The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
Adrian Bejan - One of the best experts on this subject based on the ideXlab platform.
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Counterflow Heat Exchanger with core and plenums at both ends
International Journal of Heat and Mass Transfer, 2016Co-Authors: Adrian Bejan, Sylvie Lorente, M Alalaimi, Adrian S Sabau, James W KlettAbstract:This paper illustrates the morphing of flow architecture toward greater performance in a Counterflow Heat Exchanger. The architecture consists of two plenums with a core of Counterflow channels between them. Each stream enters one plenum and then flows in a channel that travels the core and crosses the second plenum. The volume of the Heat Exchanger is fixed while the volume fraction occupied by each plenum is variable. Performance is driven by two objectives, simultaneously: low flow resistance and low thermal resistance. The analytical and numerical results show that the overall flow resistance is the lowest when the core is absent, and each plenum occupies half of the available volume and is oriented in Counterflow with the other plenum. In this configuration, the thermal resistance also reaches its lowest value. These conclusions hold for fully developed laminar flow and turbulent flow through the core. The curve for effectiveness vs number of Heat transfer units (N-tu) is steeper (when N-tu \textless 1) than the classical curves for Counterflow and crossflow. (C) 2016 Elsevier Ltd. All rights reserved.
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Counterflow Heat Exchanger with core and plenums at both ends
International Journal of Heat and Mass Transfer, 2016Co-Authors: Adrian Bejan, Sylvie Lorente, M Alalaimi, Adrian S Sabau, James W KlettAbstract:Here, this paper illustrates the morphing of flow architecture toward greater performance in a Counterflow Heat Exchanger. The architecture consists of two plenums with a core of Counterflow channels between them. Each stream enters one plenum and then flows in a channel that travels the core and crosses the second plenum. The volume of the Heat Exchanger is fixed while the volume fraction occupied by each plenum is variable. Performance is driven by two objectives, simultaneously: low flow resistance and low thermal resistance. The analytical and numerical results show that the overall flow resistance is the lowest when the core is absent, and each plenum occupies half of the available volume and is oriented in Counterflow with the other plenum. In this configuration, the thermal resistance also reaches its lowest value. These conclusions hold for fully developed laminar flow and turbulent flow through the core. The curve for effectiveness vs number of Heat transfer units (Ntu) is steeper (when Ntu < 1) than the classical curves for Counterflow and crossflow.
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Counterflow Heat Exchanger with core and plenums at both ends
International Journal of Heat and Mass Transfer, 2016Co-Authors: Adrian Bejan, Sylvie Lorente, M Alalaimi, Adrian S Sabau, James W KlettAbstract:Abstract This paper illustrates the morphing of flow architecture toward greater performance in a Counterflow Heat Exchanger. The architecture consists of two plenums with a core of Counterflow channels between them. Each stream enters one plenum and then flows in a channel that travels the core and crosses the second plenum. The volume of the Heat Exchanger is fixed while the volume fraction occupied by each plenum is variable. Performance is driven by two objectives, simultaneously: low flow resistance and low thermal resistance. The analytical and numerical results show that the overall flow resistance is the lowest when the core is absent, and each plenum occupies half of the available volume and is oriented in Counterflow with the other plenum. In this configuration, the thermal resistance also reaches its lowest value. These conclusions hold for fully developed laminar flow and turbulent flow through the core. The curve for effectiveness vs number of Heat transfer units (Ntu) is steeper (when Ntu
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Dendritic Counterflow Heat Exchanger experiments
International Journal of Thermal Sciences, 2006Co-Authors: Alexandre K. Da Silva, Adrian BejanAbstract:In this paper we report experimentally the hydraulic and thermal behavior of a balanced Counterflow Heat Exchanger in which each stream flows through a tree-shaped structure covering a circular area. The tree structure is the same on both sides of the Heat Exchanger: they have three channels reaching/leaving the center, and three branching levels (i.e., 24 channels on the periphery of the circular area). On the hot side, fluid is pumped from the center to the periphery. On the cold side, fluid is pumped from the periphery to the center, and leaves the Heat Exchanger as a single stream. Two experimental apparatuses were built and tested. In the first design, the body of the Heat Exchanger was made out of plexiglass and a peripheral plenum was used to collect or distribute the working fluid to the tree structure. The measurements showed that the use of a plenum generates undesirable volumetric flow asymmetries. These lessons led to a second design, which has two major improvements: (i) the Heat Exchanger core was made out of aluminum and (ii) individual ports (inlets/outlets) were used for each of the peripheral channels. The hydraulic results show a relation between the appearance of volumetric flow rate asymmetries and the bifurcation angles throughout the dendritic structure. The Heat transfer results are also discussed.
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System-level optimization of the sizes of organs for Heat and fluid flow systems
International Journal of Thermal Sciences, 2003Co-Authors: Juan C. Ordonez, Adrian BejanAbstract:Abstract In this paper we show that the sizes (weights) of Heat and fluid flow systems that function on board vehicles such as aircraft can be derived from the maximization of overall (system level) performance. The total weight of the aircraft dictates its fuel requirement. The principle owes its existence to two effects that compete for fuel. Components, power plants and refrigeration plants operate less irreversibly when they are larger. Less irreversibility means less fuel needed for their operation. On the other hand, larger sizes add more to the mass of the aircraft and to the total fuel requirement. This tradeoff pinpoints optimal sizes. The principle is illustrated based on three examples: a power plant the size of which is represented by a Heat Exchanger, a Counterflow Heat Exchanger without fluid flow irreversibility, and a Counterflow Heat Exchanger with Heat transfer and fluid flow irreversibilities. The size optimization principle is applicable to the organs of all flow systems, engineered (e.g., vehicles) and natural (e.g., animals).
Trung Van Nguyen - One of the best experts on this subject based on the ideXlab platform.
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An Along‐the‐Channel Model for Proton Exchange Membrane Fuel Cells
Journal of The Electrochemical Society, 1998Co-Authors: Trung Van NguyenAbstract:An along-the-channel model is developed for evaluating the effects of various design and operating parameters on the performance of a proton exchange membrane (PEM) fuel cell. The model, which is based on a previous one, has been extended to include the convective water transport across the membrane by a pressure gradient, temperature distribution in the solid phase along the flow channel, and Heat removal by natural convection and coflow and Counterflow Heat Exchangers. Results from the model show that the performance of a PEM fuel cell could be improved by anode humidification and positive differential pressure between the cathode and anode to increase the back transport rate of water across the membrane. Results also show that effective Heat removal is necessary for preventing excessive temperature which could lead to local membrane dehydration. For Heat removal and distribution, the Counterflow Heat Exchanger is most effective.
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an along the channel model for proton exchange membrane fuel cells
Journal of The Electrochemical Society, 1998Co-Authors: Jung S Yi, Trung Van NguyenAbstract:An along-the-channel model is developed for evaluating the effects of various design and operating parameters on the performance of a proton exchange membrane (PEM) fuel cell. The model, which is based on a previous one, has been extended to include the convective water transport across the membrane by a pressure gradient, temperature distribution in the solid phase along the flow channel, and Heat removal by natural convection and coflow and Counterflow Heat Exchangers. Results from the model show that the performance of a PEM fuel cell could be improved by anode humidification and positive differential pressure between the cathode and anode to increase the back transport rate of water across the membrane. Results also show that effective Heat removal is necessary for preventing excessive temperature which could lead to local membrane dehydration. For Heat removal and distribution, the Counterflow Heat Exchanger is most effective.
James W Klett - One of the best experts on this subject based on the ideXlab platform.
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Counterflow Heat Exchanger with core and plenums at both ends
International Journal of Heat and Mass Transfer, 2016Co-Authors: Adrian Bejan, Sylvie Lorente, M Alalaimi, Adrian S Sabau, James W KlettAbstract:This paper illustrates the morphing of flow architecture toward greater performance in a Counterflow Heat Exchanger. The architecture consists of two plenums with a core of Counterflow channels between them. Each stream enters one plenum and then flows in a channel that travels the core and crosses the second plenum. The volume of the Heat Exchanger is fixed while the volume fraction occupied by each plenum is variable. Performance is driven by two objectives, simultaneously: low flow resistance and low thermal resistance. The analytical and numerical results show that the overall flow resistance is the lowest when the core is absent, and each plenum occupies half of the available volume and is oriented in Counterflow with the other plenum. In this configuration, the thermal resistance also reaches its lowest value. These conclusions hold for fully developed laminar flow and turbulent flow through the core. The curve for effectiveness vs number of Heat transfer units (N-tu) is steeper (when N-tu \textless 1) than the classical curves for Counterflow and crossflow. (C) 2016 Elsevier Ltd. All rights reserved.
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Counterflow Heat Exchanger with core and plenums at both ends
International Journal of Heat and Mass Transfer, 2016Co-Authors: Adrian Bejan, Sylvie Lorente, M Alalaimi, Adrian S Sabau, James W KlettAbstract:Here, this paper illustrates the morphing of flow architecture toward greater performance in a Counterflow Heat Exchanger. The architecture consists of two plenums with a core of Counterflow channels between them. Each stream enters one plenum and then flows in a channel that travels the core and crosses the second plenum. The volume of the Heat Exchanger is fixed while the volume fraction occupied by each plenum is variable. Performance is driven by two objectives, simultaneously: low flow resistance and low thermal resistance. The analytical and numerical results show that the overall flow resistance is the lowest when the core is absent, and each plenum occupies half of the available volume and is oriented in Counterflow with the other plenum. In this configuration, the thermal resistance also reaches its lowest value. These conclusions hold for fully developed laminar flow and turbulent flow through the core. The curve for effectiveness vs number of Heat transfer units (Ntu) is steeper (when Ntu < 1) than the classical curves for Counterflow and crossflow.
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Counterflow Heat Exchanger with core and plenums at both ends
International Journal of Heat and Mass Transfer, 2016Co-Authors: Adrian Bejan, Sylvie Lorente, M Alalaimi, Adrian S Sabau, James W KlettAbstract:Abstract This paper illustrates the morphing of flow architecture toward greater performance in a Counterflow Heat Exchanger. The architecture consists of two plenums with a core of Counterflow channels between them. Each stream enters one plenum and then flows in a channel that travels the core and crosses the second plenum. The volume of the Heat Exchanger is fixed while the volume fraction occupied by each plenum is variable. Performance is driven by two objectives, simultaneously: low flow resistance and low thermal resistance. The analytical and numerical results show that the overall flow resistance is the lowest when the core is absent, and each plenum occupies half of the available volume and is oriented in Counterflow with the other plenum. In this configuration, the thermal resistance also reaches its lowest value. These conclusions hold for fully developed laminar flow and turbulent flow through the core. The curve for effectiveness vs number of Heat transfer units (Ntu) is steeper (when Ntu
Jung S Yi - One of the best experts on this subject based on the ideXlab platform.
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an along the channel model for proton exchange membrane fuel cells
Journal of The Electrochemical Society, 1998Co-Authors: Jung S Yi, Trung Van NguyenAbstract:An along-the-channel model is developed for evaluating the effects of various design and operating parameters on the performance of a proton exchange membrane (PEM) fuel cell. The model, which is based on a previous one, has been extended to include the convective water transport across the membrane by a pressure gradient, temperature distribution in the solid phase along the flow channel, and Heat removal by natural convection and coflow and Counterflow Heat Exchangers. Results from the model show that the performance of a PEM fuel cell could be improved by anode humidification and positive differential pressure between the cathode and anode to increase the back transport rate of water across the membrane. Results also show that effective Heat removal is necessary for preventing excessive temperature which could lead to local membrane dehydration. For Heat removal and distribution, the Counterflow Heat Exchanger is most effective.
J. C. H. Zeegers - One of the best experts on this subject based on the ideXlab platform.
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Counter-flow pulse-tube refrigerators.
2002Co-Authors: M. E. Will, J. C. H. ZeegersAbstract:Regenerators in standard pulse-tube refrigerators are expensive, complicated, heavy, and they contribute significantly to the losses in the cooler. In the research, the regenerators are avoided by using two identical GM-type pulse-tube refrigerators operating in opposite phase. The two regenerators are replaced by one Counterflow Heat Exchanger. This system is called the Counterflow pulse-tube refrigerator. A special feature of the system is that the pressure wave is generated by a rotating valve at low temperature. The basic principle of the processes in the Counterflow pulse-tube refrigerator are discussed and some preliminary experimental results are given.
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Counterflow pulse-tube refrigerators
Advances in cryogenic engineering, 2002Co-Authors: A.t.a.m. De Waele, J. C. H. ZeegersAbstract:The regenerators in standard pulse-tube refrigerators are large, heavy, expensive, and are a source of losses. In this contribution we avoid using regenerators by combining two pulse-tube refrigerators which operate in opposite phase. The regenerators are replaced by a Counterflow Heat Exchanger. We treat the basic thermodynamic equations, make some design considerations, and report the results of some preliminary experiments.
