please help me, thank you in advance
this is my code:
\documentclass[5p,fleqn]{elsarticle} \usepackage{lineno,hyperref} \modulolinenumbers[10] \usepackage{amsmath} \begin{document} \begin{equation} \begin{aligned} z=0, \forall r \in [R_i,R_o]: (uC_i)=(uC_i)_{in}, T=T_{in}, \\ P=P_{in}, (u_p C_{j,p})=0, \\ i=CH_4,H_2O, CO, CO_2, j=H_2O,H_2 \label{E21} \end{aligned} \end{equation} \begin{equation} \begin{split} r=r_0, \forall z \in [0,L]: \frac{\partial (uC_i)}{\partial r}=0,\\ k_a \frac{\partial T}{\partial r}=h_w (T_w-T) \label{E22} \end{split} \end{equation} \begin{equation} \begin{split} r=r_i, \forall z \in [0,L]: \frac{\partial (uC_i)}{\partial r}=0,\\ & i=CH_4,H_2O, CO, CO_2,\\ &\frac{d_p}{Pe_m}\frac{\partial (uC_j)}{\partial r}=N_m, j=H_2,\\ &\frac{\partial T}{\partial r}=0 \label{E23} \end{split} \end{equation} \end{document}
And the results attached. https://latex.org/forum/download/file.p ... w&id=10498