I have a model of recuperator. it is an assemlby in which some parts are there. I want to define porosity to those components. I go thorugh engineering database and i define one new item over there. I found many options over there like in resistance calculation formula if i want to go with dependency in velocity: what is A and B stands for? wht to enter in length and area option by default its value is 0.1m and 0.01m2 is given. any one can guide me how to define porosity to particular component and which option is to use for engineering database?