Zig-Zag Undulated Heating Surface for Skew Flow Reduction
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Solution Overview
Problem
Existing rotary regenerative air preheaters for boiler plants and industrial furnaces suffer from skew flow, which reduces thermal performance, causes temperature stratification, and complicates cleaning and washing processes due to the angled undulations in heating-surface elements.
Innovation Solution
The heating surface elements are designed with alternating regions of undulations arranged in opposite directions, ensuring that the skew flow is minimized by directing air flow in a zig-zag pattern, thereby increasing the time spent over the heating surface and improving heat exchange properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If undulated heating-surface elements with angled undulations are used, then heat exchange surface area is increased, but skew flow is generated which reduces thermal performance
Solution Approach 1:
The heating surface element is divided into multiple regions with different undulation orientations. The first region has undulations at a first angle to the flow direction, while the second region has undulations at a second angle (different from the first angle) to the flow direction. This segmentation of the heating surface into zones with different geometric characteristics allows the element to maintain increased surface area while counteracting skew flow effects through the alternating undulation patterns.
Solution Approach 2:
Different portions of the heating surface element are given different local geometries. The first region features undulations at a specific angle optimized for certain flow conditions, while the second region features undulations at a different angle optimized for other flow conditions. This local differentiation ensures that each region performs its function optimally, maintaining thermal performance while managing flow characteristics.
2Use of energy by moving object
If angled undulations are used in heating-surface elements, then heat transfer efficiency is improved, but temperature stratification occurs
Solution Approach 1:
The heating surface is segmented into multiple angular regions that process different portions of the flow. By dividing the heating surface into zones with different undulation angles, the design ensures more uniform temperature distribution across the outlet while maintaining high heat transfer efficiency in each local region.
Solution Approach 2:
The undulations in different regions are oriented at asymmetric angles relative to the flow direction. This asymmetric arrangement creates a balancing effect where the skew flow tendencies in different regions counteract each other, leading to more uniform temperature distribution while preserving the enhanced heat transfer benefits of angled undulations.
3Reliability
If angled undulations are used in heating-surface elements, then heat exchange performance is enhanced, but cleaning and washing processes become complicated
Solution Approach 1:
By segmenting the heating surface into distinct regions with different undulation patterns, the design creates more accessible surfaces for cleaning. The varied angular orientations provide better access points for cleaning fluids and mechanisms compared to uniform angled undulations, while maintaining the performance benefits of the overall undulated structure.
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 significantly reduces skew flow, enhances thermal performance, prevents temperature stratification, and simplifies cleaning processes by ensuring even air flow and reduced vortex generation.
Implementation Method 1
an open-ended cylindrical drum houses a multiplicity of spaced heating-surface elements in the form of undulated metal plates... move the elements into, successively a stream of hot flue gases and a stream of combustion air
Implementation Method 2
said streams flowing axially through the drum and between the elements in the drum
Data Source
Figure 1~4
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Figure 9~12
AI summary
A heating surface element with a zig zag arrangement of longitudinal undulations which serve to minimize the skew flow of the gas. The angle of the undulations is preferably 15° to 35° to the primary flow direction of the gas. When used in combination with a notched heat surface element, the undulation preferably crosses no more than one opposing notch before changing direction.