Low External Temperatures Research Articles

Study on correlation between wind turbine performance and ice accretion along a blade tip airfoil using CFD

In cold-region environments characterized by high wind speeds, low external air temperatures, and supercooled water droplets, wind turbines frequently experience ice formation along the leading edge of the blade tip, which has a higher angular velocity. This ice formation directly and negatively affects the wind turbine's power performance. As such, a clear understanding of the relationship between ice formation and wind turbine power performance is required. In this study, we used computational fluid dynamics (CFD) simulation methods based on the dispersed multiphase (DMP) droplet model to predict ice formation along a blade tip airfoil's leading edge. To validate the ice formation model, the CFD simulation results were compared with the previously published wind tunnel testing results. Following validation, the model was used to predict the ice formation along the leading edge of the National Advisory Committee for Aeronautics (NACA) 64-618 airfoil and estimate its aerodynamic performance under variable external environmental conditions. Steady power calculations for the National Renewable Energy Laboratory's (NREL) 5-MW wind turbine was performed using the BLADED software. The aerodynamic performance of the NACA 64-618 airfoil following ice formation and the power performance of the NREL 5-MW wind turbine were subsequently correlated. The results indicated that ice formation on the blade tip airfoil's leading edge caused wind turbine power performance to decrease by approximately 8–29%.

Short communication. Comparison of the efficacy of Apiguard (thymol) and Apivar (amitraz) in the control of Varroa destructor (Acari: Varroidae)

The present study compared the efficacy of Apivar (a.i. amitraz) and Apiguard (a.i. thymol) in controlling the mite Varroa destructor during spring 2010 and autumn 2011, in the Balearic Islands (Spain). Number of fallen mites (NFM) was counted weekly and the efficacy of treatments was evaluated by using the percentage of reduction of the average daily fallen mites (%R). During spring assay, the average NFM was highly reduced in Apiguard (89.8%) compared to Apivar (64.3%) group, with significant differences between Apiguard and control group (untreated group) in post-treatment week. In autumn assay, Apivar and Apiguard colonies had an average reduction of the NFM of 17.9% and 30.8% respectively, showing a tendency in reduction between control and Apiguard group in post-treatment week. In both assays, %R was higher in Apiguard than in Apivar, but no significant differences were found between treatments in any of the seasons. Apiguard was less efficacious during November-December, probably due to the low external temperatures that hampered an optimal volatilization of the product. The lower efficacy of Apivar is probably related to the resistance of V. destructor to this chemical miticide, which has been used during the last 30 years. Results of this study showed that in Mediterranean conditions, spring is an appropriate period for applying Apiguard to the colonies, whereas application in late autumn would decrease the efficacy of the product. Apiguard may represent an alternative product for integrated control due to the low risk of mite resistance and residues in bee products.

A virtual rat for simulating environmental and exertional heat stress.

Severe cases of environmental or exertional heat stress can lead to varying degrees of organ dysfunction. To understand heat-injury progression and develop efficient management and mitigation strategies, it is critical to determine the thermal response in susceptible organs under different heat-stress conditions. To this end, we used our previously published virtual rat, which is capable of computing the spatiotemporal temperature distribution in the animal, and extended it to simulate various heat-stress scenarios, including 1) different environmental conditions, 2) exertional heat stress, 3) circadian rhythm effect on the thermal response, and 4) whole body cooling. Our predictions were consistent with published in vivo temperature measurements for all cases, validating our simulations. We observed a differential thermal response in the organs, with the liver experiencing the highest temperatures for all environmental and exertional heat-stress cases. For every 3°C rise in the external temperature from 40 to 46°C, core and organ temperatures increased by ∼0.8°C. Core temperatures increased by 2.6 and 4.1°C for increases in exercise intensity from rest to 75 and 100% of maximal O2 consumption, respectively. We also found differences as large as 0.8°C in organ temperatures for the same heat stress induced at different times during the day. Even after whole body cooling at a relatively low external temperature (1°C for 20 min), average organ temperatures were still elevated by 2.3 to 2.5°C compared with normothermia. These results can be used to optimize experimental protocol designs, reduce the amount of animal experimentation, and design and test improved heat-stress prevention and management strategies.

CFD simulations of the night-time condensation inside a closed glasshouse: Sensitivity analysis to outside external conditions, heating and glass properties

Humidity and temperature are key factors in greenhouse climate management since they impact crop growth. For example, under high humidity and low temperatures, condensation may occur and lead to crop damage. In order to assess the condensation mechanism inside a closed greenhouse during the night, a closed monospan 100-m2 Venlo glasshouse was considered and 2D transient CFD simulations were conducted with particular attention paid to condensation and crop transpiration since this combination had rarely been considered before in CFD models. Radiative exchanges were included through a specific submodel and a user-defined function was activated to take account of both heat and mass transfers induced by crop transpiration and by condensation along the greenhouse walls. The aim was, to validate the CFD model by comparing simulations with experimental results and to analyse in detail the influence of external conditions, heating and glass properties on the greenhouse climate. Five parameters were successively tested: external temperature, wind velocity, sky temperature, emissivity of the glass and ground heat flux. Results revealed the ability of the model to predict both the air and wall temperatures of the greenhouse. The root-mean-square difference between the simulations and measurements was <1 K for all temperatures and <11% for relative humidity. Condensation appears to have a strong impact on the resulting relative air humidity inside the greenhouse. A sensitivity analysis showed that low external or sky temperatures may increase condensation because they lead to a considerable decrease in wall temperature.

Examination of the change of the overall heat transfer coefficients of building structures in function of water content

Nowadays, the most applied insulation material in the building sector is the expanded polystyrene. Different types of expanded polystyrene are used but more widely used is the graphite added type. Our research focuses on the analysis of heat conductivity and sorption properties of expanded polystyrene as these two are the most important physical properties from energy saving point of view. In this paper, the variation of heat transfer coefficient of an insulated wall is analysed in function of humidity content of insulation material. Brick and concrete walls with 0.4 m thickness were chosen for substrate and 0.1 m expanded polystyrene (30, 100, 150, 200 and the so-called grey expanded polystyrene) materials were applied as insulating layers. The investigations of sorption behaviour of the materials are important from the point of view of fundamental research and building technology as well. Sorption data taken from our previous measurements results were used for predicting the change of the overall heat transfer coefficients of different wall structures constituted this way. Practical application: The present technical note is based on our previous measurement results. Water can cause undesirable changes in the building structures and introduced in this article. During the fixing procedure of the additional insulating of a given building bad weather conditions (high relative humidity and/or low external temperature) can dominate. These phenomena can be imagined for building new houses. By the ‘in-building’ of the moisture into the wall structure, numerous and measurable change can happen in the U-value of the building envelope. The presented changes are estimations only, but can be used and can also help for planning and executing the insulating process.

Influence of temperature on the corticosterone stress–response: An experiment in the Children’s python (Antaresia childreni)

To cope with environmental challenges, organisms have to adjust their behaviours and their physiology to the environmental conditions they face (i.e. allostasis). In vertebrates, such adjustments are often mediated through the secretion of glucocorticoids (GCs) that are well-known to activate and/or inhibit specific physiological and behavioural traits. In ectothermic species, most processes are temperature-dependent and according to previous studies, low external temperatures should be associated with low GC concentrations (both baseline and stress-induced concentrations). In this study, we experimentally tested this hypothesis by investigating the short term influence of temperature on the GC stress response in a squamate reptile, the Children’s python (Antaresia childreni). Snakes were maintained in contrasting conditions (warm and cold groups), and their corticosterone (CORT) stress response was measured (baseline and stress-induced CORT concentrations), within 48h of treatment. Contrary to our prediction, baseline and stress-induced CORT concentrations were higher in the cold versus the warm treatment. In addition, we found a strong negative relationship between CORT concentrations (baseline and stress-induced) and temperature within the cold treatment. Although it remains unclear how cold temperatures can mechanistically result in increased CORT concentrations, we suggest that, at suboptimal temperature, high CORT concentrations may help the organism to maintain an alert state.

Effects of eccentricity, temperature, velocity, and polymer properties on solids compressibility in vane extruder

An experimental instrument is developed with a purpose to study solids compaction behaviors in vane extruder in a direct manner. The effects of eccentricity, temperature, velocity, and polymer properties on the compressibility of polymer solids are reported in terms of compaction coefficient as a function of rotor torque. The results show that a relatively larger eccentricity or a lower external temperature can bring a smaller compaction coefficient, which results in higher pressure in the solids conveying zone of the vane extruder. However, rotor velocities almost have no influence on the compaction coefficient under the same condition. In addition, a difference is observed between the effects of the semicrystalline polymers and the noncrystalline polymers on the compaction coefficient, which should be taken into consideration in vane extrusion processing operations. POLYM. ENG. SCI., 54:1403–1411, 2014. © 2013 Society of Plastics Engineers

Oxidative coupling of methane using carbon dioxide in an electric field over La–ZrO2 catalyst at low external temperature

Oxidative coupling of methane using carbon dioxide (CO2–OCM) as an oxidant was conducted over several La- and Zr-based catalysts in an electric field at low external temperature of 423K. Higher catalytic activity was obtained than in a conventional catalytic reaction over 10mol% lanthanum-doped zirconia (La–ZrO2) in the electric field. Although the catalytic activity for the CO2–OCM was low over the La–ZrO2 at 1173K without the application of the electric field, the electric field promoted catalytic activity even at 423K external temperature. We optimized the amount of doping-La in the La–ZrO2 system, and characterized the effect of doping-La with XRD measurement. From these examinations, 5mol% La–ZrO2 catalyst showed the highest activity. High catalytic activity was provided by the synergistic effect of the La-cation, tetragonal-ZrO2, and the electric field.

Experimental Analysis of the Performance of a Mechanical Geothermal Water Cooling Tower in South Tunisia

The paper reports the results of pilot test on the cooling performance of a direct cross flow mechanical cooling tower located in the Kebili region in the southern part of Tunisia. In this study heat and mass transfer data are measured within the tower over a period of one year and compared with external weather data collected over the same period. The data enabled the influence of different weather conditions on the performance of the cooling tower to be analyzed. The results obtained show that ambient humidity has a greater influence on performance than external temperature. In fact, significantly better cooling performance of about 80% was obtained during the high temperature, low humidity summer months than during the winter period, less than 40%, with relatively low external temperature and high humidity. These results indicate the relative importance of evaporative cooling as compared to convective cooling. The effect of wind on cooling performance was found to be considerable but was confined to those periods when wind direction coincided with the orientation of the louvers of the tower. This was observed to occur only during the summer period when compared to winter period, thus attesting the benefits of the use of proper cooling tower design for improving efficiency and conserve energy.

Levels of mortality in hens by end of lay on farm and in transit to slaughter in Great Britain

The average mortality for end of lay hens dead on arrival (DOA) was 0.27 per cent (median 0.15 per cent) in a survey of 13.3 million hens transported during 2009....

The role of ghrelin-octanoyl-acyl-transferase in thermoregulation.

Ghrelin is a gastrointestinal peptide that promotes a positive energy balance. The enzyme ghrelin O-acyltransferase (GOAT) esterifies an n-octanoic acid to the peptide, thereby enabling ghrelin to bind and activate the ghrelin receptor. Although ghrelin has previously been implicated in the control and maintenance of body core temperature (BCT), the role that this acylation may play in thermoregulation has not been examined. We aimed to investigate the endogenous role of ghrelin acylation in thermoregulation. In this study, we exposed mice lacking the enzyme GOAT as well as wild-type (WT) control mice to cold temperatures under ad libitum and fasting conditions. Additionally, we investigated the role of GOAT in metabolic adaptation to cold temperatures by analyzing BCT and energy metabolism in mice with and without GOAT that were progressively exposed to low ambient temperatures (31-7 C). We find that regardless of nutritional status, mice lacking GOAT maintain a similar BCT as their WT counterparts during an 8 h cold exposure. Furthermore, mice lacking GOAT maintain a similar BCT and metabolic adaptation asWT controls during acclimatization to low ambient temperatures. We conclude that the absence of the enzyme GOAT does not play a significant role in maintenance of BCT or metabolic adaptation during exposure to low external temperatures.

Catalytic Oxidative Coupling of Methane Assisted by Electric Power over a Semiconductor Catalyst

Abstract Oxidative coupling of methane (OCM) on La2O3 semiconductor catalysts at 423 K external temperature was investigated. DC power supplied from two electrodes in a catalyst bed enabled stable and selective production of C2H6 and C2H4 over Sr–La2O3 (Sr/La = 1/200 and 1/20), but plasma reactions proceeded over other catalysts. The electrical conductivity of the semiconductor catalyst was important for controlling this reaction. A high yield of C2 (49% selectivity, 51.3% O2 conversion) was obtained using 2.7 W of electricity at a lower external temperature (423 K).

Desenvolvimento de colônias de abelhas &lt;em&gt;Apis mellifera&lt;/em&gt; africanizadasna região de Maringá, Estado do Paraná

This research was carried out to evaluate the growing of Africanized honeybee colonies from July 1999 to June 2000, as for the percentages of occupation area with brood,food, occupied total area, to correlate them with environmental variables and to determine the tenor of crude protein in the pollen stocked in the combs by workers. Five colonies were mapped monthly, which were made the counting of the occupied area with brood, food, occupied total area and also the pollen was collected and submitted to thebromatological analysis to determine the tenor of crude protein. The medium percentages of occupation with brood (egg-larvae plus workers pupa and drones), with food (honey and pollen) and of the occupied total area they were not also different among the treatments (p>0.05). The Africanized honeybee colonies reduced their population with low external temperatures (winter) and also with excess of relative humidity of the air (summer). Themedium tenor of crude protein in the pollen during the year was 24.51%, and this value isacceptable for a good development of the colonies.

A low external temperature method for synthesis of active electrode materials for Li batteries – Part B: Synthesis of lithium iron oxides Li x Fe y O z

Anode materials for lithium-ion batteries based on iron oxides were synthesized using two different methods: a Low External Temperature Method (LETM) and a conventional Solid State Reaction Method (SSRM). Both methods lead to the formation of final products representing a mixture of two phases: approximately 75% LiFeO2 and 25% Li−xFe5O8 (0 < x ≤ 0.1). When compared with the ordinary solid state synthesis, LETM creates conditions for carrying out the synthesis at a lower external calcination temperature (200 °C) over a shorter period. The properties of the LixFeyOz obtained by the LETM were compared with those of the same compound obtained by SSR at 700 °C. Higher initial discharge capacity was displayed by the sample synthesized by the SSR method, while a superior cycling stability was shown by the sample synthesized by the LETM. The latter shows approximately double capacity at the 30th cycle as compared with the sample synthesized by SSRM.

A low external temperature method for synthesis of active electrode materials for Li batteries ? Part A: Synthesis of pure manganese spinel

A low external temperature method (LETM) of active electrode material synthesis for lithium ion batteries has been proposed. The method consists of a two-step process, which is comprised of drying fine droplets of a solution of the starting compound in a liquid drying agent at 200 °C, followed by calcination of the obtained precursor in a fluidised bed at a furnace temperature of 300 °C. The method prevents uncontrolled growth of particles during the initial thermal pre-treatment and the final firing process. Lithium manganese spinel has been selected for describing the proposed LETM of synthesis. The properties of the spinel obtained by LETM are compared with those of a spinel obtained by the classical immobilised solid state synthesis at 750 °C. On electrochemical cycling, the capacity loss after 100 cycles of the LETM spinel at 11% is significantly lower than that for the spinel prepared by solid state methods (21.5%). However, only 3% difference is seen in the total integral capacity over the 100 cycles between spinels prepared by the different methods.

Contact and non-contact thermometry in the milk acquisition process

Temperatures of the northern wall, ceiling and floor of a 2 &amp;times; 12 milking house as well as of a waiting area in front of the milking house were measured for 24 hours a&amp;nbsp;day in the winter season with an average external daily temperature of &amp;ndash;8.6&amp;deg;C. The influence of low external temperatures on the temperatures of cows&amp;rsquo; mammary glands was measured with a&amp;nbsp;non-contact thermometer RAYNGER ST 6 equipped with laser. The analysis showed that the low external temperatures and insufficiently warmed external walls [average 24-hour temperatures: (t&lt;sub&gt;st&lt;/sub&gt;&amp;nbsp;=&amp;nbsp;+1.32&amp;deg;C), ceiling (t&lt;sub&gt;s&lt;/sub&gt; = +2.65&amp;deg;C), floor (t&lt;sub&gt;p&lt;/sub&gt; = +3.29&amp;deg;C)] as well as the waiting area in front of the milking house (t&lt;sub&gt;d&lt;/sub&gt;&amp;nbsp;= +1.9&amp;deg;C) produced unsuitable temperature conditions despite of the use of heaters in the milking house, resulting in the undercooling of mammary glands and the traumatising of dairy cows. The temperatures of mammary glands of tested dairy cows were evaluated by a multifactor analysis of variance. The time and place of measuring were statistically significant on the significance level 0.05. The F -test value for the factor of time was 12.342, with probability 0.0007. The F -test value for the place of temperature measuring was 1061.979, probability 0.0000. Among the equations of curves of the dependences of teat end temperature on the milking time, the closest seemed to be the logarithmic function with determination index R&lt;sup&gt;2&lt;/sup&gt; = 0.7404. &amp;nbsp;

Bulk Nanocrystalline Ni&lt;sub&gt;3&lt;/sub&gt;Al Material Prepared by Self-Propagating High Temperature Synthesis Casting at Low External Temperature

Bulk Nanocrystalline Ni&lt;sub&gt;3&lt;/sub&gt;Al Material Prepared by Self-Propagating High Temperature Synthesis Casting at Low External Temperature

In vitro evaluation of external root temperature changes during Er:YAG laser application with five different fiber optic tip withdrawal techniques

This study evaluated in vitro the external temperature increase at the three root thirds using five different fiber optic tip withdrawal techniques in 50 human canines. Er:YAG laser was applied with a 50/28 fiber optic tip with 250 mJ input, 112 mJ output, 10 Hz, 1 mm from the apical foramen: group 1: each third was irradiated starting at the apex for 1 s on each wall, with the irradiation turned off between thirds; group 2: apical third irradiated without movement for 2 s and tip withdrawn with continuous radiation up to the cervical third; group 3: tip activated at the apex and removed to the canal entrance in a straight line; group 4: tip activated at the apex and removed to the canal entrance with circular movements touching all walls; group 5: tip activated at the apex and removed to the canal entrance with clockwise circular movements for 6 s and then reinserting and removing with counterclockwise circular movements for another 6 s, touching all walls. Group 1 had significantly lower external temperature ( p<0.01). The middle third had the greatest temperature increase ( p<0.01). We conclude that the withdrawal techniques caused an increase in external root temperature that would not damage adjacent tissues.

Ambient temperature limits above-ground activity of the subterranean rodent Spalacopus cyanus

We studied daily activity patterns of the subterranean rodent Spalacopus cyanus, in the field during summer and winter, and under laboratory conditions at two different temperatures, 15°C and 30°C. This rodent exhibited nocturnal activity in the laboratory, but diurnal above-ground activity in the field. We suggest that this discrepancy between field and laboratory results is a consequence of differential space-use inside burrows during the day, and that low external ambient temperatures appear to constrain activity of S. cyanus outside their burrows during the night in summer and winter. In contrast, we hypothesize that high summer temperatures constrain above-ground activity at midday.

Nanocrystalline ceramics from sucrose process

A variety of nanocrystalline (particle diameter <100 nm) ceramic powders has been prepared from an innovative sucrose process using metal ion–sucrose (containing 10–20 mol% polyvinyl alcohol (PVA)) solution. The process involves the dehydration of metal ion–sucrose solution to a highly viscous liquid, which on decomposition produces the precursor materials. Calcination of the precursors at low external temperatures produces the nanocrystalline ceramic powders. The examples discussed include lead zirconate titanate PbZr 0.6Ti 0.4O 3 (PZT) and spinel ferrites MFe 2O 4 (M=Co, Ni, Zn).