1. THERMODYNAMICS Branch of science dealing with nature of heat

2. Diff. between heat and temp Temperature -- average kinetic energy of molecules. (how hot or cold something is). Measured w/ thermometer in degrees Heat -- energy possessed by molecules in motion (kinetic and potential energy). Molecules vibrate, rotate and/or collide. Measured in calories or Joules http://www.yankodesign.com/images/design_news/2007/11/16/heat_page.j pg http://www.gcsescience.com/Heat-Temperature.gif

3. Effect of changing temp Changing temp allow change of state: solid liquid, liquid gas, gas plasma (cooler warmer) http://blogs.saschina.org/more na01pd2016/files/2009/10/ccr.j pg

4. Heat transfer Temp difference allow heat transfer by conduction, convection or radiation Heat always moves from hot  cold (1) conduction (direct contact between objects of diff. temp) (2) convection (in fluids [gases and liquids]), less dense material rises, more dense material sinks; (3) radiation (transfer of energy thru space) Heat transfer amount is measured in BTUs or calories

5. Molecular motion Hotter molecules have more energy Moving molecules transfer energy Confining and controlling molecular motion allows propulsion to occur Uncontrolled molecular motion = wasted energy

6. Heat can be converted to other types of energy Examples: chemical, mechanical, electric, etc. Heat engines take some energy being transferred between 2 parts of system and change it to mechanical energy (car), electric energy (power generator)

7. Useful heat transfer does work (force * distance) Different materials conduct heat at different rates. Generally metals and more dense materials conduct better. – Metals (good conductors) allow rapid heat transfer. Electrons loosely held, easy to move – Non-metals (good resistors) prevent rapid heat transfer. Electrons held tightly, hard to move – Materials are chosen for specific uses depending on their properties.

8. Wasted energy In any system, some energy is always wasted (non-recoverable) due to heat from friction New technologies seek to improve efficiency by reducing waste heat

9. Step 1. List all known values ΔT = 30.0°C – 25.0°C = 5.0°C 4184 1 kg Q Calculate the energy transferred when a block of aluminum at 80.0°C is placed in 1.00 liter (1kg) of water at 25.0°C if the final temperature becomes 30.0°C. Calculating Energy Transfer Mass of water = C p of water = Difference in temperature = C p of Al = 900. ΔT = 80.0°C – 30.0°C = 50.0°CDifference in temperature =

10. Step 2. List all unknown values Q = energy transferred m Al = mass of the Al block Step 3. Select equations to solve unknown values Step 4. Solve for Q water Calculating Energy Transfer

11. Step 5. Solve for m Al Calculating Energy Transfer

12. Step 1. List all known values ΔT = 10°C - 5°C = 5°C Δt = 1 hour = 3600s k =0.10 l = 0.04m A = 2m * 1m = 2m 2 Q Calculate the energy transfer in a wall section measuring 2m by 1m by 0.04m thick with a thermal conductivity of 0.10. Opposing sides of the wall section have a temperature of 10°C and 5°C after one hour. Calculating Energy Transfer Area of thermal conductivity = Thermal conductivity = Thickness of material = Difference in temperature = Difference in Time =

13. U-Value Overall heat coefficient The measure of a material’s ability to conduct heat Thermal Conductivity of a Material U.S. customary system Metric system

14. R-Value The measure of a material’s ability to resist heat The higher the R-value, the higher the resistance Bulk R-value = R-value Object 1 + R-value Object 2 + … = Total R-Value Thermal Resistance of a Material

15. Determine the R-value of the wall cavity below 5/8 in. drywall (R=0.56) Fiberglass batt (R=19) 1 in. foil-faced polyisocyanurate (R=7.20) 1 in. air space (R=0.17) Brick 2 ¼ x 3 ½ x 8 (R=0.8) 2x6 construction (2x6 R=6.88) 0.56 +19.00 + 7.20 + 0.17 + 0.8 = 27.7 Wall cavity R-value What is the R-value at a stud location? 0.56 + 6.88 + 7.20 + 0.17 + 0.8 =15.6 Calculating R-Value

16. Thermodynamic Equilibrium Thermal equilibrium -- when touching objects within a system reach same temperature. When thermal equilibrium is reached, system loses ability to do work. Zeroth Law of Thermodynamics: If two systems are separately found to be in thermal equilibrium with a third system, the first two systems are in thermal equilibrium with each other. Object #2 Object #3 Object #1 (Thermometer) Object #2

17. 1st Law of Thermodynamics Law of energy conservation applied to a thermal system – Thermal energy can change form and location, but cannot be created or destroyed. – Thermal energy can be increased within a system by adding thermal energy (heat) or by performing work in a system.

18. 1st Law of Thermodynamics Example: Using a bicycle pump Pumping the handle results in what? – Applying mechanical energy into system – Mechanical energy is converted into thermal energy through friction (the pump becomes hot) Total increase in internal energy (heat energy increase) of the system is equal to what? – The applied mechanical energy ©iStockphoto.com

19. 2nd Law of Thermodynamics Thermal energy flows from hot to cold When you touch cooked pizza with your hand, thermal energy flows in what direction? When you touch frozen pizza with your hand, thermal energy flows in what direction? Hand → Pizza Pizza → Hand ©iStockphoto.com

20. 2nd Law of Thermodynamics Entropy -- measure of how evenly distributed heat is within system. - Systems tend to go from order to disorder Order Disorder Firewood has low entropy (molecules in order) when stacked and high entropy when burning (molecules in disorder). Total amount of energy in the world does not change, but availability of that energy constantly decreases.

21. Applications of Thermal Energy http://www.nrel.gov

22. Examples of Solar Energy All images were obtained from the following URL: http://www1.eere.energy.gov

23. Geothermal Energy Energy generated from thermal energy stored beneath Earth’s surface (magma near surface) (A few people also refer to heat from sun collected in atmosphere, e.g., near oceans, as geothermal. Most people do not apply the term this way.)

24. Resources Energy Information Association. (n.d.). Energy kid’s page. Retrieved March 23, 2008, from http://www.eia.doe.gov/kids/energyfacts McGraw-Hill dictionary of engineering. (2nd ed.). New York, NY: McGraw- Hill. NASA. (2008). Glenn research center. Retrieved March 23, 2008 from http://www.nasa.gov/centers/glenn/home/index.html National Renewable Energy Laboratory. (2007). TroughNet. Retrieved March 23, 2008, from http://www.nrel.gov/csp/troughnet U.S. Department of Energy. (2008). Solar energy technologies program. Retrieved March 23, 2008, from http://www1.eere.energy.gov/solar