In this study,magneto-hydrodynamics (MHD) mixed convection effects of Al2O3-water nanofluid flow over a backward-facing step were investigated numerically for various electrical conductivity models of nanofluids.A uni...In this study,magneto-hydrodynamics (MHD) mixed convection effects of Al2O3-water nanofluid flow over a backward-facing step were investigated numerically for various electrical conductivity models of nanofluids.A uniform external magnetic field was applied to the flow and strength of magnetic field was varied with different values of dimensionless parameter Hartmann number (Ha=0,10,20,30,40).Three different electrical conductivity models were used to see the effects of MHD nanofluid flow.Besides,five different inclination angles between 0°-90° is used for the external magnetic field.The problem geometry is a backward-facing step which is used in many engineering applications where flow separation and reattachment phenomenon occurs.Mixed type convective heat transfer of backward-facing step was examined with various values of Richardson number (Ri=0.01,0.1,1,10) and four different nanoparticle volume fractions (Ф=0.01,0.015,0.020,0.025) considering different electrical conductivity models.Finite element method via commercial code COMSOL was used for computations.Results indicate that the addition of nanoparticles enhanced heat transfer significantly.Also increasing magnetic field strength and inclination angle increased heat transfer rate.Effects of different electrical conductivity models were also investigated and it was observed that they have significant effects on the fluid flow and heat transfer characteristics in the presence of magnetic field.展开更多
A new dimmer using a mental-oxide-semiconductor field-effect transistor (MOSFET) for alternating-current (AC) directly driven light-emitting-diode (LED) lamp was presented. The control method of proposed dimmer is pul...A new dimmer using a mental-oxide-semiconductor field-effect transistor (MOSFET) for alternating-current (AC) directly driven light-emitting-diode (LED) lamp was presented. The control method of proposed dimmer is pulse width control (PWM) method. Compared with the conventional phase-controlled dimmer, the proposed PWM dimmer can produce sine wave and did not cause harmonics problem. Furthermore, the proposed control method did not amplify the light flicker due to the independence of input voltage. Therefore, the PWM dimmer can be used as the dimmer of the AC LED lamp instead of the conventional phase-controlled dimmer. The experimental result shows that the proposed PWM dimmer has good performances.展开更多
Magnetorheological(MR) cell with multi-coil was designed to enlarge the range of controllable transmission torque by increasing the effective length. Individual input current was proposed to maximize its potential for...Magnetorheological(MR) cell with multi-coil was designed to enlarge the range of controllable transmission torque by increasing the effective length. Individual input current was proposed to maximize its potential for reducing power consumption and generating large yield stress. Finite element analysis was performed to analyze magnetic field distribution, based on which a prototype MR cell was fabricated and tested to investigate the performance of various combinations of individual input currents. A good correlation was identified between experimental results and FEA predications. The results show that the power consumption can be reduced to 42.4%, maintaining large transmission torque, by distributing the total current(2 A) to three individual magnetic coils. In addition, optimal results of four input currents considering a multi-objective function are obtained by changing the weighting factor λ. The advantage of this design, such as lower power consumption and more control flexibility, makes it more competitive in engineering applications that require large energy consumption.展开更多
Organic Rankine cycle(ORC) power plant operating with supercritical parameters supplied by low temperature slag-washing water(SWW) of blast furnace was investigated.A schematic of such installation was presented with ...Organic Rankine cycle(ORC) power plant operating with supercritical parameters supplied by low temperature slag-washing water(SWW) of blast furnace was investigated.A schematic of such installation was presented with a description of its operation and the algorithm of calculations of a supercritical power plant.Two typical organic fluids with sufficiently low critical parameters were selected as candidate working fluids in the plant to study the efficiency of the system with different organic fluids.An analysis of the influence on the effectiveness of operation of a plant was carried out.With the same temperature of slag-washing water,the specific work in turbine of fluid R143a is 45% higher than that obtained for the fluid R125,however,the specific work in pump of fluid R143a is approximate equal into that one of the fluid R125.展开更多
For efficient utilization of a limited geothermal resource in practical projects,the cycle parameters were comprehensively analyzed by combining with the heat transfer performance of the plate heat exchanger,with a va...For efficient utilization of a limited geothermal resource in practical projects,the cycle parameters were comprehensively analyzed by combining with the heat transfer performance of the plate heat exchanger,with a variation of flowrate of R245 fa.The influence of working fluid flowrate on a 500 W ORC system was investigated.Adjusting the working fluid flowrate to an optimal value results in the most efficient heat transfer and hence the optimal heat transfer parameters of the plate heat exchanger can be determined.Therefore,for the ORC systems,optimal working fluid flowrate should be controlled.Using different temperature hot water as the heat source,it is found that the optimal flowrate increases by 6-10 L/h with 5 ℃ increment of hot water inlet temperature.During experiment,lower degree of superheat of the working fluid at the outlet the plate heat exchanger may lead to unstable power generation.It is considered that the plate heat exchanger has a compact construction which makes its bulk so small that liquid mixture causes the unstable power generation.To avoid this phenomenon,the flow area of plate heat exchanger should be larger than the designed one.Alternatively,installing a small shell and tube heat exchanger between the outlet of plate heat exchanger and the inlet of expander can be another solution.展开更多
文摘In this study,magneto-hydrodynamics (MHD) mixed convection effects of Al2O3-water nanofluid flow over a backward-facing step were investigated numerically for various electrical conductivity models of nanofluids.A uniform external magnetic field was applied to the flow and strength of magnetic field was varied with different values of dimensionless parameter Hartmann number (Ha=0,10,20,30,40).Three different electrical conductivity models were used to see the effects of MHD nanofluid flow.Besides,five different inclination angles between 0°-90° is used for the external magnetic field.The problem geometry is a backward-facing step which is used in many engineering applications where flow separation and reattachment phenomenon occurs.Mixed type convective heat transfer of backward-facing step was examined with various values of Richardson number (Ri=0.01,0.1,1,10) and four different nanoparticle volume fractions (Ф=0.01,0.015,0.020,0.025) considering different electrical conductivity models.Finite element method via commercial code COMSOL was used for computations.Results indicate that the addition of nanoparticles enhanced heat transfer significantly.Also increasing magnetic field strength and inclination angle increased heat transfer rate.Effects of different electrical conductivity models were also investigated and it was observed that they have significant effects on the fluid flow and heat transfer characteristics in the presence of magnetic field.
文摘A new dimmer using a mental-oxide-semiconductor field-effect transistor (MOSFET) for alternating-current (AC) directly driven light-emitting-diode (LED) lamp was presented. The control method of proposed dimmer is pulse width control (PWM) method. Compared with the conventional phase-controlled dimmer, the proposed PWM dimmer can produce sine wave and did not cause harmonics problem. Furthermore, the proposed control method did not amplify the light flicker due to the independence of input voltage. Therefore, the PWM dimmer can be used as the dimmer of the AC LED lamp instead of the conventional phase-controlled dimmer. The experimental result shows that the proposed PWM dimmer has good performances.
基金Projects(51175265,51305207)supported by the National Natural Science Foundation of China
文摘Magnetorheological(MR) cell with multi-coil was designed to enlarge the range of controllable transmission torque by increasing the effective length. Individual input current was proposed to maximize its potential for reducing power consumption and generating large yield stress. Finite element analysis was performed to analyze magnetic field distribution, based on which a prototype MR cell was fabricated and tested to investigate the performance of various combinations of individual input currents. A good correlation was identified between experimental results and FEA predications. The results show that the power consumption can be reduced to 42.4%, maintaining large transmission torque, by distributing the total current(2 A) to three individual magnetic coils. In addition, optimal results of four input currents considering a multi-objective function are obtained by changing the weighting factor λ. The advantage of this design, such as lower power consumption and more control flexibility, makes it more competitive in engineering applications that require large energy consumption.
基金Project(2011FZ050) supported by the Applied Basic Research Program of Yunnan Provincial Science and Technology Department,ChinaProject(2011J084) supported by the Master Program of Yunnan Province Education Department,China
文摘Organic Rankine cycle(ORC) power plant operating with supercritical parameters supplied by low temperature slag-washing water(SWW) of blast furnace was investigated.A schematic of such installation was presented with a description of its operation and the algorithm of calculations of a supercritical power plant.Two typical organic fluids with sufficiently low critical parameters were selected as candidate working fluids in the plant to study the efficiency of the system with different organic fluids.An analysis of the influence on the effectiveness of operation of a plant was carried out.With the same temperature of slag-washing water,the specific work in turbine of fluid R143a is 45% higher than that obtained for the fluid R125,however,the specific work in pump of fluid R143a is approximate equal into that one of the fluid R125.
基金Project (2012AA053001) supported by High-tech Research and Development Program of China
文摘For efficient utilization of a limited geothermal resource in practical projects,the cycle parameters were comprehensively analyzed by combining with the heat transfer performance of the plate heat exchanger,with a variation of flowrate of R245 fa.The influence of working fluid flowrate on a 500 W ORC system was investigated.Adjusting the working fluid flowrate to an optimal value results in the most efficient heat transfer and hence the optimal heat transfer parameters of the plate heat exchanger can be determined.Therefore,for the ORC systems,optimal working fluid flowrate should be controlled.Using different temperature hot water as the heat source,it is found that the optimal flowrate increases by 6-10 L/h with 5 ℃ increment of hot water inlet temperature.During experiment,lower degree of superheat of the working fluid at the outlet the plate heat exchanger may lead to unstable power generation.It is considered that the plate heat exchanger has a compact construction which makes its bulk so small that liquid mixture causes the unstable power generation.To avoid this phenomenon,the flow area of plate heat exchanger should be larger than the designed one.Alternatively,installing a small shell and tube heat exchanger between the outlet of plate heat exchanger and the inlet of expander can be another solution.
