function dTout = htexr(z,T,hi,ho,Ai,Ao,wc,wh,cP)
Tc = T(1);
Th = T(2);
dTc = hi*Ai/wc/cP*(Th-Tc);
dTh = ho*Ao/wh/cP*(Th-Tc);
dTout = [ dTc dTh]';

