One-sided Heating Research Articles

A novel integrated PDB-FDB model for the prediction of flow boiling heat transfer under high sub-cooling and very high heat flux conditions

Although numerous studies on subcooled flow boiling heat transfer have been conducted, those evaluating very high heat fluxes of several MW/m2 under one-side heating conditions are limited. In this study, the heat transfer characteristics of a circular smooth channel are evaluated under one-sided heating conditions with a high heat flux of up to 11.82 MW/m2. An experiment to measure the heat transfer (including boiling performance) from single-phase to critical heat flux (CHF) under an inlet pressure of 0.1–1 MPa, mass flux of 2000–6000 kg/m2s, and inlet bulk temperature conditions of 30–140 °C is conducted. The boiling regime is analyzed by dividing it into a partially developed nucleate boiling (PDB) regime and fully developed nucleate boiling (FDB) regime, using the onset of the nucleate boiling (ONB) point and onset of the fully developed nucleate boiling (OFDB) point. A total of 15 existing subcooled flow boiling heat transfer correlations for the PDB and FDB regimes are evaluated with the experimental results. In the PDB regime, the Liu and Winterton correlation reveal good predictability within 11%. However, all the evaluated existing correlations of the FDB regime exhibit high error rates. In this study, a new FDB correlation is developed by considering the agitation heat flux (an expected heat transfer characteristic in the FDB regime) in the Liu and Winterton correlation with Python code and the AI regression method. An evaluation of the developed correlation with the data of other previous studies, such as those of Araki et al. and Jianguo Yan et al. reveals that the newly proposed correlation can predict the FDB heat transfer under conditions of higher pressure (approximately 5 MPa) and higher flow rate (approximately 10,000 kg/m2s) with a low error rate of 17%.

Scheme for Multi-Chiplet Integration With Low Thermal Budget by Asymmetric Cu-Cu Bonding With Au Passivation Bonding Structure

This study proposed a multi-chiplet integration scheme using Cu–Cu bonding with a low thermal budget by utilizing an asymmetric passivation bonding structure. The single-sided passivation structure was achieved through one-sided heating thermal compression bonding at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$150~^{\circ }\text{C}$ </tex-math></inline-formula> ; the bonding quality was enhanced by the passivation layer with small grain size. The bonding interface of the single-sided passivation structure was analyzed through transmission electron microscope, and the corresponding mechanism was inferred. Compared with original passivation structures, the single-sided passivation structure not only enhanced bonding quality but also provided higher bonding strength, and the contact resistance was lower than Cu-Cu direct bonding. Therefore, the single-sided passivation structure with low thermal budget, high bonding strength and high throughput can be applied to multi-chiplet integration.

Understanding the performance of profiled composite walls in fire

To understand the performance of structural elements subject to one-side heating, the combined effects of temperature and temperature gradient (or the non-uniform temperature increase) must be accurately considered in developing structural performance models. However, due to insufficient consideration of such effects, the direct application of current understanding of general structural performance at high temperature on structural elements like profiled composite walls (PCWs) seems insufficient because of the complex role that the different materials can have in the presence of significant temperature gradients. Therefore, more research is needed to understand the performance of these structural elements when subjected to temperature increase and temperature gradients. Only then, the performance of PCWs at high temperature can be appropriately addressed. This paper presents and verifies a structural performance model that can be used to analyse the performance of PCWs subjected to combined thermal and mechanical loadings. First, details of an analytical study are presented, including thermal stress calculation within inhomogeneous and composite cross-section by fully considering the effects of non-uniform stiffness, non-linear temperature gradient, shifting of the neutral axis, and the coupling effects between stress and thermal expansion. Second, previously published experimental results into the performance of PCWs subjected to combined mechanical loading and one-side heating are then used to verify the newly-developed analytical model. It is also argued that the methodology for stress and curvature calculation developed in this study can be used to assess the performance of any structural elements (PCWs included) subjected to one-side heating. (244 words).

Direct numerical simulation of one-sided forced thermal convection in plane channels

We carry out direct numerical simulations (DNS) of turbulent flow and heat transfer in pressure-driven plane channels, by considering cases with heating on both walls, as well as asymmetric heating limited to one of the channel walls. Friction Reynolds numbers up to ${Re}_{\tau } \approx 2000$ are considered, and Prandtl numbers from ${Pr}=0.025$ to ${Pr} = 4$ , the temperature field being regarded as a passive scalar. Whereas cases with symmetric heating show close similarity between the temperature and the streamwise velocity fields, with turbulent structures confined to either half of the channel, in the presence of one-sided heating the temperature field exhibits larger regions with coherent fluctuations extending beyond the channel centreline. Validity of the logarithmic law for the mean temperature is confirmed, as well as universality of the associated von Kármán constant, which we estimate to be $k_{\theta } = 0.459$ . Deviations from the logarithmic behaviour are much clearer in cases with one-sided heating, which feature a wide outer region with parabolic mean temperature profile. The DNS data are exploited to construct a predictive formula for the heat transfer coefficient as a function of both Reynolds and Prandtl number. We find that the reduction of the thermal efficiency in the one-sided case is approximately $20\,\%$ at unit Prandtl number; however, it can become much more significant at low Prandtl number.

Pressure and Thermal Characterisation of Dynamic Instabilities During Flow Boiling in Micro/Mini-channels at Different Azimuth Orientations

• Flow boiling in microchannels at different azimuthal orientation are investigated. • 3 instability types were identified: two-phase mixing, minor and major reverse flow. • Flow instability improves the average heat transfer coefficient by up to 52% • Top-heated channels had the greatest increase in heat transfer coefficient. • Instability frequency increased with mass flux increases and heat flux decreases. Fluid instability was investigated experimentally during flow-boiling of Perfluorohexane (FC-72) in a flat horizontal micro/mini channel with a hydraulic diameter of 909 μ m and an aspect ratio of 10 (5 mm x 0.5 mm). One-sided heating at different azimuth channel orientations ( θ ) in terms of gravity were considered, which ranged from bottom-heating ( θ = 0°) to top-heated ( θ = 180°) in 30° increments. Mass fluxes of 10, 20 and 40 kg/m 2 s were considered at a saturation temperature of 56 °C. Flow instability and the resulting thermal and pressure responses were identified and studied via high-speed video, infrared thermography, and pressure measurements. Various mass flux and heat flux combinations at each channel orientation leading to flow instabilities categorised into two-phase mixing, minor reverse flow and major reverse flow, were studied. Increased mass flux resulted in more frequent and more severe flow instability, irrespective of the channel orientation. Increased heat flux resulted in an increased number of operating conditions that were susceptible to flow instability, but the instabilities occurred at lower frequencies. In general, orientations that had a horizontal heated surface ( θ = 0° and 180°) were most susceptible to flow instability, while the intermediate azimuthal rotations ( θ = 30°, 60° and 90°) exhibited flow instability only at the highest mass flux. It was also found that flow instability often resulted in improved heat transfer performance, particularly in regions of the channel that were occupied by liquid. Where-as no direct relationship between the mass flux and the heat transfer performance improvement could be identified, it was found that better heat transfer improvements were obtained at higher heat fluxes. At the highest mass flux, cases that were horizontal and heated from above ( θ = 180°) exhibited heat transfer coefficient improvements (during instability) of up to 77% and 275% in the single-phase and two-phase regions respectively compared to baseline stable conditions.

Assessment of computational method for highly subcooled flow boiling in a horizontal channel with one-sided heating and improvement of bubble dispersion

This study employs computational and experimental methods to explore local hydrodynamic and heat transfer characteristics of subcooled horizontal flow boiling of FC-72 in a 2.5-mm × 5.0-mm rectangular channel heated along its 2.5-mm bottom wall. Limited studies have been conducted investigating the limit of the multiphase model and the way to improve the dynamic interfacial behavior between phases. The 3D CFD solver is constructed in ANSYS Fluent in which the Volume of Fluid (VOF) model is combined with the shear stress transport (SST) k-ω turbulent model, a surface tension model, and interfacial phase change model, along with a model for shear-lift force and bubble dispersion. Discussed are simulation results for void fraction distribution, pressure drop, and local fluid and wall temperatures. The simulation results are compared to experimental data to validate the solver's ability to predict the asymmetrically heated horizontal flow configuration. Body force is shown to have an appreciable impact on both predicted and measured results, the outcome of bubbles along the heated wall migrating toward the top adiabatic wall and causing asymmetry in fluid velocity and temperature within the cross-sectional area and along the channel. These asymmetrical effects are quite pronounced at low mass velocities, where the upstream fully developed liquid boundary layer is disrupted by bubble formation along the heated bottom wall. Predictions are presented for simulations, including shear-lift force with and without bubble collision dispersion force. The shear-lift force is shown to govern mostly the dynamic behavior of small bubbles stuck on the heated bottom wall and therefore has a greater impact on both heat transfer and heated wall temperature. Absent bubble collision dispersion force, the simulations show excessive bubble coalescence creating inordinate vapor pockets along the adiabatic wall. But by including this force, coalescence of densely packed bubbles in the bulk region is significantly inhibited, with larger bubbles even incurring additional breakup into smaller bubbles and culminating in far less vapor accumulation along the top wall. Including the bubble collision dispersion force is shown to yield better agreement with experimental interfacial behavior along the channel. The mean deviation and error of wall temperature across cases are 2.2 °C and 3.34%.

Experimental study on turbulent natural convection of air between the open-ended parallel plates with one-side heating

In the present study, experiments on the turbulent natural convection of air for PAS were carried out. The heat transfer and flow rate induced by buoyancy were investigated. When the heated wall is inclined upward, the heat transfer coefficient increases with the decrease of inclination angle. And the pressure loss along the channel decreases because of the decrease of the velocity gradient. Based on the experimental data, the heat transfer correlation and mass flow rate correlation considering the influence of inclination angle were proposed. And they are applicable to predict the heat transfer and flow rate for PAS. In addition, a criterion for classifying the mixed and natural convection was deduced. The research results can be applied in the analysis of the thermal-hydraulics of the PAS to improve the security of nuclear power plants.

Efficient Sensitivity Analysis for Enhanced Heat Transfer Performance of Heat Sink with Swirl Flow Structure under One-Side Heating

Excellent heat transfer performance has increasingly become a key issue that needs to be solved urgently in the development process of large-scale fusion equipment. The study of heat transfer performance improvement to scientifically and reasonably determine the design parameters of the high heat flow (HHF) components of fusion reactors based on the efficient in-depth analysis of the heat transfer mechanism and its sensitive factors is of great significance. In this paper, a liquid-vapor two-phase flow model with subcooled boiling for a large length-diameter ratio swirl tube structure in the HHF calorimeter component is proposed to analyze the effects of key design parameters (such as inlet temperature of cooling water flow, swirl tube structure parameters, etc.) on its heat transfer performance. Then, considering the high computational cost of the liquid-vapor two-phase flow model, and in order to improve the efficiency of the sensitivity analysis of these design parameters, the polynomial response surface surrogate model of heat transfer performance function was constructed based on Latin hypercube sampling. On this basis, by combining the proposed surrogate model, the sensitivity index of each design parameter could be obtained efficiently using the Sobol global sensitivity analysis method. This method could greatly improve the calculation efficiency of the design parameter sensitivity analysis of HHF components in the fusion reactor, which provides vital guidance for the subsequent rapid design optimization of related components.

Heat transfer of air turbulent mixed convection in the passive containment air-cooling system of a modular small nuclear reactor

Passive containment Air-cooling System (PAS) is an important passive system of the modular small nuclear reactor, ACP100. After a severe accident, the air in the annular gap between the steel shell and the concrete shell of the containment is heated, forming buoyancy-driven mixed convection which removes decay heat. Thus, the heat transfer of mixed convection in PAS is essential for the safety of nuclear reactor. However, there are very less related studies on this phenomenon. In the present study, experiments on the mixed convection of atmospheric air in a parallel-plate channel with one-side heating for PAS were carried out. The regions of Re, Gr and Bo range from 1.7 × 104 to 8.8 × 104, 1.0 × 108 to 1.0 × 1010 and 4 × 10−5 to 90, respectively. Furthermore, the effect of the inclination angle on heat transfer was analyzed for the dome which is an integral part of PAS. A heat transfer correlation was newly proposed, which can more accurately predict the heat transfer of PAS with an error within ±15%. In addition, the predicted values of heat transfer agree well with other experimental data of mixed convection in the rectangular channel. The present research puts forward a new model for the analysis of PAS heat transfer performance, and has the reference significance for the optimal design of PAS.

Exploring the onset of nucleate boiling with hypervapotron channel for tokamak cooling system application

In present paper, onset of nucleate boiling (ONB) of one-side heated hypervapotron (HV) channel was studied. Through sub-cooled flow boiling experiments under the conditions of a pressure of 1–10 bar, a mass flow rate of 0.071–0.284 kg/s, an inelt fluid temperature of 40–140 °C, and a heat flux of up to 10765 kW/m2, ONB heat flux was experimentally explored. As a result, the HV channel recorded an average 186.91% improvement in ONB heat flux compared to the flat channel due to the vortex secondary flow induced by the fin structure arrangement. In addition, the effect of the system parameters on the ONB heat flux of the HV channel was analyzed. In addition, it was evaluated how well the existing ONB correlations predict the ONB of the HV channel under one-side high heat load conditions. Unfortunately, they tend to under-predict the enhanced ONB of the HV channel because they are correlations developed for the circular smooth channel. Therefore, the authors of this study developed a new correlation using a Python code grafted with machine learning technology.

New correlations for the prediction of incipient nucleate boiling in a one-side heated swirl tube

• In this paper, the onset of nucleate boiling (ONB) of a swirl tube is studied. • It was found that ONB heat flux increased as sub-cooling and mass flow rate increased. • As the pressure increases, the ONB heat flux decreases due to a decrease in latent heat. • Existing ONB correlations show a high error rate in predicting ONB heat flux of swirl tube. • New ONB correlations are developed through Python code and dimensional analysis. Future tokamak cooling systems should always be maintained in a single phase during operation to avoid potential hazards caused by vapor. To this end, a correlation to accurately predict sub-cooled flow boiling onset of nucleate boiling (ONB) under the one-side high heat load condition, which is the heat flux condition inside the tokamak, is required. According to this necessity, the ONB of a one-side heated swirl tube was experimentally explored in this study. The inserted swirl tape induces a secondary swirling flow, which causes ONB to occur at a higher heat flux condition than the smooth tube. As the twist ratio of the tape decreased, the ONB heat flux enhancement rate increased. Sub-cooling and mass flow rate have a proportional relationship with ONB heat flux, whereas pressure has an inverse relationship. The prediction accuracy of the existing ONB correlations was evaluated. However, most correlations tended to under-predict the experimental values. Because they were not developed for the purpose of predicting the ONB of the swirl tube under sub-cooled flow conditions, all system parameters and the effect of the swirl tape were not reflected. Therefore, we developed new correlations using Python combined with machine learning.

Improvement of the critical heat flux correlation in a thermal-hydraulic system code for a downward-flow narrow rectangular channel

Several critical heat flux (CHF) correlations including the look-up table in the MARS code have been assessed for the prediction of CHF in a downward-flow narrow rectangular channel. For the assessment, we built an experiment database that covers pressures between 1.01 and 39.0 bar, gap sizes between 1.09 and 6.53 mm, mass fluxes up to 25,772 kg/m2s, and under one-sided and two-sided heating conditions. The results of the assessment showed that the Kaminaga correlation has the best overall prediction compared to others. However, because the correlation uses global variables, such as inlet and outlet subcooling and total heat transfer area, it is difficult to use in a system code. A new CHF correlation is then proposed by replacing the global variables in the Kaminaga correlation with local ones and adding correction factors to consider the effect of gap size, mass flux, and the number of heating walls. Additional correction factor is added to consider the effect of inlet subcooling. It is shown that the new one is better than the Kaminaga correlation and it is easy to implement to any system code.

Градієнтність структури і характеристики руйнування сталевих виливків

The effect of melt overheating over the equilibrium liquidus to temperatures of 1570 ºС, 1620 ºС and 1670 ºС and heat removal conditions (normal and rapid cooling) on the formation of a gradient structure and fracture characteristics over the cross section of castings of 25L and 30HGSL steels was investigated. The differentiated phase-structural state of rectangular castings (60x60x100 mm) was provided by the predominant one-sided heat removal in foundry molds with different heat removal capacity and average cooling rate 2 – 5 ºС/s and 300 – 350 ºС/s. Regular changes in the length of the main macrostructural zones in castings are established depending on the crystallization conditions, in particular, an increase in the zone of near-surface small crystals and the transcrystallization zone during rapid cooling of the melt. It is shown that depending on the temperature conditions of melt preparation and cooling during crystallization, the grain size in the cross section of castings varies by 4-5 numbers (steel 25L) and by 6-8 numbers (steel 30HGSL). The rapid cooling of the melt causes a significant increase in the impact strength of the cross section of the castings in the range of 50-35 J/cm2 (steel 25L) and 40-20 J/cm2 (steel 30HGSL), even under conditions of significant overheating of the melt. Under normal cooling conditions, there is a significant decrease in the values of impact strength in the cross section of the castings from 30 to 15 J/cm2. According to the results of determining the toughness in castings with differentiated structure depending on the crystallization conditions and test temperature (+20 ºС… -60 ºС) the regression equation for changing its values in the range of viscous-brittle transition temperatures and brittleness temperature (Tbrtl50) of steels in the volume of castings. The obtained results create preconditions for the development of technological principles of engineering of cast steel products to ensure the specified properties in accordance with the requirements of their operation. Keywords: steel, crystallization, gradient structure, toughness.

Dimensional analysis on incipient flow instability in one-side high heat loaded rectangular flat heat sink under sub-cooled flow boiling conditions

The onset of flow instability (OFI) is a major threat to the operation of a fusion power plant. In particular, because the divertor is loaded with a high heat flux of up to 20 MW/m2, it may be vulnerable to OFI. Therefore, in this study, the OFI of a one-side heated flat heat sink was experimentally analyzed. When the effect of the system parameters on the OFI was analyzed, the faster the vapor inside the channel could be removed, the higher was the OFI that was experimentally recorded. As the flow rate and degree of subcooling increase, the OFI increases because it induces an enhancement of the forced convective heat transfer performance and a rapid coding rate, respectively. However, when the pressure is increased, the latent heat and liquid surface tension are reduced; thus, boiling occurs at a lower heat rate, which leads to a decrease in OFI. When the prediction performance of the existing OFI correlations developed under the subcooled flow boiling condition was evaluated, it showed a tendency to overpredict this experimental value significantly. This is because the evaluated correlations were developed based on relatively low heat flux conditions and narrow rectangular channels. Therefore, in this study, we developed a new OFI correlation optimized for experimental values using an artificial intelligence (AI) regression method. Because this correlation can be utilized under one-side high heat load conditions, it is expected that it will be especially useful when establishing the operation strategy of the cooling system of a fusion power plant.

Pressure drop characteristics in single-side heated circular smooth channel under sub-cooled flow boiling conditions

In this study, the two-phase pressure drop for a one-side heated smooth channel was explored through subcooled flow boiling experiments for divertor applications. When the channel heat load was gradually increased, there was little differential pressure change in the single-phase regime, but when it exceeded the onset of significant void (OSV) heat flux, the differential pressure started to increase. It was found that as the subcooling and flow rate increased, the OSV heat flux increased, and the slope of the two-phase differential pressure decreased, This is because it is possible to condense the generated vapor more quickly under these conditions. Moreover, as the pressure increased, the OSV heat flux increased and the size of the ejected single bubble decreased under high pressure conditions. The prediction performances of existing two-phase pressure drop multiplier correlations were also evaluated. Since most of the existing correlations were developed based on channels of a small diameter, and were not evaluated at a high heat flux, that is, in the order of 10 MW/m2—they exhibited a high average error rate. Therefore, we developed a new two-phase pressure drop multiplier correlation for a smooth channel under one-side high heat load conditions using PYTHON code and artificial intelligence regression method.

The boundary layer conductance of inclined elliptical leaves under free convection

The efficiency of heat and mass exchange between leaves and their environment under low wind speed is dominated by free convection. This is commonly quantified in terms of the Nusselt number (Nu), the Rayleigh number (Ra) and the boundary layer conductance (gb). The currently available Nu = f(Ra) relations for inclined plates were mostly derived for infinite wide plates or from one-sided heat transfer studies. A comprehensive simulated data set of laminar free convection may be used to derive new Nu relations for elliptical plates at any inclination and for both plate sides. The relevant equations for free convection in 3D are solved numerically using the computational fluid dynamic (CFD) software OpenFOAM. The simulated Nusselt numbers agree very good with previous measurements for vertical and horizontal circular plates having a diameter of 84 mm. Various finite thickness (0.5 mm) elliptical plates (i.e. leaves) having aspect ratios between 1 and 3, plate length ranging from 30 to 160 mm and a range of inclinations are simulated with plate to air differences set to 1–12 K. Simulated heat fluxes from each leaf side are used to parameterize a comprehensive set of Nu relations. The new gb model predicts CFD simulated heat fluxes at both leaf sides (2 - 120 W m−2) with a relative error of 4%, whereas with two tested previous approaches the error is 31–45%.

Modeling the response of blended PVC/PET fabrics to fire environments

The fire behavior of fabrics with uncertain composition of polyvinyl chloride and polyethylene terephthalate blends presents numerous kinetic and flame spread modeling challenges. Such fabrics have extensive usage in light-weight shelters or for protective-coverings. This study details thermogravimetric analysis and one-sided heating experiments carried out for three different PVC/PET blended fabrics. A challenge with characterizing these materials is the relative contributions of PVC and PET are unknown. Only approximate ranges are often provided by manufacturers. In addition, the char/species yields are not known since blended materials (with additives) perform very differently from homogeneous PVC or PET samples. To unravel initial mass fractions and char/species yields, a new non-linear regression analysis is developed to process TGA mass loss data. This analysis is verified by Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy to confirm relative amounts. The output of the regression analysis provides important kinetic rate parameters for Arrhenius modeling used in FEA. To verify this approach, FE model predictions are compared to experiments showing good agreement to measured fabric temperature and mass loss. These results confirm the utility of using non-linear regression analysis for providing kinetic and composition information for constructing thermal degradation models of blended PVC/PET fabrics subject to fire environments.

Experimental study on CHF of one-side heated rectangular heat sink with regard to fusion divertor cooling

When the critical heat flux (CHF) is reached, the heat transfer efficiency rapidly decreases. Therefore, CHF must be considered as a potential hazard for a stable cooling system operation. In particular, securing the thermal margin of plasma-facing-components inside the tokamak loaded with ultra-high heat flux is directly related to system safety. According to this necessity, in this study, CHF of flat rectagular channel under one-side high-heat-load condition was experimentally explored. As a result of analyzing the effect of system parameters on CHF, it was observed that mass flow rate and sub-cooling had a proportional relationship with CHF, whereas pressure had an inverse relationship with CHF. This is because a high mass flow rate and high sub-cooling promote forced convection heat transfer and quickly remove vapors from the flow path, but an increase in pressure reduces liquid surface tension and latent heat, causing early boiling. In addition, the predicton performance of the existing sub-cooled flow boiling CHF correlations was evaluated under the one-side high heat load condition. However, the large difference in experimental conditions and the structural difference between circular tube and rectangular channel made them under-predict the experimental values. Accordingly, we developed new optimized CHF correlations using a Python code grafted with machine learning technology. The developed correatlion can be utilized when evaluating the thermal safety margin of the future tokamak, and can be a great help when establishing a cooling system operation strategy.

Development of a High Heat Flux Electric Joule Heating System for Testing a One-Side Heated Cooling Channel

Systems such as solar thermal systems, chip coolers, beam dumps of neutral beam injectors, and fusion reactor divertors and blankets are subjected to one-side high heat flux. Specifically, high heat flux (10 MW/m2) is applied on the fusion reactor divertor in steady state. The monoblock design in a divertor is limited by the thermal-hydraulic and mechanical stability, which thermal-hydraulic data are required for. The lack of thermal-hydraulic data for the cooling channel causes difficulties for the design of the monoblock and the determination of the thermal-hydraulic condition for the safety and conversion of energy efficiency. To analyze the mechanisms and thermal hydraulics, a high heat flux heating system is recommended for the purpose of testing one-side heated cooling channels. Comparing an e-beam system to a joule heating system, the e-beam system requires higher cost, expertise, sophisticated design, and more power consumption, which delays the development of heat transfer correlations and the mechanisms of fluid motion inside the cooling channel. The production of 10 MW/m2 heat flux using the joule heating method is challenging, since it is limited by the temperature of the heater. In this study, the limitation of the joule heating system was overcome by optimizing the material selection for the heater, the configuration of the system, and the bonding method of the components used in the system. High heat flux testing was conducted and the target heat flux of 10 MW/m2 was successfully implemented, and it showed good reproducibility of the heating system. The reliability of the newly developed heating system was validated by comparing the results of the experiments with correlation-based simulations. The comparison analysis showed that the experimental results from the new heating system are comparable to the single-phase and two-phase correlation-based simulation results within 5% and 1.5% error, respectively. Further, through the comparison of various correlation-based simulations with the experimental results, we conclude that one-side joule heating results are only describable using a one-side correlation, not using correlations developed from uniform heating systems. To optimize the design of the cooling channel in a one-side heating condition in a faster and easier manner, the newly advanced joule heating system will help contribute to the development of the thermal-hydraulic analysis of the cooling channel.

Critical Heat Flux Analysis With Single-Side Heated Swirl Tube Under Subcooled Flow Boiling Conditions

Critical heat flux (CHF) is regarded as one of the major problems in cooling system design. Specifically, because the tokamak is loaded with heat flux of several megawatts per square meter, carefully considering the CHF is crucial. This study analyzes the subcooled flow boiling CHF of the swirl tube under one-side high-heat load condition. The CHF parametric analysis results indicate that smaller swirl tape twist ratios yield higher swirl flows. As the subcooling increases, the CHF increases because the vapor inside the channel condensates more rapidly due to the lower bulk temperature. And the increase of the mass flow rate also increases the CHF because it enhances the forced convection heat-transfer performance. However, the CHF slightly decreases as the latent heat decreases with the increase in pressure. The assessment of existing CHF subcooled flow boiling indicates that the formulated correlations based on the smooth tube mainly tend to yield under-predicted results. However, most of the correlations developed according to the swirl tube tend to over-predict. Among these, the Nariai and Inasaka swirl CHF correlation has the lowest error rate; nevertheless, it tends to slightly under-predict results because of the difference between uniform and one-side heating. Accordingly, a new modified Nariai and Inasaka correlation is formulated using a Python code and artificial intelligence technology to reflect the one-side heating effect.