What Is the Cryogenic Boil-Off Rate & Pressurization Calculator?
Cryogenic boil-off analysis predicts the rate at which liquefied gases vaporize under ambient heat ingress, establishing dewar autonomy and venting requirements.
When valves are closed during transport or emergency isolation, boil-off vapor rapidly pressurizes the vessel headspace (ullage), requiring burst disc protection.
How Does the Cryogenic Boil-Off Rate & Pressurization Calculator Work?
Heat crossing the thermal barrier is absorbed exclusively by the latent heat of vaporization at constant boiling pressure.
The generated vapor expands hundreds of times in volume compared to the liquid, requiring adequate relief capacity.
Cryogenic Boil-Off Rate & Pressurization Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
Relates thermal heat flux directly to mass boil-off through latent heat of vaporization, converting to volumetric loss and ullage pressure growth.
How to Use the Cryogenic Boil-Off Rate & Pressurization Calculator
- Enter the estimated heat leak (from MLI calculation) and cryogen thermodynamic properties.
- Specify vessel capacity and headspace volume to compute daily evaporation losses and pressurization.
Step-by-Step Example Calculation
100-Liter Liquid Nitrogen Storage Dewar
Input Values:
Understanding Your Result
Daily boil-off rate (L/day and %/day) indicates storage efficiency.
Pressurization rate (kPa/hr) defines how quickly pressure relief valves will actuate if isolated.
Factors That Affect the Result
- Latent heat of vaporization: Liquid helium has extremely low latent heat (20.9 kJ/kg) and boils off ~10x faster per Watt than liquid nitrogen.
- Headspace volume: Smaller ullage spaces experience much faster pressure build-up.
When Should You Use This Calculator?
- Sizing vent valves and burst discs for cryogenic shipping dewars.
- Auditing helium consumption and recovery economics in MRI and quantum computing laboratories.
Assumptions & Limitations
- Assumes saturated thermodynamic equilibrium without thermal stratification in the liquid column.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Matches thermodynamic steady-state evaporation within ±3%.