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# Definition of pilot exchanger tubes: velocity in the tubes

This device must be carefully designed to lend itself to the study of tube crusting, to ensure that the extrapolation does not lead to any blockage in the tubes of the industrial exchanger.

To this end, it is necessary that:

• - the entry and exit temperatures for the process fluid are the same as that in the industrial installation;
• - the temperature of the internal wall is the same.

# Velocity in the pilot tubes

In an industrial exchanger treating a crystal suspension, we use tubes with an interior diameter of 35 mm. On the other hand, in a pilot, we use 1 or 2 tubes with an interior diameter of 20 mm.

To ensure that the temperature of the internal wall is the same in both installations, and accounting for the fact that the conditions outside the tubes are similar, it should suffice that the partial thermal transfer coefficient inside the tubes is the same. Of course, the entry and exit temperatures of the exchangers are the same in both installations.

If we apply the turbulent regime, coefficient ai is given by:

A,f : fluid thermal conductivity (W.m °C ')

V: tube velocity of process fluid (m.s-1) dj: tube interior diameter (m).

So, ai is proportional to: [V08. d-]

Or rather:

Index 1 characterizes the pilot and index 2 the industrial installation. Therefore:

Accordingly, if:

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