Showing papers on "Packed bed published in 2009"

Particle scale study of heat transfer in packed and bubbling fluidized beds

Abstract: The approach of combined discrete particle simulation (DPS) and computational fluid dynamics (CFD), which has been increasingly applied to the modeling of particle-fluid flow, is extended to study particle-particle and particle-fluid heat transfer in packed and bubbling fluidized beds at an individual particle scale. The development of this model is described first, involving three heat transfer mechanisms: fluid-particle convection, particle-particle conduction and particle radiation. The model is then validated by comparing the predicted results with those measured in the literature in terms of bed effective thermal conductivity and individual particle heat transfer characteristics. The contribution of each of the three heat transfer mechanisms is quantified and analyzed. The results confirm that under certain conditions, individual particle heat transfer coefficient (HTC) can be constant in a fluidized bed, independent of gas superficial velocities. However, the relationship between HTC and gas superficial velocity varies with flow conditions and material properties such as thermal conductivities. The effectiveness and possible limitation of the hot sphere approach recently used in the experimental studies of heat transfer in fluidized beds are discussed. The results show that the proposed model offers an effective method to elucidate the mechanisms governing the heat transfer in packed and bubbling fluidized beds at a particle scale. The need for further development in this area is also discussed. © 2009 American Institute of Chemical Engineers AIChE J, 2009

A Coupled DEM and CFD Simulation of Flow Field and Pressure Drop in Fixed Bed Reactor with Randomly Packed Catalyst Particles

Abstract: Packed bed unit operations are required for many commercial chemical processes. The ability to a priori predict void fraction and pressure drop in a packed bed would significantly improve reactor d...

Cationic Polymerization in Rotating Packed Bed Reactor: Experimental and Modeling

Abstract: On the basis of analysis of key engineering factors predominating in cationic polymerization, butyl rubber (IIR) as an example was synthesized by cationic polymerization in the high-gravity environment generated by a rotating packed bed (RPB) reactor. The influence of the rotating speed, packing thickness, and polymerization temperature on the number average molecular weight (Mn) of IIR was studied. The optimum experimental conditions were determined as rotating speed of 1200 r min−1, packing thickness of 40 mm and polymerization temperature of 173 K, where IIR with Mn of 289,000 and unimodal molecular weight distribution of 1.99 was obtained. According to the experimental results and elementary reactions, a model for the prediction of Mn was developed, and the validity of the model was confirmed by the fact that most of the predicted Mns agreed well with the experimental data with a deviation within 10%. © 2009 American Institute of Chemical Engineers AIChE J, 2010

Fused‐core, sub‐2 μm packings, and monolithic HPLC columns: a comparative evaluation

Abstract: Three different HPLC column technologies (i.e., monolith, fused-core particles, and sub-2 microm particles) were evaluated, comparing van Deemter plots, speed of analysis, back pressure, and mobile phase consumption. Very high linear velocities (approximately 12 mm/s) were achieved with the monolithic column using modest pressure (110 bar) at the expense of high mobile phase consumption. The minimum plate height of the monolith was similar to that of a 3 microm-particle packed column (i.e., h = 8 microm), operated at optimal linear velocities; the monolithic column showed substantially lower mass transfer dependence, however. The 2.7 microm fused-core packing material yielded efficiencies closer to the sub-2 microm material than to the 3 microm-particle packed column and could be operated at high flow rates. The fused-core column was able to achieve linear velocities similar to those attained on the sub-2 microm column, staying below 620 bar instead of almost near 1030 bar required by the sub-2 microm material. The lack of pH stability of the monolithic column prevented its use to separate basic compounds (i.e., tricyclic antidepressants) at high pH. Best separation of these components at high pH was achieved using the column packed with 1.7 microm hybrid material.

Study on medium-temperature chemical heat storage using mixed hydroxides

Abstract: It was demonstrated that chemical heat storage materials mixed with metal hydroxides were capable of storing heat at medium temperatures of approximately 200–300 °C. The performances of the developed materials were demonstrated in a thermo-balance and packed bed reactor. The mixed hydroxides can increase the operation heat storage temperature by changing the composition of mixed metal oxides in the material. MgαNi1−α(OH)2, which is a mixed hydroxide of magnesium hydroxide, Mg(OH)2, and nickel hydroxide, Ni(OH)2, is a candidate heat storage material. The mixed hydroxide was dehydrated, that is, it was capable of storing heats at 200–300 °C, at which pure Mg(OH)2 could not be dehydrated and could not store heat. The heat output performance of the material was examined in a packed bed reactor. It was shown that the mixed hydroxide material was potentially useful for chemically storing medium-temperature heat such as waste heats emitted from internal combustion engines, solar energy system and high-temperature processes.