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Rifat Bulut - One of the best experts on this subject based on the ideXlab platform.
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a comparison of total suction measurements with thermocouple psychrometer filter paper technique and chilled mirror device
GeoHunan International Conference: Challenges and Recent Advances in Pavement Technologies and Transportation GeotechnicsAmerican Society of Civil Eng, 2009Co-Authors: Daniel Mabirizi, Rifat BulutAbstract:Soil suction is one of the most important parameters describing the moisture stress condition of unsaturated soils, and its measurement is equally important for realistic applications of unsaturated soil mechanics. The thermocouple Psychrometers, filter paper method and chilled-mirror device are three soil suction measurement techniques that have found their places in describing the behavior of unsaturated soils in geotechnical engineering practice. However, as it is inherent with all the suction measurement methods there are still difficulties and uncertainties associated with these soil suction measurement techniques. In this paper, the filter paper, chilled-mirror psychrometer, and thermocouple psychrometer methods are evaluated and compared based on some recent observations and test results. These methods are used to measure total suctions of some high plasticity clay soils under very strict temperature control conditions. From the test results, the capabilities and limitations of the three methods are analyzed.
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Indirect Measurement of Suction
Geotechnical and Geological Engineering, 2008Co-Authors: Rifat Bulut, Eng Choon LeongAbstract:This paper reports on indirect soil suction measurement methods. Indirect suction measurement techniques measure the moisture equilibrium condition of the soil instead of suction. The moisture equilibrium condition of the soil can be determined by primary means as in vapor pressure, secondary means as through another porous medium or tertiary means as in measuring other physical properties of the porous medium that indicates its moisture equilibrium condition. Indirect suction measurement techniques employing primary means include thermocouple Psychrometers, transistor psychrometer and chilled-mirror psychrometer. Indirect suction measurement techniques employing secondary means includes the filter paper method and indirect suction measurement techniques employing tertiary means include thermal conductivity sensors and electrical conductivity sensors. These techniques have been widely used in engineering practice and in research laboratories. However, each of these techniques has its own limitations and capabilities, and active research into improving these techniques is ongoing in universities, research laboratories, and private sector. This paper outlines working principles, calibration, measurement, and application areas of these methods based on recent literature and practice.
M.b. Kirkham - One of the best experts on this subject based on the ideXlab platform.
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Chapter 18 – Thermocouple Psychrometers
Principles of Soil and Plant Water Relations, 2014Co-Authors: M.b. KirkhamAbstract:This chapter tells how to measure plant water potential using thermocouple Psychrometers. The theory of their use is given. It includes knowing the relation between water potential and relative humidity (called the Kelvin equation); the Peltier thermoelectric effect; Joule heating; thermoelectric power; and the relationship between vapor pressure and temperature (called the psychrometric equation). Each of these topics is discussed. A sample problem is given showing how to get partial pressure of water vapor in air, relative humidity, and dewpoint temperature from wet and dry bulb readings obtained from a psychrometer. Calibration of thermocouple Psychrometers and how one takes measurements with them are described. The importance of isothermal conditions during measurements is emphasized, and reasons for them are enumerated. Four types of thermocouple Psychrometers are distinguished: the isopiestic thermocouple psychrometer; the Spanner thermocouple psychrometer; the Richards-and-Ogata thermocouple psychrometer; and the dewpoint hygrometer. Appendices give biographies of Peltier, Joule, and Kelvin.
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chapter 18 thermocouple Psychrometers
Principles of Soil and Plant Water Relations (Second Edition), 2014Co-Authors: M.b. KirkhamAbstract:This chapter tells how to measure plant water potential using thermocouple Psychrometers. The theory of their use is given. It includes knowing the relation between water potential and relative humidity (called the Kelvin equation); the Peltier thermoelectric effect; Joule heating; thermoelectric power; and the relationship between vapor pressure and temperature (called the psychrometric equation). Each of these topics is discussed. A sample problem is given showing how to get partial pressure of water vapor in air, relative humidity, and dewpoint temperature from wet and dry bulb readings obtained from a psychrometer. Calibration of thermocouple Psychrometers and how one takes measurements with them are described. The importance of isothermal conditions during measurements is emphasized, and reasons for them are enumerated. Four types of thermocouple Psychrometers are distinguished: the isopiestic thermocouple psychrometer; the Spanner thermocouple psychrometer; the Richards-and-Ogata thermocouple psychrometer; and the dewpoint hygrometer. Appendices give biographies of Peltier, Joule, and Kelvin.
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Measurement of Water Potential with Thermocouple Psychrometers
Principles of Soil and Plant Water Relations, 2005Co-Authors: M.b. KirkhamAbstract:Thermocouple hygrometers are generally accepted as the standard for measurement of plant-water potential. They measure vapor pressure in a small chamber by using either a psychrometric (wet bulb/dry bulb) or dew-point technique. Since both are used, the more general term thermocouple hygrometer is sometimes used rather than thermocouple psychrometer. However, most people call the instruments thermocouple Psychrometers. The chapter uses thermocouple Psychrometers to determine water potential by measuring relative humidity. But it actually measures a temperature depression (either the wet-bulb or the dew-point temperature depression). To relate the temperature depression to relative humidity, the psychrometric equation is used. The chapter looks at these points now in detail. The use of thermocouple Psychrometers to measure water potential is based on a sound physical–chemical foundation. A definite, quantitative relation exists between water potential of a sample and the relative vapor pressure above it. Before discussing thermocouple Psychrometers used in plant-water measurements, the chapter reviews the thermoelectric effects on which they are based.
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Measurement of Water Potential with Pressure Chambers
Principles of Soil and Plant Water Relations, 2005Co-Authors: M.b. KirkhamAbstract:The pressure chamber described by Scholander and colleagues is the most popular method used to measure water potential of plants. The method consists of increasing the pressure around a leafy shoot until sap from the xylem appears at the cut end of the shoot, which extends outside of the chamber and is exposed to atmospheric pressure. The pressure necessary to retain this condition represents the negative pressure existing in the intact stem. It is felt that the amount of pressure necessary to force water out of the leaf cells into the xylem is a function of the water potential of the leaf cells. For accurate measurements, one should compare measurements made with a thermocouple psychrometer with those made with a pressure chamber before assuming that the pressure chamber is giving valid measurements of water potential. Since the thermocouple–psychrometer method is based on sound physics using the Kelvin equation, measurements made with thermocouple Psychrometers are the standard ones. But relatively few comparisons exist in the literature.
Eng Choon Leong - One of the best experts on this subject based on the ideXlab platform.
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Indirect Measurement of Suction
Geotechnical and Geological Engineering, 2008Co-Authors: Rifat Bulut, Eng Choon LeongAbstract:This paper reports on indirect soil suction measurement methods. Indirect suction measurement techniques measure the moisture equilibrium condition of the soil instead of suction. The moisture equilibrium condition of the soil can be determined by primary means as in vapor pressure, secondary means as through another porous medium or tertiary means as in measuring other physical properties of the porous medium that indicates its moisture equilibrium condition. Indirect suction measurement techniques employing primary means include thermocouple Psychrometers, transistor psychrometer and chilled-mirror psychrometer. Indirect suction measurement techniques employing secondary means includes the filter paper method and indirect suction measurement techniques employing tertiary means include thermal conductivity sensors and electrical conductivity sensors. These techniques have been widely used in engineering practice and in research laboratories. However, each of these techniques has its own limitations and capabilities, and active research into improving these techniques is ongoing in universities, research laboratories, and private sector. This paper outlines working principles, calibration, measurement, and application areas of these methods based on recent literature and practice.
Ik Dart - One of the best experts on this subject based on the ideXlab platform.
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Measurement of the total water potential of aqueous solutions of polyethylene glycol - A comparison between osmometer, thermocouple psychrometer and equilibrated soil cores
Soil Research, 1993Co-Authors: Im Wood, Ik DartAbstract:This study examined two polyethylene glycol (PEG) polymers (PEG 6000 and PEG 10000) and compared measurements of water potential obtained with a thermocouple osmometer and thermocouple Psychrometers at three temperatures (15, 25 and 35°C) and five osmdalities (50, 100, 200, 300 and 400 g/1000 g water). These were then compared with estimates of matric potential of three soils brought to equilibrium with PEG solutions of the same osmolalities. At the same osmolality and temperature the two PEG polymers gave essentially the same water potential. There was a significant effect of temperature on water potential which corresponded closely with changes in specific gravity of the PEG solution. There was a close correlation between the measurements of water potential of the PEG solutions obtained with the osmometer and the Psychrometers (R = 0.99). However, the psychrometer gave increasingly lower values than the osmometer as water potential decreased. The differences in the measurements between the two methods are thought to be the result of design and calibration differences. The ease of use of the osmometer is such that it is recommended for routine use. The water potentials of the soil cores brought to equilibrium with the PEG 10 000 solution were linearly related to the water potentials of the PEG solutions estimated from both the osmometer and Psychrometers (R2 = 0.84). However, there were clear deviations from a 1:l relationship. It was concluded that the results from the soil cores could not be used to determine which of the two instruments gave the more accurate measurement of water potential of PEG solutions.
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Corrigenda - Measurement of the total water potential of aqueous solutions of polyethylene glycol - A comparison between osmometer, thermocouple psychrometer and equilibrated soil cores
Soil Research, 1993Co-Authors: Im Wood, Ik DartAbstract:This study examined two polyethylene glycol (PEG) polymers (PEG 6000 and PEG 10000) and compared measurements of water potential obtained with a thermocouple osmometer and thermocouple Psychrometers at three temperatures (15, 25 and 35�C) and five osmdalities (50, 100, 200, 300 and 400 g/1000 g water). These were then compared with estimates of matric potential of three soils brought to equilibrium with PEG solutions of the same osmolalities. At the same osmolality and temperature the two PEG polymers gave essentially the same water potential. There was a significant effect of temperature on water potential which corresponded closely with changes in specific gravity of the PEG solution. There was a close correlation between the measurements of water potential of the PEG solutions obtained with the osmometer and the Psychrometers (R = 0.99). However, the psychrometer gave increasingly lower values than the osmometer as water potential decreased. The differences in the measurements between the two methods are thought to be the result of design and calibration differences. The ease of use of the osmometer is such that it is recommended for routine use. The water potentials of the soil cores brought to equilibrium with the PEG 10 000 solution were linearly related to the water potentials of the PEG solutions estimated from both the osmometer and Psychrometers (R2 = 0.84). However, there were clear deviations from a 1:l relationship. It was concluded that the results from the soil cores could not be used to determine which of the two instruments gave the more accurate measurement of water potential of PEG solutions.
Hans Janssen - One of the best experts on this subject based on the ideXlab platform.
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Hygric properties of porous building materials (IV): Semi-permeable membrane and psychrometer methods for measuring moisture storage curves
Building and Environment, 2019Co-Authors: Chi Feng, Hans JanssenAbstract:Abstract The moisture storage curve is an important hygric property of porous building materials. It describes the moisture storage characteristic of a material via the relation between the moisture content and the moisture potential. Current experimental protocols for measuring moisture storage curves are not satisfactory, as they often require extensive facilities while still lacking the capability to handle the adsorption process in most of the over-hygroscopic range. This paper proposes two novel and simple methods – the semi-permeable membrane method and the psychrometer method – to solve these issues. Measurements on calcium silicate, autoclaved aerated concrete and ceramic brick are performed and validated by comparing the experimental outcomes obtained from these two novel methods and from other existing protocols. It is proven that the semi-permeable membrane method and the psychrometer method are applicable for both adsorption and desorption processes, the latter both from saturated and capillary moisture content. Limited by the accuracy of the psychrometer and the condensation caused by temperature fluctuations, these two methods show their best applicable range for capillary pressures below −1·105 Pa. The semi-permeable membrane method and the psychrometer method also feature in low cost, simple handling and application efficiency.