Coolant Channel Research Articles

Thermal-hydraulic simulation of loss of flow accident for WWR-S research reactor

Abstract A thermal-hydraulic model has been developed by RELAP5 code to simulate the thermal-hydraulic behavior of a WWR-S research reactor under loss of flow accident (LOFA). The reactor power is 2 MW with downward flow direction and different types of fuel bundles of different power densities and different coolant flow-rates. The simulation is performed for two scenarios; protected and unprotected LOFA. In the protected LOFA scenario; Scram is triggered as soon as the coolant flow rate reaches 85 % of its nominal value while in the unprotected LOFA scenario; the reactor continues operation during pump cost-down and natural circulation flow. Once the flow is low enough, the buoyancy force increases in the core leading to flow inversion phenomenon and establishment of a natural circulation mechanism within the core coolant channels in both scenarios. In the protected LOFA scenario, the coolant remains subcooled by a vast margin during transient while bulk boiling is predicted at the upper part of the core for the unprotected LOFA scenario. The heat fluxes leading to the onset of nucleate boiling and the critical heat flux are predicted and the safety margins are determined. The results for both scenarios are analyzed and discussed.

Optimizing Flow and Heat Transfer With Guiding Pin Fins in a Wedge-Shaped Cooling Channel for Gas Turbine Blade Trailing Edge

Abstract In this study, an innovative guiding pin-fin array optimization has been developed through three-dimensional numerical simulations to enhance the cooling efficiency of gas turbine blade trailing edge. The guiding pin-fin array is optimized using the Kriging surrogate model and Genetic Algorithm (GA), aiming to significantly improve the heat transfer rates and uniformity within the wedge-shaped channel. The design parameter chosen for optimization is the deflection angle of each guiding pin fin, and the optimization process is conducted in two rounds. The first-round optimization yields a first-optimized guiding pin-fin array, which exhibits superior overall heat transfer performance and reasonable pressure loss compared to conventional circular, oblong, and parallel pin-fin arrays. For the first-optimized guiding pin-fin (1st-OGP) channel at the Reynolds number of Re = 50,000, the total Nusselt number and pressure loss are 44.1% higher and 9.9% lower than those of the baseline circular pin-fin array (CP), respectively. An experimental validation using the transient liquid crystal (TLC) thermography method is carried out and proves the effectiveness of the optimization process. However, it is noted that the first-optimized guiding pin-fin exhibits even lower heat transfer at a low Reynolds number of Re = 10,000, particularly in the channel middle region, which is mainly due to the incapable turning flow control in the root region of the wedged channel. To address this issue and further improve the heat transfer performance at low Reynolds numbers, a second-round optimization is performed by specifically adjusting the deflection angle of the selected guiding pin fins near the root region of the wedged channel. This secondary optimization demonstrates significant heat transfer improvements over the whole studied Reynolds number range with a reasonably reduced consumption of computational resources. The total Nusselt number and pressure loss are 69.3% higher and 11.9% lower than those of the baseline circular pin-fin array, respectively, at Re = 50,000. The optimization process proposed in this paper produces a high-performance cooling structure design with elaborate guiding pin-fin arrangements in the wedge-shaped channel, which indicates high heat transfer enhancement and relatively lower pressure loss in the wedged channel for the turbine blade trailing edge.

Impacts of Material and Machine on the Variation of Additively Manufactured Cooling Channels

Abstract While additive manufacturing (AM) can reduce component development time and create unique internal cooling designs, the AM process also introduces several sources of variability, such as the selection of machine, material, and print parameters. Because of these sources, wide variations in a part's geometrical accuracy and surface roughness levels can occur, especially for small internal cooling features that are difficult to post-process. This study investigates how the selection of machine and material in the AM process influences variations in surface quality and deviations from the design intent. Two microscale cooling geometries were tested: wavy channels and diamond-shaped pin fins. Test coupons were fabricated with five different additive machines and four materials using process parameters recommended by the manufacturers. The as-built geometry was measured non-destructively with computed tomography scans. To evaluate surface roughness, the coupons were cut open and examined using a laser microscope. Three distinct roughness profiles on the coupon surfaces were captured including upskin, downskin, and channel walls built at 90 deg to the build plate. Results indicated that both material and machine contribute to producing different roughness levels and very different surface morphologies. The roughness levels on the downskin surfaces are significantly greater than on the upskin or sidewall surfaces. Geometric analysis revealed that while the hydraulic diameter of all coupons was well captured, the pin cross section varied considerably. Along with characterizing the coupon surfaces, cooling performance was investigated by experimentally measuring friction factor and heat transfer. The variations in surface morphology as a function of material and machine resulted in heat transfer fluctuating by up to 50% between coupons featuring wavy channels and 26% for coupons with pin fin arrays. Increased arithmetic mean surface roughness led to increased heat transfer and pressure drop; however, a secondary driver in the performance of the wavy channels was found to be the roughness morphology, which could be described using the surface skewness and kurtosis.

Modeling and Evaluation of Fluid Flow Resistance Characteristics of the Cooling Channel in the Aircraft Oil-Cooled Electric Machine

Modeling and Evaluation of Fluid Flow Resistance Characteristics of the Cooling Channel in the Aircraft Oil-Cooled Electric Machine

Optimizing coolant loop design across the stator core: A research study

Liquid cooling is widely used on high power motors. Optimal design of the coolant loop could help rise the power density. The coolant channels are placed across the stator core in this research. The heat dissipation performances of the coolant channel with different designs are compared and analyzed through simulation. Experiments were carried out to verify the simulation results and the feasibility of the cooling method. The results show that the coolant loop should be placed tightly close to the slots. The heat dissipation performance of the optimized coolant loop is efficient compared to the jacket cooling design. The coolant channels across the stator core could remain sealed under a 0.5 Mpa pressure at least according to the air proof test. The coolant pressure within the channels could be reduced efficiently through increasing the parallel loop number or moving the channels away from the slots properly. The winding temperature of the measured values and the simulated results of the motor with jacket cooling is within 2 °C.

Modular gas-cooled reactor core optimal design and additive manufacturing performance based on SiC matrix dispersed with TRi-structural ISOtropic fuel

High-temperature gas-cooled reactors present significant technical competitiveness in various fields, such as low-carbon electricity, thermal energy, and hydrogen supply. Silicon Carbide (SiC) matrix dispersed with TRi-structural ISOtropic (TRISO) particle fuel is characterized by high-temperature tolerance, radiation resistance, and good neutron economy, which has emerged as a pivotal technological pathway for reactor core design. With the rapid advancement of SiC Additive Manufacturing (AM) technology, there is a substantial increase in core design flexibility, and an innovative gas-cooled reactor design was proposed by Monte Carlo (MC) method in this paper. The Non-uniform Rational B-spline (NURBS), Latin Hypercube Sampling (LHS), second-order polynomial response surface, as well as Genetic Algorithm (GA) were coupled to realize the optimization design for the coolant channel. Besides, a modular fuel design was proposed, and the AM SiC shell was fabricated using Binder Jetting (BJ) technology. Furthermore, the densification of the AM SiC shell and the matrix with SiC powder and SiC microspheres (TRISO simulator) was investigated by Chemical Vapor Infiltration (CVI). Finally, the microscopic morphology analysis and thermal-mechanical performance characterization of the samples were conducted, which demonstrated the technical feasibility and advanced capabilities of the SiC matrix dispersed with TRISO fuel based on AM technology.

Mechanistic Insights into Effects of Perforation Direction on Thermal Hydraulic Performance of Ribs in a Rectangular Cooling Channel

Mechanistic Insights into Effects of Perforation Direction on Thermal Hydraulic Performance of Ribs in a Rectangular Cooling Channel

Proposal for Surface Smoothing of Additive Manufactured Cooling Channel with Electrochemical Machining and Basic Research on Its Application to Straight Holes

Proposal for Surface Smoothing of Additive Manufactured Cooling Channel with Electrochemical Machining and Basic Research on Its Application to Straight Holes

Design, analysis and development of a proton exchange membrane in fuel cell

This research presents the design and fabrication of a Proton Exchange Membrane fuel cell (PEMFC) utilising open pore cellular metal foam as the material for the flow plate. Efficient housing designs are suggested for both the hydrogen and oxygen sides, achieved by implementing. The study identifies the flow regime via the open pore cellular metal foam flow plate using Computational Fluid Dynamic (CFD) modelling and analysis techniques. Energy, environmental and economic analyzes (4E) and multi-objective optimization of a PEM fuel cell equipped with coolant channels Energy analysis of a proton exchange membrane fuel cell (PEMFC) with an open-ended anode using agglomerate model: A CFD study A transient heat and mass transfer CFD simulation for proton exchange membrane fuel cells (PEMFC) with a dead-ended anode channel. This research can provide appropriate references and recommendations for future Proton Exchange Membrane Fuel Cell (PEMFC) flow channel designs. The performance improvements of flow channel designs become significant at elevated current density, and with the output voltage increasing to 25.8 %. The estimated performance power of the fuel cell was 6 W, meaning that it was unlikely that the 10 W target would be achieved. In reality, the designs proved to have an excellent open circuit voltage of over 0.9 V, however, the maximum current achieved was below the target, and thus limiting the power to only about 2.1 Watts. The purpose of this paper is to give a general theoretical guidance for current and future relevant R&D activities aiming at high-performance, durable, and low-cost fuel cells as well as a thorough overview of the issues, advancements, and perspectives of the flow-field designs for bipolar plates in PEMFC.

Additively manufactured conformal cooling channels through topology optimization

Cooling channels play a critical role in various casting and molding processes, impacting both the cycle time and quality of the product. As additive manufacturing technologies become increasingly prevalent, conventional straight-drilled channels are being progressively substituted by intricate cooling lines that conform to the contours of the fabricated part. This transition can lead to a significant reduction of the solidification time and temperature gradients, consequently lowering the occurrence of part defects. However, designing such channels becomes challenging as geometric complexity and manufacturing constraints increase. In this work, we present a density-based topology optimization approach to generate conformal cooling channels in molds and dies inserts. To mitigate temperature variations, the objective function is penalized using the temperature standard deviation of the insert cavity surface. A density-gradient-based constraint is further utilized to reduce the generation of overhanging structures and promote manufacturability. In particular, the use of this constraint leads to the generation of channels characterized by a teardrop-shaped cross section. The cooling efficiency of a selected optimized design is confirmed through computations using a body-fitted solver. The geometry is subsequently manufactured by Laser Powder Bed Fusion (LPBF) and experiments are conducted to compare its performance in comparison to a design featuring straight-drilled channels. The results demonstrate that the optimized geometry significantly enhances the heat extraction rate and further leads to a 43% reduction of the cavity temperature standard deviation.

Geometrical Parameter Optimization of Circular Cross-Section Conformal Cooling Channels in Injection Molds of Plastic Paving Block Molds

Geometrical Parameter Optimization of Circular Cross-Section Conformal Cooling Channels in Injection Molds of Plastic Paving Block Molds

Investigation of the flow-heat-vortex mechanism in hot, coolant and delivery channels in film cooling under strongly-coupled boundary conditions using direct numerical simulation

The research investigated the flow dynamics, heat transfer, and vortices in film cooling using direct numerical simulation (DNS) with various blowing ratios (Br = 0.63, 0.86, 1.18) and Reynolds numbers (Re = 1000, 1000, 500) at an injection angle of α = 20°. The strongly-coupled (SCP) boundary conditions were applied to solve the transient governing equations including to mass and momentum conservations, thermal convection and heat conduction. Jetting effects in the delivery channel were studied by the DNS method in the environment of both hot and coolant channels. Distinctive vortex structures, including the horseshoe and hairpin vortices inside the delivery channel, were successfully identified with the recirculation and high-velocity stripes inside the channel. The heat-transfer mechanisms resulting from the vortices in hot channel highlighted the presence of kidney-shaped and reverse-kidney-shaped vortices impacting the Nusselt number (Nu) and comprehensive cooling effectiveness, which was enabled by the state-of-the-art VI method of Liutex.

Viscoelastic flow instabilities for enhanced heat transfer in battery pack cooling

Effective thermal management plays a critical role in ensuring peak performance for heavy-duty electric vehicle battery packs and high-performance electronics. To address the need for effective heat dissipation, liquid coolants are employed, which exhibit higher heat transfer performance compared to traditional air-cooled systems. However, the associated increased viscosity of such liquid coolants and constricted flow path lead to reduced mixing, thereby deteriorating the thermal performance of the system. Here, we explore the potential of utilizing viscoelastic liquid coolants for enhancing heat transfer from the heated walls of a constricted flow path with obstacles, modeling features of battery coolant channels. At low-Reynolds number regime, viscoelastic fluids exhibit instabilities which can disrupt the thermal boundary layer and enhance fluid mixing in the domain, thereby facilitating wall heat transfer. We employed computational fluid dynamics simulations, validated with experimental observations, to explore the effect of the flow geometry, Weissenberg number, solvent viscosity ratio, polymer extensibility, and Reynolds number on thermal performance. Our study indicates that the heat transfer is enhanced with flow instabilities in viscoelastic fluids, which can be generated exclusively in the flow channel with obstacles by increasing the Weissenberg number, reducing the solvent viscosity ratio, increasing the polymer extensibility, and increasing the Reynolds number. The enhancement in the heat transfer can exclusively be attributed to the elastic properties of the fluid in contrast to the inelastic shear-thinning fluids exhibiting no instability. The insights from the study can play an important role in the development of advanced, high-efficiency battery cooling systems, combining surface engineering and synthesis of optimized heat transfer liquids.

A Numerical Study on Endothermic Chemical Reactions of Supercritical n-dodecane in a Regenerative Cooling Channel of Hypersonic Vehicles

A Numerical Study on Endothermic Chemical Reactions of Supercritical n-dodecane in a Regenerative Cooling Channel of Hypersonic Vehicles

Flow distribution characteristics of parallel narrow rectangular channels under deformation conditions -Part I: An experimental study

Plate-type fuel assembly has been a promising option for core miniaturization applications. The parallel coolant channels, characterized by narrow rectangular with a large aspect ratio, may generate flow distribution deviation due to structural deformation. This study is dedicated to a comprehensive investigation of flow distribution characteristics accompanied by fluid boiling at high-pressure conditions in parallel twin narrow rectangular channels. The study will be presented in two parts: Part I of this paper comprises experimental methodology and flow distribution results. The experimental setup includes an integrated parallel channels geometry designed to improve pressure-bearing capabilities. Additionally, experiments are conducted on severe channel deformation modes, such as swelling and bending, by modifying the shape and dimensions of the ceramics within the test apparatus.Based on the experimental data, including pressure difference, wall and main fluid temperatures, the flow and heat transfer performance between twin channels is analyzed. Results shows that a significant deviation in flow distribution occurs in the swelling channel. Then methods involving thermal balance and pressure difference are employed to ascertain the mass flow rate of each distinct channel. The research reveals that the impact range of flow distribution is categorized into single-phase and two-phase control regions. The corresponding flow deviation of swelling channel surges from 5% to approximately 30%, significantly exceeding the design threshold specified for plate-type fuel assembly. Regarding the bending channel, the overall deviation consistently remains within 3%. Even when the fluid transitions into two-phase region, the flow deviation does not enlarge further. Moreover, a lower mass flux and higher heat flux aggravate the uneven flow distribution, while an increase in system pressure alleviates the flow deviation. Furthermore, Part II of this investigation introduces a numerical model derived from the experimental data, and the flow distribution characteristics under various channel deformations are examined through model calculations.

Numerical Study of Coolant Flow Phenomena and Heat Transfer at the Cutting-Edge of Twist Drill

Cutting tool coolant channels play a pivotal role in machining processes, facilitating the efficient supply of cooling agents to high-stress areas and effective heat dissipation. Achieving optimal cooling at the tool’s cutting-edge is essential for enhancing production processes. Experimental investigations into tribological stress analysis can be limited in accessing complex tool–workpiece contact zones, prompting the use of numerical modelling to explore fluid dynamics and tribology. In this study, the coolant flow dynamics and heat dissipation in drilling operations were comprehensively investigated through computational fluid dynamics (CFD) modelling. Four twist drill models with varying coolant channel arrangements were studied: standard model drill, standard model drill with notch, profile model drill, and profile model drill with notch. Two distinct approaches are applied to the coolant inlet to assess the impact of operating conditions on fluid flow and heat dissipation at the cutting-edge. The findings emphasize that cutting-edge zones have insufficient coolant supply, particularly in modified drill models such as the standard model drill with notch and profile model drills with and without notch. Moreover, enhanced coolant supply at the cutting-edge is achieved under high-pressure inlet conditions. The standard model drill with a notch exhibited exceptional performance in reducing thermal load, facilitating efficient coolant escape to the flute for improved heat dissipation at the cutting-edge. Despite challenges like dead zones in profile models, the standard-with-notch model yielded the most promising results. Further analyses under constant pressure conditions at 40 and 60 bar exhibited enhanced fluid flow rates, particularly at the cutting-edge, leading to improved heat dissipation. The temperature distribution along the cutting-edge and outer corner demonstrated a decrease as the pressure increased. This study underscores the critical role of both coolant channel design and inlet pressure in optimizing coolant flow dynamics and heat transfer during drilling operations. The findings provide valuable insights for designing and enhancing coolant systems in machining processes, emphasizing the significance of not only coolant channel geometry but also inlet pressure for effective heat dissipation and enhanced tool performance.

Development of a fixed Langmuir probe system for newly installed tungsten monoblock lower divertors in KSTAR

A fixed Langmuir probe system for newly installed tungsten monoblock lower divertors in KSTAR is developed. The probe structure is designed to effectively cooled via divertor coolant using inclined contact surfaces between the probe components. The probe body is tapered, narrowing up towards the divertor surface to enhance thermal contact conductance through mechanical forces exerted by the probe-divertor assembly. The probe structure is designed for easy replacement of a probe tip in the event of its damage and to accommodate different shapes of the tip. Currently, all the installed probe tips have 16° of inclination, i.e., one-sided rooftop shape, with respect to the surrounding divertor surface protruding 1.0 mm from the divertor surface. An individual probe system occupies two mono-blocks along the direction of the coolant channel. A single divertor cassette can accommodate 52 probes having a nominal poloidal spatial resolution of 12 mm. In the newly installed KSTAR divertor system, a total of 104 probes are installed at two toroidal locations. Thermal analysis on the probe structure indicates that the one-sided rooftop-shaped probe tips can withstand a localized heat flux of 10 MW/m2 for 2 s and 5 MW/m2 for steady-state operation. Experiments with a probe-divertor mockup are conducted in a linear plasma device under a magnetic field (|B|<360 G) and steady-state plasmas of a density of the order of 1011 cm−3. Possible analysis models for the I–V characteristics are discussed with practical applications to the measured data from KSTAR.

EVALUATION OF SURFACE DETERIORATION RESULTING FROM THERMAL FATIGUE IN THE OPERATIONAL STATE OF AN H13 PRESSURE DIE CASTING DIE

The failure rate of pressure die casting dies is increasing due to cracks on the die surfaces, leading to thermal fatigue and fracture. This paper aims to investigate the thermal fatigue failure of H13 die-casting die in running conditions by measuring the surface crack dimensions at core and cavity zones of the die during regular intervals of the die-casting process. The effect of length and width of the cracks on the die surface concerning coolant channel positions was analyzed. Transient thermal analysis was performed to investigate the temperature distribution, principal stress and total deformation of the die concerning to the coolant channel position using ANSYS. The maximum deformation of core insert was 0.0094 mm. Zone C of the core insert, which was 223.52 mm from the coolant channel location and corresponding to 139,237 cycles, had the longest crack, measuring 18.98 mm. Owing to greater temperature gradients, Zone Z of the cavity insert, which is situated 76.25 mm from the coolant channel, had the largest crack width, measuring 0.29 mm. The durability of the die casting die obtained from the numerical model (2.8×105 cycles) was in agreement with experimental studies (2.89×105 cycles).

Optimization Design of Injection Mold Conformal Cooling Channel for Improving Cooling Rate

Optimizing the design of the conformal cooling channel can increase the cooling rate of injection mold. The aim of this study was the problem of low cooling efficiency of injection mold for deep-cavity plastic parts under the conventional cooling channel. Based on the analysis of the heat transfer principle of the injection mold, a mathematical description of the cooling time of the conformal cooling channel was made. By designing orthogonal experiments and using simulation methods in the Autodesk Moldflow 2019 software, with the minimum cooling time of the mold as the optimization goal, experimental optimization was carried out for the three design variables of the channel, thereby obtaining the optimal combination of design variables for the conformal cooling channel. The conformal cooling channel layout was innovatively designed, and through computer simulation experiments, it was concluded that the conformal cooling channel adopted a series flat-head layout, which has the shortest cooling time and the fastest cooling rate. Metal additive manufacturing technology was used to complete the manufacturing of the mold insert with the conformal cooling channel. After the trial production of the conformal cooling injection mold, the molding cycle was obviously shortened, and the injection molding production efficiency was significantly improved.

EFFECTS OF COOLING CHANNEL DIAMETER, DISTANCE, AND PITCH IN PLASTIC INJECTION MOLDING

A straight drilled or conventional cooling channel is a linear cooling pathway that circulates around the mold cavity to regulate temperature during the plastic injection molding process. The cooling phase accounts for 70% of the plastic injection molding process, making it crucial to design the cooling channel for reducing cycle time while upholding part quality. This study aims to analyze the effects of cooling channel parameters on the product cavity. The parameters under consideration are the cooling channel's diameter, pitch, and distance. Various designs of cooling channels were examined. This study employed a food container lid made from polypropylene (PP) as a product case study. A 3D model of the food container lid and Straight Drilled Cooling Channel (SDCC) was created using CATIA V5, and these models were subsequently imported into Autodesk Moldflow Insight for simulation analysis. Four results were obtained from the simulation analysis, namely time to reach ejection temperature, average temperature, volumetric shrinkage, and deflection. The results indicate that increasing the diameter and pitch of cooling channels leads to a decrease in the average part temperature and the time required to reach ejection temperature. Conversely, increasing the distance between cooling channels results in an increase in the average part temperature and the time required to reach ejection temperature.