Temperature in Thermal Systems

Vocabulary Pg (leave a space between words) Heat energy Heat energy Temperature difference Temperature difference Insulated Insulated Temperature Temperature Scalar Scalar Heat Heat Thermocouple Thermocouple Page 97 #1-8

Thermal systems Designed to move heat energy from warmer regions to cooler regions 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 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 The prime mover is temperature difference Written: ΔT Written: ΔT

Movement of heat Heat always moves from warm areas to cooler Heat always moves from warm areas to cooler This is undesirable in homes both in the summer and winter This is undesirable in homes both in the summer and winter Therefore we insulate the walls to reduce in heat loss and gain Therefore we insulate the walls to reduce in heat loss and gain

What is heat? What is temperature? Temperature is a scalar quantity Temperature is a scalar quantity Measured in degrees Fahrenheit or degrees Celsius Measured in degrees Fahrenheit or degrees Celsius Heat – Form of energy found in the vibrating motion of atoms and molecules 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 Temperature – A measure of the average energy of motion of the molecules in a substance Hot items have high average energy motion Hot items have high average energy motion Cool items have low average energy motion Cool items have low average energy motion

How does a thermometer work? Filled with liquid such as mercury or colored alcohol Filled with liquid such as mercury or colored alcohol When the temperature of the liquid increases it expands When the temperature of the liquid increases it expands A scale is provided to make readings A scale is provided to make readings

Temperature Scales Freezing point of water = 32 degrees Freezing point of water = 32 degrees Boiling point of water = 212 degrees Boiling point of water = 212 degrees Freezing point of water = 0 degrees Freezing point of water = 0 degrees Boiling point of water = 100 degrees Boiling point of water = 100 degrees Fahrenheit Scale Celsius Scale

Fahrenheit vs. Celsius

On a thermometer the scale shows that 100 Celsius degrees are equal to 180 Fahrenheit degrees On a thermometer the scale shows that 100 Celsius degrees are equal to 180 Fahrenheit degrees 1 C o = 1.8 F o 1 C o = 1.8 F o Writing Temp or Temp Differences 32 o F is different than 32F o 32 o F is different than 32F o

Writing Temp or Temp Differences Temperatures are degrees Celsius ( o C) or degrees Fahrenheit ( o F) Temperatures are degrees Celsius ( o C) or degrees Fahrenheit ( o F) Temperature differences are Celsius degrees (C o ) or Fahrenheit degrees (F o ) Temperature differences are Celsius degrees (C o ) or Fahrenheit degrees (F o )

Converting from one scale to another

Given: A temperature of 50 o F Given: A temperature of 50 o F Find: The same temperature in degrees Celsius ( o C) Find: The same temperature in degrees Celsius ( o C) Solution: Solution: T o C = 5/9(T o F – 32 o ) T o C = 5/9(T o F – 32 o ) T o C = 5/9(50 o – 32 o ) T o C = 5/9(50 o – 32 o ) T o C = 5/9(18 o ) T o C = 5/9(18 o ) Therefore, 50 o F is the same as 10 o C Therefore, 50 o F is the same as 10 o C

Converting from one scale to another Given: A temperature of 20 o C Given: A temperature of 20 o C Find: The temperature in degrees Fahrenheit ( o F) Find: The temperature in degrees Fahrenheit ( o F) Solution: Solution: T o F = 9/5(T o C) + 32 o T o F = 9/5(T o C) + 32 o T o F = 9/5(20 o )+ 32 o T o F = 9/5(20 o )+ 32 o T o F = 36 o + 32 o T o F = 36 o + 32 o T o F = 68 o F T o F = 68 o F Therefore, 20 o C is the same as 68 o F Therefore, 20 o C is the same as 68 o F

Converting from one scale to another Given: The temperature in the room just went up 11 C o Given: The temperature in the room just went up 11 C o Find: What is the temperature difference in degrees Fahrenheit Find: What is the temperature difference in degrees Fahrenheit Solution: Solution: 1 C o = 1.8 F o 1 C o = 1.8 F o 11 x 1 C o = 11 x 1.8 F o 11 x 1 C o = 11 x 1.8 F o 11 C o = 19.8 F o 11 C o = 19.8 F o

Converting from one scale to another Given: The temperature in the room is 68 o F but just went down 4 C o Given: The temperature in the room is 68 o F but just went down 4 C o Find: How much the temperature decreases in Fahrenheit. Find: How much the temperature decreases in Fahrenheit. Find: The new temperature in Fahrenheit Find: The new temperature in Fahrenheit Solution: Solution: 1 C o = 1.8 F o 1 C o = 1.8 F o 4 x 1 C o = 4 x 1.8 F o 4 x 1 C o = 4 x 1.8 F o 4 C o = 7.2 F o 4 C o = 7.2 F o 68 o F – 7.2 F o = 60.8 o F 68 o F – 7.2 F o = 60.8 o F

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Thermocouple thermometers Used where a normal thermometer cant be used Used where a normal thermometer cant be used Furnaces, boilers, and nuclear reactors Furnaces, boilers, and nuclear reactors Allows us to read the temperature far away from the actual measuring point 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 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 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 and constantan Metals: Iron and constantan or chromel and constantan Voltage is very low Voltage is very low Few microvolts or millivolts Few microvolts or millivolts Increasing the temperature difference increases the voltage Increasing the temperature difference increases the voltage

Thermocouple thermometers Formed by using two thermocouple junctions Formed by using two thermocouple junctions

Thermocouple thermometers Used to measure the temperature difference between a known temperature (T R ) and an unknown temperature (T) Used to measure the temperature difference between a known temperature (T R ) and an unknown temperature (T)

Thermocouple thermometers The two junctions produce separate voltages that oppose one other The two junctions produce separate voltages that oppose one other If the voltages are equal, the voltmeter will read zero and the temperatures are the same If the voltages are equal, the voltmeter will read zero and the temperatures are the same If T is greater than T R it produces a positive voltage If T is greater than T R it produces a positive voltage If T is less than T R it produces a negative voltage If T is less than T R it produces a negative voltage

Thermocouple thermometers Reference junction is usually placed in an icy-water mixture with a known temperature of 0 o C Reference junction is usually placed in an icy-water mixture with a known temperature of 0 o C