The whole field measurements of swirling flow in spin-up and spin-downprocesses via PIV are presented in the paper. Investigation of the flow patterns at H/R = 1. 50 wasexperimentally carried out for the first time in...The whole field measurements of swirling flow in spin-up and spin-downprocesses via PIV are presented in the paper. Investigation of the flow patterns at H/R = 1. 50 wasexperimentally carried out for the first time in both processes. By means of symmetry analysis, itis found that the overall flow structure in the spin-up process still keep axi-symmetric to a greatextent, but deteriorated very fast in the spin-down process. The time to settle to the state of restin the spin-down process is found to be greatly shorter than the time to achieve the steady statein the spin-up process. Temporarily oscillatory vortex breakdown was discovered during the spin-upprocess, although no breakdown in the steady state at the same Reynolds number is found in preciousresearches.展开更多
This paper presents a recent advance in the study of injection of fuel containing dissolved gas (IFCDG).Using diesel fuel containing dissolved CO2, experiments were performed under atmospheric conditions on a diesel h...This paper presents a recent advance in the study of injection of fuel containing dissolved gas (IFCDG).Using diesel fuel containing dissolved CO2, experiments were performed under atmospheric conditions on a diesel hole-type nozzle and simple nozzles. The effects of gas concentration in the fuel, injection pressure and the nozzle L/D ratio were examined. In order to reveal the controlling mechanism of IFCDG, the orifice flow pattern, pressure characteristics and their effects were also investigated. The result shows that IFCDG can produce a parabolic-shaped spray pattern with good atomization, which suggests the ekistence of a new atomisation mechanism. In terms of atomization, the beneficial effect of the IFCDG is obtained at the dissolved gas concentration above the transition and in the region of larger nozzle L/D ratio. However, under unfavorable conditions, IFCDG will lead to deterioration of atomization with coarse fuel droplets. It is found that the big difference of the oracle pressure characteristics caused by the variation of the nozzle L/D ratio has a dominant influence on the separation of the dissolved gas from the fuel inside the orifice and is verified to account for a dramatic change in the spray pattern and determine the effect of IFCDG. It is considered that the concept of IFCDG could be attractive in producing more efficient, clean engine and find use in a wide range of application.展开更多
The thermal performance of a rectangular loop with a horizontal heating segment and a partly cooling vertical leg is studied. By one-dimensional approach, traditional friction factor and empirical correlation, a modif...The thermal performance of a rectangular loop with a horizontal heating segment and a partly cooling vertical leg is studied. By one-dimensional approach, traditional friction factor and empirical correlation, a modified Grashof number Gr* which turns out to be very important in the description of circulation flow is introduced. A new correlation for Nusselt number of the horizontal heater is obtained and the comparison with experimental raines shows good agreement.展开更多
文摘The whole field measurements of swirling flow in spin-up and spin-downprocesses via PIV are presented in the paper. Investigation of the flow patterns at H/R = 1. 50 wasexperimentally carried out for the first time in both processes. By means of symmetry analysis, itis found that the overall flow structure in the spin-up process still keep axi-symmetric to a greatextent, but deteriorated very fast in the spin-down process. The time to settle to the state of restin the spin-down process is found to be greatly shorter than the time to achieve the steady statein the spin-up process. Temporarily oscillatory vortex breakdown was discovered during the spin-upprocess, although no breakdown in the steady state at the same Reynolds number is found in preciousresearches.
文摘This paper presents a recent advance in the study of injection of fuel containing dissolved gas (IFCDG).Using diesel fuel containing dissolved CO2, experiments were performed under atmospheric conditions on a diesel hole-type nozzle and simple nozzles. The effects of gas concentration in the fuel, injection pressure and the nozzle L/D ratio were examined. In order to reveal the controlling mechanism of IFCDG, the orifice flow pattern, pressure characteristics and their effects were also investigated. The result shows that IFCDG can produce a parabolic-shaped spray pattern with good atomization, which suggests the ekistence of a new atomisation mechanism. In terms of atomization, the beneficial effect of the IFCDG is obtained at the dissolved gas concentration above the transition and in the region of larger nozzle L/D ratio. However, under unfavorable conditions, IFCDG will lead to deterioration of atomization with coarse fuel droplets. It is found that the big difference of the oracle pressure characteristics caused by the variation of the nozzle L/D ratio has a dominant influence on the separation of the dissolved gas from the fuel inside the orifice and is verified to account for a dramatic change in the spray pattern and determine the effect of IFCDG. It is considered that the concept of IFCDG could be attractive in producing more efficient, clean engine and find use in a wide range of application.
文摘The thermal performance of a rectangular loop with a horizontal heating segment and a partly cooling vertical leg is studied. By one-dimensional approach, traditional friction factor and empirical correlation, a modified Grashof number Gr* which turns out to be very important in the description of circulation flow is introduced. A new correlation for Nusselt number of the horizontal heater is obtained and the comparison with experimental raines shows good agreement.
