1.7.3 Leakage model of non-asbestos gasket sealing
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NASC can be assumed to be a kind of porous media. The flow of gas through porous media includes molecular transfer and convection transfer. The leakage rate L of gases flowing through porous media can be calculated using the capillary model (Gu et al., 2007b).
where ri and lm are the radius and the average length of capillaries, respectively, c is the bending coefficient of capillaries, rj the dynamic viscosity of gases, T the Kelvin temperature of gases, M the gas molecular weight, R the gas constant, pm the average pressure, pm=(pi+p2)/2, and p1 and p2 are the pressures at the entrance and exit of capillaries, respectively.
There exists the following relationship between the number k and the radius ri of leakage paths and the gasket compressive stress c
k = fi (<7-m)
ri = f2 (7 -П ) (54)
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According to Eqs.(52)-(54), the leakage rate of gas through gasket sealing joints L can be calculated by the following formula.
where l is the gasket effective width, Al, Am, nL and nM are regression coefficients which can be obtained from experimental data, and c0 is the gasket seating stress prescribed in the corresponding gasket standards (AQSIQ,2003, AQSIQ,2008).
