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This paper discusses the mechanism for magnetic water treatment, which has been used practically for over a century but is still not completely understood. Modified crystallization and agglomeration, which produce a less tenacious scale, retain this property for hours following treatment. It is considered to be a result of magnetically modified hydration and Lorentz force effects of magnetic devices. In treated water, as a complex solution/dispersion system, they affect the kinetics of processes at solution/solid interfaces. Which effect prevails depends on the treatment regime and water composition.

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An application of specific surfactants in district heating and cooling systems can give notable economical benefits due to a reduction in friction and heat transfer attributed to a formation of an additional viscous sublayer along the pipe walls, buffering the turbulence. A mathematical three-layer model of water velocity profile is composed for the calculation of drag reduction and flow-capacity increase. At a properly chosen surfactant and concentration, the local drag can be reduced up to 80%. A computer simulation and optimization for a selected district heating network model with additive shows 4% saving in total costs because smaller pipes and weaker pumps are required.

A B S T R AC TMagnetic water treatment (MWT), an alternative solution for scale control, is discussed with emphasis on the construction of the magnetic devices and the mechanism of MWT infl uence on the scale formation. Two applications in high-temperature and high-pH conditions are presented. The treatment noticeably reduced the scale thickness on the heating spiral and removed preciously precipitated scale from hot tap-water outlet pipe; on the walls in the zone with heated alkaline water, instead of hard scale, only thin, brittle coating was formed. The morphology analyses showed the acceleration of aragonite nucleation and raised formation of fi ne suspended particles.

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The calibration procedure for the frequency determination of HeNe laser interferometers used for length metrology is described and high-level traceability at the Metrology Institute of the Republic of Slovenia (MIRS) consistent with the Mutual Recognition Arrangement drawn up by the International Committee for Weights and Measures (CIPM MRA) is presented in the article. The analyses of radiation frequency regarding stabilization time, repeatability and reproducibility are given for a case of an industrial and of a laboratory HeNe laser interferometer. Allan-deviation calculations at different sampling periods provided information for setting the optimal sampling period and proved that 100 000 samples at onesecond or 10 000 samples at ten-second long period are usually the most appropriate sets for one-day calibration measurements.