3D-modeling of swing check valve with connection to dynamic behavior used in system studies

Abstract

This Master’s Thesis is the result of the collaboration between The Technical Faculty of Lund University
and TÜV NORD Sweden AB. Focus has been directed towards the nuclear industry where this thesis is one of several other Master’s Theses regarding the dynamic modeling of a swing check valve.

It is necessary for the nuclear industry to be able to model flow transients which involve the dynamic behaviour of the swing check valve. The modeling is commonly executed by one-dimensional codes such as RELAP5, DRAKO and DYVRO. This work has applied the swing check valve theory by (Li and Liou, 2003) in order to retrieve results from three-dimensional modeling using computational fluid dynamics (CFD) to derive useful correlations for one-dimensional code implementation.

The accuracy of the CFD-model has been investigated by comparing results of interest after changing the modeling set-up in the CFD-software ANSYS FLUENT. The impact of cell density, solver dependence and choice of turbulence model are a couple of interesting preferences which have been investigated in a sensitivity analysis. The simulations are constructed to yield results for useful parameters for the swing check valve theory.

Results from CFD-simulations give resembling results compared to the experiments by (Li and Liou, 2003). One particular correlation was found regarding the coupling of the coefficients in the theory of (Li and Liou, 2003) and was implemented in RELAP5. Through this work conclusions has been made that the implementation of a general one-dimensional model based on the theory of (Li and Liou, 2003) will be complex due to coefficient dependence.

Popular Abstract

The importance of swing check valve modeling

The nuclear industry is putting a great deal of effort to master the modeling of pipe systems. The swing check valve is a common system component and the closing procedure of the valve can cause dangerous magnitudes in pressure rise.

The Swing Check Valve
It is of great importance in the nuclear industry to be able to model flow transients to determine hydraulic loads within various pipe systems. The hydraulic loads will result in stresses which can cause severe damages on pipe systems or on single components. To ensure the highest possible safety, flow transients within pipe systems are modeled to ensure that the system can withstand and cope with these loads. The hydraulic loads initially starts to propagate due to change in pressure within the system. Pressure changes can occur due to pump stops or valve operation. The figure below presents a closing scenario where water hammer is induced due to closing of a regular valve.

Back flow can be prevented or greatly reduced by a check valve. Check valves are often used in nuclear power plant applications, mainly due to design features, size variation, and economy. Check valves are one of few valves models that can operate without external control. A swing check valve commonly consists of a disc connected to a hinge pin inside the valve housing. The most basic function of a check valve is to allow throughflow in one direction and prevent in the opposite. This property is valuable when reversed flow is undesirable and must be minimized.

The modeling is commonly executed by one-dimensional codes such as RELAP5 and DRAKO. This work has used the swing check valve theory by G.Li and J.C.P. Liou in order to retrieve results from three-dimensional modeling using computational fluid dynamics (CFD) to derive useful correlations for one-dimensional code implementation

It is not suitable to simulate large pipe systems with CFD since it would most likely be too time consuming and inconvenient. That is why single components can be CFD-modeled and implemented as one-dimensional components in a larger system which can be modeled many times faster and still give accurate results, useful for constructing large systems.

CFD-simulations

The simulations in ANSYS FLUENT included both stationary cases with a fixed valve disc and transient cases where the valve disc was implemented as a dynamic zone which was allowed to move with the flow. The need of both stationary and transient simulations is due to the swing check valve theory of Li and Liou which states that the hydraulic can be divided into two components, one stationary and one rotational.

T_H = T_HS + T_HR

CFD-simulations in ANSYS FLUENT was necessary since it was not possible to set up and construct physical experiments like the authors behind the theory did. The results from CFD was compiled in order to visualize how the valve acts according to changes of flow which was set up to simulate real system pump stops, which is a common cause for back flow ion the industry.

Useable results?

Simulations in CFD gave all important parameters used in the theory of Li and Liou. Hence, it can be stated that CFD is a useful and powerful simulation tool for valve simulation. However, the implementation of a general and useful one-dimensional valve model was a difficult task, especially due to important coefficient correlations in the theory. The comparison between the closing time of the valve from CFD and one-dimensional implementation in RELAP5 showed differences for all investigated pump stops. It is troublesome to give an exact explanation for this inconsequent behavior.

The CFD-model can be used for further simulations where more correlations can be investigated, especially for transient cases which probably holds the keys for a successful crossing between the three-dimensional- and one dimensional world.

References

Li. G and J.C.P Liou. Swing Check Valve Characteristics and Modeling During Transients. Journal of Fluids Engineering,125(10):1043-1050, 2003

• author: Björk, Christoffer
• supervisor: Johan Revstedt; Faruk Selimovic
• organization: Department of Energy Sciences
• course: MVK920 20151
• year: 2015
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Swing check valve, fluid mechanics, pressure surge, waterhammer, Fluent
• report number: ISRN LUTMDN/TMHP-15/5337-SE
• ISSN: 0282-1990
• language: English
• id: 5471168
• date added to LUP: 2015-06-10 15:45:41
• date last changed: 2015-06-10 15:45:41