1.1 Symbol explanation
Meanings and units of the symbols used in this chapter are as follows:
σb——the tensile strength of materials under 20℃, Мpa;
σ5——the yield stress or constrained yield stress of materials under 20℃ (residual deformation is 0.2%), МPa;
σts——the yield stress or constrained yield stress of materials at calculated wall temperature (residual deformafion is 0.2%), МPa;
σtD——the endurance strength for 105h of materials at calculated wall temperature, Мpa;
δ5——the elongation percentage of materials under 20℃, %;
[σ]——the permissible stress, МPa;
[σ]J——the basic permissible stress, МPa;
nb——the safety coefficient corresponding to the tensile strength;
nB——the safety coefficient corresponding to yield stress or constrained yield stress;
nD——the safety coefficient corresponding to the endurance strength for 105h;
η——the correction coefficient of basic permissible stress;
tbi——the calculated wall temperature, ℃;
tJ——the rated average temperature of the medium, ℃
tb——the saturation temperature of the medium corresponding to calculation pressure, ℃ (hot water boiler is the average temperature of medium, ℃);
X——the mixability coefficient of the medium;
Δt——the temperature deviation, ℃;
β——the ratio of external diameter and internal diameter of boiler drum and header drum;
S——the wall thickness, mm;
λ——the coefficient of heat conductivity of steels, kw/(m?℃);
qmax——the maximum heat flow density, kw/m2;
a?——the coefficient of heat emission of inner wall to medium, kw/(m2?℃);
J——the current balance coefficient.
