Concider a 2-D channel where the pressure drop is 1000 Pa which is driving force for flow.Other physical quantity known are length = 0.01m, width = 0.001m, roh = 1000 Kg/m^3, mu = 10^-3 Pa-s. how can i calculate the driving force in lattice units if x_lb=y_lb=30.
Setting a lenghtscale is not enough - you need to set a timescale too to get meaningful units for forces and, uh, anything.
Timm has explained it to me here http://www.lbmethod.org/forum/read.php?3,1495
Generally, responses to your questions might be better if you formulate them as if you were asking for help. Yours sounds like an exam question.