Nucleation-Site Ejector for Heat Exchanger Pressure Drop
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Solution Overview
Problem
Packaged terminal air conditioner units face challenges due to space constraints, leading to the use of small heat exchangers that result in significant refrigerant pressure drops, reducing efficiency without adequately maintaining the refrigerant side heat transfer coefficient.
Innovation Solution
An ejector with a motive liquid passage featuring a converging section, throat, and diverging section, along with nucleation sites at the converging section, is introduced to reduce pressure drops across the heat exchanger while maintaining heat transfer efficiency, utilizing a mixing chamber and nozzle to combine refrigerant streams effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If small heat exchangers are used due to space constraints, then the packaged terminal air conditioner unit fits within space constraints, but the pressure drop across the heat exchanger increases significantly
Solution Approach 1:
The ejector changes the physical parameters of refrigerant flow by creating a mixed-phase flow regime. The device introduces liquid refrigerant into a vapor stream, creating a two-phase mixture that reduces the effective density and viscosity of the flowing refrigerant, thereby reducing pressure drop across the heat exchanger while maintaining compact dimensions
Solution Approach 2:
The ejector acts as an intermediary device between the refrigerant sources and the heat exchanger. It mixes vapor and liquid refrigerant streams to create an optimized two-phase flow that serves as an intermediate state, reducing the harmful effects of high pressure drop while maintaining the compact heat exchanger design
2Stress or pressure
If large diameter tubes or parallel tubes are used to reduce pressure drop, then pressure drop decreases, but refrigerant velocity and heat transfer coefficient are reduced
Solution Approach 1:
The ejector changes the flow parameters by creating a two-phase mixture with optimized density and velocity characteristics. The mixed-phase flow maintains higher velocities compared to single-phase flow in large diameter tubes, while the liquid-vapor mixture provides enhanced heat transfer coefficients through phase change mechanisms and turbulent mixing
Solution Approach 2:
The ejector utilizes phase transitions by mixing liquid and vapor refrigerant streams to create a two-phase flow. The presence of both phases in the flow enables enhanced heat transfer through latent heat exchange and phase change mechanisms, maintaining high heat transfer coefficients while reducing pressure drop compared to single-phase flow in larger tubes
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The ejector design effectively balances pressure drops across the heat exchanger, enhancing the efficiency of packaged terminal air conditioner units by up to five percent without significantly reducing the refrigerant side heat transfer coefficient.
Implementation Method 1
The motive liquid passage of the ejector body includes a converging section, a throat and a diverging section
Implementation Method 2
The ejector body also defines a plurality of nucleation sites at the converging section of the motive liquid passage
Data Source
AI summary
An ejector for a sealed system includes a motive liquid passage with a converging section, a throat and a diverging section. The throat of the motive liquid passage is disposed between the converging section of the motive liquid passage and the diverging section of the motive liquid passage. The ejector also includes a plurality of nucleation sites at the converging section of the motive liquid passage.