High Ambient Temperature Conditions Research Articles

Impact of metakaolin on hydration properties of magnesium phosphate cement

The degradation of mechanical properties in magnesium phosphate cement (MPC) is commonly observed under conditions of rapid heat release and high ambient temperature. To mitigate this phenomenon, the incorporation of metakaolin has been investigated as a means to reduce the hydration heat of MPC and enhance its mechanical properties at elevated temperatures. Experimental findings reveal a pronounced influence of metakaolin on the heat flow behavior of MPC. Specifically, the addition of a small fraction of metakaolin (not exceeding 20wt%) leads to an accelerated heat release rate during the initial 0.13hours, followed by a substantial reduction in the heat release rate with further increments of metakaolin. Furthermore, the inclusion of metakaolin significantly improves the mechanical properties of MPC. For instance, a composition comprising 30% metakaolin yields a notable 79.2% increase in strength after 7 days. It is worth noting that temperatures below 400℃ are found to have an adverse impact on the mechanical properties of MPC, whereas a temperature range encompassing 600℃>T>400℃ enhances these properties due to vitrification at high temperatures. Importantly, MPC incorporating metakaolin exhibits superior mechanical performance compared to its metakaolin-free counterpart across all tested temperatures, which can be attributed to the attainment of a denser microstructure facilitated by metakaolin incorporation.

Influences of a Supplemental Blend of Essential Oils Plus 25-Hydroxy-Vit-D3 and Zilpaterol Hydrochloride (β2 Agonist) on Growth Performance and Carcass Measures of Feedlot Lambs Finished under Conditions of High Ambient Temperature.

Forty-eight Pelibuey × Katahdin male intact lambs (25.12 ± 3.79 kg LW) were used in a 70-d growing-finishing trial. Dietary treatments consisted of total mixed corn-based diet supplemented with: (1) no feed additives (Control); (2) 150 mg of essential oils blend plus 0.10 mg of 25-hydroxy-Vit-D3/kg diet offered throughout the 70-d experimental period (EOD3); (3) Control diet fed during the first 35 days and zilpaterol hydrochloride (ZH) supplementation at 6 mg/kg diet offered during the final 35 days of the experiment (32 days with ZH with a withdrawal 3-d before harvest), and (4) basal diet supplemented with EOD3 during first 35 days finishing, and EOD3 in combination with ZH (EOD3 + ZH) during the subsequent 32-days with ZH withdrawal 3 days before harvest. The temperature-humidity index during the experiment averaged 80.4 ± 3.2. There were no treatment interactions (p > 0.20) on growth performance and carcass measures. Supplemental EOD3 did not affect (p = 0.43) dry matter intake (DMI), but increased (p < 0.01) carcass adjusted average daily gain (ADG, 9.2%), gain efficiency (GF, 6.7%), and observed vs. expected dietary net energy for maintenance (NEm, 4.8%) and for gain (NEg, 6.4%). Supplemental ZH did not affect dry matter intake (DMI, p = 0.50) but increased (p < 0.01) carcass adjusted ADG (14.5%), GF (13%) and observed vs. expected dietary NEm (9%) and NEg (11.7%). Compared to control lambs, the combination of both additives increased ADG (24.9%), GF (21.2%), and observed vs. expected dietary NEm and NEg (14.2% and 18.9%, respectively). There were no treatment interactions on carcass characteristics, visceral organ mass, or on gene expression of IGF1, IGF2 and mTOR in longissimus muscle (LM). Supplemental EOD3 increased hot carcass weight (HCW; 4.0%, p < 0.01) but did not affect other carcass measures. Supplemental EOD3 decreased (3%, p = 0.03) intestine mass weight (g intestine/kg empty body weight). Supplemental ZH increased HCW (6%, p < 0.01), dressing percentage (1.7%, p = 0.04), and LM area (9.7%, p < 0.01), and decreased kidney-pelvic-fat percentage (16.2%, p < 0.01), fat thickness (14.7%, p = 0.03), and visceral fat. Compared to controls, the combination of EOD3 with ZH increased HCW (10.2%). It is concluded that growth performance responses to supplemental EOD3 and ZH are additive. Both supplements can be fed in combination without detrimental effects on expected benefits when fed separately. In addition, ZH supplementation improves carcass traits.

Rolling–sliding wear and damage behaviors of 304L stainless steel laser cladding on a damaged wheel tread under high ambient temperature conditions

To prolong the service life of wheels, damage to wheel tread was repaired locally by laser cladding. However, wheels in service in open environments are subject to high ambient temperatures, especially in the southern coastal areas of China, and the repair effects have not yet been verified. Therefore, in this study, laser cladding was used to clad 304L stainless steel powder on a damaged wheel tread to implement local repair of the damaged wheel. A friction and wear test was carried out using a twin-disc tester with a climate chamber to explore the influence of different loading cycles on the wear and damage behavior of repaired wheels at a high ambient temperature. The results showed that with increasing number of loading cycles, the friction coefficient between the wheel and rail gradually stabilized at 0.30–0.35, and the wear rate exhibited a similar trend. After 1 × 105 r, the surface hardness and plastic deformation thickness remained stable. The damage form changes from small spalling pits and nonpropagating microcracks to bulk material spalling and parallel cracks with large-angle branches. A high ambient temperature had little effect on the metallurgical bonding between the cladding layer and the wheel substrate, and no crack damage occurred.

Gene expression analysis of wheat (Triticum aestivum L.) during the vegetative stage under high ambient temperature condition

Gene expression analysis of wheat (Triticum aestivum L.) during the vegetative stage under high ambient temperature condition

Characterization of PIF4 Phosphorylation by SPA1.

The PHYTOCHROME INTERACTING FACTORs (PIFs) play pivotal roles in regulating thermo- and photo-morphogenesis in Arabidopsis. One of the main hubs in thermomorphogenesis is PIF4, which regulates plant development under high ambient temperature along with other PIFs. PIF4 enhances its own transcription and PIF4 protein is stabilized under high ambient temperature. However, the mechanisms of thermo-stabilization of PIF4 are less understood. Recently, it was shown that SUPPRESSOR OF PHYA-105 1 (SPA1) can function as a serine/threonine kinase to phosphorylate PIF4 in vitro, and the phosphorylated form of PIF4 is more stable under high ambient temperature conditions. In this chapter, we describe the in vitro kinase assay of PIF4 by SPA1. In principle, this protocol can be applied for other putative substrates and kinases.

The effects of grain size and fractal porosity on thermal conductivity of nano-grained graphite: A molecular dynamics study

The thermal conductivity of isotropic graphite is a crucial parameter in mechanical and nuclear engineering. However, obtaining its value accurately is still difficult, especially under irradiation and high ambient temperature conditions. In this study, the nano-grained graphite models with different grain sizes and arrangements are designed, and corresponding thermal conductivity is calculated with equilibrium and non-equilibrium molecular dynamics methods. The results show that the thermal conductivity of nano-grained graphite varies between 3 to 5 W/(m·K) and decreases exponentially with the increase of the number of nanograins, while the arrangement of nanograins has almost no effect on the thermal conductivity. In addition, the effect of porosity of nano-polycrystalline graphite is analyzed by constructing fractal porous structures with different fractal dimensions and stages, of which the pore characteristics are determined with the initial zero-stage structure. The thermal conductivity of porous graphite increases with increasing fractal dimension and decreasing fractal porosity and the outcomes of molecular dynamics simulations are verified with the theoretical model results.

Quantifying the benefits of PV module shading for building heat gain reduction: A machine learning approach

This study investigates the indirect benefit due to the shading effect from PV rooftop systems installed on building envelopes by proposing a new method based on a machine-learning algorithm. The study gathered a year of data from a 25 kWp PV rooftop system installed on a metal sheet roofing. It classifies the dataset into four categories based on solar irradiance and ambient temperature to represent Thailand's climate. There evaluated the RTTV and case study from implemented projects with metal sheet roofing in Thailand to estimate the potential electricity bill savings from the PV module shade effect. The results reveal an inverse relationship between the percentage of heat reduction and heat gain reduction, with the most significant reduction occurring under high solar irradiance and ambient temperature conditions. The shading effect caused by the PV modules provides an indirect benefit of approximately 38 kWh/kWp/year from electricity bill savings. In contrast, the PV system production yields around 1401 kWh/kWp/year based on radiation of about 1839 kWh/m2/year. The study estimates that energy-saving possibilities range from 0.038 to 0.052 kWh/m2/day, depending on the weather conditions, equivalent to an electricity saving of approximately 6.33 kWh/m2/year from air conditioner use.

Experimental and Numerical Investigation of Thermal Performance of an Air-Cooled Battery Module Under High Ambient Temperature Conditions

Abstract Lithium-ion batteries (LiBs) are widely used in electric vehicles due to their high energy and power density. The operating temperature has a significant impact on the thermal performance and longevity of LiBs. The thermal performance of an air-cooled battery module containing 16 (4S4P) high-energy density LiBs has been investigated through a series of experiments and numerical simulations. At varying transverse and longitudinal cell spacing, airflow rates, ambient temperatures, and discharge C-rates, the thermal performance of a battery module with aligned battery cells was analyzed. For the thermal performance evaluation, the average temperature rise, temperature non-uniformity, and maximum temperature of the module’s battery cells are utilized. During discharge cycles, the rate of temperature increase is linear but becomes nonlinear at the end of the discharge cycle. In the current architecture of the battery module, a minimum space utilization ratio of 0.38 is necessary to limit maximum temperature and temperature non-uniformity to safe battery thermal management temperatures. The thermal performance was significantly affected by the airflow rate. Increasing airflow rate decreases temperature but increases pressure drop substantially. The maximum cell temperature is greatly affected by the inlet air temperature, increasing from 62.8 °C to 76.6 °C when the inlet air temperature is increased from 30 °C to 45 °C. At high ambient temperatures (over 40 °C), LiB temperatures exceed permissible limits, and air cooling alone is inadequate. This study examines the thermal performance of an air-cooled battery module working at high temperatures.

Effects of environmental temperature on the thermal runaway of lithium-ion batteries during charging process

Lithium-ion batteries with relatively narrow operating temperature range have provoked concerns regarding the safety of LIBs. In this work, a series of experiments were conducted to explore the thermal runaway (TR) behaviors of charging batteries in a high/low temperature test chamber. The effects of charging rates (0.5 C, 1 C, 2 C, and 3 C), and ambient temperature (2 °C, 32 °C and 56 °C) are comprehensively investigated.The results indicate that the cell exhibited greater thermal hazard at the high charging rate and ambient temperature conditions. As the charging rate increased from 0.5 C to 3 C, more lithium intercalated in the anode prompt the TR triggered in advance, the TR onset temperature decreased from 297.5 °C to 264.7 °C. In addition, the charging time decreased with the elevated ambient temperature, resulting in a relatively higher TR onset temperature and lower maximum temperature, and the average TR critical time declined by 115–143 s. Finally, the TR required less heat accumulation with increasing of charging rate and ambient temperature, and the heat generation of side reaction played a substantial role that accounted for approximately 54%∼63%. These results provide an insight into the charging cell thermal runaway behaviors in complex operation environments and deliver valuable guidance for improving the safety of cell operation.

Experimental performance evaluation of tracking photovoltaic system based on variable water flow rate with surface temperature

ABSTRACT A solar tracking system with an effective cooling technique is developed and implemented. Due to the solar radiation, high ambient temperature and dusty climate condition affected photovoltaic panel power production. A single east–west solar tracking system incorporating monocrystalline panel and a front surface spray water cooling system was conducted and compared to a fixed reference panel. The water flow rate is adjustable according to the set point temperature of the panel surface. The experiment was conducted during the summer season in north of Iraq (latitude 36.191° and longitude 44.009°). The study revealed that the implementation of the tracking system results in 4.19% increase in power production, while tracking with a cooling system has resulted in an improvement of up to 25.11% in Photovoltaic efficiency. The water consumption has been optimized, and the optimal cooling setting temperature was determined to be 40°C. Additionally, this model demonstrates that the performance of photovoltaic panel was decreased by only 0.2%–0.3%, when the surface temperature increased by 5°C within a range of 25–40°C.

Dietary supplementation of Ocimum gratissimum improves growth performance and immune response in broilers under high ambient temperature.

Ocimum gratissimum (OG) was found to have immunity boosting effect on Taiwan country chickens and broiler chickens raised in moderate ambient temperature in previous studies, and the current study investigates its potential on the growth performance, blood traits, intestinal traits, and immune responses in Ross 308 broilers raised in high ambient temperature which can induce mild heat-stress (26 to 33 ˚C, average 30 ˚C). Two hundred 1-d-old male/female chicks were randomly assigned to a control group, three OG (1 g/kg, 3 g/kg, and 5 g/kg)/basal diet groups, and one Amoxicillin group. Data collected during the experiment indicated that the weight gain increase of 1742 g/bird to 1815 g/bird comparing control to 5 g/kg OG supplementation was statistically significant. In addition, the production efficiency factor was also noticeably increased by OG, particularly in the 5 g/kg group, and the uric acid levels were decreased in the 3 and 5 g/kg OG groups (from 4.26 to 2.91 and 2.90 mg/dL, respectively), indicating heat-stress alleviation was observed. Several areas of the carcass saw desirable growth changes, including the increase of breast muscle ratio observed in the 5 g/kg OG group, an overall decrease in abdominal fat in all OG groups, as well as dimensional changes in several areas of the digestive system. Lastly, the hemaglutination, hemaglutination inhibition, and phytohemaglutinin tests indicated elevated immuno-response in all OG groups. In conclusion, OG has exhibited the ability to alleviate symptoms of mild heat-stress, leading to improvement of the digestive organ development and increase of carcass mass and mean weight gain for birds, and we find OG to be a potentially beneficial feed supplement for poultry raising in high ambient temperature conditions.

Математическое моделирование аварийности на автомобильном транспорте в условиях высоких температур окружающей среды

The relevance of the study is due to the lack of a systematic theoretical platform that serves to describe the effect of increasing (up to two times) the accident rate on roads in conditions of high ambient temperatures. The development of theoretical foundations capable of describing this phenomenon was the purpose of this work. Research methods: analysis and synthesis, methods of mathematical statistics. The initial data were obtained by expert method and observation of drivers of passenger taxis using the “Wialon – GPS” system/Glonass”. The main results consist in the development of a mathematical model of accidents in road transport at high ambient temperatures. With the help of the constructed model, the influence of climatic installations of various types on the reduction of accidents is determined. These results constitute the scientific novelty of the work. The practical significance of the results is to assess the effectiveness of the developed measures to reduce accidents in the hot season, which should include the organization and control of the use of air conditioners and climate control systems, which can reduce the increase in accidents to 64.1%. The directions of further research are related to the development of algorithmic and instrumental support for reducing the increase in accidents during the organization of traffic in conditions of high ambient temperatures. Recommendations. The results of the research can be recommended to the organizers of passenger and cargo transportation by road, divisions of regional and municipal authorities that have traffic management as their functionality.

Effects of Low Dietary Cation and Anion Difference on Blood Gas, Renal Electrolyte, and Acid Excretions in Goats in Tropical Conditions

Goats can suffer from intermittent heat stress in high ambient temperature (HTa) conditions, which causes sporadic respiratory hypocapnia. Obstructive urolithiasis is a common urological problem in goats. Sandy uroliths can be partially relieved by urine acidification with short-term ammonium chloride (NH4Cl) treatment. However, the outcome of urine acidification and the physiological responses to short-term NH4Cl supplementation under respiratory hypocapnia of HTa have rarely been reported. The present study investigated the effect of NH4Cl supplementation that produced a low dietary cation-anion different (l-DCAD) diet on acid-base balance and renal function under HTa conditions. The first experiment investigated the physiological responses to natural HTa to prove whether the peak HTa during the afternoon could induce HTa responses without a change in the plasma cortisol. The partial pressure of CO2 also tended to decrease during the afternoon. The second experiment examined the short-term effect of l-DCAD under HTa conditions. Although the blood pH was within the normal range, there was a clear acid-base response in the direction of metabolic acidosis. The major responses in renal function were an increase in tubular function and acid excretion. With a comparable level of creatinine clearance, the fractional excretions (FE) of chloride and calcium increased, and the FE of potassium decreased. Acid excretion increased significantly in the l-DCAD group. We conclude that under HTa conditions, the tubular excretion of electrolytes and acids was the major response to acid loading without changing the filtration rate. The l-DCAD formulation can be used to acidify urine effectively.

Experimental study of the effect of physical and chemical properties of alcohols on the spray combustion characteristics of alcohol-diesel blended fuels

To reveal the effect of different long carbon-chain alcohols blended into diesel on combustion characteristics and soot emissions under different ambient temperatures, the spray combustion processes of diesel and four sets of blends (the volume ratio of propanol/diesel, butanol/diesel, pentanol/diesel, and hexanol/diesel being 20%/80%) were investigated in a constant volume combustion chamber (CVCC) using optical techniques. It was discovered that the physical (cooling effect, dilution effect, diesel evaporation inhibition) and chemical reaction properties of alcohols have a competitive effect on the spray combustion characteristics of alcohol-diesel blended fuels. The combustion pressures of alcohol-diesel blended fuels were lower than that of pure diesel due to lower heating values, and this difference became more obvious under higher ambient temperature. Alcohols blended into diesel fuel could improve the combustion efficiency. The ignition delay times (IDTs) of alcohol-diesel blended fuels decreased with increased carbon chain lengths of alcohols under low ambient temperature conditions. However, this trend was reversed with increasing ambient temperature, and the IDTs of alcohol/diesel blends became lower than that of pure diesel at higher ambient temperatures. Propanol or hexanol blended into diesel could significantly inhibit the generation of soot at low ambient temperatures, but other alcohols promoted it. Interestingly, all alcohol-diesel blend fuels inhibited the generation of soot under high ambient temperature conditions, and propanol was the most significant.

Predicting Vehicle Refuelling Trips through Generalised Poisson Modelling

This paper presents a model to predict the number of refuelling trips by vehicles on any given day considering weather conditions and time of the year. The predicted refuelling trips were founded on count-based data, i.e., data that contain events that occur at a certain rate. The paper presents an algorithm developed using Python programming language and the statsmodels module to achieve this. The results indicate that the GP-1 model developed in this paper is statistically significant at the 95% confidence level as it was able to converge—however, precipitation and high ambient temperature conditions are considered statistically insignificant in this model. The viability of the model was further tested on the remaining 20% of the data. Sensitivity tests indicate that there is a good correlation between the actual trips and predicted trips when 70% of the data are used to train the model. Overall, the model presented can be used to predict the number of trips taken by vehicles to refuel as well as model future trends, accurately. This model, can in the future, be applied to predict the refuelling behaviour of alternative fuel vehicles such as hydrogen fuel vehicles, when such data become available.

Robust two-colour pyrometry uncertainty analysis to acquire spatially-resolved measurements

Two-colour pyrometry (2CP) has been used over several decades to study engine-relevant combustion processes, but results are generally regarded as qualitative or semi-quantitative. In many current 2CP systems, large measurement errors are introduced by parallax because the two measured wavelengths are not from the same line of sight. This work presents a spatially-resolved 2CP system with the objective of quantifying and reducing measurement uncertainty. An optical setup that eliminates parallax in 2CP is used together with pixel-by-pixel calibration of the camera sensor to increase measurement accuracy. Primary uncertainty terms are identified, and an error propagation analysis is performed to compute uncertainties in the final results of soot temperature, soot concentration parameter, KL, and soot mass. These methodologies are applied to investigate an auto-igniting fuel spray in a constant pressure flow rig at diesel-like conditions of high ambient pressure and temperature. Results show bias uncertainty of around 200 K (≈10%) for temperature and about 40%–60% for KL. High uncertainty was found to occur on the diffusion flame front where both optical thickness and soot concentrations are small. However, these uncertain measurement zones with relatively low soot concentrations contribute minimally to the total soot mass present in the reacting jet during the temporal evolution of the flame.

Thermodynamic analysis of a novel multi-target temperature transcritical CO2 ejector-expansion refrigeration cycle with vapor-injection

In the present paper, a multi-target temperature ejector-expansion subcooler vapor-injection refrigeration cycle is proposed in order to improve the performance of natural fluid CO2 refrigeration cycles. A thermodynamics model to simulate a two-phase ejector cycle integrating a vapor-injection is first established from the energetic and exergetic perspectives. The behavior of the new cycle is then analyzed, and the adjustment direction of the cooling capacity and the evaporating temperature is pointed out. Furthermore, the new cycle is also compared with the subcooler vapor-injection refrigeration cycle and the ejector-expansion refrigeration cycle. The obtained results show that the behavior of the evaporators is affected by the bypass mass ratio and the entrainment ratio, and the two parameter determines the direction of adjusting the cooling capacity distribution and the evaporating temperature. The COP of the new cycle is about 17.9–29.4% and 2.8–7.8% higher than that of subcooler vapor-injection refrigeration cycle and ejector-expansion refrigeration cycle; the exergy efficiency of new cycle is about 14–28.2% and 3.7–11.3% higher than that of subcooler vapor-injection refrigeration cycle and ejector-expansion refrigeration cycle; and it is also found that the performance of the new cycle is improved more significantly under low cooling temperature and high ambient temperature conditions.

Effect of Temperature Gradient on Chloride Ion Diffusion in Nuclear Reactor Containment Building Concrete

Chloride diffusion through concrete is influenced by harsh environmental conditions such as high ambient temperature and relative humidity. This paper examined the influence of temperature gradient on chloride diffusion in concrete under high ambient temperature conditions. Chloride diffusion tests using cylindrical concrete samples were performed in constant temperature and temperature gradient conditions. In a temperature gradient condition, a much higher chloride concentration was measured than at constant temperatures, which could not be explained only by the mass diffusion driven by the concentration gradient. A new analytical model of chloride diffusion with the mass diffusion term including the temperature effect and the thermo-diffusion term including the temperature gradient effect was applied to the results, which showed that the thermo-diffusion contribution was significant. Using the analytical model with the mass diffusion (DCl) and thermo-diffusion (DT) coefficients, the service life of reactor containment buildings (RCBs) in nuclear power plants (NPPs) in the Middle Eastern and North African (MENA) region was estimated. The results showed that the service life of the RCBs could be reduced by the temperature gradient, indicating the possible application of the proposed analytical model.

Development of Effective Protocol for Four Varieties of Large Cardamom

Large cardamom is one of the most important spices that can significantly contribute to the economical farming in the country of Nepal. It is grown in Nepal and north-eastern states of India which provide suitable agroclimatic growing conditions of high humidity, ambient temperature and high rainfall. Meeting the demand for high quality plants and yield of cardamom is challenging with traditional methods of propagation. The present study has used the plant tissue culture technique to produce high quality plants. In this regard, MS media with three different hormonal combinations were used for the development protocol for 8 weeks. Shoot length, root length, shoot number and root number were assessed at intervals. The best protocol for growth was MS media with 1 mg/L BAP + 0.5 mg/L IBA for the Ramsey variety, with no significant difference for Golsai, Dambarsai, or Sikkimae varieties. Similarly, the acclimatization and field transfer study was done. The use of any substrate composition in ratio of coco peat: soil 1:2; moss: coco peat 1:2 and sawdust: coco peat 1:2 enables transfer of healthy plants to the field. The results indicate that the varieties respond differently to the micropropagation process and to hormone concentrations indicated by differing root and shoot production. The protocol of 1mg/L BAP and 0.5mg/L IBA could be used for the Ramsai while optimal shoot production for Golsai and Sikkimae should be at 0.5mg/L and 5mg/L for shoot production. All varieties showed optimal root production at 0mg/L BAP and 0.5mg/L IBA. This study sheds light on the different responsiveness of varieties to tissue culture and hormone concentrations for both root and shoot development in micropropagation.

Influence of a Supplemental Blend of Essential Oils Plus 25-hydroxy-vitamin-D3 on Feedlot Cattle Performance during the Early-growing Phase under Conditions of High-ambient Temperature

Background: During the first stage of fattening, performance of cattle is more affected by high ambient load. A strategy to mitigate the negative effects of high ambient temperatures on energy efficiency is by monensin supplementation. However, the present concern about the use of antibiotics as feed additives has led to search for safe alternatives. Due to its nature, essential oils and supplementary vitamin D3 represent a potential substitute to monensin in cattle subjected to high environmental heat load. For this reason, The objective of this study was to compare supplemental monensin vs the novel combination essential oils plus vitamin D3 on growth performance and dietary NE of feedlot bulls exposed to elevated ambient temperature during the initial 84-d on feed. Methods: Ninety crossbreed young bulls (228.0±7.1 kg initial weight) were used in 84-d trial to evaluate a blend of essential oils plus 25-hydroxy-Vit-D3 as a feed additive to alleviate the harmful effects of the high-ambient temperature on feedlot cattle performance during the early-growing phase. Dietary treatments (9 replicates/treatment) were supplemented with: 1) 24 mg of sodium monensin/kg diet DM (MON), or with 2) 119.12 mg/kg diet DM of a combination of standardized mixture of essential oils (119 mg) plus 0.12 mg of 25-hydroxy-vitamin-D3 (EO+HyD). Average THI was 82.7±3.2. Result: There were no treatment effects on day-to-day fluctuations in DMI. However, EO+HyD tended to increase DMI (4.3%, P=0.06). Supplemental EO+HyD increased daily weight gain (8.3%, P less than 0.01) and gain-to-fed ratio (4.0%, P=0.03). Supplemental EO+HyD tended to increase estimated dietary net energy (2.5%, P=0.07) and observed-to-expected dietary NE ratio (3.0%, P=0.07). This effect can be attributed to a 7% reduction in the maintenance requirement. The combination of EO+HyD may be a valuable tool to optimize growth-performance and feed efficiency of cattle under conditions of high ambient heat load.