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Prediction of Ablation Rates from Solid Surfaces Exposed to High Temperature Gas FlowA mathematical model and a solution algorithm is developed to study the physics of high temperature heat transfer and material ablation and identify the problems associated with the flow of hydrogen gas at very high temperatures and velocities through pipes and various components of Nuclear Thermal Rocket (NTR) motors. Ablation and melting can be experienced when the inner solid surface of the cooling channels and the diverging-converging nozzle of a Nuclear Thermal Rocket (NTR) motor is exposed to hydrogen gas flow at temperatures around 2500 degrees Kelvin and pressures around 3.4 MPa. In the experiments conducted on typical NTR motors developed in 1960s, degradation of the cooling channel material (cracking in the nuclear fuel element cladding) and in some instances melting of the core was observed. This paper presents the results of a preliminary study based on two types of physics based mathematical models that were developed to simulate the thermal-hydrodynamic conditions that lead to ablation of the solid surface of a stainless steel pipe exposed to high temperature hydrogen gas near sonic velocities. One of the proposed models is one-dimensional and assumes the gas flow to be unsteady, compressible and viscous. An in-house computer code was developed to solve the conservations equations of this model using a second-order accurate finite-difference technique. The second model assumes the flow to be three-dimensional, unsteady, compressible and viscous. A commercial CFD code (Fluent) was used to solve the later model equations. Both models assume the thermodynamic and transport properties of the hydrogen gas to be temperature dependent. In the solution algorithm developed for this study, the unsteady temperature of the pipe is determined from the heat equation for the solid. The solid-gas interface temperature is determined from an energy balance at the interface which includes heat transfer from or to the interface by conduction, convection, radiation, and ablation. Two different ablation models are proposed to determine the heat loss from the solid surface due to the ablation of the solid material. Both of them are physics based. Various numerical simulations were carried out using both models to predict the temperature distribution in the solid and in the gas flow, and then predict the ablation rates at a typical NTR motor hydrogen gas temperature and pressure. Solid mass loss rate per foot of a pipe was also calculated from these predictions. The results are presented for fully developed turbulent flow conditions in a sample SS pipe with a 6 inch diameter.
Document ID
20140000507
Acquisition Source
Stennis Space Center
Document Type
Conference Paper
Authors
Akyuzlu, Kazim M.
(New Orleans Univ. New Orleans, LA, United States)
Coote, David
(NASA Stennis Space Center Stennis Space Center, MS, United States)
Date Acquired
January 31, 2014
Publication Date
November 13, 2013
Subject Category
Fluid Mechanics And Thermodynamics
Report/Patent Number
IMECE2013-65841
SADM-2200-0002
Meeting Information
Meeting: ASME 2013 International Mechanical Engineering Congress & Exposition
Location: San Diego, CA
Country: United States
Start Date: November 13, 2013
End Date: November 21, 2013
Sponsors: American Society of Mechanical Engineers
Funding Number(s)
CONTRACT_GRANT: NNS10AA92B
Distribution Limits
Public
Copyright
Other

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