Thermal - BS

Question 1

Thermal Conduction

Answer 1

• The transfer of heat from the warmer to the cooler particles of a medium or of two bodies in direct contact, occuring without perceptible displacement of the particles.
• Accounts for a very small portion of the total heat loos from the body.

Question 2

Thermal Convection

Answer 2

• The transfer of heat by the circulatory motion of the heated parts of a liquid or gas owing to a variation in density and the action of gravity. (e.g. the body gives off heat to the surrounding cooler air.
• A large differential between air and skin temperature and increased air motion induce more heat tansmission by convection.

Question 3

Latent Heat

Answer 3

Energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process that is specified in some way.

An example is latent heat of fusion for a phase change, melting, at a specified temperature and pressure.

Derived from the Latin latere (to lie hidden).

Question 4

Radiation

Answer 4

• The process by which heat energy in the form of electomagnetic waves is emitted by a warm body, transmitted through an intervening space and absored by a cooler body.
• No air motion is required for the transfer of head (ex. space).
• Light colors reflect while dark colors absorb heat; poor reflectors make good radiators.
• Heat cannot travel around corners and is not affected by air motion (ex. camp fire).

Question 5

Evaporation

Answer 5

• Heat is required for the process of converting body moisture into a vapor.
• Heat loss increases with air motion.
• This type of cooling is especially beneficial when high air temperatures, humidity and activity levels exist.

Question 6

Psychrometer

Answer 6

An instrument for measuring atmospheric humidity, consisting of two thermometers, the bulb of one being dry and the bulb of the other being kept moist and ventilated so that the coolling that results from evaporation makes it register a lower temperature that the dy one, wit the difference between the readings being a measure of the atmospheric humidity.

Question 7

Psychrometric Chart

Answer 7

• A chart that relates the wet-bulb and dry-bulb readings from a psychrometer to relative humidity, absolute humidity and dew point.
• Used by mechancial enginners to determine the amount of heat that must be added or removed by an HVAC system to achieve an acceptable level of thermal comfort in a space.

Question 8

Adiabatic Heating

Answer 8

A rise in temperature occuring without the addition or removal of heat, as when excess water vapor in the air condenses and the latent heat of vaporization of the water vapor is converted to sensible heat in the air.

Question 9

Evaporative Cooling

Answer 9

A drop in temperature occuring without the addition or removval of heat, as when moisture evaporates and the sensible heat of the liquid is converted to latent heat in the vapor.

Question 10

Resistance (R)

Answer 10

The inefficiency of a material, at some specified thickness, to conduct heat and is related to resistivity (r).

Question 11

Thermal Conductance (C)

Answer 11

A factor of the thickness and the conductive properties of a building material

Using a thicker pan, or one made from fiberglass insulation instead of metal, will heat water more slowly.

Question 12

Conductivity (k)

Answer 12

Measures the efficieny with which heat passes through a one-inch-thick, one-square-foot, piece of material.