Enhanced tube for direct expansion evaporators
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Solution Overview
Problem
Conventional shell-and-tube heat exchangers in HVACR systems face inefficiencies in heat transfer due to the lack of enhanced boiling surfaces within the heat exchanger tubes, leading to reduced refrigerant charge and increased complexity in lubricant recovery, especially in direct expansion heat exchangers.
Innovation Solution
Incorporating a cavity layer with protrusions on the inner surface of the heat exchanger tubes, which acts as an enhanced boiling surface, and a finned member on the exterior surface to promote thermal energy exchange between the working fluid and the process fluid, thereby improving heat transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional smooth tube surfaces are used in direct expansion heat exchangers, then the device complexity is low and manufacturing is simple, but the heat transfer efficiency is reduced and refrigerant charge is insufficient
Solution Approach 1:
The patent applies porous or textured surface treatments on the heat exchanger tube interior surface to create enhanced boiling surfaces. These porous structures increase the effective surface area and provide nucleation sites for bubble formation, significantly improving heat transfer efficiency during the boiling process while maintaining a relatively simple overall device structure.
Solution Approach 2:
The patent modifies the physical parameters of the tube surface by introducing cavities, protrusions, or textured patterns with specific dimensional parameters. These parameter changes create optimal conditions for bubble nucleation and growth, enhancing the boiling heat transfer coefficient without fundamentally altering the basic heat exchanger design.
2Quantity of substance
If conventional heat exchanger tubes are used without enhanced boiling surfaces, then the manufacturing process is simple, but the refrigerant charge is reduced and lubricant recovery becomes more complex
Solution Approach 1:
The porous surface treatment allows for better refrigerant distribution and increased residence time within the tube, enabling more effective utilization of the refrigerant charge. The porous structure creates capillary effects that enhance refrigerant wettability and distribution, allowing smaller refrigerant charges to achieve the same cooling effect.
Solution Approach 2:
The enhanced boiling surface optimizes the phase transition process from liquid to vapor by providing numerous nucleation sites. This improves the efficiency of refrigerant evaporation, allowing the system to achieve better heat transfer with reduced refrigerant quantities while simplifying lubricant recovery operations.
3Productivity
If smooth tube interiors are used in direct expansion evaporators, then the device structure is simple, but the heat transfer coefficient is lower and evaporation efficiency is reduced
Solution Approach 1:
The cavity layer creates a porous-like structure on the tube interior surface that enhances bubble nucleation and growth. This porous structure increases the active boiling surface area and improves liquid-vapor interface contact, significantly enhancing evaporation efficiency while maintaining a relatively simple cavity pattern that can be manufactured using conventional techniques.
Solution Approach 2:
The cavity layer introduces a new dimensional feature on the tube interior surface, transitioning from a two-dimensional smooth surface to a three-dimensional structured surface. This dimensional change creates multiple levels of surface complexity that enhance heat transfer without requiring fundamentally complex device architecture.
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 enhanced boiling surface and finned member configuration increase the heat transfer coefficient, reduce refrigerant charge and freezing risks, and simplify lubricant recovery, resulting in improved heat transfer efficiency compared to traditional direct expansion heat exchangers.
Implementation Method 1
a cavity layer on the inner surface configured to evaporate the working fluid flowing in a first flow path
Implementation Method 2
the cavity layer is an enhanced boiling surface arranged to evaporate the first fluid flowing inside the at least one tube
Implementation Method 3
a second flow path, separate from the first flow path, is configured to direct a second fluid across the tube bundle and to contact the extended member on the exterior surface of the at least one tube such that the first fluid exchanges thermal energy with the second fluid
Implementation Method 4
the two protrusions constrict a flow of the first fluid through an opening of the cavity to promote bubbling and evaporation
Data Source
AI summary
An HVACR system, a direct expansion evaporator, and a direct expansion heat exchanger tube arranged to evaporate a working fluid inside the tube are disclosed. The tube includes an exterior surface of the tube opposing an inner surface of the tube, and a cavity layer on the inner surface configured to evaporate the working fluid flowing in a first flow path arranged to direct the first fluid to flow through the tube and contact the cavity layer on the inner surface. A second flow path, separate from the first flow path, is arranged to direct a second fluid across the tube and to contact the extended member on the exterior surface of the tube such that the first fluid exchanges thermal energy with the second fluid.