chaos_zzy said:For nature convection heat transfer coefficient h =10w/m^2-k(including radiation)
For force convection, h range is more large, however you can take 25w/m^2-k for coarse estimate.
Free convection heat transfer is a type of heat transfer that occurs when a fluid, such as air or water, is in contact with a solid surface and the motion of the fluid is caused by natural buoyancy forces. This type of heat transfer is driven by differences in temperature and density within the fluid.
Free convection heat transfer is different from forced convection heat transfer in that it does not require any external force or energy to move the fluid. In forced convection heat transfer, an external force, such as a fan or pump, is used to move the fluid and enhance heat transfer.
The rate of free convection heat transfer is influenced by several factors, including the temperature difference between the solid surface and the fluid, the properties of the fluid (such as density and viscosity), the geometry and orientation of the solid surface, and the presence of any obstacles or barriers in the fluid flow.
The rate of free convection heat transfer can be calculated using mathematical equations, such as the Nusselt number correlation or the Grashof number correlation. These equations take into account the relevant parameters, such as temperature, fluid properties, and surface geometry, to determine the heat transfer rate.
Free convection heat transfer is a fundamental process that occurs in many everyday situations. Some examples include the cooling of a hot cup of coffee, the heating of a room by a radiator, and the transfer of heat from a computer's processor to its heat sink. It is also important in industrial processes, such as cooling towers and heat exchangers.