Session: 01-07-02 Industrial Fluid Mechanics

Paper Number: 62237

Start Time: August 12th, 10:50 AM

62237 - CFD Analysis of Refrigeration Cycle Ejector 

The use of ejector cycles for increased performance and efficiency is becoming more prevalent in industry. Automotive refrigeration is a prime market for the use of this technology as it yields increased HVAC performance and reduces power draw to operate the system. In an ejector, a working fluid (liquid or gaseous) flows through a jet nozzle into a tube that first narrows and then expands in cross-sectional area. The fluid leaving the jet is flowing at a high velocity which  results in it having low pressure, thus generating a low pressure region. The outer tube then narrows into a mixing section where the high velocity working fluid mixes with the fluid that is drawn in by the low pressure region, imparting enough velocity for it to be ejected, the tube then typically expands in order to decrease the velocity of the ejected stream, allowing the pressure to smoothly increase to the external pressure. The ejector device is used to enhance the performance standard vapor compression of the refrigeration cycle. Increases to the Coefficient of Performance can be on the order of 20% depending upon the working fluid. The design and analysis of such technologies has been limited by cost-prohibitive prototyping and testing. The use of Computational Fluid Dynamics (CFD) in the research and analysis of new technologies allows for rapid and reliable results paving the way for cost reduction and a decrease in first-time-engineering costs, along with subsequent optimization engineering. The goal of this study is to evaluate an HVAC system with an ejector cycle, using CFD to evaluate flow patterns, perform trade studies varying the type of refrigerant, and determine the entrainment ratio for each working fluid, over a range of boundary condition pressures, set at points along the ejector’s flow path. The 2012 Toyota Prius V is one of the first automobiles using an ejector cycle in their internal cabin refrigeration system. The Denso Corporation manufactured refrigeration system uses ejector technology to reduce overall power consumption. Denso hardware was used as the basis for the creation of geometry for the ejector. Herein, ANSYS FLUENT CFD is used to simulate the behavior in an ejector taken from a TOYOTA PRIUS hybrid vehicle refrigeration system. Working fluids examine are R134a, R245fa and R1234yf. The CFD model parametric trade study results shows the  effects on press entrainment ratio with mass flow rate as ejector inlet  pressure is varied , and mixing chamber inlet pressure is varied. The Ejector Inlet Pressure boundary condition was varied from 1.50E+05 Pa to 2.50E+05 Pa in 0.25E+05 Pa increments, with the Mixing Chamber and Outlet Pressures held constant at 1.00E+05 Pa. Each respective inlet pressure results in a unique mass flow rate. The Ejector Mixing Chamber Inlet Pressure boundary condition was varied from 9.00E+04 Pa to 1.10E+05 Pa, in a single 2.00E+04 Pa interval. The Injector Inlet Pressure was held constant at 2.00E+4 Pa, and the Injector Outlet Pressure was held constant at 1.00E+4 Pa. the Ejector Outlet Pressure boundary condition was varied from 1.10E+05 Pa to 1.20E+05 Pa, in a single 0.1E+05 Pa interval. The Injector Inlet Pressure was held constant at 2.00E+05 Pa and the Injector Mixing Chamber Inlet Pressure was held constant at 1.00E+05 Pa, showing a pressure drop internal to the mixing chamber, with a rise at the exit. Entrainment ratios varied from 1.5 to 3.0 depending upon the scenario. Details of the CFD methodology and results are provided in the paper.

 

 

Presenting Author: Kevin Anderson Calif State Polytechnic University

Authors:

Kevin Anderson Calif State Polytechnic University
Franz Forster Landshut University
Alex Deravanessian Calif. State Polytechnic Univ. at Pomona
Matthew Nazarian Calif. State Polytechnic Univ. at Pomona
Mariano Rubio Citrus College - Automotive Technology