| Under the background of energy supply and demand contradiction, energy-saving projects, changing the current inefficient way of energy utilization and to create a scientific and reasonable energy consumption systems are widely mentioned strategies to alleviate energy crisis. Absorption power cycle is an advanced heat/power conversion technology; it can efficiently convert mid/low-heat sources into power, such as industrial waster heat, solar energy and geothermal energy. So, it is of great significance for improving energy utilization efficiency. This paper focused on the development and assessment of working fluid in absorption power cycle, the research contents are as follow:First, According to the structure feature of the absorption power cycle, three binary systems HFC245fa+DMAC, HFC236fa+DMAC and HFC236fa+DMEDEG were identified as potential working fluids. The vapor-liquid equilibrium (VLE) data of these three systems were measured over a temperature range of 293.15 to 353.15 K and a pressure range of 20 to 800 kPa. The five-parameter NRTL model was used to fit the experimental data. The average relative deviations in the pressure between the experimental and calculated data for R245fa+ DMAC, R236fa+ DMAC and R236fa+ DMEDEG were 1.51%,1.61% and 1.25%, respectively, and the maximum relative deviations were 3.21%,3.52% and 2.96%, respectively. The three working fluids all displayed negative deviations from Raoult’s law, and the deviations decreased in the following order:R236fa+DMEDEG> R236fa+ DMAC> R245fa+DMAC. And the order was explained by molecular structure and H-bond between absorber and absorbent.Second, based on HFC+organic solvent systems, a new method to develop and assess the working fluid of absorption power cycle was established. The maximum value of excess Gibbs was used as the criteria to evaluate each system’s affinity; the results showed that HFC41+DMEDEG, HFC 161+DMEDEG and HFC245fa+DMEDEG have the preferable affinity. Then three systems were simulated in Rankine cycle with the same outside condition, HFC245fa+DMEDEG expressed the best efficiency. So, the performance of absorption power cycle using HFC245fa+DMEDEG as working fluid was conducted. Results showed that the cycle efficiency was 18.32%, and the heat engine sub-cycle contributed 88.32%, the chemical heat engine sub-cycle contributed 11.68%.Third, the potential of CO2+HC binary systems as working fluid were studied, CO2+propane/n-butane/iso-butane/n-pentane/iso-pentane/neo-pentane six pairs were selected, through investigate their performance in Rankine cycle, we concluded that the main advantage of CO2+HC binary system was their lower critical temperature compared with pure CO2, this peculiarity greatly reduced the pressure level of Rankine cycle, so it made the cycle produce more power and permitted a widen operation condition. In addition, binary working fluids’temperature varies in phase changing process; it helps to reduce the irreversibility of heat exchange process, and eventually improves cycle efficiency. So, CO2+HC binary systems were the feasible way to develop new working fluid. |
