Helical Low-Fin Tubes for High-Strength Heat Exchanger Materials
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Solution Overview
Problem
Conventional methods for manufacturing finned tubes with helical fins face challenges when using materials with high mechanical strength, such as stainless and duplex steels, due to progressive hardening and tool damage, leading to increased costs and production downtime.
Innovation Solution
A method involving two sequential machining operations with different angles of advancement to produce helical fins on the tube surface, minimizing hardening effects and allowing the use of high-strength materials without annealing, using a machine with a first rotating finning/grooving tool and a second rotating finning tool with distinct angles of advancement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional single-tool helical finning method is used on high-strength materials, then fin formation is achieved, but progressive hardening causes tool slipping and damage
Solution Approach 1:
The finning process is divided into two sequential operations using two different rotating tools: a first tool forms a groove at a first angle of advancement, and a second tool forms the final fin at a second angle of advancement. This segmentation distributes the mechanical load and hardening effects across multiple tools rather than concentrating them on a single tool, preventing systematic slipping and damage.
Solution Approach 2:
The invention changes the angle of advancement parameter between the two finning operations. The first tool uses a first angle of advancement to create a groove, while the second tool uses a different second angle of advancement to form the final fin. This parameter variation optimizes the distribution of mechanical stress and reduces progressive hardening effects that would otherwise cause tool failure.
2Productivity
If conventional single-tool helical finning is used, then fin production is achieved, but production downtime increases due to frequent tool replacement
Solution Approach 1:
By dividing the finning operation into two sequential steps with two dedicated tools, the system eliminates the need for frequent tool replacements. Each tool is designed for its specific function and can operate continuously without the progressive hardening that plagues single-tool systems, thereby reducing production downtime.
Solution Approach 2:
The first tool performs a preliminary groove-forming action that prepares the surface for the second tool. This preliminary action distributes the mechanical stress and reduces hardening before the final finning operation, allowing both tools to maintain their effectiveness over extended periods without replacement.
3Area of stationary object
If transverse fins are used in longitudinal flow heat exchangers, then heat exchange surface is maximized, but heat transfer efficiency decreases due to flow misalignment
Solution Approach 1:
The invention replaces transverse fins with helical fins that follow a curved path along the tube. The helical configuration aligns the fin surfaces with the longitudinal flow direction, allowing the fluid to interact more effectively with the heat exchange surface while maintaining turbulent flow patterns that enhance heat transfer.
Solution Approach 2:
The fin structure transitions from a two-dimensional transverse arrangement to a three-dimensional helical configuration. This dimensional change allows the fins to simultaneously provide large surface area and align with the flow direction, resolving the contradiction between surface area maximization and flow alignment.
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
Enables the production of finned tubes with increased heat transfer coefficients, utilizing high-strength materials like copper-nickel, stainless, and titanium steels, while reducing tool damage and production costs, and allowing for a three-dimensional surface that enhances heat transfer by a factor of 3.0-4.5 compared to smooth tubes.
Implementation Method 1
forming a first (temporary) fin/groove (22) on said tube (2) by means of said first rotating tool (32)... forming a second (main) fin (21) on said tube (2) by means of said second rotating finning tool (31)
Implementation Method 2
tubes (2) provided on at least a part of their outer surface with a plurality of low fins (21)... which allow a substantial increase in the heat transfer coefficient on the shell side
Data Source
Figure 1~3
Figure 4~5
Figure 6a~7c
AI summary
A shell and tube longitudinal flow heat exchanger comprising a containment casing 101 within which a first fluid can flow substantially parallel to the longitudinal axis of said casing 101, said containment casing 101 accommodating in its interior a bundle of tubes 2 substantially parallel to one another and parallel to the longitudinal axis of said casing 101 and a plurality of grid-shaped baffles 102 substantially transverse to the longitudinal axis of said casing 101 supporting said tubes 2, a second fluid flowing in said bundle of tubes 2. Said tubes 2 are provided on at least a part of their outside surface with a plurality of low fins 21, which are helically arranged on the outer surface of said tubes 2 with a first angle of advancement α and having a profile interrupted by helical grooves 22 having a second angle of advancement β, with α≠β.