Together with the Spiez Laboratory, the IEFE Fluid Engineering and Refrigeration Research Group has developed a new methodology for analysing the closing behaviour of explosion protection valves for protective structures. Spiez Laboratory is the Swiss centre of expertise for the protection of the population against chemical, biological, radiological and nuclear threats (CBRNe). The Spiez Laboratory also deals with the protection of people and facilities in protective structures such as civil defence facilities and bunkers. Here, explosion protection valves protect against pressure surges caused by explosions. To date, these safety valves have mainly been tested in experiments.

Precise investigation of two valve types

The new analysis method for explosion protection valves is now aimed at investigating the closing behaviour and the pressure loss of the valves using computer-aided simulation. In a first step, the research group evaluated a software solution that can simulate the behaviour of the valves under various conditions.

Two valve types (test cases) were analysed as part of the work. The first was a cylindrical explosion protection valve. It closes at overpressure by pressing the hemispherical steel element, which is held back by tension springs at normal pressure, into the seat and blocking the air flow. In the second type of valve, thin steel plates are bending (elastic deformation) in case of overpressure and thus prevent the flow.

Experiments and high-speed recordings

The function of both valve types was tested experimentally in the Spiez laboratory using the shock wave tube, a helium-filled tube with a membrane and the valve. The helium in the tube was compressed until the membrane burst and triggered a pressure wave (a so-called shock front), which blocked the air flow through the safety valve. Closing a valve takes around 1.6 milliseconds. During this process, the researchers measured the residual pressure after the valve to see how well it damped the pressure wave. The process was also photographed with a high-speed camera (one image every 0.1 ms) and documented.

Direct or indirect coupling of the simulations?

The researchers then simulated the test setup and the complex closing mechanisms of the explosion protection valves using a directly coupled simulation, in which the flow calculation and the mechanical calculation interact with each other after each time step. They compared this with an indirectly coupled simulation, which simulates the different physical phenomena separately and combines the results later. The directly coupled simulation is demanding. However, it makes it possible to model the behaviour of very complex systems, such as the deformation of the second valve type.

Simulation models safety valves well

The comparison of the experimental measurements with the results of the simulation shows that the directly coupled simulation enables significantly more precise predictions of the complex closing mechanisms of the safety valves than if an indirectly coupled simulation is used.

Based on the results of the project, the research team from the ZHAW and the Spiez Laboratory concluded that the newly developed computer-aided simulation is a good method for developing or analysing new valves. Thanks to the simulation and the images from the high-speed camera, the closing behaviour of the valves can be numerically and visually validated and thus better understood. Further studies on the material behaviour of the valves are now required.

Industry also supports the project

Thanks go to Michael Riedo and Michel Schilling from Andair AG as lead partners in an earlier research project that provided the basis for this work. In that study, an evaluation and optimisation procedure for passive explosion protection valves was developed, which ultimately led to a completely new generation of valves.

Project name
Numerical procedure to determine the performance and structural response of passive shock wave safety valves under blast loading

Project duration             May 2020 till December 2023

Participants
Project manager:             Christian Jenni, ZHAW-IEFE
Co-workers ZHAW:          Tim Altorfer, David Denzler, Sven Düzel (IMPE), Mirco Ganz, Frank Tillenkamp
Project partner:                Labor Spiez: Lorenz Brenner, André Zahnd
Industry partner:              Andair AG: Michael Riedo, Michel Schilling

Technical article in the International Journal of Protective Structures:
https://journals.sagepub.com/doi/10.1177/20414196231197702