Briefly apply the concept of laminar flow and turbulent in convection heat
transfer
Answers
Answer:
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Answer:
One of the important factors controlling heat transfer is the resistance to heat flow through the various “layers” that form the barrier between the two fluids.
The driving force for heat transfer is the difference in temperature levels between the hot and cold fluids, the greater the difference the higher the rate at which the heat will flow between them and the designer must optimise the temperature levels at each stage to maximise the total rate of heat flow.
The resistance to the heat flow is formed by 5 layers as follows:
The inside “boundary layer” formed by the fluid flowing in close contact with the inside surface of the tube.
The fouling layer formed by deposition of solids or semi-solids on the inside surface of the tube (which may or may not be present).
The thickness of the tube wall and the material used will govern the resistance to heat flow though the tube itself.
The fouling layer formed by deposition of solids or semi-solids on the outside surface of the tube (which may or may not be present).
The outside “boundary layer” formed by the fluid flowing in close contact with the outside surface of the tube.
The values to be used for [2] and [4] are usually specified by the client as the result of experience while the designer will select the tube size, thickness and materials to suit the application.
The resistance to heat flow resulting from [1] and [5], (designated the partial heat transfer coefficients) depend greatly on the nature of the fluids but also, crucially, on the geometry of the heat transfer surfaces they are in contact with. Importantly the final values are heavily influenced by what happens at the level of the boundary layers, the fluid actually in contact with the heat transfer surface.