Session: K10-03: MULTI-SCALE MULTI-PHASE HEAT TRANSFER EQUIPMENT II

Paper Number: 130976

130976 - CFD Modeling of End Effects of Gas Cooler Heat Exchanger for sCO2 Power Blocks 

Abstract: 

sCO₂ Brayton cycle power blocks for solar thermal power generation has the potential to achieve an energy conversion efficiency of up to 40% at modest temperatures of 500-550°C.  The sizing and performance of the plant & turbomachinery is strongly influenced by the sizing, rating and design of heat exchangers as they account for about 30-35% of the gravimetric density among the various components of the cycle. The gas-cooler employed in the cycle operates with sCO₂ gas on the hot-side circuit with water as a coolant in the cold-side circuit. The design of the gas cooler is predominantly influenced by the duty cycle & pressure drop constraints associated with the hot-side circuit.  Typically, microchannel heat exchangers or commonly termed as PCHE’s with plates having fin type wavy channels are a popular choice considering the thermo-structural requirements.  The channel design necessitates use of accurate physics based thermo-hydraulic performance prediction models for sizing selection & optimization of the gas cooler for meeting the required design ratings. The thermal performance of these devices is strongly influenced by the conditions prevalent on the exterior of the heat exchanger as the end effects propagate into the HX core. Modeling of the end effects though an integrated high fidelity CFD model of unit-cell coupled with a robust resistance network-based tool for the complete heat exchanger stack is the emphasis of the current work. The proposed hybrid method eliminates the uncertainties & limitations associated with the periodic unit-cell model.

The paper presents a numerical model of the Gas cooler heat exchanger for a 1 MW scale sCO2 power-block. The model consists of the conjugate heat transfer based CFD model of the unit-cell for predicting the thermo-hydraulic performance of the heat transfer surfaces. The wavy fined channels comprising of sinusoidal geometry is simplified by using coordinate transformation to an equivalent straight channel. Simplification significantly reduces the complexity of modeling by eliminating the use of periodic boundary conditions for a complex wavy channel-based unit cell. Efficacy of the computational framework is enhanced using a combination of novel grid adaptation algorithms and predictor-corrector methods. The model is extensively validated using available experimental data in the literature. Subsequently, the CFD model is coupled with a segmented thermal resistance network (TRN) framework to model the complete heat exchanger stack. Complex variations in wavy channel profiles demonstrate the improvements in thermal performance achieved for different gas cooler designs. The influence of the boundary conditions for various test cases prevailing during the duty cycle of the gas cooler highlight the importance in modeling and accounting the end effects.

Presenting Author: Vyas Duggirala Boeing Research & Technology, India

Presenting Author Biography: Vyas Duggirala 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. Vyas is currently pursing doctorate degree from the Indian Institute of Science, Bangalore.

Authors:

Vyas Duggirala Boeing Research & Technology, India
Venkata Narasimha Hedge Indian Institute of Science, Bangalore
Venkateswara Reddy Boeing Research & Technology, India
Pramod Kumar Indian Institute of Science, Bangalore
Arun Muley Boeing Research & Technology, Huntington Beach, California