--%>

Dynamic model for the paper machine headbox

Explain and derive the Dynamic model for the paper machine headbox?

E

Expert

Verified

We'll first develop a dynamic model for the paper machine headbox.

A stock balance around the headbox. A suffix hb refers to the head box.

Accumulation = Input – Output

dmhb/dt = ρqin – ρqout

Now ρ, is the stock density, but since the consistancy is 0.5% only,  ρ = ρw = Water density

d(ρVhb)/dt = ρqin – ρqout

dVhb/dt = qin – qout

Ahbdh/dt = qin – qout

where, Ahb, is the c/s area of header and assumed to be constant.

qout, is the flow out of the header, and is only through slice, and can be written as, CAs(2gh)1/2, where As, is the cross sectional area of slice perpendicular to the flow, and C is characteristic constant coefficient for the slice.

Hence,
Ahbdh/dt = qin – CAs(2gh)1/2,

To find, we can write Bernoulli's equation between Vacuum Degasser and Headbox. Suffix vd refers to vacuum degasser.

Pvd/ρ + W = (Phb + ρgh)/ρ + V2/2
 
V = {2[Pvd - (Phb + ρgh)]/ρ + 2W}1/2

qin = AinV =  Ain{2[Pvd - (Phb + ρgh)]/ρ + 2W}1/2

Hence the dynamic model is,

Ahbdh/dt = Ain{2[Pvd - (Phb + ρgh)]/ρ + 2W}1/2 – CAs(2gh)1/2,

where the rate of stock height change in head box is related to the pressure in vacuum degasser and height.

We have to linearize the non linear dynamic model.

So that the effective model will be,

τdh'/dt = KpP'hb  + Khh',

So as we see the the response of the height of stock to variations in vacuum degasser pressure is first order lag. We don't know the dynamics of level sensor or transmitter, but we'll assume it's also first order lag.

Hence the effective system will be a second order. And hence it'll be oscillatory, and we propose the PID controller for level control by manipulating the speed of fan pump.

Using MATLAB control toobox and given values of the parameters in the problem, we approximately find the following controller parameter settings.

    Kc = 9.6, τI = 2.3 min, τD = 3.5 min.

Similarly, a propotional integral controller is proposed for pressure control in head box.

The pressure in the head box is related to in flow of air, which is controlled by PI controller.
The air is available at pressure of 300 kPa.

dPhb/dt = f(Qin), where is the inlet flow rate of air.

This will be pure capacitive system, hence we propose PI controller.

We find the controller parameters for this,

Kc = 14.5, τI = 4.5 min.

   Related Questions in Mechanical Engineering

  • Q : 01 a vaccume guage connected to chamber

    a vaccume guage connected to chamber 40kpa at location where atmospheri pressure is100kpa .determine absolute pressure

  • Q : Difference between pressure vessel &

    Difference between pressure vessel & column: The Pressure vessels (cylinder or tank) are utilized to store fluids under pressure. If the pressure vessel are design in the form of column to separate the gas at u

  • Q : SI Engines Illustrate why several types

    Illustrate why several types of the sound are generated in different bikes, although they run on the SI Engines?

  • Q : Cetane Number and Octane Number

    Describe the term Cetane Number and the Octane Number?

  • Q : Excitation of Modes in Fiber A

    A multimode fiber is used to couple light into a single mode fiber. Both fibers have the same total diameter. Explain the coupling. Use equations, MATLAB, etc. if necessary. If an LED is used to excite a single mode fiber, explain the coupling of light to the fiber? U

  • Q : Mode Superposition Method Define Mode

    Define Mode Superposition Method in brief?

  • Q : Life expectancy in Product design

    Life expectancy: This part of the specification will state how long the product should remain in working order provided the customer gives reasonable care and maintenance. Also take into account technological advances and ongoing improvements that wou

  • Q : Size and weight in Product design

    Size and weight: If the product is particularly small the cost may be increased if more precise manufacturing methods are demanded. Weight restriction will as well influence materials to be utilized: this in turn will influence the manufacturing proce

  • Q : Aerospace Computational Techniques -

    Hello, I have a programming assignment that incorporates aerodynamics. I was wondering if it is possible to program the following assignment. If not, what would be the aerodynamic formulas required to do so. Thanks.

  • Q : Ergonomics in product design

    Ergonomics: This is concerned with how easy (comfort, complexity) the product is to use by the targeted market. Physical human dimensions must be considered when designing the driver's seating, instruments, and controls in a car. Slight variations bet