Heat transfer by forced convection in turbulent flow

Presented by

A.RAMACHANDRAN [11201213079]

Chemical Engineering

Heat transfer in turbulent flow over a flat plate:

Here let we calculate the rate of heat transfer coefficient for the turbulent boundary layer over a flat plate

Cont....

(i) The local friction coefficient is

for ….(1)

The fluid friction analogy

....(2)

Cont…

Substitute equation (1) in (2)

-1 = Stanton number

-1/ … (3)

Cont…

We know/

Re-arranging the above equation ….(4) 𝑁𝑁𝑢,𝑥 = 𝑁𝑆𝑡,𝑥.𝑁𝑅𝑒,𝑥/𝑁𝑃𝑟

Cont….

Substitute equation (3) in (4))-1/5

Form the above equation

4/5()1/3 …(5)

Cont…..

From this equation we can calculate the local turbulent heat transfer for a constant wall temperature.

It is valid for only but it may be used for up to 108 with less accuracy.

Cont….

(ii) The average heat transfer over the entire boundary layer laminar turbulent (i.e. heat transfer) for flow over a flat plate having laminar boundary up to

Turbulent boundary is given by Avg Nusselt number,0.8-871]1/3 ..(6)for

Cont….

(iii) For fully turbulent flow or for long plate, the Avg Nusselt number is

0.81/3 for ….(7)

Cont…

(iv) For , we can follows:[0.228()-2.584-871] ()1/3 ….(8)

In all the above equations, properties are evaluated at the free steam temperature of the fluid must be evaluated at the mean film temperature.

Cont…

(v) When the differences in temperature are great, Whitaker correlation may be used. 1/4

[(0.8-9200]

This is valid for and In this equation, all properties are evaluated at the free

steam temperature except and are evaluated at the surface and free stream temperature respectively.

2×105<𝑁𝑅𝑒 ,𝐿<5.5×106

THANK YOU