Suppose I want to add a convective load to a horizontal surface facing up. The "Buoyancy" drop down on the "General" tab on the "Surface Properties - Film/Convection Coefficient Calculator" dialogue box has several options for horizontal plate facing up, laminar flow. How do I know which option to use? What does, say, "500M<Ra<100G" mean?
The calculation of convection coefficient on some surface is an approximated calculation; Ra is one the parameter needs to be as input, Ra stands for Rayleigh number, which is a dimensionless number standing for the ratio of convective heat transfer vs. conductive heat transfer.
For the meaning of Ra, refer to attached image for the equation.