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The present study examined the effects of pulsed direct current (dc) on the performance of water electrolysis for hydrogen generation. The laboratory effort consisted of a series of tests using the Fm01‐LC electrolytic cell, manufactured by ICI Chemicals and Polymers, and rated at 38 g of H2/normalkA·normalh . Using a 10 weight percent sulfuric acid solution, the electrolytic cell performance was examined using nonpulsed dc, to determine the cells base‐line performance and pulsed dc. The pulsed dc test runs were carried out using a square pulse for seven frequencies, ranging from 10 Hz to 40 kHz, and four duty cycles of 10, 25, 50, and 80%. The hydrogen generation rate was used instead of current in order to facilitate an accurate comparison. For the range of tested parameters, the results demonstrated that the nonpulsed dc operation required the least electrical power.

The thermal stability of a layer of water between two vertical parallel plates maintained at different temperatures, T1 and T2, is investigated for the conduction regime. Three cases are considered include where: (a) the maximum density layer is within the water region; (b) is at the boundary; and (c) is outside the water region. Cubic polynomials are used to represent the density-temperature relation in the temperature range 0–55°C. The numerical results show that the critical states of stability do not depend on Prandtl number but instead depends on the combinations of T1 and T2. Of the three cases considered, the first case is the most unstable. In all three cases, the instabilities set in as a traveling wave, moving against gravity, for most T1 and T2 combinations. Stationary waves were also found for case (c).

The effects of nonuniform volumetric energy sources on the thermal stability of natural convection in a vertical fluid layer are investigated using the linear theory of stability. The neutral states of stability are obtained for four values of Prandtl number, ranging from 0.71 to 100, and for different values of β in the range 0.1 ≤ β ≤ 10. The critical parameters and the energetics of the critical disturbances are determined for each case. For all values of Prandtl number and β studied here, the critical instabilities set in as traveling waves, moving in the direction of gravity. In the low range of Prandtl number, 0.71 to 5, the critical curves approach the same asymptotic value for β ≥ 10. The critical disturbances are found to be buoyancy driven for all Prandtl numbers and β considered here, except for the low range of Prandtl number, for which they become shear driven disturbances as β increases.