Browsing by Subject "POROUS-MEDIA"

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  • Kamarainen, A.; Jokinen, K.; Linden, L. (2020)
    The addition of Sphagnum to peat-based growing media ('Sphagnum replacement') influences plant performance. The primary physical effect of Sphagnum addition appears to be enhanced water retention. Good performance of plants cultivated in Sphagnum seems partly explainable in terms of its water retention properties. The large body of nutrient solution retained in Sphagnum can delay disadvantageous changes in its concentration during cultivation. The physical quantity of Sphagnum per unit volume, i.e. its bulk density, governs the volume of retained water and thus determines the strength of effects contributing to plant performance. When subjected to severe drought, plants cultivated in Sphagnum did not show clear signs of water deficit up to at least 1,572 hPa of matric suction, which is the estimated wilting point for plants grown in light peat. Using Sphagnum to replace peat in the growing medium appears advantageous to plants not only during drought but also during ordinary greenhouse cultivation.
  • Kuva, J.; Voutilainen, M.; Mattila, K. (2019)
    The time domain-random walk method was developed further for simulating mass transfer in fracture flows together with matrix diffusion in surrounding porous media. Specifically, a time domain-random walk scheme was developed for numerically approximating solutions of the advection-diffusion equation when the diffusion coefficient exhibits significant spatial variation or even discontinuities. The proposed scheme relies on second-order accurate, central-difference approximations of the advective and diffusive fluxes. The scheme was verified by comparing simulated results against analytical solutions in flow configurations involving a rectangular channel connected on one side with a porous matrix. Simulations with several flow rates, diffusion coefficients, and matrix porosities indicate good agreement between the numerical approximations and analytical solutions.
  • Kämäräinen, A.; Simojoki, A.; Linden, L.; Jokinen, K.; Silvan, N. (2018)
    The surface biomass of moss dominated by Sphagnum fuscum (Schimp.) Klinggr. (Rusty Bog-moss) was harvested from a sparsely drained raised bog. Physical properties of the Sphagnum moss were determined and compared with those of weakly and moderately decomposed peats. Water retention curves (WRC) and saturated hydraulic conductivities (K-s) are reported for samples of Sphagnum moss with natural structure, as well as for samples that were cut to selected fibre lengths or compacted to different bulk densities. The gravimetric water retention results indicate that, on a dry mass basis, Sphagnum moss can hold more water than both types of peat under equal matric potentials. On a volumetric basis, the water retention of Sphagnum moss can be linearly increased by compacting at a gravimetric water content of 2 (g water / g dry mass). The bimodal water retention curve of Sphagnum moss appears to be a consequence of the natural double porosity of the moss matrix. The 6-parameter form of the double-porosity van Genuchten equation is used to describe the volumetric water retention of the moss as its bulk density increases. Our results provide considerable insight into the physical growing media properties of Sphagnum moss biomass.