International Conference on e-Learning’14 96

System for monitoring and control of the drying pro cess

Nikolay Valov, Irena Valova

Abstract: This article describes a proposed solution for controlling, monitoring and documenting of

the complete process of drying fruits and vegetables for teaching purposes. A complete hardware solution is being suggested and described in depth - a complete drying chamber, paired with additional measurement and control devices allowing the gathering of data throughout the whole process. The proposed software implementation is based on developed mathematical models. It works in fully automatic mode but supports changes in the parameters in order to allow the users - both students and teachers, to control the process remotely using internet connection to the workstation, connected with the chamber. Working with this system would be beneficial for the students allowing them to understand the principles of the drying process and the affect each of the input parameters have on the process.

Key words: Drying processes, Model, Kinetic curves.

INTRODUCTION Training in some topics, regarding industrial processes - preparation, conduct,

monitoring and control that are of long duration, require specific conditions and cannot be cut or divided into separate parts. Teaching hours are not long enough to allow within them to study the overall flow of these processes, making it necessary to seek other options for their follow-up and analysis. The proposed system allows extracting kinetic curves of drying, on the basis of the actual drying process, and after that they are used to investigate how changes in the drying process parameters affect it. Software packages LabVIEW and MATLAB are used for realization of the automatic control of the drying process on the bases of the kinetic curves. They allow quick adjustment of the managed system without the need of hardware manipulations on managed devices, and management of various qualitative and quantitative indicators.

DESCRIPTION OF THE PROPOSED SOLUTION The use of dried foods is particularly relevant because of the usefulness of these

foods and the desire of modern people to have a healthy lifestyle and diet. Dehydration is a way of storing fruits and vegetables, known for many years. Originally, natural sources for the withdrawal of moisture from fresh raw materials were used. Over time, it appears that the natural sources of energy are not the most suitable, especially in the industrial production of dried fruits and vegetables. Drying processes are now performed in convective drying chambers with an electric power source, causing intense drying all over the day. It is these industrial processes that are of interest to the education of students.

Different ways to reduce energy costs and improve the quality of finished products are under development currently. One step in this direction is to take curves of drying the fruit or vegetable and then to be used in industrial drying conditions [4, 5]. The kinetic curves of the drying process are created by an appropriate mathematical model and can be used in the management of the industrial drying process or for educational purposes.

The idea is to create a drying system and to implement drying cycles with different fruits and vegetables with this system. Then the collected data from these real processes to be used to determine their kinetic curves [1, 2]. These curves are then implemented in software system that is suitable to manage the proposed hardware drying oven and used to let students understand how to control and manage drying processes.

The proposed laboratory drying system for educational and experimental purposes (figure 1) allows drying of raw material up to 30kg. There are four equal square layers (with sizes 450x450mm) in the chamber, on which the raw material is arranged. The

International Conference on e-Learning’14 97

layers can be loaded with raw material having a density of 2.460÷29.630kg/m2. The volume of the heat chamber is 0.5m3. The camera has double walls, and it is fitted with two heaters – one at the top and one at the bottom, each with power 1000W. Axial fan with electric power 180W is used for the air circulation in the chamber. The fans’ speed is controlled by inverter ELDI/M. Recirculation of the air is not used.

Figure 1. Laboratory Dryer

These are the same components that are being used in industrial dryers. The only difference here is the use of electronic scale EVL for monitoring the mass change of the dried material during the process. The experimental date are collected and stored by Windows-based workstation which has the necessary interfaces and software. The RS-232 interface of the electronic scale and specialized software EVLTest can be used to collect and store readings of the scale at selected time intervals (10÷600s) depending on the dried material and the current values of the drying agent.

Parameters that affect the drying of fruits and vegetables are: temperature; air flow rate; moisture content of the drying agent.

Air, which is heated to the required temperature and is blown with the desired speed, is the most commonly used technique for drying. It is possible to use specialized absorbers to maintain the proper moisture content but they use a relatively large amount of energy and therefore, in the system that is used for learning, current moisture content of the air is only registered.

Small sensors are selected, respectively with a small inertia, and without the need of independent power supply. The power of the working PC via USB remote module DAQ-6009 is used, which is sufficient for both LM35CZ temperature sensors. The technical specifications of the sensor LM35CZ meet the following requirements: measuring range -40÷110ºC, a static error 1ºC, voltage output 10mV/ºC and power supply +5Vdc.

The temperature sensors in the chamber are two, one for the input temperature and one for the output temperature of the drying agent. The actual volume of laboratory chamber (0.5m3) is relatively small and only an input temperature sensor is enough. Generated signals from temperature sensors are measured through the analogue inputs of the NI USB-6009 module (8 analogue inputs - 14-bit, 48kS/s, 0.0003V/bit) [9]. To set the different temperature regimes is used temperature controller that is synthesized in LabVIEW and managed by digital output of NI USB-6009 (figure 2). Synchronous electric switches (SSR-relay) - CELDUC SC942160 are used for switching the heater to the mains. They can be managed directly from the digital output of the DAQ module with voltage 0÷5Vdc, and through adequate cooling may include electrical load up to 25A. The regulator operates on the principle of PWM (pulse wave modulation), by establishing the desired value for period up to 10min and supports the assignment with

International Conference on e-Learning’14 98

precision of ±1ºC. Settling time depends on the temperature difference between the ambient air and the required value of the drying agent. From the experiments conducted in real conditions of drying, setting selected temperature of the drying agent is achieved in ≤3min.

The rate of airflow in the drying chamber is changed by a fan driven by an induction motor (figure 2). The speed is maintained by an inverter Electro invent model ELDI/M–0.37kW. The analogue input of the inverter is used for speed control and the control signals are generated by the NI USB-6009 (2 analogue outputs - 12-bit, 150S/s, Vout 0÷5V). Measurements are made at no load dryer with KIMO anemometer model VT100.

Figure 2 Schematic of control system

The weight of the material subjected to drying, is the most reliable criteria for the current moisture level. The best way to determine the status of the drying process is by keeping track of this weight. For this purposes, the electronic scale EVL15 is connected to the system. It allows to measure the mass of the material in real time and to store data through specialized software (Figure 3). The module allows setting the communication port of the computer, the speed of data transmitted on the serial interface and the type of balance. By this module it is possible to choose the length of the time interval between which the values gathered will be stored in a TXT file [8]. The collected data are used to construct the kinetic curves for the drying of different materials at given temperature and speed of the airflow in the chamber. Table 1 shows a sample of the change of weight measured by the scale during the drying process. Time interval between weights values used for this experiment was nearly 1min.

Table 1 Time Mass, kg

26.7.2013 г. 16:21:34 3,54 26.7.2013 г. 16:22:34 3,54 26.7.2013 г. 16:23:37 3,54 26.7.2013 г. 16:24:37 3,538 26.7.2013 г. 16:25:48 3,538 26.7.2013 г. 16:26:48 3,536 26.7.2013 г. 16:27:49 3,534 26.7.2013 г. 16:28:50 3,534 26.7.2013 г. 16:29:50 3,53 26.7.2013 г. 16:30:54 3,534

Figure 3 Software for communication with electronic scale EVL

International Conference on e-Learning’14 99

An analytical relation is used for the construction of the drying curves. Using the experimentally obtained data for the moisture content of the material, the magnitude MR is calculated, as (1):

UUU

ro

ouMR

−−

= , (1)

where u is the moisture content in the material at the moment t, kg/kg;

U o - the moisture content at the start of the process, kg/kg;

U r - equilibrium moisture content, kg/kg; The measurement of the parameters of the ambient air, which is used as the

drying agent, is essential for energy efficient process with utilization of the potential of the atmospheric air [3]. The selected transmitter T7511 (figure 4), produced from COMET System sro, measures and records the following technical characteristics: air temperature T -30÷105ºC; relative humidity φ 0÷100% and atmospheric pressure ρ 800÷1100hPa, which meet the requirements for measurement of the drying process. With usage of this transmitter is avoided the transmission (and subsequent conversion) of the measured values in analog form. Transmitted over an Ethernet connection values are directly in digital form, which significantly eases the visualization, interpretation and subsequent management of the process. More interesting part of this transmitter is its configuration for transmission of measured parameters. Specialized software TSensor (figure 5), offered by the manufacturer [7] is used for setting. The measured from the transmitter T7511 parameters' values: Temperature, Relative humidity, Dew point and Pressure of ambient air are exported in CSV file.

Figure 4 Transmitter Т7511 Figure 5 Configuration of the communication

channel

The graphical language G of the development and control environment LabVIEW implements the software part of the project (figure 6). Kinetic curves can be described as Matlab scripts and connected to the LabVIEW system. A procedure in Matlab, which utilizes a genetic algorithm, calculates the optimal values for the parameters – speed v and temperature T of the drying agent [3, 6].

Each drying cycle is associated with concrete curve. After selecting the concrete kinetic curve, the main user window of the system is shown on figure 7. The start moisture content U o , the equilibrium moisture content U r and final moisture content

U end of fruits or vegetables have to be submitted from the user at the beginning of the drying process (figure 7, (1)). The moisture content in the ambient air at the moment Y a and the temperature of the ambient air T a have to be determined for the normal control of the drying process (figure 7, (2) and (3)). The transmitter directly measures temperature T a and the moisture content Y a is calculated in the environment LabVIEW,

International Conference on e-Learning’14 100

using dependency (3):

( )

( )eP T a

TT

aa

ws +=

+−++

15.273 2.8

15.273

723515.2730057.0345.77

, (2)

PPP

Ywsat

wsa −

=62198.0

, (3)

where Pat is the pressure measured;

Pws - calculated partial pressure of water vapor at temperature T a .

Figure 6. LabVIEW Software part of the learning system

The initial conditions and the kinetic curves of the drying process are defined and the system will work alone and will seek to move in the kinetic curve and maintain appropriate air temperature and humidity, which is blown in the chamber. Users (or students) can monitor instantaneous parameter values, graphical representation of the climate chamber temperature and values of PWM output (figure 7, (4) and (5)). If necessary, they can intervene and change the setting of the PWM output and thus the temperature (figure 7, (6)) of the drying agent and a final moisture content of the material U end .

During the practical exercises students discuss with the lecturer theoretical aspects of the process and start it. After that they get remote access to this workstation and could monitor different parameters and also can change some of the values in order to change the process flow. It is very important to know the main functions of every one of the parameters before applying any changes.

International Conference on e-Learning’14 101

Figure 7. Main user interface window of the software system

CONCLUSIONS AND FUTURE WORK With the proposed experimental system is possible to determine the kinetic drying

curves for different fruits and vegetables and to use them for automating the drying process. Collected data from the drying processes are stored in files and can be used for later analysis, validation and assessment of the process.

Management of the dryer can be used in simulation mode (for shorter time interval) for the assessment of duration of drying, at constant values of the ambient air.

It is possible to use remote control to the proposed system in case of Internet connection to the workstation on which it is installed.

For educational purposes it is necessary to develop an application with web access for different groups of users and to define different privilege policies for access to the system and setting up input parameters.

"The present document has been produced with the financial assistance of the

European Social Fund under Operational Programme “Human Resources Development”. The contents of this document are the sole responsibility of the “Angel Kanchev” University of Ruse and can under no circumstances be regarded as reflecting the position of the European Union or the Ministry of Education and Science of Republic of Bulgaria." Project № BG051PO001-3.3.06-0008 “Supporting Academic Development of Scientific Personnel in Engineering and Information Science and Technologies”

REFERENCES [1] Bon, J., Rossello, C., Femenia, A., Eim, V., Simal, S. Mathematical modeling

of drying kinetics for apricots: Influence of the external resistance to mass transfer. Drying Technology, 25, 2007, pp.1829-1835.

[2] Ivanova D., N. Valov, V. Stoyanov, I. Valova. Mathematical modeling of drying kinetics for apricots. Conference University of Ruse „Angel Kanchev“, Electrical Engineering, Electronics, Automation, 2011, ISSN 1311-3321.

1

2

3

4

5

6

International Conference on e-Learning’14 102

[3] Ivanova D., N. Valov, V. Stoyanov. Determinations of the objective function for the optimal control of the apricot drying process. Food Processing Industry Magazine. Vol.3 2012 pp.38-41, ISSN1311-0179

[4] Quirijns, E. J., van Willigenburg, L. G. and van Boxtel, A.J.B.. New perspectives for optimal control of drying processes. International symposium on Advanced Control of Chemical Processes ADCHEM 2000, pp. 437-442.

[5] Saravacos, G. D., Kostaropoulos, A. E.2002, Handbook of Food Processing Equipment, Kluwer Academic, London.

[6] Ugur Yuzgec, Yasar Becerikli, Mustafa Turker. Nonlinear predictive control of a drying process using genetic algorithms. The Instrumentation, Systems and Automation Society, Vol. 45, №4, 2006, pp. 589-602.

[7] http://www.cometsystem.com/products/temperature-humidity-pressure-transmitters-and-regulators/web-sensor-t7511-remote-thermometer-hygrometer-barometer-with-ethernet-interface/reg-T7511

[8] http://elicom-bg.com/en/cat/elicom-retail-scales-15 [9] http://www.ni.com/pdf/manuals/371303m.pdf ABOUT THE AUTHOR Nikolay Valov, Department of Automatics and Mechatronics, University of Ruse

“Angel Kanchev”, Phone: +359 82 888266, е-mail: npvalov@uni-ruse.bg Assoc.Prof. Irena Valova, PhD, Department of Computer Systems, University of

Ruse “Angel Kanchev”, Phone: +359 82 888685, е-mail: Irena@ecs.uni-ruse.bg.

The paper has been reviewed.