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| 2. |
- Oseen-Senda, K. M., et al.
(författare)
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Cooling of PEMFC with pentane boiling in minichannels : A study of flow instabilities using neutron radiography visualization
- 2006
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Ingår i: 16th World Hydrogen Energy Conference 2006. - 9781622765409 ; , s. 2885-2894
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Konferensbidrag (refereegranskat)abstract
- Compared to other heat transfer systems, Polymer Electrolyte Fuel Cells are characterized by very low heat flux. In order to analyse two-phase pentane cooling of bipolar plates, high speed neutron visualizations have been performed in a circular steel tube (Di=1.1 mm, Do=2 mm) at the Institut Laue-Langevin in Grenoble, France. The flow pattern is clearly visible and can be synchronized with time resolved temperature measurements. At low mass flow rates, the pipe wall is high above the saturation temperature and the pipe filled with vapour and liquid slugs. At higher flow rates, the wall is superheated when filled with liquid and at saturation temperature when exposed to a liquid-vapour mixture. An irregular switching between these two states was observed. Superheated liquid exists in both stable and time dependent states. The ?-radiation produced by the neutrons is shown to have an important effect on the boiling process. Simplified steady and time dependent models are proposed to explain the measured wall temperature instabilities and superheat.
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| 3. |
- von Brömssen, Mattias, et al.
(författare)
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Targeting low-arsenic aquifers in Matlab Upazila, Southeastern Bangladesh
- 2007
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 375:2-3, s. 121-132
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Tidskriftsartikel (refereegranskat)abstract
- Groundwater with high concentration of geogenic arsenic (As) occurs extensively in the Holocene alluvial aquifers of Bangladesh. Local drillers in Matlab Upazilla are constructing deeper tubewells than in the recent past, primarily because of low concentrations of dissolved Fe and As. Locally a thick layer of black to grey sediments overlies an oxidised unit of yellowish-grey to reddish-brown sediments. The correlation between the colour of both units and the groundwater redox conditions was investigated to provide an easy tool for targeting low-arsenic groundwater. Based on the sediment colour at the screen depths described by local drillers, 40 domestic shallow tubewells were selected for water sampling. Four colours were used to describe the sediments: black, white, off-white (buff) and red. Generally, the groundwater was anoxic and the As concentrations ranged from less than 5.2 to 355 mu g/L. Water derived from the black sediment is characterized by relatively higher concentrations of dissolved NH4+, DOC, Fe, P, As and by low Mn and SO42- concentrations. The off-white and red sediments had high concentration of Mn and low NH4+, DOC, Fe, P and As concentrations. The water abstracted from the black sediments indicated the most reducing environment, followed by white, off-white and red respectively. Three boreholes verified the driller's perception of the subsurface lithologic conditions. Discrepancies between the driller's and the research team description of the sediment colours were insignificant. This study shows that sediment colour is a reliable indicator of high and low-As concentrations and can be used by local drillers to target low-arsenic groundwater.
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| 4. |
- Oseen-Senda, K. M., et al.
(författare)
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The cooling of PEFC with pentane boiling in minichannels : A study of flow instabilities using neutron radiography visualization
- 2007
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Ingår i: Heat Transfer Engineering. - : Informa UK Limited. - 0145-7632 .- 1521-0537. ; 28:1, s. 49-57
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Tidskriftsartikel (refereegranskat)abstract
- Polymer electrolyte fuel cells (PEFC) operate best at a steady temperature of about 80 degrees C and have a very low heat flux compared to other heat transfer applications. Two-phase pentane cooling of bipolar plates is studied in order to optimize fuel cell cooling in transport applications. High-speed visualizations of boiling pentane in a circular steel tube (D-i = 1.1 mm, D-o = 2 mm) have been performed in a Neutrograph instrument at the Institut Laue-Langevin in Grenoble, France. The heat and mass flux were both very low and appropriate for cooling of PEFC. The spatial resolution of the images is approximately 0.15 mm and the maximum frequency is 154 Hz. In the images, the liquid-vapor differentiation is clearly visible. Time resolved measurements of the outer pipe wall temperature, synchronized with the images, show that at low mass flow rates, the pipe wall is high above the saturation temperature and the pipe filled with vapor and liquid slugs. At higher flow rates, the wall is superheated when filled with liquid, and at saturation temperature during boiling when exposed to a liquid-vapor mixture. An irregular switch between these two states was observed. The superheated wall is shown to be consistent with the superheated liquid in the pipe in both stable and time-dependent states. Unfortunately, the strong gamma-radiation produced by the neutrons has a substantial effect on the onset of boiling, which is why comparisons with non-irradiated systems might be difficult. Simplified steady and time-dependent models are proposed to explain the measured wall temperature instabilities and superheat.
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