Heat Transfer:

1. Department of Physics and Astronomy PHYS420: Physics Demonstration Heat Transfer: The Physics of Computer Cooling By Kenneth Yu

2. What is Heat? Definition: Heat is a form of energy that is transferred by a difference in temperature Examples: The heater transfers heat tothe air Our skintransfers heat to water The sun transfers heat to our skin*

3. Heater Core @ 500 Celsius Air @ 18 Celsius What is Heat?

4. You Skin @ 30 Celsius Water @ 20 Celsius What is Heat?

5. The Sun @ 5,500 Celsius Your Skin @ 30 Celsius What is Heat?

6. How Does Heat Transfer? Three Methods: Conduction Radiation Convection

7. Hot Cold Warm How Does Heat Transfer? Conduction The transfer of heat through a substance by molecular action or from one substance by being in contact with another.

8. Q = kA (Thot-Tcold) d t Q = heat transfer [J] t = time [s] k = thermal conductivity [J/msK] T = temperature [K] A = area [m2] d = thickness of barrier [m] How Does Heat Transfer? Conduction Formula K = 273 + C

9. Q = kA (Thot-Tcold) d t How Does Heat Transfer? Conduction Formula

10. How Does Heat Transfer? Thermal Conductivity k

11. How Does Heat Transfer? Conduction Demo Copper vs. Wood

12. How Does Heat Transfer? Conduction Example

13. How Does Heat Transfer? Radiation Radiation is heat transfer by the emission of electromagnetic waves which carry energy away from the emitting object.

14. What is Heat? Definition: Heat is a form of energy that is transferred by a difference in temperature

15. P = radiating power = Q/t [J] e = emmissivity σ = Stefan’s Constant = 5.6708 x 10-8[W/m2k4] A = radiating area [m2] How Does Heat Transfer? Radiation: Stefan-Boltzmann Law P = eσ A (Thot4-Tcold4)

16. How Does Heat Transfer? Radiation Example: Light Bulb

17. How Does Heat Transfer? Planck’s Radiation Curves @ 3000K

18. The Sun @ 5,500 Celsius Your Skin @ 30 Celsius How Does Heat Transfer?

19. How Does Heat Transfer? Planck’s Radiation Curves @ 6000K

20. How Does Heat Transfer? Planck’s Radiation Curves @ 1000K

21. How Does Heat Transfer?

22. How Does Heat Transfer? Planck’s Radiation Curves @ 373K

23. P = unknown e = 1 σ = Stefan’s Constant = 5.6708 x 10-8 [W/m2k4] Thot = 60+273 [K] A = 0.0252 [m2] Tcold = 23+273 [K] How Does Heat Transfer? Radiation: Does it Matter at Low Temp? P = eσ A (Thot4-Tcold4) 5cm 60 C 45 W CPU

24. How Does Heat Transfer? Radiation: Does it Matter at Low Temp? P = 1 x 5.6708 x 10-8 W/m2K4 x 0.025 m2 x (333K4-296K4) P = 0.66 Watts = 0.66 J/s Not a whole lot….

25. How Does Heat Transfer? Convection Heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it

26. m ρ= V 2. As the volume increases, density goes down How Does Heat Transfer? Convection: Air Heater 1. As air heats up, it expands 3. Less dense material floats up. 4. Cold, denser air drops down to heater.

27. How Does Heat Transfer? Convection: Convection Airflow Demo

28. Heater How Does Heat Transfer? Natural Convection: Air

29. Heater How Does Heat Transfer? Natural Convection: Water

30. How Does Heat Transfer? Forced Convection: Air Fan Heater

31. How Does Heat Transfer? Thermal Conductivity k

32. How Does Heat Transfer? Specific Heat Capacity

33. How Does Heat Transfer? Thermal Conductivity k - how fast can a material moves heat Specific Heat Capacity • how much heat can a material take • without getting too hot.

34. How Does Heat Transfer? Heat Capacity of Different Materials

35. How Does Heat Transfer? Heat Capacity of Different Materials

36. Heat Property of Water Specific Heat Capacity Q: What is a calorie? A calorie is the energy (J) required to raise the temperature of one gram of water by 1 C (1 K). One calorie = 4.184J

37. Heat Property of Water Specific Heat Capacity On a 45 W heater, how long does it increase the temperature of 100g of water by 5 K? P = 45 J/s △T = 5 K m = 0.1 kg t =? s

38. Heat Property of Water Specific Heat Capacity Hint: It takes 4184J to heat up 1kg of water by 1K It takes 5 x 4184J to heat up 1kg of water by 5 K It takes 0.1 x 5 x 4184J to heat up 0.1kg of water by 5K It takes 0.1 x 5 x 4184J = 2092 J !

39. Heat Property of Water Specific Heat Capacity Hint: It takes 0.1 x 5 x 4184J = 2092 J. The heater is pumping heat @ 45 J /s. It takes the heater 2092 / 45 seconds. It takes 46 seconds! Why did it take longer!? We needed to heat up the beaker Convection is constantly occurring

41. CPU – 50 Watts of Heat Power Supply – 30 Watts of Heat How are Computers Cooled? Heat Source Objective: Move the heat outside

42. How are Computers Cooled? What we have learned so far… Choice of computer case material - Steel, Copper, Aluminum, Silver Convection airflow - Direction of Convection current Cooling medium material - Air, Water, Mercury

43. How are Computers Cooled? What we don’t know yet… HEATPIPES!! Heatpipes are highly heat conducting pipes using the cycle evaporation and condensation of low boiling-point fluid.

45. How are Computers Cooled? Heatpipes Demo Heatpipes vs. Heat Conduction

46. Putting It All Together

47. Putting It All Together

48. Putting It All Together

49. Putting It All Together

50. Putting It All Together http://www.physics.ubc.ca/outreach/ http://www.streaming-river.com