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Engineering a Small Particle Heat Exchange Receiver for Concentrated Solar Applications

Event Type: 
Date and Time: 
Friday, April 21, 2017 - 16:15
Location: 
CTR Conference Room 103
Event Sponsor: 
Parviz Moin, Director of Center for Turbulence Research
Speaker(s): 
Professor Fletcher J. Miller, Department of Mechanical Engineering, San Diego State University and also in attendance, Dr. Miller’s Ph.D. Advisor, Dr. Arlon Hunt, former Senior Scientist at Lawrence Berkeley Laboratory

The concept of absorbing concentrated solar radiation volumetrically, rather than on a surface, is being researched by several groups with differing designs for high temperature solar receivers.  The Small Particle Heat Exchange Receiver (SPHER), one such design, is a gas-cooled central receiver capable of producing pressurized air in excess of 1000 C designed to be directly integrated into a Brayton-cycle power block to generate electricity from solar thermal power.  The unique heat transfer fluid used in the SPHER is a low-density suspension of carbon nanoparticles (diameter ~ 250 nm) to absorb highly concentrated solar radiation directly in a gas stream, rather than on a fixed absorber like a tube or ceramic foam.  The nanoparticles are created on-demand by pyrolyzing a small flow of natural gas in an inert carrier gas just upstream of the receiver, and the particle stream is mixed with air prior to injection into the receiver. The receiver features a window (or multiple windows, depending on scale) on one end to allow concentrated sunlight into the receiver where it is absorbed by the gas-particle suspension prior to reaching the receiver walls. As they pass through the receiver the carbon nanoparticles oxidize to CO2 resulting a clear gas stream ready to enter a downstream combustor or directly into the turbine.  The amount of natural gas consumed or CO2 produced is miniscule (1-2%) compared to what would be produced if the natural gas were burned directly to power a gas turbine.

The idea of a SPHER, first proposed many years ago, has been tested on a kW scale by two different groups.  In the recent work, the engineering challenges to developing a multi-MW SPHER is reported.  An in-house Monte Carlo model of the radiation heat transfer in the gas-particle mixture has been developed and is coupled to FLUENT to perform the fluid dynamic calculations in the receiver.  Particle properties (size distribution and complex index of refraction) are obtained from angular scattering and extinction measurements of natural gas pyrolysis in a lab-scale generator, and these are corroborated using SEM analysis of captured particles.  A numerical model of the particle generator has been created to allow for scale-up for a large receiver.  We have also designed a new window for the receiver that will allow pressurized operation up to 10 bar with a 2 m diameter window.  Calculations and design of a secondary concentrator and overall thermodynamic modeling of the central receiver plant will be discussed if time allows. 

Bio: 
Fletcher Miller earned a Ph.D. in Mechanical Engineering from UC Berkeley in 1988 in the area of radiation heat transfer in participating media with applications to solar energy.  After two years at the German Aerospace Center continuing research in this area, he worked at the NASA Glenn (formerly Lewis) Research Center as a member of the National Center for Microgravity Research for 16 years.  During that time he served as Principal Investigator and technical monitor for a variety of experiments on microgravity combustion and fluids in the drop facilities and on sounding rockets.  He also served as Team Lead for the Fire Prevention portion of combustion research destined for International Space Station.  In 2007 Dr. Miller joined the faculty of San Diego State University in Mechanical Engineering.  He continues to work with NASA on fire safety and microgravity combustion research as a Flight Principal Investigator, has initiated a project with NIST on modeling wind effects on wildfire, and has also been PI on several concentrating solar projects including a rival of SPHER. Also in attendance, Dr. Miller’s Ph.D. Advisor, Dr. Arlon Hunt. Dr. Hunt has a Ph.D. in Physics from the University of Arizona (1974) and spent his professional career as a Senior Scientist at Lawrence Berkeley Laboratory (1976 to 2005). He continues to be active in several areas of science and through companies he founded. Dr. Hunt has over 40 years of experience in solar thermal conversion, light scattering, instrumentation, processing of materials, and electro-optics. He was awarded a Senior Fulbright Fellowship to study industrial applications of solar thermal energy in Africa and received the Technology Transfer Award from Federal Laboratory Consortium and Excellence Award from LBNL. He also won the Energy 100 Award for the development of the Diesel Particle Scatterometer as one of the 100 most significant scientific accomplishments in the history of DOE and initiated and carried out a multinational project to build and test a solar receiver based on small particle absorption.