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 Exchangers 15. 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
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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
기화 액화
온풍 냉풍
실외 실내 압축기
확장밸프
액화 기화
냉풍 온풍
실외 실내
(실내 냉방시) (실내 난방시)
5.1 Introduction
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Ice Storage System
공조부하
건물공조시간 열원기기
용량
일반공조시스템 공조+축열 시스템
축열운전
(심야) 일반열원공조 축열분
건물공조시간 축열운전
제빙용 터보냉동기
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;
g f
g
m m
x m
5.2 Properties of Pure Substances
- The specific volumes of a two-phase are as below
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f g
f
g f
g f
g g
g f
f f
g g
f f
tot
g f
tot
g f
tot g
g g
f f f
tot tot
x
x -x)
(
m m
m m
m
m
m m
m
V V
V
m m
m m 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,
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) (
) 1 (
) (
)
1
( )
1 (
) ,
, (
f g
f
g f
f g
f
g f
g f
h h
x h
h x h
x h
u u
x u
x -x)
( u
x u
x u
m h H
m u U 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
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f g
f f
g
f f
g
f g
f g
h h
h h u
u
u u
m m
x m
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
T u
u T
T P
u
h u
T P
h u
T P
) on depend (
? known
are and
and known
are and
and known
are and
P T
P T
P h
u x
T
P h
u x
T
