Flashcards in CHAPTER 2: HEAT TRANSFER Deck (81)
Three main ways heat is transferred.
Radiation, convection, conduction.
A fourth type of heat transfer.
Induction, which takes place on a special stovetop surfaces.
What is radiation?
Rapid transfer of heat through space from a warmer object to the surface of a cooler one.
What is frictional heat?
The heat generated once molecules begin to vibrate rapidly on the surface of an object.
Why is radiation described as indirect heat?
At no time does the radiation body come into direct contact with the object.
Appliances that use radiation.
Toasters, broilers, in fared heat lamps and conventional ovens.
Do dark or light surfaces radiate more heat? Why?
Dark surfaces do because they absorb more heat energy to begin with.
Do dull or shiny surfaces radiate more heat?
Do dull black sheet pans bake food faster than bright shiny ones?
What is emissivity?
The ratio of power emitted by a body to the power emitted if it was a black body.
What is happening if something close to an oven wall is baking up darker than everything else?
"Hot spots," created by radiant energy.
Is radiation a means of transferring microwave energy?
What tube generated microwave energy?
Does microwave energy penetrate the surface of food more easily than radiant energy?
Why do microwaves heat food unevenly?
Partly because different substances absorb microwave energy differently, but also because some substances require less energy to heat up.
Why is heating with a microwave relatively fast compared to radiant energy?
Because the radiant microwaves penetrate further into the food--typically 1 to 2 inches--than radiant heat energy, which heats surfaces only.
When does conduction occur?
When heat passes from a hot area of an object to a cooler area; heat is passed molecule by molecule.
Is conduction a form of direct heat?
What happens to heat transfer when old aluminum sheet pans are pocked with bits of blackened food?
They will radiate heat unevenly.
Does conduction continue when a pan is removed from the heat source?
Yes, until the pan and food reach the she temperature.
Does water have low or high heat conductivity?
Does air have a higher or low heat conductivity than water?
Materials that conduct heat quickly are referred to as having what?
High thermal or heat conductivity.
Why do solids have higher heat conductivity than gases and liquids?
The molecules are much closer together in solids than liquids or gases; this makes it easier to pass from one molecule to the next.
Good team reference for conduction and radiation.
Two teams of ten stand next to each other. One (radiation) passes the ball from first to last while the other (conduction) can only hand it off one at a time.
Explain the conductive properties of heavy-gauge compared to this-gauge material.
Heavy-gauge material is thicker and conducts heat to food more slowly than thin-gauge.
Are heavy-gauge materials preferred over thin-gauge? Why?
Yes, because they transfer heat more evenly.
Why does marble feel cooler than wood to the touch, even in a warm bakeshop?
Marble has a greater heat conductivity than wood, so heat transfers faster from the body to marble than t does wood. Because the hand touching the marble cools more quickly, the marble seems cooler to the touch (when, in actuality the marble is now slightly warmer, because heat was transferred to it from the hand).
Put copper, silver, stainless steel and aluminum in order concerning heat conductivity.
Silver, copper, aluminum, stainless steel.