{"id":29732,"date":"2018-07-18T17:22:04","date_gmt":"2018-07-18T17:22:04","guid":{"rendered":"\/forum\/forums\/topic\/solar-distillation-process-radiation-and-natural-convection-transient-difficulty-converging\/"},"modified":"2018-07-18T17:22:04","modified_gmt":"2018-07-18T17:22:04","slug":"solar-distillation-process-radiation-and-natural-convection-transient-difficulty-converging","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/solar-distillation-process-radiation-and-natural-convection-transient-difficulty-converging\/","title":{"rendered":"Solar Distillation Process – Radiation and Natural Convection – Transient, difficulty converging"},"content":{"rendered":"

Hi, everyone!<\/p>\n

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I am quite new to CFD (Fluent 14.5) with about 4 months of reading and performing tutorials by myself. As part of my undergraduate thesis project, I need to perform a CFD analysis on a conventional solar still to determine it’s theoretical yield. The system works simply by the solar distillation process. Here is a link for a short background on the system: <http:\/\/www.solaqua.com\/solstilbas.html<\/a>><\/p>\n

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I’ve been working on this case for a month now, and my main problem, I think, is that I have a hard time choosing the correct time step rate to converge the problem and at the same time consider the number of iterations and total computing time this case will take up. Aside from that, I think I need everyone’s opinion on the quality of my case and the accuracy of the solution it will provide.<\/p>\n

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Geometry:<\/strong><\/p>\n

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Mesh:<\/strong><\/p>\n

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Nodes: 213,481<\/p>\n

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Elements: 189,069<\/p>\n

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Skewness: Max = 0.547, Ave = 0.01186<\/p>\n

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Orthogonal Quality: Min = 0.715, Ave = 0.9813<\/p>\n

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Solution Setup:<\/strong><\/p>\n

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Parallel on 2 cores<\/p>\n

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General<\/strong>: Pressure-based, absolute velocity formulation, transient case with gravity = -9.81<\/p>\n

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Multiphase<\/strong>: VOF with 3 Eulerian phases (air, water liquid, water vapor), Implicit with implicit body force checked<\/p>\n

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Energy<\/strong>: checked<\/p>\n

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Viscous: <\/strong>RNG k-epsilon withe enhanced wall treatment<\/p>\n

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Radiation<\/strong>: Surface-to-surface (S2S) with solar tracing set to experimental data<\/p>\n

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Materials: <\/strong>air, water liquid, water vapor; stainless steel, tempered glass<\/p>\n

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Phases:<\/strong> Air as primary phase, water liquid and vapor as secondary phase. Evaporation and condensation on mass interaction. Surface tension modelling with continuum surface force and wall adhesion. 72 dyn\/cm on water liquid – air and water vapor – water liquid interfaces.<\/p>\n

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Boundary Conditions: <\/strong>Bottom, glazing cover, and downcomer (collector trough) of the solar still set to constant temperature (70, 35, 35 deg C). Side walls are adiabatic with no slip condition. 45 deg contact angle for wall adhesion between phases on glazing cover. Specified operating density equal to air, least dense substance.<\/p>\n

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Solution Methods<\/strong>:<\/p>\n

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PISO Scheme. Least squares cell based. PRESTO! with second order upwind on the rest.<\/p>\n

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Default under-relaxation factors except for 0.9 on turbulent viscosity and energy (was diverging on my early attempts).<\/p>\n

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Initial conditions: Water level in the solar still is set to 3 cm at 60 deg C, while fluid is as 65 deg C (patched).<\/p>\n

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Calculation: 1 second time step size (s), 3600 time steps, with 100 max iterations per time step<\/p>\n

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I do not know how to attach my case file for the time being. I am currently solving the case again, with tweaked configuration. Anything I missed to include here kindly inform me.<\/p>\n

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WIll truly appreciate all your responses and efforts. Thanks!<\/p>\n","protected":false},"template":"","class_list":["post-29732","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t