Microchannel Heat Exchanger Manifold Layout for Low Pressure Drop
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Solution Overview
Problem
Conventional heat exchangers with micro-channel tubes and small manifolds face issues in HVAC&R applications due to high refrigerant pressure drops, mal-distribution of refrigerant, and limited refrigerant holding capacity, leading to performance inefficiencies and potential system failures.
Innovation Solution
Optimizing heat exchanger design by using vertically oriented tubes with enlarged manifolds, incorporating a liquid baffle to create chambers for refrigerant accumulation, and adjusting tube openings to minimize pressure drops and mal-distribution, allowing for improved refrigerant flow and increased refrigerant holding capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional micro-channel tubes and small manifolds are used in heat exchangers, then the heat exchanger achieves compact size suitable for automotive applications, but it experiences high refrigerant pressure drops and mal-distribution of refrigerant in HVAC&R applications
Solution Approach 1:
The patent changes the key parameter of manifold size from small (automotive convention) to large (HVAC&R requirement). The manifold internal diameter is increased to at least 1.5 times the tube width, and the manifold cross-sectional area is increased to at least 1.5 times the total tube cross-sectional area. This parameter change reduces refrigerant velocity and dynamic pressure in the manifold, thereby reducing pressure drops and improving refrigerant distribution to tubes.
Solution Approach 2:
The enlarged manifold design creates more uniform pressure distribution across the manifold, making the refrigerant pressure more equal at different tube connection points. This equipotential effect reduces mal-distribution of refrigerant flow among parallel tubes, ensuring more uniform heat exchange performance across all tubes.
2Volume of moving object
If conventional small manifolds are used, then the heat exchanger remains compact, but the refrigerant holding capacity is limited leading to performance inefficiencies
Solution Approach 1:
The manifold volume is increased by enlarging its cross-sectional area and optimizing its length-to-diameter ratio. The manifold internal diameter is increased to at least 1.5 times the tube width, which directly increases the refrigerant holding capacity within the manifold. This allows the heat exchanger to accommodate varying refrigerant charge levels and maintain performance across a broader operating range.
3Productivity
If tube openings are reduced to increase heat transfer area, then heat transfer rate increases, but pressure drop and mal-distribution worsen
Solution Approach 1:
The patent optimizes the tube opening parameters including hydraulic diameter, cross-sectional area, and number of openings. By carefully selecting these parameters, the patent achieves high heat transfer coefficients while maintaining acceptable pressure drops. The enlarged manifold compensates for the pressure drops caused by multiple tube openings, ensuring uniform refrigerant distribution.
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 achieves consistent and predictable heat transfer, higher heat transfer rates, and increased energy efficiency by reducing pressure drops and refrigerant mal-distribution, expanding the operational range of refrigerant charge levels and improving system performance.
Implementation Method 1
When the heat exchanger is used as a condenser, condensed refrigerant liquid can accumulate in the lower manifold header
Implementation Method 2
Heat exchanger having opposed parallel header tubes
Implementation Method 3
exchanging heat between an ambient heat exchange medium and a refrigerant
Data Source
AI summary
The invention is directed to a heat exchanger with optimal performance and a method of optimizing the performance of a heat exchanger. The heat exchanger has a first manifold, a second manifold and tubes extending therebetween. The tubes have at least one opening which extends through the entire length of the tubes. The method may include: governing the pressure drop in the heat exchanger by selecting different size openings or configurations of the tubes depending upon the type of refrigerant used and the properties thereof; optimizing the dimensions of the first manifold and second manifold, such that the ratio of manifold to tube size or manifold to tube opening cross sectional area yields low pressure drops and minimized the effects of pressure drop in the manifold and tube combination; and optimizing the ratio of the mass flow capacity of the first and second manifolds to the tubes flow capacity such that the first manifold has minimal or negligible mal-distribution effect when providing refrigerant to the tubes, thereby improving the overall performance of the heat exchanger.