5. Conclusions

Rea <sup>¼</sup> <sup>D</sup><sup>2</sup>

<sup>h</sup><sup>0</sup> <sup>¼</sup> NuKsol Dt

UC <sup>¼</sup> hi<sup>0</sup> <sup>h</sup><sup>0</sup> hi<sup>0</sup> þ h<sup>0</sup>

LMTD <sup>¼</sup> <sup>Δ</sup>tq � <sup>Δ</sup>tf

ln Δtq=Δtf

Replacing Eqs. (74) and (75) in Eq. (73), the following is given:

54 Heat Exchangers– Design, Experiment and Simulation

Eqs. (80) and (81) present the LMTD calculation.

(Nc) are given by Eqs. (83)–(85), respectively.

project is found (Eq. (82)).

<sup>a</sup> Nρsol μsol

The LMTD will be calculated considering the agitation system operating on countercurrent.

Finally, replacing Eqs. (68), (79), and (81) in Eq. (52), the necessary heat exchange area for this

The total pipeline length (L), the number of pipelines (Nt), and the number of tubes per baffle

4 baffles <sup>3</sup> tubes

Hence, the vessel described by the given example must have four vertical tubular baffles, and each one must have three tubes. If the tank's heating were to be carried out with agitation promoted by a radial impeller, the ho coefficient should be calculated by the equation

<sup>L</sup> <sup>¼</sup> <sup>A</sup> πDe

Nb <sup>¼</sup> Nt

Nt <sup>¼</sup> <sup>L</sup>

<sup>¼</sup> <sup>Δ</sup>tf � <sup>Δ</sup>tq

ln Δtf =Δtq

Pr <sup>¼</sup> <sup>C</sup>pμsol Ksol

¼ 424654:5 (74)

¼ 14:52 (75)

Nu ¼ 1247:14 (76)

<sup>¼</sup> <sup>343</sup>:76W=m2 °C (77)

<sup>¼</sup> <sup>331</sup>:78W=m2 °C (78)

(80)

UD <sup>¼</sup> <sup>313</sup>:47W=m<sup>2</sup> °C (79)

LMTD ¼ 56:4°C (81)

<sup>A</sup> <sup>¼</sup> <sup>2</sup>:72m2 (82)

¼ 17:9m (83)

baffles (85)

<sup>H</sup> <sup>¼</sup> <sup>11</sup>:5 tubes≅12 tubes (84)

Comparing the value obtained to the areas for both impellers, the agitation with radial impeller is much more efficient in terms of heat transfer when compared to the axial impeller, due to the large turbulence promoted by the radial impeller and to the fact that the radial impeller sends the fluid directly to the tank's wall, where the vertical tubular baffles are located. However, the power consumed by the mechanical impeller must also be analyzed in order to find the most economical rotation with the maximum heat exchange.

Therefore the choice of the kind of heat transfer surface suitable for the process to be projected in agitated vessels (jackets, helical coils, spiral coils, and vertical tube baffles) must be done very strictly, specially doing an analysis between the kind of impeller and its interaction with the adopted surface, because, as present on this paper, the difference between the areas obtained by each kind of surface can vary significantly.
