Heat transfer occur when there is Delta T Across the two bodies.. heat always flow from hot side to cold side. Heat transfer may occur under natural draft or under forced circulation.

Industrial heat transfer equipment are mostly occur under forced condition.

As discussed above, one can conclude that the flow characteristics of the fluid on any side will pay an important role!!

We may recall our old books and some jargon like ‘ boundary layer’, ‘Lamina Flow’ , ‘Turbulent Flow’ etc.

Lay-Mann says: As we break the boundary layer.. more new fluid molecule come in contact with the surface & more heat they will carry.. So in Laminar flow the heat transfer will be less as fluid wall touching the heating surface is not leaving the place & core will remain unaffected! while in turbulent flow the boundary wall will brake & better heat transfer will occur.

This ‘Turbulent’ thing can be identified scientifically using Reynolds analogy . Same is represented with Reynold’s Number.

Reynold’s number can be calculated as:

While there is one more parameter which plays an important role in heat transfer which is ‘Prandtl number’, which shows how heat will diffuse in fluid during convectio heat transfer..

Prandtl Number can be calculates as

Where v is Kinematic Viscosity & k is thermal conductivity of fluid

As you have noticed, Reynold’s number is depends on carrier geometry & fluid properties, while Prandle number is depends on fluid property only.

Now how to use these number to evaluate heat transfer??

Wait for my next Scrap..


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