Analysis of a combined absorption cycle for power and cooling production using a novel oil-free co-rotating scroll expander.

This paper presents the integration of a novel scroll expander into a combined power and cooling absorption cycle driven by low grade heat sources such as solar energy and waste heat. The scroll device used here is based on a co-rotating technology which allows to work without internal lubrication. The mathematical model adopted for the cycle incorporates a simplified semi-empirical model that predicts the performance of the scroll expander. Ammonia-water has been selected as the working fluid mixture because of its nature-friendliness. Some operating parameters such as the heat source (155-205°C), sink (16-34°C) and chilled water (8-18°C) temperatures have been varied to investigate the behaviour of the cycle. The results show that increasing the
heat source temperature is beneficial to power generation but detrimental to cooling production. However, increasing the sink temperature is favourable for both power and cooling modes. Increasing the chilled water temperature is detrimental to both outputs. It was found that at the nominal conditions of heat source, sink and chilled water temperatures of 180°C, 27°C and 7°C respectively and an expander rotational frequency of 116.7 Hz; the cycle generated 87 kW of net mechanical power and 562 kW of cooling while the effective first law and exergetic efficiencies were 18.6 and 58.8% respectively.