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

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

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

**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

**Unit of Power** Maxim Confidential

**Energy Units Conversions** Maxim Confidential

**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

**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

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

**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

**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

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

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

**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

**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

**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

**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

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

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

**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

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

**Pressure Conversions:** Maxim Confidential

**Remember:** 1 TORR = 1mmHg 1 bar = 100kPa Maxim Confidential

**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

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

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

**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

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

**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

**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

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

**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

**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

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

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

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

**General Equation:** PVn = C Maxim Confidential

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

**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

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

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

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

**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

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

**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

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

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

**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

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