What is mechanistic and empirical models are?

Answer 1

Both of the flow models are used to predict the flow pattern of the complex fluid behavior.

Empirical approach use experimental data to make flow models and the correlated parameters are dimensionless. For instance, Moody diagram, where friction factors are the function of Reynolds number. Empirical flow models are hard to improve and usually have errors in the range of 20%.

Mechanistic flow models comparing to empirical one, talks about the complex flow occurrences in pipes. "The use of mechanistic models is expected to improve both its accuracy and extrapolation capability to any operation conditions" (Answers.com). The mechanistic model approaches include all important variables - laboratory and field data, which helps to predict methods.

Answer 2

Mechanistic models aim to understand the underlying mechanisms that govern a system by using fundamental principles and equations. Empirical models, on the other hand, rely on data and observations to describe relationships within a system without necessarily understanding the underlying mechanisms.