Heat transfer coefficient calculation

Shell-Side Heat-Transfer Coefficient Calculation... 

The heat transfer coefficient calculated numerically using an exact model with regard to the heat transferred through the solid substrate represents the correct variation of the Nusselt number with respect to the Reynolds number. 

The overall heat transfer coefficient calculated using the joint parameter estimation and data reconciliation approach is shown in Fig. 9. It is evident from this figure that the overall heat transfer coefficient remains fairly constant throughout the whole operating cycle of the pyrolysis reactor. Near the end of the cycle, the heat transfer coefficient drops to a comparably low value, signifying that the reactor needs to be regenerated. 

The heat-transfer coefficient calculated from this relation is the average value over the entire length of tube. Note that the Nusselt number approaches a constant value of 3.66 when the tube is sufficiently long. This situation is similar to that encountered in the constant-heat-flux problem analyzed in Chap. 5 [Eq. (5-107)], except that in this case we have a constant wall temperature instead of a linear variation with length. The temperature profile is fully developed when the Nusselt number approaches a constant value. 

Compare the heat-transfer coefficient calculated with Eq. (6-34) with the value obtained in Example 6-9. 

For shells with triple or double segmental baffles, the heat-transfer coefficient calculated for turbulent flow (DG/fi greater than 8000) should be multiplied by a value of 1.3. 

Lower values n 0.5 have only been found for substances with low boiling points, such as helium. The quanitity c is strongly dependent on the material properties of the boiling liquid and the structure of the heating surface. If, for example, c is known for a particular liquid that boils at a given pressure on a flat, polished, steel tube, then the heat transfer coefficient calculated with this quantity may not be used if the same liquid was boiling on a rough steel tube or a copper tube. 

Select a convection tube arrangement that will give a maximum flue gas mass velocity of about 0.3 to 0.4 pounds per square foot per second. Calculate the mass velocity, G. For precise ratings, calculate the gas film coefficient using Figures 1-12, 1-13 and 1-14 and equations for f, the factor for wall radiation in the convection section and he, the convective heat transfer coefficient. Calculate the in tube coefficient using any applicable method. Then calculate the overall transfer coefficient from the equation for Ue, the convective heat transfer velocity. 

The operation of an industrial-size gas-oil-water spray column (13 ft high, 1.3 ft diam) was reported by Barbouteau (B3). The relatively low overall heat-transfer coefficients calculated from his data, up to 1250Btu/ft /hr/°F, seems to suggest operation at relatively low holdup. Umano (Ul) studied spray column in the course of his work on direct-contact freezing units for water desalination. 

The parameter h, which combines several effects, must be at least as large as the convective heat transfer coefficient calculated from the jfj factor correlations discussed in Section 12.5. It is given by an expression of the form... 

Scaling laws of flow boiling instabilities can also be applied to heat transfer. In Brutin et al. [9], the heat transfer coefficient calculated is based on the average surface and fluid temperature. A total heat flux is provided (Qw). whereas locally the heat flux is redistributed inside the aluminum rod. Thus, the local surface and fluid... 

The heat transfer in calorimeters is described in terms of the effective heat transfer coefficient, involving the heat transfer of convection, conduction and radiation. In calorimetry, it is more common to use coefficient G, called the heat loss coefficient, which is equivalent to the effective heat transfer coefficient calculated for the whole surface S. 

It should be noted that the Prandtl number term in these two equations is somewhat speculative, since the experimental data did not cover a sulficient range for good correlation. Equations (12) and (13) include Pr to the 0.33 power, based on the expectation that dependence is similar to that for single spheres, as shown in Eq. (11). In applying heat transfer coefficients calculated by Eqs. (12) and (13), it is important to use a model that considers the particles to be well mixed and the gas to be in plug flow, in order to be consistent with the definition of as discussed above. 

Reaction calorimetry, as discussed in Sections 7.2.2 and 7.2.3, allows the heat transfer coefficient of the reactor to be estimated. The information of the heat transfer coefficient calculated on a daily basis can be very useful to detect the level of fouling in the reactor walls and to anticipate and therefore carry out actions that minimize its deleterious effects on the performance of the reactors [31]. 

Figure A2.12 Heat transfer coefficients calculated for a flow of coolants in Generation IV, AGR, and PWR reactors in a bare tube at nominal operating pressures and at mass fluxes close to...

Fig. A2.13 shows heat transfer coefficients calculated for all coolants (including FLiNaK) for the generic conditions G = 1000 kg/m s, = 970kW/m K, Dhy = 8 mm.

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