1 NATS 101 Lecture 4 Temperature and Heat Transfer

2 4” by 6” Cards Today’s assignment Name, SID – legible penmanship What worked What didn’t and needs clarification

3 Surface Station Model Temperate ( o F) Pressure (mb) Last three digits Dew Point (later) Moisture Wind Barb Direction and Speed Cloud Cover Tenths total coverage Decimal point

4 Upper Air Station Model Temperate ( o C) Height (m or dam) Three digits given Leading and/or last digit(s) missing Dew Point Depression Moisture (later) Wind Barb Direction and Speed Always missing digit(s)

5 Practice Surface Station Temperate ( o F) Pressure (mb) Last three digits Dew Point (later) Moisture Wind Barb Direction and Speed Cloud Cover Tenths total coverage Ahrens, p Decimal point What are Temp, Dew Point, SLP, Cloud Cover, Wind Speed and Direction?

6 Practice Surface Station Sea Level Pressure Leading 10 or 9 is not plotted Examples: plotted as plotted as plotted as 360 Ahrens, p Decimal point What are Temp, Dew Point, SLP, Cloud Cover, Wind Speed and Direction?

7 What is Temperature? Microscopic View Energy due to random jiggling of molecules Related to average molecular speed; 500 m/s at room temperature for air

8 Temperature and Density Consider volume of air If air is warmed: The molecules will move faster, have “stronger” collisions, and tend to become spaced farther apart Volume increases, so density decreases Warmer  less dense

9 Temperature Scales Fahrenheit ( o F) - relative US public standard Celsius ( o C) - relative Freezing point 0 o C Boiling point 100 o C o C= 5/9 ( o F-32) Kelvin (K) - absolute K= o C+273 Ahrens p27

10 What is Heat? Heat-Energy in the process of being transferred from a warmer object to a cooler object Consider a pot of water on a hot burner. Consider the following questions: Williams, p. 19

11 Heat Transfer Questions What causes the… Pan bottom and handle to get warmer? Top of the water to become warmer? Water temperature to not exceed 100 o C? Region away from side of pan to feel warm? Williams, p. 19

12 Conduction Heat transfer due to collision of molecules. Conduction warms the bottom of the pan! Conductivity - rate of heat transfer across a 1 cm thick slab of material if one side is kept 1 o C warmer than the other Cheap Experiment: Touch your chair! 1 cm Metal WaterAir Heat Transfer 1oC1oC 0oC0oC

13 Heat Conductivity

14 Specific Heat Capacity Heat required to raise temperature of 1 gm of substance 1 o C. Metal has lower heat capacity than water!

15 Convection Heat transfer due to vertical exchange of mass Occurs in fluids (liquids, gases) because of gravity Warm, buoyant air rises - Cool, dense air sinks Convection warms top of liquid! Warm Cool Warm Cool Warm Cool heat below - convectionheat side - convectionheat top - no convection gravity

16 Convection Movies 2D Convection Tank Animation2D Convection Tank Animation  2D Convection Model Ra=10**6 2D Convection Model Ra=10**7 IC1 2D Convection Model Ra=10**7 IC2 3D Rayleigh-Benard Convection Model3D Rayleigh-Benard Convection Model 

17 Energy States and Water Phases water molecules are tightly packed in a crystal alignment that prevents them from changing shape LOW ENERGY STATE attractive forces btw molecules weaken and individual molecules can move around each other, but they can not break away SLIGHTLY HIGHER ENERGY STATE water molecules move very rapidly and are not bound together EXTEMELY HIGH ENERGY STATE Small Energy Change Large Energy Change

18 Latent Heat Ahrens, p 28 Weak attraction between molecules +540 cal/gm +80 cal/gm -540 cal/gm -80 cal/gm -620 cal/gm +620 cal/gm Strong attraction between molecules Some attraction More Ordered Phase Less Ordered Phase Surrounding air warms Surrounding air cools

19 Modes of Heat Transfer Williams, p. 19 Latent Heat

20 Take Home Concepts Heat-Energy transfer due to temperature differences Three modes of heat transfer Conduction – molecule to molecule Convection – transport of fluid Radiation – electromagnetic waves Next lecture! Latent Heat – energy of phase changes

21 Reading Assignment Ahrens Pages Problems 2.7, 2.9