lecture 10: property tables - sjtu
TRANSCRIPT
1.1
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 : [email protected] 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
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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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