Helical Coil Steam Generator Test Loop

The helical coil steam generator is a specific type of Tube and Shell Heat Exchanger known for having a higher heat transfer coefficient than many other designs.

We have designed, constructed, and operated three test facilities with main focus on the shell side flow for a specific design of the helical coil steam generator. The three facilities include:

one-to-one curved single interface between bundles,
one-to-one curved five bundle test section and
one-to-one straight five bundle test section.

Studies focus on the effect the complex geometry plays on flow properties. The state of the art facilities use refractive index matching Particle Image Velocimetry (PIV), Laser Doppler Anenometry (LDA), and Hot Film Anenometry, to study the cross-flow behavior of the fluid between bundles.

Pressure measurements across the bundles are also conducted to compare the effect that the different geometry has on current tube and shell pressure drop correlations. Dynamic Pressure Transducers and Pressure Sensitive Paint (PSP) are also used to study the change in pressure around the surface of the individual rods within a bundle.

Experimental Studies

Flow Visualization Studies

Particle Image Velocimetry (PIV) was utilized to study the fluid structures that form in the shell-side of the novel heat exchanger design. The area below the tubes is of particular interest due to the formation of recirculation, or eddies, that form and shed – a phenomena known as vortex shedding. The development and movement of these structures specifically related to the unique geometric configurations was studied. The following videos show the streamline plots and the velocity magnitude of the flow within the center of the test section.

Flow Induced Vibration Studies

Results from the flow visualization studies showed that complex fluid structures form around the tubes within the shell-side of the heat exchanger geometry. This led to a study on the effect that the vortex shedding had on the potential motion of the tubes. Previously rigid tubes were allowed to vibrate under flow when vibration dampening springs were attached to the ends. Visualization modules allowed a high speed camera to capture the motion of the tubes The following videos show the vibration response of a single tube from the center of the tube bundle, and the vibration response for adjacent tubes.

Computational Fluid Dynamics (CFD) Simulations

The laboratory has conducted simulations of helical coil steam generator (HCSG) to further investigate the flow in these components using with large eddy simulation (LES) methods. Open-source, high-order spectral element CFD code Nek5000 is largely utilized in the laboratory. Special analysis techniques (Spectral analysis and wavelet analysis) are conducted to extract important information of the flow behavior. Validation of Nek5000 model was performed using the experimental results obtained from the test sections operated in the laboratory.

References

1) Mustafa Alper Yildiz, Haomin Yuan, et al. (2020). “Numerical Simulation of Isothermal Flow Across Slant Five-Tube Bundle with Spectral Element Method Code Nek5000”. Nuclear Technology 206 ,pp. 296–306.

2) Mustafa Alper Yildiz, Elia Merzari, and Yassin Hassan (2019). “Spectral and Modal Analysis of the Flow in a Helical Coil Steam Generator Experiment with Large Eddy Simulation”. International Journal of Heat and Fluid Flow, 2019, 80.108486,pp. 1–16.