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Guo C.-L.,Chongqing University | Guo C.-L.,Key Laboratory of Low grade Energy Utilization Technologies and Systems | Zhu X.,Chongqing University | Zhu X.,Key Laboratory of Low grade Energy Utilization Technologies and Systems | And 8 more authors.
Bioresource Technology | Year: 2011

In this study, a biofilm photobioreactor with optical fibers that have additional rough surface (OFBP-R) was developed and it was shown that additional rough surface greatly enhanced the biofilm formation and thus increased the cell concentration, leading to an improvement in the hydrogen production performance. The effects of operational conditions, including the influent substrate concentration, flow rate, temperature and influent medium pH, on the performance of OFBP-R were also investigated. The experimental results showed that the optimum operational conditions for hydrogen production were: the influent substrate concentration 60. mM, flow rate 30. mL/h, temperature 30 °C and influent medium pH 7. Under the optimal operation conditions discovered in this work, the OFBP-R yielded fairly good and stable long-term performance with hydrogen production rate of 1.75. mmol/L/h, light conversion efficiency of 9.3% and substrate degradation efficiency of 75%. © 2011 Elsevier Ltd.


Zhou N.,Key Laboratory of Low grade Energy Utilization Technologies and Systems | Zhou N.,Chongqing University | Yang C.,Key Laboratory of Low grade Energy Utilization Technologies and Systems | Yang C.,Chongqing University | And 3 more authors.
International Journal of Hydrogen Energy | Year: 2015

Direct-fired fuel cell gas turbine hybrid power system responses to open-loop transients were evaluated using a hardware-based simulation of an integrated solid oxide fuel cell gas turbine (SOFC/GT) hybrid system, implemented through the Hybrid Performance (Hyper) facility at the U.S. Department of Energy, National Energy Technology Laboratory (NETL). A disturbance in the cathode inlet air mass flow was performed by manipulating a hot-air bypass valve implemented in the hardware component. Two tests were performed; the fuel cell stack subsystem numerical simulation model was both decoupled and fully coupled with the gas turbine hardware component. The dynamic responses of the entire SOFC/GT hybrid system were studied in this paper. The reduction of cathode airflow resulted in a sharp decrease and partial recovery of the fuel cell thermal effluent in 10 s. In contrast, the turbine rotational speed did not exhibit a similar trend. The transfer functions of several important variables in the fuel cell stack subsystem and gas turbine subsystem were developed to be used in the future control method development. The importance of the cathode airflow regulation was quantified through transfer functions. The management of cathode airflow was also suggested to be a potential strategy to increase the life of fuel cells by reducing the thermal impact of operational transients on the fuel cell subsystem. © 2014 Hydrogen Energy Publications, LLC.


Zhu Y.,Tianjin University | Li W.,Tianjin University | Sun G.,North China Electrical Power University | Tang Q.,Key Laboratory of Low grade Energy Utilization Technologies and Systems | Bian H.,Key Laboratory of Low grade Energy Utilization Technologies and Systems
International Journal of Greenhouse Gas Control | Year: 2016

Present investigation entails carbonic anhydrase (CA) immobilization and its influence on accelerating CO2 absorption in post-combustion CO2 capture. CA was immobilized in alginate polymers with the glutaraldehyde cross-linking method, subsequently maintained 56.3% of its original activity. The pH and thermal stabilities of the immobilized CA were significantly greater than their free counterparts. The immobilized CA also had improved resistance to chemical impurities typically found in flue gas scrubbing liquids. Batch-scale studies with immobilized CA revealed that the rate of CO2 absorption was promoted by the addition of immobilized CA. The gas flow was the main factor affecting CO2 absorption with low enzyme load, while the enzyme load became the main parameter with the increase of gas flow. The catalytic absorption of CO2 with immobilized CA was remarkable with the gas flow of 650 mL min-1 and enzyme load of 1 mg in vertical reactor. The immobilized enzymes showed better operational stability, and the surface of immobilized CA was characterized with porous structure through scanning electron microscope. It was concluded that immobilized CA in alginate polymers would have the potential for CO2 capture by biomimetic route. © 2016 Elsevier Ltd. All rights reserved.


Feng L.,Chongqing University | Shi W.-Y.,Chongqing University | Shi W.-Y.,Key Laboratory of Low grade Energy Utilization Technologies and Systems
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2015

In this work, the influence of eddy effect of coils on magnetic, flow, and temperature fields in an electromagnetically levitated molten droplet was investigated by a serial of axisymmetric numerical simulations. In an electromagnetic levitation device, both metal droplet and coils are conductive materials, therefore the distributions of current density in them should be non-uniform as a result of the eddy effect. However, in previous works, the eddy effect was considered alone in metal droplet but ignored in coils usually. As the distance of coils and metal droplet is several millimetres in general, the non-uniform distribution of current density in coils actually gives important influences on calculations of magnetic, flow, and temperature fields. Here, we consider the eddy effect both in metal droplet as well as that in coils simultaneously. Lifting force, absorbed power, fluid flow, and temperature field inside a 4-mm radius molten copper droplet as a typical example are then calculated and analyzed carefully under such condition. The results show that eddy effect leads to higher magnetic force, velocity, and temperature in both levitating and melting processes than those when the eddy effect is ignored. What is more, such influence increases as the distance of droplet and coils becomes closer, which corresponds to experimental measurement. Therefore, we suggest that eddy effect of coils should be considered in numerical simulation on this topic to obtain more reliable result. © 2015, The Minerals, Metals & Materials Society and ASM International.


Feng L.,Chongqing University | Shi W.-Y.,Chongqing University | Shi W.-Y.,Key Laboratory of Low grade Energy Utilization Technologies and Systems
ISIJ International | Year: 2016

This work presents a transient simulation of electromagnetically levitated deformed droplet based on Arbitrary Lagrangian-Eulerian method. The magnetic, flow, temperature fields as well as free surface deformation of a molten aluminum droplet are coupled to investigate the influence of coil angle arrangement on dynamic deformation and stability of the droplet under terrestrial conditions. Our results confirm that the Arbitrary Lagrangian-Eulerian method can trace the interface of molten droplet more precisely and the calculation of surface effect is more reliable than that of VOF method. Simulation results show that the electromagnetically levitated molten droplet tends to oscillate in vertical direction and the sphere shape deforms largely at the very beginning of simulation. The dynamic deformation of the molten droplet is small during vertical oscillations since the density of aluminum is small. With the increasing of coil angle, the maximum velocity inside droplet decreases gradually and an over 10% difference is observed comparing with 0 and 30 degree coil angles. At the same time, the temperature of droplet declines significantly with the increasing of coil angles, which is of potential interest for temperature control improvement and undercooling processes in electromagnetic device. The deformation of droplet is observed to be most serious with a coil angle of 12 degree, which should be avoided in future coil design for the purpose of stable levitation of massive materials. © 2016 ISIJ.


Rao W.-J.,Chongqing University | Rao W.-J.,Key Laboratory of Low Grade Energy Utilization Technologies and Systems | Zhao L.-J.,Chongqing University | Zhao L.-J.,Key Laboratory of Low Grade Energy Utilization Technologies and Systems | And 4 more authors.
Applied Thermal Engineering | Year: 2013

This paper has proposed a combined cycle, in which low-temperature solar energy and cold energy of liquefied natural gas (LNG) can be effectively utilized together. Comparative analysis based on a same net work output between the proposed combined cycle and separated solar ORC and LNG vapor system has been done. The results show that, for the combined cycle, a decrease of nearly 82.2% on the area of solar collector is obtained and the area of heat exchanger decreases by 31.7%. Moreover, exergy efficiency is higher than both two separated systems. This work has also dealt with the thermodynamic analyses for the proposed cycle. The results show that R143a followed by propane and propene emerges as most suitable fluid. Moreover, with a regenerator added in the cycle, performance improvement is obtained for the reduction on area of solar collector and increase on system efficiency and exergy efficiency. © 2013 Elsevier Ltd. All rights reserved.


Tian X.-H.,Chongqing University | Shi W.-Y.,Chongqing University | Shi W.-Y.,Key Laboratory of Low Grade Energy Utilization Technologies and Systems | Tang T.,Chongqing University | Feng L.,Chongqing University
ISIJ International | Year: 2016

In order to investigate the influence of static magnetic field on behavior of rising single bubble in conductive fluid, a series of axisymmetric numerical simulations are carried out. A uniform vertical magnetic field with intensities ranging from 0 to 0.4 T (Ha=0-16.97) is superposed and the bubble radii range from 2 mm to 6 mm (R∗=0.2-0.6). The rising velocity, instantaneous bubble shape and terminal height are discussed and whether the magnetic field restrains bubble rising simply or transits from positive effect to negative one with the increasing of magnetic field intensities is analyzed clearly. Besides, the discrepancy of bubble motion under magnetic field with weak or strong surface tension is compared. Numerical results show that vertical magnetic field elongates the bubble shape along vertical direction and a stronger magnetic field intensity contributes to a longer bubble shape. The imposed magnetic field has an inhibitory effect on the rising velocity for bubbles with strong surface tension as well as bubbles with weak surface tension but small sizes. However, for bubbles with weak surface tension but large sizes, the rising velocity is promoted by weak magnetic field intensities whereas inhibited by strong magnetic field intensities. The peak Hartmann number reaching the strongest positive effect and the critical Hartmann number turning from positive effect to negative effect are determined respectively. © 2016 ISIJ.


Feng L.,Chongqing University | Shi W.-Y.,Chongqing University | Shi W.-Y.,Key Laboratory of Low grade Energy Utilization Technologies and Systems
International Journal of Heat and Mass Transfer | Year: 2016

The influence of Marangoni effect on electromagnetically levitated molten droplet under a static magnetic field is investigated by a series of numerical simulations based on Arbitrary Lagrangian-Eulerian method. Firstly the motions and dynamic deformation as well as flow and temperature fields of droplet without Marangoni effect are calculated under various static magnetic fields, then Marangoni effect is introduced and clear comparisons are conducted. The results show that the static magnetic field could dynamically suppress the oscillation and enhance the levitation stability of molten droplet. With the increase of magnetic field intensity, the oscillation amplitude of droplet is decreased and the dynamic deformation during the oscillation is reduced. When the droplet eventually achieves the equilibrium position, the deformation can also be reduced by static magnetic field. Meanwhile the convection inside molten droplet is suppressed and the temperature difference grows, creating a suiting situation for Marangoni effect. The influence of Marangoni effect on behaviors of molten droplet can be divided into two aspects. On one hand, when the static magnetic field is less than 2T, considering of Marangoni effect will dynamically enlarge the deformation due to the linear decrease of surface tension. But further increasing of magnetic field, the shape difference between cases with and without Marangoni effect gets minished gradually because of the strong suppression effect of magnetic field on droplet deformation. On the other hand, when static magnetic field is over 2T, the Marangoni effect would produce a new vortex near the equatorial surface of droplet. With the increasing of magnetic field, firstly the maximum velocity area shifts into zones near the free surface due to the competition between electromagnetic force and thermocapillary force. Then it returns to the free surface and on this occasion, the flow near the equatorial areas is totally dominated by thermocapillary force. Undoubtedly, the Marangoni effect plays an important role in electromagnetic levitation process and it is necessary to take the Marangoni effect into consideration in future numerical simulations for precise prediction of droplet behavior. © 2016 Elsevier Ltd.


Li Y.-R.,Chongqing University | Li Y.-R.,Key Laboratory of Low grade Energy Utilization Technologies and Systems | Yuan X.-F.,Chongqing University | Wu C.-M.,Chongqing University | Hu Y.-P.,Chongqing University
International Journal of Heat and Mass Transfer | Year: 2011

In order to understand the characteristics of natural convection of cold water near its density maximum between horizontal cylinders, a series of unsteady two-dimensional numerical simulations were conducted by using finite volume method. The radius ratio of horizontal cylinders ranged from 1.2 to 2.0, density inversion parameter from 0 to 1, and the vertical eccentricity from 0 to 1.0 for eccentric annulus. The results show that the flow pattern mainly depends on the density inversion parameter and Rayleigh number. The formation of small cell at the top or bottom of annulus corresponds to the Rayleigh-Bénard instability within the converse density gradient layer. The width of annulus has slightly influence on the flow structure. However, the number of Bénard cells decreases with the increase of the radius ratio. For the oscillatory flow at a large Rayleigh number, the vertical converse density gradient in the top of annulus or the horizontal density gradient in the middle of annulus plays an important role for the formation of oscillatory flow when the density inversion parameter is in a small or moderate range. But the vertical density gradient in the bottom of annulus and the horizontal density gradient in the middle of annulus work together for oscillatory flow when the density inversion parameter is high. Average Nusselt number on the inner wall increases with the increase of Rayleigh number and radius ratio. However, there exists the minimum value of average Nusselt number at a moderate density inversion parameter. The flow pattern in eccentric annulus has the characteristics of coupling flows in the narrow-gap at the bottom with in the large-gap at the top of annulus. With the increase of the eccentricity, heat transfer is enhanced and the average Nusselt number increases slightly. Based on the simulation results, the new heat transfer correlation has been proposed according to the multiple linear regression technique. © 2011 Elsevier Ltd. All rights reserved.


Hu A.,Key Laboratory of Low grade Energy Utilization Technologies and Systems | Li L.,Key Laboratory of Low grade Energy Utilization Technologies and Systems | Chen S.,Key Laboratory of Low grade Energy Utilization Technologies and Systems | Liao Q.,Key Laboratory of Low grade Energy Utilization Technologies and Systems | Zeng J.,CAS Guangzhou Institute of Energy Conversation
International Journal of Heat and Mass Transfer | Year: 2013

In this paper, a single-component pseudo-potential model is analyzed by modifying corresponding equation of state. Simulation results show that with the modified vdW equation, this model is capable to simulate the multiphase flow with greater range of density ratio than other existing multiphase models and some drawbacks of pseudo-potential model such as large spurious currents are avoided as well. Besides, the influences of the modified method on surface tension are studied. Also, two other typical equations of state are employed, and the simulation results show that both of them work very well under any characteristic temperature and the greatest density ratio could be up to 10 9. © 2013 Published by Elsevier Ltd.

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