View
147
Download
0
Category
Preview:
DESCRIPTION
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. - PowerPoint PPT Presentation
Citation preview
11Maxim Confidential
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
1. Heat ; Q
2. Potential ; PE
3. Kinetic ; KE
4. Internal ; U
5. Flow ; Wf
6. Enthalpy ; H = U + Wf
7. 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
English MkS-cgs SI
1 hp = 1 eng hp = 1 arabian horse
1 french horse = 1 Chueval Vapuer
Watt, J/s, Nm/s
1 mule = 1 mola 1 Pfer Starkey
1 hp = 550 lbf – 1 ft / sec
= 33000 lbf – 1 ft / min
1 met hp = 75kgs – m/1 sec
Maxim Confidential 6
Energy Units Conversions
English MKS SI
BTU Cal J
Ft-lbf Dyne-cm N-m
Therm erg
Maxim Confidential 7
Conversion of Energy Units
1 BTU = 778.16 ft-lbf 1 kgf = 9.8066 N1 BTU = 1.055 KJ 1 erg = 1 dyne -
cm1 J = 1 N-m1 J = 107 dyne-cm1 J = 107 erg1 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
eng mks SI
1 slug-ft/lbf-s2 = 1 gm – cm/dyne - s2 = 1 kgm – m/N - s2 =
32.174 lbm – ft/lbf-s2 = 9.8066 kgm – m/kgf - s2 = 9.8066 kgm – m/kgf - s2
1010Maxim 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. 0.025c. 0.889d. 1.228
Maxim Confidential 11
2. The ratio of the density of a substance to the density of some standard substance is called
a. relative densityb. specific gravityc. specific densityd. relative density
Maxim Confidential 12
3. The S.I unit of force
a. 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 called
a. 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 efficiencyn = (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:Eng Mks SI
14.7 lbf/in2 = 1.0332 kgf/cm2 = 101.325 kPa or KN/m2 =
29.92 inHg = 760 mmHg = 0.76 mHg =
34 ftH20 = 10330 mmH20 = 10.33 mH20
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 to
a. 1000 dynes/cm2
b. 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 to
a. -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 is
a. 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
Point Functions
• Temp
• Pressure
• Volume
• Entropy
• Internal energy
• Enthalpy
Path Functions
• Heat
• Work
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
0 1 K -∞ to + ∞ + ∞
Isobaric/Isopiestic
Isothermal Isentropik/reversible adiabatic
Polytropic Isometric/Isochoric/
Isovolumeric
Maxim Confidential 38
15. In a sealed and rigid system, the constant is
a. 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 to
a. 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
NFW (Closed System)
• Piston
- mass will not cross the boundary
SFW (Open System)
• Turbine
• Pump
- mass and energy 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
Recommended