Designed to move heat energy from warmer regions to cooler regions
In an automobile we have a fan, water pump, radiator, hoses, thermostat, coolant fluids, and air
Temperature Difference acts like a Force
The prime mover is temperature difference
Written: ΔT
Movement of heat Heat always moves from warm areas to cooler This is undesirable in homes both in the summer and winter Therefore we insulate the walls to reduce in heat loss and gain
What is heat? What is temperature?
Temperature is a scalar quantity Measured in degrees Fahrenheit or degrees Celsius
Heat – Form of energy found in the vibrating motion of atoms and molecules
What is heat? What is temperature?
Temperature – A measure of the average energy of motion of the molecules in a substance
Hot items have high average energy motion Cool items have low average energy motion
How does a thermometer work?
Filled with liquid such as mercury or colored alcohol When the temperature of the liquid increases it expands A scale is provided to make readings
Temperature Scales Fahrenheit Scale Freezing point of water = 32 degrees Boiling point of water = 212 degrees
Celsius Scale
Freezing point of water = 0 degrees Boiling point of water = 100 degrees
Fahrenheit vs. Celsius
Fahrenheit vs. Celsius
On a thermometer the scale shows that 100 Celsius degrees are equal to 180 Fahrenheit degrees 1 Co = 1.8 Fo
Writing Temp or Temp Differences
32oF is different than 32Fo
Writing Temp or Temp Differences
Temperatures are degrees Celsius (oC) or degrees Fahrenheit (oF)
Temperature differences are Celsius degrees (Co) or Fahrenheit degrees (Fo)
Converting from one scale to another
Converting from one scale to another Given: A temperature of 50oF Find: The same temperature in degrees Celsius (oC)
Solution: o o o T C = 5/9(T F – 32 ) o o o T C = 5/9(50 – 32 ) o o T C = 5/9(18 ) o o Therefore, 50 F is the same as 10 C
Converting from one scale to another Given: A temperature of 20oC Find: The temperature in degrees Fahrenheit (oF)
Solution: ToF = 9/5(ToC) + 32o o o o T F = 9/5(20 )+ 32 o o o T F = 36 + 32 o o T F = 68 F Therefore, 20oC is the same as 68oF
Converting from one scale to another
Given: The temperature in the room just went up 11 Co Find: What is the temperature difference in degrees Fahrenheit Solution: 1 Co = 1.8 Fo 11 x 1 Co = 11 x 1.8 Fo o o 11 C = 19.8 F
Converting from one scale to another Given: The temperature in the room is 68oF but just went down 4 Co Find: How much the temperature decreases in Fahrenheit. Find: The new temperature in Fahrenheit
Solution: 1 Co = 1.8 Fo o o 4 x 1 C = 4 x 1.8 F o o 4 C = 7.2 F 68 oF – 7.2 Fo = 60.8 oF
Thermocouple thermometers Used where a normal thermometer can’t be used Furnaces, boilers, and nuclear reactors Allows us to read the temperature far away from the actual measuring point
How does a thermocouple thermometer work?
Temperature measuring device that depends on changes in electrical properties of certain metals
When two specific metals are joined together a small voltage develops across the connecting joint when opposite ends are at different temperatures
How does a thermocouple thermometer work?
Metals: Iron and constantan or chromel or constantan Voltage is very low Few microvolts or millivolts
Increasing the temperature difference increases the voltage
Thermocouple thermometers
Formed by using two thermocouple junctions
Thermocouple thermometers Used to measure the temperature difference between a known temperature (TR) and an unknown temperature (T)
Thermocouple thermometers
The two junctions produce separate voltages that oppose one other
If the temperatures are the same, the voltages are equal and opposite and the voltmeter senses zero
If T is greater than TR it produces a positive voltage If T is less than TR it produces a negative voltage
Thermocouple thermometers
Reference junction is usually placed in an icy-water mixture with a known temperature (TR) of 0oC
