New correlation to predict the onset of flow instability (OFI) heat flux of one-side heated hypervapotron channel for fusion reactor application

Park

2021

Eng. Res. Express

In order to stably operate the equipment inside the tokamak, which is loaded with a heat flux of several MW/m2 under the one-side heating condition, it is necessary to thoroughly prepare for various thermal engineering limits that may occur under the high heat flux load condition. In this study, we have experimentally explored critical heat flux (CHF) and onset of flow instability (OFI), which are considered potential threats in a DEMO fusion power plant. Specifically, the effect of system parameters on CHF was investigated. The results indicate that with an increase in subcooling and mass flux, the CHF increased, as it induced a faster bubble condensation near the CHF. As the system pressure increased, the CHF also increased. This is because the bubble size reduction effect was dominant in the pressure range of 1–10 bar. Most of the existing CHF correlations could evaluate the CHF with reasonable accuracy of within 25%; especially, the Boscary CHF correlation yielded the highest accuracy with an average error of 12%. Similar to CHF, OFI, which is a measure of the sudden fluctuations in the system pressure caused by a large amount of vapor generated due to the high heat flux, tended to increase as the subcooling, mass flow rate, and system pressure increased. Most of the existing OFI correlations yielded large error rates (more than 135%) as these correlations were primarily developed for micro-channels. Therefore, in this study, a new OFI correlation was developed using a Python code, in combination with an artificial intelligence (AI) regression method. The developed correlation can be used in the cooling system design of tokamaks, which involve a high-heat load condition on one-side of the reactor.

Section: Experimental Methods 21 Experimental Loopmentioning

confidence: 99%

Experimental study of thermal limits with one-side heated smooth channel for plasma facing component safety

Park

2021

Eng. Res. Express

“…Current flow in the loop was prevented through the installation of di-electric union fittings at the front and rear ends of the channel, with extra precautions taken through the grounding the electric wire of the pump. Detailed information on the selection of experimental equipment and loop design process can be found in previous reports [8,10,18,20]. Table 1 summarizes the experimental ranges and uncertainties of the primary equipment.…”

Section: Test Loopmentioning

confidence: 99%

“…Most previous thermo-hydraulic performance evaluation studies of screw tubes assessed CHF performance to determine whether the tube could withstand the ultra-high heat flux within a tokamak. However, the cooling system of a power plant operating under subcooled flow conditions is designed to function in an SP regime, as the vapor produced within a channel under a two-phase regime is a potential hazard in terms of flow instability [18], increased two-phase pressure drop [8,10], and CHF. Figure 2 shows the three flow regimes that occur inside a channel under the subcooled flow boiling and one-side heating conditions.…”

Section: Introductionmentioning

confidence: 99%

Study on onset of nucleate boiling with screw tube for fusion reactor application

Park

2022

Nucl. Fusion

Self Cite

The onset of nucleate boiling (ONB) is the point at which the heat transfer mechanism in fluids changes and is one of the thermo-hydraulic factors that must be considered when establishing a cooling system operation strategy. Because the high heat flux of several MW/m2, which is loaded within a tokamak, is applied under a one-side heating condition, it is necessary to determine a correlative relation that can predict ONB under special heating conditions. In this study, the ONB of a one-side-heated screw tube was experimentally analyzed via a subcooled flow boiling experiment. The helical nut structure of the screw tube flow path wall allows for improved heat transfer performance relative to smooth tubes, providing a screw tube with a 53.98% higher ONB than a smooth tube. The effects of the system parameters on the ONB heat flux were analyzed based on the changes in the heat transfer mechanism, with the results indicating that the flow rate and degree of subcooling are proportional to the ONB heat flux because increasing these factors improves the forced convection heat transfer and increases the condensation rate, respectively. However, it was observed that the liquid surface tension and latent heat decrease as the pressure increases, leading to a decrease in the ONB heat flux. An evaluation of the predictive performance of existing ONB correlations revealed that most have high error rates because they were developed based on ONB experiments on micro-channels or smooth tubes and not under one-side high heat load conditions. To address this, we used dimensional analysis based on Python code to develop new ONB correlations that reflect the influence of system parameters.

“…However, several engineering problems still have to be solved to generate electricity using fusion energy. Among them, a high heat flux of up to 20 MW m −2 loaded on the divertor [2] is a major threat to system damage in terms of thermal-hydraulics and materials. To * Author to whom any correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 99%

“…The purpose of this study is as follows: (1) to explore the OFI of a one-side-heated swirl tube through a subcooled flow-boiling experiment. (2) To analyze the effect of system parameters (inlet pressure, subcooling, mass flowrate) and twisted tape on the OFI heat flux.…”

Section: Introductionmentioning

confidence: 99%

Onset of flow instability with one-side heated swirl tube for fusion reactor safety

Lee

et al. 2021

Nucl. Fusion

Self Cite

In this study, the onset of flow instability (OFI) heat flux of a one-side heated swirl tube is experimentally investigated. The OFI heat flux means the minimum heat flux that can cause flow instability by the vapor generated in the flow path. An analysis of the effect of system parameters on the OFI heat flux indicates that as the pressure increases, the bubble size decreases. Therefore, the void fraction decreases and, consequently, the OFI heat flux tends to increase. Similarly, the higher the flow rate and degree of subcooling, the faster the vapor can be removed; thus, the OFI heat flux increases. In addition, the prediction performances of the existing OFI correlations developed under the subcooled flow-boiling condition are evaluated. Therefore, although the Wang correlation indicates the lowest error rate, it yields a high mean absolute error rate of 87.75%. Thus, it is difficult to predict the OFI heat flux of a one-side heated swirl tube using the existing OFI correlations. Therefore, in this study, a new correlation is developed using a Python code created by employing an artificial intelligence regression method. The developed correlation incorporates the impact of one-side heating, swirl tape, mass flow rate, subcooling, and pressure (mean absolute error = 12.17%, root mean square error = 14.99%).