Multi-Pass Microchannel Heat Exchanger for Low-Charge Stability

Solution Overview

Problem

Microchannel heat exchangers are sensitive to refrigerant charge imbalances due to their small internal volume, leading to performance degradation and nuisance shutdowns, especially when using low global warming potential refrigerants, which are subject to charge reduction limitations.

Innovation Solution

A multi-pass microchannel heat exchanger design with fluidly distinct chambers and a separator to separate liquid and vapor refrigerant, incorporating a bypass conduit to manage refrigerant flow and reduce the refrigerant charge, while maintaining efficient heat transfer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If microchannel heat exchangers are used to reduce refrigerant charge, then refrigerant charge is reduced, but the system becomes extremely sensitive to overcharge situations causing performance degradation and nuisance shutdowns

Engineering Contradiction:

Improverefrigerant chargeVSAvoidsystem stability

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The heat exchanger is divided into multiple passes with distinct liquid and vapor chambers separated by partition walls. This segmentation allows independent management of liquid refrigerant distribution and vapor refrigerant flow, reducing sensitivity to charge variations while maintaining low overall refrigerant charge volume.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A liquid-vapor separator is introduced as an intermediary component between the liquid chamber and vapor chamber. This separator mediates the refrigerant flow by separating liquid and vapor phases, ensuring proper distribution to respective passes and preventing overcharge sensitivity issues.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Quantity of substance

If the internal volume of heat exchanger is reduced to lower refrigerant charge, then refrigerant charge decreases, but heat transfer effectiveness is compromised

Engineering Contradiction:

Improverefrigerant chargeVSAvoidheat transfer effectiveness

Core Design Contradiction:

Quantity of substanceVSUse of energy by moving object

Solution Approach 1:

The patent transitions from conventional single-pass two-dimensional flow to a multi-pass three-dimensional configuration with vertical and horizontal flow paths. This dimensional change increases the heat transfer surface area within a compact volume, maintaining effectiveness while reducing refrigerant charge.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The heat exchanger is divided into multiple passes with distinct liquid and vapor chambers separated by partition walls. This segmentation allows independent management of liquid refrigerant distribution and vapor refrigerant flow, reducing sensitivity to charge variations while maintaining low overall refrigerant charge volume.

Inventive Principle:

Principle #1Segmentation

3Volume of moving object

If parallel flow heat exchanger configuration is used, then compactness and structural rigidity are improved, but refrigerant distribution imbalance occurs leading to performance degradation

Engineering Contradiction:

Improveheat exchanger compactnessVSAvoidrefrigerant distribution balance

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The heat exchanger is divided into multiple passes with distinct liquid and vapor chambers separated by partition walls. This segmentation allows independent management of liquid refrigerant distribution and vapor refrigerant flow, reducing sensitivity to charge variations while maintaining low overall refrigerant charge volume.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different passes are designed with locally optimized characteristics - liquid passes focus on even distribution through properly sized inlet openings, while vapor passes focus on efficient condensation. This local quality optimization ensures balanced refrigerant distribution across the compact parallel flow structure.

Inventive Principle:

Principle #3Local quality

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 multi-pass configuration reduces the inner volume and refrigerant charge, enhancing system efficiency and reducing the risk of shutdowns by optimizing refrigerant distribution and heat transfer, thereby improving the performance of heat exchangers in heat pump applications.

Implementation Method 1

a separator configured to separate a liquid and vapor refrigerant is arranged between the first pass and the second pass

Methodology Applied

Scientific EffectDensity gradient separation: Density Gradient

Implementation Method 2

a plurality of heat exchange tubes arranged in spaced parallel relationship and fluidly coupled to the first manifold and the second manifold

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 3

refrigerant is distributed and flown in a parallel manner through the heat exchange tubes

Methodology Applied

Scientific EffectConvection: Convection

Data Source

PatentUS10184703B2Multipass microchannel heat exchanger

Publication Date: 2019.01.22 CARRIER CORP

AI summary

A heat exchanger is provided including a first manifold, a second manifold, and a plurality of heat exchange tubes arranged in spaced parallel relationship and fluidly coupled to the first manifold and the second manifold. At least one divider plate is arranged within the first manifold such that the first manifold has a fluidly distinct first chamber and second chamber and the heat exchanger has a multi-pass flow configuration. The first chamber is configured to receive at least a partially liquid refrigerant and has a length between about 20% and about 60% a length of the first manifold.