Refractory metallic foams can increase heat transfer efficiency in gas-to-gas and liquid metal-to-gas heat exchangers by providing an extended surface area for better convection, i.e. conduction into the foam ligaments providing a "fin-effect, " and by disruption of the thermal boundary layer near the hot wall and ligaments by turbulence promotion. We present the relative contributions of the heat transfer mechanisms stated above, and show how the design of a gas regenerator or liquid metal-to-gas heat exchanger can be optimized for use in high-temperature Brayton cycle applications for nuclear power generation or hydrogen production. Our results include temperature and thermal stress distributions for several densities of Nb1Zr, Mo and W foams compared to Cu. For instance, the simulations reveal that unconnected W foam can increase the convective heat transfer coefficient by almost a factor of two compared to an open rectangular channel and a factor of three if the foam ligaments are thermally connected to the sidewalls under the same flow conditions. The effect of ligament thermal conductivity is also highlighted by comparing the performance of W foams to identical Cu foams and the use of SiC foams in thermal barrier applications. The studies indicate that thermal stresses increase with foam density, but are not clearly correlated with pore cell size. For thermal management applications, the presence of the connected foam minimizes the thermal stresses in the wall, by concentrating them in the ligaments where the temperature gradients are higher. In addition, the large number of small connected ligaments provides a modest degree of compliance for thermal expansion of the hotter walls in relation to the colder portions of the heat exchanger. These CFD studies have led to design strategies for creating compact, high-temperature, high-pressure heat exchangers that are easily fabricated and perform better than plate-type heat exchangers.
Chemical vapor deposited (CVD) silicon carbide (SiC) has superior resistance to tritium permeation even after irradiation. Prior work has shown Ultrametfoam to be forgiving when bonded to substrates with large CTE differences. The technical objectives are: (1) Evaluate foams of vanadium, niobium and molybdenum metals and SiC for CTE mitigation between a dense SiC barrier and steel structure; (2) Thermostructural modeling of SiC TPB/Ultramet foam/ferritic steel architecture; (3) Evaluate deuterium permeation of chemical vapor deposited (CVD) SiC; (4) D testing involved construction of a new higher temperature (> 1000 C) permeation testing system and development of improved sealing techniques; (5) Fabricate prototype tube similar to that shown with dimensions of 7cm {theta} and 35cm long; and (6) Tritium and hermeticity testing of prototype tube.
An electromagnetic analysis is performed on different first wall designs for the ITER device. The electromagnetic forces and torques present due to a plasma disruption event are calculated and compared for the different designs.
Electrical discharge in a fluid produces a transient pressure wave, which should be taken into account when designing structural components of pulsed power machines. By combining theoretical approaches for underwater explosive theory with a self-consistent approach for modeling water as a compressible non-flow material, finite element models can be used to investigate mechanical response to arc driven pressure waves. Water switch testing included impulse measurements of both multiple and single arc gaps to compare with theory. Pressure wave interactions seen in computer models were in good agreement with peak pressures measured from a three-electrode water switch. Pressure measurements from a single electrode water switch were in close approximation to predictions based on explosive theory. Structural damage tests were also conducted in which damage to machine parts were related to arc energies.