Study of the heat transfer characteristics and entropy generation rate for the reacting flows inside tubes

Highlights: • The effect of equivalence ratio on the heat transfer and entropy generation is obtained. • Non-premixed and 3D combustion of CH₄ in air has been simulated numerically. • The maximum heat transfer coefficient changes linearly with the equivalence ratio for ∅ < 1. • The CoD is maximum at ∅ = 1. -- Abstract: In the present work, a numerical method is used for the simulation of the heat transfer and entropy generation for the non-premixed combustion of CH₄-air. The standard K-ε model is established for the simulation of turbulence. Furthermore, the PDF (Probability Density Function) approach is used for the simulation of the reaction between the species. Twenty species are considered in this simulation. The model is validated by comparing the values of the outlet species mass fraction between the present numerical work and the previous experimental works. The effect of the equivalence ratio, on the heat flux, heat transfer coefficient, wall temperature, entropy generation rate and the outlet species mass fraction is obtained. Based on the results, two correlations are proposed for the prediction of the maximum heat transfer coefficient. These correlations show that if the equivalence ratio is doubled the maximum heat transfer coefficient is doubled too for ∅ < 1 while it decreases by 56.4% for ∅ > 1. Furthermore, it was found that in the first region of the tube the maximum values of the heat flux, wall temperature and heat transfer coefficient occur.