Reverse osmosis temperature control

Abstract: Baxter develops medical devices that take advantage of reverse osmosis to purify water that’s being used in dialysis fluids. Reverse osmosis is a commonly used water purification process that removes unwanted particles from the water. The membrane that is used to purify the water has a temperature dependency that changes the performance of the membrane when the temperature is changed. When lowering the temperature of the water the purification of the water is increased. In this thesis the possibilities of lowering and controlling the temperature of the water was investigated. The goal was to implement a solution on a physical water device and to analyse the performance. Several solutions for the problem was presented where one of the solutions was selected for implementation on the real system. The final solution was a Peltier assembly which transfer heat from a flow of water and dissipating the heat through a second flow of water. The heart of the solution was a Peltier module which is a solid state heat pump that has no moving parts. A test rig was set up in a lab at Baxter with the water device and other components. In order to control the temperature of the water a controller was implemented and tuned. To analyse the performance several tests were performed. The results showed that the temperature could be lowered but not as much as the initial goal. A major issue was the low flow of the dissipating water. The effect of the low water flow was that the efficiency of the Peltier assembly was decreased.