CFD study of heat transfer enhanced membrane distillation using spacer-filled channels

[[abstract]]Membrane distillation (MD) can utilize low level thermal energy and holds high potential to replace conventional energetically intensive separation technologies. Direct contact membrane distillation (DCMD) is suitable for the applications of desalination and concentration of aqueous solutions. Employing spacer-filled channels can enhance the mass flux of the DCMD modules, which can further result in the increase of energy utilization efficiency of the separation. The trans-membrane mass flux is controlled by the boundary layer heat transfer of both fluid channels. The estimation of heat transfer coefficients is critical to the analysis and design of MD modules. This paper presents the results of a comprehensive 3-D computational fluid dynamics (CFD) simulation which covers the entire length of the module and takes into account the trans-membrane heat and mass transfer. The model was verified with experimental data in the literature. The contour maps show that spacers create high velocity regions in the vicinity of the membrane. The trans-membrane heat and mass fluxes both show fluctuating patterns corresponding to the repetitive structure of the spaces and the fluxes are much higher than that of the modules using empty channels. The heat transfer coefficient enhancement factors obtained from CFD simulation are significantly higher than the predictions from literature correlations. The model can serve as an effective tool for developing correlations of heat transfer coefficients and optimal design of spacer-filled MD modules.[[sponsorship]]Masdar Institute of Science and Technology[[incitationindex]]EI[[conferencetype]]國際[[conferencedate]]20150328~20150331[[booktype]]電子版[[iscallforpapers]]Y[[conferencelocation]]Abu Dhabi, United Arab Emirate

A PROFESSIONAL COMPETENCE EVALUATION SYSTEM FOR COLLEGE STUDENT

[[conferencetype]]國際[[booktype]]電子版[[iscallforpapers]]Y[[conferencelocation]]青海省西寧市, 中

Simulation of membrane distillation modules for desalination by developing user's model on Aspen Plus platform

[[abstract]]This paper presents a simulation study of direct contact membrane distillation (DCMD) and air gap membrane distillation (AGMD) for desalination. Simulation models are built on Aspen Plus® platform as user defined unit operations for these two types of modules, respectively. Large scale modules for practical industrial applications are simulated and studied for the effects of design and operation variables, as well as the importance of heat and mass transfers of each phase. For each type of modules with heat recovery design, the response surface method (RSM) is applied to develop the performance-variables quadratic model, followed by the multivariable optimization. Optimal designs can realize separation efficiencies, defined as the ratio of water produced to the feed, of 8.2% and 5.8% for DCMD and AGMD, respectively.[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙

Modeling and optimization of a solar driven membrane distillation desalination system

[[abstract]]The desalination technology using membrane distillation driven by solar energy is a feasible solution for reducing the energy cost. A dynamic simulation model for a solar driven membrane distillation desalination system (SMDDS) is developed on the Aspen Custom Modeler® (ACM) platform for the system performance and optimization study. The rigorous model for the spiral-wound air gap membrane distillation (SP-AGMD) module takes into account the heat and mass transfer resistances associated with each composing layer. The effects of adopting different objective functions, solar radiation conditions, thermal storage tank configurations, as well as the flowrates of the membrane distillation module and the thermal storage tank on the optimized performance are reported. Simple thermal storage tank and lower flowrate of the membrane distillation module are advantageous to higher water production rate. A control system using conventional PI (Proportional/Integral) controllers is proposed and the water production rate can reach about 87% of the optimal result for clear sky operation.[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙

CFD simulation of direct contact membrane distillation modules with rough surface channels

[[abstract]]Membrane distillation (MD) can utilize low level thermal energy and holds high potential to replace conventional energetically intensive separation technologies. Direct contact membrane distillation (DCMD) is suitable for the applications of desalination and concentration of aqueous solutions. Employing spacer-filled channels can enhance the mass flux of the DCMD modules, which can further result in the increase of energy utilization efficiency of the separation. The trans-membrane mass flux is controlled by the boundary layer heat transfer of both fluid channels. The estimation of heat transfer coefficients is critical to the analysis and design of MD modules. This paper presents the results of a comprehensive 3-D computational fluid dynamics (CFD) simulation which covers the entire length of the module and takes into account the trans-membrane heat and mass transfer. The model was verified with experimental data in the literature. The contour maps show that spacers create high velocity regions in the vicinity of the membrane. The trans-membrane heat and mass fluxes both show fluctuating patterns corresponding to the repetitive structure of the spaces and the fluxes are much higher than that of the modules using empty channels. The heat transfer coefficient enhancement factors obtained from CFD simulation are significantly higher than the predictions from literature correlations. The model can serve as an effective tool for developing correlations of heat transfer coefficients and optimal design of spacer-filled MD modules.[[sponsorship]]Masdar Institute of Science and Technology[[incitationindex]]EI[[conferencetype]]國際[[conferencedate]]20150328~20150331[[booktype]]紙本[[iscallforpapers]]Y[[conferencelocation]]Abu Dhabi, United Arab Emirate

Experimental and simulation study of a solar thermal driven membrane distillation desalination process

[[abstract]]Being capable of directly utilizing solar thermal energy, the solar membrane distillation desalination system (SMDDS) has evolved as a promising green technology for alleviating the water resource problem. This paper reports the experimental and simulation study of a SMDDS which utilizes the air gap type membrane distillation. A laboratory system with automatic control function was established. A control scheme for fully automatic operation was designed using the PI (proportional–integral) control algorithm, which is robust and commonly employed by industries. The control structure adopted PI temperature control for the solar thermal and the membrane distillation subsystems. A dynamic mathematical model including the control algorithm for the overall system was developed, built on Aspen Custom Modeler® platform, and verified by the experimental results. The optimization analysis using the model reveals the operation strategy for maximum water production. Because of the unpredictable solar irradiation, the corresponding optimal dynamic operation cannot be pre-determined and implemented during system operation. However, the proposed PI control scheme could provide a fairly good level of performance, for example up to about 80% of the maximum water production for sunny day operation.[[notice]]補正完畢[[journaltype]]國外[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙本[[countrycodes]]NL

Simulation Study of an Integrated Methanol Micro Fuel Processor and Fuel Cell System

[[abstract]]The micro fabrication technology has facilitated the development of micro fuel processing systems to provide hydrogen for portable fuel cells. Methanol is a suitable liquid fuel for its high energy intensity and low operating temperature. In this study, a dynamic model for an integrated methanol micro fuel processing system and fuel cell is developed. The micro fuel processor employs plate-type micro devices. The steady state simulation analysis identifies the significant operating conditions for the micro FP/FC process, which are the feed flow rate and steam/carbon ratio of the steam reformer and the feed flow rate of the combustor. The dynamic simulation analysis compares the responds for the voltage change demand of PEMFC of three proposed control schemes, including the structures using double feedforward with double feedback control loops (CS1), double feedforward with single feedback control loops (CS2) and single feedforward with single feedback control loops (CS3). The CS2 plus a lag of 30 s is the best control structure.[[journaltype]]國外[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙本[[countrycodes]]GB

Computational Fluid Dynamics-Based Multiobjective Optimization for Catalyst Design

[[abstract]]For an industrial secondary methane steam reformer with regular packing, catalyst design is accomplished by an integrated optimization approach, which includes the design of experiment, computational fluid dynamics (CFD) simulation, a response surface method, and a genetic algorithm, for multiobjective optimization. Both spherical and cylindrical catalysts are studied. The reactor performance considered for the catalyst design includes the pressure drop and hydrogen production, which constitute the binary objective functions for optimization. The optimal solutions reveal that a large pore diameter, near 1 μm, should be adopted for spherical catalysts. For cylindrical catalysts, the optimal design suggests the use of a 1-big-hole shape with a larger particle and pore size, 10−13 mm and near 1 μm, or a 4-hole shape with a smaller particle size of 6−8 mm.[[booktype]]紙

CFD simulation of the two-phase flow for a falling film microreactor

100學年度研究獎補助論文[[abstract]]Falling film microreactors, which provide very high specific interfacial area, have become a promising solution to the fast and strongly exothermic/endothermic gas–liquid reaction systems. A computational fluid dynamic simulation of the two-phase flow for a falling film microreactor is presented using the volume of fluid (VOF) model. The hydrodynamic characteristics, from both 2-D and 3-D simulations, including liquid film thickness, velocity, pressure and shear stress profiles, are analyzed. 2-D simulation is adopted for the study of the relationship of liquid flow rate and film thickness, as well as the effects of gas flow rate, surface tension, liquid viscosity and pressure difference on the liquid flow rate. 3-D simulation is necessary to provide the comprehensive flow profiles. Although the system is in the laminar flow regime, the liquid film features a wavy structure and the velocity profiles are complex.[[incitationindex]]SCI[[booktype]]紙

Dynamic Optimization for Solar Desalination Systems Using Membrane Distillation

[[conferencetype]]國際[[conferencedate]]20140727~20140801[[booktype]]電子版[[iscallforpapers]]Y[[conferencelocation]]Tokyo, Japa