Troy Symes

Development of a smart monolayer application system for reducing evaporation from farm dams: introductory paper

Abstract Chemical monolayer films are potentially an economical low-impact means of reducing evaporative loss from farm water storages. However, their performance can be highly variable as they are affected by climatic and environmental factors: principally wind, wave action and bio-degradation. Some of this observed variability is associated with the monolayer materials themselves and their interaction with the water-surface physics and biology, but the fact that they are only a few nanometres thick means that a very small amount of material has to be distributed over a very large area. Therefore, appropriate and timely autonomous application of monolayer, with regard to prevailing (and changing) wind conditions on-site, is required. Although a number of autonomous application systems for monolayer already exist, none has proved overly successful. It is argued that while this is in part due to sub-optimal performance of monolayer materials, it is also due in large measure to inaccuracies and/or inappropriate design in both application systems and particularly application strategies, which are not adaptive to the prevailing environmental conditions. Therefore a control system is being developed to adaptively and spatially vary monolayer application rates according to changing conditions monitored on-site. This will form part of an autonomous electromechanical system for the optimal application and spreading of any given chemical monolayer. This paper reports progress towards this objective; firstly by evaluation of the design requirements for automated systems at a range of spatial scales; and secondly via the construction of a first pre-prototype to act as an evaluation platform and concept demonstrator.

Assessment of the performance of evaporation suppressant films: Analysis and limitations of simple trialling methods

Abstract The potential utility of monomolecular layers (“monolayers”) and other surface film materials for the reduction of open water evaporation has long been argued. However, outside the laboratory, trials to quantify the effectiveness of artificial surface films have produced highly variable results after application to water surfaces, whether natural water bodies or managed farm storages. This paper briefly reviews the physical mechanisms involved in evaporation suppression and the biophysical literature on aquatic surface microlayers. The wide-ranging results from 16 months of outdoor trough-scale and (simultaneous) replicated bucket-scale evaporation reduction trials are interpreted using biophysical measurements made on microlayer and immediate subsurface water samples taken from the experimental troughs. When the prevailing environmental conditions and other ancillary measurements are taken into account, plausible hypotheses arise to account for at least some of the observed trial-to-trial differences in evaporation reduction and surface film performance. Results for the commercial monolayer product are inconclusive, as the concentration of the active ingredient in its formulation lacked the uniformity required for the accuracy at which these trials were conducted. Results for the temperature differential between open (unprotected) water and film-covered water, and the influence of windspeed on evaporative loss, indicate that the mechanism of evaporation suppression for mono-molecular (monolayer) organic films differs from that for thicker silicone oil films. These results have implications for both small-scale trialling of evaporation suppressants and the deployment and management of artificial surface film materials on agricultural water storages. In addition, it concluded that despite the attractiveness of simple side-by-side comparisons of performance, meaningful interpretation of results must consider prevailing meteorological conditions, and a timescale of hours rather than days.