Performance assessment of a new type of heat exchanger for wind tunnels

Abstract

A major upgrade to the Boeing Transonic Wind Tunnel included the replacement of an air exchanger with a brazed aluminum plate fin heat exchanger. This is the first known installation of this type of heat exchanger in an aerodynamic test facility. The inherent properties of the plate fin heat exchanger make it ideally suited for use in a wind tunnel. Very low blockage is achieved by having all piping connections outside of the wind tunnel. The high heat transfer effectiveness of the plate fin heat exchanger allows for a much smaller face area than conventional wind tunnel heat exchangers, and the mechanical arrangement provides turbulence reducing and flow straightening qualities much like a honeycomb. The key benefits of the plate fin heat exchanger that led to its installation in the Boeing Transonic Wind Tunnel are discussed in this paper. Model scale and full scale measurements are presented that summarize the performance benefits. *Senior Engineer, Member AIAA 1 Manager, Senior Member AIAA * Associate Technical Fellow, Senior Member AIAA Copyright © 2002 by The Boeing Company. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. Background The Boeing Transonic Wind Tunnel (BTWT) is a continuous flow, atmospheric facility with an 8 foot high by 12 test section containing 16 slots, giving a porosity of 11%. The 55,000 horsepower electric motor drives a two-stage fixed geometry fan. Maximum Mach number is about 1.12 with no model in the test section. A major upgrade to the BTWT was completed in 2001 and included replacing the air exchange system with a brazed aluminum plate fin heat exchanger. Heat exchangers are used to remove the heat of compression from the tunnel drive fan. Heat exchangers must be efficient and practical at removing heat with a minimum of air-side pressure loss. Air-side pressure loss is typically traded against heat exchanger frontal area a larger frontal area results in lower approach velocities and lower pressure drop. Air-side pressure loss can be a measurable component in the total wind tunnel circuit pressure loss, therefore the air side pressure loss must be balanced against the penalty of increased tunnel drive fan motor power and shell cost to accommodate the heat exchanger frontal area. Prior to the installation of a plate fin type heat exchanger in the BTWT, wind tunnel heat exchangers have been limited to various forms of finned tube heat exchangers. A typical finned tube arrangement is presented in Figure 1. There are a number of heat exchanger materials available to the wind tunnel designer to best fit each tunnel application. A typical finned tube heat exchanger arrangement would include a series of modules installed within a support structure placed in the tunnel. For this type of arrangement, it is not uncommon for the blockage due to the structural support to be as high as 25%. 1 American Institute of Aeronautics and Astronautics (c)2002 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.