Vibration Excitation Force Measurements in a Rotated Triangular Tube Bundle Subjected to Two-Phase Cross Flow

Abstract

Two-phase cross flow exists in many shell-and-tube heat exchangers. Flow-induced vibration excitation forces can cause tube motion that will result in long-term fretting-wear or fatigue. Detailed vibration excitation force measurements in tube bundles subjected to two-phase cross flow are required to understand the underlying vibration excitation mechanisms. An experimental program was undertaken with a rotated-triangular array of cylinders subjected to air/water flow to simulate two-phase mixtures over a broad range of void fraction and mass fluxes. Both the dynamic lift and drag forces were measured with strain gage instrumented cylinders. The experiments revealed somewhat unexpected but significant quasi-periodic forces in both the drag and lift directions. The periodic forces appeared well correlated along the cylinder with the drag force somewhat better correlated than the lift forces. The periodic forces are also dependent on the position of the cylinder within the bundle.

Thermal hydraulic considerations of nuclear reactor systems: Past, present and future challenges

“…The occurrence of these phenomena depends on the flow regime, which is associated with physical properties of fluids, inlet flow conditions, local void fraction, and flow channel geometries. Cross flow two-phase FIV exists in shell-and-tube heat exchangers (Mitra et al, 2009;Sasakawa et al, 2005;Zhang et al, 2007;Kanizawa et al, 2012) and U-tube region in PWR steam generators (Pettigrew et al, 1998). With regards to internal two-phase FIV, flow turning elements are considered as one of the major sources for causing FIV by generating sudden change in momentum flux, pressure fields, or creating secondary vortices due to boundary layer separation (Belfroid et al, 2010;Cargnelutti et al, 2010;Pontaza and Menon, 2011;Yamano et al, 2011).…”

Two-phase flow induced vibration in piping systems

“…Two-phase FIV on cross flow exists in shell-and-tube heat exchangers (Kanizawa et al, 2012;Khushnood et al, 2004;Mitra et al, 2009;Nakamura et al, 1986Nakamura et al, , 1992Pettigrew and Knowles, 1997;Sasakawa et al, 2005;Zhang et al, 2007), U-tube region in the pressurized water reactor (PWR) steam generators (Pettigrew et al, 1998), and offshore structures (JSME, 2003). Cross flow generally involves either isolated cylinder or bundles of cylinders.…”

Experimental assessment of equivalent loads and dynamic parameters on vibration induced by two-phase crossflow in tube bundles

“…Conversely, only few experimental data for turbulence-induced vibration mechanism under conditions twophase flow are available, which is somehow surprising since this vibration mechanism is unavoidable, and is always present in heat exchanger tube bundles. Actually, more recent experimental studies (ZHANG et al, 2007;PERROT et al, 2011) have shown that there is a lack of knowledge in this mechanism since they found out that it consists of turbulence and periodic components, which have not been reported in literature before.…”

“…Despite the difficulties, several methodologies to measure flow -induced forces in tube bundles have been proposed. For example, Zhang et al (2007) measured dynamic forces on both directions, transverse and parallel to flow main velocity, via strain gauge instrumented cylinders. In order to do that, the instrumented tubes were designed so that the fundamental natural frequency was higher than 150 Hz, which is considerably higher than both the expected force frequencies to be analyzed and the range of tube resonance frequencies in real heat exchangers.…”

“…Despite this, in most cases flow-induced forces imply distributed forces and the instrumentation up-to-date can hardly estimate its characteristics directly (say frequency components and amplitude), unless a set of hypotheses is adopted. For this reason, and for the sake of easiness, some authors (ZHANG et al, 2007;PERROT et al, 2011) prefer the estimation of an equivalent force that is capable of representing a set of forces under some hypotheses.…”