열과유체, 에너지와친해지기 KAIST 기계공학과정상권

열과유체, 에너지와친해지기 KAIST 기계공학과정상권

이번시간에는! 열역학 - 세상을움직이는스마트한법칙 물과공기로움직이는기계 사라지지않는에너지 / 증가하는엔트로피

열역학 - 세상을움직이는스마트한법칙 KAIST 기계공학과정상권

[ 학습목차 ] Thermofluids Energy conservation principle Energy Work (boundary work)

#1 1. Thermofluids

1. Thermofluids #2 Phase : identified as having a distinct molecular arrangement that is homogeneous throughout and separated from the others by easily identifiable boundary surfaces

1. Thermofluids What is a fluid? - Fluid is a material whose shape is determined by the shape of a container. - A substance which moves and deforms continuously as a result of an applied shear stress of any magnitude. - A solid can resist shear stress by static deflection; a fluid cannot resist shear stress.

Thermodynamic properties 1. Thermofluids - Thermodynamic properties describe the state of a system. - Three primary thermodynamic properties are 1) pressure, 2) temperature 3) density. 1) Pressure (p): compressive stress at a point in a static fluid (Pa, psi). 2) Temperature (T): related to the internal energy level of a fluid ( C, F). 3) Density (ρ): mass per unit volume. Air : ρ (at 1 atm, 4 C) = 1.205 kg/m 3 Water: ρ (at 1 atm, 4 C) = 1000 kg/m 3

1. Thermofluids Newtonian fluid : Shear stress is linearly proportional to the rate of shearing strain (e.g. water, air, and oil). du dy μ : the coefficient of viscosity A Newtonian fluid has a constant coefficient of viscosity. #3

1. Thermofluids Coefficient of viscosity μ: coefficient of viscosity (dynamic viscosity) Water at 1 atm, 20 C = 1.0 10-3 kg/m s Air at 1 atm, 20 C = 1.8 10-5 kg/m s ν: kinematic viscosity = μ / ρ Water at 1 atm, 20 C = 1.0 10-6 m 2 /s Air at 1 atm, 20 C = 1.5 10-5 m 2 /s Absolute Viscosity, μ N.s/m 2 10-2 10-3 10-4 10-5 Water Air 0 20 40 60 80 100 Temperature (ºC)

1. Thermofluids #4 #5 #6 #7 #8

#9 1. Thermofluids

#10 1. Thermofluids

#11 1. Thermofluids

#12 1. Thermofluids

영국일간가디언은최고최저온도기록을소개했다. 1922 년리비아알 - 아지지야는 57.7ºC, 1983 년 7 월남극보스토크는 -89ºC 를기록했다. 1. Thermofluids Some typical low temperature Tropics Human body Room temperature Ice point Salt + water (cryogen) Antarctic winter Solid carbon dioxide Liquid oxygen Liquid nitrogen Liquid helium Absolute zero Temperature Celsius (ºC) Absolute (K) 45 318 37 310 20 293 0 273-18 255-50 223-78 195-183 90-196 77-269 4-273 0

1. Thermofluids Basket ball Circumference: 75 78 cm Weight: 600 ~ 650 g Optimal pressure: 0.6 ~ 0.7 kg/cm 2. gauge Volley Ball 0.42 ~ 0.48 kg/cm 2. gauge Soccer Ball Circumference 68~70cm Weight 410~430g Pressure 0.6~1.1 bar. gauge #14 #13 #15

1. Thermofluids PRESSURE #16 #17

Control volume System vs. Control volume: 1. Thermofluids - System: a fixed mass with a boundary - Control volume: a "window" for observation in the flow: region of interest System boundary Control Surface System Control Volume

1. Thermofluids Conservation laws of fluid mechanics - Conservation of mass - Conservation of linear momentum - Conservation of angular momentum - Conservation of energy

2. Energy conservation principle Energy can be neither created nor destroyed; it can only change forms. E in - E out =(Q in -Q out ) + (W in -W out ) = E system Internal energy, U #18

#19 3. Energy

3. Energy Internal energy, U #20

3. Energy Internal energy : U Specific heat #21

3. Energy Specific heat #22

3. Energy Liquid and solid are incompressible (compared to gas) C p ( ) C v C Lead 0.128 Mercury 0.139 Argon 0.520 Tin 0.217 R-12 0.917 CO2 0.846 Copper 0.386 Methanol 2.550 Air 1.005 Iron 0.450 Water 4.184 Steam 1.8723 Wood 1.760 Ammonia 4.800 H2 14.31 Unit : kj/kg.k

4. Work (boundary work) Boundary work (PdV work or moving boundary work) is the work associated with the expansion or compression of a gas in a piston-cylinder device. #23 #24

[ 학습목차 ] Thermofluids Energy conservation principle Energy Work (boundary work)

자료출처 #1 Earth, https://static.pexels.com/ #2 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.113 #3 F.M. White, Fluid Mechanics, 7th ed., McGaw-Hill, 2009, p. 26 #4 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.114 #5 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.114 #6 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.114 #7 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.115 #8 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.115 #9 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.115 #10 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.116 #11 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.119 #12 Solar system, https://camo.githubusercontent.com/

자료출처 #13 Basketball, https://upload.wikimedia.org/ #14 Volley ball, https://upload.wikimedia.org/ #15 Soccer ball, http://wwwchem.uwimona.edu.jm/ #16 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.23 #17 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.25 #18 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.174 #19 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.119 #20 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.126 #21 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.178 #22 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.178 #23 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.166 #24 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.167

물과공기로움직이는기계 KAIST 기계공학과정상권

[ 학습목차 ] Energy conservation principle Work production Heat engine Refrigerator System modeling

1. Energy conservation principle Energy can be neither created nor destroyed; it can only change forms. The first law of thermodynamics E in - E out =(Q in -Q out ) + (W in -W out ) = E system #1

1. Energy conservation principle #2

2. Work production #3 #4

2. Work production 1 2 #5 #6 1 2

2. Work production #7 에너지변환과정으로움직이는기계 #8

3. Heat engine Heat engines are devices that convert heat to work. Heat engines differ considerably from one another, but all can be characterized by the following: #9 1. They receive heat from a high-temperature source (solar energy, oil furnace, nuclear reactor, etc.). 2. They convert part of this heat to work (usually in the form of a rotating shaft). 3. They reject the remaining waste heat to a low-temperature sink (the atmosphere, rivers, etc.). 4. They operate on a cycle.

3. Heat engine Working fluid is the fluid to and from which heat and work is transferred while undergoing a cycle in heat engines and other cyclic devices. Thermal efficiency is a measure of the performance of a heat engine and is the fraction of the heat input to the heat engine that is converted to net work output. Thermal efficiency th is the ratio of the net work produced by a heat engine to the total heat input, th = W net /Q in.

#10 3. Heat engine

3. Heat engine #11 #12

4. Refrigerator Refrigerators are cyclic devices which allow the transfer of heat from a low-temperature medium to a high-temperature medium. #13

4. Refrigerator Refrigerant is the working fluid used in the refrigeration cycle. Coefficient of performance COP is the measure of performance of refrigerators and heat pumps. COP = Desired output Required input = Q L W net,in #14

#15 5. System modeling

#16 5. System modeling

#17 5. System modeling

#18 5. System modeling

5. System modeling Otto cycle is the ideal cycle for sparkignition reciprocating engines. It consists of four internally reversible processes: 1-2 Isentropic compression, 2-3 Constant volume heat addition, 3-4 Isentropic expansion, 4-1 Constant volume heat rejection. #19

#20 5. System modeling

5. System modeling Brayton cycle is used for gas turbines, which operate on an open cycle, where both the compression and expansion processes take place in rotating machinery. Aircraft propulsion & electric power generation. #21 1-2 Isentropic compression (in a compressor), 2-3 Constant pressure heat addition, 3-4 Isentropic expansion (in a turbine), 4-1 Constant pressure heat rejection.

5. System modeling #22 #23

5. System modeling #24 Application of thermodynamics!

[ 학습목차 ] Energy conservation principle Work production Heat engine Refrigerator System modeling

자료출처 #1 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.174 #2 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.10 #3 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.166 #4 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.166 #5 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.167 #6 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.167 #7 Car, https://upload.wikimedia.org/ #8 Car, http://3.bp.blogspot.com/ #9 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.282 #10 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.283 #11 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.284 #12 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.284

자료출처 #13 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.288 #14 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.288 #15 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.488 #16 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.488 #17 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.492 #18 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.500 #19 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.497 #20 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.508 #21 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.508 #22 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.508 #23 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.509 #24 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.4

사라지지않는에너지 / 증가하는엔트로피 KAIST 기계공학과정상권

[ 학습목차 ] Energy conservation principle The second law of thermodynamics Entropy Application of the second law of thermodynamics Refrigerator

1. Energy conservation principle Energy can be neither created nor destroyed; it can only change forms. The first law of thermodynamics E in - E out =(Q in -Q out ) + (W in -W out ) + (E mass, in - E mass, out ) = E system

1. Energy conservation principle Bernoulli equation (by energy conservation) 1 1 p V gz p V gz 2 2 2 2 1 1 1 2 2 2 Venturi tube #1 By mass conservation, smaller area higher speed (V 1 < V 2 ) By Bernoulli equation, higher speed lower pressure (p 1 < p 2 ) >

1. Energy conservation principle Boundary layer : the layer of reduced velocity in fluids, that is immediately adjacent to the surface of a solid past which the fluid is flowing. No slip condition! #2 #3

1. Energy conservation principle Boundary layer : the layer of reduced velocity in fluids, that is immediately adjacent to the surface of a solid past which the fluid is flowing. #4

2. The second law of thermodynamics Direction of the process #5 #6

2. The second law of thermodynamics Direction of the process #7

2. The second law of thermodynamics Direction of the process #8

2. The second law of thermodynamics Direction of the process #9

2. The second law of thermodynamics Clausius statement of the second law : It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lowertemperature body to a higher-temperature body. #14

2. The second law of thermodynamics Entropy (from a classical thermodynamics point of view) is a property designated S and is defined as ds =( Q/T) int rev. Entropy (from a statistical thermodynamics point of view) can be viewed as a measure of molecular disorder, or molecular randomness. The entropy of a system is related to the total number of possible microscopic states of that system, called thermodynamic probability p, by the Boltzmann relation, expressed as S = k ln p where k is the Boltzmann constant. Boltzmann s constant, k has the value of 1.3806 10 23 J/K.

2. The second law of thermodynamics #10

2. The second law of thermodynamics Second law of thermodynamics the entropy of an isolated system during a process always increases or, in the limiting case of a reversible process, remains constant Entropy generation S gen is entropy generated or created during an irreversible process, is due entirely to the presence of irreversibilities. Entropy generation is always a positive quantity or zero. Its value depends on the process, and thus it is not a property.

2. The second law of thermodynamics Reversible process is defined as a process that can be reversed without leaving any trace on the surroundings. Irreversible processes are processes which, once having taken place in a system, cannot spontaneously reverse themselves and restore the system to its initial state. Irreversibilities are the factors that cause a process to be irreversible. They include friction, unrestrained expansion, mixing of two gases, heat transfer across a finite temperature difference, electric resistance, inelastic deformation of solids, and chemical reactions.

#11 3. Entropy

3. Entropy Energy can be neither created nor destroyed; it can only change forms. Entropy can be generated. Tds relations relate the Tds product to other thermodynamic properties. The first Gibbs relation is Tds = du + Pdv. The second Gibbs relation is Tds = dh vdp.

#12 3. Entropy

#13 3. Entropy

3. Entropy Energy can be neither created nor destroyed; it can only change forms. Entropy can be generated. #14

4. Application of the second law of thermodynamics Clausius statement of the second law : It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lowertemperature body to a higher-temperature body. #15

4. Application of the second law of thermodynamics Throttling process! Abrupt pressure drop of flow #16

4. Application of the second law of thermodynamics By the first law of thermodynamics, Q = 0, W = 0, H in = H out and U in > U out in non-ideal gas T in > T out

4. Application of the second law of thermodynamics Enthalpy H is a property and is defined as the sum of the internal energy U and the PV product. #17

5. Refrigerator #18 #19

5. Refrigerator Application of thermodynamics! #20

[ 학습목차 ] Energy conservation principle The second law of thermodynamics Entropy Application of the second law of thermodynamics Refrigerator

자료출처 #1 Venturi tube, https://encrypted-tbn1.gstatic.com/ #2 Homsy et al., Multimedia Fluid Mechanics, 2nd ed., Cambridge University Press #3 Homsy et al., Multimedia Fluid Mechanics, 2nd ed., Cambridge University Press #4 F.M. White, Fluid Mechanics, 7th ed., McGaw-Hill, 2009, p. 266 #5 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.281 #6 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.280 #7 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.280 #8 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.280 #9 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.281 #10 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.335

자료출처 #11 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.338 #12 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.340 #13 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.340 #14 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.377 #15 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.288 #16 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.239 #17 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.176 #18 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.288 #19 çengel, Y.A. and Boles, M.A. Thermodynamics An Engineering Approach, 5th Edition, McGraw-Hill, 2006, p.288 #20 Refrigerator, https://encrypted-tbn2.gstatic.com/i