CHAPTER ONE
1.0 INTRODUCTION
1.1 Background
The drying process is a complex process of heat and mass transfer resulting in a direct transfer of
humidity from some substance into hot air. The heat transfer, necessary for that process, can be
direct, convective from the drying agent which flows around the drying material, or indirect, by
different procedure (Salemović et al., 2014). Drying process has long been used from the time of
old to dry food. For example, foods like meat, fish and so on were dried using sun as the drying
medium to preserve them and prevent growth of micro –organisms (Dagbe et al., 2014). Majorly,
substances are/were dried for the following reasons:
1. To remove moisture content which may otherwise lead to corrosion. One example is
drying of gaseous fuels or benzene prior to chlorination.
2. To reduce the cost of transportation.
3. To make material more suitable for handling, as for soap powders, dye stuffs and
fertilizers.
4. To provide definite properties, such as for example maintaining free flowing of salt.
5. To mitigate the activities of the micro-organisms that can cause spoilage and decay in
food products if moisture were present in the food.
Modeling of drying processes and kinetics is a tool for process control and necessary to choose
suitable method of drying for a specific product. Developed models fall into three categories
namely the theoretical, semi-theoretical and empirical. Semi-theoretical models offer a
compromise between theory and ease of application (Khazaei and Daneshmandi, 2007). Semi
2
theoretical models are Lewis, Page, Henderson and Pabis, logarithmic, two terms and two terms
exponential, models are used widely for designing as well as selection of optimum drying
conditions and for accurate prediction of simultaneous heat and mass transfer phenomena during
drying process. It also leads to the production of high quality product and increase in the energy
efficiency of drying system. Thin-layer drying models have been used to describe the drying
process of several agricultural products.
In the Chemical Engineering Laboratory of Afe Babalola University the PID controller of our
tray drier system has been giving unsatisfactory performances. It is envisaged to replace the
controller in future with an advanced one-model predictive controller. In order to carry out this
efficiently a low dimensional lumped parameter is sought. Some model in literature are too
complex (PDE’s) to be used for control purposes or do not match the mechanics of the tray drier
of interest. However, the greatest drawback of the tray dryer is uneven drying because of poor
airflow distribution in the drying chamber that can be removed by implementing some
modification in the dryer design. (Katiyar et al., 2013). Thin layer drying kinetics is needed for
design, operation and optimization of food crops dryers (Olawale et al., 2012). Therefore this
project is aimed at developing lumped parameter model that will be suitable for control, since
most of the models developed are too emperical, strongly non linear, and too complex to
characterize tuning parameters in a control system.
1.2 Statement of Problem
The PID controller in our laboratory tray dryer has been giving unsatisfactory performances. It is
envisaged to replace the controller in future with a more advanced one – model predictive
controller. To be able to do this easily and efficiently, a low dimensional lumped parameter
3
model is sought. Some available in literature are either too complex (PDEs) to be used for
control purposes or do not match the mechanics of the tray dryer of interest.
1.3 Scope of Study
The scope of study covers the modelling and simulation of a convective drying process of a thin
slice layers of potato, using a tray dryer as the drying medium and MATLAB software will be
employed as the simulation tool for this project.
1.4 Aim of Study
The aim of this work is to derive a mathematical model suitable for control. Potato will be dried
in a tray dryer in order to define the essential drying parameters of a static thin layer of potato
and plantain of known magnitude of thickness which could be used subsequently for control of
these agricultural products and similar natural products in a ‘Tray dryer’.
1.5 Objectives
The following objectives are expected to be carried out:
i) Study and analyze existing mathematical models developed for tray dryer system
drying some agricultural products
ii) Develop a mathematical model for a tray dryer using potato as the sample in the tray
dryer.
iii) Simulation of the models using MATLAB software
iv) Compare the result with experimental data.
4
1.6 Justification
Since most of the models developed are too emperical, strongly non linear, and too complex
complex to characterize tuning parameters in a control system. This project is aimed at
developing lumped parameter model that will be suitable for control.
