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King Saud University
Chemical Engineering Dept.
CHE-405: Final Exam (Closed Book) /3/1424H)
Student Name: Student no.:
Part I
Q1. Given the following lab data which represents the response of the level in a tank to a step change in the feed flow rate of 0.1 cm3/min.:
Time(min)h (cm)04204.5405.6606.5807.31007.91208.31408.61608.91809.12009.42209.62409.8260102801030010320103401036010
(1) Determine the initial and steady state value of the process variable. Draw the data and determine the process order and its characteristic parameters.
(2) If the given data is generated from a closed-loop system using a proportional controller, can you find the true static gain and time constant of the process. If the set point was 10 cm, determine the offset.
(3) Does the level response contain overshoot. If yes, then calculate the overshoot.
Q2. For the temperature experiment: how many measured variables are available, how many of them can be measured simultaneously. Name the possible controlled variables and manipulated variables of the process. How many controlled variable can be controlled at the same time.
Part II
Choose the right answer:
Open-loop dynamic of temperature sensors:
All temperature sensors used have the same time constant. (yes/no)
A thermocouple with a large time constant has a fast dymaics. (True/False)
The time constant of the sensors changes with the volume of the boiler vessel. (True/False)
All temperature sensors used have the same static gain. (yes/no)
Open-loop dynamics of interacting tanks:
The time response of the level in the second tank is similar to that of a first-order system. (yes/no)
The first tank has (equal/larger/smaller) static gain than that for the second tank.
For a step change in the inlet flow rate, the response of the level in the second tank is (overdamped, underdamped, critically damped).
By interacting we mean that the level in the second tanks affects the level in the first tank. (true/false).
Open-loop dynamics of stirred tanks:
The tanks concentration has a bell-shape response for a step change in the feed concentration. (yes/no).
The response of the third tank takes longer time to reach steady state because its dynamics follows that of (first/second/third) order system.
In case of step change in the feed flow, the concentration in all tanks returns back to its initial value. (yes/no)
The salt concentration is measured by a conductivity meter. (yes/no)
Pressure control of a gas-storage tank:
The controlled variable is the outlet flow. (yes/no)
The process is insensitive to disturbances in the air inlet flow because of its large residence time. (True/false).
Offset decreases with (increasing/decreasing) proportional band.
The addition of derivative control eliminates offset (True/False).
Level automatic control with outlet flow:
(P/PI/PD) controller eliminates offset but suffers from oscillation.
When increasing kc in the PID controller, the response becomes (without offset/ sluggish, faster)
The manipulated variable is the (inlet flow/outlet flow/pump).
The pump speed is a possible disturbance to the level of the tank (yes/no).
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