Convection experiments

The hulk solution may become depleted. In free-convection experiments, the cathode and anode compartments are often separated by a diaphragm to prevent interaction of the convection patterns. Under these conditions, replenishment of the catholyte does not take place. Examples of sagging limiting-current plateaus caused by bulk depletion can be found in... 

Using the Grashof and the Reynolds numbers, we can indicate whether forced or free convection dominates in a particular case. Because Re equals inertial forces/viscous forces (Eq. 7.19) and Gr equals buoyant x inertial forces/(viscous forces)2 (Eq. 7.20), Re2/Gr equals inertial forces/buoyant forces. Thus Re2/Gr reflects forced convection/free convection. Experiments reveal that forced convection accounts for nearly all heat transfer when Re2/Gr is greater than 10, free convection accounts for nearly all heat transfer when Re2/Gr is less than 0.1, and the intervening region has mixed convection (i.e., both forced and free convection should then be considered, especially for Re2/Gr near 1). Using Equations 7.19 and 7.20, we obtain... 

E. M. Sparrow and M. Charmichi, Natural Convection Experiments in an Enclosure Between Eccentric or Concentric Vertical Cylinders of Different Height and Diameter, Int. J. Heat Mass Transfer (26/1) 133-143,1983. 

Eckert, K., Besterhorn, M., and Thess, A. (1998) Square cells in surface-tension-driven Benard convection experiment and theory. J. Fluid Mech. 356 155-197. 

In the investigation of L. I. Tchemieva [3.33], in order to exclude the effect of convection, experiments were carried out at temperature gradients on two measuring cells (with clearances of 0.34 and 0.43 mm) with the thermostats being set at equal temperatures. The temperature drop in the experiments was small. The results of the measurements agree with the data of other researchers, and the discrepancy corresponds with the evaluated experimental error ( 2.5%). 

A limited number of natural convection experiments have been performed with chemicals in flat bottom orientations within aquatic microsms simulating solid sediment surfaces. Solid sodium chloride blocks positioned in upward-facing orientations of 60° from vertical yielded data for the following correlation ... 

Results from a mixed convection experiment with uniform wall heat flux are shown in Figure 4(b). The Reynolds number was about 10,000. Under such conditions heat transfer was found to be strongly impaired due to the influence of buoyancy. It can be seen that the local values of Nusselt number lie well below the curve for forced convection calculated using the Petukhov equation. The observed behaviour is very similar to that found in an earlier study by Li [6] using a uniformly heated test section of similar dimensions (see Jackson and Li [7]). 

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