Multichannel Evaporator Manifold for Liquid-Vapor Flow Separation
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Solution Overview
Problem
In multichannel heat exchangers, the separation of liquid and vapor refrigerant phases during expansion leads to inefficient heat transfer as vapor tends to separate from liquid, resulting in some tubes receiving only vapor and not absorbing heat effectively.
Innovation Solution
A heat exchanger design with a first manifold that partially separates a mixed phase flow of liquid and vapor, forming a pool of liquid, and a second manifold with multichannel tubes that direct liquid phase flow from below the pool and vapor phase flow from above, ensuring optimal distribution of refrigerant phases through the flow paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If refrigerant expansion is performed using a conventional expansion device, then the temperature and pressure of the refrigerant are lowered, but liquid and vapor phases separate resulting in inefficient heat transfer
Solution Approach 1:
The heat exchanger is divided into multiple independent flow channels, each receiving controlled amounts of liquid and vapor refrigerant. This segmentation ensures that each channel operates efficiently with appropriate phase distribution, preventing complete vapor separation that occurs in conventional single-channel systems.
Solution Approach 2:
Different regions of the heat exchanger are designed with different flow characteristics. The manifold distributes refrigerant phases non-uniformly, with liquid-rich flows to channels needing cooling and vapor-rich flows to channels needing heating, optimizing local heat transfer efficiency throughout the system.
2Productivity
If vapor refrigerant separates from liquid refrigerant during expansion, then some tubes receive only vapor and cannot absorb heat effectively, but maintaining mixed flow increases device complexity
Solution Approach 1:
The manifold is segmented into multiple outlets that independently control refrigerant distribution to different tube groups. This allows selective delivery of liquid-rich or vapor-rich refrigerant to specific channels based on their thermal requirements, maintaining heat absorption efficiency without requiring complex active control mechanisms.
Solution Approach 2:
Instead of attempting to prevent phase separation through complex mixing mechanisms, the design inverts the approach by accepting phase separation and strategically distributing separated phases to different channels. Liquid-rich refrigerant is directed to channels requiring cooling, while vapor-rich refrigerant is directed to channels requiring heating, turning a problem into a solution.
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
This design enhances heat transfer efficiency by ensuring that all flow paths receive either liquid or vapor refrigerant, preventing inefficient heat absorption and improving overall heat exchange performance.
Implementation Method 1
The mixed phase flow partially separates in the first manifold to form a pool of liquid
Implementation Method 2
the refrigerant changes phases while flowing through heat exchangers in which evaporation and condensation occur
Implementation Method 3
the refrigerant may enter an evaporator heat exchanger as a liquid and exit as a vapor
Implementation Method 4
the refrigerant may enter a condenser heat exchanger as a vapor and exit as a liquid
Implementation Method 5
Heat exchangers transfer heat by circulating a refrigerant through a cycle of evaporation and condensation
Data Source
AI summary
Heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems and heat exchangers are provided which include tube and manifold configurations designed to promote separation of vapor phase and liquid phase fluid. The manifolds contain multichannel tubes of various end geometries designed to dispose flow channels at different heights within the manifold. Individual tubes also may be disposed at different heights within the manifold. The various flow channel and tube heights permit direction of vapor phase and liquid phase refrigerant to certain flow channels.