Hello... In the surface evaporation of water, what is the representative Rayleigh's number?
The Rayleigh number is equal to the Grashof number times the Prandtl number and is often used to form empirical correlations from experimental data. The Grashof number is often used to characterize natural convection (as might occur over the surface of a pond or lake). The Prandtl number is often used to relate heat transfer and fluid flow. Representative Rayleigh numbers would come from the paper(s) presenting the experimental data, of which there are many on evaporation from various water bodies. I have personally done a lot of work with large ponds used to cool power plants, specifically Braidwood and Wolf Creek Nuclear Plants. What aspects of this topic are you investigating?
Hello... Thank you Mr. Dudley J Benton for taking the time to answer my question.
The purpose of my research is about the Rayleigh number in small open reservoirs that are under the influence of evaporation due to solar radiation and wind speed.
I have done a lot of lake, pond, reservoir, and estuary modeling. My favorite software for this is EFDC. I helped with several enhancements, including dynamic memory allocation. The source code is available so that you can add features if it doesn't already have them. It's also free. I have dozens of animations based on EFDC models. (You have to download the GIF to see the animation, as RG doesn't play animations anymore.)
As an academic point, dimensionless groups such as Ra were originally used where the appropriate natural forces were considered when correlating data for a range of fluids under similar conditions. Thus, Re is the ratio of turbulent drag to viscous drag; Nu the ratio of convective to conductive heat transfer. The more complicated groups, like Ra =Gr.Pr arose later from practical experience of plotting data. Gr is a ratio of bouyancy to viscous forces; Pr is a physical properties ratio that allows well for significant interface effects.
For this and other projects... There is a chapter in the CRC Handbook of Chemistry and Physics that contains several tables, including: a list of dozens of dimensionless numbers and what variables and properties are in each one. There is also a table of properties and which dimensionless numbers contain them. From these tables you can discover a list of every dimensionless number that might have something to do with the process or phenomenon you are studying. When you are studying something relatively new or for which there isn't a large body of literature, this is one way of considering how it might be related to other areas of study. There is also a nice list on Wikipedia https://en.wikipedia.org/wiki/List_of_dimensionless_quantities
Rayleigh's number is a dimensionless number used in fluid dynamics and heat transfer to determine the occurrence of convection or buoyancy-driven flow in a fluid system. Rayleigh's number (Ra) represents the ratio of buoyancy forces to viscous forces within a fluid undergoing heat transfer. It helps determine whether natural convection will dominate the heat transfer process.
Unfortunately, there is no direct way to calculate the Damköhler number for coal combustion models in ANSYS CFX. However, you can calculate the Damköhler number using the kinetic data for coal provided in the ANSYS CFX library. To do this, you will need to divide the rate of the reaction by the diffusion rate of the reactant used in the combustion model. The Damköhler number is typically used to measure the relative rate of reaction to the rate of diffusion.
Ra is a dimensionless term used in the calculation of natural convection and is a good indication as to whether the natural convection boundary layer is laminar or turbulent.
So if it is turbulent that will increase the amount of evaporation.
- Badges
- Science method
- Similar topics
- Methodology
- Crystallography
- X-ray Diffraction