Design of a water Vapour Pressure Manometer |
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| Affiliation: | 1. Key Laboratory of Desert and Desertification/Dunhuang Gobi and Desert Research Station/Research Station of Gobi Desert Ecology and Environment in Dunhuang of Gansu Province, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China;2. Institute of Desertification Studies, Chinese Academy of Forestry, Beijing 100091, China;1. Key Laboratory of Mechanics on Western Disaster and Environment, Lanzhou University, Lanzhou 730000, China;2. Department of Mechanics, Lanzhou University, Lanzhou 730000, China;3. School of Electronical and Mechanical Engineering, Xidian University, Xi’an 710071, China;1. Key Laboratory of Mechanics on Western Disaster and Environment, Department of Mechanics, Lanzhou University, Lanzhou 730000, PR China;1. Key Laboratory of Desert and Desertification/Dunhuang Gobi and Desert Research Station, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 730000, China;2. Institute of Desertification Studies, Chinese Academy of Forestry, Beijing, 100091, China |
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| Abstract: | The theory of measurement of water vapour exerted by a food sample with a Vapour Pressure Manometer (VPM) is analysed in this paper. It is shown that the change in volume of the measured system when the water is eliminated from the air-water vapour mixture must be taken into account in calculations. A correction factor is proposed, the value of which is dependent on the design characteristics of the VPM and on the actual readings of h1 and h2. Analysis of the design characteristics of the VPM has shown that the volume between the valves and the manometer liquid level at the ‘0’ reading should be relatively large in comparison with the volumes of free space in sample and desiccant flasks. Correct proportioning of these volumes enables large readings of h1 and a correction factor below 2 to be obtained.The value of the correction factor greatly affects the variance of aw. The standard deviation of aw is smaller the closer the correction factor is to 1.A design calculation procedure for the VPM is proposed, and also a method of calibrating the completed manometer. |
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