Formation of asphalt aggregates and their deposition on the pore s u~a c e s of a porous

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In this paper, the effect of partial-or full-block placement along the flow channels 15 of PEM fuel cells is numerically studied. Blockage in the channel of flow-field diverts the flow into the 16 gas diffusion layer (GDL) and enhances the mass transport from the channel core part to the catalyst 17 layer, which in turn improves the cell performance. By partial blockage, only a part of the channel flow 18 is shut off. While in full blockage, in which the flow channel cross sections are fully blocked, the only 19 avenue left for the continuation of the gas is to travel over the blocks via the porous zone (GDL). In 20 this study, a 3D numerical model consisting of a 9-layer PEM fuel cell is performed. A wide spectrum 21 of numerical studies is performed to study the influences of the number of blocks, blocks height, and 22 anode/cathode-side flow channel blockage. The results show that the case of full blockage enhances 23 the net electrical power more than that of the partial blockage, in spite of higher pressure drop. 24Performed studies show that full blockage of the cathode-side flow channels with five blocks along 25 the 5 cm channel enhances the net power by 30%. The present work provides helpful guidelines to 26 bipolar plate manufacturers. 27 1. Introduction 29 With the limitations of fossil fuel resources and crises in environmental pollution, 30 recent attention to alternative power sources for various applications has been very 31 serious. Proton Exchange Membrane Fuel cells (PEMFCs) with high efficiency and high 32 environmental compatibility have attracted considerable interest within academic and 33 industrial area as a potential power source for transportation and other mobile 34 applications [1-2]. 35 Bipolar plates (BPP) employ various patterns of grooves or flow-field channels to 36 feed reactant gases to the electrode of PEM fuel cells. Several numerical and 37 experimental investigations have attempted to visualize and quantify the characteristics 38 of different flow-field designs [3-8]. For example, Spernjak et al. [8] compared water 39 content and dynamics by simultaneous neutron and optical imaging for three PEM fuel 40 cell flow-fields: parallel, serpentine, and interdigitated. They concluded that the 41 serpentine flow-field showed stable output across the current range and the highest 42 limiting current in comparison to parallel and interdigitated flow-fields which exhibited 43 substantially higher water contents. However, the serpentine flow-field also experienced 44 the highest pressure drop. Li and Sabir [9] presented a review of the flow-field layouts 45 developed by different companies and research groups and their associated pros and 46 cons. Manso et al. [10] also reviewed recent works ralated to the influence of geometric 47 parameters of flow channels on overall PEMFC performance. Based on this work, 48 homogeneous gas distribution in the gas flow channel can provide a uniform current 49 density throughout the active area and, hence, a uniform temperature distribution, 50causing...

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Asphalt formation and precipitation under primary oil recovery conditions as well as secondary recovery by immiscible gas injection were studied. The crude oils were from a carbonate and highly fractured reservoir. No asphalt precipitated under these conditions. Since the oil reservoir had experienced significant formation damage and plugging of its well's tubing due to asphalt formation and precipitation, the absence of asphalt precipitation in our experiments points to the important influence on asphalt formation of flow of the oil, the streaming potentials arising from the flow, and their interaction with the electrical properties of the asphalt aggregates. Also investigated was asphalt precipitation when an enriched gas was injected into the oil under dynamic (multiple contact) miscibility conditions. Only trace amounts of asphalt precipitated when the dilution ratio R was high enough. However, significant asphalt precipitation occurred in completely miscible injections. For this case, we report extensive new experimental data for the amount of the precipitated asphalt formed with various precipitation agents over wide ranges of pressure, temperature, and crude oil composition. Increasing the pressure decreases the amount of asphalt precipitation. However, depending on the crude oil, two opposite trends in the amount of the precipitated asphalt were observed when the temperature of the system was raised. A scaling equation of state is shown to provide accurate predictions for the data. The scaling equation also yields a novel analytical equation for R c , the critical dilution ratio (measured in cm 3 of the diluent or the precipitation agent per gram of crude oil) at the onset of the precipitation given by R c ) c(MT) 1/4 , where M is the (average) molecular weight of the precipitation agent, T is the temperature in °C, and c is a constant on the order of 10 -2 . The predictions of this equation are in excellent agreement with the experimental data. Thus, this equation may be used in the design of gas injection operations for enhanced oil recovery, such that precipitation of the asphalt aggregates in the reservoir can be prevented.

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