Multi-Pass HVAC Heat Exchanger for Stable Refrigerant Distribution
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Solution Overview
Problem
Microchannel heat exchangers in residential air conditioning and heat pump systems are sensitive to refrigerant charge imbalances due to their small internal volume, leading to performance degradation and nuisance shutdowns, and face limitations in refrigerant charge reduction, necessitating a more efficient design to meet regulatory efficiency and sound constraints.
Innovation Solution
A heat exchanger with a multi-pass configuration and a flow restricting element, such as a porous insert or orifice, is used to create a pressure drop between fluid passes, resulting in different saturation temperatures and optimizing the refrigerant distribution, which includes a first and second header with heat exchange tubes arranged in parallel, and a flow control valve to adjust fluid flow, enhancing refrigerant management and system efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If microchannel heat exchangers are used to reduce refrigerant charge, then refrigerant charge volume is reduced, but the system becomes overly sensitive to refrigerant charge imbalances causing performance degradation and nuisance shutdowns
Solution Approach 1:
A porous insert is positioned within the second header to restrict fluid flow between the first and second passes. The porous structure creates a pressure drop that establishes different saturation temperatures in each pass, preventing refrigerant charge imbalance issues while maintaining reduced refrigerant charge volume.
Solution Approach 2:
The invention changes the pressure parameter by introducing a flow restricting element that creates a pressure drop between passes. This pressure difference results in different saturation temperatures, which stabilizes refrigerant distribution and prevents charge imbalance sensitivity in microchannel heat exchangers.
2Reliability
If a flow restricting element is added to create different saturation temperatures, then refrigerant distribution is optimized and charge sensitivity is reduced, but device complexity increases
Solution Approach 1:
The porous insert provides a compact flow restriction mechanism that can be easily integrated into the existing header structure. The porous material's inherent structure creates the necessary pressure drop without requiring complex mechanical components, thus minimizing the increase in device complexity.
Solution Approach 2:
The flow restricting element acts as an intermediary component between the two passes, mediating the fluid flow to create the desired pressure and temperature difference. This simple intermediary element achieves the complex function of refrigerant distribution optimization without requiring a complete system redesign.
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 solution increases the frost-defrost cycle time and heating seasonal performance factor (HSPF), allowing for cost and space savings by optimizing the heat exchanger size, while maintaining efficient refrigerant use and reducing refrigerant charge sensitivity, thus addressing the limitations of current microchannel heat exchanger designs.
Implementation Method 1
The flow restricting element comprises a porous insert positioned within the second volume adjacent at least the second portion of the plurality of heat exchange tubes, the porous insert being configured to restrict a fluid flow path between the first fluid pass and the second fluid pass
Implementation Method 2
The flow restricting element comprises a porous insert positioned within the second volume adjacent at least the second portion of the plurality of heat exchange tubes
Implementation Method 3
a plurality of heat exchange tubes arranged in spaced parallel relationship and fluidly coupling the first and second header
Implementation Method 4
During operation, the heat transfer fluid conveyed through the first volume has a first saturation temperature and the heat transfer fluid conveyed through the second volume has a different second saturation temperature
Data Source
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AI summary
A heat exchanger 22 is provided including a first header 30 and a second header 32 and a plurality of heat exchange tubes 34 arranged in spaced parallel relationship and fluidly coupling the first and second header 30, 32. A flow restricting element 80 defining a first volume and a second volume is positioned within one of the first and second header 30, 32. The heat exchanger 22 has a multi-pass configuration such that a first portion of the plurality of heat exchange tubes 34 are coupled to the first volume and form a first fluid pass of the heat exchanger 22 and a second portion of the plurality of heat exchange tubes 34 are coupled to the second volume and form a second fluid pass of the heat exchanger 22. During operation, the heat transfer fluid conveyed through the first volume has a first saturation temperature and the heat transfer fluid conveyed through the second volume has a different second saturation temperature.