State the movement of heat lost by the human body during evaporation,respiration from physical property .Did you get this value?
Answers
Answer:
Let us consider the following factors to calculate the heat exchange between human body and surroundings
1) Human Response to heat
Cold Environment: shivering
Hot Environment : sweat
2) Heat balance equation:
S = M-W-E-Q
where,
S = rate of heat storage of human body, W/m2
M = metabolic rate of human body, W/m2
W = mechanical work produced by human body, W/m2
E = rate of total evaporative loss due to evaporation of sweat, W/m2
Q = total rate of heat loss from skin (dry heat exchange), W/m2
3) Metabolic Rate
degree of muscular activities,
environmental conditions, and
body size.
4) Mechanical Work
External work developed by the human body is positive while mechanical impact acted on the human body is said to be negative.
5) Evaporative Heat Loss
Evaporative heat loss consists of two components:
(a) Respired Vapour Loss, Eres
(i) Latent Respiration Heat Loss, Erel
(ii) Convective or Sensible Respiration Heat Loss, Erec
(b) Evaporative Heat Loss from Skin Surface, Esk
Evaporative heat loss from skin surface has two parts:
(i) Evaporative Heat Loss by Skin Diffusion, Edif
(ii) Heat Loss due to Regulatory Sweating, ErsW
Mathematically, Evaporative heat loss is expressed as:
6) Dry Heat Exchange
Dry heat exchange represents the heat exchange between the human body and the environment through convective and radiative heat transfer.
Effect of Clothing Insulation
(a) Thermal Insulation of Clothing
The addition of thermal resistance due to clothing affects heat transfer mechanisms between the human body and the environment. "Clo" value is a numerical representation of a clothing ensemble's thermal resistance, 1 Clo = 0.155 m2K/w.
(b) Evaporative Resistance of Clothing
The evaporative resistance is a measure of moisture permeability which affects the latent heat transfer from the skin through the clothing layer and affects evaporative heat loss from skin surface Esk.
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Joseph Guindi
Joseph Guindi, Thermodynamics engineer
Answered Jul 9, 2014 · Author has 683 answers and 4.3m answer views
ASHRAE have done many studies on this, and there is no simple answer, because it depends a lot on the level of activity, clothing worn, climate, and on windspeed. For higher levels of activity, the amount of heat lost by evaporation increases exponentially.
Taking the case of a person sitting at a desk working, or walking lightly, at 24C, dry air, and at a low windspeed; it would be 75W sensible heat and 55W latent heat. Of that 75W sensible heat, 60% of it is radiant. Also, a person wearing shoes would experience little or no conduction loss. So for that case, it would be (0,23,42,25)% respectively.
Taking the case of a person of someone doing athletics, and a high windspeed; it would be 210W sensible heat and 315W latent heat. Of that 210 W sensible heat, 19% of it is radiant. For that case, it would be (0,32,60,8)% which is quite different from the previous case.