We represent a two-dimensional model of polydisperse granular mixtures with a power-law size distribution. The model consists of smooth hard disks in a rectangular box with inelastic collisions,driven by a homogeneous...We represent a two-dimensional model of polydisperse granular mixtures with a power-law size distribution. The model consists of smooth hard disks in a rectangular box with inelastic collisions,driven by a homogeneous heat bath at zero gravity.The width of particle size distribution is characterized by the only parameter,namely,the fractal dimension D.The energy dissipation of the mixture is increased as D increases or as e decreases.Furthermore,it is found that the steady-state properties of the mixture such as the collision rate,granular temperature,kinetic pressure and velocity distribution depend sensitively on size distribution parameter D.展开更多
Combustion characteristics of nanofluid fuels containing aluminum nanoparticles were investigated in half-opening slot tubes from the fundamental view. The effects of particle loading rates(0.25% and 2.5% by weight), ...Combustion characteristics of nanofluid fuels containing aluminum nanoparticles were investigated in half-opening slot tubes from the fundamental view. The effects of particle loading rates(0.25% and 2.5% by weight), type of base fuels(ethanol and butanol),and fuel flow rates(0.2, 0.6, and 1 mL/min) were studied in details. The combustion characteristics of the nanofluid fuels and pure based fuels were also examined to provide a comparison. Flame was unstable with reignition, stable state, nearly extinguishment repeatedly at low flow rate. At medium flow rate, flame height was increased and flame tended to be stable. At high flow rate,flame became unstable and was disturbed by the droplet forming and dripping significantly. Al atoms inside the oxide layer should be melted before the particles combustion, while Al oxide layer should be melted before the particles aggregates combustion. The effects of particles on the combustion characteristics, especially on the evaporation rate of base fuel, were discussed. The reasons for various combustion phenomena of nanofluid fuels were given, which can provide the useful guidance for the experimental research and practical applications of nanofluid fuels.展开更多
We present an experimental study on the motion of a spherical droplet in a plane traveling sound wave.The experiments were performed in the test section of a tunnel with two loudspeakers at the two ends of the tunnel....We present an experimental study on the motion of a spherical droplet in a plane traveling sound wave.The experiments were performed in the test section of a tunnel with two loudspeakers at the two ends of the tunnel.By adjusting the amplitude ratio and the phase difference between the two speakers,a plane traveling sound wave field can be achieved in the test section of the tunnel,which we checked by measuring the amplitudes and phases of the sound pressure along the tunnel and by simultaneously measuring the velocity field of the air flow at three different locations in the tunnel.When a liquid droplet was introduced in the test section,the motion of the droplet and the velocity of the air flow around the droplet were recorded by high speed cameras,from which we analyze and obtain the ratio of the velocity amplitudes and the phase difference between the particle motion and the fluid motion.The experimental data confirm the theoretical result from the wave equations in the long-wavelength regime,i.e.,when the particle size is much smaller than the wavelength.Moreover,we showed that in this regime,the theory on particle motion in an unsteady uniform fluid,when the history term is included,also yields the same results that are in agreement with the experimental data and the wave equation.Our result extends the parameter range over which the theory on particle motion in unsteady fluid is checked against experiments,especially to the range of particle-fluid density ratio that is of important practical applications.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos.10675048 and 1068006
文摘We represent a two-dimensional model of polydisperse granular mixtures with a power-law size distribution. The model consists of smooth hard disks in a rectangular box with inelastic collisions,driven by a homogeneous heat bath at zero gravity.The width of particle size distribution is characterized by the only parameter,namely,the fractal dimension D.The energy dissipation of the mixture is increased as D increases or as e decreases.Furthermore,it is found that the steady-state properties of the mixture such as the collision rate,granular temperature,kinetic pressure and velocity distribution depend sensitively on size distribution parameter D.
基金supported by the National Natural Science Foundation of China(Grant No.51576100)the Jiangsu Provincial Natural Science Foundation of China(Grant No.BK20140034)the Jiangsu Provincial Project of“Six Talent Summit”(Grant No.2014-XNY-002)
文摘Combustion characteristics of nanofluid fuels containing aluminum nanoparticles were investigated in half-opening slot tubes from the fundamental view. The effects of particle loading rates(0.25% and 2.5% by weight), type of base fuels(ethanol and butanol),and fuel flow rates(0.2, 0.6, and 1 mL/min) were studied in details. The combustion characteristics of the nanofluid fuels and pure based fuels were also examined to provide a comparison. Flame was unstable with reignition, stable state, nearly extinguishment repeatedly at low flow rate. At medium flow rate, flame height was increased and flame tended to be stable. At high flow rate,flame became unstable and was disturbed by the droplet forming and dripping significantly. Al atoms inside the oxide layer should be melted before the particles combustion, while Al oxide layer should be melted before the particles aggregates combustion. The effects of particles on the combustion characteristics, especially on the evaporation rate of base fuel, were discussed. The reasons for various combustion phenomena of nanofluid fuels were given, which can provide the useful guidance for the experimental research and practical applications of nanofluid fuels.
基金This work was supported partially by the National Natural Science Foundation of China(Grant No.11988102)and by Tsinghua University.
文摘We present an experimental study on the motion of a spherical droplet in a plane traveling sound wave.The experiments were performed in the test section of a tunnel with two loudspeakers at the two ends of the tunnel.By adjusting the amplitude ratio and the phase difference between the two speakers,a plane traveling sound wave field can be achieved in the test section of the tunnel,which we checked by measuring the amplitudes and phases of the sound pressure along the tunnel and by simultaneously measuring the velocity field of the air flow at three different locations in the tunnel.When a liquid droplet was introduced in the test section,the motion of the droplet and the velocity of the air flow around the droplet were recorded by high speed cameras,from which we analyze and obtain the ratio of the velocity amplitudes and the phase difference between the particle motion and the fluid motion.The experimental data confirm the theoretical result from the wave equations in the long-wavelength regime,i.e.,when the particle size is much smaller than the wavelength.Moreover,we showed that in this regime,the theory on particle motion in an unsteady uniform fluid,when the history term is included,also yields the same results that are in agreement with the experimental data and the wave equation.Our result extends the parameter range over which the theory on particle motion in unsteady fluid is checked against experiments,especially to the range of particle-fluid density ratio that is of important practical applications.
