Designing The Primary Nozzle Configuration of a Phase Change Ejector as an Expansion Device in the R134A Air-Water Heat Pump Cycle

Abstract

The aim of this study is to develop a thermodynamic model for designing the primary nozzle (P-N) of a phase change ejector utilized in the Air-Water Heat Pump (AWHP) cycle. This expansion device is proposed to replace the conventional expansion devices with high irreversibilities losses in order to enhance the overall cycle efficiency. This simulation study is modelled using MATLAB software with REFPROP database used to obtain R134a thermodynamic properties. A comparison analysis of AWHP using valve, turbine or ejector as expansion devices is conducted. The ejector results is then used in the P-N design simulation. In addition, a sensitivity analysis to investigate the effects of varying R134a velocity at the P-N inlet on the design parameters is performed. The results show that ejector cycle has achieved higher COPh and second law efficiency by 3.25 and 6.6% respectively. In addition, the exergy evaluation demonstrates that using the ejector reduces the total exergy destruction by 51.7 and 48.5% compared to valve and turbine cycles respectively. The results also show that 20.7 J of exergy is destroyed in the ejector, of which 15.9 J of this destruction occurs in the P-N. The sensitivity analysis show that the P-N has a converging-diverging configuration with an inlet diameter ranging between 4.9-3.2 mm, while the throat diameter is between 3.11-2.7 mm and the outlet diameter is almost constant at 7mm. In addition, at the throat section, R134a reaches supersonic speed and highest mass flux and maintain the supersonic speed at the nozzle exit.