thank you for your time
actually for darcy number 0.1 when i change richardson number from 0.01 to 5 the value of nusselt number changes in paper but my value does not change. i am using grasoff number 10^4 and the value of fluid properties are density =998 dynamic viscosity 0.000855 beta value=0.000332 and cp=4180. for the porous material i use copper. The value of viscous resistance i have taken 10,100,1000 and 11884. the value of porosity is 0.9. also if you see in my results the value of streamlines are also not matching with the darcy number 0.1 and richardson number 1. it makes me feel something is wrong in my analysis. 
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