Effect of the injection pressure and orifice diameter on the spray characteristics of biodiesel

The purpose of this study was to analyze the influence of the injection pressure and orifice diameter on the spray characteristics of soybean biodiesel.The macroscopic spray characteristics of the spray tip penetration(STP)and spray cone angle(SCA)were tested with a high-speed camera system.The microscopic spray characteristics,such as the statistical size distribution,Sauter mean diameter(SMD),representative diameters and dispersion boundary,were obtained using a Malvern laser particle size analyzer(PSA).The test results showed that with an increasing injection pressure,the STP and the SCA of the biodiesel increased,but the curves of size-volume distribution and cumulative volume distribution of the atomized droplets shifted to smaller diameters.The SMD and representative diameters decreased,and the dispersion boundary was reduced.Moreover,with a decreasing orifice diameter,longer STP and smaller SCA values were observed.Similarly,the size distribution curves of the atomized biodiesel droplets shifted to smaller diameters.The SMD and representative diameters were reduced,and the relative size range of the atomized biodiesel droplets was enlarged.Higher injection pressures and smaller orifice diameters improved the biodiesel atomization;however,the smaller orifice diameters caused an inhomogeneous size distribution of the atomized biodiesel droplets.

A criterion for flow mechanisms through vertical sharp-edged orifice and model for the orifice discharge coefficient

According to the experimental data of the orifice discharge coefficient for the flow through a vertical sharp-edged orifice obtained in the previous study of this work,a theoretical criterion for flow mechanisms of small orifice（viz.thick-walled orifice and nozzle） and large orifice（viz.thin-walled orifice） was proposed based on the ratio of orifice diameter to plate thickness.It can help explain the dissipation of the mechanical energy loss in the flow process for the two flow mechanisms under different operating regimes.The main parameters such as orifice diameter,plate thickness and liquid head were correlated,and a semi-empirical model for orifice coefficient and an empirical model with high precision at the stable region were developed.

Improved Correlation for the Volume of Bubble Formed in Air-Water System

In order to address the bubble formation and movement in air-water two-phase flow,single bubble rising in stagnant water is experimentally studied by digital image processing.Bubbles are released individually from the submerged orifices with different diameters(1.81 mm,2.07 mm,2.98 mm,3.92 mm)at different detachment frequency.Images are recorded by a high-speed video camera and processed by digital image processing technique. The factors impacting the formed volume of bubble are discussed.The experimental results showed that a threshold of gas flow rate(400 mm 3 ·s- 1)divides the bubble formation into two regimes:the constant volume regime and the growing volume regime.Especially for the growing volume regime,the surface tension is taken into account.The bubble volume is consisted of two parts:the surface tension impacting part and the gas volume flow rate impacting part.An improved correlation for bubble volume prediction is developed for the two regimes and better coincidence with the experiment data than the previous models is obtained.

Modified Model of Bubble Formation in Non-Newtonian Fluids

Based on the comprehensive forces balance model, a modified model of the formation of a single bub-ble in non-Newtonian fluid under constant flowrate was developed by taking account of the effect of the ingoing gas through orifice as well as its variation on the radial expansion of bubble. The modified model involves the radial expansion equation of bubble surface and the forces balance equation in vertical direction of the bubble respec-tively. The shape variation of bubbles formed in polyacrylamide (PAM) aqueous solutions under various conditions was predicted numerically. The practical formation of bubbles was real-time visualized and recorded by a CCD camera and a computer by means of a special laser image measurement system. Results show that the predicted shapes of the bubbles by the present model agree well with experimental observation.