Heat & Thermodynamics

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Heat & Thermodynamics

  1. 1. HEAT AND THERMODYNAMICS By : Arra C. Quitaneg
  2. 2. HEAT AND THERMODYNAMICS OBJECTIVES: - Define heat, temperature, specific heat capacity. - Solve problems on thermal expansion heat transfer, quantity of heat and temperature conversion. - Describe different heat transfer mechanisms. - Apply concepts on building or house design.
  3. 3. What is temperature?
  4. 4. TEMPERATURE • http://ippex.pppl.gov/interactive/fusion/contr olatomtemp.html
  5. 5. - A quantity that tells how warm or cold an object is with respect to a standard - related to the random motion of the molecules in a substance. - it is proportional to the average kinetic energy of molecular translational motion.
  6. 6. Kelvin Scale named after British physicist Lord Kelvin Zero is assigned to the lowest possible temperature absolute zero - 2730C
  7. 7. Celsius Scale Named after a Swedish astronomer Anders Celsius Zero is assigned to the temperature at which water freezes, and 100 is the temperature at which water boils. Farenheit Scale Named after a German physicist G.D Farenheit 32 is assigned to the temperature at which water freezes 212 is assigned to the temperature at which water boils.
  8. 8. TEMPERATURE SCALE CONVERSION • °C = K - 273.15° • K = °C + 273.15 °C = (°F - 32°)/1.8 °F= 1.8•°C + 32°
  9. 9. • Internal energy = the grand total of all energies inside a substance.
  10. 10. THERMAL EQUILIBRIUM Objects that are in thermal equilibrium are at the same temperature. A B
  11. 11. THERMAL EXPANSION Why are there thermal expansion joints in roads? -When the temperature of a substance is increased, molecules or atoms move faster and tend to move farther apart, resulting to an expansion of the substance. -Expansion of liquids is greater than the expansion of solids.
  12. 12. How does a thermometer work? Is the expansion of the liquid same as that of the glass?
  13. 13. THERMOMETER
  14. 14. Linear Expansion • ∆L = change in length • = coefficient of linear expansion • L0 = initial length of the material • ∆T = is the change in temperature
  15. 15. Volume expansion • ∆V = change in volume • = coefficient of volume expansion • V0 = initial volume of the material • ∆T = is the change in temperature
  16. 16. Problem-solving • You place a small piece of melting ice in your mouth. Eventually, the water all converts from ice at T1= 320F to body temperature T2= 98.60F. Express the temperatures in 0C and in K and find T in both cases. Solution: 0F to 0C °C = (°F - 32°)/1.8 °C = (32°F - 32°)/1.8 = 0°C °C = (98.6°F - 32°)/1.8 = 37°C K = °C + 273.15 K = 0°C + 273.15 = 273.15K K = 37 °C + 273.15 = 310.15K Solution: T = T2-T1 T = 370C - 00C = 370C T = 310.15 K – 273.15K = 37 K
  17. 17. Problem-solving • A surveyor uses a steel measuring tape that is exactly 50 m long at a temperature of 200C. What is its length on a hot summer day when temperature is 350C. steel = 1.2x10-5 K-1 • SOLUTION • Lf – L0= L0 T • Lf = L0 T + L0 • Lf = L0 ( T + 1) • Lf = 50m (1.2x10-5 K-1 15K + 1) • Lf = 50.009 m
  18. 18. • A gas flask with volume 200cm3 is filled to the brim with mercury at 200C. How much mercury overflows when the temperature of the system is raised to 1000C? glass = 0.4 x10-5 K-1 mercury = 18 x 10-5 K-1 . Solution: glass = 3 Vglass = 3(0.4 x10-5 K-1 ) 200 cm3 80K Vglass = 0.192 cm3 Vmercury = (18 x10-5 K-1 ) 200 cm3 80K Vmercury = 2.88 cm3 Solution: Volume of mercury which overflows Vmercury - Vglass =2.88 cm3 - 0.192 cm cm3 = 2.69 cm3
  19. 19. • Solution • = L/L0 T • = (40.148cm – 40.125cm) / (40.125cm)(450C - 200C) • = 2.29 x 10-5 K • A metal rod is40.125 cm long at 200C and 40.148 cm long at 450C. Calculate the average coefficient of linear expansion of the rod.
  20. 20. Seatwork 1. A gas flask with volume 1000cm3 at 0 0C is completely filled with mercury at this temperature. How much mercury overflows if the flask is warmed at 550C? glass = 0.4 x10-5 K-1 mercury = 18 x 10-5 K-1 2. The steel bed of suspension bridge is 200 m long at 200C. If the extremes of temperature to which it might be exposed are – 30 0C to + 400C, how much will it contract and expand?
  21. 21. 3. What is the change in length of a column of mercury 3.0 cm long if its temperature increases from 370 to 400 C? mercury = 60 x10-6 / C0
  22. 22. THERMAL EXPANSION OF WATER
  23. 23. THERMAL EXPANSION OF WATER Water is densest at 40C. As the water is cooled below 4 deg C however, it expands! If water were like most other materials, the very cold water would sink and lakes would freeze from the bottom up.
  24. 24. Why is it that some foods remain hotter much longer than others?
  25. 25. • The quantity of heat required to change the temperature of a unit mass of the substance by 1 deg Celsius. • Thermal inertia- resistance of a substance to change its temperature
  26. 26. Quantity of Heat • Q = amount of heat • m= mass • c=specific heat capacity • T = change in temperature • If Q and T 0, heat enters the body and its temperature increases • If Q and T 0, heat leaves the body and its temperature decreases
  27. 27. Calorimetry and Phase Change • Calorimetry – measuring heat • Phase – state of matter Q= quantity of heat m=mass L = latent heat of fusion or vaporization
  28. 28. Phase change
  29. 29. Evaporation How is fire-walking possible? Why do dogs pant?
  30. 30. Evaporation  Evaporation is a change of phase from liquid to gas.  Cooling process  Endothermic – heat is bsorbed
  31. 31. I really love mud!!!
  32. 32. CONDENSATION Change of phase from gas to liquid Warming process Exothermic = heat is released Steam burn is more damaging than a burn from boiling water
  33. 33. It is warm inside the shower room after taking a bath because condensation is a warming process.
  34. 34. Problem- solving: 1. How much heat is required to raise the temperature of an empty 20 kg vat made of iron from 100C to 900C?What if the vat is filled with 20 kg of water? Ciron = 450 J/kgC0 C water = 41860C 2. What is the specific heat of a metal substance if 135kJ of heat is needed to raise 5.1 kg of the metal from 200C to 300C?
  35. 35. PROBLEM SOLVING 3. How much energy does a refrigerator have to remove from 1.5 kg water at 200C to make ice at -120C? Lf =334x103 J/kg, Cice = 2100 J/kgC0 4. How much heat is needed to melt 16.5 kg of silver that is initially at 200C? Melting pt of silver = 960.80C Lf =88.3x103 J/kg Csilver=234 J/kgC0
  36. 36. 5. An ice cube tray of negligible mass contains 0.350 kg of water at 180C . How much heat must be removed to cool the water at 00C and freeze it? 6. How much heat is required to convert 12.0 g ice at -100C to steam at 1000C? Lv =2256 x103 J/kg Csteam =2010 J/kgC0
  37. 37. Answers 1. A) 6, 697, 600 Joules, b) 720 000 Joules 2. 2, 647 Joules 3. 664, 380 Joules 4. 5, 089, 378.8 Joules 5. 143, 271.8 Joules 6. 36, 355.2 Joules
  38. 38. • Heat is transferred from hotter substance to colder substance upon contact with each other. • Heat conduction occurs by electron and molecular collisions. • Metals are good conductors of heat.
  39. 39. Conduction • http://www.absorblearning.com/media/attac hment.action?quick=aj&att=750
  40. 40. Particle to particle interaction
  41. 41. • Liquids and gases, are poor conductors. • Air is a very poor conductor.
  42. 42. CONDUCTION
  43. 43. Does it feel so cold inside an ice hotel? No, it’s not that cold. Thanks to the poor heat conductivity of ice 
  44. 44. Snow is a poor conductor of heat. Snow does not provide heat, it slows down the loss of heat they generate. Insulating materials delay the transfer of heat.
  45. 45. Thanks to snow’s poor heat conductivity! 
  46. 46. In desert regions that are hot in the daytime and cold at nightime, the walls of houses are often made of mud. Why is it important that the mud walls be thick?
  47. 47. • Liquids and gases transmit heat by convection • Heat transfer by actual motion of the fluid – by currents.
  48. 48. CONVECTION AND HOT WATER BASED BOARDS What will happen if the heating system is not placed on the floor?
  49. 49. • Heat transfer in an empty space. • Energy radiated is radiant energy.
  50. 50. Absorber and Emitter of radiation • A perfect absorber reflects no radiant energy and appears perfectly black • Good reflectors are poor absorbers
  51. 51. Think…think…think… • Why does the evaporation of water cool the air near the water’s surface? • What color should you paint your house (light or dark colored) to stay cooler in summer. Why? • Next time you go to a coffee shop, when should you pour the creamer on the coffee to maintain its hotness? (immediately after receiving it or when you are about to drink it)
  52. 52. • A tile floor may feel uncomfortably cold to your bare feet, but a carpeted floor in an adjoining room at the same temperature feels warm. Why? • Nowadays, in the Philippines, it is extremely hot during summer. You won’t even notice a difference in temperature inside and outside your house. As an architect, what can you suggest to minimize heat transfer from the surrounding to the house? When you give your suggestion, environmental considerations should not be taken for granted.
  53. 53. • The different mechanism of heat transfer become important in reducing heating and cooling costs in buildings. • Reducing this flow of heat saves money. • Putting insulation in the walls and ceilings reduces conduction. House insulation
  54. 54. • Using thicker insulation in the ceiling counteracts one effect of convection. • Using window shades, and canopies to keep direct sunlight out during the summer reduces heat transfer by radiation.

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