L2: Heat balance & Clothing

Question 1

What is conduction?

Answer 1

Transfer of heat through direct contact with a solid material

Question 2

What is convection? and what are the two types of convection?

Answer 2

Movement of air or fluid past the skin which carries heat.
Force: wind
Natural: Heating of air

Question 3

What is radiation?

Answer 3

Transfer of heat via electromagnetic radiation

Question 4

What is evaporation?

Answer 4

Transition from a liquid to vapour utilises heat

Question 5

How does metabolic heat production work?

Answer 5

Energy is required by cells and is utilised in the form of ATP. Majority of the stored energy from ATP is released as HEAT as negligible amount is converted into mechanical work.

Question 6

What is the heat balance equation?

Answer 6

(M-W) = (K+C+R+Esk) + S

Question 7

What are the 6 parameters for determining temperature change?

Answer 7

Temperature 
Vapour pressure 
Air speed 
Radiation 
Clothing 
Metabolic rate

Question 8

Dry heat loss formula?

Answer 8

(Temperature of skin - temperature of ambient) / insulation of clothing and air layers

Question 9

evaporative heat loss formula?

Answer 9

PH2O skin - PH20 ambient / vapour resistance of clothing and air layers.

Question 10

How does heat loss occur (fundamental principles)

Answer 10

Skin temperature is greater than ambient temperature. The greater the difference the greater the temperature drop.

Question 11

What is the cross over temperature point in which heat gain occurs?

Answer 11

around 35 degrees

Question 12

How does temperature and vapour pressure effect evaporative heat loss?

Answer 12

Vapour pressure increases for a given relative humidity when temperature increases. This is due to increased water molecules caused by greater kinetic energy. When vapour pressure increases beyond the vapour pressure of the skin (5 - 6kPa) condensation on the skin occurs.

Question 13

Why can individuals survive at higher temperatures with a low relative humidity?

Answer 13

Lower relative humidity means a reduction in absolute vapour pressure for a given temperature. This means that a higher temperature can be achieved before ambient vapour becomes higher than that of the skin (5 - 6kPa)

Question 14

what percentage of heat loss is attributable to respiration?

Answer 14

10%

Question 15

What is the limit of climate cooling power?

Answer 15

For a given heat production (gain) the ability of the environment to dissipate that heat needs to be equal or greater. The limit of climate cooling power is determined by the difference between the skin temperature and ambient temperature along with the skin vapour pressure and ambient vapour pressure (Evaporative heat loss)

Question 16

How does radiation effect the climate cooling power limit AND why?

Answer 16

Radiation adds heat to the body thus requiring increased heat loss to maintain homeostasis. This extra heat loss will shift the cooling power limit to the left (thus reducing temperature heat loss is evaporative heat loss is great enough)

Question 17

How does a lower relative humidity effect limit of climate cooling power?

Answer 17

At a lower relative humidity evaporative heat loss is greater due to a great difference in vapour pressure at higher temperatures. Consequently evaporative heat loss can be enough to higher temperatures

Question 18

What is the rate limiting factor for cooling power at 20% relative humidity?

Answer 18

The physiological cooling power (ability to sweat enough) is non-compensable

Question 19

What are the factors that negatively impact the body cooling power in heat?

Answer 19

1. higher ambient temperature
2. Higher vapour pressure
3. solar radiation
4. air movement (also positive)
5. Clothing heat resistance

Question 20

what are the factors that positively impact the body cooling power in heat?

Answer 20

1. Skin temperature
2. Skin vapour pressure
3. Clothing vapour permeability
4. Clothing ventilation
5. air movement (if air is cooler)