An experimental study of refrigerant lubricated sliding contact between the main components of a scroll expander system
Start date: 11 May 2010
In this study a scroll expander device was studied which is the main component of a small domestic Combine Heat and Power (CHP) system. Sliding tests were performed using mixture of refrigerant and lubricant in a modified micro-friction machine. Refrigerant and lubricant scroll fluids were used during the operational time period. The refrigerant was the driving force of the scroll while the lubricant was protecting the scroll from severe wear.
The test specimens used within the sliding experiments included high performance fluoroelastomer and high carbon steel. These are the main interacting materials of the scroll expander. The wear found across their interface was determined to be excessive and critical for the performance of the system.
The experimental conditions were adjusted to those of the industrial applications. Initial tests involved the use of lubricant only. Afterwards a mixture of refrigerant/lubricant was introduced inside an environmental pressurised chamber. Further sliding tests were conducted. The duration was one hour for each of the experiments and load was kept constant while the sliding velocity was varied.
The rational behind these experiments was to assess the durability, performance and understand the wear mechanisms of the scroll expander system. An interesting observation was that friction coefficient significantly increases when refrigerant is added to the mixture. In some cases friction coefficient of the refrigerant/lubricant mixture was determined to be twice the value of that in a lubrication regime. Moreover the volume loss and the specific wear rate were estimated.