Flow In Cooling Channels Research Articles

Study on the influence of the hydrogen–oxygen stoichiometric ratio on the power performance improvement in a large-scale PEMFC stack

This study aims to determine the optimized hydrogen–oxygen stoichiometric ratio for power performance improvement in a large-scale proton exchange membrane fuel cell (PEMFC) stack by analyzing the characteristics of internal heat and mass distributions. The power performance of a large-scale PEMFC stack consisting of the designed stack cells with the counter flow directions of hydrogen and oxygen and a coolant flow channel was experimentally evaluated. Temperatures in the central stack cell were monitored. The coupled numerical simulation model was built to analyze the power performance as well as heat and mass distribution characteristics inside a stack cell. It was found that the greatest power performance of the PEMFC stack occurred at a specific hydrogen–oxygen stoichiometric ratio, and this performance had good uniformities of the temperature and water mass fraction distributions at the proton exchange membrane (PEM). The distribution characteristics of the hydrogen and oxygen mass fractions at the interfaces between the gas diffusion layer (GDL) and the catalytic layer (CL) due to the diffusion effect were analyzed. The mechanism of enhancing power performance from an electrochemical reaction was revealed by the greater gas distribution uniformities. Furthermore, a parameter of energy conversion ratio was employed to quantify the hydrogen utilization degree.

Research Progress of Enhanced Thermal Evacuation and Cooling Technology for High-Speed Motors

In high-speed motors, there is a huge amount of heat generation from core and winding losses, which may result in thermal failures or motor performance deterioration. In the prevention of heat accumulation, efficient cooling technology is critical for smooth and reliable motor movement. This paper summarizes the diverse application of high-speed motor and thermal requirements, such as in electrical devices, turbo-machinery, and high-precision machine tools. Three paths of case convection—cooling, internal ventilation cooling and spindle core cooling—are analyzed. Methods for configuring thermal resistance and improving cooling efficiency are summarized. Among them, coolant flow characteristics and flow channel shapes, gas supply ventilation systems, and methods to reduce air resistance, as well as axial cooling and integrated heat pipe structures, are extensively investigated. Finally, the development prospects of high-speed motor cooling are also forecasted. At present, the primary research directions are to reduce the heat generated by the heat source, utilize the latent heat of the coolant, optimize the cooling flow path of the shell, design an axial air-cooling circulation system, and enhance the heat dissipation of the spindle.

Collaborative optimization on cooling channel flow resistance and winding temperature for integrated cooling of motor and controller

The efficiency and working performance of the motor and controller system in micro-electric vehicles depends mainly on its thermal performance, which is contingent upon effective and active cooling. The working temperature of the motor and controller may be too high during operation, which properly causes motor power reduction or motor breakdowns. Therefore, it is crucial to design a good cooling channel for better cooling the integrated motor and controller system. This work proposes an integrated cooling channel of motor and controller, and the fluid-solid coupling analysis is applied for analyzing the velocity, pressure distributions of the cooling channel, and temperature distributions of motor solid components. Meanwhile, the collaborative optimization method based on the multi-island genetic algorithm (MIGA) is used to attain optimal design parameters of the integrated cooling channel of the motor and controller for obtaining a better cooling channel design with lower flow resistance and lower winding temperatures. Results show that the original cooling channel’s flow resistance and maximum winding temperature are 31.87 kPa and 120.04°C, respectively. The flow resistance and winding temperature are pretty significant. After optimization, the local vortex flow and zero velocity area in optimal cooling channel design are improved, the coolant flow velocity becomes more uniform, and the flow resistance is significantly reduced. The flow resistance and maximum winding temperature of the optimal cooling channel design are 12.5 kPa and 116.76°C, respectively, which are decreased compared with the original cooling channel structure, with a decrease of 39.4% and 2.7%, respectively. The research findings in this work can provide theoretical reference for solid components temperature evaluation of motor and give valuable data to cooling performance evaluation and optimization of integrated cooling channel for motor and controller system.

Experimental study of the thermal and power performances of a proton exchange membrane fuel cell stack affected by the coolant temperature

The optimization of thermal management (i.e. improving heat generation and dissipation) in a proton exchange membrane fuel cell (PEMFC) is a vital method to enhance its energy conversion efficiency. However, few studies have focused on the temperature uniformity in a massive PEMFC stack with a coolant flow channel. The aim of this study is to investigate the temperature characteristics and power performance affected by the inlet coolant condition in a massive PEMFC stack and establish a correlation of the temperature uniformity with the affected inlet coolant temperature for thermal management and power performance improvements in PEMFCs. The power density of a massive PEMFC stack with an active area of 326 cm2 (302 mm × 108 mm) of the designed stack cells with a coolant flow channel were experimentally evaluated, and the thermal characteristics were also analyzed using monitored temperatures inside specific stack cells by considering the different inlet coolant temperatures of 50 °C, 60 °C and 70 °C. It was found that the stack had the greatest power performance and minimum temperature increment of the inlet coolant at a temperature of 70 °C. The water phase transition heat transfer inside the stack was found to play a significant role in the thermal balance. The temperature distribution of the stack cell had a symmetrical convex curve from the center to the margin. The temperature gradient of the stack cell along the coolant flow direction was introduced to characterize the temperature uniformity. The linear development between the temperature gradient and the current density was determined adequately using a curve fitting. In addition, a lower fitting linear slope was obtained for a higher inlet coolant temperature, and this signified that a higher inlet coolant temperature could improve the temperature uniformity and power performance of PEMFCs.

The Effect of Curvature on the Heat Transfer Performance of Regenerative Cooling Passages for a High-Area-Ratio Nozzle

Abstract Numerical studies on the flow and heat transfer characteristics of rectangular regenerative cooling passages with lateral curvature for a high-area-ratio nozzle are presented. Unlike regular geometries of coolant paths used in various engineering applications, high-area-ratio rocket nozzles have steeply curved surfaces over which the cooling passages are provided. Though the inherent inward curvature benefits heat transfer enhancement in the throat region, it is insufficient to circumvent peak heat dissipation demand. Hence, the heat transfer enhancement due to lateral curvature of the coolant fluid passages provided near the throat region is explored in this study. Extensive numerical simulations have been performed to analyze the effect of the geometry of the cooling channel on its flow and heat transfer characteristics. The compressible turbulent flow field inside the nozzle has been resolved to understand the realistic local wall heat transfer characteristics of the typical high-area-ratio rocket nozzle using Advection Upstream Splitting Method (AUSM) scheme-based finite volume solver. Menter’s Shear Stress Transport k–ω turbulence model is used to model the turbulent flow inside the nozzle. Simulations of the incompressible coolant flow and conjugate heat transfer in regenerative cooling passages have been performed with realistic spatially varying local heat flux profiles, resulting due to compressible gas expansion in the convergent–divergent nozzle. Secondary flow structures are formed due to the lateral curvature of the coolant fluid passages and are found to enhance the heat transfer considerably. Further, the effect of coolant flowrate and channel curvature have been examined to explore its suitability to negotiate the peak heat flux dissipation demand at the throat region of the nozzle.

CFD based study of fluid flow and heat transfer effect for novel turning tool configured with internal cooling channel

Internal-cooling method due to its numerous advantages has been used during the machining of hard to cut and difficult to machine materials. Cooling channels developed in the cutting inserts, drills, end mills and grinding wheels are used for the heat removal which is concentrated at a smaller region during machining process. So, these cooling channels play a vital role in decreasing the temperature and wear rate of the tools. The heat generation and transfer rate depend upon the physical configuration of the cooling channel. This research work presents novelty in the concept of developing internal cooling channel cutting inserts with different profiles. Three different profiles have been developed to investigate cooling effect on the turning tool insert with different shapes. The results have been compared with the standard tool having no cooling channel. Computational Fluid Dynamics (CFD) has been used to simulate temperature rise for all profiles. A temperature drop of 188 K has been found for internally cooled cutting insert in comparison to the standard tool having no channel. It has also been found that the temperature difference of range 20 K–88 K can be achieved by varying the profile of the channel. Besides this, an increase in the inlet pressure of the cutting fluid has been found to make the coolant profile more efficient in terms of heat removal. Through the velocity vector results, it has been found that with more flow velocity of coolant inside the channel more heat transfer takes place. Turbulence Kinetic Energy (TKE) results showed that the heat transfer rate can be increased with an increase in the TKE value which in turn depends upon the profile of the coolant flow channel. This CFD study in turn has laid the platform for setting the optimum parameters during the turning of Titanium alloy with internal cooling channels.

Study of a Flow Field Design Suitable for Scaled-Up Fuel Cell Stacks

Fuel cells are used for automotive and stationary backup applications due to their lower operating temperature and high power density. The performance and robustness of Proton Exchange Membrane Fuel Cells are susceptible to the reactant distributions in the flow fields, operating pressure and humidity. It is crucial to maintain the critical parameters within the operating range to achieve improved performance. Moreover, water flooding on the cathode side is one of the significant issues associated with the scaled-up cells at higher power densities, leading to a drop in performance in PEMFC. This paper describes a novel flow field configuration used on the cathode side. In the present work, simulation and experimental validation are carried out on the scaled-up design consisting of oval and round shape patterns with uniform distribution at the inlet and outlet of the cathode side. A serpentine flow channel on the anode side and dual serpentine flow channel configuration as coolant flow channels are considered. This design achieves higher performance, low parasitic power requirement and uniform reactant distribution. The simulation results are validated against experiments and show good agreement with experiment results. A current density of 1.05 A/cm 2 at 0.58 V is obtained with the scaled-up design.

Preliminary Design of a Heat Pipe-Cooled Blanket for CFETR

Blankets are a difficult problem for fusion engineering design. Because of the complex flow channels, the design, production, processing, and accident maintenance of blankets are all huge challenges for traditional water/gas-cooled blankets. Blankets are the bridge for heat transfer and tritium production. A high-performance blanket with simplified structure is obviously beneficial for engineering, safety, and the economy. In this study, gravity heat pipes instead of coolant flow channels are adopted to remove the heat. Compared with coolant-cooled systems, heat pipes may be simpler and more reliable. The in-vessel and in-box loss of coolant accident (LOCA) will not occur because there is no coolant in the blanket. Moreover, a damaged heat pipe may be replaced easily compared to a damaged water-cooled blanket. In this study, a hypothetical heat pipe-cooled blanket for the China Fusion Engineering Test Reactor (CFETR) was proposed and one module of the blanket was analyzed by numerical simulation. The results were compared with those of a water-cooled blanket, and the temperature distribution of the heat pipe-cooled blanket is more uniform. This study verified the preliminary feasibility of heat pipe-cooled blankets and provided a fresh idea for blanket design.

Numerical simulation of single-phase flow in a single square tube with blockage

CFETR was built to study and harness fusion energy, whose Coolant channel consists of square parallel tubes. Under certain operating conditions, such as foreign object entering, the coolant flow channel may be blocked. In this point, the flow of coolant through the blocked channel will decrease, and cause a rise in wall temperature, which will lead to local evaporation and eventually material damage and radioactive material leakage. In this paper, ANSYS FLUENT is used to calculate and study the case with 20%, 40%, 60% and 80% blockage of the cross-section area of the square tube in the middle of the flow channel, respectively. Different turbulence models and Reynolds numbers are considered. From the calculated results the following conclusions are drawn: (1) The increase of Reynolds number or the increase of area blockage share will lead to the increase of local pressure drop, up to about 17000 Pa. (2) With the increase of the blockage area share, the vortex radius of the downstream of the blockage becomes larger and larger, and the maximum value can reach about 40 mm. (3) The center of the vortex goes further and further away from the blockage object. (4) The SST k-ω model is recommended.

Transient 3D conjugate heat transfer simulation of a rectangular GOX–GCH4 rocket combustion chamber and validation

This paper aims to predict the transient temperature fields of rocket combustion chambers. This is important for design and lifetime estimation. A thermally coupled simulation (conjugate heat transfer) model was developed and validated using a combustion chamber experiment with rectangular cross-section and the propellant combination gaseous oxygen–methane. The simulation is based on a thermal finite element model of the structure, Reynolds-averaged Navier–Stokes simulations of nine cooling channel flows and a Reynolds-averaged Navier–Stokes simulation with flamelet extension of the hot-gas flow. A pseudo-transient, implicit Dirichlet–Neumann scheme is used for calculating the equilibrium of structure and fluids. A comparison with experiment shows good agreement with the axial, vertical and transverse temperature distribution in the structure, the transient behavior and the wall heat flux through the cooling channels. It is shown that wall functions in the coolant domains can efficiently decrease the computational effort.

Effect of nonuniform isoflux heating on natural convection heat transfer in a prismatic modular reactor

A high temperature and pressure dual-channel facility has been designed and developed at Multiphase Reactors Engineering and Applications Laboratory (mReal) at Missouri University of Science and Technology (Missouri S&T) to investigate the thermal hydraulics of natural circulation under the loss of flow accident scenario (LOFA) in the core of a prismatic modular reactor (PMR). An advanced heat transfer measurement technique consisting of a series of heat flux foil sensors and thermocouples is adapted and implemented along the coolant flow channels (riser and downcomer channels). This study presents the effect of nonuniform isoflux heating (1.432 kW/m2 to 3.152 kW/m2, in form of stepwise-reducing and stepwise-increasing) on natural circulation heat transfer using air as a coolant at 413.7 kPa. The results showed a reversal in the direction of heat transfer and reduction in temperature fields as well as observed within the riser flow channel close to the exit (Z/L = 0.773) due to the end effect. A significant reduction of the average field temperatures along the riser channel is observed to be 24.5% and 22.4% for inner surface and air centerline temperatures, respectively for stepwise-reducing. Moreover, for stepwise-increasing, a significant reduction of the average riser channel temperature fields is observed with decreasing stepwise-increasing heating by 25.6% and 23.1% for the inner surface and air centerline temperatures, respectively. The average values of the heat transfer coefficient(h¯L) and the average Nusselt number (Nu¯L) along the riser channel were decreased with reducing the heating by 38% and 19% for stepwise-reducing heating, respectively, and by 32% and 13% for the stepwise-increasing heating, respectively.

Effects of Coolant Flow Characteristics and Channel Surface Temperature on Nucleate Boiling Heat Transfer in IC Engine Cooling System

Effects of Coolant Flow Characteristics and Channel Surface Temperature on Nucleate Boiling Heat Transfer in IC Engine Cooling System

Heat Transfer and Combustion Simulation of Seven-Element / Rocket Combustor

In the present Paper, the simulation of the flow inside an experimental rocket thrust chamber is undertaken. The combustor’s injector consists of seven individual coaxial injector elements, while the chamber and nozzle segments are water cooled. The results presented in this Paper are obtained with three-dimensional Reynolds-averaged Navier–Stokes simulations using an adiabatic flamelet formulation for the chemistry modeling. The main focus is placed on examining the effect of the different turbulence models on the flame structure and on the resulting pressure and wall heat flux. The obtained numerical values are compared to experimental measurements, delivering good agreement in the heat flux profile at the combustion chamber wall and a slight underestimation of the pressure profile of approximately 2.5%. Greater discrepancies are observed in the heat flux of the nozzle segment but are largely attributed to the experimental setup. A conjugate heat transfer simulation of the structure and cooling channel flow confirms this assumption, and results for both one-way and two-way couplings are shown. It is demonstrated that a one-way coupling between hot gas and structure is sufficient due to the low sensitivity of the wall heat flux on the wall temperature. The azimuthal variation of the heat flux is also examined, and interestingly the heat flux showcases a local minimum at the position directly above the injector element. It is shown that an increased concentration of colder fuel-rich gas directly above the injector due to a strong vortex system leads to the local minimum in heat flux values and is strongly influenced by the injector/injector interaction near the face plate.

An Acoustic Quench Detection Method for CICC Conductor Operating in Gas or Liquid

A method using micro-electro-mechanical system (MEMS) acoustic sensor technology to detect a quench and abnormal behavior of a superconductor is discussed. MEMS of microphone chips are installed along the coolant space of a superconducting conductor to monitor the coolant condition. By arranging the acoustic sensor array in a coolant flow channel, it is possible to quickly detect a change in the local condition of the coolant with precise spatial resolution. This method is useful for monitoring superconducting magnets and power cables, especially those made with a cable-in-conduit-conductor (CICC) configuration. The methodology described in this work will also be very useful for a high temperature superconducting (HTS) conductor, such as REBCO tape conductors.

Performance improvement in a proton exchange membrane fuel cell with separated coolant flow channels in the anode and cathode

Thermal management is critical for improving the performance of a proton exchange membrane fuel cell (PEMFC). Operation temperature can directly affect the saturated water vapour pressure and thus the water transport between the anode and cathode in PEMFCs. However, current researches on the effect of operation temperature on the performance are based on convenient design of a joint coolant flow channel for the anode and cathode. Consequently, the independent effect of the temperature on the anode or cathode is ignored. In this study, a single PEMFC with separated coolant flow channels in the anode and cathode is fabricated to investigate the effects of different anode and cathode operation temperatures on the performance. The results show that different anode and cathode operation temperatures could affect the performance of PEMFCs. A lower anode temperature improved the electro-osmotic drag role of water transport from anode to cathode. Hence, the PEMFC performance increased both with the increasing cathode operation temperature and the temperature differences between the cathode and anode. Higher operation temperature improves the activity of the catalyst, and water management and elevated operation pressure affect the kinetics of the electrochemical reaction. Peak performance is obtained through the balance of operation temperature, pressure and water management, particularly for different anode and cathode operation temperatures of PEMFCs.

Heat transfer in PEM cooling flow field with high porosity metal foam insert

Conventional cooling channel flow fields of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) introduce some challenges that would reduce the cell total performance. So presenting novel ideas to improve the cooling flow fields is fully appreciable. The more common conventional flow fields include the serpentine, parallel and multichannel would be precisely studied in this paper. In order to see the effect of porous materials in heat transfer, metal foams were introduced to the channels. Unlike continuous long flow passages in conventional channels, metal foams provide randomly interrupted flow passages. Re-circulation of fluid, due to randomly distributed tortuous ligaments, enhances the heat transfer in these new channels. Moreover, to assess the features of utilizing metal foams in cooling channels, different parameters like metal type, porosity percentage and also the cooling media were investigated. Since both thermal and hydraulic points of view are important in cooling engineering, the heat transfer and pressure drop for all three channel types were verified. The results showed that enhancing the porosity of the metal foam would decrease both heat transfer and pressure drop. Also the multi-channel type revealed the best heat transfer behavior in presence of metal foams.

Impact of Flow Conditions in Cooling Channels on Thermal Cycling

In order to improve the set-up of industrial press hardening processes, companies and researchers are spending considerable efforts in the design and positioning of cooling channels. Following the increasing demands for modelling options, FEA software vendors have implemented corresponding features in their codes. Modeling cooling channels in FEA simulation facilitates a more accurate prediction of the location and dimensions of hot spots on the tool surface.The present simulation case study is based on a complete tool set up for a typical part. The FE-model of tool set-up, including a suitable cooling channel design, has been utilized for a study on press hardening of 22MnB5. The effectiveness of cooling channel design is determined by the flow conditions of the cooling media - here water. The flow rate and cooling media temperatures are the parameters with most influence on the thermal behavior of the tool. The impact of variations in these parameters on the final surface temperature distribution on tools, and the ramp-up of this distribution to thermal steady state, are the subject of this study. Beyond tool temperature distribution, the impact of the above parameters on the quality of produced parts is assessed by evaluating typical part quality metrics: hardness, martensite volume fraction in the part’s microstructure, and thermal distortion.It is observed that due to the complexity of the press hardening process, the details of cooling channel flow conditions do not carry a direct and proportional impact on part quality outcomes. This observation clearly indicates that engineers can derive descriptions of the cooling channel flow conditions from easy-to-use analysis tools that are fully integrated with the simulation of the forming process, rather than resort to extended, time consuming “offline” flow computations. An analytical method for calculation of cooling channel flow conditions is also introduced by the authors.

Enhancement of the Cooling System Performance of the Proton-exchange Membrane Fuel Cell By Baffle-restricted Coolant Flow Channels

The performance of proton-exchange membrane fuel cell cooling system using coolant flow channels enhanced with baffles was numerically investigated. To do this, the maximum temperature of the cooling plate, temperature uniformity and also pressure drop along the flow channels were compared for different cases associated with number of baffles and their dimensions inside the channels. The governing equations by the finite-volume approach in three dimensions were solved. Numerical results indicate that the baffle-restricted cooling flow channels, generally improved the performance of the fuel cell in such a way that a reduced maximum temperature of the cell and a better temperature uniformity in the cooling plates were determined. As the pressure drop increases by incorporating the baffles inside the coolant flow channels, one needs to compromise between the improvement of cooling system performance and the total pressure drop.

Improvement on film cooling effectiveness by a combined slot-effusion scheme

Experimental tests are performed in the current study to explore the overall cooling performance of a combined slot injection/effusion array cooling structure. The pure slot injection and pure effusion array cooling schemes are taken into consideration for the comparison purpose. In addition, numerical simulations on the adiabatic and overall cooling effectiveness are also performed to illustrate the conjugated effects, such as internal convective heat transfer inside the coolant flow channel, thermal conduction inside the perforated plate, and internal cooling in the multiple holes, on the film cooling performance. The combined cooling scheme overcomes respective drawback of slot injection cooling in its decayed stage and effusion array cooling in its developing stage, thus producing a more ideal cooling performance over the entire protected surface under the same coolant usage. Due to the conjugated effects, the influence of adding slot injection on improving overall cooling effectiveness is significantly weaker than that on the adiabatic cooling effectiveness. Related to the pure slot injection or effusion array cooling scheme, the benefit of combined cooling scheme on the film cooling improvement is dependent on the blowing ratio. Under a combination of Msl=0.5 and Meff=0.4, it produces more obvious improvement on overall cooling effectiveness. While under a combination of Msl=0.5 and Meff=1.2, the overall cooling effectiveness in the front zone of effusion array is a little less than the pure injection scheme.

Carbon fiber composites with 2D microvascular networks for battery cooling

Electric vehicle (EV) batteries require both thermal regulation and crash protection. A novel battery packaging scheme is presented that uses microvascular composite panels with 2D channel networks to accomplish both objectives. Microvascular carbon fiber/epoxy composite panels are fabricated by vacuum assisted resin transfer molding, with the channel network formed by post-cure vaporization of an embedded polylactide channel template. Panel cooling performance is evaluated for parallel, bifurcating, serpentine, and spiral channel designs at different coolant flow rates and channel diameter. The spiral design provides the best thermal performance, but requires high pumping pressure (>100kPa) at the flow rates needed for adequate cooling (>30mLmin−1). The bifurcating design and a network obtained by computational optimization offer much lower pressure with slightly reduced thermal performance. Channel diameter has negligible effect on cooling performance, but strongly affects pumping pressure. Computational fluid dynamics (CFD) simulations are also performed and correlate well with the experimental data. Simulations confirm that microvascular composite panels can cool typical battery cells generating 500Wm−2 heat flux below the target temperature of 40°C.