Fluid dynamics and Usability Improvement of a Hygiene System

Sammanfattning

This thesis investigates how the disinfection system in a medical bathtub can be im- proved with both performance and usability in mind. The current system has oppor- tunities for improvement regarding disinfectant concentration stability, sensitivity to inlet pressure variations, and the adjustment process for caregivers. Addressing these areas reduces the risk of incorrect dosing, unnecessary waste of water and disinfec- tant, and helps ensure consistent disinfection between patients. The project followed an iterative product development process based on the Double Diamond design process, including concept generation, prototyping, and iterative testing. Several alternative concepts for mixing disinfectant and water were explored, including Venturi injectors, hydro pumps, air-driven systems, and electric pumps. A physical test rig was built to replicate the existing system and enable controlled testing under varying pressures and configurations. Initial tests confirmed that the existing Venturi solution is sensitive to pressure changes, resulting in variations in concentration. Through iterative testing and design modifications, improved injector geometries were developed, showing stable perfor- mance across a wide operating range. In parallel, user-centered design methods were applied to improve ergonomics and interaction. The final concept shows promise in providing a stable disinfectant mixture and aims to reduce the need for repeated manual adjustments with a redesigned venturi injec- tor. By relocating the adjustment interface to an accessible position and introducing a clearly labelled dial around the adjustment knob, the new concept is intended to make the disinfection process easy, intuitive and not physically demanding for the caregiver. The results of the report show that even relatively small design changes can have the potential to make a noticeable difference in both system reliability and overall user experience.