One-Dimensional Heat Transfer Analysis of an Annular Gas Turbine Combustor Liner with Integrated Ammonia Cracker

Le résumé fourni par la source

Ammonia is a promising alternative fuel for net-zero commercial aviation. However, its direct combustion is largely inefficient. This can be solved with an onboard catalytic cracking unit to produce hydrogen, which can significantly improve combustion. One potential approach is integrating the cracking unit hardware around the combustor liner, utilizing heat from the combustion process. A one-dimensional thermal energy balance model is developed by analyzing both internal and external radiation, convective, and conductive heat transfer. The radiative exchange is modeled using a nonluminous gray-body assumption, with water vapor (H2O) being the primary radiating species. The convective coefficients are the most difficult term to calculate due to rapid changes of velocity and properties by the combustion process and also the chamber geometry. This study compares two approaches to evaluate the heat transfer modes: a two-surface radiative enclosure (infinite length) using classical Dittus-Boelter relations for convection, and a four-surface enclosure (finite length) using a modified Gnielinski correlation. The analytical approach uses the conjugate heat transfer (CHT) method to solve the energy balance. For the four-surface enclosure, the radiative view factors are calculated using Hottel Strings approach with reciprocity and summation laws. This analytical study can serve as an initial design tool for the estimation of liner temperatures and evaluating the relative contributions and magnitude of heat flux through the liner. Results indicate using Dittus-Boelter under predicts the internal convective load by ~50% compared to using the modified Gnielinski’s solution. The internal radiation heat flux increases by ~120kW/m2 when using the four-surface model due to the wall boundaries contributing significantly to radiation. By keeping the power supplied constant and reducing the mass flow rate of ammonia by factors of 2, there was a boost in conversion efficiency up to ~12%. This is due to the lower energy requirement for cracking less moles of ammonia.

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