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ME 200 –Thermodynamics I Spring 2016

Lecture 10: Property tables

Yong Li Shanghai Jiao Tong University

Institute of Refrigeration and Cryogenics 800 Dong Chuan Road Shanghai, 200240, P. R. China

Email : liyo@sjtu.edu.cn Phone: 86-21-34206056; Fax: 86-21-34206056

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Lecture Outline

Last lecture: » Definition of a pure substance, its phase, and associated phase

change processes » Importance of property diagrams, especially phase diagram, p‐v

and T‐v diagrams, for thermodynamic analysis » Structure of p-v and T-v diagrams

This lecture: » Property Tables » Several more examples » Objectives

– Be able use the property tables better – Linear interpolation

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Property tables & Enthalpy

Property tables::: list specific properties such as v, u in terms of either p or T

Property tables provide easy way of listing relevant properties and looking them up during analysis

Other listed specific properties are “enthalpy” and “entropy”

Enthalpy::: a property defined for simplicity and convenience » Total Enthalpy::: H = U + pV » Specific Enthalpy::: h = u + pv

Enthalpy is commonly used in the analysis of open systems (control volume)

More about “Entropy” later (2nd Law)

ConCepts

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Property tables

Property information available for compressed liquid, saturated liquid, liquid-vapor mixture, saturated vapor, and superheated vapor for many pure substances

Tables A-1 through A‐16 (SI units) list these properties for water, some refrigerants (R‐12, R‐134a, ammonia), and propane

Tables A-17 through A‐28 (SI units) list Separate tables for substances modeled as ideal gas

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Property tables

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Property tables

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Property tables

Recall: compressed (sub‐cooled) liquid (CL), saturated liquid (SL), saturated liquid‐vapor mixture (SLVM), saturated vapor (SV) and superheated vapor (SHV)

Saturated liquid and vapor tables list saturated state properties (SL and SV, SLVM properties found by interpolation)

Separate tables for sub‐cooled liquid (CL) and superheated vapor (SHV) although tables for CL are sparse because we don’t need them in general

Properties listed with respect to some reference state » i.e.: only differences important (not absolute values)

Listed with respect to T or p

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Property tables

Saturated liquid and saturated vapor properties denoted by f and g subscripts, respectively

Liquid‐vapor mixture properties denoted by f g subscript

Saturated Water Tables

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Example

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Saturated liquid‐vapor mixture (SLVM) Quality

During vaporization substance exists as part liquid and part vapor i.e. mixture of SL and SV Under the wet dome, define a parameter in addition to T and p to

specify state completely Proportions of each phase in mixture Quality, x::: ratio of mass of vapor to total mass of mixture:

x always between 0 and 1, i.e. x=0 for SL and x=1 for SV

x can be used as one of two independent, intensive properties to fix state Properties of SL and SV are same in mixture as if alone

ConCepts

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SLVM Properties

Always assume SLVM is homogeneous mixture

x has no meaning outside of the wet dome

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SLVM Properties

Phase change properties:

At any point inside the wet dome，the property y:

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Home work

Problems: » See website

For next class, please read the text book: » 3.3