Lower Temperature Distribution Research Articles

A model predictive fault‐tolerant control strategy for non‐redundant T‐inverters with multiphysics‐circuit coupling loss analysis

SummaryThis paper presents a multiobjective optimal power prediction fault‐tolerant control (MO2PPC) approach for mitigating DC link neutral‐point voltage imbalance and current ripple problems in three‐level T‐type inverter (3LT2I). Additionally, an auxiliary thyristor is employed to isolate and reconstruct the faulty phase into an 8ST2I for ensuring uninterrupted operation during phase failure. A method called injected bias current‐MO2PPC (IBC‐MO2PPC) fault‐tolerant strategy is proposed for this structure. This approach eliminates the need for DC or AC current sensors to reconstruct the three‐phase current, thereby reducing neutral‐point oscillation caused by phase deficiency and ensuring full power output after failure. Additionally, nonfaulty phase power loss is compared and analyzed to verify the stability of this method following a phase fault. The internal losses and temperature distribution of an IGBT module in a bridge arm before and after a fault are verified through a multiphysics‐circuit model in COMSOL‐Simulink coupling simulation presented last. The model shows reduced conduction losses and overall lower temperature distribution in the IGBT module after fault reconstruction. Experiments and multiphysics simulations have demonstrated that this approach displays exceptional robustness and sustainability throughout the entire fault cycle.

Numerical Simulation of the Effect of Particle Size Distribution on Fluidized Bed Gasifier

The rapid development of technology and industrialization has confronted humanity with two important problems: the depletion of fossil energy resources and environmental damage. This study aims to determine the effect of the particle size distribution of the bed on the composition of the produced syngas which has the potential to replace fossil fuels. The particle bed used is silica sand with 4 variations of particle size distribution with a diameter of 600-1000 µm. The results of this study indicate that the larger the particle size distribution of the bed can reduce the temperature distribution and composition of the syngas produced. The highest temperature distribution was found in the 1st particle size distribution variation of 1060.23 K. The highest syngas composition was found in the 3rd particle size distribution variation of 2.21% CH4, 19.68% CO, 6.21% CO2, and 18.51% H2The highest syngas composition was found in the 3rd particle size distribution variation of 2.21% CH4, 19.68% CO, 6.21% CO2, and 18.51% H2. The lowest temperature distribution was obtained in the 3rd particle size distribution variation of 1057.77 K. The lowest syngas composition was found in the 4th particle size distribution 1.99% CH4, 17.71% CO, 5.63% CO2, and 16.66% H2.

Energy, economic, and environmental analysis of converging air-based photovoltaic-thermal (air/PV-T) systems: A yearly benchmarking

Two converging channel configurations of photovoltaic-thermal (PV-T) systems, i.e., inlet and outlet at different sides (Case 1) and the inlet at the middle and outlets at the sides (Case 2), are investigated numerically. The results reveal that Case 1 features a nearly uniform and lower temperature distribution (up to 7 °C) for practical air flows, and the appropriate convergence ratio is 2:1 (inlet to outlet channel height) for which the PV surface temperature is lower by 8 °C than that of a similar conventional collector. Meanwhile, energy analyses based on the so called ‘rate of extra energy gain per PV surface area, E˙Ac (W/m2)’ show that the air mass-flow rate has an optimal limit of ∼0.1 kg/m2. s for a typical conventional power plant conversion factor (PPCf) of 0.3–0.4. At this limit, up to 500 W extra power per unit area of PV module can be gained by changing a PV to its proposed counterpart PV-T system reducing the levelized cost of energy (LCOE) by an order of magnitude for the PV-T (0.02–0.054 $/kWh) compared to a standalone PV (0.037–0.146 $/kWh). Such PV-Ts show 10% and 150% net CO2 mitigation in comparison to the conventional PV-Ts and the corresponding standalone PVs.

A new generation of a ceiling air outlet using multi-objective optimization technique

The proper selection of ceiling air outlets represents an important step in efficient space comfort conditions. Square louver face ceiling diffusers are the most ceiling outlets used in the air conditioning applications. A small change in the geometry of this diffuser has well effect on the air flow distribution and occupant's thermal comfort inside the room. In the present work, with the aid of optimization methodology and computational fluid dynamics, different simulations and surrogate models are performed to obtain the optimal design of the diffuser by changing the variable parameters (blade and lip angles) of the standard diffuser. The optimization results of three surrogate models showed that the most suitable objective functions are jet velocity, terminal velocity and temperature difference, and the optimal diffuser shape is 64° blade angle and 2° lip angle. In addition, the reported results showed that the average terminal velocity of the optimal diffuser across the room (0.126–0.257 m/s) is higher than that provided by the conventional diffuser (0.107–0.228 m/s), and neither value exceeds ASHRAE standard conditions. Also, with a temperature difference of 1.25 °C for the optimal diffuser, the temperature distribution across the room shows a lower temperature distribution than that shown for the standard diffuser. Finally, the air with an optimal diffuser shape reaches comfort conditions faster than with conventional diffusers, which directly leads to minimising energy consumption.

Effect of fin width ratio on thermal performance of fin based-heat sink with phase change materials

The rapid development of electronics, coupled with need of miniaturization in the design and manufacture, makes heat dissipation, which is critical for the performance, lifetime, and reliability of the components extremely challenging. To achieve higher heat dissipation rates, novel fin geometry with variable cross-section considering melting behaviour in medium is presented for PCM-based heat sink beyond previous efforts in literature. In this experimental study, effect of different variable cross-section, which refer different fin width ratio (s = 1, 0.5, 0.2 and 0) values are performed on the thermal performance of plate fin-based heat sink with PCM to enhance melting heat transfer. Decreasing fin width ratios point out increasing heat transfer surface area downwardly. N-eicosane is used. The constant input power is provided at the heat sink base. Thermal performance of novel fin design is evaluated by time-dependent temperature distributions, solid–liquid interface tracking photographs, reliable operating time, enhancement ratio, and thermal conductance. The results reveal that the proposed plate-fin geometry has a significant effect on the cooling performance of PCM-based heat sink. With the decrease of fin width ratio, higher temperature profile with more uniformity of 52% in the PCM medium, and so lower temperature distribution of 4.5% on the heat sink base are provided. Reliable operating time and thermal conductance values go up 15 % and 38%, respectively, for proposed fin geometry. The improvement on the thermal performance is achieved by the form of the plate-fin, which has increased surface area downward. This provides a great contribution to the conduction and convection heat transfer mechanisms at the lower half of the enclosure. Further, in this study, nearly the same reliable operating time is figured out with proposed fin geometry and fin number of s = 0 compared to higher fin number installation of s = 1 previously reported.

Temperature characteristic of a gain fiber core in distributed side-coupled cladding-pumped fiber amplifiers with different pump schemes

In this paper, we study the temperature characteristic of a gain fiber core in distributed side-coupled cladding-pumped (DSCCP) fiber amplifiers by optical frequency domain reflectometry (OFDR). To the best of our knowledge, this is the first temperature distribution measurement of a fiber core in DSCCP fiber lasers. The temperature distributions are also firstly measured among forward, backward, and bidirectional pump schemes. In addition, the bidirectional pump scheme has lower temperature distribution than unidirectional pump schemes. The experimental fiber core temperature is in according with the numerical simulation, which was once introduced for the temperature study of DSCCP fiber amplifiers. By experimental measurement and theoretical modeling, it is found that the maximum core temperature is several tens of centimeters away from the injected end of the DSCCP fiber, such that it will distribute the heat load along the longitudinal direction and reduce the maximum thermal load with better thermal management advantages than ordinary double cladding fiber (DCF).

An efficient numerical scheme for fractional characterization of MHD fluid model

How to precisely characterize the fractional modeling and physical treatment is an ongoing challenge in fluid mechanics and numerical techniques, especially in nonlinear complex models. A model study is conducted to report fractional time-dependent mixed convection incompressible fluid flow inside a channel. The physical system is under the impacts of viscous dissipation, electrical and magnetic fields. Three fractional operators Atangana Baleanu Caputo (ABC), Caputo Fabrizio (CF), and classical Caputo (CC) are involved into the temporal derivative. Transformations are used to convert the physical model into equivalent fractional partial differential equations (FPDEs). The computational code is developed for finite difference schemes and code validation is made for different fractional operators. The simulations have been performed to check the appropriate fractional operator and a comparison is made to check the accuracy and efficiency. Additionally, a set of graphs is asserted to show the velocity and temperature distribution for various values of parameters. Velocity is analyzed as decreasing function with an enhancement in the Rayleigh number while the higher fractional parameter (α) causes a dominant drop. A dropped velocity is analyzed in the absence of oscillation and enhanced velocity for higher oscillation, while a more dominant increment in the velocity is noted when Λ0 is non-zero. A decrease in the thermal layer is observed for higher Pe, and a more dominant impact is noted for smaller values of the fractional parameter. The pattern of the thermal profile is observed enhancing when there is an involvement of radiative parameter while lower temperature distribution is noted in the absence of the radiative term.

Heat transfer intensification by EHD conduction pumping for electronic cooling applications

Liquid based cooling has become a new prospect in the thermal management of electronic devices. This work numerically investigates the potential of EHD conduction pumping to remove heat from a high density flux heat source, as commonly encountered in electronic cooling applications. A 2-D horizontal plate configuration with a heated patch releasing uniform heat flux has been considered. EHD conduction flow of dielectric fluid generated by the space charge developed due to the Onsager effect has been considered. The coupled set of governing equations are incorporated into the finite-volume framework of OpenFOAM®. The numerical implementation in OpenFOAM® is validated against experimental and numerical benchmark results. Present results exhibit good agreement with the benchmark solutions. Combined interaction of natural convective flow and EHD conduction pumping induced flow is studied. The effects of Rayleigh number and electric Reynolds number are investigated. The flow morphology of thermal convection is altered by the EHD conduction pumping flow. Flow strength is intensified and lead to heat transfer augmentation. Lower temperature distribution and higher mean Nusselt numbers are observed along the heated patch. The heat transfer intensification obtained by EHD conduction pumping is more prominent at lower Rayleigh numbers and higher electric Reynolds numbers. A maximum heat transfer enhancement of up to 31.2% is obtained for the configuration and parameters considered in this study.

Investigation of thermal comfort performance and optimization of a novel refrigerant-heated radiator

In this study, a novel refrigerant-heated radiator (RHR) was introduced and a computational fluid dynamics (CFD) model was developed to investigate the influence of RHR structure parameters on indoor thermal comfort under heating and cooling conditions. Results show that the heating capacity and thermal comfort are improved with the increase of length-to-height ratio, while the thermal comfort is infringed if the length-to-height ratio is too large in cooling conditions. The length-to-height ratio of the RHR with 2.22–3.71 is recommended to meet the thermal comfort requirements in heating and cooling conditions. Comparisons were made between the RHR and air conditioner on indoor thermal comfort, which indicates that the RHR has a better thermal comfort in heating conditions in terms of temperature field, velocity field and thermal comfort indices. Under cooling conditions, the air conditioner has lower temperature distribution and more uniform vertical temperature distribution in human activity area, while the RHR has the excellent performance in the velocity distribution and thermal comfort indices. The findings show RHR has a better thermal performance than air conditioners in terms of overall thermal comfort. The research provides a guide to the benefit of RHR and improves the thermal comfort of ASHP system.

Thermal Performance of Finned Heat Sinks Embedded with Form-Stable Myristic Acid Phase Change Material in Photovoltaic Cooling for Green Energy Storage

Photovoltaic (PV) panels must be equipped with a cooling system to increase their electrical output generation. Despite numerous publications on the fabrication of form-stable phase change material (FSPCM) for thermal energy storage application, studies on the usage of FSPCM for PV cooling are incredibly limited. In this work, the cooling performance of myristic acid FSPCM encapsulated with cross-linked nitrile rubber (NBR) was investigated. A fin heat sink (FHS) was employed to hold the FSPCM. The thermal performance of the FHS embedded with FSPCM (FHS-FSPCM) was preliminarily tested in an indoor setup. Results show that the FHS-FSPCM has a lower temperature distribution curve than the bare FHS, highlighting the increase in cooling capability of fabricated FSPCM. Field-testing of PV panels integrated with an FHS-FSPCM displayed that FSPCM manages to reduce the operating temperature of the panel by 4 to 15 °C and increase power output generation by 38.61%.

Design and Simulation of Ethylene Cooled Microchannel Heat Exchanger for Micro Processors

In this study, a microchannel heat exchanger with operating with ethylene was proposed instead of air-cooled microprocessor heat sinks and flow and heat transfer simulations were made using Flo-EFD software. First, the temperature distribution of the air domain and the microprocessor in the computer case was obtained for air-cooled heat sink, and then the flow paths of the air coming from the outside with the help of the fan were observed. Afterwards, the system with the proposed micro channel heat exchanger was subjected to the same processes and the results were compared. As a result of the study, it was revealed that the micro channel heat exchanger reduced the processor temperature between 54-55°C and 18-19°C. It has also been observed that removing the heat sink allows the air drawn from the outside environment to circulate more efficiently around other heat generating elements in the computer case. Hence more homogeneous and lower temperature distribution within the computer case was obtained.

Heat Dissipation of Three Permanent Magnet Synchronous Motors Integrated with Heat Pipes

Three kinds of novel permanent magnet synchronous motors (PMSM) integrated with heat pipe whose evaporator is treated in different ways for electric vehicle are designed in order to decrease the end winding temperature. The influence of the geometric parameter of the cooling water channel on the thermal–hydraulic performance is analyzed. The temperature difference between the cooling water and the housing decreases, while the pressure loss increases with the spiral number increasing. Channel width and channel height have little influence on the temperature difference but have an apparent effect on the pressure loss. FLUENT, CFD software, is used to simulate the heat dissipation performance of the PMSMs. The highest temperatures of the end winding are 149.9 °C, 140.1 °C, 133.5 °C, and 139.6 °C for the traditional PMSM and the three new PMSMs, respectively. The lowest temperatures of the lamination of the four PMSMs are close. So are the highest temperatures of the lamination. The lowest temperature distribution profiles of the housing of the three new PMSMs do not change apparently compared with that of the traditional PMSM. It shows that after the optimization of the cooling water channel, the cooling water system of the new PMSMs works efficiently although more heat is transferred to the housing. Among the traditional PMSM and the three new PMSMs, new PMSM b shows the best heat transfer capacity.

A numerical investigation of friction stir welding parameters in joining dissimilar aluminium alloys using finite element method

Friction stir welding is a relatively new solid-state welding process which has several superiorities over generic welding methods. In this study, aluminium alloys (AA5083-O and AA6061-T6) are selected to investigate effects of three welding variables namely tool rotation speed, tool traverse speed, and tool diameter on temperature distribution, weld width, weld depth, and heat affected zone width using finite element method. The Johnson-Cook plasticity model is implemented into Abaqus software to simulate the material plastic deformation occurring during welding process. The results demonstrated that increasing rotational speed and tool diameter lead in an increase in material temperature. Increasing traverse speed resulted in lower temperature distribution. Temperature distribution, as well as the size and shape of welding areas, are also different due to different mechanical and thermal properties. The wider heat affected zone predicted for the AA6061-T6 can be explained by its higher thermal conductivity and lower specific heat. [Submitted 16 October 2018; Accepted 25 May 2019]

Overall numerical simulation and experimental study of a hybrid oblique-rib and submerged jet impingement/microchannel heat sink

In this work, two submerged jet impingement/microchannel heat sink (JIMHS) models were proposed, i.e., straight-rib jet impingement/microchannel heat sink (SJIMHS) and oblique-rib jet impingement/microchannel heat sink (OJIMHS). The heat transfer and flow characteristics of the two models were investigated by overall numerical simulation and experiment. In the numerical simulation, the effects of heat flux, pressure drop and rib arrangement on the internal flow and heat transfer of the heat sink were studied. The results indicate that under the same heat flux and inlet condition, the heat transfer surface of OJIMHS achieves more uniform and lower temperature distribution compared with that of SJIMHS, and the average convective heat transfer coefficient of the OJIMHS is obviously higher than that of SJIMHS in all calculation cases, with an increase of about 20%. In addition, the performance of OJIMHS was tested experimentally. The comparison indicates that the maximum relative errors of average temperature and heat transfer coefficient between simulation and experiment were less than 9%. When the volume flow rate is 0.5 L/min and the heat flux is 100 W/cm², the average temperature of the heat transfer surface is still lower than 60°C. Besides, the averaged heat transfer coefficient of 2.8W/(cm2·K) was achieved under the inlet fluid temperature of 283K and volume flow rate of 2.5 L/min in the experiment.

Effect of heat sink design on the thermal characteristic in computational fluid dynamics analysis

The thermal management in the electronic device or system using the heat sink is important to ensure the device or system operating under the allowable temperature. The present study aims to investigate the thermal characteristic (i.e., temperature distribution) of the various heat sink designs via computational fluid dynamics (CFD) analysis. The electronic cooling process of the heat sink is carried out via CFD software. The temperature distribution of the various heat sink designs (i.e., plate fin, circular pin fin and rectangular fin) was analyzed and compared. The CFD analysis revealed the plate fin heat sink has lowest temperature distribution on the fin region. High temperature distribution was observed on the pin fin heat sink. The non-uniform temperature distribution was attributed by the direction of inlet airflow, whereas the low temperature was found in the region that close to the inlet airflow. Thus, the research findings indicated the design of heat sink significantly affects the temperature distribution during the electronic cooling process.

Determination of an Optimal Oil Jet Nozzle Layout for Helical Gear Lubrication: Mathematical Modeling, Numerical Simulation, and Experimental Validation

To provide a basic guidance for the selection of nozzle layout, a mathematical model of the impingement depth for helical gears under oil jet lubrication is established. Furthermore, computational fluid dynamics (CFD) methods are adopted to validate the effectiveness and accuracy of the derived impingement model. Firstly, the distribution characteristics of the oil volume fraction and oil-gas pressure in meshing area were obtained in flow field simulation. Meanwhile, the influence of spray angle, jet velocity, and gear ratio on lubrication effect was obtained. Then, the transient temperature field of the tooth surface was simulated by the method of thermal-fluid coupling analysis, and the lowest temperature distribution and the corresponding oil jet velocity were determined. Finally, experiments on the temperature characteristics measured by an infrared thermal imager of helical gears with different nozzle parameters were carried out in a gear test rig. The simulation results of transient temperature field are in good agreement with those obtained by experiments, and it indicates that the thermal-fluid coupling analysis method is correct and feasible to predict the temperature field of the helical gear pair under oil injection jet lubrication.

A Numerical Investigation of Friction Stir Welding Parameters in Joining Dissimilar Aluminum Alloys Using Finite Element Method

Friction stir welding is a relatively new solid-state welding process which has several superiorities over generic welding methods. In this study, aluminium alloys (AA5083-O and AA6061-T6) are selected to investigate effects of three welding variables namely tool rotation speed, tool traverse speed, and tool diameter on temperature distribution, weld width, weld depth, and heat affected zone width using finite element method. The Johnson-Cook plasticity model is implemented into Abaqus software to simulate the material plastic deformation occurring during welding process. The results demonstrated that increasing rotational speed and tool diameter lead in an increase in material temperature. Increasing traverse speed resulted in lower temperature distribution. Temperature distribution, as well as the size and shape of welding areas, are also different due to different mechanical and thermal properties. The wider heat affected zone predicted for the AA6061-T6 can be explained by its higher thermal conductivity and lower specific heat. [Submitted 16 October 2018; Accepted 25 May 2019]

Effect of ultrasonic energy on the spot weldability of aluminum alloy AA6061

This study investigates the effects of superimposed ultrasonic vibration on resistance spot welding (RSW) of aluminum alloy AA6061-T6. A novel ultrasonically assisted resistance spot welding process, referred to as ultrasonic resistance welding (URW), is applied to weld AA6061 at various conditions and compared with the results from RSW. Lap shear tensile tests of URW welds show significantly improved mechanical properties, including higher strength, better ductility and higher amount of energy absorbed prior to failure compared with RSW welds. Optical micrographs of the weld cross section show that the ultrasonic vibration enhances nugget formation and minimizes porosities defects. Besides, equiaxed crystal structure is generally observed in the nugget center of URW welds whereas the majority of RSW fusion zone is dominated with columnar grain structure. In situ thermal imaging of the two processes shows a lower temperature distribution, smaller heating and cooling rates during URW. This is attributed to the ultrasonically assisted fracture and breakdown of surface oxides and contaminates, which reduces the contact resistance and accordingly heat generation rate.

Three-dimensional simulation of solid oxide fuel cell with metal foam as cathode flow distributor

In this study, the use of metal foam as a flow distributor at cathode is evaluated numerically by a comprehensive three-dimensional solid oxide fuel cell (SOFC) model. The results show that the adoption of metal foam improves the power density by 13.74% at current density of 5000 A m−2 in comparison with conventional straight channel design. It is found that electronic overpotential, oxygen concentration and reaction rates distribute more uniformly without the restriction of ribs. The effects of cathode thickness on the two different flow distributors are compared. Compared with conventional straight channel, the metal foam is found to be more suitable as a distributor for anode supported SOFC with thin cathode gas diffusion layer. Moreover, when metal foam is applied to the fuel cell with a larger reaction area, a more uniform velocity distribution and a lower temperature distribution can be achieved. It is also found that an appropriate permeability coefficient should offer a reasonable pressure drop, which is beneficial for the fuel cell system performance improvement.

Experimental and Numerical Investigation of Temperature Distribution in the Cutting Zone with Different Coated Tools in Orthogonal Turning Operations

In orthogonal turning operations, the mechanical energy is converted into heat. The generated heat influences tool life and wear, and the accuracy and quality of workpieces. In the current work, the temperature distribution at cutting zone was studied experimentally and numerically. The K-type thermocouple was utilized to measure the cutting zone temperature during turning process for steel AISI 1010. DEFORM-2D has been utilized to simulate the turning operation, which was carried out using many coated and uncoated carbide tools. The experimental tests were implemented at constant depth of cut with different feed rates and cutting speeds. The results of numerical and experimental tests are illustrated. The influences of coated and uncoated tools, feed rate and cutting speed in temperature distribution at cutting zone are discussed, whereby the TiN/Al2O3/TiCN coated tool has the lowest temperature distribution at cutting zone compared to the other coated and uncoated tools, while the uncoated tool has the highest temperature distribution compared to coated cutting tools. Also, the increasing of cutting speed and feed rate led to an increase of temperature at the cutting zone.