Date of Award

Winter 1-1-2019

Degree Type

Thesis

Degree Name

Master of Science In Mechanical Engineering Degree

Department

Mechanical Engineering

First Advisor

Zhang, Wei

Second Advisor

Dr. Asuquo Ebiana

Third Advisor

Dr. David Davis

Abstract

Boundary-layer bleed is typically used in supersonic aircraft inlets to improve inlet performance and enhance inlet stability. At Mach numbers above 3.0, the bleed air is at high temperature and low pressure, necessitating large bleed ducts that add significant weight and volume to the vehicle. A heat exchanger using cryogenic fuel as the working fluid is a potential method of rapidly cooling the bleed air. An initial proof-of-concept design has been proposed by NASA Glenn Research Center (GRC). However, the feasibility and efficiency of such a device remains unknown. This project intends to create a combined fluid & thermal model of the heat exchanger to predict its efficiency and load capabilities, and then investigate how the design can be improved. A computational fluid dynamics model was set up using two different available tools to investigate different aspects of the design: tube orientation and tube profile. First, variations on the original heat exchanger were tested with different tube angles relative to the incoming flow. Then more complicated geometry was investigated where the profile of the straight tubes was twisted to create the appearance of plaited strands. These twisted braids were a way to increase the turbulence of the air flow past the tubes. The results of the simulations found that a twisted tube configuration gives the highest heat transfer rate and results in the greatest number of elements cooled at or below the liquefaction temperature of air. However, a straight-tubed configuration represented by a cross-section in the twisted tube models performed almost as well as both twisted configurations. Due to ease in manufacturing, this may be the most practical heat exchanger design for this application. The ability to efficiently cool bleed air through a compact heat exchanger could iii have potential benefits in aerospace applications. If the air could be cooled to the point of liquefaction, it could serve as an auxiliary coolant aboard aircraft and space vehicles, and potentially as an oxidizer in an auxiliary propulsion unit. This study will establish the performance of a proof-of-concept heat exchanger in support of future aerospace projects.

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