Search results for "Nusselt number"
showing 7 items of 17 documents
Internal geometry and coolant choices for solid high power neutron spallation targets
2014
Abstract The next generation of neutron spallation sources envisages high power proton beam interaction with a heavy metal target. Solid targets have potentially higher spallation efficiency due to the possibility to use metals with higher density than used in liquid metal targets, but to realize this potential the solid fraction must be high enough. As the power released in the form of heat can reach several MW in the target volume of typically 10 l, target cooling can be a serious challenge. Heat evacuation efficiency for different solid fraction geometries at high power is analyzed for different coolant options (helium, water and gallium) using empirical correlations for friction factors…
Magnetic Control of Convection in Liquid Metal Heated from Above
1999
We investigated experimentally the buoyancy driven convection induced by localized central heating from above in cylindrical tanks filled with liquid metal eutectic alloy (low-Prandtl-number liquid). The experiments were carried out for two aspect ratios A = (radius/height) = 4.125 and 0.333. Time-averaged local temperature distributions and radial and azimuthal velocity components in the liquid at different distances from heater axis were measured. It is shown that maximum temperature gradient is centered in vicinity heater. Temperature difference in radial direction creates pressure gradient between heater and cold wall regions. This gradient leads to upraising of liquid nearly heater and…
On the influence of curvature and torsion on turbulence in helically coiled pipes
2014
Turbulent flow and heat transfer in helically coiled pipes at Ret=400 was investigated by DNS using finite volume grids with up to 2.36×10^7 nodes. Two curvatures (0.1 and 0.3) and two torsions (0 and 0.3) were considered. The flow was fully developed hydrodynamically and thermally. The central discretization scheme was adopted for diffusion and advection terms, and the second order backward Euler scheme for time advancement. The grid spacing in wall units was ~3 radially, 7.5 circumferentially and 20 axially. The time step was equal to one viscous wall unit and simulations were typically protracted for 8000 time steps, the last 4000 of which were used to compute statistics. The results sho…
Fully developed laminar flow and heat transfer in serpentine pipes
2015
Abstract A serpentine pipe is a sequence of parallel straight pipe segments connected by U-bends. Its geometry is fully characterized by pipe radius, a , bend curvature radius, c and length of the straight segments, l . The repeated curvature inversion forces the recirculation (secondary flow) pattern to switch between two specular configurations, which may enhance mixing and heat or mass transfer with respect to a constant-curvature pipe at the cost of an increase in pressure drop. In the present work, fully developed laminar flow and heat transfer in serpentine pipes were investigated by numerical simulation. The curvature δ = a / c was made to vary between 0.1 and 0.5 while the paramet…
Numerical prediction of turbulent flow and heat transfer in helically coiled pipes
2010
Abstract Computational results were obtained for turbulent flow and heat transfer in curved pipes, representative of helically coiled heat exchangers. Following a grid refinement study, grid independent predictions from alternative turbulence models ( k – ɛ , SST k – ω and RSM– ω ) were compared with DNS results and experimental pressure drop and heat transfer data. Using the SST k – ω and RSM– ω models, pressure drop results were in excellent agreement with literature data and the Ito correlation. For heat transfer, the literature is not comparably complete or accurate, but a satisfactory agreement was obtained in the range of available data. Unsatisfactory results, both for pressure drop …
CFD prediction of flow, heat and mass transfer in woven spacer-filled channels for membrane processes
2021
Abstract Flow and heat or mass transfer in channels provided with woven spacers made up of mutually orthogonal filaments were studied by Computational Fluid Dynamics. The problem addressed was the combined effect of the parameters that characterize the process: pitch to height ratio P/H (2, 3 and 4), flow attack angle θ (0, 7, 15, 20, 30, 40 and 45°) and Reynolds number Re (from ~1 to ~4000). The Prandtl number was 4.33, representative of water at ~40°C, while the Schmidt number was 600, representative of NaCl solutions. Simulations were performed by the finite volume code Ansys CFX™ 18.1 using very fine grids of ~6 to ~14 million volumes. For Re > ~400, the SST turbulence model was used to…
Application of computational fluid dynamics technique in membrane distillation processes
2022
This Chapter illustrates the application of CFD to spacer-filled channels for membrane distillation. The topics discussed cover finite volume grids and grid independence, the unit-cell treatment of spatially periodic net spacers, and the dependence of flow and thermal fields and overall performance parameters (pressure drop and mean heat transfer coefficients) upon geometry and operating conditions (Reynolds number, flow attack angle, pitch-to-height ratio, spacer thermal conductivity, thermal boundary conditions, and one-side vs. two-side heat transfer).