In the construction of the ``common'' model, two main assumptions were made: one is a constant which depends only on the liquid metal material, and two) many terms in the energy equation (Bernoulli's equation) can be neglected. Unfortunately, the examination of the validity of these assumptions was missing in all the previous studies. Here, the question when the ``common'' model valid or perhaps whether the ``common' model valid at all is examined. Some argue that even if the model is wrong and do not stand on sound scientific principles, it still has a value if it produces reasonable trends. Therefore, this model should produce reasonable results and trends when varying any parameter in order to have any value. Part of the examination is done by varying parameters and checking to see what happen to trends.