Comparison of experimental and analytical model results of a subsonic ejector performance for geothermal applications
Author: Gunnar Dagur Jónsson
Year: 2024
Supervisors: Guðrún Arnbjörg Sævarsdóttir, María Sigríður Guðjónsdóttir, and Ximena Guardia Muguruza
Abstract:
An ejector is a stationary device designed to transform the pressure of a high-pressure primary stream into kinetic energy, decreasing the pressure and allowing the entrance of a fluid from a low-pressure secondary source. Subsequently, these two streams mix and are discharged at an intermediate outlet pressure [1], [2].
A subsonic ejector comprises of five components: primary converging nozzle, suction chamber, constant-pressure mixing section, constant-area mixing section (CAMS), and a diffuser. Flow in subsonic ejectors does not pass sonic conditions (Mach < 1) [3].
An analytical model developed by Andal [4] was used to design and predict the performance of subsonic ejectors made for laboratory experiments. Four subsonic ejectors (4, 5, 7 and 9 mm CAMS) were made and tested using the same conditions and procedure for all experiments in a test rig at Reykjavik University, created to simulate a geothermal field. Results from the experiments were used to verify and upgrade the analytical model. Performance of the subsonic ejectors was evaluated with entrainment ratio (ER), gained pressure (GP) and exergy (∆ ˙ψi) [4]. Best results were with the 5 mm CAMS ejector which got an ER of 0.13, GP of 0.73 bar-g and exergy gain of 0.16 kW.
The upgraded analytical model was used to design a subsonic ejector to connect Well X to the steam gathering system at Hellisheidi power plant. Wells 1, 2, 3 and 4 were evaluated as the primary flow source for the system. An ejector with either wells 1 or 2 as the primary
well does achieve sufficient GP and outlet pressure. When actual steam conditions were used for the design: Well 1 could entrain 2.1 kg/s of flow from well X and 0.32 MWe of added electric power could be achieved. Well 2 could entrain 0.85 kg/s and provide 0.10 MWe in added electric power production. If only saturated steam would be used for the design: Entrainment of flow from well X paired with well 1 would be 0.85 kg/s and added electric power production would be 0.35 MWe. Well 2 could entrain 0.47 kg/s of flow from well X and increase the electric power production by 0.18 MWe.
URL: https://hdl.handle.net/1946/48712