Experimental and numerical investigation of heat and mass movement in unsaturated clays

Singh, Rao Martand 2007. Experimental and numerical investigation of heat and mass movement in unsaturated clays. PhD Thesis, Cardiff University.

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Abstract

The study of heat transfer and moisture movement in liquid and vapour phase has attracted the attention of scientists from the beginning of 19th century. The study is very important to many geotechnical and geoenvironmental problems like diurnal heat mass movement in ground, performance assessment of nuclear waste disposal repositories, buried hot pipes, buried high voltage electric cables and landfill liners. Significant experimental and theoretical development has been made in this field but still there is a lack of experimental data available specially for highly swelling clays. The heat transfer and liquid moisture movement theories for clays more or less are very well established but vapour transfer theory is still based upon rigid matrix granular soils. Therefore, this thesis presents an experimental, theoretical and numerical investigation of the heat and moisture movement in unsaturated clays. A new apparatus termed a thermo-hydraulic (TH) cell has been designed, fabricated and calibrated in-house to perform thermal gradient, thermo-hydraulic gradient and isothermo-hydraulic gradient tests on two types of clays namely Speswhite kaolin and MX-80 bentonite. The TH cell is capable of measuring the transient temperature, relative humidity, volume flow rate of incoming water and swelling pressure. It also facilitates the determination of moisture content, dry density and chemical composition (anions and cations concentration) of the soil samples at the end of the tests. In the thermal test, the clay sample is subjected to fixed temperatures of 85 C at the bottom end and 25 C at the top end. In the thermo-hydraulic test, same thermal gradient is used like the thermal test and in addition to this deionised and de-aired water was supplied at the top end under a pressure of 0.6 MPa. In the isothermal test, the clay sample is supplied deionised and de-aired water from the top end under a pressure of 0.6 MPa and the temperature kept at 25 C at both ends of the clay sample. The test results show that there is a cycle of vapour and liquid moisture movement within the clay sample, vapour moves from the hot end to the cold and condense to liquid at the cold end and liquid moisture moves to the hot end. The accumulation of chloride ions near the hot end indicate that liquid moisture moved from the cold end to the hot end. An empirical method has been developed to calculate the vapour fluxes using the variation of chloride ions concentration with time. The vapour fluxes calculated empirically found to be much lower than that determined by existing vapour theories. Therefore, the existing vapour theory has been modified to more closely predict the observed vapour fluxes. The new modified vapour transfer theory has been incorporated in transient finite element code and validated against the experimental work carried out in this study. The numerically simulated results match reasonably with the experimental heat and mass results. Further research is necessary to explore the new vapour theory application to large scale tests.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Engineering
Subjects:	T Technology > TP Chemical technology
ISBN:	9781303209499
Date of First Compliant Deposit:	30 March 2016
Last Modified:	12 Feb 2016 23:12
URI:	https://orca.cardiff.ac.uk/id/eprint/54608

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