Review of the Development of Compact, High Performance Heat Exchangers for Gas Turbine Applications

Abstract

This study provides a review of the current state-of-the-art in compact heat exchangers and their application to gas turbine thermal management. Specifically, the challenges and potential solutions for a cooled cooling air system using the aircraft fuel as a heat sink were analyzed. As the sensible heat absorbed by the fuel in future engines is increased, the fuel will be exposed to increasingly hotter temperatures. This poses a number of design challenges for fuel-air heat exchangers. The most well known challenge is fuel deposition or coking. Another problem encountered at high fuel temperatures is thermo-acoustic oscillations. Thermo-acoustic oscillations have been shown to occur in many fluids when heated near the critical point, yet the mechanism of these oscillations is poorly understood. In some cases these instabilities have been strong enough cause failure in the thin walled tubes used in heat exchangers. For the specific application of a fuel-air heat exchanger, the advantages of a laminar flow device are discussed. These devices make use of the thermal entry region to achieve high heat transfer coefficients. To increase performance further, heat transfer enhancement techniques were reviewed and the feasibility for aerospace heat exchangers was analyzed. Two of the most basic techniques for laminar flow enhancement include tube inserts and swirl flow devices. Additionally, the effects of these devices on both coking and instabilities have been assessed.