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Transcript of Heat Transfer
Shelby Scott Heat Transfer Conduction Radiation LIVE DEMO Energy transfer from particle to particle within certain materials that are in direct contact. As one molecule is heated, it begins to rapidly vibrate, causing other nearby molecules to vibrate also, and spread the heat energy.
Some good conductors are aluminum, steel, iron, copper, and gold.
EX: Touching a hot metal spoon in a pot of boiling water. Convection Movement of the heated substance itself such as by currents in a fluid. Whenever a substance is heated, it rises as a gas, and expands because it is less dense. Once the substance cools, it becomes more dense, and falls. This movement creates a convection current.
EX: Heated molecules expand and rise out a hot radiator, and once they cool, they began to fall and become more dense. Heat energy transmitted by electromagnetic waves.
EX: Sun radiates heat to earth NOW LET'S CHECK OUR EXPERIMENT! Way to remember Convection Math Example Quiz! 1. What color absorbs thermal energy? What color emits thermal energy?
2. Name 3 examples of good conductors.
3. The sun transmitting heat towards the earth is an example of what kind of heat transfer? Q= kA Tt L Q: amount of heat (Joules)
k: thermal conductivity (J/s * m *degrees Celsius)
A: cross sectional area (m^2)
T: temperature change of the substance (degrees Celsius)
L: thickness of the substance (m) 4. What variable is used in the math equation for conduction of heat?
D. Square root How much heat is conducted to Lauren's hand from the touch of Mike's hand if the temperature of Mike's hand is 33 degrees Celsius, the temperature of Lauren's hand is 28 degrees Celsius, the space between their hands is .018 m, and the total surface area of Lauren's hand is .31 m^2? Find the amount of heat that reaches Lauren's hand in 2 minutes. Also, the thermal conductivity of Mike's hand is .15 J/s * m * degrees Celsius. Q= kA Tt L Q= (.15J/s x m x C)(.31m^2)(33C-28C)(120s) (.018 m) 5. How much heat from the fire is conducted to an iron bar if the temperature of the fire is 150 degrees Celsius , the iron is .084 m thick, the iron has a total surface area of 2.8 m^2, and the temperature of the iron is 20 degrees Celsius? Find the amount of heat that reaches the iron in forty minutes. Also, thermal conductivity of the iron bar is .22 J/s * m * degrees Celsius. Q= (27.9) J*m (.018)m Q= 1550 J
(or) 1.55 x 10^3 J Direction of the Sea Breeze (Night and Day) Ground is hotter than water during the day, making heat rise from its surface. Then, as heat expands upward, the colder air on top of water takes place of the warm air that is rising, in order to prevent a vacuum. (That's why it's called a sea breeze) At night, the water is warmer than the ground, and the warm air rises. Like before, the cool air from the land takes the place of the warm air rising. Just in the opposite direction. Why does rising warm air become cooler? Warm air rises because it is less dense, and the vibration of molecules cause it to expand. As the warm air rises toward space, it faces less atmospheric pressure, and starts to cool. Then once the warm air cools, it begins to become dense and starts to sink downwards. Colors and Thermal Energy Convection can be related to that indecisive person who can't chose between the swimming pool and the hot tub. Because the person is too cold, they go to the hot tub. Yet, whenever the person gets too hot, they go back to the swimming pool. This pattern keeps occurring until the person gets out of the water because the bats are starting to swoop towards their hair. Conduction can be described like dominos being knocked down. The fall of one domino, causes the fall of other dominos, and they all stay in their place. This is like conduction, where the vibration of one molecule causes the vibration of another molecule and the transfer of heat energy. Yet, all of the molecules stay in place. Whoa, look at that convection current! Way to remember Conduction Way to remember Radiation Radiation is like telepathy. It travels through walls, empty space, and doesn't have a barrier to stop it. It is an invisible force that doesn't need a material medium to travel. Light and heat are forms of energy and the way they interact determines which colors appear to absorb heat.
If something is dark, it absorbs more radiant energy. Dark colors absorb a lot more heat than lighter ones because they absorb more light energy. Black absorbs thermal energy.
Light colors emits energy instead of absorbing it. Light colors are perceived that way because most light wavelengths are reflected back to our eyes. Since most light is reflected, little light (or heat) is absorbed. White emits thermal energy.