function Ti=hx(To,Tf)
global mc mh Cp
UA=536*283; 
cstar=mc/mh;
ntu=UA/(mc*Cp);
epsi=(1-exp(-ntu*(1-cstar)))   / (1-cstar*exp(-ntu*(1-cstar)));
% should be 0.6285
Q=epsi*mc*Cp*(To-Tf);
Tho=To-Q/(mh*Cp);
Ti=Tf+Q/(mc*Cp);


