Содержание
- 2. Radiation The intense thermal radiation of sun can be perceived The normal radiation loss from the
- 3. All bodies above a temperature of absolute zero emit thermal radiation. Thermal radiation is produced by
- 4. Convection Heat transfer by convection implies the physical movement of a fluid past the body, which
- 5. Evaporative Heat Loss The production and evaporation of sweat is the body´s most powerful temperature control
- 6. Respiration Loss Inspired air is both warmed and humidified on its passage to the lungs, where
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Слайд 2Radiation
The intense thermal radiation of sun can be perceived
The normal radiation loss
Radiation
The intense thermal radiation of sun can be perceived
The normal radiation loss
from the body to the surroundngs is not felt directly, but it is still important
In normal indoor conditions a person loses roughly equal quantities of heat by convection to the air and by radiation to the surrounding surfaces
The loss of heat by radiation becomes noticeable when sitting near a cold window, and is felt as a radiation draught.
In normal indoor conditions a person loses roughly equal quantities of heat by convection to the air and by radiation to the surrounding surfaces
The loss of heat by radiation becomes noticeable when sitting near a cold window, and is felt as a radiation draught.
Слайд 3All bodies above a temperature of absolute zero emit thermal radiation.
Thermal
All bodies above a temperature of absolute zero emit thermal radiation.
Thermal
radiation is produced by the vibration of the molecules of the emitting substance.
Bodies which emit radiation also absorb it.
This results in a net flow of energy from the hotter to the cooler bodies.
The interventing medium, normally air, is assumed to play no part in the radiation exchange.
Mean radiant temperature gives a single figure to measure the strenght of the radiation field at a point and allows an estimate of the radiation exchange with the surroundings of a real body at a point.
Bodies which emit radiation also absorb it.
This results in a net flow of energy from the hotter to the cooler bodies.
The interventing medium, normally air, is assumed to play no part in the radiation exchange.
Mean radiant temperature gives a single figure to measure the strenght of the radiation field at a point and allows an estimate of the radiation exchange with the surroundings of a real body at a point.
Слайд 4Convection
Heat transfer by convection implies the physical movement of a fluid past
Convection
Heat transfer by convection implies the physical movement of a fluid past
the body, which serves to carry away the heat.
Normally the surface temperature of a person will be warmer than the surrounding air.
The layer of air in contact with his skin and clothing is warmed.
This warm air may the be blown away by a draught; in the absence of a draught, the natural boyance of the warmed air will cause to rise and it will the be replaced by cooler air.
In both cases air which has been warmed by the body is removed and the heat with it.
Normally the surface temperature of a person will be warmer than the surrounding air.
The layer of air in contact with his skin and clothing is warmed.
This warm air may the be blown away by a draught; in the absence of a draught, the natural boyance of the warmed air will cause to rise and it will the be replaced by cooler air.
In both cases air which has been warmed by the body is removed and the heat with it.
Слайд 5Evaporative Heat Loss
The production and evaporation of sweat is the body´s most
Evaporative Heat Loss
The production and evaporation of sweat is the body´s most
powerful temperature control mechanism.
When a substance changes from liquid to vapor, a quantity of heat, known as latent heat, has to be supplied from somewhere.
When liquid sweat evaporates on the skin surface, the necessary latent heat is extracted from the body, so that a cooling effect is produced.
It is the evaporation of sweat, not its production, that cools the body.
Any sweat that drips off the skin has produced no cooling at all; sweat that soaks into the clothing and then evaporates extracts heat from the clothing and the cooling effect is produced.
When a substance changes from liquid to vapor, a quantity of heat, known as latent heat, has to be supplied from somewhere.
When liquid sweat evaporates on the skin surface, the necessary latent heat is extracted from the body, so that a cooling effect is produced.
It is the evaporation of sweat, not its production, that cools the body.
Any sweat that drips off the skin has produced no cooling at all; sweat that soaks into the clothing and then evaporates extracts heat from the clothing and the cooling effect is produced.
Слайд 6Respiration Loss
Inspired air is both warmed and humidified on its passage to
Respiration Loss
Inspired air is both warmed and humidified on its passage to
the lungs, where it reaches almost a complete saturation and a temperature equal to the deep body temperature.
This heat is not all lost on expiration.
However, there is a net loss of heat on respiration.
This heat is not all lost on expiration.
However, there is a net loss of heat on respiration.
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