Simulating safe extraction of harmful gases in laboratories to save 200 tons annually of CO2 equivalent emissions per year

Protecting humans and the environment

Fume cupboards are essential for laboratories that generate airborne hazardous substances during experiments, processes and scale-up. They are designed to capture and remove gases, vapors and aerosols to reduce the risk of exposure to a safe level.

In the 30 years that Clean Air Limited (Clean Air) has been designing, manufacturing and installing fume cupboards, protecting people has always been its priority. One of Clean Air’s unique selling points is its commitment to lead the fume cupboard industry in environmental safety and sustainability.

Sulfur hexafluoride (SF₆) is used to prove the effectiveness of a fume cupboard during testing, but it has been identified as the most damaging greenhouse gas. The equivalent of approximately three tons of carbon dioxide (CO₂) is released during type testing, and another ton is released during onsite testing. Most fume cupboards are tested with the on site test, so roughly 1t CO₂e per cupboard then 3t per ‘type’ of fume cupboard.

An obvious solution would be to use a safer gas for testing, but none have proven to be as effective as SF₆. It is a heavy gas so it can be detected down to levels of parts per billion – far better than any other known gas for this use.

Instead, Clean Air has developed a new process that replaces design testing with computational fluid dynamics (CFD) simulation, ensuring that performance and safety is guaranteed without impacting the environment.

Clean Air used Siemens Digital Industries Software’s Simcenter™ STAR-CCM+™ software and worked with Siemens partner Maya HTT to build a digital twin of the fume cupboard. Simcenter is part of the Siemens Xcelerator portfolio of software, hardware and services and is designed to help enable digital transformation.

Replacing harmful gas with simulation

Instead of physical tests, the new process performs static, clearance and dynamic design tests digitally using a range of dynamic meshing techniques and passive scalars to represent contaminated gas. To validate lab tests, Clean Air has also built its own bespoke array of anemometers to measure airflow and perform tests onsite.

The purpose of the static test is to understand how the fume cupboard performs in a normal operating condition. To do this, Clean Air imports a computer-aided design (CAD) model into Simcenter STAR-CCM+ and runs a transient simulation that shows the typical air flow of the fume cupboard to confirm it would extract gas in the expected way. This enables the calculation of the average face velocity – the speed at which the air enters the extraction opening. Typically, this should be between 60 and 100 feet per minute (FPM) although some applications have different requirements. Using Simcenter STAR-CCM+ allows engineers to easily make changes to boundary conditions to adjust the design until they reach the desired face velocity. This test uses passive scalars to contaminate the fume cupboard to 100 percent – more than can be done with physical testing – and check if any gas is escaping.

Dr. Andy Manning, manager of research and development (R&D), explains this makes testing far more accurate than previously possible. “Our Simcenter STAR-CCM+ simulations for static and dynamic testing have been published in a peer review journal and proven to be three times more accurate than physical testing with sulfur hexafluoride,” he says.

The clearance test assesses how well the fume cupboard is purged. The simulation calculates how quickly gas is replaced by fresh air. It also measures how long it takes to remove 99.99 percent of the contaminated air to ensure extraction fans remain on for long enough once the fume cupboard is switched off.

The dynamic test measures how the fume cupboard contains gas when the external air is disturbed. This simulates equipment moving past the cupboard and calculates how this will cause air to leave the fume cupboard.

Once the fume cupboard is installed onsite, engineers conduct further testing to ensure it matches up with the simulated results.

Scaling reductions in emissions, costs and time

When developing a fume cupboard, each design iteration must be tested to assess its performance, releasing harmful SF6 each time. By replacing SF₆ testing with CFD simulation, Manning estimates that Clean Air reduces its environmental impact by approximately 200 tons of CO₂ equivalent per year.

Additionally, the company has saved significant time and money by reducing the number of prototypes that are built, speeding up the design process. “Using Simcenter STAR-CCM+ gives us much better optimization than the tools we used previously,” says Manning. “I can take a new geometry, place it into my model and the rest of the parameters stay consistent. This means that it takes just one hour for the preparation and post-processing rather than half a day.”

The collaboration with Maya HTT was a vital part of developing the new testing procedures as Manning was able to call on their expertise throughout the project. “Working with Maya HTT shortened the learning curve significantly,” he says. “They helped us develop testing templates and streamline our results analysis with Simcenter STAR-CCM+. They were always on hand when we needed them and have saved us several days of work by optimizing our processes.”

Average Face Velocity (velocity in m/s over time [s]).

Velocity Magnitude [m/s].

Regulatory approval and enhanced simulation

Manning is working with national and international organizations to see if the Clean Air CFD tests can receive regulatory approval, which could revolutionize the industry globally.

He is also continuing to collaborate with Maya HTT to get even more value from CFD simulation. “Together with Maya HTT we’re investigating the use of reduced order modeling to speed up design and help us improve our products,” he says. “We’re also aiming to simulate fume cupboards with objects inside. This will show how equipment inside the cupboard affects airflow and purging to further enhance safety when it is in use.”

Contamination within the fume cupboard
(% of contamination over time [s]).

Contamination Field Plot [%].