Thermal Gradient Control in Thin Shell Drying Rolls
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Solution Overview
Problem
Thermal stresses occur in Honeycomb drying rolls due to temperature differences and varying coefficients of thermal expansion between thin metal strips and thick end members, leading to high stress conditions and reduced efficiency in the drying process.
Innovation Solution
A rotating, foraminous thin-shelled roll design with alternating straight and undulated strips, featuring a blocking mechanism to prevent axial airflow between layers, using either thin metal plates or cast inserts to reduce thermal gradients by blocking axial channels and controlling heat transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If heated air flows axially along channels between corrugation layers, then the shell structure is heated efficiently, but thermal stresses increase at the connection between thin strips and thick end members
Solution Approach 1:
The shell is divided into multiple corrugation layers with axial channels between them, allowing segmented airflow paths that control heat distribution. The blocking mechanism further segments the axial flow by introducing blocking elements in these channels, preventing direct thermal coupling between layers and reducing stress concentration at connections.
Solution Approach 2:
A blocking mechanism (blocking element) is introduced as an intermediary component within the axial channels between corrugation layers. This blocking element mediates the thermal interaction by preventing direct axial airflow and hot air leakage to the end members, thereby reducing thermal stresses at the connection points while maintaining shell heating efficiency.
2Adaptability or versatility
If the sheet width does not precisely match the exposed shell width, then heated air leaks by the end of the sheet, but this causes higher temperature exposure of the shell ends
Solution Approach 1:
The blocking mechanism acts as an intermediary that prevents hot air leakage from the axial channels at the shell ends. By introducing blocking elements in these channels, the system maintains temperature control even when sheet width does not precisely match the shell width, preventing excessive heating of the shell ends while allowing for width flexibility.
3Strength
If thick end members are used to support the thin shell, then structural strength is improved, but thermal expansion differences cause higher stresses
Solution Approach 1:
The blocking mechanism serves as a thermal intermediary that prevents direct thermal coupling between the thin shell strips and the thick end members. By blocking axial airflow channels, it reduces the transmission of thermal expansion forces from the heated shell to the cooler end members, thereby reducing thermal stresses while maintaining the structural strength provided by the thick end members.
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 reduces thermal stresses, extends the life of the production roll, and improves process efficiency by minimizing fatigue and reducing the time required for warm-up and cool-down cycles.
Implementation Method 1
the thin shell structure therefore operates at a significantly higher temperature than the more massive supporting end members. This temperature difference causes the support structure to exert significant restraining forces on the shell, resulting in high stress conditions
Implementation Method 2
when the end members are manufactured from materials having a smaller coefficient of thermal expansion than that of the thin strips, these stresses at the connection between the elements are exacerbated. The thin straight and undulated strips absorb heat and expand more rapidly than the thick metal end members
Implementation Method 3
The heated process air travels through the web and between the shell openings formed by the alternating layers of straight strips and undulated strips
Implementation Method 4
Cylindrical Honeycomb drying rolls... are well known in the art and typically these rolls are large and expensive apparatuses. The air permeable shells of such rolls comprise alternating thin straight and thin undulated strips
Data Source
AI summary
Described herein are devices and methods for reducing thermal stresses in a rotating, foraminous thin-shelled roll for drying permeable and semi-permeable webs by blocking axial flow of heated air through an axial channel formed between two corrugated layers in the shell. The axial channels extend between spaced-apart, parallel end members each having an inner face, and a plurality of alternating straight thin divider strips and bent thin strips extending axially between and evenly-spaced around the circumference of the inner faces of the end members to form an annular cylinder with radial channels therethrough. Affixing at least one impermeable insert into a radial channel so that it extends through the radial channel and across at least a portion of the faces of the two tiers of bent strips blocks the axial channel therebetween and prevents the passage of air therethrough to the end member.