SU1260762A1 - Method of determining convection diffusion factor in wet porous materials - Google Patents

Abstract

The invention relates to methods for determining heat and mass transfer coefficients that are used to calculate rational drying regimes for various porous materials, for example, gypsum building products. The purpose of the invention is to improve the accuracy of determining the convective diffusion coefficient of wet porous materials by eliminating the error associated with changes in humidity due to the displacement of pore moisture from the sample during the measurement process. The method consists in measuring the time dependence of the air pressure as it flows from the chamber through the humidified sample into the atmosphere. Before the air is introduced into the chamber and the measurements are taken, the sample is blown with air at a pressure corresponding to the pressure during the measurements until a steady flow of air through the sample occurs. 1 il. About "S sl S u o C o d o a Is9

Description

one

The invention relates to instrumentation engineering, in particular, to methods for determining diffusion parameters in moist porous materials, and can be used to calculate drying processes for wet porous materials in various industrial fields and, in particular, in industrial materials for calculations and to build rational modes drying gypsum building products.

The purpose of the invention is to increase the accuracy of determination by eliminating errors associated with changes in humidity due to the displacement of pore moisture from the sample during measurements.

The drawing shows a diagram of the device. the implementation of the proposed method. sob.

The device for determining the coefficient; Convective Diffusion Cient consists of a metal cylinder 1 with a sample 2 formed in it, installed between the plates 3 with sealing gaskets 4. A valve 5 connects the chamber 6 formed by the sample 2 and the walls of the cylinder 1 with the feed system compressed air, which through valve 7 and water separator 8 is connected to the first chamber 9. The water separator has a valve 10 for draining the water displaced from the sample, and the air that has passed through the sample is removed through valve 1 I. Installation 1-5 has exemplary gauges 12 and 13 for measuring and controlling system pressure.

The diffusion coefficient is determined as follows. Sample 2 is molded into cylinder i, then the cylinder with sample is weighed and placed between plates 3

,

with sealing gaskets 4.

Then the valves 5 and 11 are opened, and the valve 7 is closed and compressed air of constant pressure is supplied to the upper part of the chamber 6. After the removal of steam moisture (fixed by the onset of a constant flow of compressed air, the valve 7 opens, and the valve 11 closes and, after reaching air pressure in the second and first chambers b and 9, to pressurized 1.1 compressed air when blowing sample, valve 5 is closed. After a slow shutter speed (for

one

-

1260762

Monitoring the complete tightness of the chamber J-opens rapidly to Gen II and records the pressure change of the reference pressure gauge 12 over time.

The magnitude of the convective diffusion coefficient QP is determined by the formula

ten

(fhP, -fnP,) f, 2,,

° P x (G. -

-

-

15

.20

25

thirty

35

40

45

50

55

where x / O-yx-TT, is found from the expression X tg - x (C „-5) p. -G, -.

Vj, 5 - sample volume,

V is the volume of the second chamber over 21

sample, m;

P is the initial air pressure.

P, R,

N / m

air pressure value

N / m

, H and P .i

at times with, respectively

. PO.: - sample thickness, m; weight of water and dry sample, kg; G is the average weight of the sample in the process of pressure relaxation, kg; The mouth is the ratio of the density of a dry sample to the density of a liquid.

Claims (1)

Invention Formula A method for determining the convective diffusion coefficient in humid porous materials, which consists in blowing air up to a constant pressure in two sealed I chambers separated by a sample. of the blown material, the connection of the first chamber with the atmosphere and the subsequent recording of the change in air pressure in the second chamber over time, according to which the diffusion coefficient is calculated, characterized in that, in order to improve accuracy, before the inlet of air into both chambers, it is injected into the second chamber in which the measurements are carried out, keep this pressure constant over time and maintain the sample at the same time until the onset of a steady flow of air through the sample. jfll -t ja 13 Editor M. Tovtin Compiled by A. Koshcheev Tehred, I. Popovich Order 52 9/40 Circulation 778 Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, st. Project, 4 Proofreader V. Sinitska