# Electrohydrodynamic Propeller as One of the Alternatives to Replace Conventional Propulsion Systems
## 3 EHD Propulsion System Prototype Design
For the purpose of operating the device, it was necessary to ensure a constant supply of ambient air entering the space between the individual stages of electrodes. Therefore, the furrow was comprised of a DN 125 Novodur pipe, which was cut in half. The furrow ends were equipped with stoppers to prevent undesired movements of the electrodes. The Novodur pipe was placed freely on a steel stand in order to increase stability during the measurement process. The electrohydrodynamic (EHD) propeller was specifically designed for the use of electrostatic forces in order to create a flow of a working medium-the air. The first task in the designing process was to design a cross-sectional area of the flow for the electrode pairs. A circular shape was chosen for all the electrode pairs, as the circular \begin{table}
\begin{tabular}{c c c}
**Absolute Pressure \(p\)** & **Relative Humidity RH** & **Temperature t\({}_{\text{zz}}\)** \\
98,950 pa & 0.584 (1) & 24.6 \({}^{\circ}\)C \\ \end{tabular}
\end{table} 
Table 1: Physical parameters of the air. Figure 3: Measurement set with the EHD propeller. shape of the cross-sectional area of the flow minimises the aerodynamic resistance and ensures a smooth air flow; moreover, it minimises a turbulent flow. A circular profile is naturally aerodynamic and hence reduces the air flow turbulences and losses. Considering the output velocity of the accelerated medium, which is measured using a propeller anemometer, a conical shape (with symmetrical rotation) is an advantage. Emitter electrodes typically have sharp edges or tips or thin wires, which facilitate achieving the highest possible intensity of the electric field near their surface. It may be constructed of conductors with small diameters, wires or sharp metal objects. In order to maximise the effective length, a thin copper wire was used. Collector electrodes of a cathode are located farther from the high-voltage electrode and are typically of round or flat shapes, designed with an aperture or a grid. The key principle is to achieve the lowest possible aerodynamic resistance. Electrodes of both types may be constructed of various metals or any other electrically conductive materials since a voltage drop caused by their resistance is negligible due to its magnitude. Due to the presence of high voltage, the entire system should be carefully designed with the aim of avoiding undesired spark discharges or corona losses outside the area in question. The individual EHD propeller prototypes were designed while respecting the aforesaid axioms. In the research conducted so far, two different structural arrangements of emitters and various structural arrangements of collectors were tested and compared with the aim of validating the achieved velocity of the accelerated medium in terrestrial conditions. The Type 1 coronating electrodes (Figure 4) consisted of a ring made of PETG, which had a ridge that served for the placement of a copper coiled wire. The depth of the ridge cavities was 5 mm; the effective length of the coronating electrodes was 2700 mm; the spacing between the ridge channels was 4 mm; and the internal diameter of the electrode frame was 108 mm, i.e., the cross-sectional area of the flow was 0.00916 m\({}^{2}\). The outer diameter was identical to the inner diameter of the PVC pipe. This facilitated avoiding the necessity of using guide bars. The frame of the Type 1 collector (Figure 5) had inner and outer diameters identical to those of the frames of the emitters. The conductors were comprised of identical grounding straps with a thickness of 0.5 mm and a width of 15 mm. They were conductively connected using a semi-arch strap placed in the back part of the collector. Due to the presence of sharp cutting edges, the front side was covered with a 3 mm thick PTFE ring, attached using a captone adhesive tape in order to facilitate the dismounting. Specifically, the individual strip electrodes with a total effective length of 2360 mm can be removed if needed. Figure 4: Type 1 emitter. Figure 5: Type 1 collector.