Page 535 - Design and Operation of Heat Exchangers and their Networks

518 Appendix

Crossflow.m (MatLab code)

% dt_h/dx = t_c - t_h = - dt_c/dy, t_h(0,y) = 1, t_c(x,0) = 0
% t_h_m = exp(-x-y)∗sum < j = 1,inf >{y∗∗(j-1)/j!∗sum < k = 0,j-1 >{x∗∗k/k!}}
% x = NTU_h, y = R_h∗NTU_h
function [t_h_m] = crossflow_t_h_m (x, y)
if (x == 0)
t_h_m = 1;
elseif (y == 0)
t_h_m = exp(- x);
else
CAS_EXP_350 = 1.0070908870280796E152;
n = 1;
sx = 1;
sy = 1;
ay = 1;
ex =-x-y;
while (abs(sx) > abs(sy) ∗ 1E-8)
n=n+1;
ay = ay ∗ y/n;
if (abs(ay) > CAS_EXP_350)
ay = ay / CAS_EXP_350;
sy = sy / CAS_EXP_350;
ex = ex + 350;
end
ax = ay;
sx = ay ∗ n;
for k=1 :1:n-1
ax = ax ∗ x/k;
if (abs(ax) > CAS_EXP_350)
ax = ax / CAS_EXP_350;
sx = sx / CAS_EXP_350;
ay = ay / CAS_EXP_350;
sy = sy / CAS_EXP_350;
ex = ex + 350;
end
sx = sx + ax ∗ (n - k);
end
sy = sy + sx;