METHOD OF MEASUREMENT OF MOISTURE DIFFUSION COEFFICIENT IN CAPILLARY POROUS SHEET MATERIALS

摘要

FIELD: machine building. ^ SUBSTANCE: method of measurement of moisture diffusion coefficient in capillary-porous sheet materials consists in placement of examined sheet material on flat substrate of moisture-proof material and in pulse point moistening surface of examined material at initial moment of time. Further, values of a signal of galvanometric sensor of moisture content is recorded at a time-constant step. There is determined maximal value of signal Emax. Examined specimen placed of the substrate is covered with a plate of a moisture-proof material. A through orifice for supply of moisture is drilled in centre of the plate. Electrodes of the galvanometric sensor of moisture content with a known calibration characteristic are set at specified distance from the centre of this orifice. Directly before the moment of pulse point moistening the examined specimen there is recorded an initial value of the sensor signal E0. Tests are completed when a current value of the galvanometric sensor signal of moisture content is lowered to a value of EëñE0+0.6(Emax-E0) upon reaching a maximal value of Emax. After completion of the experiment at each time step there is calculated ratio equal to ratio of difference between a current value of the galvanometric sensor signal of moisture content E and an initial value of the signal E0 to difference between a maximal value of the signal Emax and initial value of the signal E0. There are fixed two moments of time corresponding to values of ratio =0.48 and =0.62, while values of desired coefficient of diffusion is determined by formulas: where a'm is coefficient of diffusion determined at a moment of time ä' corresponding to =0.48; ''m is coefficient of diffusion determined at a moment of time ä" corresponding to =0.62; r0 is coordinate of placement of sensor of local moisture content; z' is major root of equation zexp(1-z)= at =0.48; z" is less root of equation zexp(1-z)= at =0.62; also, as a medium value of coefficient m + " of diffusion there is accepted the value ^ EFFECT: raised accuracy and performance of measurement of moisture diffusion coefficient in capillary-porous materials. ^ 3 dwg