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A Multi-Zone Model for Hydrogen Accumulation and ventilation in Enclosures

Runefors, Marcus LU orcid and Johansson, Nils LU orcid (2023) Tenth International Conference on Hydrogen Safety
Abstract
Due to the small characteristic molecular size of hydrogen, small leaks are more common in hydrogen systems compared to similar systems with hydrocarbons. This, together with the high reactivity, makes an efficient ventilation system very important in hydrogen applications. There are several models available for ventilation sizing that are based on either a well-mixed assumption or a fully stratified situation. However, experiments show that many realistic releases will be neither, and therefore additional models are needed. One possibility is to use CFD-models, but the small release sizes for pinhole releases (<<1 mm) make it difficult to find an appropriate mesh without excessive computational time (especially since the simulations... (More)
Due to the small characteristic molecular size of hydrogen, small leaks are more common in hydrogen systems compared to similar systems with hydrocarbons. This, together with the high reactivity, makes an efficient ventilation system very important in hydrogen applications. There are several models available for ventilation sizing that are based on either a well-mixed assumption or a fully stratified situation. However, experiments show that many realistic releases will be neither, and therefore additional models are needed. One possibility is to use CFD-models, but the small release sizes for pinhole releases (<<1 mm) make it difficult to find an appropriate mesh without excessive computational time (especially since the simulations need to be iterated to find the optimum ventilation size). An alternative approach, which is described and benchmarked in the current paper, is to use a multi-zone model where the domain is divided into several large cells where the mass exchange is simplified compared to CFD, and thus simulation time is reduced. The flow in the model is governed by mass conservation and density differences, due to concentration gradients, using the Bernoulli equation. The release of gas generates a plume which is modelled based on an empirical plume model which gives the entrainment and hydrogen source term for each cell. The model has a short run time and will therefore allow optimization in a short time frame. The model is benchmarked against five experiments with helium at the Canadian Nuclear Laboratories (CNL) in Canada and one hydrogen experiment performed at Lodz University of Technology in Poland. The result shows that the model can reasonably well reproduce accumulation in the experiments with small release without ventilation, but appears to slightly underestimate the level of stratification and the interface height for ventilated cases where the source is elevated from the floor level. (Less)
Abstract (Swedish)
Due to the small characteristic molecular size of hydrogen, small leaks are more common in hydrogen systems compared to similar systems with hydrocarbons. This, together with the high reactivity, makes an efficient ventilation system very important in hydrogen applications. There are several models available for ventilation sizing that are based on either a well-mixed assumption or a fully stratified situation. However, experiments show that many realistic releases will be neither, and therefore additional models are needed. One possibility is to use CFD-models, but the small release sizes for pinhole releases (<<1 mm) make it difficult to find an appropriate mesh without excessive computational time (especially since the simulations... (More)
Due to the small characteristic molecular size of hydrogen, small leaks are more common in hydrogen systems compared to similar systems with hydrocarbons. This, together with the high reactivity, makes an efficient ventilation system very important in hydrogen applications. There are several models available for ventilation sizing that are based on either a well-mixed assumption or a fully stratified situation. However, experiments show that many realistic releases will be neither, and therefore additional models are needed. One possibility is to use CFD-models, but the small release sizes for pinhole releases (<<1 mm) make it difficult to find an appropriate mesh without excessive computational time (especially since the simulations need to be iterated to find the optimum ventilation size). An alternative approach, which is described and benchmarked in the current paper, is to use a multi-zone model where the domain is divided into several large cells where the mass exchange is simplified compared to CFD, and thus simulation time is reduced. The flow in the model is governed by mass
conservation and density differences, due to concentration gradients, using the Bernoulli equation. The release of gas generates a plume which is modelled based on an empirical plume model which gives the entrainment and hydrogen source term for each cell. The model has a short run time and will therefore allow optimization in a short time frame. The model is benchmarked against five experiments with helium at the Canadian Nuclear Laboratories (CNL) in Canada and one hydrogen experiment performed at Lodz University of Technology in Poland. The result shows that the model can reasonably well reproduce accumulation in the experiments with small release without ventilation, but appears to slightly underestimate the level of stratification and the interface height for ventilated cases where the source is
elevated from the floor level.

The software presented in this paper is freely available at: https://doi.org/10.5281/zenodo.8037661 (Less)
Please use this url to cite or link to this publication:
author
and
organization
publishing date
type
Contribution to conference
publication status
published
subject
keywords
confinement, stratification, ventilation flow
pages
11 pages
conference name
Tenth International Conference on Hydrogen Safety
conference location
Québec City, Canada
conference dates
2023-09-19 - 2023-09-21
language
English
LU publication?
yes
id
1f5c7e46-0a44-4dd3-b777-8dbefe425f26
date added to LUP
2024-02-20 12:26:49
date last changed
2024-03-13 11:36:48
@misc{1f5c7e46-0a44-4dd3-b777-8dbefe425f26,
  abstract     = {{Due to the small characteristic molecular size of hydrogen, small leaks are more common in hydrogen systems compared to similar systems with hydrocarbons. This, together with the high reactivity, makes an efficient ventilation system very important in hydrogen applications. There are several models available for ventilation sizing that are based on either a well-mixed assumption or a fully stratified situation. However, experiments show that many realistic releases will be neither, and therefore additional models are needed. One possibility is to use CFD-models, but the small release sizes for pinhole releases (&lt;&lt;1 mm) make it difficult to find an appropriate mesh without excessive computational time (especially since the simulations need to be iterated to find the optimum ventilation size). An alternative approach, which is described and benchmarked in the current paper, is to use a multi-zone model where the domain is divided into several large cells where the mass exchange is simplified compared to CFD, and thus simulation time is reduced. The flow in the model is governed by mass conservation and density differences, due to concentration gradients, using the Bernoulli equation. The release of gas generates a plume which is modelled based on an empirical plume model which gives the entrainment and hydrogen source term for each cell. The model has a short run time and will therefore allow optimization in a short time frame. The model is benchmarked against five experiments with helium at the Canadian Nuclear Laboratories (CNL) in Canada and one hydrogen experiment performed at Lodz University of Technology in Poland. The result shows that the model can reasonably well reproduce accumulation in the experiments with small release without ventilation, but appears to slightly underestimate the level of stratification and the interface height for ventilated cases where the source is elevated from the floor level.}},
  author       = {{Runefors, Marcus and Johansson, Nils}},
  keywords     = {{confinement; stratification; ventilation flow}},
  language     = {{eng}},
  month        = {{09}},
  title        = {{A Multi-Zone Model for Hydrogen Accumulation and ventilation in Enclosures}},
  url          = {{https://lup.lub.lu.se/search/files/173689766/Runefors_et_al_-_Multi-zone_hydrogen.pdf}},
  year         = {{2023}},
}