Session: 06-01-01 Product And Process Design

Paper Number: 90097

90097 - Understanding the Expected Deformation of Rectangular Ductwork 

This paper presents results of a study that was performed to investigate the effects of aspect ratio, material gauge, material properties, joint spacing, loading type and magnitude on the mechanical performance of rectangular ductwork. Current rectangular ductwork design standards were reviewed, and theoretical equations contained in the existing literature were identified and evaluated. These design standards utilize plate models to predict maximum deflections and set stress limitations. One goal of the study was to verify the mode A and B design methods described in the design standards.  A secondary objective of this study was to elucidate the limitations and ranges of applicability of the plate equations underlying design methods A and B. One particular calculation addressed the case of a 10 gauge galvanized steel duct with a stiffener spacing of 30 in. and a panel width of 90 in. at an internal pressure of positive 10 in. wg. This example was selected because measured deformation data supplied were available for comparison. Additional cases were chosen to address the instances where the stiffener spacing to panel width ratio  and  These cases correspond to the situation where mode A and mode B deformations, respectively, were expected to generally prevail. An attempt was made to duplicate the published maximum pressure and deflection limitation in existing design standards, using their prescribed calculation procedure. Allowing for round-off error, the calculations performed in this investigation agreed closely with the standard design approach. The apparent disagreements between predictions based on the design procedure and the entries in the design standard duct selection tables were resolved. A non-linear finite element shell-beam composite model of a rectangular duct was developed to predict duct deformations at various pressures for the 10 gauge and 16 gauge duct walls. The finite element predictions of duct deformation were intermediate to available experimental data and those obtained using the standard design procedures, for both 10 gauge and 16 gauge wall thicknesses and twelve load cases. The present study qualitative agreement between the deflections measured from full-scale testing and the deformation contours generated by the finite element simulation. However, there was quantitative disagreement between the measured and predicted deflections. The exact reason for this is currently unknown. One possibility is that manufacturing the elements of the real system produces residual stresses, which are not taken into account in the finite element modeling because of their presently unknown nature.

Presenting Author: Stephen Idem Tennessee Tech Univ

Presenting Author Biography: Dr. Stephen Idem is a professor in the Department of Mechanical Engineering at Tennessee Tech University. He received his Ph.D. in Mechanical Engineering from Purdue University. He has more than 34 years of experience in the areas of fluid flow measurement, scale model testing, and thermal modeling. He participated in many studies related to the measurement of air flow and pressure loss characteristics of typical residential and commercial duct systems. He has created a numerical model of downdraft evaporative cooling tower performance, which was verified experimentally. He has extensive experience performing flow and pressure measurements on scale models of primary and secondary air supply ducts, windboxes, and exhaust stacks of coal-fired power plants in order to improve their thermal performance. He has developed an on-line cleanliness factor model of the convection passes in coal-fired power plants, and has likewise created numerical models of steady and transient heat exchanger performance. Currently he is developing a real-time coal-fired power plant heat rate monitoring protocol.

Authors:

Cameron Schaff Bennett & Pless
Matthew Crispi Tower Engineering Professionals
Jane Liu Tennessee Tech University
John Peddieson Tennessee Tech University
Stephen Idem Tennessee Tech Univ