Heat Removal Capability Research Articles

Thermal Effects in the End-Winding Region of Electrical Machines

The main heat transfer mechanism in the end-winding region of electrical machines is convection. In order to increase the air motion, the rotor is equipped with a series of blades. Their geometry is reflected in the fanning factor, i.e., the ratio between the rotor peripheral speed and air velocity. An accurate calculation procedure for the fanning factor has not yet been given. Knowing its value is crucial for the determination of air velocity and heat transfer coefficient (HTC), as the latter describes the end-winding heat removal capability. In this study, the convective heat transfer phenomena between the end winding and air inside the end-winding region were analyzed, with the heat generated only in the end winding, mimicked with a custom designed coil, and air moved by the blades. The analysis was performed by experimental testing and computational fluid dynamics (CFD) modeling. Measurements data were used to build a reliable CFD model. Further on, CFD results were used to derive a generalized analytical equation for calculation of the end-winding HTC, related to blade geometry and rotor rotational speed. The developed analytical model significantly improves the quality of real-time lumped circuit thermal modeling of electrical machines and, thus, enriches this field of science.

Investigation of flow and heat transfer behavior of integrated pin fin-aluminum foam heat sink

• A novel aluminium foam heat sink (AFHS) consisting of pin fin inserts is proposed. • The developed mathematical model is validated with experimental data. • Thermo-hydraulic characteristics of proposed heat sinks are numerically studied. • Pin fin inserts lead to an enhancement on the heat removal capability of AFHS. • Pressure drop along the flow direction increases with pin fin insertion into AFHS. With the rapid development in the electronics industry, the thermal management of high power density electronic products (HPDEPs) has become very important and requires innovative heat removal technologies. In this study, an integrated heat sink (IHS) fabricated by combining aluminum foam and pin-finned heat sink configurations that are frequently used in the cooling of electronic products has been proposed as an effective solution for the thermal management of HPDEPs. The heat removal and pressure drop characteristics of the IHS were numerically investigated for its various design conditions such as the length/height ratio ( L/H ), fin profile, fin/foam height ratio ( H fin /H foam ), and heat sink/fin volume ratio ( V hs /V f ) over the range of Reynolds ( Re Dh ) number from 500 to 3500 by using the COMSOL Multiphysics v5.4. Before the numerical study was performed, to verify the outcomes of the developed simulation models, some of the IHS subjected to the numerical study were fabricated and their pressure drop and heat removal performances were experimentally examined in the range of Re Dh from 596 to 3551. As a result of the study, it was found that the thermal contact resistance ( TCR ) between the IHS and the heated surface has a greater effect on the Nusselt ( Nu ) number compared to the TCR between the solid fins and aluminum foam. The in-line or staggered arrangement of pin fins inside the aluminum foam did not lead to any significant difference in the overall performance of investigated IHS. For all the IHS examined, an increase in Re Dh results in a similar increase in the Nu and ΔP along the flow direction. In general, the most efficient IHS among the investigated ones in terms of the H fin /H foam ratio is the IHS with half-length fins, H fin /H foam =15/30. Average values of thermal performance factor ( ƞ) of the IHS with H fin /H foam ratio of 15/30 in in-line and staggered arrangement over the Re Dh number studied are 1.3 and 1.25 times higher relative to IHS with H fin /H foam ratio of 30/15. For a fixed number of fins, η of the IHS with fins of 4mm diameter is superior up to Re Dh =2000, after which, the situation varies in favor of the 8mm solid finned aluminum foam heat sink. Increasing the fin diameter from 4mm to 12mm in both fin configurations worsens the average value of ƞ by 10%. For a constant fin diameter, IHSs with 9 fins in in-line and 8 fins in staggered configuration have the highest ƞ when the Re Dh is greater than 2500 and 2000, respectively. Among the fin profiles examined, the IHS with elliptical fins is found to have the highest η , with a value of 1.24, at Re Dh =3500.

Analysis of cooling performance using evaporation enthalpy of product water for a lightweight aviation fuel cell system

In air mobility vehicles, weight reduction has a significant impact on extending flight duration and increasing payload. However, as the power demand of the fuel cell increases, a large cooling capacity is required, which increases the weight of the entire cooling system including the coolant. Therefore, this study investigates ways to reduce the volume and weight of the thermal management system of the 20kW high-power fuel cell system. Instead of removing the external humidification system for both the anode and cathode, the effect of humidification is evaluated using the product water discharged from the stack. In addition, a method to maximize the cooling effect of the radiator by using the latent heat of evaporation of generated water is proposed. Also, system designs with more effective heat removal capability are derived by dividing the case into two according to the system arrangement. Before the analysis, a stack model capable of simulating the complex physics of the fuel cell was developed using Aspen Custom Modeler®. As a result, it was confirmed that the minimum specification (required overall heat transfer coefficient, UA) of the radiator can be reduced by using each product water discharged from the stack.

Pool boiling enhancement via biphilic surface comprising superhydrophilic TiO2 and superhydrophobic Teflon arrays

The ever-increasing power density overloads the heat removal capability of miniaturized power electronic devices and thus an efficient liquid cooling method needs to be strategized. Herein, we introduce a biphilic surface consisting of both superhydrophilic TiO2 and superhydrophobic Teflon. The purpose of this unique combination is to decrease the superheat (Tsat) by efficiently releasing vapor bubbles via the superhydrophobic surface and to increase the critical heat flux (CHF) using efficient wetting supplied by the superhydrophilic surface. The superhydrophilic TiO2 layer was deposited by the room temperature aerosol deposition method, whereas the superhydrophobic Teflon dots were deposited by the atmospheric supersonic cold spraying method. Each Teflon dot was 1 mm in diameter and the dots were patterned in the form of n×n arrays, where n varied from 1 to 5. The optimal CHF (187 kW·m−2), superheat, and effective heat transfer coefficient (4.6 kW·m−2·k−1) were observed for the 4 × 4 sample, beyond which the cooling effect deteriorated because of the excessive area covered by the Teflon dots. While the Teflon dots facilitated efficient bubble release, securing sufficient flow passage with the aid of a hydrophilic wetting area was also critical; thus the combination of the superhydrophobic and superhydrophilic surfaces was optimally balanced.

Design and thermal-hydraulic analysis for CFETR divertor Dome

The main function of China Fusion Engineering Test Reactor (CFETR) Divertor Dome is to isolate neutral particles and impurity particles as well as improve the ability of particle exclusion. For the CFETR Divertor Dome, a new integral hybrid divertor-blanket structure was proposed in previous study. The new Dome should also be compatible with the Remote handling (RH) requirements due to neutron activation of in-vessel components, thus special RH channels are designed on the front of the plasma-facing units (PFUs). Due to direct bombardment or sputtering of plasma, the Dome will suffer heat flux up to 10 MW/m2 and nuclear heat under 1.5 GW fusion power during steady-state operation, which puts forward critical and tricky requests for the design of cooling system. While for the RH channels, the situation is even direr due to its location and poor cooling conditions. In this paper, cooling system of the Dome is proposed, and cooling channels with special thermal transfer structure are designed in the PFUs to guarantee them with heat removal ability up to 10 MW/m2. Special PFUs and cooling system are designed to adapt to the RH, to shadow them from the direct bombardment of plasma and provide enough heat removal capability. Thermal-hydraulic analysis is carried out to verify the heat transfer ability of the Dome cooling system. The results will provide supports to the electromagnetic and structure analysis of Dome and promote the final design of CFETR water-cooled divertor.

Enhancing Heat Removal and H2O Retention Capability of Passive Air-Cooled Polymer Electrolyte Membrane Fuel Cells by Tailoring Cathode Flow-Field Design

This paper reports novel cathode flow-field designs for passive typed air-cooled polymer electrolyte membrane fuel cells (PEMFCs) to help alleviate electrolyte dehydration and performance degradation issues under excess dry air supply conditions. The proposed flow-field designs include 7 three-dimensional (3D) patterned designs in addition to a parallel channel configuration equipped with rectangular baffles to control the airflow for more efficient heat removal. The designs were evaluated numerically using 3D, two-phase PEMFC simulations. Compared to a typical parallel flow channel configuration, the proposed flow-field designs show better heat removal and water retention capability. The improvement in single cell voltage was around 13–75 mV at an operating current density of 0.5 A cm−2, whereas the larger pressure drops around = 6.9–317.6 Pa cm−1 were required because of the more complex flow-field configurations compared to the simple straight parallel channel geometry ( = 7.4 Pa cm−1). This work presents a comprehensive understanding of air-cooled PEMFC operating characteristics under excessive dry air supply conditions and a new design strategy for cathode flow-fields.

Development of Poloidal Horseshoe Limiter Concept for JA DEMO

In the development of a DEMO fusion reactor, mitigating the heat load deposited on the breeding blanket at steady-state operation is one of the challenging issues because of the localized high heat flux brought by charged particles and low thermal conductivity of the reduced activation ferritic/martensite (RAFM) steel structural material. This study proposes a concept of limiter for JA DEMO; a horseshoe-shaped limiter which is continuous poloidally in the first wall (FW) except for the diverter area, and discretized toroidally. The limiter is protruded from the FW to shade the blankets from the charged particles, which move along the magnetic field lines. To enhance the heat removal capability and neutron irradiation tolerance, a tungsten mono-block using RAFM heat sink was applied as the plasma-facing unit (PFU) on the limiters. The heat removal capability of the limiter’s PFU was evaluated as 4.6 MW/m2. The limiter shape satisfying this value was determined basing on the utilization of heat load evaluation with 3-D magnetic field line tracing. Three limiter shape parameters; protrusion height, protrusion width and the FW set-back, were investigated to understand the variation of charged particle load distribution. Both cylindrical and box-shaped blanket concepts were considered, and design windows for the limiter shape were acquired to discuss the optimum parameter. The optimum limiter shape fulfilling the requirement of steady-state operation has been defined, and the limiter’s occupied area amounts to 1.2% of the FW area for both blanket options.

Design of the Cooling Water System for the EAST Lower Divertor

The new lower tungsten divertor is a crucial component to achieve the targets of long pulse and high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> H-mode operation of Experimental Advanced Superconducting Tokamak (EAST) device. The cooling water system (CWS) of lower divertor should have sufficient heat removal capability and be able to cope with pressure transients caused by the potential water hammer events, which makes the design challenging. In this study, the system process and details of main component are determined based on the design requirements. The thermal-hydraulic analysis model has been developed by Flowmaster (FLOWMASTER) to conduct the heat transfer analysis. Furthermore, the system water hammer transients under one pump trip condition have been analyzed. The results show that the flow distribution of each client is uniform, and the pressure and temperature of key points meet the design requirements. The maximum pressure fluctuation, 0.16 MPa, caused by the sudden closing of the check valve is within the acceptable range. The experiment data are in good agreement with the simulation values, which proves the correctness of the model and the feasibility of the design.

Numerical Analysis of Liquid Metal MHD Flow and Heat Transfer for Open-Surface Li Divertor in FNSF

Within the ongoing U.S.-based program on the development of liquid metal plasma-facing components, numerical simulations and analyses are performed to address the feasibility of the open-surface Li divertor. In the previous scoping studies (Smolentsev, 2021), heat-removal capabilities of the divertor were assessed using a simplified flow model for a slug-type velocity profile and constant flow thickness. Here, new analyses take into account forces acting on the flowing Li layer. Three reduced-order mathematical models are applied under the conditions of the U.S. Fusion Nuclear Science Facility (FNSF) to access magnetohydrodynamic (MHD) flow development effects, velocity distribution, and surface waves: 1) fully developed MHD flow; 2) quasi-2-D developing MHD flow; and 3) multiphase MHD flow. The obtained results for MHD flows and the surface heat flux computed with the plasma code scrape-off layer plasma simulation for ITER (SOLPS-ITER) are then used as input data to compute the temperature distribution in the divertor by solving the convection–diffusion energy equation.

Towards Efficient Thermal Management within Intercalation Batteries through Electrolyte Convection

Ubiquitous in consumer electronics and emergent in transportation and stationary applications, lithium-ion batteries (LIB) are the state-of-the-art energy storage technology due to their energy density, roundtrip efficiency, and cycle life.1,2 While the past decade has seen a steady decline in battery price and concomitant increase in energy density due to a combination of materials development, manufacturing advances, and market scale,3,4 current LIBs are still unable to meet the often incongruous power and energy requirements of newer applications (e.g., fast charging of energy-dense batteries).5,6 In addition, these more extreme operating environments challenge battery longevity and safety, necessitating responsive balance-of-plant systems which include thermal management systems that control cell temperatures using heat transfer media. At elevated temperatures, accelerated solid-electrolyte interphase growth and component decomposition may lead to capacity/power fade,7,8 and, in the worst cases, thermal runaway and hazardous releases. Within the battery cell, temperature gradients lead to non-uniform electrode reaction distribution, and subsequently reduced cell performance and cycle life.8 Thus, typical LIB operating temperature ranges are constrained between 20 ℃ and 40 ℃, with minimal temperature differences across the cell. Most current thermal management systems rely on heat exchange through the surface or tab of the cell with a cooling media (air, liquid, phase-change materials, etc.).9,10 While generally sufficient under many of today’s applications (low C-rates), this approach can be challenged by newer applications, such as those that require high power input/output (EV fast charging, electric aviation), or need large battery formats (stationary storage systems).In this presentation, we will describe a novel concept of thermal management through forced convection of the electrolyte through the porous electrodes and separator. By leveraging battery simulation and dimensional analysis, we demonstrate that: (1) electrolyte convection provides efficient heat removal capability by carrying the generated heat out of the cell through the flowing medium; (2) the elimination of electrolyte concentration gradient by flow, and the resulting smaller ohmic resistance, concentration and activation overpotentials, help prevent cell temperature rise through reduced heat generation rate. Compared to current thermal management systems, this approach offers several important potential advantages, including (1) reduced internal temperature gradient, (2) rapid response time to temperature regulation, (3) simplifications to manufacturing, and ultimately, and (4) reduced system costs and improved battery safety.

Numerical Study of Large Footprint (24 × 24 mm2) Silicon-Based Embedded Microchannel Three-Dimensional Manifold Coolers

Abstract Silicon-based embedded microchannel with three-dimensional (3D) manifold (MF) μ-cooler offers lower pressure drop and increased heat removal capability (&amp;gt;1 kW/cm2) for microprocessors and power electronics cooling using single-phase water. In this paper, we present a thermal–fluidic numerical analysis of silicon-embedded microchannel cooling. We develop a full-scale computational fluid dynamics (CFD) model of a large footprint (24 × 24 mm2) device having embedded microchannels and a 3D manifold. It is found that the pressure/velocity distributions at three different critical regions inside the inlet manifold have a significant impact on the temperature distribution. A previous study reported a shift of the chip temperature hot-spot at high flow rates; this study delves deep into the flow and pressure variations within the MF and cold plate (CP) that leads to this shift. This study also investigates the degree of flow maldistribution, first between the manifold channels caused by the plenum and then between the cold plate channels caused by individual MF channels. Finally, this study concludes with a comparison between two different 3D manifold inlet channel heights. The comparison reveals that the manifold with 1.5 mm thickness can reduce the pressure drop by a factor of 4 while maintaining the same thermal resistance of 0.04 K cm2/W, thus indicating an increase in the coefficient of performance (COP) by a factor of 4, compared with a manifold thickness of 0.7 mm.

Local hotspot thermal management improved by ionic wind generator coupled with porous materials

Ionic wind is induced by corona discharge caused by extremely inhomogeneous electric field between two electrodes. Due to its compact size, energy saving, flexible design, and easy integration, ionic wind technique exhibits great potential to improve hotspot cooling, especially for compact electronic devices. However, the heat removal capability towards high power density is relatively low due to the limited heat transfer area and low air thermal conductivity. The principle and designs are still lacking for local hotspot cooling. Here, an ionic wind generator with a novel architecture coupled with porous medium is conceived to enhance cooling performance. It is demonstrated that when a porous medium block is coupled, heat transfer can be significantly boosted due to the modified heat and mass transfer in the porous block. It is also found that electrode configuration significantly influences the device performance. There is a trade-off between heat transfer area and airflow impediment in the device. The geometry and property parameters of the porous block are critical for the cooling performance, which is attributed to the modified flow field by changing porous structure. Based on this principle, another ionic wind generator improved by a coupled heat sink with porous fins is proposed, whose performance can be further enhanced by optimizing its design parameters. The optimized heat sink structure can maintain the max temperature of the cooling surface below 83.2 °C at a heat flux of 90 kW/m2. This study provides a promising way for air-side thermal management of hotspot. The findings are helpful for understanding EHD-induced airflow heat transfer in porous medium and shed new light on designing ionic wind generators with better performance.

3D simulation of transient thermal-hydraulic characteristics in CEFR during emergency shutdown event

Safe shutdown behavior of China Experimental Fast Reactor (CEFR) in emergency status is one of the key points in its safety assessment. The CEFR design incorporates a pool-type structure. However, the flow and heat transfer characteristics in the pool are complex, which results in obvious three-dimensional (3D) effects. Therefore, obtaining the 3D flow paths and accurate temperature distribution characteristics using a one-dimensional system code is difficult. In the present work, 3D computational fluid dynamics simulations were performed on the pool-type sodium-cooled fast reactor CEFR in full-scale. The “decoupling modeling and coupling calculation” method was used for performing numerical simulation to comprehensively investigate the 3D thermal and flow characteristics under emergency shutdown conditions. The convection and the corresponding heat transfer effects were evaluated by investigating both inter-flow and intra-flow paths in the reactor core. FLUENT 18.0 results were compared and verified with system code SELTAC simulation results. The results revealed that the residual heat was mainly dissipated by the intra-subassembly flow under reactor emergency shutdown conditions. The maximum core outlet temperature did not exceed 543.4 °C under emergency shutdown event, which is lower than the safety limit. This phenomenon indicates that if the heat-removal capability is maintained in the main heat exchange system, CEFR shutdown protection is effective. The three-dimensional results of the present work provide important numerical references for CEFR safety analysis.

Calorimetry system for heat load in long-pulse discharges on EAST tokamak

A calorimetry system has been developed in Experimental Advanced Superconducting Tokamak (EAST). It is employed to evaluate the heat load exhausted by cooling water. Full poloidal coverage is achieved after the upgrade in 2019. The experimental results show that the heat load exhausted by cooling water is 64%–86% of the injected energy. Moreover, the heat load increases faster in the case with a higher heating power, and this is qualitatively confirmed by the simulation. In addition, a longer time is required for the temperature of the cooling water to achieve its maximum for a higher heating power. And in the decay phase of the water temperature, it shows an exponential characteristic. The averaged time constant of the thermal decay obtained by exponential fitting for the upper and the lower divertor are 12.1 s and 107.9 s, respectively. It indicates that the heat removal capability of the upper tungsten divertor outperforms the lower graphite divertor.

Thermal management of parallel cells — Methodology based on non-linear dynamics

Battery thermal management is crucial to ensure an efficient, safe, and durable use of battery. Yet despite various efforts devoted, there is still few methodologies available to guide either the design or the control of the battery thermal management system (BTMS) to maintain predefined limit on the temperature difference (△ T ) among cells subjected to various forms of non-uniformity. Our work aims to develop such methodology using the theory of non-linear dynamics. The theoretical framework is introduced using the preheating of two parallel-connected cells under simplified conditions as an example. Two types of portraits with zero and non-zero △T are revealed in phase plane. The one with a single stable focus in the vicinity of the diagonal is preferred as it represents a small △ T . A methodology to determine the region of control parameters so as to maintain △ T within a prescribed limit is developed using bifurcation analysis, and validated with the preheating experiments. The restriction of factors, including the frequency, acceptable △ T , target temperature and preheating time, on such region are examined, thereby establishing an optimal region capable of simultaneously meeting the multiple design criteria for fast and uniform preheating. Utilizing the optimal region, engineer can identify the cells' steady-state temperature, estimate the power requirements of heating equipment, and determine the heat removal capability of BTMS, etc. in design stage, and optimize the control strategy in usage stage. • A methodology of thermal management is developed using phase plane and bifurcation. • The methodology can be applied to the design and control of both preheating and charge. • Two types of portraits with zero and non-zero temperature difference are revealed. • A region of control parameters is determined to enable fast and uniform preheating.

Design of a Fischer-Tropsch multi-tube reactor fitted in a container: A novel design approach for small scale applications

Small-scale Fischer-Tropsch Synthesis (FTS) plants for waste or biomass to liquid applications are more appropriate than mega-scale FTS plants because of different drivers, including environmental protection, economic development, and social progress. A novel design approach for multi-tube reactors for small-scale FTS plants was proposed where the activity of the catalyst was varied so that when the reactor tubes are scaled up, the maximum temperature in the reactor tube never exceeds a set upper limit. When designing multi-tube reactors in conventional commercial FTS plants, typically a suitable catalyst is identified using experiments run in laboratory reactors. The laboratory data is scaled up, and the measured catalyst activity is used directly in the design; however, this could result in the maximum temperature in the catalyst bed exceeding the safe catalyst operating range. The new design method was demonstrated by designing a multi-tube reactor for a mobile FTS plant that can fit into a commercial container. The performance for reactor tubes of different diameters, including CO conversion and productivity, was firstly predicted using CFD simulations. Simulations were conducted at the same safety constraint for temperature rise in order to utilize the corresponding heat removal capabilities efficiently. Catalyst activity and space velocity were set as controllable parameters in each simulation to ensure that the maximum temperature in the catalyst bed would meet, but not exceed, the temperature rise limit. Thereafter the diameter of single tube was optimized for total productivity, under the same space limit of the multi-tube reactor and tube bundle arrangement of the multi-tube reactor. According to the simulation results, the designed multi-tube reactor can obtain a productivity of 15.3 kg/h at the conditions: tube diameter of 3/4’, SV of 300/h, and catalyst activity of 695% of that in the base case. In the optimized case, approximately 2.2 tons of municipal solid waste or 2.0 tons of wood chips per day will be consumed by the containerized FTS plant. • A tubular reactor design for small-scale Fischer-Tropsch applications was proposed. • Designing the reactor for a containerized plant was taken as example. • Selection of tube diameter and optimization of catalyst activity were integrated. • A limit for temperature rise was set for maximum heat removal of tube and safety. • Productivity for reactor with a given space was optimized by simulation.

Preliminary thermal and mechanical analysis on the reactor core of a new heat pipe cooled reactor applied in the underwater environment

The heat pipe cooled nuclear reactor (HPR) has great potential in the underwater applications, as a reliable energy system provider, due to its advantages in the passive heat removal capability and avoidance of single point failure. For the newly proposed HPR concept design, NUclear Silence ThermoElectric Reactor (NUSTER), the thermal and mechanical analysis is performed, on the three-dimensional detailed solid core model, through the coupling of ANSYS Fluent and Mechanical. The safety limits are preliminarily proposed for the NUSTER, based on which the paper analyzes the reactor thermal and mechanical characteristics under the normal and heat pipe failure accidents. It is found that the core components, including the fuel rods, matrix and heat pipe can operate with large thermal margin in the normal condition. The heat pipe failure accidents will cause the large temperature increase of the fuel rods, matrix and heat pipes and significantly change the thermal stress distribution in the fuel Molybdenum (Mo) cladding and matrix. The Mo matrix temperature exceeds its temperature limit and the average thermal stress increases significantly in the two adjacent heat pipes failure accident of the 1/8 reactor core, indicating the further optimization of the matrix material in the future design.

Continuous process for the epoxidation of terpenes using mesoscale oscillatory baffled reactors

Continuous epoxidation of terpenes with H2O2 was carried out using mesoscale oscillatory baffled reactors (meso-OBRs) in a solvent-free environment. The performance of the new 3D-printed single, tri- and multi-orifice baffles was compared with helical and integral baffles. The performance investigated includes mixing intensity, induction period, steady-state attainment, and heat removal capability of the meso-OBR. Moreover, passive isothermalisation was also investigated using meso-OBR in a heat pipe assembly. The tri- and multi-orifice baffles were able to overcome mixing limitations and achieved a comparable rate of reaction to batch at mixing conditions of Reo > 850 and Reo > 500, respectively. Both baffles exhibited rapid steady-state attainment, shorter induction period (t = 1.5τ) and better reproducibility with product variation of ∼1.3%. The meso-OBR designs demonstrated effective heat transfer capability, allowing the reaction to being operated isothermally with ±1 °C temperature variation in solvent-free conditions. This removes the need for a solvent, thus reducing reaction volume by a 5-fold. The timescale for the reaction was reduced from ∼8 h in a conventional process to 30 min in the multi-orifice meso-OBR, a 16-fold reduction. A better process has been developed for a continuous epoxidation of terpenes with H2O2 using multi-orifice meso-OBRs, with a potential intensification factor of ∼80.

High heat flux testing for W/Cu monoblock PFUs with varying defects

The full tungsten divertor is the key component of Experimental Advanced Superconducting Tokamak (EAST) to exhaust excessive heat loads. After EAST discharge operation, defects may appear in the tungsten/copper (W/Cu) joints of W/Cu monoblock plasma-facing units (PFUs). In order to evaluate the heat removal capability and thermal fatigue stability of W/Cu PFUs with defects, the specific heat treatments are used for PFUs to introduce defects of varying degrees. Then, high heat flux (HHF) tests for PFUs with defects are performed on a 100 kW electron-beam (e-beam) device at ASIPP. The W/Cu joints defects and W surface conditions have no significant differences after HHF tests. And the test results show that the fewer defects or the larger water mass flow is, the better heat removal capability of the W/Cu monoblock has. The surface temperature of W/Cu PFUs with major defects (> 2 × 3 mm) is 12% - 17% higher than that of PFUs with minor defects (≈ 2 × 3 mm), and the minor defects PFUs is 6% - 8% higher than the non-defects one (< 2 × 3 mm). Besides, the temperature curves of three W/Cu PFUs are exponentially fitted in cooling down phase, and the obtained average thermal decay time constants are 11.1 s, 8.5 s and 7.4 s, respectively. The time constants quantitatively explain the cooling performance of PFUs with various defects, and provides a feasible method for non-destructive inspection of PFUs defects during EAST experiment. These results are conducive to understanding the relationship between damage degree and heat transfer performance, and can provide relevant basis for improving the acceptance criterion of qualified W/Cu PFUs.

Numerical investigation of two-component single-phase natural convection and thermal stratification phenomena in a rod bundle with axial heat flux profile

The most numerical investigations of the thermal-hydraulic phenomena following the loss of the residual heat removal capability during the mid-loop operation of the pressurized water reactor were performed according to simplifications and are not sufficiently accurate. To perform more accurate and more reliable predictions of thermal-hydraulic accidents in a nuclear power plant using computational fluid dynamics codes, a more detailed methodology is needed. Modelling results identified that thermal stratification and natural convection are observed. Temperatures of lower monitoring points remain low, while temperatures of upper monitoring points increase over time. The water in the heated region, in the upper unheated region and the pipe region was well mixed due to natural convection, meanwhile, there is no natural convection in the lower unheated region. Water temperature in the pipe region increased after a certain time delay due to circulation of flow induced by natural convection in the heated and upper unheated regions. The modelling results correspond to the experimental data. The developed computational fluid dynamics methodology could be applied for modelling of two-component single/two-phase natural convection and thermal stratification phenomena during the mid-loop operation of the pressurized water reactor or other nuclear and non-nuclear installations at similar conditions.