The Experts below are selected from a list of 162 Experts worldwide ranked by ideXlab platform
Aldo Steinfeld - One of the best experts on this subject based on the ideXlab platform.
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design of packed bed thermal energy storage systems for high temperature industrial process heat
Applied Energy, 2015Co-Authors: Giw Zanganeh, Andrea Pedretti, Andreas Haselbacher, Aldo SteinfeldAbstract:A previously validated quasi-one-dimensional transient two-phase heat transfer model is used to assess the effect of operational and design parameters on the performance of thermocline thermal energy storage (TES) based on a packed bed of rocks and high-temperature air from process heat as heat transfer fluid. The performance indicators are thermal losses, pumping work, discharge outflow temperature, and overall storage efficiency. A 7.2GWhth TES unit is used as a baseline design. It is found that initial charging of the TES prior to cyclic operation significantly improves its performance at the expense of additional storage material. The temperature drop during the discharge phase is reduced and the efficiency is increased by decreasing the Tank Diameter-to-height ratio and the rock Diameter at the expense of increased pressure drop and pumping work. Increasing the cone angle results in reduced storage size, but increases the temperature drop during discharging. It is shown that thin insulation layers are sufficient to ensure low thermal losses. For all investigated cases, the overall efficiency of the storage stays above 95%.
Zhengming Gao - One of the best experts on this subject based on the ideXlab platform.
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influence of impeller Diameter on local gas dispersion properties in a sparged multi impeller stirred Tank
Chinese Journal of Chemical Engineering, 2015Co-Authors: Yuyun Bao, Jie Yang, Bingjie Wang, Zhengming GaoAbstract:Abstract The impeller configuration with a six parabolic blade disk turbine below two down-pumping hydrofoil propellers, identified as PDT + 2CBY, was used in this study. The effect of the impeller Diameter D, ranging from 0.30T to 0.40T (T as the Tank Diameter), on gas dispersion in a stirred Tank of 0.48 m Diameter was investigated by experimental and CFD simulation methods. Power consumption and total gas holdup were measured for the same impeller configuration PDT + 2CBY with four different D/T. Results show that with D/T increases from 0.30 to 0.40, the relative power demand (RPD) in a gas–liquid system decreases slightly. At low superficial gas velocity VS of 0.0078 m·s− 1, the gas holdup increases evidently with the increase of D/T. However, at high superficial gas velocity, the system with D/T = 0.33 gets a good balance between the gas recirculation and liquid shearing rate, which resulted in the highest gas holdup among four different D/T. CFD simulation based on the two-fluid model along with the Population Balance Model (PBM) was used to investigate the effect of impeller Diameter on the gas dispersion. The power consumption and total gas holdup predicted by CFD simulation were in reasonable agreement with the experimental data.
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Influence of the Top Impeller Diameter on the Gas Dispersion in a Sparged Multi-impeller Stirred Tank
Industrial & Engineering Chemistry Research, 2012Co-Authors: Yuyun Bao, Jie Yang, Lei Chen, Zhengming GaoAbstract:The impeller configuration with a hollow half-elliptical blade dispersing turbine below two up-pumping wide-blade hydrofoils, identified as HEDT+2WHU and recommended in previous work, was used in this study. The effect of the top impeller Diameter, ranging from 0.33T to 0.50T, on gas–liquid flow in a stirred Tank of 0.48 m Diameter was investigated by experimental and CFD methods. Power consumption, total gas holdup, and local void fraction were measured for the impeller configurations with different top impeller Diameters. Results show that while the ratio of top impeller Diameter to Tank Diameter (Dtop/T) increases from 0.33 to 0.50, the relative power demand (RPD) in a gas–liquid system decreases slightly. The increase of total gas holdup with rising gas flow rate becomes less evident as Dtop/T increases from 0.33 to 0.50. Local void fractions at the measurement points above the height of 0.8T increase significantly with the increase of top impeller Diameter. When Dtop/T = 0.50, there is an extremely l...
Zhipeng Li - One of the best experts on this subject based on the ideXlab platform.
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piv experiments and large eddy simulations of single loop flow fields in rushton turbine stirred Tanks
Chemical Engineering Science, 2011Co-Authors: Zhipeng LiAbstract:Abstract The single-loop flow fields in Rushton turbine stirred Tanks with clearance C =0.15 T ( T is Tank Diameter) were investigated by using particle image velocimetry (PIV) experiments and large eddy simulation (LES) methods. The velocity and turbulent kinetic energy (TKE) were carefully measured and resolved with high resolution camera. The regions with high TKE are affected by the movement of the trailing vortices generated behind the impeller blades. The effects of both geometrical configuration and Reynolds number were discussed. It is found that the Reynolds number has little effect on the mean flow for the configuration of impeller Diameter D = T /3, C =0.15 T . However, the single-loop flow pattern is changed into a double-loop one if D is increased from T /3 to T /2. The LES results were compared with the PIV experiments and the laser Doppler anemometry (LDA) data in the literature. The effect of the grid was validated, and the levels of local anisotropy of turbulence near the impeller discharge regions were investigated. Both the phase-averaged and phase-resolved LES results are in good agreement with the PIV experimental data, and are better than the predictions of the k – e model. The agreement shows that the LES method can be used to simulate the complex flow fields in stirred Tanks.
Farhad Einmozaffari - One of the best experts on this subject based on the ideXlab platform.
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using electrical resistance tomography images to characterize the mixing of micron sized polymeric particles in a slurry reactor
Chemical Engineering Journal, 2011Co-Authors: Parisa Tahvildarian, Michael J Damato, Stephan V Drappel, Farhad Einmozaffari, Simant R UpretiAbstract:Abstract Electrical resistance tomography (ERT) was employed to study the solid–liquid mixing in a slurry reactor equipped with a top-entering axial-flow impeller. The ERT data were used to reconstruct the tomogram using the linear back projection algorithm and calculate the degree of homogeneity. In this study, the effects of the impeller speed (252–400 rpm), impeller pumping mode (downward and upward), impeller type (A310, A100, A200, A320, A315, 3AM), impeller off-bottom clearance ( T /3.8– T /2.5, where T is the Tank Diameter), impeller Diameter to Tank Diameter ratio ( D / T = 0.29–0.47), particle size (5.2–9.1 μm), and solids concentration (15–30 wt%) on the degree of homogeneity of micron sized latex particles in a slurry reactor were explored. The results showed that the level of homogeneity in a solid–liquid mixing system improved with the increase in impeller speed. However, after achieving the maximum level of homogeneity, any further rise in the impeller speed had a detrimental effect on the level of homogeneity. A310 impeller, with D / T ratio of 0.31, demonstrated the highest level of homogeneity while the upward pumping direction was found to be more efficient than the downward one. In addition, a clearance of T /3 proved to create the highest level of homogeneity. The results also showed that a rise in the size and concentration of particles decreased the level of homogeneity. Thus, 5.2 μm latex particles with the concentration of 15 wt% demonstrated the highest level of homogeneity.
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cfd investigation of the mixing of yield pseudoplastic fluids with anchor impellers
Chemical Engineering & Technology, 2009Co-Authors: Poonam Prajapati, Farhad EinmozaffariAbstract:The study was carried out to simulate the 3D flow domain in the mixing of pseudoplastic fluids possessing yield stress with anchor impellers, using a computational fluid dynamics (CFD) package. The multiple reference frames (MRF) tech- nique was employed to model the rotation of the impellers. The rheology of the fluid was approximated using the Herschel-Bulkley model. To validate the model, the CFD results for the power consumption were compared to the experimental data. After the flow fields were calculated, the simulations for tracer homogenization were performed to simulate the mixing time. The effects of impeller speed, fluid rheology, and impeller geometry on power consumption, mixing time, and flow pattern were explored. The optimum values of c/D (impeller clearance to Tank Diameter) and w/D (impeller blade width to Tank Diameter) ratios were determined on the basis of minimum mixing time.
Hongyuan Wei - One of the best experts on this subject based on the ideXlab platform.
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the effect of impeller to Tank Diameter ratio on draw down of solids
Chemical Engineering Science, 2003Co-Authors: Gul Ozcantaskin, Hongyuan WeiAbstract:Abstract The effect of impeller-to-Tank Diameter ratio ( D / T ) on the draw down of solids was investigated using a mixed flow impeller (pitched blade turbine) and a narrow blade hydrofoil (LE-20) of D = T /2 and T /3. Operational conditions (impeller speed and power consumption) at which solids do not remain at the liquid surface for more than 2– 4 s were determined for a given solid type (polyethylene particles) at a given concentration ( X =1%). Under selected conditions, liquid velocity values were obtained from LDA measurements and CFD simulations to better interpret the findings. Both upward and downward pumping modes were studied with the impeller mounted over a range of submergences, and different mechanisms of draw down were noted. For LDA measurements and CFD simulations, only the upward pumping PBT was considered. These were carried out under conditions where draw down did not occur through air ingesting vortices. When solids were drawn down without air being entrained from the surface, a smaller Diameter impeller ( D = T /3) was more energy efficient, although it required higher speeds to achieve draw down. Results from LDA measurements and CFD simulations showed that the discharge flow from a larger impeller has a stronger radial component of flow, and as a result the liquid is directed towards the vessel walls rather than the surface which supported this finding. The only exception to this was when solids were drawn down along with air through vortices. In this case, the power demand could be lower with a larger Diameter impeller.
