Publications

Youchison, Dennis L.; Lenard, Roger X.

Abstract not provided.

Fusion Engineering and Design

Tanaka, T.J.; Bauer, F.J.; Lutz, Thomas J.; McDonald, Jimmie M.; Nygren, Richard E.; Troncosa, K.P.; Ulrickson, M.A.; Youchison, Dennis L.

This paper describes the liquid metal integrated test system (LIMITS) at Sandia National Laboratories1. This system was designed to study the flow of molten metals and salts in a vacuum as a preliminary study for flowing liquid surfaces inside of magnetic fusion reactors. The system consists of a heated furnace with attached centrifugal pump, a vacuum chamber, and a transfer chamber for storage and addition of fresh material. Diagnostics include an electromagnetic flow meter, a high temperature pressure transducer, and an electronic level meter. Many ports in the vacuum chamber allow testing the thermal behavior of the flowing liquids heated with an electron beam or study of the effect of a magnetic field on motion of the liquid. Some preliminary tests have been performed to determine the effect of a static magnetic field on stream flow from a nozzle. © 2004 Elsevier B.V. All rights reserved.

Youchison, Dennis L.; Lutz, Thomas J.; McDonald, Jimmie M.; Nygren, Richard E.

Abstract not provided.

Surface and Coatings Technology

Youchison, Dennis L.; Gallis, Michail A.; Nygren, Richard E.; McDonald, Jimmie M.; Lutz, Thomas J.

The development of advanced thermal barrier coatings of yttria stabilized zirconia (YSZ) that exhibit lower thermal conductivity through better control of electron beam-physical vapor deposition (EB-PVD) processing is of prime interest to both the aerospace and power industries. Recently, processing technology was developed to create graded TBCs by coupling ion beam assisted deposition (IBAD) with substrate pivoting in the alumina-YSZ system. The Electron Beam-1200 kW (EB-1200) PVD system was used to deposit a variety of TBC coatings with micron layered microstructures and reduced thermal conductivity of 1.5 W/mK. The use of IBAD produced fully stoichiometric coatings at a reduced substrate temperature of 600 °C and a reduced oxygen background pressure of 0.1 Pa. In addition to the process technology, the results of Direct Simulation Monte Carlo plume modeling and spectroscopic characterization of the PVD plumes are presented. © 2003 Elsevier B.V. All rights reserved.

Youchison, Dennis L.

A FORTRAN computer code has been written to calculate the heat transfer properties at the wetted perimeter of a coolant channel when provided the bulk water conditions. This computer code is titled FILM-30 and the code calculates its heat transfer properties by using the following correlations: (1) Sieder-Tate: forced convection, (2) Bergles-Rohsenow: onset to nucleate boiling, (3) Bergles-Rohsenow: partially developed nucleate boiling, (4) Araki: fully developed nucleate boiling, (5) Tong-75: critical heat flux (CHF), and (6) Marshall-98: transition boiling. FILM-30 produces output files that provide the heat flux and heat transfer coefficient at the wetted perimeter as a function of temperature. To validate FILM-30, the calculated heat transfer properties were used in finite element analyses to predict internal temperatures for a water-cooled copper mockup under one-sided heating from a rastered electron beam. These predicted temperatures were compared with the measured temperatures from the author's 1994 and 1998 heat transfer experiments. There was excellent agreement between the predicted and experimentally measured temperatures, which confirmed the accuracy of FILM-30 within the experimental range of the tests. FILM-30 can accurately predict the CHF and transition boiling regimes, which is an important advantage over current heat transfer codes. Consequently, FILM-30 is ideal for predicting heat transfer properties for applications that feature high heat fluxes produced by one-sided heating.

Fusion Technology

Youchison, Dennis L.; North, Mark T.

Helium-cooled, refractory heat exchangers are now under consideration for first wall and divertor applications. These refractory devices take advantage of high temperature operation with large delta-Ts to effectively handle high heat fluxes. The high temperature helium can then be used in a gas turbine for high-efficiency power conversion. Over the last five years, heat removal with helium was shown to increase dramatically by using porous metal to provide a very large effective surface area for heat transfer in a small volume. Last year, the thermal performance of a bare-copper, dual-channel, helium-cooled, porous metal divertor mock-up was evaluated on the 30 kW Electron Beam Test System at Sandia National Laboratories. The module survived a maximum absorbed heat flux of 34.6 MW/m2 and reached a maximum surface temperature of 593 °C for uniform power loading of 3 kW absorbed on a 2-cm2 area. An impressive 10 kW of power was absorbed on an area of 24 cm2. Recently, a similar dual-module, helium-cooled heat exchanger made almost entirely of tungsten was designed and fabricated by Thermacore, Inc. and tested at Sandia. A complete flow test of each channel was performed to determine the actual pressure drop characteristics. Each channel was equipped with delta-P transducers and platinum resistance temperature devices (RTDs) for independent calorimetry. One mass flow meter monitored the total flow to the heat exchanger, while a second monitored flow in only one of the channels. The thermal response of each tungsten module was obtained for heat fluxes in excess of 5 MW/m2 using 50 °C helium at 4 MPa. Fatigue cycles were also performed to assess the fracture toughness of the tungsten modules. A description of the module design and new results on flow instabilities are also presented.

Youchison, Dennis L.

Abstract not provided.

Nygren, Richard E.; Youchison, Dennis L.; McDonald, Jimmie M.; Lutz, Thomas J.; Miszkiel, Mark E.

In the authors initial high heat flux tests on small mockups armored with W rods, done in the small electron beam facility (EBTS) at Sandia National Laboratories, the mockups exhibited excellent thermal performance. However, to reach high heat fluxes, they reduced the heated area to only a portion ({approximately}25%) of the sample. They have now begun tests in their larger electron beam facility, EB 1200, where the available power (1.2 MW) is more than enough to heat the entire surface area of the small mockups. The initial results indicate that, at a given power, the surface temperatures of rods in the EB 1200 tests is somewhat higher than was observed in the EBTS tests. Also, it appears that one mockup (PW-10) has higher surface temperatures than other mockups with similar height (10mm) W rods, and that the previously reported values of absorbed heat flux on this mockup were too high. In the tests in EB 1200 of a second mockup, PW-4, absorbed heat fluxes of {approximately}22MW/m{sup 2} were reached but the corresponding surface temperatures were somewhat higher than in EBTS. A further conclusion is that the simple 1-D model initially used in evaluating some of the results from the EBTS testing was not adequate, and 3-D thermal modeling will be needed to interpret the results.