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

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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

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,

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)(

)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

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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