Abstract
Recent studies have shown that the presence of dissolved salts in water can exhibit peculiar flow boiling and two-phase flow regimes. Two-phase flow and convective flow boiling are typically characterized with the help of void fraction measurements. To quantitatively improve our understanding of two-phase flow and boiling phenomenon with seawater coolant, void fraction data are needed, which can not be obtained from optical imaging. In this paper, we present experimental void fraction measurements of saturated flow boiling of tap water and seawater using X-ray radiography. X-rays with a maximum energy level of 40 KeV were used for imaging the exit region of the heated test section. At lower heat flux levels, the two phase flow in seawater was bubbly and homogeneous in nature, resulting in higher void fractions as compared to tap water. With an increase in heat flux, the flow regime was similar to slug flow, and void fraction measurements approached similarity with tap water. The predicted pressure drop using the measured void faction shows good agreement with the measured total pressure drop across the test section, demonstrating the validity of the measurement process.
Highlights
In loss of coolant accidents, it is sometimes necessary for reactor cores to be flooded with raw water or seawater from adjacent large bodies of water [1,2]
This paper presents the findings from void fraction measurements during flow boiling in an annular test section and comparisons are presented between seawater and tap water
Initial tests were conducted with tap water and the same set of experiments with the same power levels were repeated with seawater, allowing the system to stay at quasi-steady state for three hours
Summary
In loss of coolant accidents, it is sometimes necessary for reactor cores to be flooded with raw water or seawater from adjacent large bodies of water [1,2]. Understanding the influence of raw water emergency injection on the ability to maintain long-term core cooling is critical for safety analysis. While there have been fundamental investigations aimed at developing our understanding of salt crystallization or deposition under boiling, the more practical scenarios for understanding the effect of crystallization or deposition fouling on heat transfer have involved empirical studies on a large scale. To fully understand and correlate the mutually-coupled role of dissolved salts and heat transfer on the overall scale formation—which in turn affects the coolability— carefully-controlled experiments with high-fidelity data on flow boiling and two-phase flow are needed. This paper presents the findings from void fraction measurements during flow boiling in an annular test section and comparisons are presented between seawater and tap water
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