A comparison of flow boiling heat-transfer in in-line mini pin fin and plane channel flows

The use of a boiling fluid as a coolant is an attractive option for electronic devices as electrical power densities increase. However, for systems working at the micro-scale, design methods developed for evaluating heat transfer in macro-scale evaporators are not appropriate for passages with hydraulic diameter of the order of 1 mm and below.Heat-transfer coefficients and pressure drops are reported for two surfaces, a pin-fin and a plate surface, each with 50 mm square base area. The pin-fin surface comprised of 1 mm square pin fins that were 1 mm high and located on a 2 mm square pitch array covering the base. The channel was 1 mm high and had a glass top plate. The data were produced while boiling R113 at atmospheric pressure. For both surfaces, the mass flux range was 50–250 kg/m²s and the heat flux range was 5–140 kW/m². The results obtained have been compared with standard correlations for tube bundles.The measured heat-transfer coefficients for the pin-fin surface are slightly higher than those for the plate surface. Both are dependent on heat flux and reasonably independent of mass flux and vapour quality. Thus, heat transfer is probably dominated by nucleate boiling and is increased by the pin fins due to the increase in area and heat-transfer coefficient. The pin-fin pressure drops were typically 7 times larger than the plate values.The pin-fin heat-transfer coefficients and pressure drops are compared to macro-scale tube bundle correlations. At low vapour qualities the heat-transfer coefficients are in reasonable agreement with the correlations, but, as the vapour quality increases, they do not show the convective enhancement which would be expected for a conventionally-sized tube bundle. Measured two–phase pressure drops are in reasonable agreement with the tube bundle correlation.     

Potential leakage at the Khersan 3 Dam Site,Iran: a hydrogeological approach

The paper discusses the investigations into the Khersan 3 Dam site in the Zagros Zone, southern Iran, where the Rig, Shorom and Laki Anticlines meet. The Asmari Limestone is the main aquifer system in the area of the dam site and its reservoir. Marly bands within the Lower Asmari Unit create three confined sub-aquifers under artesian pressure overlain by one unconfined sub-aquifer. The impounded water will be in direct contact with the Asmari Limestone hence leakage may occur through existing karst features. As the recharge zone of the artesian sub-aquifers is higher than the normal water level in the reservoir, no direct leakage through the artesian sub-aquifers is anticipated. However, when the water head in the unconfined sub-aquifer rises with the construction of the dam, leakage may occur and further karstification develop.      

The effect of H<Subscript>2</Subscript>S on the selectivity of light alkenes in the FE-Mn-catalyzed Fischer-Tropsch synthesis

Iron-manganese oxides are prepared using a co-precipitation procedure and studied for the conversion of synthesis gas to light olefins. In particular, the effect of a range of preparation variables is investigated in details. In this investigation, sulfur absorption and effect of sulfur poisoning on Fe-Mn catalysts have been studied. In the Fischer-Tropsch synthesis process, the poisoning of the catalyst is one of the important parameters causing a decrease in the catalyst activity, declaring the sulfur compounds as virulent poisons in this process. In the present investigation, poisoning of Fe-Mn catalysts were performed in a gas circulation system and H₂S was injected into a circulation loop. The prepared catalysts were exposed to a mixture of H₂S and N₂ at about 450°C in the stainless-steel micro reactor via co-precipitation method. H₂S was produced by addition of H₂SO₄ to Na₂S × H₂O and this gas was mixed with an inert carrier gas (N₂). Comparing the activity and selectivity of fresh and poisoned catalysts, indicates that the selectivity and CO conversion are affected by high-level sulfur adsorbed on the catalysts. The results show that the CO conversion and selectivity with respect to methane production and coke formation were decreased, but the selectivity of light alkenes such as propylene was increased over poisoned catalysts. Characterization of both precursors and calcined catalysts by powder X-ray diffraction, BET specific surface area and thermal analysis methods such as TGA and DSC showed that the poisoning of Fe-Mn catalysts influenced the catalyst structure.