The Influence of Ultrasonic Frequency on Particle Size in Atomized Spraying

Ultrasonic nozzles are a type of atomizer that makes use of a piezoelectric transducer to generate high-frequency vibrations at the nozzle tip, creating capillary waves in the liquid film. When the amplitude of these waves reaches a imperative peak (determined with the aid of the usage of the power diploma furnished through the generator), they cease up too excessive to hold themselves, and each wave tip releases tiny droplets, for that cause carrying out atomization.

The most important elements influencing the preliminary measurement of atomized droplets are vibration frequency, surface tension, and liquid viscosity. Typically, the range of frequency from 25–180 kHz, which is past the vary of human hearing. Higher frequencies produce finer atomized particles.

According to documents, median droplet measurement is inversely proportional to frequency; as frequency increases, median droplet dimension decreases. However, the viscosity and density of the liquid additionally have an effect on droplet size. Generally speaking, greater viscosity effects in largedroplets, whilst greater density effects in smaller droplets. Furthermore, parameters such as nozzle design, spray angle, liquid go with the flow rate, and strain additionally have an impact on atomization quality.

Calculation Formula

Droplet measurement relies upon on frequency and chemical properties, in accordance to the governing mathematical equation: the place f is the frequency of the vibrating surface, σ is the floor anxiety of the liquid, and ρ is the density of the liquid. Lang later proved this equation experimentally and installed the following empirical equation.

Median Particle Size

What is the median particle size? The numerical median diameter defines the 50% factor in droplet size; that is, half of of the droplets in the spray have a diameter large than this value, and the different half of have a diameter smaller than this value.

Droplet distribution is obtained by dividing the droplet population into a set of size ranges (channels) and calculating the fraction of droplets that fall within each channel. The channel width is chosen to be 4 microns. For the 60 kHz nozzle distribution shown on the right, 2% of the droplets fall within the channel covering the 10-14 micron range, 4.5% fall within the 14-18 micron range, and so on.

Because the droplet diameters are plotted on a logarithmic scale, the channel widths appear narrower as the diameter increases. However, each channel is 4 microns wide. The peak represents the median droplet diameter of the distribution.

In ultrasonic atomization, droplet measurement is decided via the nozzle's vibration frequency, the liquid's surface tension, and its density. Frequency is the most indispensable factor; greater frequencies end result in smaller median droplet diameters.

Generally speaking, the droplet measurement distribution produced by using ultrasonic nozzles follows a ordinary distribution curve. The chart above suggests the cumulative droplet dimension distribution for water at one of a kind frequencies. Several parameters can be used to describe the imply and median of a precise droplet distribution. The range median diameter is the 50% droplet measurement point, that means that half of the droplets have a diameter large than this cost and half have a diameter smaller than this value.

Both the number-mean diameter and volume-mean diameter are common diameters. The number-mean diameter is calculated by way of summing the diameters of all droplets in a spray pattern and dividing it by using the variety of droplets. The volume-mean diameter is calculated by means of summing the volumes of all droplets in a spray pattern (volume is proportional to the cube of the diameter), taking the cube root of this sum, and then dividing via the range of droplets.