1. Chapter 3.4 Notes Thermal Rates

2.  The amount of heat that is transferred per unit time is the heat flow rate  Equation for heat flow rate = heat / time  Heat = Q  Hfr = Q / t

3. If an air conditioner has a heat flow rate of 15,000 Btu per hour and runs for 3 hours, what amount of heat is transferred? If an air conditioner has a heat flow rate of 15,000 Btu per hour and runs for 3 hours, what amount of heat is transferred?  Hfr = Q / t 15,000 = Q / 3 15,000 = Q / 3 Q = 15,000 x 3 Q = 15,000 x 3 Q = 45,000 Q = 45,000

5.  When heat is transferred to a colder object, the atoms vibrate faster and faster as the temperature increases.  The transfer of thermal energy arising from a temperature difference between adjacent parts of an object is called heat conduction.

6.  For heat conduction to take place, their must be a temperature difference within the object.  The thermal conductivity (k) of a material is a measure of its ability to conduct heat.

7.  Metal have a large thermal conductivity because they are good heat conductors.  Heat conduction rate = (thermal conductivity x area x temperature difference) / thickness  Q rate = (k x A x  T)/x

8. A wall of a house has 3 inch thick fiberglass insulation. The thermal conduction =.32. The wall measures 10 ft by 10ft. The inside temperature is 68 degrees and the outside temperature is 32 degrees. What is the heat flow rate? A wall of a house has 3 inch thick fiberglass insulation. The thermal conduction =.32. The wall measures 10 ft by 10ft. The inside temperature is 68 degrees and the outside temperature is 32 degrees. What is the heat flow rate?  Q rate = (k x A x  T)/ x  Q rate =.32 x (10x10) x (68-32) 3  Q rate =.32 x 100 x 36 / 3 = 384 J

10.  Convection is a transfer of heat by movement of fluid. Convection  The circulation of fluid by the transfer of energy due to temperature differences is called natural convection.  Examples – Earth’s Atmosphere and cold spots in lakes

11.  When natural convection takes place in the Earth’s atmosphere it causes wind.  When convection is forced by a fan or pump it is called forced convection.  Examples – Body’s circulation system, air conditioners

14.  All objects radiate energy in the form of electromagnetic radiation.  The rate of energy radiated by an object depends on the object’s temperature, area, and type of material.

15.  Radiation transfers energy from one body to another through empty space. Radiation  A hot object radiates energy, some of which is absorbed by a cooler object.  The cooler object also radiates energy but not as much as the hot object and so it absorbs more energy that it gives off.  Energy is transferred from the sun to all planets in the solar system by radiation.

16. Radiometer

17. Black Balloon Demo