Multi-Pass Folded Microchannel Heat Exchanger for Frost Tolerance
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Solution Overview
Problem
Microchannel heat exchangers used in HVAC&R systems tend to freeze faster than conventional heat exchangers, leading to reduced efficiency and more frequent defrosts, due to poor frost tolerance, which affects their performance and utilization time.
Innovation Solution
A microchannel heat exchanger design with a multi-pass configuration, featuring tube segments arranged in a bent configuration with distinct flow orientations and partitioned manifolds to optimize refrigerant distribution and airflow, reducing frost formation by varying the number of tube segments in each pass and using a longitudinally elongated distributor insert for improved refrigerant distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a microchannel heat exchanger is used to improve compactness and heat transfer performance, then the heat exchanger becomes more compact and efficient, but it freezes faster and requires more frequent defrosts
Solution Approach 1:
The heat exchanger is divided into multiple passes with different numbers of tube segments in each pass. The first pass has a different number of tube segments than the second pass, creating intentional flow maldistribution that redirects airflow to areas less prone to frosting, thereby improving overall frost tolerance while maintaining compact heat transfer surfaces
Solution Approach 2:
Different passes are designed with different numbers of active tube segments to create localized airflow patterns. The first pass has fewer active segments while the second pass has more, allowing specific regions to have different frost accumulation characteristics. This local variation in flow distribution prevents uniform frosting across all surfaces
2Reliability
If the number of tube segments is varied between passes to reduce frost formation, then frost tolerance improves, but the device complexity increases
Solution Approach 1:
The manifold is segmented into multiple sections using dividers, with each section feeding a different pass. The first manifold has a first divider creating a first section, and the second manifold has a second divider creating a second section. This segmentation allows independent control of refrigerant flow to each pass, enabling the different numbers of tube segments per pass while maintaining a manageable structural organization
Solution Approach 2:
Distributor inserts are introduced as intermediary components within the manifold sections to control and distribute refrigerant flow. These distributors act as mediators between the refrigerant source and the various passes, enabling precise flow maldistribution patterns that favor frost reduction without requiring complex external control systems
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 design enhances frost tolerance and operational efficiency by maintaining a favorable temperature difference between air and refrigerant, reducing frost accumulation and the need for defrosts, while optimizing refrigerant pressure drop and heat transfer performance.
Implementation Method 1
a longitudinally elongated distributor insert being disposed within the second manifold second section
Implementation Method 2
efficient exchange of thermal energy between the heating/cooling fluid and the surrounding environment
Implementation Method 3
heat exchanger to reject or accept heat between the refrigerant circulating within the system and surroundings
Implementation Method 4
The fins have a corrugated pattern, incorporate louvers to further enhance heat transfer
Implementation Method 5
moisture present in the airflow provided to the heat exchanger for cooling may condense and then freeze on the external heat exchanger surfaces
Implementation Method 6
The ice or frost formed may block the flow of air through the heat exchanger
Data Source
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AI summary
A heat exchanger is provided including a first manifold and a second manifold separated from one another. A plurality of tube segments arranged in a spaced parallel relationship fluidly couple the first and second manifold. The plurality of tube segments includes a bend defining a first slab and a second slab. The second slab is arranged at an angle to the first slab. The heat exchanger has a multi-pass configuration relative to an air flow including at least a first pass and a second pass. The first pass has a first flow orientation and the second pass has a second flow orientation. The second flow orientation is different from the first flow orientation.