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.

Real-fluid effects on standing-wave thermoacoustic instability

“…Around the PB region, the highly nonlinear coupling between pressure, temperature and density (thermodynamic nonlinearity) has been proposed by Herring & Heister (2006) as the reason for undesired effects such as thermoacoustic instabilities in high-pressure combustion chambers (Casiano, Hulka & Yang 2010; Poinsot & Veynante 2011) or bulk-mode oscillations in pressurized fuel heat exchangers (Hines & Wolf 1962; Faith, Ackerman & Henderson 1971; Linne et al. 1997; Hitch & Karpuk 1998; Herring 2007; Palumbo 2009; Hunt & Heister 2014; Wang et al. 2015; Hunt 2016), often leading to catastrophic hardware failure.…”

“…In particular, for fluids in transcritical, or pseudo-boiling (PB) conditions (Fisher & Widom 1969;Tucker 1999;Banuti 2015), wave-induced compressions and dilatations could be so large that periodic transitions from liquid-like fluid (pseudo-liquid) to gas-like fluid (or pseudo-gas) would occur (see figures 1 and 2). Around the PB region, the highly nonlinear coupling between pressure, temperature and density (thermodynamic nonlinearity) has been proposed by Herring & Heister (2006) as the reason for undesired effects such as thermoacoustic instabilities in high-pressure combustion chambers (Casiano, Hulka & Yang 2010;Poinsot & Veynante 2011) or bulk-mode oscillations in pressurized fuel heat exchangers (Hines & Wolf 1962;Faith, Ackerman & Henderson 1971;Linne et al 1997;Hitch & Karpuk 1998;Herring 2007;Palumbo 2009;Hunt & Heister 2014;Wang et al 2015;Hunt 2016), often leading to catastrophic hardware failure. These phenomena are similar to the multiphase instabilities called density wave oscillations (O'Neill & Mudawar 2018).…”

Quantitative evaluation of oxide impurities in bright annealed stainless steels for deep drawing

“…Impurities of the inhert gases for bright annealing treatment or impurities carried by the strip in the furnace or oxides deriving from previous operations of rolling may generate some oxide impurities on the surface of SS strips [1]. These impurities, which can be present at different degrees and have dimensions of the order of less than 1 lm, are often extremely resilient and can have negative effects if the SS is used for deep drawing [2].…”