Cryogenic Liquid Boil-Off Rate Calculator
Cryogenic process engineering: Compute boil-off mass rate ($\dot{m}_{boil}$), daily volumetric loss, percentage boil-off rate (%BOR), and dewar holding time across liquid $He, N_2, H_2, CH_4$, and $O_2$.
Cryogen & Vessel Specifications
Boil-Off Loss & Holding Time
Volumetric Boil-Off Rate
--
liters / day
Percentage Boil-Off (%BOR)
--
% of inventory lost per day
Mass Boil-Off Rate
--
kg / day
Vessel Holding Time
--
days to complete dry-out
Initial Cryogen Mass
--
kg in tank
STP Gas Generation
--
$\text{Nm}^3$ / day (expanded gas)
Dewar Inventory Depletion Over Time
Liquid level drops linearly assuming constant heat in-leak. Liquid helium is particularly vulnerable due to its exceptionally small latent heat of vaporization (20.9 kJ/kg).
Thermodynamic Boil-Off Governing Equations
In steady state, heat leaking through the dewar vacuum jacket, structural supports, and neck piping vaporizes cryogenic liquid at its normal boiling point:
$$\dot{m}_{boil} = \frac{\dot{Q}_{leak}}{\Delta H_{vap} + \eta_{sh} \int_{T_{sat}}^{T_{amb}} C_p(T) dT}$$
$$\%\text{BOR} = \frac{\dot{m}_{boil} \times 24 \times 3600}{M_{\text{inventory}}} \times 100\%$$
For Liquid Helium ($LHe$), sensible heat capacity of the rising cold vapor ($C_p \approx 5.2 \text{ kJ}/(\text{kg}\cdot\text{K})$) is over 70 times larger than latent heat of vaporization! Utilizing vapor-cooled radiation shields dramatically reduces boil-off.
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