This notebook is about Liquid Argon thermodynamic properties.  Liquid argon is commonly being used for very large neutrino detectors. 

With this notebook we can perform calculations of the argon phase (liquid, solid, gas) as a function of temperature and pressure. 

Mathematica provides a library of thermodynamic data.  The numbers are very accurate. First let’s look at the plot from the Engineering Toolbox website.

We can then show these same plots and data obtained from Mathematica from their database.  Let’s first get the data for the triple and critical points.  

To convert to celcius, we have to add -273.15 
83.8058 K  = -189.344 (not the same as the above plot )  

Pressure is in Pascal.  We will do an exercise in pressure units later. 

But for reference here is a conversion
1 bar = 100000 Pascal =  0.1 MPa = 0.986923 ATM = 14.5038 pounds per Sq-inch.

ThermodynamicData["Argon","TriplePointTemperature"]

ThermodynamicData["Argon","TriplePointPressure"]

ThermodynamicData["Argon","CriticalPressure"]

ThermodynamicData["Argon","CriticalTemperature"]

TmpB2[p_Real]:= QuantityMagnitude[ThermodynamicData["Argon","LiquidVaporPhaseBoundary",{"Pressure"->Quantity[p,"Bar"]}]]

TmpS2[p_Real]:= QuantityMagnitude[ThermodynamicData["Argon","SolidLiquidPhaseBoundary",{"Pressure"->Quantity[p,"Bar"]}]]

SL= Plot[TmpS2[p],{p,0.1,50},PlotRange->{{0.1,50},{70.,160.}},PlotStyle -> Red, Frame -> True  , FrameStyle -> Bold, LabelStyle -> {Medium, Bold, Italic} ]

GL=Plot[TmpB2[p],{p,0.1,50},PlotRange->{{0.5,50},{70.,160.}}, PlotStyle -> Black, Frame -> True  , FrameStyle -> Bold, LabelStyle -> {Medium, Bold, Italic} ]

Show[{SL,GL,Graphics[Text["Triple Point", {6,86}] ], 
Graphics[Text["Solid", {20,75}] ], Graphics[Text["Gas ", {5,130}] ], 
Graphics[Text["Liquid", {20,120}] ], Graphics[Text["Critical Point", {45,150}] ]}, FrameLabel->{"Pressure (bar)","Temperature (K)"}]

Show[Graphics[Circle[{0,0},1]], Graphics[Text["Triple Point", {2,2}]], Frame -> True]

Notice what we can do:   if we increase the pressure,  we can liquify argon at higher temperatures. In fact it can be as high as -122 C if we are willing to pressurize to 50 bar. 

Typical liquification temperatures for various gases at standard pressure (1 ATM) are 

N2  -  77 K  
O2  - 90.2 K  
CO2 -  194.65 K  (sublimates means becomes gas to solid directly)

Let’s do some exercises in Pressure units.  There are several units commonly used.  

Pounds per Square inch: PSI  
Newtons per meter-squared:  Pascal  
kilo-pascal,  MPascal, 
Atmospheres.  
Bar = 100000  Pascal. 
Milimeters of mercury

?UnitConvert

UnitConvert[Quantity[1,"Bars"], "Pascals"]

UnitConvert[Quantity[1,"Atmospheres"], "Bars"]//N

UnitConvert[Quantity[1,"Atmospheres"], "PSI"]//N

UnitConvert[Quantity[1,"Atmospheres"], "MillimetersOfMercury"]//N

UnitConvert[Quantity[1,"Pascals"], "MillimetersOfMercury"]//N

UnitConvert[Quantity[1,"Pascals"], "Imperial"]//N

UnitConvert[Quantity[1,"Bars"], "newtons/cm^2"]

Often in  US a unit is used caled kg/cm^2.  This does not have the units of pressure,  but assumes gravity  g=9.8 m/sec^2. It is as if having a kg of weight on your thumb.