1 Thermal and Fluids in Architectural Engineering 5. Thermodynamic Properties Jun-Seok Park, Dr. Eng., Professor. Dept. of Architectural Engineering Hanyang Univ.
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1
Thermal and Fluids
in Architectural Engineering
5. Thermodynamic Properties
Jun-Seok Park, Dr. Eng., Professor.
Dept. of Architectural Engineering
Hanyang Univ.
Where do we learn in this chaper
1. Introduction
2.The first law
3.Thermal resistances
4. Fundamentals of fluid mechanics
5. Thermodynamics
6. Application
7.Second law
8. Refrigeration,
heat pump, and
power cycle
9. Internal flow
10. External flow
11. Conduction
12. Convection
14. Radiation
13. Heat Exchangers15. Ideal Gas Mixtures
and Combustion
5.1 Introduction
5.2 Properties of Pure Substances
5.3 Internal Energy and Enthalpy in Two-Phase
5.4 Properties of Real Liquids and Solids
5.5 The State Principle
5. Thermodynamic Properties
5.1 Introduction
□ Thermal properties of a system, P, T, ν, u, and h,
are changed in a phase change process
- Solid ↔ Liquid (Change of Internal Energy/heat flowed)
- Liquid-Gas (Change of Internal Energy/heat flowed)
□ Examples in buildings
- Refrigerator in HVAC system
- Heat Pump
- Refrigerator
- Ice Storage System
M W - Q ΔE
5.1 Introduction
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냉각탑
응축기
압축기
증발기
확장밸프
냉매(고온/고압)
냉매(저온/고압)
냉매(저온/저압)
냉매(고온/저압)
냉수
온수
Refrigerator in HVAC system
5.1 Introduction
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Heat Pump
압축기
확장밸프
기화액화
온풍 냉풍
실내실외 압축기
확장밸프
액화기화
냉풍 온풍
실내실외
(실내 냉방시) (실내 난방시)
5.1 Introduction
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Ice Storage System
공조부하
건물공조시간
열원기기용량
일반공조시스템 공조+축열 시스템
축열운전(심야) 일반열원공조
축열분
건물공조시간축열운전
제빙용터보냉동기
빙축열조
기계실
5.2 Properties of Pure Substances
□ Specific volume of a pure substance is defined
- Specific Volume of a substance is more useful to
calculate mass and internal energy when phase of the
substance is changed or mixed
- Tables of experimental values are available for a variety
of pure substance (Appendix A-12)
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m
V
1
5.2 Properties of Pure Substances
□ Thermodynamic properties, T, P, and ν of a
pure substance is changed according to the
phase of the substance and heat flow
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T
ν
Saturated vapor
Saturated liquid
Liquid Liquid
Vapor
Vapor
Superheated
vapor
Subcooled
liquid
T
ν
Saturated vapor
Saturated liquid
Heat flow (from surrounding to the system)
Heat flow (from the system to surrounding)
5.2 Properties of Pure Substances
□ In saturated liquid-vapor region, the specific
volume of a mixture depends on the relative
proportion of liquid and vapor present
- Quality is defined as below
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d)German wor from liquid (f; gf
g
mm
mx
5.2 Properties of Pure Substances
- The specific volumes of a two-phase are as below
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fg
f
gf
gf
gg
gf
ff
ggfftot
gftot
gftotg
g
gf
f
ftot
tot
x
x-x)(
mm
m
mm
m
mmm
VVV
mmmm
V
m
V
m
V
1
) ( ; ;
5.2 Properties of Pure Substances
□ From T-ν(P const.), P- ν(T const.), and P-T
(ν const.) figures, the phase and the properties
of a pure substance will be identified.
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P
ν
Critical point
Liquid
Liquid
Vapor
Vapor
T1
T2
T3
No Heat flow (< Work of P)
5.3 Internal Energy and Enthalpy in two-phase systems
□ P, T, and ν(of a substance decide internal
Energy and enthalpy
- In two-phase of a system, internal energy and enthalpy
can be expressed as below,
M W - Q ΔE
)(
)1(
)(
) 1 ( )1(
) , ,(
fgf
gf
fgf
gfgf
hhxh
hxhxh
uuxu
x-x)(uxuxu
m
Hh
m
Uu
m
V
5.3 Internal Energy and Enthalpy in two-phase systems
- Quality in two-phase of a system, is expressed as below,
- Thermodynamic properties, P, T, ν, u, and h are
changed from the phase change or phase
M W - Q ΔE
fg
f
fg
f
fg
f
gf
g
hh
hh
uu
uu
mm
mx
5.4 Properties of Real liquids and Solids
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□ In a real liquids and solids, there are expansions
of liquid or solids.
- thermometer, bridges, buildings
- For real solids and liquids, internal energy and enthalpy
are typically strong functions of temperature, and weak
functions of Pressures
5.5 The State Principle
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□ Intensive properties of a system are independent
of a size of it (T, P, ν, u, and h)
□ Extensive properties of a system are dependent
of a size of it (V, U, and H)
5.5 The State Principle
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□ From the state principle
- In ideal gas
- In two-phase mixture
)on depend ( ?known are and
and known are and
and known are and
and known are and
TuuT
TPu
huTP
huTP
)on depend ( ?known are and
and known are and
and known are and
PTPT
PhuxT
PhuxT
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