What are the applications for spray form?

Different spray methods have their own characteristics. People use their characteristics to apply them to different combustion and non-combustion equipment to exert their functions.

⑴Solid nozzle spray

Solid spray means that fuel or other working fluids are evenly distributed on the cross-section of the spray cone. This type of nozzle can be divided into two types: one is a simple direct injection nozzle, whose injection cone angle is very small (less than 15), and even approximates a straight line injection. It has a long range and a powerful impact. It is also widely used in combustion equipment. It is also used in non-combustion equipment, such as cleaning equipment, spraying, cooling, lubrication, fire prevention and other industries.

The other is to install swirl blades in the nozzle housing, and the spray cone angle can be 50° to 120°. , the impact is small. It is widely used in non-combustion equipment and can also be used for cleaning, cooling, fire prevention, humidification, dust prevention, etc. Generally, the particle size of solid spray is relatively coarse. In order to reduce the particle size, air or steam can be used to assist atomization.

⑵Hollow nozzle spray

Among the various spray methods listed above, it is the one with strict requirements on spray quality (especially used in aviation and ground gas turbine combustion chambers). In addition to being widely used in industrial furnaces, boilers, internal combustion engines, gas turbines and other combustion equipment, this type of nozzle is also widely used in non-combustion equipment. Because it can obtain a small average particle size, under the same spray pressure, spray flow rate and angle, the surface area of ​​the workpiece can be increased and processed more delicately, which has a greater impact on the movement of materials. For this reason, hollow spray nozzles can produce good results in gas cooling, air humidification, metal processing, dust control, gas cleaning and chemical reactions. They are widely used in equipment in many industries such as powder preparation and spraying. Hollow spray nozzles can also use air or steam to assist atomization.

3) Fan nozzle spray

Fan-shaped spray can be produced by spraying the working fluid through multiple small holes or multi-tube rakes in the nozzle clamp; it can also be sprayed out by the working fluid through a round hole and impact the exit curved surface or through a long round hole cross-section nozzle, and then formed through the V-shaped slit outside the nozzle. Its impact is second only to the direct nozzle with a small spray angle. It can use one or more rows of drainage (cleaning fluid) curtains arranged at a certain distance to clean large quantities of crushed gravel, workpieces and fruits and vegetables arranged at a certain distance in a streamlined manner. It can also use the jet of cold (hot) air flow to cool, dry, and wash parts.

(3)Nozzle layout

It can be seen from the above various spray modes: the spray cone angle (or fan angle) starts from the nozzle end face, and as the axial distance increases, the spray dispersion cross section (or lateral size) becomes larger. For gas turbine annular combustion chambers, there are multiple (up to more than 30) distributed on the circumference; a large number of nozzles are also arranged for cleaning, lubrication, external coating and other devices on non-combustion equipment. All require a relatively uniform flow distribution (or spray volume flux) to meet the functional requirements of the equipment. To this end, inappropriate liquid mist overlap must be prevented and the layout of the nozzles must be arranged.

Strictly speaking, it is confirmed that under basically equal conditions such as the flow rate of the nozzle, spray cone angle, spray quality, and spray volume flux (that is, the liquid volume passing through the unit detection area of ​​the sampling body per unit time) (of course, these data must be obtained through pre-detection), the nozzle spacing is arranged according to the annular or strip plane to confirm the equal flow distribution.

In actual engineering applications, it is difficult to implement according to the above requirements, and some are corrected and improved through practical effect testing. For example, the nozzle arrangement (or consistency) on the combustion chamber of early aircraft engines was determined after extensive testing. Whether the nozzle spacing is appropriate or not will be reflected in the following performance:

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1) Changes in the outlet temperature field, generally the nozzle spacing is too large. The outlet temperature distribution coefficient (or outlet hot spot distribution coefficient OTDF) is too large (especially under high power conditions);

2) Combustion performance deteriorates under low operating conditions. Generally, the spacing between nozzles is too small, that is, there are too many nozzles. Under the same nozzle size and total fuel supply, each nozzle supplies less fuel, which will inevitably reduce the fuel supply pressure difference, worsen the fuel atomization quality, reduce combustion efficiency, and make ignition difficult. Poor combustion stability. These performance parameters and performance can be determined through selectivity tests of the combustion chamber scheme, and then a compromise can be made to select the number of nozzles.

1) Different types of combustion chambers have different consistencies for the same type of nozzles, such as single-tube or combined-pipe types using pressure atomization nozzles.

For combustion chambers, the general consistency value is about 1.1, which is enough to leave enough space for the installation size of the flame tube and the uniform air intake requirements in the circumferential direction of the flame tube; for an annular combustion chamber, the spray cone is compressed by the air intake from the flame tube head and the outer wall of the main combustion area, and its longitudinal section must be elliptical. In order to prevent the oil cone from overlapping, the nozzle consistency value is 1.3-1.5.

2) On the annular combustion chamber, the consistency of different types of nozzles and their installation methods are also different:

a. The branch pipe consistency of the T-shaped evaporation tube oil supply method is less than 1, and the R-shaped one is less than 0.5. This is because the oil-gas mixture jet ejected from the branch pipe cannot produce a large spray cone and immediately enter the corresponding return flow area of ​​​​the head.

b. The tangentially installed pressure atomizing nozzle has a larger consistency, generally lx/hf>1.5, such as GTCP36-300, WTQ-l, etc. If circumferential classification is adopted, in order to confirm the performance under high operating conditions, the consistency will be about 1.5.

c. The spray cone angle of the oil return nozzle becomes larger under low operating conditions, and its consistency can be larger, with its spray angle reaching 90°±5°. ． So the consistency reaches about 2.

d. The situation of the fan-type nozzle has been discussed before, and its consistency value also reaches about 2.

E. The air atomizing nozzle (including combined air atomizing device) is an independent oil and gas supply device, which is less affected by the air intake at the head of the flame tube. Especially the combined type, the atomizing air volume accounts for a large proportion of the total air, so the consistency value is relatively small. For example, the consistency of CT7 is about 1.2.

The nozzle consistency value principles summarized above are mainly based on the data of large and ultra-small engine combustion chambers. These principles are also basically applicable to large engines. The arrangement of nozzle groups in cleaning, spraying, lubrication, cooling and other equipment of non-combustion equipment also requires the flow of the nozzles used.

The basic properties such as volume, spray cone angle, and flow distribution are similar, and then the nozzle layout is initially determined based on the height from the nozzle end to the working platform, the spray pressure, and the properties of the working fluid. Generally, fan-shaped spray nozzles are often used. Its spray volume flux is distributed in a mountain shape (the outer flow is less), so there is a certain amount of spray overlap. The spray volume flow rate of a solid spray nozzle is similar to that of a fan spray, except that its distribution is more like a donut shape. The longitudinal section of the hollow spray is like a saddle shape (that is, there is less flow in the center). Regardless of the spray form, the amount of overlap in coverage is considered, and it is difficult to give specific data.