Liquid Tank with Valve and Pump Outlets

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• The simulator: liquid_tank.exe.

Description of the simulated system

A liquid tank with inflow and outflow is simulated. The tank has straight walls. You can adjust the inflow and the control signal to the outlet valve and the outlet pump during the simulation.

A mathematical model of the tank can be derived using mass balance of the liquid. The model is

where A is the cross sectional area, q_in is the volumetric inflow, q_p is the volumetric outflow through the pump and q_v is the volumetric outflow through the valve.

Aim

The aim of this simulator is to develop an understanding of the dynamic properties of a liquid tank, and the differences between having a valve and a pump in the outlet.

Motivation

Liquid tanks are common in industrial process plants. It is therefore useful to understand the dynamic properties of liquid tanks.

Tasks

1. Explain that the liquid level is proportional to the integral of the inflow. Verify the integrator behaviour with a simulation (set both the valve outflow and the pump outflow to zero).
2. Pump outflow (no valve outflow): Explain that the liquid level is proportional to the integral of the pump control signal. Is the outflow dependent of the level? Verify your answer to these two questions with a simulation (set the inflow to zero, and fill the tank with water using the reset-button, and then set the pump control signal to e.g. 1).
3. Valve outflow (no pump outflow): Explain that the liquid level is not proportional to the integral of the valve control signal. Is the outflow dependent of the level? Verify your answer to these two questions with a simulation (set the inflow to zero, and fill the tank with water using the reset-button, and then set the valve control signal to e.g. 1).
4. A process is said to be self-regulating if the process variable (state variable) stabilizes at some constant value when the system is excited by constant input signal(s). Is the tank self-regulating with pump outlet (no valve)? What if there is valve outlet (no pump)? Verify your answers with simulations.

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Updated 18 August 2017. Developed by Finn Haugen. E-mail: finn@techteach.no.