Mechanisms of water transport through soil from a pervaporative irrigation system
File(s)
Author(s)
Todman, Lindsay Caroline
Type
Thesis
Abstract
This thesis presents the results of an investigation into the transport
of water through soil from a pervaporative irrigation tube. This irrigation
system uses a selective polymer membrane that allows water to cross by the
process of pervaporation, which releases water into the soil in vapour phase.
The polymer membrane is formed into a tube, buried in the soil and filled
with saline water. The selectivity of the membrane retains salt within the
tube whilst water is released, so the system treats the water and distributes
it for irrigation simultaneously. The distribution of water from the system,
rather than the treatment efficiency, was the focus of this project.
Although in the field the system will interact with the plants it irrigates,
in this work, for simplicity, plants were neglected. Instead a series of laboratory
experiments were conducted to quantify the flux from the pervaporative
tube in different soil types and in different humidity conditions. The results
of these experiments highlighted, for the first time, the significance of vapour
flow and condensation in the soil during the pervaporative irrigation process.
Soil types with high water sorption at low relative humidity (e.g. saline sand)
had an increased amount of condensation in the soil which resulted in an
increased flux from the pipe. A moisture sorption isotherm was a useful predictor
of this behavior.
A numerical model was then developed to simulate the experimental findings.
Experimental results had demonstrated that diffusion and condensation
of water vapour through the soil were significant processes hence these were
the main focus of the modelling work. Liquid flow was also simulated when
the water content in the soil was sufficient. To simplify the representation of
the pervaporative tube it was assumed that the membrane acted as a 100%
humidity boundary in the soil thus it was assumed that it was the transport
of water through the soil that limited the flux of water from the pervaporative
tube rather than the membrane structure itself. The similarity between the
observed and simulated results supported the basis of this conceptual understanding
of pervaporative irrigation.
This research raises a number of further questions regarding the interaction
between plants and pervaporative membranes. These include how plants
might interact with vapour flows through the soil and the influence of soil
salinity on the interaction between the pervaporative membrane and the plant
roots.
of water through soil from a pervaporative irrigation tube. This irrigation
system uses a selective polymer membrane that allows water to cross by the
process of pervaporation, which releases water into the soil in vapour phase.
The polymer membrane is formed into a tube, buried in the soil and filled
with saline water. The selectivity of the membrane retains salt within the
tube whilst water is released, so the system treats the water and distributes
it for irrigation simultaneously. The distribution of water from the system,
rather than the treatment efficiency, was the focus of this project.
Although in the field the system will interact with the plants it irrigates,
in this work, for simplicity, plants were neglected. Instead a series of laboratory
experiments were conducted to quantify the flux from the pervaporative
tube in different soil types and in different humidity conditions. The results
of these experiments highlighted, for the first time, the significance of vapour
flow and condensation in the soil during the pervaporative irrigation process.
Soil types with high water sorption at low relative humidity (e.g. saline sand)
had an increased amount of condensation in the soil which resulted in an
increased flux from the pipe. A moisture sorption isotherm was a useful predictor
of this behavior.
A numerical model was then developed to simulate the experimental findings.
Experimental results had demonstrated that diffusion and condensation
of water vapour through the soil were significant processes hence these were
the main focus of the modelling work. Liquid flow was also simulated when
the water content in the soil was sufficient. To simplify the representation of
the pervaporative tube it was assumed that the membrane acted as a 100%
humidity boundary in the soil thus it was assumed that it was the transport
of water through the soil that limited the flux of water from the pervaporative
tube rather than the membrane structure itself. The similarity between the
observed and simulated results supported the basis of this conceptual understanding
of pervaporative irrigation.
This research raises a number of further questions regarding the interaction
between plants and pervaporative membranes. These include how plants
might interact with vapour flows through the soil and the influence of soil
salinity on the interaction between the pervaporative membrane and the plant
roots.
Version
Open Access
Date Issued
2013-02
Date Awarded
2013-07
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Butler, Adrian
Templeton, Michael
Ireson, Andrew
Sponsor
Engineering and Physical Sciences Research Council
Douglas Bomford Trust
Research Partnership to Secure Energy for America
Publisher Department
Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)