Experimental study of hypervapotron channel with square fin structure for divertor cooling by one-side, electric joule heating system

2021

Eng. Res. Express

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The heat removal capacity of a flat heat sink was studied using subcooled flow boiling experiments, to address the thermal peaking problem. Based on the Bowring criteria, the boiling curve is divided into a partially developed nucleate boiling regime (PDB) and fully developed nucleate boiling regime (FDB), and the existing heat transfer correlations for each flow regime are evaluated. In the PDB regime, the Baburajan correlation exhibited the highest prediction rate with an average error rate of 10.92%; however, the FDB regime heat transfer correlations exhibited high error rates at very high heat flux conditions. Therefore, the authors developed a new FDB correlation using the artificial intelligence technique by correlating the bubble agitation effect, which is a mechanism of the FDB regime, and then, evaluated the qualification assessment on this basis. The mono-block plasma-facing component with a flat heat sink was found to meet all criteria (except #1.2, shutdown plasma ratcheting), and to succeed in the actual fabrication.

Section: Experimental Methods 21 Experimental Facilitiesmentioning

confidence: 99%

A numerical-experimental analysis of qualification assessment for mono-block plasma-facing component with flat heat sink

2021

Eng. Res. Express

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“…Therefore, in this part, by cooling the amount of heat loaded in the test-section, the thermal steady state can be maintained in the closed loop. Further details on the selection of experimental equipment and design of the experimental loop can be found in our previous studies [23][24][25][26], and the experimental range of and the uncertainty of the measured variables in this study can be found in table 2.…”

Section: Experimental Methods 21 Experimental Loopmentioning

confidence: 99%

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

2021

Eng. Res. Express

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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.

“…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%

“…Additionally, an AlN plate with a very low HTC was installed on top of the FeCrAl heater to prevent heat loss over the channel. Detailed information on the heater development process and material selection can be found in a previous papers [10,20,23].…”

Section: One-side Joule Heating Assemblymentioning

confidence: 99%

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

2022

Nucl. Fusion

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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.