Search

The development of the Fluoride-salt-cooled High-temperature Reactor (FHR) is ongoing. The molten salt coolant provides several inherent safety characteristics that traditional water-cooled nuclear reactors lack. The first test reactor to be built in China is a pebble-bed type. Research efforts are currently focused on determining the heat transfer characteristics of such a reactor. In the past, the pebble-bed geometry has been studied for the development of the High Temperature Gas-cooled Reactor (HTGR). The previous work has indicated that the profile of the Nusselt number depends on both the lattice structure and pebble contact. In this work, a new series of simulations is sought to characterize heat transfer in an FHR pebble-bed. Due to the physical properties of molten salt and the FHR design, the Reynolds number is roughly three orders of magnitude lower than the HTGR while the Prandtl number is roughly an order of magnitude higher. Thus, the flow in an FHR lattice is expected to be unlike the HTGR counterpart. Three different lattices (Simple Cubic (SC), Body Centered Cubic (BCC), and Face Centered Cubic (FCC)) are considered. The study found that the different lattice geometries have a significant impact on the heat transfer characteristics. The SC lattice has a simplified flow that minimizes pressure-drop and Nusselt number. The BCC and FCC lattice have a complicated flow structure resulting in an order of magnitude higher pressure-drop and almost double the Nusselt number. It was concluded that heat transfer characteristics in a random pebble-bed would be highly sensitive to the mixing, and thus turbulent heat transfer, along the flow path. It was also found that while an interstitial gap allows heat transfer characteristics to be replicated, the pressure loss is significantly lower, while the computational costs increase. Correlations available in the literature (developed primarily for HTGRs) have a mixed performance in prediction of the Nusselt number. The result suggests that new experimental efforts are necessary to develop correlations that pertain to FHR conditions. [ABSTRACT FROM AUTHOR]

An investigation of tape layup process of a thermoplastic composite (APC-2) using a nitrogen torch is conducted. The distribution of heat transfer coefficient along the surfaces of the composite is estimated via a three-dimensional flow analysis, and the surface temperature of the composite is obtained through a two-dimensional heat conduction analysis using the finite element method (FEM). The heat transfer coefficient and the surface temperature are so interrelated that it poses a conjugate heat transfer problem. Thus, the heat transfer coefficient and the surface temperature of the composite are sought simultaneously in an iterative fashion. The computational results are presented for a specific case. KEY WORDS: thermoplastic; tape layup; conjugate heat transfer; flow analysis. [ABSTRACT FROM AUTHOR]

Resin cure following mold filling is an essential element in resin transfer molding. To fabricate a composite part with high dimensional stability and minimize residual stress, uniform resin cure should be achieved. This study considers a three-part resin system composed of epoxy, hardener and accelerator. The cure kinetics can be controlled by the accelerator concentration at the injection gate. A numerical method that can predict degree of cure distribution based on accelerator concentration at the gate was proposed. The degree of cure distribution is obtained by solving the resin flow, heat transfer, accelerator concentration and cure problems sequentially. Utilizing this numerical method, an optimal variation of accelerator concentration during mold filling was sought by solving a constrained optimization problem. The effect of accelerator control on degree of cure distribution was investigated and its validity was examined for two different geometries. [Copyright &y& Elsevier]

Systems containing interfaces between dissimilar materials can exhibit lower thermal conductivity than their pure constituents, with important implications for thermal management and thermoelectric energy conversion. However, the heat transfer processes at such interfaces, in particular those between organic and inorganic materials, remain for the most part uncharacterized. We use vacuum thermal evaporation to grow archetypal multilayer thin films of copper phthalocyanine (CuPc) and Ag or Al, and measure their thermal conductivity as a function of interface density. We observe large thermal boundary resistance values (7.8×10-8 m2 K/W for CuPc/Ag and 2.0×10-8 m2 K/W for CuPc/Al), attributable to acoustic mismatch, heat carrier mismatch, and weak bonding. [ABSTRACT FROM AUTHOR]

• Most correlations overestimate Nusselt number in comparison to numerical results. • Similar to experiments, the onset of turbulence occurs earlier in FCC than BCC. • Good agreement in surface-averaged parameters between RANS and LES models. • Significant differences in flow profile at high flowrates for the more tortuous FCC. The Fluoride salt-cooled High-temperature Reactor (FHR) is a subset of next-generation Nuclear Reactors that are under active development. The proposed pebble-bed FHR designs use a high Prandtl number molten salt coolant, 2LiF–BeF 2 , with spherical fuel elements. In order to determine convective heat transfer coefficients, packed-bed correlations available in the literature are used. However, past correlations were developed for either gas or water as the coolant, which have a low Prandtl number ( N Pr ≈ 1). This study assesses the applicability of such correlations using numerical simulations. A range of Reynolds numbers ( 10 2 ⩽ N Re ≤ 2.25 · 10 3 ) is evaluated that encompass the proposed FHR designs ( N Pr ≈ 16). The study finds that most conventional correlations miss the qualitative and quantitative trend predicted by both k ε and LES turbulence models. The Meng correlation (Meng et al., 2012) was found to provide a good agreement with numerical results. Both turbulence models have good agreement up to N Re < 10 3 for surface-averaged parameters. At higher flowrates, the secondary flows are more prominent for the LES solutions – however, the impact on the convective heat transfer coefficient is minimal. [ABSTRACT FROM AUTHOR]