RESPONSE SURFACE BASED OPTIMIZATION OF SOLAR COLLECTOR INTEGRATED WITH AN AMMONIA-WATER COMBINED POWER/COOLING CYCLE SUPPORTED BY EXERGY ANALYSIS

摘要

Finding optimal operating conditions of solar-based power and cooling systems is always a challenge. Performance of these systems is highly dependent on several important parameters, which not only impact the long-term efficiency but also its technical and economic feasibility. This paper studies the operation/configuration problem of an ammonia-water power and cooling cycle using an exergetic analysis. Thermodynamic performance of the combined cycle was addressed by using analysis of variance and multiple linear regression analysis. Modeling was done in Matlab®, using Refprop 9.0 to calculate the thermodynamic properties of the ammonia-water mixture. Convergence issues were observed on the thermodynamic properties estimation carried out by Refprop when the stream had high ammonia mass fraction. To solve this issue an averaging algorithm was implemented online to estimate such properties using pure ammonia data and high, but stable, ammonia concentration data. After this implementation, small differences between current and reference model were seen. Optimum operating conditions were obtained using response surface technique. The response variable used was the ratio between exergetic efficiency and exergy destruction. Results showed that the response variable is mainly influenced by the ammonia concentration, pressure ratio, turbine efficiency and temperature gradient in the heat exchanger. Finally integration of the power/cooling cycle with a solar field was performed using two types of concentrated solar collectors: Linear Fresnel Collector (LFC) and Parabolic Trough Collector (PTC). The analysis showed that LFC technology can be a viable alternative for small scale applications combined with power/cooling systems.