Improved models for cryogenic fuel boiloff (MIT-LAE#29)

* better saturation fuel properties * better model for fuel venting * removed println from mission() * rewrote fuel calc in mission! for clarity * added mylar as insulation opt for vapor layers * simplified FFC calc in mission! * fixed bug geom vars not updated * increased font in tank diagrams * better saturation fuel properties * better model for fuel venting * better density and enthalpy of vap for cryo fuels * removed println from mission() * rewrote fuel calc in mission! for clarity * integrated new fuel_properties in read_input * better latent heat of vaporization in tank models * bug fix + new test for fuel_properties * accounted for mass of ullage gas in tank * updated tests after changing ullage calculation * updated docs to reflect new ullage method
askprash · May 3, 2024 · 02dca5a · 02dca5a
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diff --git a/docs/src/assets/cryo_tank.svg b/docs/src/assets/cryo_tank.svg
diff --git a/docs/src/assets/doublewalled_tank.svg b/docs/src/assets/doublewalled_tank.svg
diff --git a/docs/src/structures/fueltanks.md b/docs/src/structures/fueltanks.md
@@ -130,9 +130,9 @@ However, alternate fuels such as cryogenic liquid hydrogen require additional st
     ```
     where ``K=\frac{1}{6}(AR^2+2)`` is a factor that accounts for the ellipsoidal aspect ratio (``AR``). Once the wall thicknesses have been determined, the internal tank radius is given by ``R_{t,i}=R_{t,o}-t_{s,cyl} ``. The volume required for the fuel is 
     ```math
-        V_{fuel} = (1+f_{ull})\frac{m_{fuel}}{\rho},
+        V_{fuel} = \frac{m_{fuel}}{\rho_{mix}},
     ```
-    where ``f_{ull}>0`` is a factor to account for the fact that the tank must contain some empty volume to account for ullage. The internal volume of a hemiellipsoidal cap is given by 
+    where ``\rho_{mix} = f_{ull}\rho_g + (1-f_{ull})\rho_l`` is the density of the saturated mixture inside the tank, ``\rho_g`` and ``\rho_l`` are the densities of the fuel in saturated gas and liquid phases, and ``f_{ull}>0`` is a factor to account for the fact that the tank must contain some gas volume for ullage. The internal volume of a hemiellipsoidal cap is given by 
     ```math
         V_{cap} =  \frac{2πR_{t,i}^3}{3AR}.
     ```
@@ -143,7 +143,7 @@ However, alternate fuels such as cryogenic liquid hydrogen require additional st
     Once this length is known, the masses of the tank and insulation layers can be found from their respective volumes and densities. To support the tank, stiffener rings that go around the tank circumference are needed. It is assumed that the inner vessel contains two of these stiffeners, which are sized following the process below.
 
     #### Outer vessel
-    If the insulation layer contains a vacuum layer, an additional tank wall is needed to contain the vacuum. Unlike the inner vessel, this outer wall does not fail due to excessive stress, instead, it fails by buckling or collapse[^3]. To prevent buckling, stiffener rings can be used to reduce the effective cylindrical lenght that can collapse. The unsupported cylinder length is
+    If the insulation layer contains a vacuum layer, an additional tank wall is needed to contain the vacuum. Unlike the inner vessel, this outer wall does not fail due to excessive stress, instead, it fails by buckling or collapse[^3]. To prevent buckling, stiffener rings can be used to reduce the effective cylindrical length that can collapse. The unsupported cylinder length is
     ```math
         L =  \frac{l_{cyl}}{N_{stiff} -1},
     ```