The Proceedings of the Eighth International Conference on Creationism (2018)

been powered electrically and the inlet and exhaust valve system which is passive in the beetle, is actively controlled electronically. The results have been immediately impressive with a fast expulsion of water and steam which can only be achieved with a vapour explosion. What has been particularly encouraging has been the ability to control the droplet sizes and the frequency of ejection. The beetle can eject with an astonishingly small interval of approximately 2 msecs (which corresponds to a frequency of 500Hz – hence the distinct note that the beetle makes upon ejection). These larger experimental prototype rigs (with a typical chamber size of 2 cms) have reached a frequency of approximately 100 - 200 Hz. This is of great interest to industry because it has been found that the droplet sizes can be controlled by different chamber characteristics such as temperature and pressure of the chamber as well as the diameter of the outlet tube. The work has led to interest from industry with a raft of practical applications including fuel injectors, fragrance spray devices, fire extinguishers and pharmaceutical sprays. Once the beetle valve system had been understood, the aim was to build first a theoretical model to indicate the level of importance of pressure to ejecting the mixture of steam and water (and in the case of the beetle the caustic chemicals as well). Then when this was understood the aim was then to build an experimental working model. 1. A computerized model Having deduced the process behind the beetle’s remarkable spray system, the next step was to deduce the role of pressure in producing the spray system both in the beetle and in the device which would eventually be built. To estimate the trigger pressure and other key characteristics, such as the temperature of the liquid and the diameter of the exit nozzle, a theoretical model of the combustion chamber was constructed using computational fluid dynamics (CFD). The model used a small cylindrical chamber measuring 0.6 mm in diameter and 0.3 mm in length, which is about the same size and volume (0.1 mm 3 ) as real beetle chambers. The cylinder was then joined to an exit nozzle 0.1 mm in length that could have any diameter in the range 0.1–0.5 mm. The CFD simulations began with the water in the main chamber under pressure, and then the separation between the chamber and the exit nozzle was removed as an initial condition – thus simulating the exhaust valve. The simulation was run at a range of trigger pressures (1.15, 1.1 and 1.05 × 10 5 Pa), each of which has an associated saturation temperature – i.e. after the valve is opened, the liquid in the chamber is assumed to be at the saturation temperature for that particular trigger pressure. For example, for 1.1 × 10 5 Pa, the saturation temperature is approximately 105°C. The chamber was also modeled in a second computer experiment without the restricted exit valve, where the fluid is allowed to boil as soon as it is hot enough, and the results compared to the results where the exhaust valve was used. The model assumes that the flow is laminar based on the observed velocities in the experiments of Eisner (Aneshansley and Eisner 1999), and based on the velocities generated numerically here. Consequently, the Reynolds number is low and at its maximum is of the order of 100. The important finding was that the flash-evaporation process is much more powerful than direct boiling without an exhaust valve. This is because the increased pressure exerted on the fluid significantly increases the ejection velocity. This reduces the time taken to squirt all the fluid out from over 10 ms without the pressure valve, to as little as 1 ms with it in place. The CFD model also managed to closely reproduce the velocities and timescales observed with real beetles for a trigger pressure of 1.1 × 10 5 Pa and a nozzle diameter of 0.2 mm. (Beheshti and McIntosh 2007b). 2. An experimental device A. Description of experimental facility The prospect of a spray technology where droplet size, temperature and velocity could be closely controlled, led to considerable interest from industry and the building of an experimental rig (a bio-inspired vapour explosion device) which mimics the important combustion chamber and valve system of the bombardier beetle. Based upon the computer simulation work conducted, an experimental demonstration facility (fig. 6) was built, which implemented the principles of the liquid atomization method of the bombardier beetle and incorporated a Malvern laser to measure droplet sizes. The catalytic chemistry of the beetle was not copied in these experiments, and instead, the heating is done electrically. In a similar way to the bombardier beetle and the CFD simulation work, the core of this system is the chamber and valves, but with the electrical heat source. Unlike the bombardier beetle and the simulation work, the inlet and exhaust valves of the physical system are not opened passively by a buildup of pressure in the chamber, but instead the these valves are controlled electronically, resulting in an actively controlled pulsed spray. There are also other valves in the system, which control the refill flow into the chamber between McIntosh and Lawrence ◀ Design of the bombardier beetle ▶ 2018 ICC 271 Figure 5. Explosion chamber of bombardier beetle. Hydrogen peroxide and hydroquinone react in the presence of the catalysts catalase and peroxidase, to yield benzoquinone and water. The overall reaction is exothermic and heats the aqueous solution which is ejected under pressure due to the valve system whereby the inlet valve closes under pressure and the exhaust valve opens at a prescribed pressure slightly above ambient.