Dryer Bar Spacing for Uniform Paper Dryer Temperature
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Solution Overview
Problem
High-speed papermaking machines face challenges in achieving uniform dryer surface temperature profiles due to condensate-related heat transfer issues, leading to non-uniform drying and potential fiber sticking, linting, and runnability problems, especially when using stationary syphons which require lower steam pressures and may not adequately evacuate condensate.
Innovation Solution
The use of dryer bars configured at quarter-resonant spacing to minimize heat transfer while maintaining temperature uniformity, with fewer bars and increased spacing to reduce condensate depth and turbulence, allowing for lower steam pressures and reduced thermal energy transfer, thereby addressing the non-uniformity and high-temperature issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If dryer bars are used to improve temperature uniformity, then heat transfer rate increases, but dryer surface temperature becomes too high causing fiber sticking and linting
Solution Approach 1:
The patent changes the spacing parameter of dryer bars from conventional resonant spacing to quarter-resonant spacing (4 times larger), which fundamentally alters the heat transfer characteristics and condensate turbulence pattern, achieving temperature uniformity without excessive heat transfer rates that cause fiber sticking
Solution Approach 2:
The patent utilizes resonant vibration principles by spacing bars at quarter-resonant distances to generate controlled turbulence in the condensate layer, which enhances heat transfer uniformity while avoiding the harmful effects of excessive turbulence and heat transfer
2Stress or pressure
If stationary syphons are used to reduce steam pressure requirements, then operating differential pressure decreases, but condensate evacuation becomes inadequate at high speeds
Solution Approach 1:
The patent transitions from stationary syphons to rotating syphons that move with the dryer cylinder, enabling the syphon to effectively evacuate condensate at high rotational speeds by maintaining proper orientation and utilizing centrifugal forces dynamically
3Use of energy by moving object
If syphon clearance is reduced to minimize residual condensate, then heat transfer rate increases, but temperature profile uniformity deteriorates
Solution Approach 1:
The patent changes the bar spacing parameter to quarter-resonant spacing, which optimizes the interaction between bars and condensate layer to achieve both adequate heat transfer rates and uniform temperature profiles simultaneously
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 results in a significantly improved cross-machine temperature profile uniformity and lower dryer surface temperatures, reducing the risk of fiber sticking and improving machine runnability while maintaining efficient heat transfer, as demonstrated by temperature profile measurements and reduced standard deviation.
Implementation Method 1
The steam inside the dryer cylinders transfers its heat to the paper through the dryer shell
Implementation Method 2
As the heat is transferred from the hot steam to the wet paper, the steam inside the dryer condenses
Implementation Method 3
A number of turbulance bars are disposed within the enclosure, each of the turbulance bars extending in a cross machine direction in contact with the inner surface. The bars are circumferentially spaced equidistantly around the inner surface of the dryer shell for generating turbulance within the layer
Implementation Method 4
A syphon is disposed within the enclosure for controlling a layer of condensed steam accumulating adjacent to the inner surface of the dryer shell during operation of the apparatus
Data Source
AI summary
A dryer bar apparatus of a dryer for drying a web in a papermaking machine includes a number of turbulence bars circumferentially spaced equidistantly around the inner surface of the dryer shell for generating turbulence within a layer of condensate. The arrangement is such that uniformity of the transfer of thermal energy in the cross machine direction is maximized while the transfer of thermal energy through the dryer shell from the inner to the outer surface is minimized. Also, the number of turbulence bars is determined by the equation: N=int{2πRi/[4π(Ri/d)½+W]}in which: N=the number of turbulence bars in the dryer shell; int=an integer number of a value in {} brackets; π=3.1415; Ri=the inside radius of the inner surface of the dryer shell in inches; d=an average depth of the layer in inches; W=a width of each of the turbulence bars in inches.