Influence of variable heat transfer coefficient of fireworks and crackers on thermal explosion critical ambient temperature and time to ignition

To study the effect of variable heat transfer coefficient of fireworks and crackers on thermal explosion critical ambient temperature and time to ignition, considering the heat transfer coefficient as the power function of temperature, mathematical thermal explosion steady state and unsteady-state model of finite cylindrical fireworks and crackers with complex shell structures are established based on two-dimensional steady state thermal explosion theory. The influence of variable heat transfer coefficient on thermal explosion critical ambient temperature and time to ignition are analyzed. When heat transfer coefficient is changing with temperature and in the condition of natural convection heat transfer, critical ambient temperature lessen, thermal explosion time to ignition shorten. If ambient temperature is close to critical ambient temperature, the influence of variable heat transfer coefficient on time to ignition become large. For firework with inner barrel in example analysis, the critical ambient temperature of propellant is 463.88 K and the time to ignition is 4054.9s at 466 K, 0.26 K and 450.8s less than without considering the change of heat transfer coefficient respectively. The calculation results show that the influence of variable heat transfer coefficient on thermal explosion time to ignition is greater in this example. Therefore, the effect of variable heat transfer coefficient should be considered into thermal safety evaluation of fireworks to reduce potential safety hazard.

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.

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.

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.