Influence Of Initial Diameter Research Articles

Droplets bouncing on rotating curved surfaces with elevated temperatures

In this work, droplets bouncing on curved surfaces with elevated temperatures are reported. The bouncing and depositing phenomena of different lubricant droplets are confirmed. The influence of initial diameter, tangential velocity, and surface roughness on the impact dynamics of silicone oil droplets on wetted curved surfaces is investigated, and the temperature dependence of the bouncing phenomenon is highlighted. Bouncing and depositing thresholds under various conditions are summarized. It is found that surface roughness has the most significant negative effect on the bounceable velocity range, followed by initial diameter and tangential velocity. A theoretical model and force analysis are established to explain the bouncing mechanism. The modified Bond numbers and Ohnesorge numbers are introduced to predict the bouncing thresholds. This work provides sufficient experimental and theoretical insights into manipulating droplets bouncing on wetted and curved surfaces with elevated temperatures.

The Effects of Initial Diameter on Sooting and Burning Behavior of Isolated Droplets under Microgravity Conditions

The influence of initial droplet diameter on the sooting and burning behavior of isolated droplets under microgravity conditions was investigated by measuring soot volume fraction, ƒv, soot mass, m s, soot and burning rate. Theƒ v, and m s, soot were measured using a full-field light extinction and tomographic inversion technique. The experiments were conducted at the NASA-Lewis 2·2 second droptower in Cleveland, OH. The ƒ v, and m s, soot measurements represent the first quantitative assessment of the influence of initial diameter on the sooting behavior in microgravity conditions. Results indicate that ƒ v(which provides information regarding the local magnitude of sooting) and m s, soot (which is related to overall sooting magnitude) are sensitive to the initial droplet size. It is believed that the spatial extent of the flame which is proportional to the droplet size, influences the residence time for fuel vapor transport. Thus, larger droplets will provide longer residence time for fuel pyrolysis, soot precursor formation and carbonization. The increase in the sooting behavior and enhanced radiation heat losses for larger droplets indicate that the initial diameter can influence the droplet burning behavior.

Interaction Between Weed Control and Loblolly Pine,Pinus taeda, Seedling Quality

Third-year heights, third-year root-collar diameters, and 3 yr volume growth of loblolly pine seedlings were examined in relation to a) root-collar diameter class at time of planting and b) herbaceous weed control. Treatments were a) no weed control and b) complete control for 2 yr. For both weed control treatments, means for third-year heights, groundline diameters, and volume growth were related positively to initial seedling diameter. The influence of initial seedling diameter on third-year diameters and heights did not differ among weed control treatments. However, the influence of initial diameter on volume growth did differ among weed control treatments. Thus, when using herbaceous weed control, additional gains in early volume growth can be realized by planting seedlings with large root-collar diameters.

The influence of initial diameter on the combustion of single drops of liquid fuel

Previous studies of the combustion of single drops have been confined almost entirely to large drops (greater than 1 000μ) and application of the results to practical systems is hindered because the mean drop size in practical sprays is less than one tenth of this value. The influence of initial diameter on the combustion of single drops in the size range 150 to 2 000μ has therefore been measured. The drops were suspended on fine silica fibres in a controlled atmosphere, ignited by a spark discharge and photographed using a modified drum camera. The effect of initial diameter on the combustion characteristics was as follows: (i) At a given diameter during burning, the rate of combustion was lower for drops which were initially small. The results indicate that the burning rate of drops in sprays will be about 25 per cent less than the values predicted from studies of large single drops; (ii) The ratio of flame ‘radius’ to drop radius at a given drop diameter increased with a reduction in initial drop diameter. These effects were explained quantitatively by postulating that the larger drops burnt in an upward stream of gas induced by natural convection, the velocity of which was independent of drop size during burning, but was a function of initial drop diameter. The influence of the oxygen content of the ambient gas on burning rate was significantly greater for large drops than for small ones. Initial diameter did not appear to affect the influence of fuel type on burning rate.