## Lab Station: Air Heater
## Description of the system
Figure 1 shows an air
tube with heater and temperature sensor(s). University College of Sout-Eastern
Norway, Department of Electrical Engineering, IT and Cybernetics on campus Porsgrunn,
has 26 copies of this lab station, being used in several control courses in
both bachelor and master programmes in technology.
## Video presenting the air heater
## Mathematical model
An input-output
mathematical model that has proven to describe quite well the dynamic
behaviour of the outlet air temperature is given by Eqs. 1 and 2 given
below. T where: ·
T ·
T ·
T T theta where: ·
u [V] is the control signal to the heater. ·
theta ·
K ·
theta Note that the above model
is not derived by mechanistic (first-principles) modeling based on energy
balance. In stead, the model expresses the typical "time-constant with
time-delay" dynamics of thermal processes. In the literature, Eq. 1 is
often referred to as a “First Order Plus Time-Delay” (FOPTD) model. (However,
under idealized assumptions, mechanistic energy balance modeling of the
contents of a heated tank with inflow and outflow and heat transfer with the
environment through the tank walls, actually gives a model like Eq. 2.) In a simulator based on
this model a proper initial value of the state variable T The parameter values vary
somewhat between the lab stations. However, the following values are typical
and can be used (e.g. in a simulator) unless you have found other values from
experiments: ·
K ·
theta ·
theta Furthermore,
you may assume - T
_{env }= 20 deg C
## Experimental data
airheater_logfile.txt contains data from an experiment on the air
heater. (The fan speed was kept constant during the experiment.) The file containes three colums of data: - Time, t [s]
- Control signal to the heater, u [V]
- Outlet temperature, T_out [C].
## Technical information
Each air heater consists
of the following items: 1.
One plywood plate on which the devices are mounted 2.
Plastic box containing all electrical devices 3. One plastic tube 4.
One air fan (originally a PC fan) 5.
One potensiomter (variable resistance) for manual adjustment of the
voltage controlling the fan speed. 6.
One electric power cable (for connection to mains outlet, e.g. 220 V) 7.
Two temperature sensors, type Pt100, with measurement signal converter
from resistance to current: INOR miniPack-L 8. One heating element (coil) for electric heating of air. The coil is originally used in a shoe dryer. Power (assuming 220 VAC) is 250 W. 9. One electrical AC-DC converter from 220 VAC to 24 VDC. Datasheet_power_supply.pdf 10. One Pulse-width modulator (PWM): Carlo Gavazzi RN F23V30. Datasheet_ssr_pwm.pdf ## Publication
·
F. Haugen, Fjelddalen E, Edgar T., Dunia R., Updated
3 November 2018 by Finn Aakre Haugen. E-mail Finn.Haugen@usn.no. |