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The effect of flow arrangement on the pressure drop of plate heat exchangers

MIURA, Raquel Y.; GALEAZZO, Flavio C. C.; TADINI, Carmen C.; GUT, Jorge A. W.
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
66.41%
For the optimal design of plate heat exchangers (PHEs), an accurate thermal-hydraulic model that takes into account the effect of the flow arrangement on the heat load and pressure drop is necessary. In the present study, the effect of the flow arrangement on the pressure drop of a PHE is investigated. Thirty two different arrangements were experimentally tested using a laboratory scale PHE with flat plates. The experimental data was used for (a) determination of an empirical correlation for the effect of the number of passes and number of flow channels per pass on the pressure drop; (b) validation of a friction factor model through parameter estimation; and (c) comparison with the simulation results obtained with a CFD (computational fluid dynamics) model of the PHE. All three approaches resulted in a good agreement between experimental and predicted values of pressure drop. Moreover, the CFD model is used for evaluating the flow maldistribution in a PHE with two channels Per Pass. (c) 2008 Elsevier Ltd. All rights reserved.; FAPESP (The State of Sao Paulo Research Foundation)

Two-phase flow patterns and pressure drop inside horizontal tubes containing twisted-tape inserts

Kanizawa, Fábio Toshio; Ribatski, Gherhardt
Fonte: PERGAMON-ELSEVIER SCIENCE LTD; OXFORD Publicador: PERGAMON-ELSEVIER SCIENCE LTD; OXFORD
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
66.36%
This paper presents an experimental study on two-phase flow patterns and pressure drop of R134a inside a 15.9 mm ID tube containing twisted-tape inserts. Experimental results were obtained in a horizontal test section for twisted-tape ratios of 3, 4, 9 and 14, mass velocities ranging from 75 to 250 kg/m(2) s and saturation temperatures of 5 and 15 degrees C. An unprecedented discussion on two-phase flow patterns inside tubes containing twisted-tape inserts is presented and the flow pattern effects on the frictional pressure drop are carefully discussed. Additionally, a new method to predict the frictional pressure drop during two-phase flow inside tubes containing twisted-tape inserts is proposed. (C) 2012 Elsevier Ltd. All rights reserved.; CNPq (The National Council for Scientific and Technological Development, Brazil) [474403/2008-4]; CNPq (The National Council for Scientific and Technological Development, Brazil)

Estudo teórico e experimental sobre padrões de escoamento e perda de pressão durante escoamentos monofásicos e bifásicos no interior de tubos com fitas retorcidas; Theoretical and experimental study on flow pattern identification and pressure drop during single and two-phase flow in tubes with twisted tape inserts

Kanizawa, Fabio Toshio
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 14/07/2011 Português
Relevância na Pesquisa
66.44%
A presente dissertação trata de um estudo teórico-experimental sobre escoamento monofásico e bifásico no interior de tubos com fitas retorcidas. Esta técnica tem sido utilizada há várias décadas para a intensificação de troca de calor para escoamento monofásico e evaporação convectiva no interior de tubos. No entanto, com sua utilização, o aumento do coeficiente de troca de calor é acompanhado pelo incremento da perda de pressão. Portanto a compreensão dos fenômenos relacionados aos incrementos da perda de pressão e troca de calor são fundamentais para engenheiros projetistas. Neste estudo, inicialmente, é apresentada uma extensa revisão bibliográfica sobre padrões de escoamento, modelos para estimativa de fração de vazio e metodologias para previsão da perda de pressão em tubos com e sem fitas retorcidas para escoamentos bifásicos e monofásicos. Foram realizados experimentos em bancada experimental utilizando seção de testes com diâmetro interno de 15,9 mm e dois metros de comprimento com fitas apresentando razões de retorcimento de 3, 4, 9, 14 e , a última correspondente ao tubo sem inserto. Os experimentos foram executados para o refrigerante R134a, velocidades mássicas entre 75 e 250 kg/m²s...

Estudo teórico-experimental da transferência de calor e da perda de pressão em um dissipador de calor baseado em microcanais; A theoretical and experimental study on heat transfer and pressure drop in a heat sink based on microchannels

Nascimento, Francisco Júlio do
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 28/05/2012 Português
Relevância na Pesquisa
66.41%
A presente dissertação trata de um estudo teórico-experimental sobre escoamento monofásico e bifásico em um dissipador de calor baseado em microcanais. Este tipo de dissipador de calor tem sido usado para a intensificação da troca de calor em sistemas compactos e de alto desempenho. A intensificação da troca de calor promovida pelo escoamento em microcanais é acompanhada de um incremento na perda de pressão, portanto o estudo destes dois parâmetros é essencial para o entendimento dos fenômenos relacionados e fundamental para o desenvolvimento de ferramentas de projeto para dissipadores de calor baseados em microcanais. Inicialmente, um levantamento bibliográfico extenso sobre a ebulição convectiva em microcanais de reduzido diâmetro foi realizado. Este estudo da literatura trata de critérios de transição entre micro- e macro-escala, padrões de escoamento, métodos de previsão do coeficiente de transferência de calor e perda de pressão. Atenção específica foi dada a estudos de dissipadores de calor baseados em microcanais. Com base nesta análise da literatura, uma bancada experimental foi confeccionada para que dados experimentais de transferência de calor e perda de pressão pudessem ser levantados a partir de um dissipador de calor de microcanais. O dissipador de calor fabricado para este estudo é constituído de 50 microcanais retangulares dispostos paralelamente com 15 mm de comprimento...

Estudo teórico-experimental da perda de pressão durante a ebulição convectiva de refrigerantes halogenados no interior de microcanais circulares; Experimental and theorical study on pressure drop in microchannels during convective boiling of halogen refrigerants

Silva, Jaqueline Diniz da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 27/09/2012 Português
Relevância na Pesquisa
66.51%
A presente dissertação trata de um estudo teórico-experimental sobre a perda de pressão em canais de diâmetro reduzido durante escoamento bifásico de refrigerantes halogenados. Trocadores de calor baseados na ebulição convectiva, em condições de micro-escala são amplamente estudados devido à intensificação da troca de calor proporcionada e a possibilidade de compactação de sistemas de resfriamento. Proporcionam também a redução do inventário de refrigerante e do material utilizado no processo de fabricação do trocador. Porém, o incremento da transferência de calor é acompanhada pelo aumento da perda de pressão, parâmetro também fundamental para o desempenho do sistema. Para o projeto satisfatório e otimizado destes dispositivos são necessários métodos de previsão de transferência de calor e perda de pressão. Entretanto, no caso de canais de diâmetro reduzido, tais ferramentas não encontram-se disponíveis e trocadores de calor baseados em escoamentos bifásicos no interior de canais de diâmetro reduzido vêm sendo desenvolvidos heuristicamente. Desta forma, inicialmente neste estudo, realizou-se uma revisão crítica da literatura envolvendo critérios de transição entre padrões de escoamento...

Estudo teórico e experimental sobre padrões de escoamento, fração de vazio e perda de pressão durante escoamento bifásico água-ar cruzado ascendente externo a banco de tubos; Theoretical and experimental study on flow pattern, void fraction and pressure drop during air-water two-phase upward crossflow through tube bundles

Kanizawa, Fábio Toshio
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 21/11/2014 Português
Relevância na Pesquisa
66.41%
O presente trabalho envolve um estudo teórico e experimental do escoamento bifásico externo a banco de tubos. Inicialmente, apresenta-se uma ampla revisão da literatura sobre padrões de escoamento, fração de vazio e perda de pressão, durante escoamentos monofásicos e bifásicos externos a banco de tubos. Nesta análise são também descritos os métodos de previsão destes parâmetros. Verificam-se diferenças significativas entre as estimativas proporcionadas por eles, fato que indica a inexistência de métodos generalizados. Posteriormente é apresentada uma descrição detalhada da bancada experimental projetada e construída durante o doutoramento. O aparato completo compõe-se da seção de testes, circuito de água, sistema de compressão e condicionamento de ar, e seções de injeção dos fluxos e condicionamento do escoamento. A seção de testes consiste em um banco de tubos distribuídos segundo configuração triangular normal, com os tubos apresentando diâmetro externo de 19,1 mm, comprimento de 381 mm, e espaçamento transversal de 24 mm. Os experimentos foram realizados para escoamento vertical ascendente de misturas água-ar e velocidades superficiais da fase líquida e gás de 0,020 a 1,500 m/s e de 0,10 a 10...

Pressure drop correlation for oil-refrigerant R134a mixture flashing flow in a small diameter tube

Castro, Heryca O. S.; Gasche, Jose Luiz; Prata, Alvaro T.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 421-429
Português
Relevância na Pesquisa
66.37%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); This paper presents an experimental investigation of the ester oil ISO VG10/refrigerant R134a mixture flashing flow in a 6.0 m long, 3.22 mm ID tube, which is one of the primary steps towards the construction of a methodology for the study of the lubrication and gas leakage in refrigeration compressors. The phase change starts with solubility reduction of the refrigerant in the oil as the pressure decreases due to the friction forces. in this flashing flow the foam pattern is observed at the end of the tube as vapor quality reaches high values, and this is a particular phenomenon of this kind of mixture flow. In order to study this pressure drop, an experimental apparatus was designed to allow the measurement of both pressure and temperature profiles along the tube as well as the visualization of the flow patterns. Pressure and temperature distribution along the flow were measured for saturation pressure ranging from 450 to 650 kPa, mass flux ranging from about 2000 to 3000 kg/(m(2)s), temperatures around 303 K, and inlet refrigerant concentration varying between 0.2 and 0.4 kg ref/kg mixt. An available correlation proposed to predict the frictional pressure drop for a mixture composed by the mineral oil SUNISO 1GS and refrigerant R12 flowing in small diameter tubes yielded large deviations in predicting the ester oil and refrigerant R134a mixture flow. A new correlation has been proposed that fitted the experimental data with rms deviations of 24%. (C) 2008 Elsevier Ltd and IIR. All rights reserved.

Effect of apparent viscosity on the pressure drop during fluidized bed drying of soursop pulp

Telis-Romero, J.; Beristain, C. I.; Gabas, A. L.; Telis, V. R. N.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 684-694
Português
Relevância na Pesquisa
66.41%
Pressure drop and minimum fluidization velocity were experimentally studied in a vibro-fluidized bed of inert particles subjected to different vibration intensities during drying of soursop pulp. Maltodextrin was added to the pulp in order to prevent stickiness between particles and the consequent bed collapse. Pulps were initially concentrated, resulting in pastes with different soluble solids content, and a constant fraction of maltodextrin was guaranteed in the final pulp samples. The pulp theological behavior as affected by temperature and total soluble solids content, including maltodextrin, was evaluated and the effect of pulp apparent viscosity on pressure drop and minimum vibro-fluidization velocity were investigated. Two types of inert particles -3.6 mm glass beads and 3 mm Teflon cylinders (length and diameter) - were tested and, due to lower pressure drop presented by Teflon cylinders during operation of the dry vibro-fluidized bed, these particles were adopted for pulp drying process. Increasing pulp apparent viscosity caused a considerable increase in the vibro-fluidized bed pressure drop during pulp drying and, as a consequence resulted in a larger value of minimum vibro-fluidization velocity. on the other hand, the negative effect of increasing apparent viscosity could be attenuated by increasing the fluidized bed vibration intensity...

Direct Numerical Simulation of the Pressure Drop through Structured Porous Media

Malico, I.; Ferrão; Ferreira de Sousa, P. J. S. A.
Fonte: Universidade de Évora Publicador: Universidade de Évora
Tipo: Aula
Português
Relevância na Pesquisa
66.41%
Following the development of an immersed boundary method for the study of flow through porous media [1,2], this paper presents direct numerical simulations for structured porous media composed of equal size staggered square cylinders. Different Reynolds numbers are simulated in order to capture the dependence of the pressure drop and friction factor with the Reynolds number. Results are compared to available and widely used empirical correlations. These correlations assume that the additional pressure drop caused by the entrance and exit flow adjustments is unimportant as compared to the pressure drop imposed by the porous medium core. Following this line of though, many of the studies and books on flow though porous media neglect these entrance and exit effects and at best mention them in passing. Through the representation of the pressure drop per unit length for several Reynolds numbers, the authors obtain for a regular matrix composed of equal size square cylinders, the influence of the porous medium entrance. This influence is a function of the Reynolds number.

Pressure drop coefficients for elliptic and circular sections in one, two and three-row arrangements of plate fin and tube heat exchangers

Bordalo,Sérgio Nascimento; Saboya,Francisco Eduardo Mourão
Fonte: The Brazilian Society of Mechanical Sciences Publicador: The Brazilian Society of Mechanical Sciences
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/1999 Português
Relevância na Pesquisa
66.32%
The objective of the present work is the experimental determination of pressure drop coefficients (loss coefficients) for elliptic and circular sections in one, two and three-row arrangements of plate fin and tube heat exchangers. The experiments permitted to correlate the dimensionless loss coefficient with the flow Reynolds number in the rectangular channel formed by the plate fins. The experimental technique consisted of the measurement of the longitudinal pressure distribution along the flow channel, for several values of air mass flow rate. The total number of data runs, each one characterized by the flow Reynolds number, was 216. The present geometry is used in compact heat exchangers for air conditioning systems, heaters, radiators, and others. Also, it is verified the influence of the utilization of elliptic tubes, instead of circular ones, in the pressure drop. The measurements were performed for Reynolds numbers ranging from 200 to 1900.

Pressure Drop in Vertical Core-Annular Flow

Prada,José Walter Vanegas; Bannwart,Antonio Carlos
Fonte: The Brazilian Society of Mechanical Sciences Publicador: The Brazilian Society of Mechanical Sciences
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2001 Português
Relevância na Pesquisa
66.41%
An experimental apparatus for the study of core annular flows of heavy oil and water at room temperature has been set up and tested at laboratory scale. The test section consists of a 2.75 cm ID galvanized steel pipe. Tap water and a heavy oil (17.6 Pa.s; 963 kg/m³) were used. Pressure drop in a vertical upward test section was accurately measured for oil flow rates in the range 0.297 - 1.045 l/s and water flow rates ranging from 0.063 to 0.315 l/s. The oil-water input ratio was in the range 1-14. The measured pressure drop comprises gravitational and frictional parts. The gravitational pressure drop was expressed in terms of the volumetric fraction of the core, which was determined from a correlation developed by Bannwart (1998b). The existence of an optimum water-oil input ratio for each oil flow rate was observed in the range 0.07 - 0.5. The frictional pressure drop was modeled to account for both hydrodynamic and net buoyancy effects on the core. The model was adjusted to fit our data and shows excellent agreement with data from another source (Bai, 1995).

A new correlation for single and two-phase flow pressure drop in round tubes with twisted-tape inserts

Kanizawa,Fabio T.; Hernandes,Renan S.; Moraes,Anderson A. U. de; Ribatski,Gherhardt
Fonte: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM Publicador: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2011 Português
Relevância na Pesquisa
66.36%
Twisted-tape inserts are frequently used in heat exchangers as a passive and inexpensive heat transfer enhancement method. However, their use results not only heat transfer coefficient increments, but also pressure drop penalties. The present study analyses the literature on single and two-phase frictional pressure drop inside tubes with twisted-tape inserts focusing on the physical mechanism and the effects of the use of twisted-tape in comparison to plain tubes. Experimental data were gathered from the open literature and compared against the available correlations developed in order to predict two-phase frictional pressure drop in tubes containing twisted-tape inserts. It was found that none of the correlations was able to predict such a database accurately. A new correlation to estimate the friction factor for two-phase flows inside tubes with twisted-tape is also proposed. Contrarily to previous studies, the proposed correlation presents reasonable predictions under single and two-phase flow conditions and obeys the trends when the twisted-tape ratio tends to zero and infinite.

A combined CFD modeling with population balance equation to predict pressure drop in venturi scrubbers

Sharifi, Azam; Mohebbi, Ali
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em //2014 Português
Relevância na Pesquisa
66.44%
A venturi scrubber is one of the most important devices for air pollution control. Although there are different models for predicting the pressure drop in venturi scrubbers, most of them have some defects and cannot predict the pressure drop correctly. In this study, for the first time, an Eulerian–Eulerian computational fluid dynamics (CFD) model is combined with a population balance equation to predict the pressure drop in venturi scrubbers. This simulation takes into account a multiple size group model for droplet dispersion and droplet size distribution, which is based on a population balance equation. Flow field has been calculated by solving the time averaged continuity and Navier–Stokes equations along with the standard k–ε turbulence model. The equations included drag, turbulent dispersion, and buoyancy forces. The calculated pressure drop with and without considering the population balance equation was compared with the experimental data to evaluate the accuracy of the CFD modeling. The size distribution of droplets in the venturi scrubber was studied at different points for different liquid to gas ratios and throat gas velocities. The results show that the maximum break-up of droplets happens at the liquid injection point. Finally...

A pressure drop correlation for low Reynolds number Newtonian flows through a rectangular orifice in a similarly shaped micro-channel

Zivkovic, V.; Zerna, P.; Alwahabi, Z.; Biggs, M.
Fonte: Inst Chemical Engineers Publicador: Inst Chemical Engineers
Tipo: Artigo de Revista Científica
Publicado em //2013 Português
Relevância na Pesquisa
66.36%
Current microfabrication methods mean that rectangular orifices in similarly shaped micro-channels are often found in microfluidic devices. The power required to overcome the pressure drop across such orifices is often of importance. In the contribution reported here, numerical results for low Reynolds number incompressible Newtonian fluid flow through rectangular orifice in similarly shaped micro-channel have been used to develop a correlation for pressure drop arising from the orifice. The correlation, which was motivated by theoretical developments, indicates that the pressure drop is proportional to the average velocity through the orifice, and a function of the orifice contraction ratio, length-to-width ratio and, most particularly, aspect ratio.; V. Zivkovic, P. Zerna, Z.T. Alwahabi, M.J. Biggs

On the pressure drop in plate heat exchangers used as desorbers in absorption chillers

García-Hernando, Néstor; Almendros-Ibáñez, José Antonio; Ruiz, G.; Vega, Mercedes de
Fonte: Elsevier Publicador: Elsevier
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/article Formato: application/pdf
Publicado em /02/2011 Português
Relevância na Pesquisa
66.43%
The influence of the pressure drop in Plate Heat Exchangers (PHE) in the boiling temperature of LiBr H₂O and NH₃ H₂O solutions is studied. For the NH₃H₂O solution, the pressure drop-temperature saturation relationship estates that high pressure drops can be allowed in the solution with negligible changes in the saturation temperature, and in the PHE performance. Besides, in the case of the LiBr H₂O solution, as the working pressure is usually very low, the analysis of the pressure drop must be taken as a main limiting parameter for the use of Plate Heat Exchangers as vapour generators. In this case, the pressure drop may considerably change the boiling temperature of the solution entering the heat exchanger and therefore a higher heating fluid temperature may be required. A guideline to design these systems is proposed; This work has been partly supported by the ‘‘Ayuda a grupos” of CAM under the project numbers CCG07 UC3M/AMB 3412 and CCG08 UC3M/AMB 4227

Direct numerical simulation of the pressure drop through structured porous media

Malico, Isabel; Ferrão, Célia; Ferreira de Sousa, Paulo J. S. A.
Fonte: Trans Tech Publications Inc. Publicador: Trans Tech Publications Inc.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
66.38%
This paper presents direct numerical simulations for the flow through regular porous media composed of equal size staggered square cylinders obtained with a compact finite differences immersed boundary method. Different moderate Reynolds numbers are simulated in order to capture the dependence of the pressure drop with the Reynolds number in the Forchheimer regime. The pressure drop predictions agree well with the Hazen-Dupuit-Darcy model; however, when compared to a widely used semi-empirical correlation, the modified Ergun equation, the agreement is poor. A better agreement is found if the particle diameter is taken to be equal to the cylinder diameter. From the intrinsic-averaged pressure calculated along the flow direction, it can be seen that, for the porous media studied, the bulk pressure drop dominates and the entrance and exit effects are negligible.

Heat transfer, pressure drop, and dissolved gas effect during flow boiling in microchannels

Steinke, Mark
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado Formato: 625812 bytes; 3355869 bytes; 121742 bytes; 2 bytes; 2061 bytes; 698 bytes; 5612 bytes; 49 bytes; 625812 bytes; 3355869 bytes; application/pdf; application/pdf; text/plain; text/plain; text/plain; application/octet-stream; application/octet-stream; applica
Português
Relevância na Pesquisa
66.32%
Microchannels are being considered in many advanced heat transfer applications, including automotive, fuel cells, and electronics cooling. However, there are a number of fundamental issues still unresolved with respect to heat transfer and fluid mechanics perspective. An experimental investigation of the heat transfer, pressure drop, and flow patterns during flow boiling in microchannels is performed. Six parallel microchannels with a mean hydraulic diameter of 207 micron are manufactured and tested. Flow patterns have been observed in the channels under diabatic conditions. Observations suggest that the conventional flow patterns also occur in microchannels, however, the Reynolds number range is significantly lower in microchannels than in conventional channels (hydraulic diameter of 3 mm or higher). The effect of dissolved gas in water has also been investigated. A novel method for the removal of dissolved air has been applied and used to achieve several different levels of degassing. It was found that if the water is degassed to oxygen levels of 5.4 ppm, 3.2 ppm, and 1.8 ppm, behaves as predicted by correlations. The water that contained dissolved gas with an oxygen level of 8.0 ppm first exhibits a decrease in heat transfer and then an enhancement. The range of parameters are: mass flux - 160 to 1827 kg/m2s...

Experimental study of flow patterns, pressure drop, and flow instabilities in parallel rectangular minichannels

Balasubramanian, Prabhu; Kandlikar, Satish
Fonte: Taylor & Francis Publicador: Taylor & Francis
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
66.4%
Flow boiling heat transfer in parallel minichannels and microchannels is one of the solutions proposed for cooling high heat flux systems. The associated increase in the pressure drop poses a problem that needs to be studied in detail before the small diameter channels can be implemented in practical systems. The pressure drop fluctuations and the flow instability in a network of parallel channels connected by a common header also need to be addressed for the stable operation of flow boiling systems. The current work focuses on studying the flow patterns, pressure drop fluctuations, and flow instabilities in a set of six parallel rectangular minichannels, each with 333 μm in hydraulic diameter. Deionized and degassed water was used for all the experiments. The pressure fluctuations are recorded and signal analysis is performed to find the dominant frequencies and their amplitudes. These pressure fluctuations are then mapped to their corresponding flow patterns observed using a high speed camera. The results help us to relate pressure fluctuations to different flow characteristics and their effect on flow instability.; RIT community members may access full-text via RIT Libraries licensed databases: http://library.rit.edu/databases/

Modeling pressure drop of two-phase gas/liquid flow in PEM fuel cell channels

Grimm, Michael
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
66.42%
Modern energy concerns have resulted in the necessity to create and understand alternative energy sources and develop systems to effectively utilize them. One such source is hydrogen, which can be utilized in a Proton Exchange Membrane Fuel Cell (PEMFC). This fuel cell has moved to the forefront for adaptability to the automotive industry. With this increased prominence the understanding of two-phase flow phenomena within the anode and cathode channels is needed. Much research has been performed in the area of two-phase flow within macro, mini, and micro-channels of both circular and rectangular cross-sections. However previous research has been performed with a constant water and air introduction at the beginning of the channel. In a PEMFC water is introduced periodically along the length of the channel, resulting in more water at the end of the channel than at the beginning. A situation arises where the two-phase flow phenomena of the channel changes with distance, and the pressure drop model needs to be modified for the instantaneous flow phenomena. Previous studies have attempted to provide transition equations between the observed flow regimes, and several approaches have been taken. The two-phase flow in the gas channels of proton exchange membrane fuel cell (PEMFC) is studied with an ex-situ setup using a gas diffusion layer (GDL) as the sidewall of the channel. Air is introduced at the channel inlet with continuous uniform water introduction through the GDL. This is different from that used in two-phase studies reported in literature...

In situ measurement, characterization, and modeling of two-phase pressure drop incorporating local water saturation in PEMFC gas channels

See, Evan
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
66.5%
Proton Exchange Membrane Fuel Cells (PEMFCs) have been an area of focus as an alternative for internal combustion engines in the transportation sector. Water and thermal management techniques remain as one of the key roadblocks in PEMFC development. The ability to model two-phase flow and pressure drop in PEMFCs is of significant importance to the performance and optimization of PEMFCs. This work provides a perspective on the numerous factors that affect the two-phase flow in the gas channels and presents a comprehensive pressure drop model through an extensive in situ fuel cell investigation. The study focused on low current density and low temperature operation of the cell, as these conditions present the most challenging scenario for water transport in the PEMFC reactant channels. Tests were conducted using two PEMFCs that were representative of the actual full scale commercial automotive geometry. The design of the flow fields allowed visual access to both cathode and anode sides for correlating the visual observations to the two-phase flow patterns and pressure drop. A total of 198 tests were conducted varying gas diffusion layer (GDL), inlet humidity, current density, and stoichiometry; this generated over 1500 average pressure drop measurements to develop and validate two-phase models. A two-phase 1+1 D modeling scheme is proposed that incorporates an elemental approach and control volume analysis to provide a comprehensive methodology and correlation for predicting two-phase pressure drop in PEMFC conditions. Key considerations...