# Innovative Ultrasonic Spray Methods for Indoor Disinfection
## 2 Development of Ultrasonic and Combined Spraying Devices for Disinfectant Liquids
### Ultrasonic Liquid Layer Sprayers  
The ultrasonic atomizer consists of an ultrasonic oscillating system (ultrasonic nozzle) and an electronic generator for its power supply. The design of the oscillating system is shown in Figure 1.  
The design scheme of the ultrasonic atomizer developed by the authors is based on the half-wave Langevin transform. It consists of a concentrator (1), a spray surface (2), piezoceramic elements (3), and a reflective pad (4). The type of conversion of electrical energy into mechanical vibrations is piezoelectric. Inside, in the center of the Langevin converter, a through channel (5) is made for feeding the sprayed liquid to the spray surface (2). The atomizer is installed in a housing (6), in the rear flange (7) of which there are places for connecting the liquid supply systems (8) and for inputting an electric cable (9) (for exciting vibrations of the piezoelectric elements). When liquid is fed from the hole (5), it spreads on the surface (2) in a thin layer. Ultrasonic vibrations generate standing capillary waves on the liquid surface. Droplets detach from the crests of these waves and are ejected with an initial velocity perpendicular to the surface. Therefore, by changing the shape of the spray surface (for example, making it a cone with a different angle at the top), we can change the direction of droplet separation and, accordingly, the width of the spray torch, making it wider or narrower. The number of capillary waves per unit area of the spray surface is finite, depending on the frequency of ultrasonic vibrations [15]. At a given frequency (which determines the size of the droplets), the spray performance is dictated by the area of the spray surface. The larger the surface area, the higher the spray performance. Thus, the shape of the spray surface determines the geometric characteristics of the spray torch, and the area of the spray surface determines the spray performance. The shape and size of the spray surface may vary depending on the specific purpose of the sprayer. The liquid flowing from the opening onto the spray surface spreads out into a circular layer with a radius \(R_{0}\), as shown in Figure 2a. The value of this radius is determined by the viscosity and surface tension of the liquid and can be determined by the dependencies presented in the work [17]. If the radius of the spray surface exceeds the value of \(R_{0}\), then it becomes necessary to make additional channels on the spray surface to ensure increased spray performance. The location and number of additional channels for delivering liquids to the spray surface are determined from the condition of ensuring its uniform coverage with a layer of sprayed liquid. Figure 2 shows the optimal location of additional channels for supplying the sprayed liquid. Figure 1: Piezoelectric oscillatory system of ultrasonic atomizer. 1—radiating pad-concentrator; 2—spray surface; 3— piezoceramic elements; 4—reflective pad; 5—internal channel for supplying sprayed liquid; 6—housing; 7—housing flange; 8—threaded hole for supplying liquid; 9—ultrasonic sprayer power cable; 10—power cable connector. To ensure the complete coverage of the spray surface, additional holes must be positioned at intervals of \(2R_{0}\) along the cone generatrix (Figure 2b). In this case, the most rational is to place additional holes (in addition to the central hole made at the top of the cone) on the circles (Figure 2c). Figure 2d shows that the radius of these circles will increase by \(2\ R_{0}\sin\frac{7}{2}\) with each new circle located further from the center of the cone. The number of circles is calculated so that they are located at a distance of \(2R_{0}\) from each other and at a distance of \(R_{0}\) from the outer edge. With a known radius of the spray surface R, the length of the cone generatrix will be equal to \(N=\frac{R}{\sin\frac{7}{2}}\).