E (VE) on different body temperature traits and stress hormone and glucose levels in heat-stressed growing rabbits. Rabbits were fed diets with no supplementation (control group) or supplemented with 15 g of EVOO, 400 mg of LGEO, 500 mg of GA, 1000 mg of BET, 500 mg of VC, or 200 mg of VE per kg of diet. All tested feed additives, especially EVOO, had a lowering effect on various rabbit temperature traits. Both triiodothyronine (T3) and tetraiodothyronine/thyroxine (T4) were increased (p<0.05) by the addition of BET, VC, EVOO, and VE. With the exception of the VC group, all dietary groups showed no significant changes in the insulin level compared to the control group level. In contrast, the cortisol and glucose levels were diminished (p<0.05) in all treated groups compared to the control levels. The results suggested that all tested supplementations had positive ameliorating effects on growing rabbits under a severe heat load in terms of lowered body temperatures and a favourable stress hormone balance, with the most favourable results found in the EVOO, VC, and BET supplementation groups.

Effects of chromium supplementation on weight gain, feeding behaviour, health and metabolic criteria of environmentally heat-loaded Holstein dairy calves from birth to weaning

ABSTRACTThe objectives of this study were to investigate the effects of chromium (Cr) supplementation on feed intake and meal pattern, weight gain and skeletal growth, and health and metabolic criteria of environmentally heat-loaded dairy calves during the pre-weaning period. Forty-eight newborn female calves were allotted randomly to a control group (no Cr supplement; Cr−) or a Cr group (Cr+) receiving 0.05 mg Cr (as Cr-methionine)/kg BW0.75. Cr was provided in the liquid feed (colostrum and milk) during the pre-weaning period. The average maximum temperature–humidity index was 83.7 U, indicating severe environmental heat load. Despite reduced meal frequency and increased in inter-meal interval, Cr supplementation tended to increase starter feed intake and total dry matter intake as a result of increased meal size and duration. Respiration rate was lower in Cr+ calves. Calf growth, rectal temperature, faecal score and incidence of diarrhoea or pneumonia were not affected by Cr supplementation, but number of days with diarrhoea and treatment duration decreased during the pre-weaning period. Cr supplementation tended to increase resting time and decreased time devoted to non-nutritive oral behaviours. At weaning, serum concentration of glucose was lower but total protein and globulin concentrations were higher in Cr+ calves. In Cr+ calves, the activity of glutathione peroxidase was higher and lower on d 49 and 63 of the study, respectively, compared to the control calves. Activity of catalase was increased on d 21 and tended to decrease on d 35 in Cr+ calves. In general, Cr supplementation to environmentally heat-loaded dairy calves decreased non-nutritive oral behaviours, improved feed intake and decreased days with diarrhoea and treatment duration, but had minimal effects on weight gain, metabolism and indicators of oxidative stress or insulin function.

Numerical study on flow characteristic of the KSTAR PF cryogenic loop using supermagnet code

Operation stability study for a large-scale superconducting magnet is of particular importance to protect the magnet from permanent damage. Especially, for a fusion magnet, severe heat load by AC loss needs to be effectively removed during operation to achieve required temperature margin. A unique feature of KSTAR PF (poloidal field) magnet is that all the supercritical helium inlets and outlets of PF1∼4UL (PF upper and lower) coils are located at high field region. Therefore, major heat loads are localized both at the inlets and outlets, so that a drastically reduced or even no temporal cryogen flow is frequently observed at the inlets of PF1∼4UL coils. This kind of temporal blockage of cryogenic loop can seriously affect the thermo-hydraulic analysis of a superconducting magnet system. As a preliminary study on this issue, we compared thermos-hydraulic analysis results of a simplified PF1UL model with a semi full scale PF1∼4UL model by using the SUPERMAGNET code. The numerical simulations were also compared to empirical results.

Inner cladding influence on mode interaction in symmetry-free photonic crystal fibers under heat load

A further output power scaling of Yb-doped double-cladding photonic crystal fiber lasers, required for practical applications in many industrial fields, is currently prevented by thermal effects, which significantly worsen the beam quality. In this work the mode interaction and, consequently, the single-mode regime of Yb-doped air-silica symmetry-free photonic crystal fibers have been numerically investigated in different heat load conditions using simulation tools based on the finite element method. The effect of the main inner cladding geometric parameters, in particular of the inner cladding dimension, on the guided-mode delocalization has been analyzed, with the aim to identify a design of the large mode area active fiber providing single-mode operation despite the presence of thermal effects. Simulation results have demonstrated that the inner cladding enlargement causes a stronger coupling between core-guided and cladding modes, as well as an increase of the differential overlap between fundamental and first higher-order mode for moderate heat load values. However, the inner cladding influence becomes less important under severe heat load, being the fiber behaviour mainly affected by the thermally-induced refractive index change in the doped core.

Precompensation of the thermal-induced refractive index changes into a fully aperiodic LPF for heat load resilience.

In this paper, a strategy consisting of precompensating the thermal-induced transverse refractive index changes is undertaken to push further the appearance threshold of a multimode regime. First, a standard air-silica large pitch fiber (LPF) and a fully aperiodic large pitch fiber are confronted in regard to their heat load resilience and capabilities for single-mode emission. Thereafter, slight refractive index depressions are judiciously introduced into the active core area. This approach enhances the delocalization of the high-order modes even under severe heat load levels. This combination of aperiodic cladding microstructuration and index-precompensation theoretically increases the multimode regime threshold while preserving large mode field areas. This investigation is performed at 1.03 and 2 μm operating wavelengths.

Full-vector modeling of thermally-driven gain competition in Yb-doped reduced symmetry photonic-crystal fiber

A new model to study gain competition in high-power fiber amplifiers, which accounts for the full-vector nature of the propagating modes and thermal effects on core overlap, is applied to simulate the performance of an active rod-type fiber under severe heat load. Model tests on a Yb-doped large-pitch reduced symmetry photonic-crystal fiber show a successful analysis of gain competition.

Measurement of lithium target surface velocity in the IFMIF/EVEDA lithium test loop

In the framework of the Engineering Validation and Engineering Design Activities (EVEDA) project of the International Fusion Materials Irradiation Facility (IFMIF), we measured surface velocity fields of a lithium (Li) target at the EVEDA Li test loop under specifically-designated IFMIF conditions (target speeds of 10, 15, and 20m/s, vacuum pressure of 10−3Pa, and Li temperature of 250°C). In the current design of the IFMIF, the free surface of the Li target is under a most severe heat load condition with respect to Li boiling. The objective of this study is to measure the actual free-surface velocity under these IFMIF conditions to evaluate the heat removal performance of the Li target. The measured results (using the surface-wave tracking method that our team developed) showed two-dimensional time-averaged velocity distributions around the IFMIF beam footprint being virtually uniform, and close to the cross-sectional average velocity. The uniformity of the velocity distributions was less than 1m/s. The comparison between the measured and analyzed surface velocity at the beam center showed that the analysis accurately predicts the measurement results within a margin of 3%. Finally, it was confirmed that the Li target delivers adequate heat removal performance in the IFMIF as designed.

Thermal modeling of gain competition in Yb-doped large-mode-area photonic-crystal fiber amplifier.

We propose a new model for gain competition effects in high-power fiber amplifiers, which accounts for the thermal effects of heat load on the doped core overlap of the propagating light field. The full-vectorial nature of the fiber modes is modeled by an embedded finite-element method modal solver, and the temperature profile is calculated by a simple and efficient radial heat propagation solver. The model is applied to a Yb³⁺-doped LPF45 air-clad photonic-crystal fiber amplifier for coand counter-propagating pumping setups, showing gain competition in conditions of severe heat load.

Thermal Response and Ablation Research of EPDM Thermal Protection Material in Ramjet

Thermal protection materials are required to preserve the metal components of motor that suffer severe heat load. The research on thermal response of insulation of ramjet combustion chamber was carried out by the ground test and numerical simulation. During the working time of the ramjet, the back-face temperature of the thermal protection material was measured. The scanning electron microscope of samples was investigated. The calculation of thermo-chemical flow was solved by the CFD software FLUENT to provide the heat load boundary for simulation of heat transfer of EPDM insulation. The heat transfer model was solved by the FEA software ANSYS. Comparison of the temperature profile at the ablating surface between calculation and measurement shows the two results agree with each other. The simulation results can provide the temperature rising trend of insulation in a certain extent.

Short-term exposure to heat stress attenuates appetite and intestinal integrity in growing pigs.

Acute heat stress (HS) and heat stroke can be detrimental to the health, well-being, and performance of mammals such as swine. Therefore, our objective was to chronologically characterize how a growing pig perceives and initially copes with a severe heat load. Crossbred gilts (n=32; 63.8±2.9 kg) were subjected to HS conditions (37°C and 40% humidity) with ad libitum intake for 0, 2, 4, or 6 h (n=8/time point). Rectal temperature (Tr), respiration rates (RR), and feed intake were determined every 2 h. Pigs were euthanized at each time point and fresh ileum and colon samples were mounted into modified Ussing chambers to assess ex vivo intestinal integrity and function. Transepithelial electrical resistance (TER) and fluorescein isothiocyanate-labeled dextran (FD4) permeability were assessed. As expected, Tr increased linearly over time (P<0.001) with the highest temperature observed at 6 h of HS. Compared to the 0-h thermal-neutral (TN) pigs, RR increased (230%; P<0.001) in the first 2 h and remained elevated over the 6 h of HS (P<0.05). Feed intake was dramatically reduced due to HS and this corresponded with significant changes in plasma glucose, ghrelin, and glucose-dependent insulinotropic peptide (P<0.050). At as early as 2 h of HS, ileum TER linearly decreased (P<0.01), while FD4 linearly increased with time (P<0.05). Colon TER and FD4 changed due to HS in quadratic responses over time (P=0.050) similar to the ileum but were less pronounced. In response to HS, ileum and colon heat shock protein (HSP) 70 mRNA and protein abundance increased linearly over time (P<0.050). Altogether, these data indicated that a short duration of HS (2-6 h) compromised feed intake and intestinal integrity in growing pigs.

The effect of bermudagrass hybrid on forage characteristics, animal performance, and grazing behavior of beef steers1,2

Bermudagrass (Cynodon dactylon [L.] Pers.) is a major feed source for ruminants across the southeastern United States. In 4 consecutive yr, 3 different bermudagrass hybrids, Alicia, Jiggs, and Tifton-85, were evaluated under a low stocking rate as forage and hay sources. The nutritive value, in situ DM digestibility, and performance and grazing behavior of beef steers under similar management were evaluated. Sampling day had an effect (P < 0.05) on all forage variables. Percentages of CP and TDN decreased while concentration of ADF, NDF, lignin, and nonfiber carbohydrates (NFC) increased as grazing season advanced. Alicia had lower nutritive value, showing greater lignin (5.3%) and indigestible fraction (44.9%) compared to Jiggs (4.9 and 35.6%, respectively) and Tifton-85 (4.5 and 40.1%, respectively). Tifton-85 contained the lowest concentration of NFC (11.8%). Steers grazing Jiggs and Tifton-85 had greater ADG (0.51 and 0.55 kg, respectively) and BW gain per hectare (258 and 279 kg, respectively) than those on Alicia (0.36 kg and 184 kg/ha, respectively); results that are probably explained by the lower nutritive value characteristics of the latter. Most grazing behavior variables were affected (P < 0.05) by time of the day (TOD) and grazing period. Two major grazing events were observed at dawn and dusk. Grazing time (32 min) was lowest (P = 0.003) while standing (140 min) and lying (98 min) time were greater (P = 0.001 and 0.04, respectively) from 1100 to 1559 h, probably as an effect of temperature and humidity at that time of the day. During summer, the temperature humidity index (THI) is above 72 (mild heat load) for the entire season and above 79 (severe heat load) during most of the daylight hours from June to August. Heat load likely affected animal performance and grazing behavior; however, some characteristics associated with these bermudagrass hybrids, especially with Alicia, such as its percentages of lignin and indigestible fraction may also partially explain the poor animal performance. In the conditions of the study, environmental variables (temperature and humidity), as well as the type of bermudagrass hybrid, affected animal performance and grazing behavior of recently weaned beef steers.

Effect of glucocorticoid depletion on heat-induced Hsp70, IL-1β and TNF-α gene expression

When exposed to heat, conscious naive rats may develop lethal heatstroke, depending on heat load, i.e., time spent at high body core temperature. The occurrence of heatstroke was hypothesized to result from a defective glucocorticoid secretion related to altered heat-stress responses. We thus investigated the potential involvement of glucocorticoids in heat tolerance and its consequences on physiological responses, heat shock protein 70 (Hsp70), and cytokine mRNA expressions. Two hours before heat exposure, the animals were injected either with metyrapone, an inhibitor of corticosterone synthesis, or with its vehicle. Heat exposure lasted for 15, 30, 45 or 60 min. Thereafter, the rats were distributed into three groups according to their heat load: null, moderate (without any lethal risk) and intense (with lethal risk). Physiological responses were evaluated with colonic temperature, plasma lactate and hematocrit. Brain responses were assessed in frontal cortex through Hsp70, interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) mRNA expressions. The animals with a severe heat load exhibited a high hematocrit, increased plasma lactate level and enhanced brain IL-1β and Hsp70 mRNA expressions. Independent of the heat load, Metyrapone rats showed the same thermophysiological responses and IL-1β and Hsp70 mRNA expressions when compared with vehicle rats. However, the Metyrapone rats experiencing an intense heat load exhibited an increased TNF-α mRNA expression. In conclusion, these data (i) confirm that heat load is important in the calibration of the risk attached to heat exposure; and (ii) suggest that corticosterone synthesis inhibition may favor TNF-α mRNA expression without any effect on Hsp70 mRNA expression.

A Comparison between Divertor Heat Loads in ELMy and HRS H-Modes on JFT-2M

A comparison between divertor heat loads in ELMy and High Recycling Steady (HRS) H-modes was carried out by fast measurements of the two dimensional Dα emission, and the divertor electron temperature and ion saturation current on JFT-2M. The heat load for the HRS H-mode was maintained at the same level as the time-averaged heat load for the ELMy H-mode, indicating that the HRS H-mode has the attractive advantage of avoiding the severe ELM heat load. An enhancement of particle transport dominated the heat load for the HRS H-mode, whereas the large ELM heat load was induced by abrupt increases of both heat and particle transport.

Responses of Photosynthesis and Biomass Allocation of an Understorey Herb, Pteridophyllum racemosum, to Gradual Increases in Irradiance

In wave-regenerating Abies forests in central Japan, light availability on the forest floor of a mature-tree stand increases gradually over 4 to 5 years during the senescence of trees. The understorey evergreen perennialPteridophyllum racemosum Sieb. et Zucc. (Papaveraceae) is commonly found in such forests. To determine the acclimation characteristics of this species to gradual changes in light availability, leaf photosynthetic traits and biomass allocation patterns were determined along a transect running from fully shaded understorey to a canopy gap. Along the transect, the photon flux density on the forest floor relative to full sun (RPFD) varied from 2.3–36.7%. The light-saturated net photosynthetic rate of field-grown plants increased as the light environment increased from 2.3–14.1% RPFD. However, as light conditions increased from moderate (14.1%) to high (36.7%), the light-saturated net photosynthetic rate decreased to a level comparable to that exhibited by low-light grown plants. On the other hand, root mass per unit leaf area (RMA) increased with increasing light conditions. A higher RMA contributes to a higher water uptake capacity per unit leaf area which in turn supports higher rates of photosynthesis and transpiration in high light. We conclude that in wave-regenerating forests P. racemosum can survive in high-light environments by avoiding a severe water deficit and heat load by increasing RMA.