Design and Analysis of an Optimized Rotational Molded Defroster Plenum

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Gibur, Amanda
Lind, Jason
Huang, Jiawei
Patel, Rikenkumar
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Our team has worked to optimize New Flyer's Xcelsior defroster plenum in terms of air distribution, defrost time, noise level, weight, installation time, and number of points on the assembly line in which the plenum can be installed. We have also analyzed the feasibility of rotational molding for the plenum based on cost, longevity, and the number of pieces it will take to manufacture the plenum. Research was conducted into the benefits and downfalls of the rotational molding process. New Flyer’s vendor, Plasticom, was contacted for cost estimates and further feedback. Using the information gathered, our team determined that rotational molding was not a feasible manufacturing method due to the large probability of thermal expansion. Upon recommendation from Plasticom, our team then explored the manufacturing method of vacuum forming to determine whether this would be a suitable option. Research was once again conducted along with a cost analysis, and it was concluded that vacuum forming would be the most appropriate and cost effective method for manufacturing the plenum. In order to optimize the plenum, the various design requirements were weighted and concept generation and scoring took place. The main focus of the new concepts was redesigning the middle wedge and adding fins. However, the focus changed to that of redesigning the vents when New Flyer purchased a competing bus manufacturer and examined their more reliable defroster system. After much CFD analysis and consideration of designs, it was proposed to maintain the current shape of the plenum. This ensures that the cost per piece of the plenum does not increase, since its complexity does not increase. Instead it is proposed that the vents located in the dash be altered. The new vents are large, with a width of 0.8 inches and a length of 7 inches. The total outlet area of the vents is 44.574 in 2. It is also recommended to eliminate the fins within the vents, and instead maintain an open vent area. This will prevent a choking phenomenon and air will be able to easily flow through the openings, as proven by our CFD models provided.