A heat transfer sheet assembly with an intermediate spacing feature
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Solution Overview
Problem
Conventional heat transfer sheets in rotary regenerative air preheaters face a trade-off between structural rigidity and operational efficiency, with high soot blowing pressures causing mechanical damage and reduced efficiency due to increased pressure drop and fouling, especially at the cold-end elements.
Innovation Solution
A heat transfer sheet assembly with a first sheet element having a first profile and a second sheet element with a complementary profile, featuring parallel sheet spacing features and lobular undulations, which form close-sided channels to enhance structural rigidity and heat transfer efficiency while withstanding higher soot blowing pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional sheet spacing features are used to provide structural integrity, then the assembly can withstand soot blowing pressures, but the channels remain open-sided allowing high velocity uninterrupted flow that reduces heat transfer efficiency
Solution Approach 1:
The channel is segmented into multiple sections by dividing the sheet spacing features into first and second sets that form separate channel sections. This segmentation allows the channel to be closed-sided while maintaining structural integrity and promoting turbulent flow through the segmented structure.
Solution Approach 2:
The invention transitions from open-sided to closed-sided channels by adding spacing features in both longitudinal directions, effectively closing the channel in the transverse dimension while maintaining the longitudinal flow path. This dimensional change enables turbulent flow and improved heat transfer.
2Productivity
If turbulent flow is promoted through the channels to increase heat transfer efficiency, then heat transfer improves, but pressure drop across the preheater increases requiring higher fan power
Solution Approach 1:
Turbulent flow is promoted locally within the closed-sided channels through their specific geometry and configuration, while the overall flow path remains optimized to minimize pressure drop. The channel sections are designed to create turbulence where it benefits heat transfer while maintaining efficient flow through the assembly.
3Productivity
If higher soot blowing pressures are used to clean the heat transfer sheets, then cleaning effectiveness improves, but mechanical damage to the sheets increases
Solution Approach 1:
The sheet spacing features include rounded corners and curved surfaces rather than sharp edges. This curvature design allows soot blowing pressure to be distributed more evenly across the sheet surfaces, preventing concentrated stress points that could cause mechanical damage while maintaining effective cleaning.
Solution Approach 2:
The closed-sided channel structure and rounded spacing features act as a cushioning mechanism that absorbs and distributes the impact of high pressure soot blowing, protecting the heat transfer sheets from direct mechanical damage while maintaining cleaning effectiveness.
4Loss of energy
If the heat transfer sheet assembly weight is reduced to decrease rotation power requirements, then energy efficiency improves, but structural rigidity and ability to withstand soot blowing pressures deteriorates
Solution Approach 1:
The heat transfer sheet assembly uses a composite structure combining multiple sheet layers with integrated spacing features formed from the sheet material itself. This composite design provides high structural rigidity and strength-to-weight ratio, enabling the assembly to withstand soot blowing pressures while maintaining reduced weight for efficient rotation.
Solution Approach 2:
The segmented channel structure created by multiple sets of spacing features distributes mechanical loads across the assembly, enhancing overall structural rigidity without requiring additional weight. The segmented design allows each section to support itself, reducing the total material needed while maintaining strength.
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 assembly maintains thermal performance and mechanical stability under higher soot blowing pressures, reducing mechanical damage and fan power requirements, and improves heat transfer efficiency by promoting turbulent flow without negatively impacting operational efficiency.
Implementation Method 1
The heat transfer sheets absorb heat from the flue gas stream and transfer this heat to the combustion air stream
Implementation Method 2
Some heat transfer sheets include undulation patterns between the sheet spacing features to impede flow in a portion of the channel and thereby causing turbulent flow which increases heat transfer efficiency
Data Source
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AI summary
A heat transfer sheet assembly (7) for a rotary regenerative heat exchanger, has first and second heat transfer sheet elements (8, 9) stacked one against the other with a first repeat R1 of a first profile on one sheet element (8) opposing a second repeat R2 of a second profile on the other sheet element (9). The sheet elements (8, 9) are spaced apart by a plurality of wide-gauged parallel sheet spacing features (21, 22) of the first profile repeat R1 and (23, 24) of the second profile repeat R2 to form a generally close sided elongate channel (25) for gaseous flow therethrough. The second profile of repeat R2 further comprises an elongate fifth sheet spacing feature (26) in the form of a lobe contacting undulations (29) of the adjacent first profile of repeat R1. In an embodiment, the first and second sheet elements each have a composite third profile including both the first repeat of the first profile and the second repeat of the second profile.