Convection in a fluid-saturated porous layer at high Rayleigh numbers is briefly reviewed. When a saturated porous layer is subjected to bottom heating, steady convection sets in with the increase of the Rayleigh number R beyond the critical value. If the porous layer has an infinite horizontal extent, the critical value is R = 4π₂= 40. Further increase of the Rayleigh number transforms steady convection to a time-dependent or oscillatory state. In a two-dimensional square the transition from steady to oscillatory state takes place at R = 390. The first oscillatory convection characterized by the oscillation of average heat flux (Nusselt number) exhibits a simply periodic state. The frequency at the onset of the oscillation is about 83 in a diffustion time. The oscillation frequency in general increases with the Rayleigh number. The flow and temperature fields possess center-symmetric patterns. At the Rayleigh number somewhere between 800 and 1000 the convective state becomes chaotic with a broad band noise in a spectral power diagram of the Nusselt number oscillation. The flow and temperature patterns at the chaotic state no longer possess the center-symmetry. The physical mechanism responsible for the oscillation is identified as a thermal boundary layer instability.
It has been also established that oscillatory condition exists in a three-dimensional space. The onset of oscillation takes place at R = 575. The first oscillatory state is simply periodic with the frequency 170. At R = 650 the convection becomes a more complex state with at least two fundamental frequencies. Key words: natural convection, porous medium, heat transfer, oscillatory convection, chaotic convection

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In order to improve the efficiency of aquifer thermal energy storage [ATES], a fundamental knowledge of heat transfer in saturated-unsaturated soil zone is required. Experiments to determine the characteristics of heat transfer in saturated soil zone have been conducted. An insulated large column, filled with water or fine sand, was used in the heat transfer experiments. After estimating the loss of heat from the column, thermal conductivity and temperature changes in the soil column were examined.
Furthermore, experimental data were simulated, using the one-dimensional model of heat transfer considering the loss of heat. As a result, the following points become clear:
(1) In case of the experiments extending over more than several hours, the loss of heat from the column cannot be neglected.
(2) Under these experimental conditions, most of heat transfer in saturated soil can be explained only by the heat-conduction term, and the influence of natural convection on heat transfer can be neglected.
(3) The thermal conductivity of the saturated soil evaluated from these experiments is in good agreement with that measured independently by the twin transient-state cylindrical-probe method. Key words: aquifer thermal energy storage, heat transfer, thermal conductivity, natural convection

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A solar-heat pump system was researched and developed by the authors at the Kitami Institute of Technology. Being simplified and reduced, it was introduced into a residence to test it under every day conditions for a long period.
The solar system works only for a hot water supply, and the heat pump works for space-heating using ground water as a heat source. In the usual case, two bore holes are necessary: one for production and one for returning water. However, this particular method, namde a“direct siphon well”systm, could be done by only one bore hole. Namely, a pump is set directly under the water surface, by which ground water is pumped up and forced into the heat pump, and after absorbing heat through an evaporator, the cold water is returned to a lower point in the same well. Water discharged from the heat pump flows partially into a road-heating system, and then flows out through a drainpipe. The ratio of the drainage to the returning water is 7: 3 in average for the cold seasons, and the temperature of the water pumped up is 8.5 to 9.0°C throughout the year.10 MJ / h of the extracted heat per bore hole is expected by this technique. The system is now working very well to make environment inside the house comfortable.
Advantages of the solar-heat pump system using the direct siphon well method are as follows:

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The adsorptive removal of tetrachloroethylene (perchloroethylene: PCE), one of the contaminants of groundwater, onto activated carbon fibers(ACFs) in liquid phase was experimentally examined.
The adsorption capacities of ACFs were larger than that of granular activated c arbon (GAC), and the adsorption isotherms of PCE onto ACFs and GAC were of Freundlich type.
The amounts of PCE adsorbed onto ACFs were inversely proportional to the specific surface area, the pore volume and the amount of water adsorbed, significantly.
In addition, the amount of PCE adsorbed on to ACF in liquid phase is rising with the ACF surface of being hydrophobic.

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