Page 479 - Design and Operation of Heat Exchangers and their Networks

462 Appendix

clear

d_i = 0.016; % tube inner diameter, m
delta_w = 0.001; % tube wall thickness, m
d_o = d_i + 2 ∗ delta_w; % tube outside diameter, m
N_tube = 53; % number of tubes
t_h_in = 100; % inlet temperature of hot water (tubeside), °C
t_h_out = 80; % outlet temperature of hot water (tubeside), °C
t_c_in = 20; % inlet temperature of cold water (shellside), °C
t_c_out = 70; % outlet temperature of cold water (shellside), °C
Q = 350; % heat duty, kW
alpha_c = 1500; % shellside heat transfer coefficient, W/m2K
lambda_w = 40; % thermal conductivity of the tube wall, 40 W/mK

delta_t_LM = ((t_h_in - t_c_out) - (t_h_out - t_c_in)) ...
/ log((t_h_in - t_c_out) / (t_h_out - t_c_in));
% logarithmic mean temperature difference, K
kA = Q ∗ 1000 / delta_t_LM;
t_h_m = (t_h_in + t_h_out) / 2;
t_c_m = (t_c_in + t_c_out) / 2;
[cp_h, lambda_h, mu_h] = water_properties(t_h_m);
% isobaric heat capacity, J/kg; thermal conductivity, W/mK; K; viscosity,
% sPa
Pr_h = mu_h ∗ cp_h / lambda_h; % Prandtl number
G_h = Q ∗ 1000 / (cp_h ∗ (t_h_in - t_h_out)) / (N_tube ∗ pi ∗ d_i ^ 2 / 4);
% tubeside mass velocity, kg/m2s
Re_h = G_h ∗ d_i / mu_h; % tubeside Reynolds number
f8 = (1.82 ∗ log10(Re_h) - 1.64) ^ (-2) / 8;
R_w_i = d_i ∗ log(d_o / d_i) / 2 / lambda_w;
% conductive thermal resistance of the tube wall per unit inner area, m2K/W

L = 0; % assumed tube length, m
Pr_w = Pr_h; % assumed Prandtl number at the tubeside wall
for iter = 1 : 1000
if (L == 0)
s=1;
else
s=1+ (d_i / L) ^ (2 / 3); % entrance correction
end
Nu_h = f8 ∗ (Re_h - 1000) ∗ Pr_h / (1 + 12.7 ∗ sqrt(f8) ...
∗ (Pr_h ^ (2/3) - 1)) ∗ s ∗ (Pr_h / Pr_w) ^ 0.11;