Water vapor diffusion coefficient unsteady state measurement device and method thereof

Abstract

The invention discloses a water vapor diffusion coefficient unsteady state measurement device and a method thereof. The device comprises a constant-temperature constant-humidity box, an organic glass box, a forced convection device, a capacitor type relative-humidity sensor, a data acquisition unit and a computer, wherein the constant-temperature constant-humidity box is used for providing a high-relative-humidity environment; the organic glass box internally contains anhydrous calcium chloride and is used for providing low relative humidity; the forced convection device is used for balancing the relative humidity of a tank interior; the capacitor type relative-humidity sensor is used for determining the interior of a to-be-measured sample and the relative humidity of the environment; the data acquisition unit is used for acquiring the relative humidity determined by the relative-humidity sensor and corresponding determining time; the computer is used for combining with the Fick second law representing water vapor unsteady state diffusion, and the relative humidity of the sample interior and the corresponding detection time, and utilizing Boltzmann transformation inversion problem processing to obtain a water vapor diffusion coefficient of the to-be-measured sample at different relative humidity. The water vapor diffusion coefficient unsteady state measurement device and the method thereof have the characteristics of simple structure, high measurement precision and short measurement time.

Description

technical field [0001] The invention relates to the technical field of physical property measurement, in particular to an unsteady-state measuring device and method for water vapor diffusion coefficient in the building field. Background technique [0002] With the rapid development of the economy and the continuous growth of the population, the energy problem has become a major social problem faced by all mankind. At present, construction, industry, and transportation are listed as China's three major energy-intensive industries. Most of the building envelopes used are porous materials such as concrete, shale bricks, wood, etc. In hot and humid climates, there is a strong moisture migration process in the porous envelope, and its heat and moisture migration and moisture accumulation have an important impact on building thermal performance, building energy consumption, and indoor environment. For example, since the thermal conductivity of water is about 24 times that of air...

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Problems solved by technology

However, due to the slow transfer of water vapor in porous building materials, a steady-state experiment takes several weeks, and only one water vapor diffusion coefficient can be measured in a steady-state experiment, and it may take several years to fully characterize the water vapor transfer performance of porous building materials. Therefore, the development of efficient and reliable unsteady test methods is of great significance for scientific research and engineering applications

[0005] Arfvidsson et al. established the quality of porous building materials when the relative humidity of the environment changes stepwise in "Building and Environment" 2000 3rd period (A transient technique for determining diffusion coefficients in hygroscopic materials, 2000, 35(3): 239-249). Test the experimental bench, and propose a method to calculate the water vapor diffusion coefficient with the Kirchhoff potential as the driving force based on the experimental data. The calculation results are consistent with the steady-state experimental results, but this method needs to obtain the moisture absorption curve of the material through the steady-state experiment , still takes a long time

In "Journal of Building Physics" 2012, No. 3 (A Boltzmann transformation method for investigation of water vapor transport in building materials, 2012, 35(3): 213-223), Pavlík et al. used time-domain reflectometry to build a water vapor transport in porous building materials. Vapor diffusion coefficient unsteady-state test bench, however, the author uses the steady-state "cheers" method to measure the relative humidity of the water vapor diffusion coefficient on the diffusion coefficient curve measured by the unsteady method is about 64%, which is the same as "cheers" The relative humidity condition of the law is 0 / 50% inconsistent, the reliability is not high, and the time domain reflectometer is expensive

[0006] Although some researchers have carried out research on non-steady-state measurement techniques for water vapor diffusion coefficient of porous building materials, these methods still have problems such as time-consuming, low accuracy, and high cost.

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