The Experts below are selected from a list of 27945 Experts worldwide ranked by ideXlab platform
Kui Jiao - One of the best experts on this subject based on the ideXlab platform.
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Effect of cooling design on the characteristics and performance of thermoelectric generator used for internal combustion engine
Energy Conversion and Management, 2015Co-Authors: Hai Diao, Zhiqiang Niu, Guobin Zhang, Gequn Shu, Kui JiaoAbstract:By developing a thermoelectric generator (TEG) model coupled with exhaust and cooling channels for an exhaust-based TEG (ETEG) system, the influence of the cooling type, coolant Flow rate, length, number and location of bafflers, and Flow Arrangement are investigated. It is found that the net output power is generally higher with liquid cooling than air cooling. Since a very low velocity of liquid coolant is sufficient for cooling the TEG modules, the Flow resistance is negligible, and inserting a baffler, increasing the baffler length or the Flow velocity generally improves the performance. However, both the baffler length and Flow velocity of air cooling need to be moderate. Placing one baffler in front of a TEG module is sufficient to guide the cooling Flow. The performance is generally unaffected by the change of baffler location. By maintaining sufficient temperature difference for all the TEG modules, the counter-Flow Arrangement leads to higher output power than the co-Flow Arrangement. Although liquid cooling is more complicated, and extra cooling power may be needed to cool down the circulating coolant, the temperature increment of liquid coolant through cooling channel is insignificant for cooling 20 TEG modules producing about 250 W of power.
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Numerical and analytical modeling of lithium ion battery thermal behaviors with different cooling designs
Journal of Power Sources, 2013Co-Authors: Kui Jiao, Kui JiaoAbstract:Abstract Thermal management is critically important to maintain the performance of lithium ion battery stacks. In this study, a numerical model and an analytical model for the thermal management of lithium ion battery stacks are developed to investigate the thermal behaviors of flat-plate and cylindrical stacks during discharging processes. It is found that for the same volume ratio of cooling channel and battery of flat-plate design, changing the channel size and the number of channels results in similar average battery temperatures, however, increasing the channel size improves the cooling energy efficiency but leads to more unevenly distributed temperature, and vice versa. The volume ratio of cooling channel to battery needs to be higher than 0.014 for flat-plate design when the Reynolds number of cooling air is around 2000 or higher with a high discharging rate of 2 C. The cylindrical battery stacks considered in this study are generally less compact and more energy-efficient in cooling than the flat-plate battery stacks, and the general thermal behaviors are similar between these two designs. A counter-Flow Arrangement of the cooling channels or changing the Flow direction of the co-Flow Arrangement periodically may also help the thermal management.
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measurement of current distribution in a proton exchange membrane fuel cell with various Flow Arrangements a parametric study
Applied Energy, 2012Co-Authors: Ibrahim Alaefour, Gholamreza Karimi, Kui JiaoAbstract:Understanding of current distributions in proton exchange membrane fuel cells (PEMFCs) is crucial for designing cell components such as the Flow field plates and the membrane electrode assembly (MEA). In this study, the spatial current density distributions in a single PEMFC with three serpentine Flow channels are measured using a segmented bipolar plate and printed circuit board technique. The effects of key operating conditions such as stoichiometry ratios, inlet humidity levels, cell pressure and temperature on the local current density distributions for co-, counter-, and cross-Flow Arrangements are examined. It is observed that the local current density distribution over the MEA is directly affected by the cell operating conditions along with the configuration of the Flow Arrangement. It is also found that among the different Flow configurations tested under the various operating conditions, the counter Flow Arrangement provides the optimum average current density and the lowest variations in the local current densities along the Flow channels.
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Measurement of current distribution in a proton exchange membrane fuel cell with various Flow Arrangements – A parametric study
Applied Energy, 2012Co-Authors: Ibrahim Alaefour, Gholamreza Karimi, Kui JiaoAbstract:Understanding of current distributions in proton exchange membrane fuel cells (PEMFCs) is crucial for designing cell components such as the Flow field plates and the membrane electrode assembly (MEA). In this study, the spatial current density distributions in a single PEMFC with three serpentine Flow channels are measured using a segmented bipolar plate and printed circuit board technique. The effects of key operating conditions such as stoichiometry ratios, inlet humidity levels, cell pressure and temperature on the local current density distributions for co-, counter-, and cross-Flow Arrangements are examined. It is observed that the local current density distribution over the MEA is directly affected by the cell operating conditions along with the configuration of the Flow Arrangement. It is also found that among the different Flow configurations tested under the various operating conditions, the counter Flow Arrangement provides the optimum average current density and the lowest variations in the local current densities along the Flow channels.
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Experimental study on the effect of reactant Flow Arrangements on the current distribution in proton exchange membrane fuel cells
Electrochimica Acta, 2011Co-Authors: Ibrahim Alaefour, Kui Jiao, Gholamreza Karimi, S. Al ShakhshirAbstract:Abstract Current distribution in a proton exchange membrane fuel cell (PEMFC) is significantly influenced by reactant Flow configurations. In this study, the current distribution has been measured experimentally using a segmented Flow-field plate and printed circuit board (PCB). Local current distributions for a PEMFC with serpentine Flow field and three different Flow Arrangements including co-Flow, cross-Flow, and counter-Flow Arrangements for the anode and cathode streams are investigated along with the effect of Flow channel orientation. It is shown that the counter-Flow Arrangement yields most uniform distribution for the current density, whereas the co-Flow Arrangement results in a considerable variation in the current density from the reactant gas stream inlet to exit. Flow channel orientation can also impact the cell performance and the current distribution appreciably. The limiting hydrogen concentration at the anode side due to the low stoichiometry condition can have a predominant effect on the current distribution and cell performance.
Hua Wang - One of the best experts on this subject based on the ideXlab platform.
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low grade heat utilization by supercritical carbon dioxide rankine cycle analysis on the performance of gas heater subjected to heat flux and convective boundary conditions
Energy Conversion and Management, 2018Co-Authors: Yiqiang Zhang, Yecheng Yao, Guoli Tang, Hua WangAbstract:Abstract The design and optimization of gas heater in supercritical carbon dioxide Rankine cycles faces some challenges, among which an urgent one is the effect of thermal boundary condition on the performance of gas heater. This work focused on performance comparison and effects of major operating parameters under two most common thermal boundary conditions regarding to low-grade heat sources, by employing a modified Shear-Stress Transport model where a variable turbulent Prandtl formulation was incorporated. Results show that in the pseudo-critical region thermal boundary condition obviously affected the performance of supercritical carbon dioxide gas heater. Compared with the uniform heat flux condition, at convective boundary condition impairment occurred in both the local enhancement at high mass flux and local deterioration at low mass flux, due to the self-regulation in local heat input. A nearly uniform thermal field under convective boundary condition was achieved by increasing the mass flux of heat source fluid, while increasing the inlet temperature of source fluid was ineffective to that end. Opposite to constant-property fluid heater, Flow Arrangement dramatically affected axial profiles of local heat transfer coefficient while had a much weaker effect on local heat flux in supercritical gas heater. Temperature distribution of supercritical carbon dioxide along the heater was insensitive to the Flow Arrangement. Further studies reveal that thermal boundary effect was closely related to the buoyancy effect. Thermal boundary condition has a minimal effect on heat transfer of supercritical carbon dioxide when buoyancy effect is negligible. Under heavy influence of buoyancy, thermal boundary effect was obvious in the form of much weaker local deterioration under convective boundary. Finally, the Jackson Nusselt correlation was found applicable to the prediction of overall heat transfer rate under convective boundary condition, with relative deviations within ±15%.
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a novel Flow Arrangement of staggered Flow in double layered microchannel heat sinks for microelectronic cooling
International Communications in Heat and Mass Transfer, 2016Co-Authors: Yuling Zhai, Zhouhang Li, Hua WangAbstract:Abstract A novel Flow Arrangement of staggered Flow (the fluid staggers Flow along each layer) is presented to remove higher heat flux and obtain more uniform bottom temperature in double-layered microchannel heat sinks. Compared to the counter Flow, the heat transfer performance of two types of staggered Flow is studied numerically. The distribution of the total temperature, average bottom temperature, maximum temperature difference and thermal resistance is presented for different Flow Arrangements under similar pumping power. The results show that the Flow Arrangement with staggered Flow 2 (the fluid Flows along the x direction at the second layer, while fluid staggers along the y direction at the first layer) provides the lowest maximum and most uniform temperature under similar working condition. Moreover, the thermal resistance of staggered Flow 2 is much lower than that of counter Flow and staggered Flow 1 under the similar pumping power, which indicates that it has better cooling capacity for microelectronic cooling.
Xuhui Gao - One of the best experts on this subject based on the ideXlab platform.
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Production of Hydrogen by Methane Steam Reforming Coupled with Catalytic Combustion in Integrated Microchannel Reactors
Energies, 2018Co-Authors: Junjie Chen, Baofang Liu, Xuhui GaoAbstract:This paper addresses the issues related to the rapid production of hydrogen from methane steam reforming by means of process intensification. Methane steam reforming coupled with catalytic combustion in thermally integrated microchannel reactors for the production of hydrogen was investigated numerically. The effect of the catalyst, Flow Arrangement, and reactor dimension was assessed to optimize the design of the system. The thermal interaction between reforming and combustion was investigated for the purpose of the rapid production of hydrogen. The importance of thermal management was discussed in detail, and a theoretical analysis was made on the transport phenomena during each of the reforming and combustion processes. The results indicated that the design of a thermally integrated system operated at millisecond contact times is feasible. The design benefits from the miniaturization of the reactors, but the improvement in catalyst performance is also required to ensure the rapid production of hydrogen, especially for the reforming process. The efficiency of heat exchange can be greatly improved by decreasing the gap distance. The Flow rates should be well designed on both sides of the reactor to meet the requirements of both materials and combustion stability. The Flow Arrangement plays a vital role in the operation of the thermally integrated reactor, and the design in a parallel-Flow heat exchanger is preferred to optimize the distribution of energy in the system. The catalyst loading is an important design parameter to optimize reactor performance and must be carefully designed. Finally, engineering maps were constructed to design thermally integrated devices with desired power, and operating windows were also determined.
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Millisecond methane steam reforming for hydrogen production: A computational fluid dynamics study
International Journal of Hydrogen Energy, 2018Co-Authors: Junjie Chen, Xuhui Gao, Longfei YanAbstract:Abstract The potential of methane steam reforming to produce hydrogen in thermally integrated micro-chemical systems at short contact times was theoretically explored. Methane steam reforming coupled with methane catalytic combustion in microchannel reactors for hydrogen production was studied numerically. A two-dimensional computational fluid dynamics model with detailed chemistry and transport was developed. To provide guidelines for optimal design, reactor behavior was studied, and the effect of design parameters such as catalyst loading, channel height, and Flow Arrangement was evaluated. To understand how steam reforming can happen at millisecond contact times, the relevant process time scales were analyzed, and a heat and mass transfer analysis was performed. The importance of energy management was also discussed in order to obtain a better understanding of the mechanism responsible for efficient heat exchange between highly exothermic and endothermic reactions. The results demonstrated the feasibility of the design of millisecond reforming systems, but only under certain conditions. To achieve this goal, process intensification through miniaturization and the improvement in catalyst performance is very important, but not sufficient; very careful design and implementation of the system is also necessary to enable high thermal integration. The channel height plays an important role in determining the efficiency of heat exchange. A proper balance of the Flow rates of the combustible and reforming streams is an important design criterion. Reactor performance is significantly affected by Flow Arrangement, and co-current operation is recommended to achieve a good energy balance within the system. The catalyst loading must be carefully designed to avoid insufficient reactant conversion or hot spots. Finally, operating windows were identified, and engineering maps for designing devices with desired power were constructed.
Jean-yves Billard - One of the best experts on this subject based on the ideXlab platform.
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two phase couette taylor Flow Arrangement of the dispersed phase and effects on the Flow structures
Physics of Fluids, 2004Co-Authors: Henda Djeridi, Celine Gabillet, Jean-yves BillardAbstract:This study investigates the mutual interactions between a continuous and a dispersed phase~noncondensable or condensable! in the well-known Couette–Taylor Flow between two concentric cylinders at low Reynolds numbers, where the outer cylinder is immobilized. In this experiment, the turbulent structures take place progressively. The noncondensable dispersed phase ~air! is introduced either by ventilation, generated by agitation of a free surface situated at the top of the gap between the two cylinders. The condensable dispersed phase is generated by cavitation due to a drop in pressure. Comparisons are made between the single phase Flow patterns and those observed in ventilated or cavitating Flow. Two particular Arrangements of the dispersed phase are experimentally evident, according to the Reynolds number of the Flow. For low Reynolds numbers, bubbles are trapped in the core of the Taylor cells, whereas they migrate to the outFlow regions near the inner cylinder for higher Reynolds numbers. Assessment of the forces applied to the bubbles and computation of their equilibrium position can act as a base in describing the bubble capture. When bubbles are located near the wall in the outFlow region, it is found that the three first instabilities are strongly influenced by the dispersed phase. The cavitating Flow is also characterized by an earlier appearance of the third instability.
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Two-phase Couette–Taylor Flow: Arrangement of the dispersed phase and effects on the Flow structures
Physics of Fluids, 2004Co-Authors: Henda Djeridi, Celine Gabillet, Jean-yves BillardAbstract:This study investigates the mutual interactions between a continuous and a dispersed phase~noncondensable or condensable! in the well-known Couette–Taylor Flow between two concentric cylinders at low Reynolds numbers, where the outer cylinder is immobilized. In this experiment, the turbulent structures take place progressively. The noncondensable dispersed phase ~air! is introduced either by ventilation, generated by agitation of a free surface situated at the top of the gap between the two cylinders. The condensable dispersed phase is generated by cavitation due to a drop in pressure. Comparisons are made between the single phase Flow patterns and those observed in ventilated or cavitating Flow. Two particular Arrangements of the dispersed phase are experimentally evident, according to the Reynolds number of the Flow. For low Reynolds numbers, bubbles are trapped in the core of the Taylor cells, whereas they migrate to the outFlow regions near the inner cylinder for higher Reynolds numbers. Assessment of the forces applied to the bubbles and computation of their equilibrium position can act as a base in describing the bubble capture. When bubbles are located near the wall in the outFlow region, it is found that the three first instabilities are strongly influenced by the dispersed phase. The cavitating Flow is also characterized by an earlier appearance of the third instability.
Junjie Chen - One of the best experts on this subject based on the ideXlab platform.
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Production of Hydrogen by Methane Steam Reforming Coupled with Catalytic Combustion in Integrated Microchannel Reactors
Energies, 2018Co-Authors: Junjie Chen, Baofang Liu, Xuhui GaoAbstract:This paper addresses the issues related to the rapid production of hydrogen from methane steam reforming by means of process intensification. Methane steam reforming coupled with catalytic combustion in thermally integrated microchannel reactors for the production of hydrogen was investigated numerically. The effect of the catalyst, Flow Arrangement, and reactor dimension was assessed to optimize the design of the system. The thermal interaction between reforming and combustion was investigated for the purpose of the rapid production of hydrogen. The importance of thermal management was discussed in detail, and a theoretical analysis was made on the transport phenomena during each of the reforming and combustion processes. The results indicated that the design of a thermally integrated system operated at millisecond contact times is feasible. The design benefits from the miniaturization of the reactors, but the improvement in catalyst performance is also required to ensure the rapid production of hydrogen, especially for the reforming process. The efficiency of heat exchange can be greatly improved by decreasing the gap distance. The Flow rates should be well designed on both sides of the reactor to meet the requirements of both materials and combustion stability. The Flow Arrangement plays a vital role in the operation of the thermally integrated reactor, and the design in a parallel-Flow heat exchanger is preferred to optimize the distribution of energy in the system. The catalyst loading is an important design parameter to optimize reactor performance and must be carefully designed. Finally, engineering maps were constructed to design thermally integrated devices with desired power, and operating windows were also determined.
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Millisecond methane steam reforming for hydrogen production: A computational fluid dynamics study
International Journal of Hydrogen Energy, 2018Co-Authors: Junjie Chen, Xuhui Gao, Longfei YanAbstract:Abstract The potential of methane steam reforming to produce hydrogen in thermally integrated micro-chemical systems at short contact times was theoretically explored. Methane steam reforming coupled with methane catalytic combustion in microchannel reactors for hydrogen production was studied numerically. A two-dimensional computational fluid dynamics model with detailed chemistry and transport was developed. To provide guidelines for optimal design, reactor behavior was studied, and the effect of design parameters such as catalyst loading, channel height, and Flow Arrangement was evaluated. To understand how steam reforming can happen at millisecond contact times, the relevant process time scales were analyzed, and a heat and mass transfer analysis was performed. The importance of energy management was also discussed in order to obtain a better understanding of the mechanism responsible for efficient heat exchange between highly exothermic and endothermic reactions. The results demonstrated the feasibility of the design of millisecond reforming systems, but only under certain conditions. To achieve this goal, process intensification through miniaturization and the improvement in catalyst performance is very important, but not sufficient; very careful design and implementation of the system is also necessary to enable high thermal integration. The channel height plays an important role in determining the efficiency of heat exchange. A proper balance of the Flow rates of the combustible and reforming streams is an important design criterion. Reactor performance is significantly affected by Flow Arrangement, and co-current operation is recommended to achieve a good energy balance within the system. The catalyst loading must be carefully designed to avoid insufficient reactant conversion or hot spots. Finally, operating windows were identified, and engineering maps for designing devices with desired power were constructed.