| |
Materials
For DE
PROJECTS
Recuperator
Alloys/Heat Exchangers
Advanced,
high efficiency microturbines will require improved high-temperature
performance and reliability from their recuperators in order to
achieve higher efficiency. This means that materials with more oxidation
and corrosion resistance and tensile/creep strength at higher temperatures
are required. Existing alloy candidates are much too costly, so
lower cost alternatives are being sought. ORNL is working with microturbine
manufacturers and material suppliers to develop advanced alloy,
high temperature recuperators.
Projects
Advanced
Alloys for High-Temperature Recuperators
- Dr. Philip Maziasz
Recuperator
Alloys – Composition Optimization for Corrosion
Resistance
- Dr. Bruce Pint
Recuperator
Materials Testing
- Dr. Edgar Lara-Curzio
Characterization of Porous Graphite Foam as Material for Compact Recuperators
- Dr. Tony Straatman & Beth Armstrong
Accomplishments
New Recuperator Alloy Commercialized (FY 05/06)
ORNL Facility Evaluates High Temperature Recuperator Materials (FY 04)
Long-Term Testing of Recuperator Alloys Provides Insight into Oxidation Mechanisms (FY 04)
Posters
Recuperator Materials Testing (PDF 797KB)
Advanced
Alloys for High-Temperature Recuperators
Contact:
Dr. Philip Maziasz
Oak Ridge National Laboratory
Bethel Valley Rd
PO Box 2008
Oak Ridge, TN 37831-6116
(865) 574-5082
maziaszpj@ornl.gov
Recuperators for industrial turbines and microturbines have traditionally been made from 347 stainless steel, but problems with performance and durability occur as temperatures approach or exceed 650-700°C, particularly in moist air. Previous ORNL work has shown HR120 and 625 alloys have better creep and oxidation performance at these temperatures. Foil testing in the ORNL Recuperator Test Facility has further shown that HR 120 is better than HR230, and is vastly superior to 347 steel, in this temperature range.
In 2003-2004 Allegheny-Ludlum (AL) introduced a new high temperature alloy AL2025+Nb. In 2005, ORNL and AL engaged in a joint project to produce a range of commercial foils and sheets from the new AL20-25+Nb alloy, and to supply foils to commercial microturbine recuperator producers for manufacturing trials. ORNL and Allegheny-Ludlum further performed an initial mill-scale experiment to adjust sheet/foil processing parameters for improved alloy creep resistance. The initial results showed excellent creep resistance for the 4-5 mil foils, improved behavior compared with HR120 and much better creep-resistance compared to 347 steel. Processing experiments continue to boost the creep resistance of the 10-15 mil sheet products required for brazed plate and fin recuperators. Initial manufacturing trials at Ingersoll-Rand indicate similar, or better, manufacturing behavior for the AL20-25+Nb compared with 347 steel.
Initial alloy development efforts on ORNL-modified 347 steels and Fe-20Cr-20Ni alloys were completed in FY 2005, and further emphasis will be on aluminum-modified versions of 347 steel, which show outstanding oxidation resistance, but currently lack creep strength. These new alloys (with oxidation resistance based on alumina scale formation) have the potential to offer significant improvements in performance and temperature capability, particularly in alternate fuel environments, relative to commercial austenitic stainless steels, alloys, or nickel-based superalloys. The goal is to develop and down-select the most promising composition for commercial scale-up and foil processing.
|
 |
 |
The latest and archived Quarterly Progress Reports are
available in the on-line material in the Reports section.
Recent Publications: Refer to the Bibliography section
for more publications
P.J. Maziasz, J.P. Shingledecker, B.A. Pint, N.D. Evans, Y. Yamamoto, K.L. More, and E. Lara-Curzio, "Overview of Creep Strength and Oxidation of Heat-Resistant Alloy Sheets and Foils for Compact Heat Exchangers," ASME PAPER #GT2005-68297, presented at IGTI TurboExpo 2005, Reno, NV, June, 2005. (PDF 1,342KB)
P.J. Maziasz, B.A. Pint, J.P. Shingledecker, K.L. More, N.D. Evans, and E. Lara-Curzio, “Austenitic Stainless Steels and Alloys With Improved High-Temperature Performance for Advanced Microturbine Recuperators,” ASME paper #GT2004-54239, presented at IGTI Turbo Expo 2004, Vienna, Austria, June 14-16, 2004. (PDF 1,738KB)
Maziasz, P. J., Swindeman, R. W., Shingledecker, J. P. More, K.L. Pint, B. A., Lara-Curzio, E., and Evans, N.D., “Improving High-Temperature Performance of Austenitic Stainless Steels for Advanced Microturbine Recuperators”, Parsons 2003: Engineering Issues in Turbine Machinery, Power Plants and Renewables, 1057-1073, (2003). (PDF 1,078KB)
Recent Presentations: Refer to the Bibliography section for more presentations
P.J. Maziasz, J.P. Shingledecker, B.A. Pint, N.D. Evans, Y. Yamamoto, K.L. More, and E. Lara-Curzio, “Overview of Creep Strength and Oxidation of Heat-Resistant Alloy Sheets and Foils for Compact Heat-Exchangers”, GT2005-68927, ASME Turbo Expo 2005, June 2004, Reno, Nevada. (PDF 2,133KB)
P.J. Maziasz, J.P. Shingledecker, B.A. Pint, N.D. Evans, K.L. More, and E. Lara-Curzio, "Overview of Creep Strength and Oxidation of Heat-Resistant Alloy Sheets and Foils for Compact Heat Exchangers," ASM Materials Solutions, Fuel Cells: Materials, Processing, & Manufacturing Technologies Symposium, October 2004, Columbus, OH. (PDF 6,145KB)
N. D. Evans, P.J. Maziasz, and J.P. Shingledecker, “Creep-Testing Foils and Sheets of Alloy 625 for Microturbine Recuperators”, 6th International Superalloys Symposium
October, 2005, Pittsburgh, PA. (PDF 5,644KB)
Recuperator
Alloys – Composition Optimization for Corrosion Resistance
Contact
Dr. Bruce Pint
Oak Ridge National Laboratory
Bethel Valley Rd
PO Box 2008
Oak Ridge, TN 37831-6156
(865) 576-2897
pintba@ornl.gov
Stainless steels currently used in microturbine recuperators are limited to temperatures of about 675oC because of excessive oxidation due to the presence of water vapor in the exhaust gas. It has been widely recognized that higher-alloyed steels are needed in microturbine recuperators to resist the accelerated attack. The use of more expensive alloys has increased manufacturer’s recuperator durability goals from 40,000 to 80,000 hours. Therefore, it is crucial to quantify the degradation rate for new candidate alloys in order to model performance over this extended time scale. Prior work has yielded a better understanding of the alloy degradation mechanism in air with water vapor. In the presence of water vapor, Cr is lost more rapidly during long-term exposures due to the evaporation of chromium oxy-hydroxide from the surface. Depletion in the metal leads to the rapid formation of thick Fe-base surface oxides, which degrades heat transfer in the recuperators and eventually leads to failure.
The goal of this work is to determine Cr loss rates for several new commercial and laboratory-produced alloy foil materials (such as HR120, AL 20-25+Nb, 625) as a function of time and temperature (650°-700°C) to assist in the development of a more accurate lifetime models. Chromium loss rates will be measured after 1,000-10,000 hour laboratory exposures. These results will be compared to Cr losses observed for similar materials exposed in the ORNL microturbine recuperator test facility in order to determine a scaling factor for the measured laboratory Cr loss data. The latest and archived Quarterly Progress Reports are
available in the on-line material in the Reports section.
Recent Publications: Refer to the Bibliography section for more publications
B. A. Pint, K. L. More, R. Trejo and E. Lara-Curzio, (2006) “Comparison of Recuperator Alloy Degradation in Laboratory and Engine Testing,” ASME Paper #GT2006-90194, to be presented at the International Gas Turbine & Aeroengine Congress & Exhibition, Barcelona, Spain, May 8-11, 2006. (PDF 261KB)
B.A. Pint, "The Effect of Water Vapor on Cr Depletion in Advanced Recuperator Alloys," ASME PAPER #GT2005-68495, presented at IGTI TurboExpo 2005, Reno, NV, June, 2005. (PDF 192KB)
B.A. Pint and P.J. Maziasz, "Development of High Creep Strength and Corrosion-Resistant Stainless Steels," NACE Paper #05-449, presented at NACE Corrosion 2005, Houston, TX, April 2005. (PDF 326KB)
B. A. Pint and K. L. More, (2004) "Stainless Steels with Improved Oxidation Resistance for Recuperators,” ASME Paper #GT2004-53627, presented at the International Gas Turbine & Aeroengine Congress & Exhibition, Vienna, Switzerland, June 14-17, 2004.
Recent Presentations: Refer to the Bibliography section for more presentations
Recuperator
Materials Testing and Evaluation
Contact:
Dr. Edgar Lara-Curzio
Oak Ridge National Laboratory
Bethel Valley Rd
PO Box 2008
Oak Ridge, TN 37831-6098
(865) 574-1749
laracurzioe@ornl.gov
The objectives of this project are to screen and to evaluate candidate materials for the next generation of microturbine recuperators, and to identify the mechanisms responsible for alloy degradation after exposure to a microturbine exhaust environment in ORNL’s Microturbine Recuperator Test Facility (MRTF). The objectives have been achieved by placing foils of candidate alloys at the entrance of the annular recuperator in a Capstone microturbine modified to operate at turbine exit temperatures as high as 850°C. Using specially-designed sample holders, the test specimens can be stressed mechanically, thus recreating the conditions of stress, temperature and environment that are expected to exist in the next generation of advanced microturbine recuperators.
During FY05, numerous alloys (including HR120®, HR214®, AL 20-25+Nb, IN 625, and ORNL-modified stainless steels) were exposed to temperatures up to 760°C for 500 hour test campaigns for accumulated exposure times greater than 3000 hours. Post-exposure mechanical and microstructural characterization provided insight into the mechanisms that lead to the formation of oxide scales, alloy compositional changes, and precipitation of complex phases at alloy grain boundaries.
In the future, the exposure and evaluation of these materials, and particularly HR120® and AL 20-25+Nb, will continue. Complete exposures of test specimens of these alloys for periods of time approaching 10,000 hours at temperatures as high as 760°C is planned. Such information will be invaluable to support the formulation and verification of life prediction models for microturbine recuperators.
Thermal cycling is a potential limiting factor on the durability of microturbine recuperator materials, particularly for microturbines that would be used under variable loading profiles. To investigate this effect, a device that inserts and retrieves test specimens at regular time intervals was built for ORNL’s MRTF. This device will be used to investigate the effect of intermittent microturbine operation on the durability of candidate alloys in parallel to static exposure experiments. Intermittent exposure experiments, coupled with post-test mechanical, microstructural and chemical characterization of the test specimens will be used to understand the factors that affect durability under thermal cycling conditions and to further aid in the formulation of life prediction models. The latest and archived Quarterly Progress Reports are
available in the on-line material in the Reports section.
Recent Publications: Refer to the Bibliography section for more publications
E. Lara-Curzio, R. Trejo, K.L. More, P.J. Maziasz, and B.A. Pint, "Evaluation and Characterization of Iron- and Nickel-Based Alloys for Microturbine Recuperators," ASME PAPER #GT2005-68630, presented at IGTI TurboExpo 2005, Reno, NV, June, 2005. (PDF 2,056KB)
E. Lara-Curzio, R. Trejo, K.L. More, P.A. Maziasz, and B.A. Pint, “Screening and Evaluation of Materials for Microturbine Recuperators,” ASME Paper #GT2004-54254, presented at the International Gas Turbine & Aeroengine Congress & Exhibition, Vienna, Switzerland, June 14-17, 2004. (PDF 1,707KB)
Lara-Curzio E., Maziasz, P. J., Pint B. A., “Test Facility for Screening and Evaluating Candidates Materials for Advanced Microturbine Recuperators,” ASME Technical Paper GT 2002- 30581. (PDF 359KB)
Presentations: Refer to the Presentations section for additional presentations
Lara-Curzio, E., Trejo, R. M., More, K. L., Dryepondt, S., Maziasz, P. A. and Pint. B. A., “Screening and Evaluation of Materials for Advanced Microturbine Recuperators”, ASME Presentation, Reno, Nevada, June 2005. (PPT 11,333 KB)
Lara-Curzio, E., Trejo, R. M., More, K. L., Maziasz, P. A. and Pint. B. A.,”Screening and Evaluation of Materials for Advanced Microturbine Recuperators” ASME Presentation, Vienna, Austria, June 2004. (PPT 13,145 KB)
Characterization of Porous Graphite Foam as Material for Compact Recuperators
Contact: Ms. Beth Armstrong
Oak Ridge National Laboratory
Bethel Valley Rd
PO Box 2008
Oak Ridge, TN 37831-6063
(865) 241-5862
armstrongbl@ornl.gov
Cast or foamed materials such as porous graphite foam typically have an open, interconnected void structure which enables fluid exposure to internal surface area and have the potential for significant convective heat transfer. Thus, such materials have the potential for wide application in energy exchange and heat recovery. Porous graphite foam is produced by a process of foaming, carbonization and subsequent graphitization of a carbon-based precursor material. This foam has a higher conductivity than aluminum foams of similar porosity, and a larger internal surface area than metal foams. It is this combination of high material conductivity and high internal surface area that makes porous graphite foam attractive as a heat transfer material for both single and multiphase applications.
|
 (Left)Electron micrograph of the Carbon Foam surface; (Right) Electron micrograph of the Carbon Foam, the porosity=0.9 and the pore diameter=400 um. |
This work first explores the heat transfer and pressure drop obtained when passing fluid through the internal structure of three different porous graphite foam specimens of different porosity and pore diameter in a small-scale test rig. The pressure drop depends on the pore diameter and porosity, but is also strongly affected by the size of the cell windows connecting the spherical pores. This is due to the large hydrodynamic loss associated with the fluid contracting/expanding through the windows. The heat transfer depends on the effective conductivity and the internal surface area, as might be expected. The results to date suggest that there may be a significant advantage for using porous graphite foam as an extended surface convective enhancement material in energy exchange and electronic cooling applications.
The latest and archived Quarterly Progress Reports are available in the on-line material in the Reports section.
Recent Publications: Refer to the Bibliography section for more publications
Yu, Q, Straatman, A. G., Thompson, B. E., “Carbon-Foam Finned Tubes in Air-Water Heat Exchangers,” Applied Thermal Engineering, 26, 131-143, 2006. (PDF 514KB)
Straatman, A. G., Gallego, N., Thompson, B. E., Hangan, H., “Thermal Characterization of Porous Carbon Foam – Convection in Parallel Flow,” Accepted in Int. J. Heat Mass Transfer, December 2005.
Betchen, L. J., Straatman, A. G., “Interface conditions for a non-equilibrium heat transfer model for conjugate fluid/porous/solid domains,” The 13th Annual Conference of the CFD Society of Canada, St. John’s, Canada, July 2005. (PDF 224KB)
Yu, Q., Thompson, B. E., Straatman, A. G., “Carbon Foam – New Generation of Enhanced Surface Compact Recuperators for Gas Turbines,” Proceedings of ASME Turbo Expo 2005, Reno-Tahoe, Nevada, June 6-9, 2005. (PDF 281KB)
Yu, Q., Thompson, B. E., Straatman, A. G., “Thermal Engineering Model of a Heat Exchanger with Finned-Tubes Made from Porous Carbon Foam,” CSME Forum 2004, The University of Western Ontario, London, Canada, June 2004. (PDF 415KB)
Recent Presentations: Refer to the Bibliography section for more presentations
Lara-Curzio, E., Maziasz, P. J., Pint, B. A., Stuart, M., Hamrin, D., Lipovich, N., DeMore, D., “Test Facility for Screening and Evaluating Candidates Materials for Advanced Microturbine Recuperators,” ASME Presentation, Amsterdam, The Netherlands, June, 2002. (PDF 979KB)
|
