function res= bubble(T)

x1=0.2;
x2=0.8;

K1=1.584+5.247*10^(-2)*T-4.067*10^(-4)*T.^(2)+7.259*10^(-7)*T.^(3);
K2=1.415+3.955*10^(-2)*T-2.976*10^(-4)*T.^(2)+5.056*10^(-7)*T.^(3);


y1=K1*x1;
y2=K2*x2;
res=y1+y2-1;
