Variable Diameter Link Pipe for Thermal Stress Distribution
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Solution Overview
Problem
Supercritical pressure vertical once-through heat recovery steam generators face challenges in structural stability due to severe thermal expansion of the outlet head, leading to thermal stress and a high risk of breakage.
Innovation Solution
The design incorporates a once-through heat exchanger with a plurality of tubes, heads, and link pipes that include variable diameters and inclined link parts to distribute thermal stress, reducing the concentration of heat and stress on specific areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional fixed-diameter link pipe is used to connect heads and manifold, then the structure is simple and easy to manufacture, but thermal stress concentrates at the outlet head causing high risk of breakage
Solution Approach 1:
The link pipe transitions from a fixed diameter to a variable diameter structure, where the inner diameter gradually changes along the pipe length. This parameter change allows the pipe to accommodate thermal expansion differences between the outlet head and manifold, distributing thermal stress throughout the pipe rather than concentrating it at specific locations, thereby preventing breakage while maintaining structural integrity
Solution Approach 2:
The variable diameter link pipe creates a dynamic structure that can adapt to thermal expansion and contraction forces. The gradual change in diameter allows different sections of the pipe to expand and contract at different rates, absorbing thermal stress dynamically and preventing the concentration of stress at the outlet head connection point
2Productivity
If the outlet head is heated to high temperature for supercritical pressure operation, then steam generation efficiency is improved, but thermal expansion distorts tube arrangement and concentrates thermal stress
Solution Approach 1:
The variable diameter link pipe compensates for thermal expansion by allowing controlled dimensional changes in the pipe structure itself. The gradual diameter reduction from the outlet head side toward the manifold side creates a stress distribution pattern that counteracts the distortion caused by high-temperature thermal expansion, maintaining tube arrangement stability even under supercritical pressure conditions
3Reliability
If link pipes with large diameter are used to reduce thermal stress, then stress concentration is reduced, but the pipe occupies more space and becomes more complex
Solution Approach 1:
Instead of using a uniformly large diameter pipe that would occupy excessive space, the invention employs a variable diameter design where the pipe starts with a larger diameter near the outlet head to accommodate thermal expansion, then gradually reduces to a smaller diameter toward the manifold. This optimized parameter variation provides effective stress distribution while minimizing overall space occupation and structural complexity
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 configuration significantly reduces thermal stress and the risk of piping breakage by evenly distributing steam flow and reducing thermal stress concentrations, thereby enhancing the structural stability of the heat exchanger.
Implementation Method 1
severe thermal expansion of an outlet head of a final superheater. Heating and thermal expansion of the outlet head by steam heated to a high temperature distorts tube arrangement and concentrates thermal stress
Implementation Method 2
a once-through heat exchanger that includes a plurality of tubes (156, 157), a plurality of heads (155) connected to the tubes
Data Source
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AI summary
Disclosed herein is a once-through heat exchanger that includes a tube stack including a plurality of tubes, a plurality of heads connected to the tubes and configured to accommodate heated steam, a manifold connected to the heads and configured to accommodate heated steam, and a first link pipe and a second link pipe configured to connect the heads and the manifold. The heads are spaced in a direction crossing a longitudinal direction thereof, and the first link pipe and the second link pipe include a first inclined link part or a second inclined link part, respectively, extending at an angle to each other.