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Dynamics of Heat Transfer/CC > 1 > Flashcards

1 Flashcards

1
Q

What do the Laws of Thermodynamics state?

A

Energy is conserved and can be transferred. Systems seek equilibrium.

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2
Q

What is the 0th Law of Thermodynamics?

A

If two systems are in equilibrium to a third system, they’re all in equilibrium to each other.

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3
Q

What is the 1st Law of Thermodynamics?

A

Energy is not created nor destroyed.

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4
Q

What is the 2nd Law of Thermodynamics?

A

Entropy in an isolated system that’s not at equilibrium will increase over time.

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5
Q

What is the 3rd Law of Thermodynamics?

A

As temperature comes close to absolute zero (molecules stop moving), there’s little change to entropy.

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6
Q

What is the difference between temperature and heat?

A

Temperature is the average speed per particle (intensive). Heat is energy that flows from a hot body to a cold one (extensive).

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7
Q

What is enthalpy?

A

The amount of energy within a system.

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8
Q

What is entropy?

A

The amount of disorganization within a system.

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9
Q

Exergonic processes _____ free energy.

A

release

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10
Q

Endergonic processes _____ free energy.

A

require

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11
Q

What is conduction?

A

The transfer of heat with direct contact from another surface.

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12
Q

The tighter the molecules are, the better they are at _____.

A

conducting

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13
Q

What is heat capacity?

A

The amount of heat required to change the temperature of a substance.

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14
Q

What is conductivity?

A

The ability of a substance to conduct heat.

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15
Q

How do you measure density?

A

Mass/Volume

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16
Q

The more dense an object is, the more conductivity will occur, T/F?

A

True

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17
Q

ALL FOODS TRANSMIT HEAT TO CORE BY _____.

A

CONDUCTION

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18
Q

Conduction works from the surface to the _____.

A

core

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19
Q

Temperature rise in conduction depends on what?

A

The thermal conductivity of the object and the specific heat.

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20
Q

Why are we able to digest potatoes after they have been cooked?

A

Because the starch is altered when heated to a high enough temperature.

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21
Q

What is “specific heat”?

A

The amount of heat required to raise the temperature of 1 kg of a substance by 1 C (metals need to absorb more heat).

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22
Q

What is “latent heat”?

A

When material changes from state to state. (When we freeze ice i.e. we have to remove a large amount of latent heat.)

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23
Q

What is convection?

A

The transfer of heat from a fluid (a gas/liquid) to it’s surroundings. The fluid is kept in motion and is able to take heat from the hot body to the cold body.

24
Q

Boiling, simmering, deep frying and baking are all examples of what?

A

Convection

25
Q

If a piece of meat is 1/4 of the original’s thickness, by how much should you cut the cooking time?

A

In half

26
Q

If a piece of meat is 1/4 of the original’s length, by how much should you cut the cooking time?

A

None!

27
Q

ALL FOODS TRANSMIT HEAT TO CORE BY _____.

A

CONDUCTION

28
Q

Are electromagnetic waves the same as sound waves?

A

No

29
Q

How are electromagnetic waves formed? *

A

Hydrogen atoms fuse together to make helium, energy and photons are shot out from this, as these photons go through space, electric and magnetic forces cause this to be repelled or come closer due to attraction.

30
Q

Higher frequency waves have _____.

A

shorter wavelengths and deliver more energy.

31
Q

Darker colored substances do what more than white or shiny substances?

A

They absorb more radiant energy.

32
Q

What are some modes of cooking that rely on radiation (radiant energy)?

A

Grilling, broiling, roasting, microwaving, etc.

33
Q

Black/dark colors absorb light or reflect light?

A

Absorb

34
Q

White/light colors absorb light or reflect light?

A

Reflect

35
Q

Warm air _____.

A

rises

36
Q

Cold air _____.

A

sinks

37
Q

Why should the water not be boiling if you are poaching something?

A

Boiling will cause the outside to cook faster than the inside, eventually causing breakage in the food.

38
Q

How does refrigeration display convection?

A

Coils cool down air and this air sinks to the bottom of the refrigerator keeping the environment cool/cold.

39
Q

What is an example of forced convection?

A

Using a convection oven, a blast freezer etc. The fan/pump/propeller acts as a catalyst and speeds up the rate of heat transfer, and gives an even distribution of heat.

40
Q

Why does stirring a pot of boiling water calm it down?

A

You’re mixing the water molecules and also mixing the temperature, making it constant throughout.

41
Q

What is a nucleation site?

A

A site where phase change can occur.

42
Q

Does boiling water transfer heat easier than air does?

A

Yes

43
Q

Describe the origins of a boil.

A

Microscopic cracks on the bottom of the pot allow for the hot body to transfer heat energy to the water, which then creates steam. Steam builds up and condenses, steam bubbles break free and cooler water is left behind.

44
Q

What is dry-bulb temperature?

A

The set temperature of the oven independent of surface moisture or humidity.

45
Q

What is wet-bulb temperature?

A

The depression in surface temperature of foods due to evaporative cooling.

46
Q

Is wet-bulb temperature ever greater than dry-bulb temperature?

A

No, never.

47
Q

Wet-bulb temperature increases with increasing _____.

A

relative humidity

48
Q

Water boils when what equals what?

A

Water boils when vapor pressure is equal to atmospheric pressure.

49
Q

What are examples of extensive properties?

A

Weight and volume, etc.

50
Q

What are examples of intensive properties?

A

Temperature, density, and thermal conductivity, etc.

51
Q

Describe why water cooked the potato in the experiment better than the other two mediums, air and oil?

A

Water has the highest heat capacity

52
Q

What is evaporative cooling?

A

A reduction in temperature resulting from the evaporation of a liquid, which removes latent heat from the surface in which evaporation takes place.

53
Q

As a piece of bread darkens while toasting, it’s reflectivity _____.

A

decreases

54
Q

What is a black body?

A

Any substance that absorbs every ray of light that strikes it.

55
Q

Wood-fired ovens cook by _____.

A

radiation

56
Q

The darker the bread, the more energy it absorbs, T/F?

A

True

Dynamics of Heat Transfer/CC (5 decks)

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