Heat Leak Results
Heat Transfer Area (A):
-
Overall UA:
-
Heat Leak (Q̇):
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Boil-Off Gas (BOG)
BOG Mass Rate:
-
BOG Volumetric Rate:
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Pressure Rise (Screening)
Vapor Space Volume:
-
Rate of Rise (dP/dt):
-
Time to Target P:
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Q̇ = UA · (T_amb − T_cry)
UA = 1 / (t/k + 1/(h_conv + h_rad)) · Area
ṁ_BOG = Q̇ / ΔH_vap
dP/dt ≈ (Z·R·T / V_vap) · (ṁ_BOG) [No Vent]
Technical Notes
Scope & Assumptions
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Screening Tool: Estimates steady-state heat leak
and BOG. Not for transient cooldown or rigorous safety relief
design.
-
Heat Path: Models series resistance (Insulation +
External Film). Inner wall resistance neglected.
-
Pressure Rise: Assumes "No Vent" scenario with
constant vapor temperature (ideal gas mass accumulation).
Variable Definitions
- Q̇: Total heat leak rate (W or Btu/h).
- UA: Overall thermal conductance (W/K).
-
Tamb / Tcry: Ambient and
stored liquid temperatures.
-
hout: External convection coefficient.
- ε: Surface emissivity for radiation.
Formulas
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Resistances: Rcond = t/k, Rext
= 1/(hconv + hrad).
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Radiation: Linearized hrad ≈ 4εσT³ (if
enabled).
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BOG: Derived from energy balance Q̇ = ṁ ·
ΔHvap.
-
Volume: Varies by geometry (Cylinder vs Sphere)
and liquid level.
References
- API 625 / 620 (Refrigerated Tank Storage).
- ISO 12241 (Thermal Insulation Rules).
- Ideal Gas Law (for screening pressure rise).
-
EN 14620 (Design & construction of refrigerated LNG tanks) –
general guidance context.
- NFPA 59A (LNG Facilities) – general safety/design context.
-
API 2000 / API 521 – venting/relief philosophy context (pressure
rise here is screening only).