Critical Ambient Temperature Research Articles

A Comparison of Exhaust Condensation Trail Forecast Algorithms at Low Relative Humidity

Abstract The Schrader and Schumann contrail forecast algorithms and a third algorithm are evaluated under low relative humidity conditions using a dataset of asynoptic atmospheric soundings and 318 coincident ground-based aircraft and contrail observations collected near Dayton, Ohio. Aircraft were positively identified and their flight altitudes were determined using either Federal Aviation Administration flight logs or data collected with the Wright–Patterson Air Force Base air traffic control radar. The sounding data were used with assumed aircraft performance parameters to prepare nowcasts of contrail critical temperatures. The nowcasts were examined subjectively by comparing the distribution of correct and incorrect forecasts as a function of the difference between critical temperature and ambient temperature. Objective evaluation against the contrail observations also was done using several common statistical measures. The third algorithm produced critical temperatures that were systematically too c...

The effect of exchangeable cations on low-temperature oxidation and self-heating of a Victorian brown coal

The effect of inorganic additives, when applied into a coal by ion-exchange, on low-temperature oxidation and self-heating of a Victorian brown coal is studied in this article. Acid-washed coal, and acid-washed coal ion-exchanged separately with seven additives, were prepared. Each of the samples was then tested in a wire-mesh reactor to obtain its critical ambient temperature, above which thermal runaway occurs. The relative effectiveness of the additives is determined by comparing their critical ambient temperatures with that of the acid-washed coal. Magnesium acetate (Mg(Ac) 2), calcium chloride (CaCl 2), and sodium chloride (NaCl) were found to inhibit low-temperature oxidation, while copper acetate (Cu(Ac) 2), potassium acetate (KAc), and sodium acetate(NaAc), promote the reaction. The effect of additive loading was also investigated for NaAc and Ca(Ac) 2. The effectiveness of NaAc to promote low-temperature oxidation is enhanced with an increase in its loading, while that of Ca(Ac) 2 remains unchanged with varying additive loading. Low-temperature oxidation kinetics were estimated by a transient energy balance and compared with the low-temperature oxidation and self-heating behaviour of the samples.

A laboratory study of spontaneous combustion of coal: the influence of inorganic matter and reactor size

A laboratory investigation into the effect of inorganic matter on spontaneous combustion behaviour of a Victorian brown coal. Fourteen samples were prepared, namely, the raw coal, water-washed coal, acid-washed coal, and acid-washed coal doped with 11 additives. Each of the samples was then tested in an isothermal reactor to obtain its critical ambient temperature, above which spontaneous combustion occurs. The relative effectiveness of the additives was determined by comparing their critical ambient temperatures with those of the raw coal and the acid-washed coal. Potassium chloride, Montan powder, and sodium chloride were found to be the most effective inhibitors, followed by magnesium acetate, and calcium chloride. The presence of sodium nitrate and ammonium chloride in the coal samples did not show any significant influence on the spontaneous combustion. However, calcium carbonate, sodium acetate, potassium acetate, and pyrite promoted the spontaneous combustion. The effect of additive loading was also investigated for an inhibition agent (KCl) and a promotion agent (NaAc). It was revealed that the effectiveness of these promotion and inhibition agents was enhanced with an increase in the additive loading. Low-temperature oxidation kinetics were also estimated by an energy balance approach and compared with the self-heating potential of these samples. The effects of reactor size and reactor specific surface area on the critical ambient temperatures are also discussed.

Low-temperature oxidation of coal studied using wire-mesh reactors with both steady-state and transient methods

This paper reports a low-temperature oxidation study of a Victorian brown coal using seven cylindrical wire-mesh reactors of different sizes, with both steady-state and transient methods. The steady-state method enables determination of the critical ambient temperature, above which spontaneous combustion occurs, as a function of the reactor’s size. These critical ambient temperatures are then used to calculate the low-temperature oxidation kinetics. The transient method is also applied to directly estimate the rate of oxidation by determining the crossing point, when the thermal conduction term near the center of a cylinder becomes zero. The kinetic constants determined from both steady-state and transient methods are then used to estimate the critical thickness of a layer of coal deposit (infinite slab), above which the deposit is capable of spontaneous combustion. The critical thickness predicted from the steady-state method compares well with those from the transient method, particularly at higher temperatures. This paves a way for future testing using the transient method for a more cost-effective assessment of spontaneous combustion of different materials.

Kinetic parameters of oxidation of coals by heat-release measurement and their relevance to self-heating tests

From heat-release rates made in oven heating experiments, kinetic parameters of oxidation of a number of bituminous coals are determined. Calculations are performed to determine the critical ambient temperature for ignition of each coal in a 3 m shipping hold, and rates of heat release at that temperature are calculated for each coal. These are found to be the same for each coal and it is suggested that this can provide a criterion for an alternative approach to assessing self-heating hazards with such materials.

Lower critical temperature under the influences of seasonal cold acclimatization due to the two types of clothing

This paper studied the changes in the lower critical temperature under the influences of seasonal cold acclimatization due to the two types of clothing, one with the legs covered, the other with uncovered legs. The subjects in the skirt group always wore knee-length skirts during the daytime, while those in the trouser group dressed in full trousers during the identical period. After the 3 months acclimatization from September to November, the lower critical temperature and thermal physiological responses were compared between subjects wearing the two types of clothing during a gradual fall of ambient temperature from 24 to 10°C over 1 h. The results showed that the lower critical ambient temperature in December was 18.2°C in the skirt group and 22.8°C in the trouser group and critical mean body temperature in December was 34.40°C in the skirt group and 34.89°C in the trouser group. Internal conductance (W M −2 °C −1) in December was 12.39 in the skirt group and 13.27 in the trouser group, which might be responsible for the lower critical temperature in the skirt group.

Leaf Temperature Kinetics Measure Plant Adaptation to Extreme High Temperatures

Leaf temperature kinetics were studied as a function of the rate of change of ambient temperature (Vt), light conditions, plant age, and genotypic and species diversity for Zea mays, Cucumis sativus, Lycopersicon esculentum, Phaseolus vulgaris, Beta vulgaris, Cucurbita pepo and Raphanus sativus. Ambient temperature was varied from 26 to 60�C at rates from 0.5 to 8�C/min. Leaf-air temperature differences (LATD) were registered with differential copper-constantan thermocouples. As the ambient temperature rose LATD increased because stomata had been closed in darkness. Still in the darkness, at some critical ambient temperature stomata opened and the leaf temperature reduced dramatically as result of stomatal transpiration. The critical temperature is strongly dependent upon Vt. Simple equations for the calculation of a threshold of plant temperature sensitivity and of a time constant for stomatal signal transduction have been obtained. These parameters show a high correlation with plant heat tolerance both in genotypic and species aspects. This is consistent with the idea that temporal organisation of plant regulatory systems plays a leading role in evolution and in adaptation to extreme environmental conditions. Both characteristics measured tend to change with plant age. It is concluded that the measurement of leaf temperature kinetics is a very convenient procedure for estimating plant adaptive ability to high temperatures.

Is Hyperthermia a Constraint on the Diurnal Activity of Bats?

Bats are normally nocturnal, despite some potential advantages of being active during the day. A possible constraint on diurnal activity is hyperthermia. We evaluated the hyperthermia hypothesis by constructing a biophysical model which considered all the heat fluxes across a bat's wing during diurnal flight and predicted a critical ambient air temperature (Tacrit) above which a bat would be unable to fly without experiencing fatal hyperthermia. Many factors had important influences on Tacrit , including time of day, latitude, cloud cover and foliage cover. Ground surface temperature and ground albedo had significant but mutually opposed effects. Important organismal factors included body mass (larger bats were more susceptible to overheating), aspect ratio (lower aspect ratios more susceptible), flight speed (slower more susceptible), and the albedo and transmittance of the wing membranes (darker more susceptible). Using the expected latitudinal variation in the environmental components we suggest hyperthermia will constrain the diurnal flight of large bats (c. 900 g) at about 85% of sites between 40°S and 40°N. For intermediate sized bats (90 g) hyperthermia will constrain diurnal activity at 50-60% of sites between 20 and 30°N and °S but is less important around the equator (constrained at only 10% of sites). For small bats (9 g) hyperthermia will constrain diurnal activity at about 30-40% of sites between 20 and 30°N and °S, but less than 1% of sites at the equator. For all sizes of bats hyperthermia probably constrains flight in the day at less than 1% of sites above 50°N or °S.

The self-heating of damp cellulosic materials: I. High thermal conductivity and diffusivity

In this series of papers the effects of moisture content on the self-heating characteristics of stockpiles of cellulosic materials are analysed. The model includes the effects of oxidation, hydrolysis, and the evaporation and condensation of water. In this paper the authors derive the full reaction-diffusion model for the system and then look closely at the case of high thermal conductivity and diffusivity, i.e. the spatially uniform case. Degenerate singularity theory is used to show the model can exhibit at least twenty-five distinct bifurcation diagrams. In particular it is seen that the model can exhibit periodic behaviour (a phenomenon observed experimentally for moist systems), a jump to an intermediate steady state (which could represent smouldering), and a substantial decrease in the critical ambient temperature when moisture content is taken into account.

The Upper Critical Ambient Temperature in Neonatal Chicks

Heat production, dry matter, and water loss in the body and yolk sac of neonatal broiler chicks were measured during 24 h exposure to constant temperatures from 30.8 to 38.8 C. Average initial body and yolk sac weights were 41.6 and4.4 g, respectively. Chicks housed at 30.8 C lost 3.5 g/day and chicks housed at 38.8 C lost 5.7 g/day of total body weight. Between 30.8 and 35.1 C, weight loss of the yolk sac was 1.9 g/day. At 38.8 C, weight loss of the yolk sac was 1.4 g/day. Weight lost from the yolk sac consisted of equal amount of dry matter and water. Water loss from the remainder of the chick's body (the total body without yolk sac) increased from 1.8 to 4.4 g as environmental temperature was raised from 30.8 to 38.8 C. This increase occurred mainly above about 35 C. Chick heat production increased with ambient temperature. Heat production as determined per subsequent 3-h period decreased with increasing duration of exposure from 34.6 to 28.2 kJ/kg per hour (1 kJ = .239 kcal) at 30.8 C and from 44.1 to 35.5 kJ/kg per hour at 38.8 C. The upper critical temperature was derived from regression of heat production on temperature. Results showed that this critical temperature was between 36 and 37 C.

Dynamics of behavioral thermoregulation in the rat

Past studies have found that the laboratory rat placed in a temperature gradient prefers temperatures that are markedly below its lower critical ambient temperature (LCT), whereas other rodents (e.g., mouse, hamster, and guinea pig) generally select thermal environments associated with minimal metabolic expenditure. To further study the rat's thermoregulatory behavior, a temperature gradient was designed to monitor the selected ambient temperature (STa) and motor activity (MA) of food-deprived rats of the Long-Evans (LE), Fischer 344 (F344), and Sprague-Dawley (SD) strains over a 22-h period. All three rat strains selected relatively cool STas of 21-26 degrees C during the first 1-3 h in the temperature gradient. This was followed by a gradual increase in the STa that peaked at 4 (F344) to 6 h (SD and LE) after being placed in the gradient. The LE strain had a significantly lower STa during the initial period in the gradient. There were slight decreases in the STa during the nocturnal phase in the F344 and SD strains concomitant with marked increases in MA. These results indicate that the rat requires a relatively long adjustment period in a temperature gradient before it exhibits STas that are associated with minimal metabolic expenditure. Given adequate time for accommodation, behavioral thermoregulatory responses of the rat appear to be similar to those of other rodents.

The ignition of boron particles

For the reaction mechanism generally assumed in the literature as a model of boron particle ignition, an analysis of the ignition phenomenon is carried out. It is shown that for a boron particle residing in a stagnant oxidizing atmosphere, the model assumptions made by previous authors entail a very high critical ambient temperature for ignition. As this is in agreement with experiment, it is concluded that an alteration of the experimental conditions (e.g., a change to higher total pressures and a reduction of the particle size) should be made in order to obtain critical phenomena of a different kind at lower ambient temperatures.

On predicting spontaneous combustion

This paper introduces a method for estimating the critical conditions for the occurrence of spontaneous combustion in beds of finely divided fuel. The basis is a mathematical hypothesis, and the efficacy of the solution is compared with computer models and with classical theory. It is shown that an adequate estimate for the critical ambient temperature may be readily obtained by simple computational methods. Furthermore it is demonstrated that the hypothesis may be used to derive a key item of data from laboratory estimates. We can thus extrapolate the results of laboratory experiments to “plant-size” conditions using mathematical techniques that are adequately served by a hand calculator.

Shorn and unshorn Awassi sheep III. Respiration rate

1. Respiration rate of shorn and unshorn sheep was compared; animals were maintained in the shade and in direct sunlight during various seasons of the year, and at different hours of the day. The average respiration rate, for all seasons when sheep were maintained in the shade, was 55 and 32 respirations per minute, for the unshorn and shorn sheep, respectively.The diurnal trend of the respiration rate of shorn sheep resembled that of the ambient temperature. There was a delay in the lowering of respiration rate of the unshorn sheep during the evening hours.2. The critical temperature for the increase in respiration of animals maintained in the shade was 22° C. and 26–30° C. for the unshorn and shorn sheep, respectively.When the animals were exposed to the direct sunlight the critical ambient temperature for the increase in respiration rate was 15–18° C. and 18–22° C. for the unshorn and shorn sheep, respectively. The respiration rate of the shorn sheep exceeded that of the unshorn but decreased very steeply when the animals returned to the shade.3. The effect of humidity was noted particularly with ambient temperatures exceeding 27° C. The respiration rate of the unshorn sheep increased and that of the shorn decreased with the rise in the relative humidity. In the sun there was a rise in the respiration rate of both groups with increase in humidity. The rise was steeper in the shorn animals.4. The effect of the wind in reducing respiration rate was particularly noted on shorn sheep and at elevated ambient temperatures.5. With equal rectal temperature, the respiration rate of shorn sheep was lower than that of the unshorn ones. Assumed critical rectal temperature for the rise in respiration rate was lower in the unshorn sheep.6. The differences between the respiration responses of the unshorn and shorn sheep stemmed from the variation in their thermal balance. The latter resulted from the differences in the insulating characteristics of body surface and the differences between the macroclimate and the microclimate existing in the fleece.

EFFECT OF AMBIENT TEMPERATURE ON THERMAL RESPONSES TO DRUGS

Thermal responses to a variety of drugs have been investigated at various ambient temperatures, using unanesthetized rats, either lightly restrained or paralyzed with tubocurarine. The results indicate that ambient temperature is a major factor determining thermal responses to many drugs. Experiments on lightly restrained rats demonstrated that the critical ambient temperature, the temperature above which hyperthermia is evoked and below which hypothermia is produced, is about 30 °C (in the thermoneutral range) for Hydergine, ergotamine, LSD-25, and serotonin. The critical ambient temperature for chlorpromazine is approximately 36 °C, and that for 2,4-dinitrophenol, 20 °C. Reserpine produced a consistent hypothermia at 23 °C, but somewhat inconsistent effects at ambient temperatures above this up to 39 °C. Complete curarization abolished the hypothermic effects of all the above agents except chlorpromazine. The production of both hyperthermia and hypothermia by most of the drugs studied suggests that they influence temperature-regulating centers of the central nervous system.

EFFECT OF AMBIENT TEMPERATURE ON THERMAL RESPONSES TO DRUGS

Thermal responses to a variety of drugs have been investigated at various ambient temperatures, using unanesthetized rats, either lightly restrained or paralyzed with tubocurarine. The results indicate that ambient temperature is a major factor determining thermal responses to many drugs. Experiments on lightly restrained rats demonstrated that the critical ambient temperature, the temperature above which hyperthermia is evoked and below which hypothermia is produced, is about 30 °C (in the thermoneutral range) for Hydergine, ergotamine, LSD-25, and serotonin. The critical ambient temperature for chlorpromazine is approximately 36 °C, and that for 2,4-dinitrophenol, 20 °C. Reserpine produced a consistent hypothermia at 23 °C, but somewhat inconsistent effects at ambient temperatures above this up to 39 °C. Complete curarization abolished the hypothermic effects of all the above agents except chlorpromazine. The production of both hyperthermia and hypothermia by most of the drugs studied suggests that they influence temperature-regulating centers of the central nervous system.