Page 539 - Design and Operation of Heat Exchangers and their Networks

522 Appendix

Example 4.1 Nucleate boiling of R134a on a horizontal
tube (MatLab code)

% Example 4.1 Nucleate boiling of R134a on a horizontal tube
% Calculate the nucleate boiling heat transfer coefficient of R134a on a
% horizontal plain cupper tube at the saturation temperature of 15.12°C
% and q = 12.77 kW/m2. The roughness of the tube surface is assumed to be
% 0.4E-6 m.

clear

q = 12770; % heat flux, W/m2
t_s = 15.12; % saturation temperature, °C
R_a = 0.4; % roughness of the tube surface, micrometer
p_s = refpropm('P', 'T', t_s + 273.15, 'Q', 0, 'R134a');
% saturation pressure, kPa
M = refpropm('M', 'C', 0, 'T', 0, 'R134a');
p_cr = refpropm('P', 'C', 0, 'T', 0, 'R134a'); % critic pressure, kPa
q_0 = 20000; % reference heat flux, W/m2
p_r_0 = 0.1; % reference reduced pressure
p_0 = p_r_0 ∗ p_cr; % reference pressure, kPa
dpdtsat_0 = refpropm('E', 'P', p_0, 'Q', 0, 'R134a');
% saturation pressure, kPa
sigma_0 = refpropm('I', 'P', p_0, 'Q', 0, 'R134a');
% Surface tension, N/m
p_r = p_s / p_cr; % reduced pressure

% 1. Cooper correlation
alpha_Cooper = 90 ∗ q ^ 0.67 / M ^ 0.5 ∗ p_r ^ (0.12 - 0.2 ∗ log10(R_a)) ...
/ (- log10(p_r)) ^ 0.55;

% 2. Gorenflo correlation
alpha_0 = 3580 ∗ (dpdtsat_0 ∗ 1000 / (sigma_0 ∗ 1E6)) ^ 0.6;
% reference heat transfer coefficient, W/m2K
n = 0.95 - 0.3 ∗ p_r ^ 0.3;
F_q = (q / q_0) ^ n;
F_p_r = 0.7 ∗ p_r ^ 0.2 + 4 ∗ p_r + 1.4 ∗ p_r / (1 - p_r);
F_w = 1;
alpha_Gorenflo = alpha_0 ∗ F_q ∗ F_p_r ∗ F_w;

fprintf('alpha_Cooper=%f,alpha_Gorenflo=%f\n',alpha_Cooper,alpha_Gorenflo);