Session: 13-08 Heat Exchangers (II)

Paper Number: 129516

129516 - Modeling of Metal Matrix Concentrated Solar Receivers for sCO2 Power Blocks 

sCO2 Brayton-cycle power blocks have the potential to achieve an energy conversion efficiency of up to 40% which can significantly reduce the lifetime costs associated with a concentrating solver power system.  A metal matrix compact source heat exchanger for transfer of solar thermal energy via molten salt to sCO2 is an attractive proposition for a central receiver system. However, challenges to realize the heat exchangers involve the ability to withstand a high temperature corrosive environment on the molten salt side and high pressures & temperatures (> 100 bar & 700 °C) on the sCO2 side. These challenges impose stringent material requirements which necessitates the use of advanced creep resistant Nickel alloys such as Haynes-242.

The Heat exchanger sizing & detailed thermo-hydraulic analysis is a critical aspect to realize these novel configurations. A cylindrical heat exchanger with corrugated sinusoidal channels embedded inside a molten salt pool is studied for a thermo-hydraulic performance for various plant operating scenarios. A CFD based transient coupled conjugate modeling of molten salt pool using enthalpy-porosity technique that is coupled with a high-fidelity convection-diffusion modeling on sCO2 inside wavy microchannels.  The thermo-hydraulic performance of the heat exchanger is evaluated by converting a sinusoidal wavy channel into an equivalent rectangular channel through coordinate transformations. The transformed system is solved numerically within a 3D finite volume framework using a combination of gradient-based adaptive gridding and convergence acceleration methods.

The present work evaluates the thermal performance of integrated heat exchanger for various popular molten salts such as ternary chloride molten salt mixture of MgCl2/NaCl/KCl. Further, Zinc-Aluminum based eutectic alloys is also evaluated as thermal storage media. A thermodynamic model of sCO2 based power cycle is utilized to estimate the requirements of pressure drop along with the associated implications of power plant equipment sizing on the heat exchanger performance. Transient simulations are carried out on different microchannel arrangements along with a parametric study of wavy microchannels to estimate the relative sensitivity of channel amplitude & pitch on the thermo-hydraulic performance. The thermal model of the compact heat exchanger is evaluated for effectiveness, weight & pressure drop penalties along the sCO2 side. The thermal performance results of the cylindrical heat exchanger are compared against literature standard configurations such as the compact honeycomb heat exchanger to gauge the relative benefits of the proposed cylindrical configuration. The results of the parametric study along with channel arrangements are used to determine the set of geometric & flow variables to maximize the power density while limiting the sCO2 pressure drop to within 1% of the inlet pressure.

Presenting Author: Vyas Duggirala Indian Institute of Science, Bangalore

Presenting Author Biography: Vyas is a PhD research scholar at Indian Institute of Science, Bangalore working on CFD modeling & optimization of heat exchangers for sCO2 power cycle applications. Vyas joined Boeing Research & Technology-India, Integrated Vehicle Systems group as a mechanical systems design & analysis engineer in May 2019. Vyas`s expertise is in the development of numerical conjugate heat transfer-based methods and tools for thermal-fluid system design and analysis. He is actively working in the areas of CFD based methodologies for thermal-hydraulic performance characterization of novel AM enabled heat transfer surfaces, modeling and analysis of extreme environment heat exchangers and development of physics-based semi empirical correlation methods. He has collaborated extensively with BR&T teams in the US during development of these capabilities, and transitioning them to business units. Of late his research interests are towards hybrid modeling approaches for heat exchangers, AM process thermal modeling, and development of medium and high-fidelity methods and tools for two-phase heat transfer systems. Prior to Boeing, Vyas worked at Honeywell Aerospace and Indian Space Research Organization for about 7 years in the areas of Thermal management of electronics and spacecraft payloads. He received his BE in Mechanical Engineering from Osmania University, India in 2010 and M.Tech in Mechanical Engineering from Indian Institute of Technology, Bombay in 2015.

Authors:

Vyas Duggirala Boeing Research & Technology
Venkatanarasimha Hegde Indian Institute of Science
Venkateswara Reddy Boeing Research & Technology, India
Pramod Kumar Indian Institute of Science