Percentage contribution of natural convention heat transfer in combined forced and natural convection heat transfer processes.
Hello Dr. HariPrasad,
The ratio of Gr.Re-2 is widely used to characterize the relative magnitudes of natural convection and forced convection in mixed convection flows.
Here, Gr and Re represent the Grashof and Reynolds number of the flow respectively.
If this is an existing system and you can perform changes to the heat duty and/or surface temperature, you may obtain the total heat transfer coefficient from the heat flux and temperature measurements. By changing the surface temperature/heat flux you will change the free convection contribution to the heat transfer coefficient, whereas the forced convective contribution will remain unchanged (assuming fluid properties are not significantly affected). In this way you may be able to quantify the forced and free convection contributions.
Hello Hari Prasad
I first suggest to check whether the natural convection is important based on the ratio Gr.Re-2. If the ratio is >> 1, than natural convection dominates, if
Hai HariPrasad Sir,
As Joshi correctly mentioned, to determine the dominance of free or forced convection in a area of their coexistence, we could use Richardson number (Ri=Gr/Re2).
if Ri>>1, then natural/free convection dominates
if Ri
There are several articles available on-line regarding the Richardson and Nusselt numbers. You might also look up "Dimensionless Groups" in the CRC Chem Physics Handbook. There you will find an entire section with every imaginable dimensionless number with a list of what they're used for and even a cross reference of which groups contain which items, such as thermophysical properties, length, area, volume, time, etc. and to what powers.
The first step is to describe the geometry. If it is a flat vertical plate, you should obtain the thesis by L. W. Swanson titled "Mixed Turbulent Convective Heat Transfer in Vertical Ducts" . It can be found by googling his name.
For super critical flows also the same is applicable or we have to use different equations, if so where do we find the literature.
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