Model, simulation and experiments for a Buoyancy Organic Rankine Cycle

Abstract

Organic Rankine Cycle (ORC) systems are increasingl y gaining relevance in the renewable and sustainable energy scenario. Recently our research group published a manuscript identifying a new type of thermodynamic cycle entitled Buoyancy Organ ic Rankine Cycle (BORC) (Schoenmaker et al., 2011). In this work we present two main contribut ions. First, we propose a refined thermodynamic model for BORC systems accounting for the specific heat of the working fluid. Considering the refined model, the efficiencies for Pentane and Dic hloromethane at temperatures up to 100°C were estimated to be 17.2%. Second, we show a proof of c oncept BORC system using a 3 m tall, 0,062 m diameter polycarbonate tube as a column-fluid reser voir. We used water as a column fluid. The thermal stability and uniformity throughout the tub e has been carefully simulated and verified experimentally. After the thermal parameters of the water column have been fully characterized, we developed a test body to allow an adequate assessme nt of the BORC-system’s efficiency. We obtained 0,84% efficiency for 43,8oC working temper atu e. This corresponds to 35% of the Carnot efficiency calculated for the same temperature diff erence. Limitations of the model and the apparatus are put into perspective, pointing directions for f urther developments of BORC systems.