Heat dissipation during hovering and forward flight in hummingbirds

Flying animals generate large amounts of heat, which must be dissipated to avoid overheating. In birds, heat dissipation is complicated by feathers, which cover most body surfaces and retard heat loss. To understand how birds manage heat budgets during flight, it is critical to know how heat moves from the skin to the external environment. Hummingbirds are instructive because they fly at speeds from 0 to more than 12 m s −1 , during which they transit from radiative to convective heat loss. We used infrared thermography and particle image velocimetry to test the effects of flight speed on heat loss from specific body regions in flying calliope hummingbirds ( Selasphorus calliope ). We measured heat flux in a carcass with and without plumage to test the effectiveness of the insulation layer. In flying hummingbirds, the highest thermal gradients occurred in key heat dissipation areas (HDAs) around the eyes, axial region and feet. Eye and axial surface temperatures were 8°C or more above air temperature, and remained relatively constant across speeds suggesting physiological regulation of skin surface temperature. During hovering, birds dangled their feet, which enhanced radiative heat loss. In addition, during hovering, near-body induced airflows from the wings were low except around the feet (approx. 2.5 m s −1 ), which probably enhanced convective heat loss. Axial HDA and maximum surface temperature exhibited a shallow U-shaped pattern across speeds, revealing a localized relationship with power production in flight in the HDA closest to the primary flight muscles. We conclude that hummingbirds actively alter routes of heat dissipation as a function of flight speed.

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Numerical Investigation of the Tube Layout Effects on the Heat Losses of Solar Cavity Receiver

Journal of Thermal Science and Engineering Applications ◽

10.1115/1.4036792 ◽

2017 ◽

Vol 10 (1) ◽

Cited By ~ 3

Author(s):

Jiabin Fang ◽

Nan Tu ◽

Jinjia Wei ◽

Tao Fang ◽

Xuancheng Du

Keyword(s):

Heat Loss ◽

Convective Heat ◽

Radiative Heat ◽

Calculation Model ◽

Heat Losses ◽

Radiative Heat Loss ◽

Water Steam ◽

Convective Heat Loss ◽

Circulation Mode ◽

Lower Heat

The effects of tube layout on the heat losses of solar cavity receiver were numerically investigated. Two typical tube layouts were analyzed. For the first tube layout, only the active surfaces of cavity were covered with tubes. For the second tube layout, both the active cavity walls and the passive cavity walls were covered with tubes. Besides, the effects of water–steam circulation mode on the heat losses were further studied for the second tube layout. The absorber tubes on passive surfaces were considered as the boiling section for one water–steam circulation mode and as the preheating section for the other one, respectively. The thermal performance of the cavity receiver with each tube layout was evaluated according to the previous calculation model. The results show that the passive surfaces appear to have much lower heat flux than the active ones. However, the temperature of those surfaces can reach a quite high value of about 520 °C in the first tube layout, which causes a large amount of radiative and convective heat losses. By contrast, the temperature of passive surfaces decreases by about 200–300 °C in the second tube layout, which leads to a 38.2–70.3% drop in convective heat loss and a 67.7–87.7% drop in radiative heat loss of the passive surfaces. The thermal efficiency of the receiver can be raised from 82.9% to 87.7% in the present work.

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Heat dissipation in subterranean rodents: the role of body region and social organisation

Scientific Reports ◽

10.1038/s41598-021-81404-3 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

František Vejmělka ◽

Jan Okrouhlík ◽

Matěj Lövy ◽

Gabriel Šaffa ◽

Eviatar Nevo ◽

...

Keyword(s):

Surface Temperature ◽

Heat Dissipation ◽

Ventral Surface ◽

Body Region ◽

Subterranean Rodents ◽

Ambient Temperatures ◽

Social Species ◽

Body Regions ◽

Body Heat ◽

Solitary Species

AbstractThe relatively warm and very humid environment of burrows presents a challenge for thermoregulation of its mammalian inhabitants. It was found that African mole-rats dissipate body heat mainly through their venter, and social mole-rats dissipate more body heat compared to solitary species at lower temperatures. In addition, the pattern of the ventral surface temperature was suggested to be homogeneous in social mole-rats compared to a heterogeneous pattern in solitary mole-rats. To investigate this for subterranean rodents generally, we measured the surface temperatures of seven species with different degrees of sociality, phylogeny, and climate using infrared thermography. In all species, heat dissipation occurred mainly through the venter and the feet. Whereas the feet dissipated body heat at higher ambient temperatures and conserved it at lower ambient temperatures, the ventral surface temperature was relatively high in all temperatures indicating that heat dissipation to the environment through this body region is regulated mainly by behavioural means. Solitary species dissipated less heat through their dorsum than social species, and a tendency for this pattern was observed for the venter. The pattern of heterogeneity of surface temperature through the venter was not related to sociality of the various species. Our results demonstrate a general pattern of body heat exchange through the three studied body regions in subterranean rodents. Besides, isolated individuals of social species are less able to defend themselves against low ambient temperatures, which may handicap them if staying alone for a longer period, such as during and after dispersal events.

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Convective heat loss and change in body temperature of grasshopper and locust nymphs: Relative importance of wind speed, insect size and insect orientation

Journal of Thermal Biology ◽

10.1016/s0306-4565(97)00037-5 ◽

1998 ◽

Vol 23 (1) ◽

pp. 5-13 ◽

Cited By ~ 13

Author(s):

Derek J. Lactin ◽

Dan L. Johnson

Keyword(s):

Wind Speed ◽

Body Temperature ◽

Heat Loss ◽

Convective Heat ◽

Relative Importance ◽

Convective Heat Loss

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An air curtain surrounding the solar tower receiver for effective reduction of convective heat loss

Sustainable Cities and Society ◽

10.1016/j.scs.2021.103007 ◽

2021 ◽

pp. 103007

Author(s):

Qiliang Wang ◽

Yao Yao ◽

Mingke Hu ◽

Jingyu Cao ◽

Yu Qiu ◽

...

Keyword(s):

Heat Loss ◽

Convective Heat ◽

Air Curtain ◽

Convective Heat Loss ◽

Effective Reduction

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Modeling of convective heat loss from a cavity receiver coupled to a dish concentrator

Solar Energy ◽

10.1016/j.solener.2018.10.060 ◽

2018 ◽

Vol 176 ◽

pp. 496-505 ◽

Cited By ~ 7

Author(s):

Muhammad Uzair ◽

Timothy N. Anderson ◽

Roy J. Nates

Keyword(s):

Heat Loss ◽

Convective Heat ◽

Convective Heat Loss

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Mechanisms of thermal stability during flight in the honeybee apis mellifera

Journal of Experimental Biology ◽

10.1242/jeb.202.11.1523 ◽

1999 ◽

Vol 202 (11) ◽

pp. 1523-1533 ◽

Cited By ~ 11

Author(s):

S.P. Roberts ◽

J.F. Harrison

Keyword(s):

Thermal Stability ◽

Heat Loss ◽

Heat Production ◽

Radiative Heat ◽

Carbon Dioxide Production ◽

Metabolic Heat Production ◽

Evaporative Heat Loss ◽

Radiative Heat Loss ◽

Convective Heat Loss ◽

Metabolic Heat

Thermoregulation of the thorax allows honeybees (Apis mellifera) to maintain the flight muscle temperatures necessary to meet the power requirements for flight and to remain active outside the hive across a wide range of air temperatures (Ta). To determine the heat-exchange pathways through which flying honeybees achieve thermal stability, we measured body temperatures and rates of carbon dioxide production and water vapor loss between Ta values of 21 and 45 degrees C for honeybees flying in a respirometry chamber. Body temperatures were not significantly affected by continuous flight duration in the respirometer, indicating that flying bees were at thermal equilibrium. Thorax temperatures (Tth) during flight were relatively stable, with a slope of Tth on Ta of 0.39. Metabolic heat production, calculated from rates of carbon dioxide production, decreased linearly by 43 % as Ta rose from 21 to 45 degrees C. Evaporative heat loss increased nonlinearly by over sevenfold, with evaporation rising rapidly at Ta values above 33 degrees C. At Ta values above 43 degrees C, head temperature dropped below Ta by approximately 1–2 degrees C, indicating that substantial evaporation from the head was occurring at very high Ta values. The water flux of flying honeybees was positive at Ta values below 31 degrees C, but increasingly negative at higher Ta values. At all Ta values, flying honeybees experienced a net radiative heat loss. Since the honeybees were in thermal equilibrium, convective heat loss was calculated as the amount of heat necessary to balance metabolic heat gain against evaporative and radiative heat loss. Convective heat loss decreased strongly as Ta rose because of the decrease in the elevation of body temperature above Ta rather than the variation in the convection coefficient. In conclusion, variation in metabolic heat production is the dominant mechanism of maintaining thermal stability during flight between Ta values of 21 and 33 degrees C, but variations in metabolic heat production and evaporative heat loss are equally important to the prevention of overheating during flight at Ta values between 33 and 45 degrees C.

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Assessment of Convective Heat Loss From Humans in Cold Water

Journal of Biomechanical Engineering ◽

10.1115/1.3426190 ◽

1978 ◽

Vol 100 (1) ◽

pp. 7-13 ◽

Cited By ~ 3

Author(s):

L. A. Kuehn

Keyword(s):

Heat Loss ◽

Convective Heat ◽

Cold Water ◽

Water Immersion ◽

Physiological Data ◽

Direct Calorimetry ◽

Biophysical Models ◽

Convective Heat Loss ◽

Different Temperatures ◽

Body Heat

Convective heat loss is a primary cause of hypothermia in humans undergoing water immersion, particularly for swimmers and divers at relatively shallow depths. Various biophysical models have been advanced to account for body heat loss in water of different temperatures and cold stress, most of which have made use of physiological data obtained with easily applied classical thermometry techniques. Explicit techniques for the determination of body heat loss must involve direct calorimetry or the use of heat flow transducers, techniques which are difficult to apply in realistic simulations of actual cold water exposure. This paper describes these latter two techniques in some detail, concentrating on the accuracy to be attained and the calibration necessitated with each method. Results obtained with each method specific to heat loss determination at surface and both dry and wet hyperbaric exposures are shown, illustrating the types of data that can be attained.

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Wind Chill*

Bulletin of the American Meteorological Society ◽

10.1175/1520-0477-29.10.487 ◽

1948 ◽

Vol 29 (10) ◽

pp. 487-493 ◽

Cited By ~ 30

Author(s):

Arnold Court

Keyword(s):

Low Temperature ◽

Heat Loss ◽

Convective Heat ◽

Human Body ◽

Empirical Formula ◽

Heat Removal ◽

The Body ◽

Total Heat ◽

Wind Chill ◽

Convective Heat Loss

The rate of heat removal from the human body by wind and low temperature was termed Wind Chill by Siple and expressed by an empirical formula. This paper discusses the formula critically, pointing out that this measure of the convective heat loss may be less than three-quarters of the total heat lost by the body. Siple's formula is compared with those of others, and the use of the formula is discussed.

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