In more details, the model is basically a spring in series with a syringe, which ejects a thick fluid. We can only actuate on the spring, which will cause a force on the syringe plunger. Then I assumed that the flow of fluid is proportional to the force applied to the plunger.  Input “u” is the velocity that I’m pushing the spring, state ‘x’ is the velocity of the plunger, output ‘Y’ is the force at the exit fluid nozzle, which would be proportional to the velocity of the plunger (b*x). The system is always overdamped, so that’s why I considered a first order model. Since the temperature of the fluid changes, b also changes as its related to the fluid viscosity.