Experimental and Theoretical Study of Oscillatory Two-Phase Flows with Heat and Mass Transfer

Open Access
- Author:
- Beck, Faith Rose
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 14, 2018
- Committee Members:
- Fan-Bill B Cheung, Dissertation Advisor/Co-Advisor
Fan-Bill B Cheung, Committee Chair/Co-Chair
Rui Ni, Committee Member
Susan E Trolier-Mckinstry, Committee Member
Diane Marie Henderson, Outside Member
Horacio Perez-Blanco, Special Member
Gita Talmage, Special Member
Steven M. Bajorek, Outside Member - Keywords:
- oscillatory reflood
liquid carryover
stability analysis
heat and mass transfer
thermal-hydraulics
liquid entrainment - Abstract:
- This dissertation presents experimental and theoretical analyses of oscillatory two- phase flows with heat and mass transfer on liquid carryover behavior during reflood of a simulated nuclear reactor core. In a hypothetical large break loss of coolant accident (LBLOCA), associated with a break in one of the hot- or cold-legs, the emergency core cooling system (ECCS) must provide sufficient coolant to the core to remove decay heat and prevent the cladding from exceeding 1477.6 K. During reflood, flow to the core is gravity-driven, resulting in an oscillatory delivery of coolant. These oscillations have been attributed to vapor generation in the core and a dynamic response of the downcomer water level. Nearly all reflood simulation experiments have been conducted with constant reflood rates, and have not considered the effect of oscillations on rod bundle thermal-hydraulics. The few studies that have been conducted with oscillating flow indicated enhanced entrainment and carryover of liquid from the quench front. While higher entrainment can provide precursory cooling ahead of the quench front, it can also expel more coolant out of the system during oscillatory reflood. The amount of liquid entrained can be significant because, in an accident scenario, the quench rate will be slowed, and it can take longer to fully recover the core. At the Nuclear Regulatory Commission (NRC)/Penn State University (PSU) Rod Bundle Heat Transfer (RBHT) Test Facility, an electrically heated 7×7, 3.66 m (full-length) rod bundle array has the capability of performing both constant and oscillatory forced flooding rate experiments. The facility is heavily instrumented, equipped with seven spacer grids with which to analyze droplet and heat transfer phenomena. The system can vary the oscillation period (2 to 10 s), magnitude (±0.0254 to 0.0762 m/s), system pressure (0.14 to 0.41 MPa), and subcooling (5 to 55 °C) in order to study the entrained droplet dynamics and heat transfer under constant and oscillatory flow conditions. This dissertation includes the analysis of forced oscillatory reflood experiments, which concentrate on the effects of flow (frequency, magnitude, and nominal flooding rate) and system parameters (pressure, subcooling, and bundle fouling) on heat transfer and entrained droplet dynamics. Major findings from the experimental work include: 1) decreasing the oscillation period decreases the peak cladding temperature and the steam temperatures, as well as enhances the liquid carryover when compared with constant reflood experiments; 2) decreasing the system pres- sure enhances the effect of flow oscillations; and 3) the presence of bundle fouling improves cooling and decreases the amount of liquid carryover. To the author’s knowledge, experiments with the parameters varied in this work, coupled with the rod bundle geometry, have not been explored previously. This dissertation utilizes the unique dataset collected at the NRC/PSU RBHT to perform a stability analysis of oscillatory two-phase flows. The governing equations established for this flow incorporate Floquet and viscous-potential flow theories. From the analysis, it is found that the stability at the two-phase interface is highly dependent on the flow orientation and heat transfer to the system. In addition, a correlation is developed for the liquid carryover that uses parameters derived from the stability analysis to predict the carryover during oscillatory reflood. The correlation is the first of its kind to include the effects of a moving quench front on the liquid carryover. The carryover model is validated using NRC/PSU RBHT data, as well as other relevant rod bundle data, and the NRC’s TRACE code.