My experience teaching this material is that take more than simester to good student to have good undersding of this complex material. Yet to give very minimal information is seems to me esential to the derstanding of the venting design. I made a great effort to disscuse the physics with minimum mathematical detials. I found Shapiro's book to be excelent soure for those who want to know in creater details this material. I will appreciat comments from the readers on how to present this complex issue without bourning the reader with exrta mathematical/physics stuff.