Clothing & comfort Evaporation

 Clothing & comfort  Evaporation

Evaporation: 

 Evaporation is exclusively a cooling process. 

 At lower temperature, evaporation plays an insignificant role in the human body heat balance.

  At higher temperature, when heat loss by radiation and conduction can not occur, evaporation becomes the prominent factor for body heat loss. 

 When each gram of water evaporates from human body surface, 0.58 calories of heat is lost. 

 Water evaporates insensibly from the skin and lung, which causes continual heat loss at a rate of 12 – 16 calories per hour. 

 When human are highly active, more metabolic heat is produced with a corresponding increase of evaporating heat loss. 

 A person engaged with hard physical work may sweat as much as 0.25 gallon of fluid in an hour. 

 The flow rate of sensible heat loss depends upon the temperature difference between body skin and surrounding air. 

 Depending on the surrounding temperature , humidity, and air velocity, the skin may very from 4◦c to 41 °c even though the body core temperature remain constant. 

 Velocity of surrounding air increases evaporative heat loss rate from human body.