This project offers the investigation of a new design concept for screw rotors that have partial helical contact along the longitudinal axis of the intermeshing rotors. The rotor set is intentionally manufactured to ensure there are defined areas of contact and non-contact for the threaded section of the rotors. Using this concept, it is possible, under suitable operating conditions, to drive the rotors without the need for lubricating oil to be added, or for the requirement for timing gears to prevent the rotors from contacting each other. This concept is particularly applicable to waste heat recovery from steam. By ensuring there is no rotor contact at the hot steam inlet end to the machine, contact damage between the rotors can be eliminated, it will also allow steam at temperatures previously beyond contacting screw expanders to be handled. As the steam is expanded there is a reduction in temperature of the fluid and contact between the rotors may then be allowed to occur. By using partially contacting rotors, the cost effectiveness, operating range and reliability of machines may be significantly improved. The project will use the latest computer simulation techniques to quantify the technological benefits of using rotors designed in this manner.