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Topic: Spray System and nozzle design for chemical spraying to clean household molds  

Background

As our project Wipeout integrates spray system and roller system in a handheld device with suction support for users to handle the wiping process of mold easily. Given that average size of household molds in Hong Kong, it would be around 100cm^2, the spray system and nozzle need to be designed for the chemical spraying in a pattern onto the wall. 
 
The design parameters of the spray design are shown below.

  • Able to pump up to 2m vertical height as this are mainly the height for Hong Kong Household

  • Able to cover sufficient area for spraying onto the wall molds.

  • Provides a stable spraying pattern of the chemicals.

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Chemical Selection

We chose tea tree oil, which major constituents to kill molds are terpinen-4-ol, γ-terpinene, 1,8-cineole, α-terpinene, α-terpineol, p-cymene, and α-pinene. This element provides strong antifungal activity against mold and works by disrupting the cell membrane, inhibiting growth, and interfering with biofilm formation. 

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Design Process

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In our first version of the prototype of Wipeout, the spray nozzle is facing towards the wall. After a testing on flat fan nozzle (as shown in the photo), we find that the diameter covered by the nozzle is around 10-15cm, it helps cover a big area for the wipe of molds.

However, the required distance for the nozzle head and the wall required 10cm, which is not feasible for our system as the device sticks on the wall and no tolerance for the distance between the suction and the wall. 

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Therefore, modifications are made, as shown in the photo, the pump is mounted onto the chassis, and the nozzle contains the flat fan nozzle and a long tube with several holes on it, which the back is sealed. We want to make the water comes out from the hole of the tube.

After the water goes through the flat fan nozzle and decreases the pressure of the water, the water goes through the tube, and it allows the water to spray out from the holes on the tube. On the handle, there is a switch to control the nozzle in spray/rest mode 

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Results

The nozzle successfully sprays out the chemical, while during the final demonstration we used water to mimic the chemicals due to safety concerns.

After the spraying, the cleaning effect of the walls is increased compare to the whole device without opening the spraying system. 

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However, for the sprayed chemicals, the amount of it is insufficient for cleaning molds with large surface area. Other than that, due to the faulty of the flat fan nozzle, the nozzle spills out some of the water out from the connections between the tubes and the nozzle itself. 

Further possible improvements can be made:

  1. The size of holes on the long tubes for the chemical spraying out can be increased for more chemicals to spray out.

  2. The placement of the whole system can be considered to put onto the sideways of the device(First spray then let the roller role, thus allowing the chemical to stay on the molds and make it easier to clean).

  3. Integrating the Roller and the spray systems by mounting the spray system in front of the roller can be considered

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