The effect of bubbles between electrodes on efficiency of hydrogen production by water electrolysis was experimentally investigated. The water electrolysis of 10wt% potassium hydroxide (KOH) aqueous solution was conducted under atmospheric pressure using Ni-Cr-Fe alloy as electrodes. In order to examine void fraction between electrodes, the following parameters were controlled: current density, with or without separator, system temperature, space, height, inclination angle and surface wettability of electrodes. The efficiency of water electrolysis was qualitatively evaluated by the voltage drop value at a certain current density. The experimental results showed that increase of void fraction between electrodes by decreasing the electrode space brought about decrease of the electrolysis efficiency; i.e. there is an optimum condition of water electrolysis at a certain current density. In addition, a physical model of void fraction between electrodes was presented, which was found to represent a part of the qualitative tendency of experimental results.

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Programmed software was developed in order to numerically simulate time variation of the temperature field and snow depth around a pipe-in-pile snow-melting system, using meteorological data. The system utilized underground piles as the heat exchanger between underground soil and water flowing inside the pipes. The water was pumped into heat dissipation pipes embedded beneath the pavement surface, on which snow melted. The unsteady three-dimensional heat conduction inside the pavement and the underground soil was numerically solved. On the surface, the heat balance of conduction, convection, and radiation was considered. Snow fall depth was estimated by rainfall weather data, ratio of snowfall to rainfall, and dry density of snowfall. For simulating the snow layer, an unsteady one-dimensional heat conduction was solved while incorporating partial absorption of solar radiation. Experiments for measuring time variation of the temperature field and snow depth around the system were conducted for verification of the software. The obtained simulation results showed good agreements with experimental data, demonstrating the utility and validity of the software.