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DESIGN AND FABRICATION OF A COMPUTER AUTOMATED DRYER FOR THIN LAYER GRAIN DRYING
ABSTRACT
This paper presents the design and fabrication of the laboratory model of a computer
automated dryer for thin layer drying of grain kernel. A blower forces air through the grains
placed in the heating chamber. Various process parameters from corresponding sensors are
acquired at specified intervals for certain duration of time by a PCL-207 card interfaced with
Pc. The temperature of the drying chamber is kept constant by triggering a thyristor at different
firing angles with the help of PCL-207 card, which controls the input voltage to the heater.
Weight of sample versus time curves have been plotted at different temperatures and the results
are found to be satisfactory.
1. INTRODUCTION
The basic purpose of drying grain is to reduce its moisture content to a level acceptable
for safe storage [1]. Conventional dryers use bulk quantity of grain for drying. Even the
laboratory model fabricated for drying operation is voluminous. Moreover, many of its operations
are manual and hence, less accurate. For the purpose of study of the property of grain drying,
one needs a single-kernel or at best a thin layer drying process. The aim of the present work
is to design and fabricate a laboratory model of computer automated dryer for the study of
thin layer grain drying process.
2. DESIGN AND FABRICATION
The setup has been fabricated based on forced air-drying. It consists of a blower
(combination of a motor and fan) to force air through the sample placed in a drying chamber
and a heater to make the drying faster. A digital thermometer and a digital hygrometer have
been used for the measurement of temperature as well as humidity of the drying chamber. A
digital anemometer measures the velocity of forced air and a computer compatible electronic
balance measures the weight of sample placed in the drying chamber. Data acquisition from
the sensors as well as temperature control is performed by a PC equipped with suitable I/O
card PCL-207 [2]. The schematic diagram of the setup has been depicted in fig. 1.
J. Instrum. Soc. India 34 (3) 187-194
188
Fig. 1. Schematic representation of the setup
2.1 Digital Thermometer
The digital thermometer has dimension of 14.2 x 4.6 x 2.8 cm and weight of 130 gms
[3]. It receives its power from a standard 9V battery. Its measurement rate is 3 measurements
per second. The digital thermometer uses a semiconductor type temperature sensor, which
operates on the principle that the base-emitter voltage of a forward biased transistor is directly
proportional to the temperature. The voltage signal is further conditioned by an electronic circuit
after which it is fed to INHI (pin 31) and INLO (Pin 30) of the 7106 IC, which produces the
required digital display. The advantage of this instrument is that it has high sensitivity and
linearity over a range of –500° C and 1500° C.
2.2 Digital Hygrometer
The digital hygrometer has dimension of 168x80x35 mm and weight of 325 gms [4].
The power supply to the instrument is from a 9V battery. It has the measuring range of 10%
to 95% relative humidity (RH) with resolution 0.1 % RH. The instrument uses a high precision
thin-film capacitance sensor for fast response. The variation in capacitance is a measure of
the relative humidity as the capacitance has got linear relationship with the moisture content.
The detection circuit consists of a solid-state capacitance bridge, output of which is proportional
to humidity. After further conditioning, the analog voltage is fed to the INHI (Pin 31) and
INLO (Pin 30) of the 7106 IC that produces the required digital display.
2.3 Digital Anemometer
The digital anemometer has dimension of 168x80x35 mm and weight of 325 gms [5]. It
receives its power supply from a 9V battery. It has a sensor head, which is basically a vanewheel
fitted with eight numbers of vanes and its axis parallel to flow of air. The vanes rotate
freely when air impinges on them; the angular velocity is proportional to the air velocity.
Velocity is measured by counting the rate at which the vanes pass a given point, using a
capacitive proximity pickup to produce voltage pulses. The pulses are fed to a frequency to
voltage converter, which provides an analog output voltage signal corresponding to the flow
rate. After further conditioning, the signal it is fed to the input INHI (Pin 31) and INLO (Pin
30) of the 7106 IC that produces the required digital display.
U.C. Pati, M.K. Ghosh, S. Bal and G. Panda
189
2.4 Electronic Balance
It is a sophisticated electronic device, which is serially equipped with an integrated data
input keyboard and a program package for the laboratory operation. It has dimension of
220x235x60 mm and weight of 4.5 kg [6]. The electronic balance utilizes a displacement sensor
(strain gauge) null detector, an amplifier, and a torquing coil in a servo system to balance the
difference between the unknown weight and a standard weight. The balance operating program
permits adoption of balance to various ambient conditions at the point of use and to different
weighing requirements plus selection of various weight units. Automatic tare weight systems
subtract container weight from total weight to give net weight when material is placed in the
container. Additionally, it is provided with a data interface. Transmission of weight data to
connected peripherals and commands to the keyboard or the toploader is done via the full
duplex RS-232C or RS-423C interface. The data output occurs either by an externally produced
print command or synchronously with the display changes.
2.5 Drying Chamber
The drying chamber is designed to cover the platform of the weighing balance to eliminate
environmental effects. Its dimensions as well as openings depend upon the size of the weighing
balance, diameter of the blower tube, opening for manual placing of the test material on the
balance pan and the size of the sensors. The chamber is made of perspex sheets. Dimensions
of the chamber are 0.3 x 0.24 x 0.2 meter.
3. HARDWARE DESCRIPTION
The hardware description of the developed computer automated dryer is divided into
following two sections.
3.1. PC-based Data Acquisition System
The sensing and signal processing circuit of digital instruments are used in the present
work to get the analog voltages, which are proportional to the different process parameters
such as temperature, velocity, and humidity. The block diagram of the data acquisition scheme
is shown in fig. 2.