104 C.Jiang性al/aem 33.Boundary conditions 65 5.0 4.5 ◆Da=10 25 3.4.Nusselt number 华 aw-微州 (25) 05.00000的000广 For solid: Rax10 uu=-心 26) The average total Nusselt number 44]is given by: 3.5.Numerical procedure and code verification a-瓜（欲ls+微n 27 =10 H=100 (left).fluid phase e(right)for Da-1 and5 under the non3.3. Boundary conditions The non-slip conditions are imposed for the two velocity com￾ponents on the solid walls. The temperature boundary conditions are as follows: (1) left vertical wall (X = 0.5): hf = hs = 0.5; (2) right vertical wall (X = 0.5): hf = hs = 0.5; (3) top and bottom horizontal adiabatic walls (Y = 0.5, 0.5): @hf/@ Y = @hs/@ Y = 0 3.4. Nusselt number calculation In order to compare total heat transfer rate, the Nusselt number is used. The average Nusselt number at the hot wall is defined as follows: For fluid: Numf ¼ Z 0:5 0:5 @hf @X     X¼0:5 dY ð25Þ For solid: Nums ¼ Z 0:5 0:5 @hs @X     X¼0:5 dY ð26Þ The average total Nusselt number [44] is given by: Num ¼ 1 ð1 þ KÞ Z 0:5 0:5 K@hf @X     X¼0:5 þ @hs @X     X¼0:5 dY ð27Þ 3.5. Numerical procedure and code verification The governing equations, Eqs. (15)–(19) are discretized by the finite-volume method (FVM) on a uniform grid system. The Fig. 6. Effect of H on the streamlines (left), fluid phase temperature (middle) and solid phase temperature (right) for Da = 103 , cRa = 106 and e = 0.5 under the non￾gravitational condition. Fig. 7. Effect of Darcy number on the average Nusselt number for e = 0.5 under the non-gravitational condition. 104 C. Jiang et al. / International Journal of Heat and Mass Transfer 91 (2015) 98–109