Thermal measuring and testing – Thermal testing of a nonthermal quantity – Of fluid volume
Patent
1997-09-22
2000-04-11
Miska, Vit
Thermal measuring and testing
Thermal testing of a nonthermal quantity
Of fluid volume
73 6177, 261104, G01N 2556, G01N 3318, G01N 1910
Patent
active
060480912
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an atmometer, and in particular to a gas exchange atmometer for determining water loss to the atmosphere through transpiration in plants, crops, soil etc in the agricultural environment, and in other environments where transpiration evaporation and humidity levels need to be determined (e.g. a baby's humidicrib). The invention will be described in the agricultural context, but it should be appreciated that the invention is not limited to such applications.
BACKGROUND ART
An atmometer is an instrument used or measuring evaporation. Atmometers have been known for some time, and can either be of a design whereby measurement of the rate of evaporation of water from a wet surface is determined or measurement of the rate of evaporation of water through a porous surface is determined. In the past, problems have been experienced in obtaining accurate and reproducible readings from atmometers, and it has been proposed in the scientific literature that existing atmometers are susceptible to windy conditions, causing inaccuracies in readings.
It has become increasingly important to simulate and estimate vapour loss through transpiration in plants, particularly plants subjected to, or growing in, dry environments. Transpiration from a plant leaf is a two-stage process. Moisture first evaporates from a wet surface of parenchyma cells within the leaf, which cells are surrounded by air spaces necessary for exchange of gasses during photosynthesis. Typically water evaporated into the small amounts of air in these spaces is at saturation vapour pressure for the temperature of the leaf. In the second stage of this process, the saturated air diffuses from within the leaf through the stomatal openings in the leaf surface and mixes with ambient air to be removed by wind action.
It would be advantageous if an instrument could be provided that at least partially simulates this process to provide some indication of the evaporation of water in agricultural environments.
SUMMARY OF INVENTION
The present invention provides an atmometer including a chamber having arranged in an interior region a medium in fluid communication with a liquid source and adapted for releasably retaining liquid, the chamber also having at another region an opening to the surrounds over which a gas permeable medium is arranged, in one mode of use the atmometer being positionable such that ambient air moving over the gas permeable medium causes at least a portion of any evaporated liquid in the chamber to diffuse through the gas permeable medium.
When the term "gas permeable medium" is used throughout the present specification, it includes a medium that is permeable to both gas and vapour.
By employing such a chamber in said one mode of use, the effects of wind may be at least partially ameliorated.
It is preferred that the medium is a pad arranged at a first side wall of the chamber adjacent to and covering a chamber inlet for the liquid source. In this regard, the pad can be configured so that the liquid source supplies sufficient liquid thereto and such that, in use, gas within the chamber is saturated with the vapour from the liquid, for a given ambient temperature and pressure. With an atmometer so configured, the conditions occurring in the two-stage transpiration process in a leaf can be closely simulated.
It is preferred that the gas permeable medium is arranged to cover an opening in a side wall of the chamber opposing the first side wall. By arranging the gas permeable medium in this way, a humidified environment (preferably approaching 100% relative humidity) can be achieved in the chamber.
Preferably one or more electrodes are applied to or are incorporated within the pad and are adapted for providing in use an electrical signal that is indicative of pad liquid content and/or variations thereof through the pad.
In this regard a fluid control circuit can be connected to the chamber inlet and can be adapted for responding to the electrical signal so as to feed liquid to the pad to maint
REFERENCES:
patent: 4324132 (1982-04-01), Williams
patent: 4709585 (1987-12-01), Altenhofen
patent: 5311769 (1994-05-01), Hetzel
patent: 5389311 (1995-02-01), Hetzel
patent: 5423206 (1995-06-01), Hetzel
Holawe Franz
McIntyre Graeme N.
Penfold Herbert Bruce
Worth Gary Douglas
Miska Vit
The University of Newcastle Research Associates Limited
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