Session: 08-02-01: Fundamentals and Applications of Thermodynamics

Paper Number: 70524

Start Time: Wednesday, 11:05 AM

70524 - Analysis and Modeling of Vapor-Liquid Interactions in Condensing Ejectors 

Ejectors are compact mechanical devices that utilize the expansion of a high-pressure primary fluid to entrain and compress a low-pressure secondary fluid by means of momentum transfer between the two streams of fluid. Compared to ejectors with two vapor streams that are widely used for work recovery in vapor-compression refrigeration systems, condensing ejectors feature both momentum and heat transfer through the interaction between the vapor and liquid streams, and have been applied in liquid-metal magnetohydrodynamic power cycles, condensers in Rankine cycles, underwater propulsion systems, and passive cooling for nuclear reactors. This paper focuses on the thermodynamic analysis and computational modeling of the vapor-liquid interactions in two specific types of condensing ejectors – one with primary liquid and secondary vapor flows, and the other with primary vapor and secondary liquid flows. Control volume analysis of the mass, momentum, and energy balance in each phase and across the interface based on one-dimensional (1D) slug flow was conducted for the ejectors. The main assumptions for slug flow thermodynamic analysis include: (1) 1D steady flow, (2) the static pressure is also 1D and uniform in each axial location, (3) the dominant heat transfer is from the interface to the liquid region, while the heat transfer from the vapor region to the interface is negligible, (4) heat transfer through the tube wall and axial conduction is also negligible, and (5) the liquid is incompressible, while the vapor is saturated or slightly superheated. The friction coefficient on the inner wall of the ejectors and the interfacial heat transfer coefficient are identified as controlling parameters for the ejector performance in terms of pressure and temperature distributions along the axis. The 1D slug flow models for both types of ejectors are validated with published results in the literature for condensing ejectors with a constant-area mixing section. The quantities evaluated for model validation include the axis distributions of static pressure, vapor and liquid temperatures, condensation rate, vapor flow rate and March number, and primary flow jet velocity and radius. After validation, detailed parametric studies are conducted to scrutinize the effects of the major geometric parameters (such as diameters at the inlet for the primary and secondary flows, and the mixing region diameter and length) and operating conditions (including friction coefficient, interfacial heat transfer coefficient, and primary inlet flow pressure, temperature, and velocity) on the performance of both types of ejectors. Future work on the experimental determination of the key parameters in the 1D slug flow model is recommended.

Presenting Author: Nanqiao Wang Mississippi State University

Authors:

Nanqiao Wang Mississippi State University
Nirmal Bhatt Mississippi State University
Shanti Bhushan Mississippi State University
Heejin Cho Mississippi State University
Like Li Mississippi State University