The Experts below are selected from a list of 1545 Experts worldwide ranked by ideXlab platform
Mart H J M De Croon - One of the best experts on this subject based on the ideXlab platform.
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single phase fluid Flow distribution and heat transfer in microstructured reactors
Chemical Engineering Science, 2011Co-Authors: Evgeny V Rebrov, J Jaap C Schouten, Mart H J M De CroonAbstract:Single-phase microreactors and micro-heat-exchangers have been widely used in industrial and scientific applications over the last decade. In several cases, operation of microreactors has shown that their expected efficiency cannot be reached either due to non-uniform distribution of reactants between different channels or due to Flow Maldistribution between individual microreactors working in parallel. The latter problem can result in substantial temperature deviations between different microreactors resulting in thermal runaway which could arise from an exothermic reaction. Thus advances in the understanding of heat transfer and fluid Flow distribution continue to be crucial in achieving improved performance, efficiency and safety in microstructured reactors used for different applications. This paper presents a review of the experimental and numerical results on fluid Flow distribution, heat transfer and combination thereof, available in the open literature. Heat transfer in microchannels can be suitably described by standard theory and correlations, but scaling effects (entrance effects, conjugate heat transfer, viscous heating, and temperature-dependent properties) have often to be accounted for in microsystems. Experiments with single channels are in good agreement with predictions from the published correlations. The accuracy of multichannel experiments is lower due to Flow Maldistribution. Special attention is devoted to theoretical and experimental studies on the effect of a Flow Maldistribution on the thermal and conversion response of catalytic microreactors. The review concludes with a set of design recommendations aimed at improving the reactor performance.
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single phase fluid Flow distribution and heat transfer in microstructured reactors
Chemical Engineering Science, 2011Co-Authors: Evgeny V Rebrov, J C Schouten, Mart H J M De CroonAbstract:Single-phase microreactors and micro-heat-exchangers have been widely used in industrial and scientific applications over the last decade. In several cases, operation of microreactors has shown that their expected efficiency cannot be reached either due to non-uniform distribution of reactants between different channels or due to Flow Maldistribution between individual microreactors working in parallel. The latter problem can result in substantial temperature deviations between different microreactors resulting in thermal runaway which could arise from an exothermic reaction. Thus advances in the understanding of heat transfer and fluid Flow distribution continue to be crucial in achieving improved performance, efficiency and safety in microstructured reactors used for different applications. This paper presents a review of the experimental and numerical results on fluid Flow distribution, heat transfer and combination thereof, available in the open literature. Heat transfer in microchannels can be suitably described by standard theory and correlations, but scaling effects (entrance effects, conjugate heat transfer, viscous heating, and temperature-dependent properties) have often to be accounted for in microsystems. Experiments with single channels are in good agreement with predictions from the published correlations. The accuracy of multichannel experiments is lower due to Flow Maldistribution. Special attention is devoted to theoretical and experimental studies on the effect of a Flow Maldistribution on the thermal and conversion response of catalytic microreactors. The review concludes with a set of design recommendations aimed at improving the reactor performance.
David P Wilkinson - One of the best experts on this subject based on the ideXlab platform.
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numerical investigation of the impact of two phase Flow Maldistribution on pem fuel cell performance
International Journal of Hydrogen Energy, 2014Co-Authors: Yulong Ding, Xiaotao Bi, David P WilkinsonAbstract:Abstract Flow Maldistribution usually happens in PEM fuel cells when using common inlet and exit headers to supply reactant gases to multiple channels. As a result, some channels are flooded with more water and have less air Flow while other channels are filled with less water but have excessive air Flow. To investigate the impact of two-phase Flow Maldistribution on PEM fuel cell performance, a Volume of Fluid (VOF) model coupled with a 1D MEA model was employed to simulate two parallel channels. The slug Flow pattern is mainly observed in the Flow channels under different Flow Maldistribution conditions, and it significantly increases the gas diffusion layer (GDL) surface water coverage over the whole range of simulated current densities, which directly leads to poor fuel cell performance. Therefore, it is recommended that liquid and gas Flow Maldistribution in parallel channels should be avoided if possible over the whole range of operation. Increasing the gas stoichiometric Flow ratio is not an effective method to mitigate the gas Flow Maldistribution, but adding a gas inlet resistance to the Flow channel is effective in mitigating Maldistribution. With a carefully selected value of the Flow resistance coefficient, both the fuel cell performance and the gas Flow distribution can be significantly improved without causing too much extra pressure drop.
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numerical investigation of the impact of two phase Flow Maldistribution on pem fuel cell performance
International Journal of Hydrogen Energy, 2014Co-Authors: Yulong Ding, Xiaotao Bi, David P WilkinsonAbstract:Abstract Flow Maldistribution usually happens in PEM fuel cells when using common inlet and exit headers to supply reactant gases to multiple channels. As a result, some channels are flooded with more water and have less air Flow while other channels are filled with less water but have excessive air Flow. To investigate the impact of two-phase Flow Maldistribution on PEM fuel cell performance, a Volume of Fluid (VOF) model coupled with a 1D MEA model was employed to simulate two parallel channels. The slug Flow pattern is mainly observed in the Flow channels under different Flow Maldistribution conditions, and it significantly increases the gas diffusion layer (GDL) surface water coverage over the whole range of simulated current densities, which directly leads to poor fuel cell performance. Therefore, it is recommended that liquid and gas Flow Maldistribution in parallel channels should be avoided if possible over the whole range of operation. Increasing the gas stoichiometric Flow ratio is not an effective method to mitigate the gas Flow Maldistribution, but adding a gas inlet resistance to the Flow channel is effective in mitigating Maldistribution. With a carefully selected value of the Flow resistance coefficient, both the fuel cell performance and the gas Flow distribution can be significantly improved without causing too much extra pressure drop.
Evgeny V Rebrov - One of the best experts on this subject based on the ideXlab platform.
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single phase fluid Flow distribution and heat transfer in microstructured reactors
Chemical Engineering Science, 2011Co-Authors: Evgeny V Rebrov, J Jaap C Schouten, Mart H J M De CroonAbstract:Single-phase microreactors and micro-heat-exchangers have been widely used in industrial and scientific applications over the last decade. In several cases, operation of microreactors has shown that their expected efficiency cannot be reached either due to non-uniform distribution of reactants between different channels or due to Flow Maldistribution between individual microreactors working in parallel. The latter problem can result in substantial temperature deviations between different microreactors resulting in thermal runaway which could arise from an exothermic reaction. Thus advances in the understanding of heat transfer and fluid Flow distribution continue to be crucial in achieving improved performance, efficiency and safety in microstructured reactors used for different applications. This paper presents a review of the experimental and numerical results on fluid Flow distribution, heat transfer and combination thereof, available in the open literature. Heat transfer in microchannels can be suitably described by standard theory and correlations, but scaling effects (entrance effects, conjugate heat transfer, viscous heating, and temperature-dependent properties) have often to be accounted for in microsystems. Experiments with single channels are in good agreement with predictions from the published correlations. The accuracy of multichannel experiments is lower due to Flow Maldistribution. Special attention is devoted to theoretical and experimental studies on the effect of a Flow Maldistribution on the thermal and conversion response of catalytic microreactors. The review concludes with a set of design recommendations aimed at improving the reactor performance.
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single phase fluid Flow distribution and heat transfer in microstructured reactors
Chemical Engineering Science, 2011Co-Authors: Evgeny V Rebrov, J C Schouten, Mart H J M De CroonAbstract:Single-phase microreactors and micro-heat-exchangers have been widely used in industrial and scientific applications over the last decade. In several cases, operation of microreactors has shown that their expected efficiency cannot be reached either due to non-uniform distribution of reactants between different channels or due to Flow Maldistribution between individual microreactors working in parallel. The latter problem can result in substantial temperature deviations between different microreactors resulting in thermal runaway which could arise from an exothermic reaction. Thus advances in the understanding of heat transfer and fluid Flow distribution continue to be crucial in achieving improved performance, efficiency and safety in microstructured reactors used for different applications. This paper presents a review of the experimental and numerical results on fluid Flow distribution, heat transfer and combination thereof, available in the open literature. Heat transfer in microchannels can be suitably described by standard theory and correlations, but scaling effects (entrance effects, conjugate heat transfer, viscous heating, and temperature-dependent properties) have often to be accounted for in microsystems. Experiments with single channels are in good agreement with predictions from the published correlations. The accuracy of multichannel experiments is lower due to Flow Maldistribution. Special attention is devoted to theoretical and experimental studies on the effect of a Flow Maldistribution on the thermal and conversion response of catalytic microreactors. The review concludes with a set of design recommendations aimed at improving the reactor performance.
Lars Finn Sloth Larsen - One of the best experts on this subject based on the ideXlab platform.
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performance of residential air conditioning systems with Flow Maldistribution in fin and tube evaporators
International Journal of Refrigeration-revue Internationale Du Froid, 2011Co-Authors: Martin Ryhl Kærn, Brian Elmegaard, Wiebke Brix, Lars Finn Sloth LarsenAbstract:Refrigerant and airFlow Maldistribution in fin-and-tube evaporators for residential air-conditioning was investigated with numerical modeling. Fin-and-tube heat exchangers usually have a pre-defined circuitry. However, the objective in this study was to perform a generic investigation of each individual Maldistribution source in an independent manner. Therefore, the evaporator and the condenser were simplified to be straight tubes for the purposes of this study. The numerical model of the R410A system, its verification and an investigation of individual Maldistribution sources are presented in this paper. The Maldistribution sources of interest were: inlet liquid/vapor phase distribution, feeder tube bending and airFlow distribution. The results show that Maldistribution reduced the cooling capacity and the coefficient of performance of the system. In particular, different phase distribution and non-uniform airFlow distribution reduced the performance significantly. Different feeder tube bendings only caused a minor decrease in performance.
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Compensation of Flow Maldistribution in fin-and-tube evaporators for residential air-conditioning
International Journal of Refrigeration, 2011Co-Authors: Martin Ryhl Kærn, Brian Elmegaard, Wiebke Brix, Lars Finn Sloth LarsenAbstract:Compensation of Flow Maldistribution in multi-channel fin-and-tube evaporators for residential air-conditioning is investigated by numerical modeling. The considered sources of Maldistribution are distribution of the liquid and vapor phases in the distributor and non-uniform airFlow distribution. Fin-and-tube heat exchangers usually have a predefined circuitry, however, the evaporator model is simplified to have straight tubes, in order to perform a generic investigation. The compensation of Flow Maldistribution is performed by control of the superheat in the individual channels. Furthermore, the effect of combinations of individual Maldistribution sources is investigated for different evaporator sizes and outdoor temperatures. It is shown that a decrease in cooling capacity and coefficient of performance by Flow Maldistribution can be compensated by the control of individual channel superheat. Alternatively, a larger evaporator may be used.
Sanjeev Kumar - One of the best experts on this subject based on the ideXlab platform.
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effects of Flow inlet angle on Flow Maldistribution and thermal performance of water cooled mini channel heat sink
International Journal of Thermal Sciences, 2019Co-Authors: Sanjeev Kumar, Pawan K SinghAbstract:Abstract The cooling capacity of the mini-channel heat sink can be increased by making the Flow distribution uniform through all the parallel mini-channels. The present study proposes a minichannel heat sink with modified novel inlet/outlet arrangement with different Flow inlet angle such as (θ = 90°, θ = 105°, and θ = 120°) for better Flow distribution and heat transfer performance. This proposed minichannel heat sink has been analyzed numerically with the help of ANSYS-Fluent. Water is used as a working fluid and aluminum is selected as a heat sink material. Total 28 numbers of parallel mini channels are considered having the hydraulic diameter of 1.5 mm. It is found that Flow distribution changes with this Flow inlet angle and minimum Flow Maldistribution is observed for proposed inlet/outlet arrangement with θ = 105° and results in better and uniform cooling of the heat sink. Further increment in Flow inlet angle increases the non-uniformity of Flow. The thermal performance also has been found best for θ = 105° and the value of maximum base temperature was also lowest for this configuration. It is suggested that the performance of mini channel heat sink can be improved if coolant enters the distributor header with Flow inlet angle θ = 105° and exit from the middle of the collector header.
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A novel approach to manage temperature non-uniformity in minichannel heat sink by using intentional Flow Maldistribution
Applied Thermal Engineering, 2019Co-Authors: Sanjeev Kumar, Pawan Kumar SinghAbstract:Abstract Flow Maldistribution is an uncalled phenomenon in water-cooled heat sink and accountable for the depreciation in thermal performance of the same. However, this study is proposed to manage temperature non-uniformity at the base of the mini-channel heat sink by taking advantage of Flow Maldistribution under non-uniform heating. Four different types of Flow arrangements such as I-Type, Z-Type, C-Type and N-Type and five different types of heating arrangements such as uniform, center streamline, left streamline, right streamline and dual streamline heating are considered. A comprehensible numerical study has been performed using ANSYS-Fluent to explicate the combined effect of different Flow arrangements and different heating arrangements on the thermal performance of the heat sink. The results show that for uniform heating, I-Type Flow arrangement has better thermal performance with the lowest value of thermal resistance. For non-uniform heating, better thermal performance can be achieved for cases such as center streamline heating, right streamline heating, left streamline heating and dual streamline heating with I-Type, Z-Type, C-Type, and N-Type Flow arrangements respectively. Hence, a suitable Flow arrangement should be considered for a given heating arrangement to acquire the optimal thermal performance of the heat sink.