Broadening the knowledge base: Nozzle performance data

Nozzle performance is evaluated by examining data such as pressure/flow rate, pressure/spray angle, flow distribution, spray impact distribution, droplet size, etc. But nozzle manufacturers have not always tested the performance of their products in every conceivable situation. Consequently, even manufacturers who possess the necessary measurement devices may not always have on hand the entire (and vast) spectrum of data that pertains their standard range of nozzles. The reason for this is that major manufacturers' printed product catalogs typically contain several tens of thousands of standard nozzles, so an enormous amount of time and money would be required to obtain complete data on every product. Furthermore, it is conceivable that obtaining data for each nozzle would increase the cost of the nozzle itself. Almost all nozzle manufacturers do posses measurement devices for their own research and development. A customer may be charged by a manufacturer for carrying out tests at the user's request.

Pressure/flow-rate characteristics data | Pressure/spray-angle characteristics data |
Flow distribution data | Spray impact distribution data | Droplet size data

Pressure/Flow-rate characteristics data In almost all cases, nozzle flow rate varies according to inlet pressure. In manufacturers' product catalogs, pressure values (typically contrasted with flow rate values) are listed for each model. A formula (provided in the manufacturer's product catalog) can be used to determine the flow rate value at pressures not shown in the catalog, or the manufacturer's advice can be sought. (For nozzles that spray liquids, the SGS will, on demand, generate a graph that represents the relationship between pressure and flow rate. This simplifies the task of obtaining pressure values that are not given in catalogs.) An example of an SGS generated Pressure/Flow-rate graph Click to view full-sized page

Pressure/spray-angle characteristics data In almost all cases, spray angle varies according to inlet pressure. In manufacturers' product catalogs, pressure values (typically contrasted with spray angle values) are listed for each model. To determine a spray angle value at a pressure not given in a catalog, the manufacturer's advice should be sought. An example of a Pressure/spray angle graph

Flow distribution data

Flow distribution refers to the density of flow of the scattered droplets at a given spray distance, measured along a cross-section of the spray pattern. Nozzle manufacturers have devised their own methods to measure flow distribution. One such method is to arrange containers on a level surface and to measure the water level in each after spraying for a certain period of time (as shown in this illustration).

Flow distribution is classified into three types, concave, convex, and trapezoid, with the type of flow distribution varying according to the type of nozzle. Moreover, flow distribution readings vary from manufacturer to manufacturer (even if the nozzles in question actually produce the same spray pattern). Normally, nozzle manufacturers standardize the flow distribution characteristics of their products according to nozzle type, but they may accept an order for a custom-made nozzle whose flow distribution is a tailored to satisfy a customer's requirements.

Spray impact distribution data

Spray impact distribution refers to the distribution of the force of the spray as it comes into contact with the target. Each nozzle manufacturer contrives their own measurement device for this data, but there are only a small number of manufacturers in the world who possess such measurement devices. Fundamentally, pressure is proportional to spray impact in a given nozzle. When different nozzles deliver the same flow rate, spray impact is proportional to the square root of pressure (i.e. the velocity of the flow). The theoretical formula being as follows:
As the relationship between spray impact and flow rate is proportional, spray impact distribution is similar in shape to flow distribution (for the same nozzle).Spray impact and distribution vary according to a type of nozzle and manufacturer. Like flow distribution, spray impact distribution is also generally classified into three types (concave, convex, and trapezoid).

Droplet size data

Droplet size refers to the mean diameter of liquid droplets or drop size distribution. This data is essential not only for manufacturers and scientists, but also for engineers working at enterprises concerned with the evaluation of experimental results relating to nozzles. (ILASS Japan)

(1) Measurement by laser beam
	This method to uses a laser beam to measure falling droplets while they are in the atmosphere. As the droplets are not touched, this method is extremely accurate. Several thousands of droplets can be measured in an instant, and various kinds of mean diameters and distribution data are obtainable.
(2) Measurement by CCD camera and stroboscope
	A high-performance strobe is directed at the stream of falling droplets and a CCD camera, positioned opposite the strobe on the other side of the spray, captures the scene. The droplets (which are not touched and which appear stationary as a result of the flashing strobe) are displayed on a monitor where mean diameter and distribution can be measured by means of image analysis.
(3) Photographic measurement by microscope
	Droplets are captured on a surface coated with silicone oil and photographed under a microscope. This is a relatively simple method of measurement. Mean diameters of droplets and their distribution is measured by ruler.