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THERMODYNAMICS Prepared by: Engr. Darwin Mañaga

THERMODYNAMICS Prepared by: Engr. Darwin Mañaga. Thermodynamics – transformation of heat energy into other forms of energy and vice versa. Forms of Energy Heat ; Q Potential ; PE Kinetic ; KE Internal ; U Flow ; W f Enthalpy ; H = U + W f Mechanical Work ; W.

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THERMODYNAMICS Prepared by: Engr. Darwin Mañaga

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  1. THERMODYNAMICS Prepared by: Engr. Darwin Mañaga Maxim Confidential

  2. Thermodynamics – transformation of heat energy into other forms of energy and vice versa Maxim Confidential

  3. Forms of Energy • Heat ; Q • Potential ; PE • Kinetic ; KE • Internal ; U • Flow ; Wf • Enthalpy ; H = U + Wf • Mechanical Work ; W Maxim Confidential

  4. Power ; P = energy / unit time Energy ; E = the ability or capacity to do work Work = Force*distance ( always parallel to the axis of motion ) Maxim Confidential

  5. Unit of Power Maxim Confidential

  6. Energy Units Conversions Maxim Confidential

  7. Conversion of Energy Units 1 BTU = 778.16 ft-lbf 1 kgf = 9.8066 N 1 BTU = 1.055 KJ 1 erg = 1 dyne - cm 1 J = 1 N-m 1 J = 107 dyne-cm 1 J = 107 erg 1 cal = 4.18 J 1 lbf = 4.4482 N Maxim Confidential

  8. Heat Energy ; Q Qs = sensible heat = MCp(t2-t1) Cp- specific heat at constant pressure QL = latent heat ( only phase change ) - solid to liquid: QL = mhfi ; hfi – latent heat of fusion of ice hfi = 144 BTU/lbm = 8000Kcal/kgm = 335 KJ / kgm - liquid to gas: QL = mhfg ; hfg – latent heat of fusion of air hfg = 970.3 BTU/lbm = 540Kcal/kgm = 2257 KJ / kgm Maxim Confidential

  9. Kinetic Energy – due to velocity KE = 0.5 mv2/k ; k – proportional constant Maxim Confidential

  10. 1. If the mass of a typical neutron is 1.66x10-24 gram and the velocity is approximately 2200m/s. What is the kinetic energy of this neutron in electron volt. Note: 1 ev = 1.6x10-12 erg.a. 1.025b. 0.025 c. 0.889d. 1.228 Maxim Confidential

  11. 2. The ratio of the density of a substance to the density of some standard substance is calleda. relative densityb. specific gravityc. specific densityd. relative density Maxim Confidential

  12. 3. The S.I unit of forcea. poundb. Newtonc. kilogramd. Dyne Maxim Confidential

  13. Remember the conversions: 1 pound = 1 lb 1 pond = 1 gram 1 poundal = 32.174-1 pound Maxim Confidential

  14. 4. Heat normally flowing from a high temperature body to a low temperature body wherein it is impossible to convert heat without other effects is calleda. second law of thermodynamicsb. first law of thermodynamicsc. third low of thermodynamicsd. zeroth law of thermodynamics Maxim Confidential

  15. Laws of Thermodynamics: 1st Law: Law of conservation of energy • Energy can neither be created nor destroyed but it can be transformed from on form to another Ein = Eout Maxim Confidential

  16. 2nd Law: Law of degradation of energy • Heat is moving from heat body to cold body • No engine w/ 100% thermal efficiency n = (W/QA)x100% = ((QA – QR)/QA)*100% = ((TMAX – TMIN)/ TMAX)*100% Note: Use absolute temp for T R = deg F + 460 ; K = deg C + 273 Maxim Confidential

  17. 3rd Law: Law of absolute zero temperature - @ absolute zero temp. line, all molecules of a crystalline substance are dead & the degree of disorder of molecules is equal to 0 & heat is eventually equal to 0. Maxim Confidential

  18. Zeroth or 4th Law: - made by Filipino - keyword: 3rd body Maxim Confidential

  19. Potential Energy – due to elevation = Weight*distance ; N*m or J Maxim Confidential

  20. 5. The weight of a 100kg mass body at a given elevation is 0.9804kN. If the variation from the standard gravitational acceleration is –0.004mps2 per 1000m. Determine the elevation at this point.a. 550mb. 50mc. 660md. 650m Maxim Confidential

  21. Pressure Pabs = Pbaro + Pg =Pbaro – Pvac Note: If Pbaro is not mentioned, use Pbaro = 1 atm Maxim Confidential

  22. Pressure Conversions: Maxim Confidential

  23. Remember: 1 TORR = 1mmHg 1 bar = 100kPa Maxim Confidential

  24. 6. The pressure of a boiler is 9.5 kg/cm2 . The barometric pressure of the atmosphere is 768mm of mercury. Find the absolute pressure in the boiler in MPa.a. 1.03b. 2.03c. 3.03d. 4.03 Maxim Confidential

  25. 7. How many metric horse power are there in 10 kW?a. 13.4b. 13.59c. 15.16d. 16.33 Maxim Confidential

  26. 8. A pressure of 1 millibar is equivalent toa. 1000 dynes/cm2b. 1000 cm Hgc. 1000psid. 1000kg/sq.cm Maxim Confidential

  27. 8. What is the minimum pressure required to force blood from the heart to top of the head if the vertical distance is 27 in? Assume the density of the blood to be 1.04gm/cm3 and neglect friction. Express the answer in mmHg.a. 54.42b. 52.44c. 42.25d. 25.54 Maxim Confidential

  28. Remember: Pressure in mmHg = (Specific Gravity of substance)(h) 13.6 Maxim Confidential

  29. 9. A water temperature rise of 18 deg F in the water cooled condenser is equivalent in deg C toa. -7.78b. 10c. 265.56d. -9.44 Maxim Confidential

  30. 10. If the temperature is held constant and increased beyond the saturation pressure, we have a a. saturated vaporb. compressed liquidc. saturated liquidd. sub-cooled liquid Maxim Confidential

  31. Flow Energy ; Wf - aka resistance energy Wf = (Pressure)(Volume) Maxim Confidential

  32. 11. A piston was moved at a distance of 75cm by a gas pressure of a 450kPa. If the work done is 15kJ, the piston diameter in cm isa. 23.79b. 27.93c. 29.37d. 32.79 Maxim Confidential

  33. 12. The change of water from the solid to vapor phase.a. always must occur in two steps-solid to b. liquid to liquid then liquid to vaporb. can occur directly at elevated pressurec. can occur directly at extremely low pressured. can occur directly at room temperature Maxim Confidential

  34. 13. Which of the following is an example of path function?a. temperatureb. volumec. workd. entropy Maxim Confidential

  35. Path Functions • Heat • Work Point Functions • Temp • Pressure • Volume • Entropy • Internal energy • Enthalpy Maxim Confidential

  36. 14. What is the process if n = negative to positive infinity?a. isobaricb. isothermalc. polytropicd. isentropic Maxim Confidential

  37. General Equation: PVn = C Maxim Confidential

  38. 15. In a sealed and rigid system, the constant isa. volumeb. pressurec. temperatured. entropy Maxim Confidential

  39. 17. In a sealed and rigid system, determine the output atmospheric pressure if the input atmospheric pressure is 2 atm. The temperature at the input is 27 deg C w/c increases to 100 deg C at the output.a. 0.725 atmb. 0.625 atmc. 0.825 atmd. 0.925 atm Maxim Confidential

  40. 18. Non flow work is applicable toa. closed systemb. open systemc. impact systemd. solar system Maxim Confidential

  41. Work Non Flow Work: Wn = ∫ Pdv Steady Flow Work: Ws = - ∫ Vdp Maxim Confidential

  42. SFW (Open System) • Turbine • Pump - mass and energy cross the boundary NFW (Closed System) • Piston - mass will not cross the boundary Maxim Confidential

  43. 19. Pressure of octane and air were mixed and produced 86.1 kPa. Determine the pressure of air considering the following parameters: mass of octane = 0.0624 kg. R of octane = 8.314/114; mass of air = 0.91 kg. R of octane = 8.314/29. At a temperature of 290 K.a. 84.6 kPab. 94.6 kPac. 64.6 kPad. 44.6 kPa Maxim Confidential

  44. Daltons Law - mixture of gases is equal to the summation of the pressures PTOTAL = ∑ P = P1 + P2 + P3 . . . + PN Maxim Confidential

  45. 20. A 20x10-3 kg bullet running at 250m/sec hit a target and travelled 12 cm after the impact. Determine the force.a. 4280Nb. 5280Nc. 6280Nd. 7280N Maxim Confidential

  46. Internal Energy; U - due to the movement of molecules U = mCV(t2 – t1) Maxim Confidential

  47. Enthalpy; U - sum of internal energy and flow energy H = U + Wf = mCpt + PV = mCp(t2 – t1) Maxim Confidential

  48. Mechanical work or energy ; W - due to shaft rotation or piston movement W = (force)(distance) ω = (Frequency of rotation)(radius) = Torque = rad/sec Power = (Torque)(ω) = watt Maxim Confidential

  49. Maxim Confidential

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