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International Journal of Engineering and Technology Volume 6 No.8, August, 2016
ISSN: 2049-3444 © 2016 – IJET Publications UK. All rights reserved. 260
Development of Software for Design and Construction of Rotary Dryer for
Drying Ground Cassava
Ademiluyi F. T Department of Chemical/Petrochemical Engineering. Faculty of Engineering,
Rivers State University of Science and Technology,
Nkpolu, Port Harcourt, Nigeria
ABSTRACT
A software was developed in this study using Microsoft Visual Basic.Net for the design of rotary dryer for drying ground cassava.
Basics equations which are needed for the design of part of the dryer is also presented. A graphical user friendly interface and 2D/3D
graphics for determination of Heat load required for drying, Diameter of dryer, Length of dryer, Number of flights, Radial height of
flight, the thickness of rotary shell, the thickness of insulation, Air blower power, the power of motor for feed drive, the power of
motor to drive drum of dryer and the total heat resistance through the dryer were developed. The data generated from the software
developed "Rotcassavsim" v1.0 was also used to construct a bench scale rotary dryer. This software developed is a useful tool for
engineers, operators, and designers of rotary dryer for drying ground cassava.
Keywords: Rotary Dryer, Drying, Software, Design, Ground Cassava, Rotcassavsim, Construction
1. INTRODUCTION
The rotary dryer is one of the most popular types of
convective dryers used in the chemical industry for large-
scale production. Apart from being commonly operated in the
agricultural, chemical and pharmaceutical industry; rotary
dryers have become increasingly important in other sectors
because they cover a wide range of material, sizes and shapes.
This type of dryer permits easy scale up of pilot dryer to
industrial.[1] Drying is the best method of preservation of
fermented and unfermented ground cassava, and the rotary
dryer was proposed to be the best dryer for drying ground
cassava [2,3] The rotary dryer is good for continuous
operation, and can dry large quantity of ground cassava , it's
easy to operate, with low maintenance cost.
According to the Food and Agriculture Organization of the
United Nations [4], more than 228 million tons of cassava
were produced worldwide in 2007, of which Africa accounted
for 52%. In 2007, Nigeria produced 46 million tons making it
the world's largest producer of cassava. Unfermented ground
cassava can be processed into Unmodified starch, modified
starch and glucose which are used for many purposes: directly
as cooked starch food, custard and other forms; thickener
using the paste properties of starch in the manufacture of
baby foods. They are also use as filler contributing to the
solid content of pills and tablets and other pharmaceutical
products etc.; binder, to consolidate the mass and prevent it
from drying out during cooking (sausages and processed
meats); and stabilizer, owing to the high water-holding
capacity of starch. Starch makes a good natural adhesive.
There are two types of adhesives made of starches, modified
starches and dextrins: roll-dried adhesives and liquid
adhesives. Cassava dextrin is preferred in remoistening gums
for stamps, envelope flaps and so on, because of its adhesive
properties and its agreeable taste and odour. Unfermented
cassava with high starch content, which are not good for
human consumption was also recommended for production of
ethanol in the work of Ademiluyi et al., [5]. Local polymer
(cassava starches) can also be used as a substitute for
imported sample in viscosity and fluid loss control of water
based drilling mud [6] .
Dry fermented ground cassava is a favourite food in Nigeria
and is produced mainly by female small-scale gari processors.
More than 90% of the gari produced from cassava is toasted
in open steel-pans while the rest is toasted in open clay-pots
[7]. Despite the various applications of cassava products,
preservation of cassava after harvest before processing into
cassava starch is still a problem in Africa. The Cost of rotary
dryer is not affordable to farmers in Nigeria and Africa hence
the need to make available design equations that can be used
to fabricate major parts of the rotary dryer for medium scale
and large scale drying. and also provide solution to the
storage problem of cassava after harvest.
Some of the equations available for designing of rotary dryers
are scattered in Engineering books and few in journals. Most
authors only look into the modeling and kinetic aspect of the
drying using rotary dryer [8,9,10]. Other only give equations
for determination of diameter of dryer, design of Flights,
residence time and length of dryer [11,12] but most past
works did not provide enough information on how to
determine the thickness of plate used in the fabrication of
Rotary Drum of the dryer, determine the thickness of
insulation for the rotary dryer, sizing the power of air blower,
sizing the motor to drive the feed, and sizing the motor to
drive drum of dryer etc. Drying softwares [13-17] available
International Journal of Engineering and Technology (IJET) – Volume 6 No. 8, August, 2016
ISSN: 2049-3444 © 2016 – IJET Publications UK. All rights reserved. 261
are not suitable for design of component part of rotary dryer
for drying fermented ground cassava.
Hence the objectives of this work are to provide an insight
into design equations for designing a rotary dryer and
development a user friendly software which can be easy used
by fabricators of Rotary dryers for drying ground cassava.
2. MATERIALS AND METHODS
2.1. Parameters required for Rotary Dryer design
A.Required Input Parameters
Dryer inlet Air Velocity
Product Inlet Mass Flow Rate
Mass of cassava to be dried
Density of cassava to be dried.
Air Inlet Temperature.
Rotational speed of feed drive
Torque to drive feed
Material for construction of dryer
Material for insulation of rotary drum
B. Required Output Parameters for Rotary Dryer
Heat load required for drying Q
Diameter of dryer, D
Length of dryer. L
Design of Flight
o Number of flights.
o Radial height of flight
the thickness of Dryer
the thickness of insulation.
Material of insulation: Rock wool or glass wool
Material of construction of dryer: stainless steel
Air blower power
the power of motor for feed drive
the power of motor to drive drum of dryer
The total resistance RT
Resistance of hot air
Resistance of stainless steel dryer
Resistance of insulation (rock wool)
Resistance of stainless steel cylinder covering
insulator
Resistance of air at surrounding of dryer
2.2. Design equations and models for Drying ground
cassava in a rotary dryer.
2.2.1. Determination of Heater load Required for Drying
The heat transfer within a control volume has been considered
in terms of an overall or volumetric heat transfer coefficient
defined by the equation
lmv TaVUQ (1)
where Tlm is the logarithmic mean of the temperature
differences of the air and the product at the inlet and outlet of
each dryer element. The coefficient Uva consists of the
product of a heat transfer coefficient, Uv, based on the
effective area of contact between the gas and the solids, and
the ratio a of this area to the dryer element volume. The use
of this coefficient eliminates the need to specify the area over
which heat transfer occurs.
where Uva will be calculated using the Myklestad equation
[18]
8.0
52.0
A
GaU a
v (2)
The Heater load will be used to size the heater for drying the
material:
For fermented ground cassava Ademiluyi et al., [19]
determined the Specific heat load empirically as a function of
the inlet air temperature, the inlet air velocity and mass flow
rate of feed (fermented ground cassava) as presented in
equation 3.
Q = Heat load of rotary dryer =
)889.291172.30358.0541.0( faiai MT kJ /kg
hr (3)
where
Tai = inlet air temperature in oC
Vai = velocity m/s,
Mf = mass flow rate of feed kg/hr
2.2. Diameter of dryer
The diameter of dryer is obtained from the mass flow
rate of air and the mass flow velocity of air
Area of dryer
=
s) m(kg/ air of velocity Mass
(kg/s)air of rate flow Mass2
m2
(4)
Diameter of dryer =
21
aM
4
aGx
m (5)
Input parameters for calculation of Diameter of dryer:
Ga = Mass velocity of air kg/m2 sec
Ga = ( - 0.0028 (Tai +273) + 1.9967* Va ) kg/m2 sec
(6)
Ma = Mass flow rate of air kg/s [20] =
)()1( aoaipaa TTCY
Q (7)
where for fermented ground cassava
Ya = absolute humidity of air (kg water/ kg dry air)
Tai = inlet air temperature of dryer (oC)
Va = is the specific volume of air m/s
Tao = outlet air temperature (oC)
Cpa = Specific heat capacity of air = 1.026 kJ/kg oC
International Journal of Engineering and Technology (IJET) – Volume 6 No. 8, August, 2016
ISSN: 2049-3444 © 2016 – IJET Publications UK. All rights reserved. 262
Mf = mass flow rate of feed kg/hr
2.2.3. Length of dryer
The length of dryer is obtained from equation 8 [20] once the
diameter and heat load Q has been calculated from equations
1 and 5.
L =
lma TDG
Q
67.0
25.59
1000*
(8)
Where
Q = Heat load = (Q' x Mc) /3600) kJ/s
Mc = Mass of cassava to be dried kg
D= diameter of dryer m
Ga= Mass velocity of air = Ga = ( -0.0028 (Tai +273) +
1.9967* Va ) kg/m2 sec
Where the log mean temperature difference in
equation 8 is
.)/()(In
)()(
vaovai
vaovaiLM
TTTT
TTTTT
(9)
Tai = inlet air temperature oC
Tao= outlet air temperature oC
Tv =(Vaporization temperature) was obtained from Nt
Nt
.)(
)(
vao
vai
TT
TTIn
so that )1(
)(
Nt
aiao
Nt
v
TTT
(10) for an air–water system, where Nt is the number of transfer
units that lies within the range 1.5–2.5 for an economic
design of a rotary dryer, Tai is the inlet air temperature, and
Tao is the outlet air temperature. The L2/D ratio for a dryer
should be between 3 – 10.
Total length of dryer L 2 = L + 2L1
Fig 1 Schematic diagram of dryer and insulator
2.2.4. Design of Flights
Number of flights = (πD/off Distance between flight)
(11)
Assume Distance between flight to be 10%
Lip angle of flights = 360/( number of flights)
(12)
Radial height of flight hrf (Radial flight height: D/12 to
D/8)
hrf = (Diameter of drum)/12 (13)
2. 2.5.Calculation of the thickness of stainless rotary
Dryer [21]
) 2(
)1000* (t d
i
i
Pfjxx
DxP
.+ corrosion allowance (mm )
(14)
Where: td is the minimum thickness of dryer m, Pi = Design
pressure N/mm2, (take as 10-15 per cent above operating
pressure), , D= Diameter of Dryer m, f = Design stress based
on material of fabrication N/mm2 =100 and Maximum design
dryer temperature take j=1 (assume full radiograph)
Therefore the outer Diameter of rotary drum
Do = D + 2 x td (15)
2.2.6.Calculation of the thickness of insulator cover shell
[21]
) 2(
1000) (
i
Si
scPjxfx
xDxPt
.mm + corrosion
allowance (16)
Where: tsc is the minimum thickness of insulator shell m, Pi =
internal pressure N/m2, DS = Diameter of insulator shell m, f
= Design stress of insulator shell based on material of
fabrication N/m2
2.2.7. Determination of the thickness of insulation of
rotary dryer. tisl
The thickness of insulation is important in the design of
rotary dryer. A good insulation will reduce heat lost and
reduced drying time. Fermented cassava need to gelatinize
properly in the rotary dryer before drying and good insulation
will make this possible. Rock or glass wool can be used as
insulator. In order to determine the insulator to be used in the
design, we will consider the heat resistance through the dryer
wall, insulator , insulator cover and the surrounding air. Fig 2
and 3, shows a cross section of the dryer and the heat
resistances
Fig 2 Cross section of Rotary Dryer
L
L2
L1 L1
Insulator cover
D/2 + td + tisl + tsc
Dryer
Insulator
International Journal of Engineering and Technology (IJET) – Volume 6 No. 8, August, 2016
ISSN: 2049-3444 © 2016 – IJET Publications UK. All rights reserved. 263
Fig 3 Rotary Dryer and insulator and resistances.
Heat lost by dryer to surrounding is
Q = (Tai – Tatm)/RT (17)
The total resistance RT = Resistance of hot air + Resistance of
stainless steel dryer + Resistance of insulation (glass wool) +
Resistance of stainless steel cylinder covering insulator +
Resistance of air at surrounding of dryer as shown in Figure
2 above.
RT = R1+R2+R3+R4+R5 (K/W) (18)
Calculate Resistance of hot air R1 using equation 19 [22]
R1 =LDhva *)2/(**2*(
1
(K/W) (19)
Where heat transfer coefficient for hot air in dryer hva
))(4/(
)(
2
atmai
atmai
va
TTD
Q
TTA
Qh
(W/m2K
R2 = Resistance of stainless steel dryer = )***2(
)/( 12
sdkL
rrIn
(21)
Ksd conductivity of stainless steel dryer = 17 W/m K , td =
thickness of rotary dryer drum
R3 = Resistance of insulation (glass wool) =
)***2(
)/( 23
inskL
rrIn
(22)
Kins conductivity of insulation (rock wool) = 0.04 W/m K , tisl
= thickness of insulation round dryer
Resistance of stainless steel cylinder covering insulator
R4=)***2(
)/( 34
sckL
rrIn
(23) Ksc
conductivity of stainless steel dryer insulator cover = 17
W/m K and tsc = thickness of stainless steel cylindrical
insulator cover
Resistance of air at surrounding of dryer
R5 = 1/((hout*2*π*(tisl + D/2 + td + tsc )*L)) (24)
Where hout is heat transfer coefficient for air outside dryer
W/m2 K =15W/m2K
Tai = inlet air temperature of dryer
Tatm = atmospheric temperature
Tos= temperature of the outside surface and π =3.142
Hence summing equation 19 -24 gives equation 25
RT =
LDhva *)2/(*142.3*2*(
1+
)**142.3*2(
)/( 12
sdkL
rrIn+
)***142.3*2(
)/( 23
inskL
rrIn+
)**142.3*2(
)/( 34
sckL
rrIn+
Lhout *) t+ t+ D/2 + t(*142.3*2*(
1
scdisl
(25)
Rate of heat loss per m length of dryer = rate of heat lost
from the atmosphere.
T
amai
R
TTQ
=
5R
TTQ amos (26)
hence
atmos
amaiT
TT
TTRR
5 (27)
where RT = total heat resistance through the rotary dryer
Equating equation ( 25 ) and ( 27 ) we have equation (28)
LDhva *)2/(*142.3*2*(
1+
)**142.3*2(
)/( 12
sdkL
rrIn+
)***142.3*2(
)/( 23
inskL
rrIn+
)**142.3*2(
)/( 34
sckL
rrIn+
Lhout *) t+ t+ D/2 + t(*142.3*2*(
1
scdisl
=
Lhout *) t+ t+ D/2 + t(*142.3*2*(
1
scdisl atmos
amai
TT
TT
(28)
Replacing the Radius with Diameter of drum we have
equation (28)
R1
R2
R3
R4
R5
Hot
Dryer Air
International Journal of Engineering and Technology (IJET) – Volume 6 No. 8, August, 2016
ISSN: 2049-3444 © 2016 – IJET Publications UK. All rights reserved. 264
LDhva *)2/(*142.3*2*(
1+
)**142.3*2(
)2//)2/(
sd
d
kL
DtDIn +
)**142.3*2(
)2//(tD/2t disl
ins
d
kL
tDIn +
)**142.3*2(
)2//(tD/2t disl
sc
dislsc
kL
tDttIn +
Lhout *) t+ t+ D/2 + t(*142.3*2*(
1
scdisl
=
Lhout *) t+ t+ D/2 + t(*142.3*2*(
1
scdisl atmos
amai
TT
TT
(29)
Choose tisl (thickness of insulation) beginning from (0.03-
0.3m) till left and right hand equation of equation 29 are
equal.
2.2.8. Determination of Diameter of insulator cover
plate (DSD)
Let DS = Diameter of insulator shell, from geometry
Ds = D + 2 td +2tisl (30)
so that the diameter of insulator cover plate
DSD = Ds +2ts (31)
Where D = Diameter of drum dryer. td= the thickness of drum
dryer shell and tisl= thickness of insulator. ts is thickness of
insulator cover shell
The insulator cover plate for the two ends of the insulator
shell are two in number.
Fig 4 Diameter of insulator shell and cover plate
2.2.9. Calculation of the Speed of rotation of the dryer
Revolutions per minute N = Peripheral Speed/Circumference
of Dryer
Assume the peripheral speed of rotation to be 1.5m/s =90
m/min.
Circumference of Dryer drum = πDs
2.2.10. Determination of the power required to drive
the rotary dryer drum
)000,100(
)73.0390.130.34( WWDDwNBHP SD
(32)
Where:
BHP: Break horse power required to drive drum [23]
N : No of revolution per minute
D in m = diameter of drum dryer m
DSD in m = Shell diameter .(rotary drum +insulator shell)
w = Load of material to be dried (kg) = volume of the shell x
density of ground cassava
Assume 10% hold up (H) then
w = 4
1LDH m (33)
W = weight of rotary drum of dryer + weight of material
+weight of insulation + weight of stainless steel cylinder
covering dryer insulator + weight of stainless plate to cover
insulating cylinder of dryer.
W=
4
)( 2
1
2
2 LDDsd +
4
1LDH m+
4
)( 2
2
2
3 LDDsli
+
4
))( 2
3
2
3 LDtD scsc +
4
))(2
2
1
2
3 LDtDx
scsp ( 34)
ρsd= Density of stainless drum
ρm = Density of material to be dried
ρisl= Density of insulator
ρsc= Density of insulator cover
ρsp= Density of stainless plate used to cover ends of rotary
dryer
D1 = diameter of rotary dryer drum.
D2 = Di+2td = diameter of rotary dryer drum + 2*Thickness
of rotary drum of dryer (td)
D3= D2 + 2tisl ( where tisl= thickness of insulator)
2.2.11. Determination of Air Blower Power for Dryer
The power of air blower is a function of volume of air
entering the blower and the air inlet temperature. The blower
power is expressed as: [22]
Power of blower = 2.72 x 10-5 Q * P (34)
Ds
DSD
International Journal of Engineering and Technology (IJET) – Volume 6 No. 8, August, 2016
ISSN: 2049-3444 © 2016 – IJET Publications UK. All rights reserved. 265
But Q = ( Mamx* Tai * 22.4)/(29 *Tst) so that
Power of blower (Pb) =2.72 x 10-5 *(( Mamx* Tai *
22.4)/(29 *Tst) ) * P ( 35)
Q - volume of air m3/hr
Tai -Temperature of inlet air
P – blower operating pressure, cm water column= 100 cm
water column
Mamx = Maximum Mass flow of air required for drying kg/hr
(Similar to Ma in equation 4)
Temperature of inlet air = Tatm
2.2.12. Determine the power required to drive the feed
The power required to drive the feed is expressed as:
to drive the feed
where HP =
5252
(torque) T x N (36)
HP = horse power
n = rotational speed of feed motor rpm,
T = Torque, lbf- ft
The power to drive the feed and the power required to drive
the rotary dryer drum were calculated in horsepower because
most motors are normally rated in horsepower.
2.2.13. Material of insulation of rotary dryer drum:
Rock wool or glass wool
2.2.14. Material of construction of rotary drum: Stainless
steel is recommended as material of construction for drying
ground cassava because of the high moisture content of
cassava and end use of the dried products are used for food
and drug related products.
2.2.15. Experimental Work
In order to generate input data and test the validity of the
software developed using equations above and obtain input
data such as Dryer inlet Air Velocity, Product Inlet Mass
Flow Rate, Mass of cassava to be dried, Density of cassava to
be dried, Air Inlet Temperature and optimum rotational
speed of feed drive motor. A known cassava cultivar was use
in this study - TMS 30572. The choice of this cassava cultivar
TMS 30572 was based on its preference by farmers, because
of its high yield and suitability for gari processing [24]. The
cassava was peeled, washed, grated and packed in sack for
pressing. The dewatered mash was allowed to ferment
naturally for 72hrs; sieved with a mesh of 3.5mm and then
dried in a bench rotary dryer. Changes of the air conditions,
including air temperature and moisture loss along the dryer
length was measured as drying progresses. The Data obtained
from previous works on Modeling drying kinetics of
fermented ground cassava in a rotary dryer and Effects of
Drying Parameters on Heat Transfer during Drying of
Fermented Ground Cassava in a Rotary dryer carried out by
Ademiluyi et al., [3] and Ademiluyi et al., [19] was also used
in the design.
2.2.16. Algorithmic Formulations For Software
Development
A Programs was written using all the design equation with
Microsoft Visual basic .NET (2013) to create a user friendly
package for determination of output parameters for designing
a rotary dryer for drying fermented ground cassava. The
algorithm used is shown in Fig 5.
International Journal of Engineering and Technology (IJET) – Volume 6 No. 8, August, 2016
ISSN: 2049-3444 © 2016 – IJET Publications UK. All rights reserved. 266
Fig. 5 Flow Chart for Software Development
3. RESULTS AND DISCUSSION
3.1. Description of Software package
The software developed in this work for the determination of
parameters needed for the design of rotary dryer for drying
ground cassava is referred to as "Rotcassavsim" v1.0. Fig. 6
shows the main window of the software which contains the
main menu. This software featured a user–friendly graphic
interface. A click on the menu bar and then the rotary dryer
input window will popup. Fig 7 shows input window, on this
window all the input data needed for the calculation of major
part of the rotary dryer will be entered. The first input data
"Drying air velocity/flow rate" involves the velocity of inlet
air from the air blower which, from the work of Ademiluyi
(2009) is within the range of 1 - 1.55m/s for proper
gelatinization of ground cassava during drying.
The second input data is "Product inlet mass flow rate"
(kg/hr). This is the mass flow rate of the ground cassava to be
dried within a specified time. The change in this value will
affect the heat load, length, Diameter of the rotary dryer. The
"air-inlet temperature" is also an important input data which
for fermented ground cassava should be between 140 - 190oC
for proper gelatinization and unfermented ground cassava
(dried starch) should between 70oC - 100oC. A thermocouple
and temperature controller should be installed to keep the
temperature constant in the design.
Figure 6. Main window of software
The fourth data on the input window is the rotational speed
of the drum, and for fermented ground cassava the speed of
the drum should be slow enough to allow proper
gelatinization of the product (i.e 6 - 12rpm Ademiluyi et al.,
[19] while for unfermented cassava a faster rotational speed is
needed since the product is not expected to gel. The torque to
drive the feed is also necessary. The torque needed to drive
the feed should be specified in a way that the ground cassava
will not clog the hopper chamber due to high moisture
content. Ground cassava's moisture content is expected not to
Compute R3, R4, R5, RT, RT2
Declare and initialize
variable used
If Abs(RT -
RT2) <=
0.0001
Start
Compute Tv , deltaTlm, Q
Compute Ga , Ma, Dd, ,L
Compute Nf, hrf, td , Di , hva, R1, R2, R3, tsc
Let tisl = 0.03
Compute tisl = tisl+ 0.01
If Abs(RT -
RT2) <= 0.002
Print Q, Dd, L, Nf, hrf, td, Di, tisl, R1,
R2, R3, R4, R5, RT, Ds, tsc, N, w, W,
BHP, Qvol, Pb, HP
Compute Ds, N ,w , D1, D2, D3,
W BHP , Qvol, Power for blower, HP
Stop
International Journal of Engineering and Technology (IJET) – Volume 6 No. 8, August, 2016
ISSN: 2049-3444 © 2016 – IJET Publications UK. All rights reserved. 267
be greater than 50% moisture on wet basis if rotary drying is
required for the drying. A screw press should be constructed
alongside the rotary dryer during the design. The material of
insulation should be rock wool, or glass wool. Insulation of
dryer is very important to avoid excess heat losses. The
insulation material used in this software was rock wool and
all the properties of rock wool were used in the soft ware.
Other input data like "atmospheric temperature" in oC was
specified on the input data window. The material of
construction of used in this soft ware is stainless steel and the
density of material was inculcated in the software.
The percentage hold up of ground cassava inside the dryer
was also specified on the input data window. The last input
data box is the density of ground cassava (kg/m3) to be dried.
A click on the compute box lunches the data output form and
all the parameters needed for the design of the rotary dryer is
displayed as shown in Fig. 7.
Fig 7 Input data window for ground cassava rotary dryer design
software
The output data window for design of rotary dryer for drying
fermented ground cassava is shown in Fig. 8. The first output
data box is the heat load required for drying. The value
obtained will enable the designer determine the rating of
heater required for the drying. The heat load actually
determines the length of the dryer. The second and third box
on the left displays the diameter and length of dryer. The ratio
of L/D for a dryer should be between 3 - 10. The value of L/D
obtained for this design was 5.0 which falls within the
acceptable limits.
The number of flights inside the dryer and the radial height of
flight is also displayed, which doe this design is 8. Flight are
essential in design of rotary dryer for drying ground cassava
to avoid lump formation of product as drying progresses. The
thickness of shell used to construct the stainless drum of the
rotary dryer, the thickness of the material of insulation
(preferable glass or Rockwool), thickness of insulator shell
are displayed on the output data window of Fig 6. The
resistance of heat through the wall of the dryer, insulator,
insulator cover and shell are also displayed so as to motor the
heat loss through the wall of the dryer.. The value obtained
for this design in Fig 6 for the total heat resistance RT was
1.81k/W which shows that the total heat loss through the wall
from the dryer is negligible.
Fig 8 Output data window for ground cassava rotary dryer
design software
The speed of rotation of the rotary dryer drum is also
displayed on Fig 8 . In practical terms this can only be
achieved by installing a speed controller alongside the motor
for the rotary dryer. The speed controller must be installed to
step down the speed at which the feed is driven through the
feed hopper since manufacturers speed of most motors are
high than 1000rpm.The power of the motor of the air blower
and the power for the feed drive motor were also displayed in
Fig 8.
3.2. Construction of Rotary dryer
The output data from Fig 8 were used to construct a bench
rotary dryer for drying of fermented ground cassava with a
capacity of 4kg/hr to validate the software. Fig. 9a- d shows
the parts of the rotary drawn with Autodesk Inventor
professional 2016. Fig 9a is the sectional diagram of rotary
drum, Fig 9b is sectional diagram of the product receiver. the
design of the product receiver is based on the geometry of the
rotary drum, Fig. 9c is the heater housing which were also
designed based on the geometry of the rotary drum. Fig.9d is
the dryer stand. Fig 9e and f. display a pictorial diagram of
International Journal of Engineering and Technology (IJET) – Volume 6 No. 8, August, 2016
ISSN: 2049-3444 © 2016 – IJET Publications UK. All rights reserved. 268
the rotary dryer designed at different elevations while Fig. 10
is the rotary dryer constructed from the software developed.
Fig 9a Sectional diagrams of Rotary dryer drum and
insulating Shell
Fig 9a Sectional diagrams of Rotary dryer product
receiver
Fig 9c Sectional diagrams of Rotary dryer heater
housing
Figure 9d shows the hopper attached to the rotary drum, the
sizing of the hopper is based on the design of the feed drive
motor. From the result from the output data box in Fig 8, a
one Horsepower (~ 1 Hp) motor will be adequate for this
design. The diameter of the shaft of the feed motor
determines the size of the hopper orifice in Fig 9d
.
Fig 9d Sectional diagrams of Rotary dryer hopper
International Journal of Engineering and Technology (IJET) – Volume 6 No. 8, August, 2016
ISSN: 2049-3444 © 2016 – IJET Publications UK. All rights reserved. 269
Fig 9e shows the rotary dryer stand. The design of the stand is
based on geometry of rotary dryer, heater housing and product
receiver.
Fig 9f Showing pictorial diagrams of rotary dryer
constructed at different elevations from the data
generated from the software designed.
.
Fig 8 Rotary dryer Constructed
4. CONCLUSION
Development of Software for Design and Construction of
Rotary Dryer for Drying Ground Cassava was carried out in
the study. A program was written using Microsoft Visual
Basic.NET 2013 and all the basics equations which are
needed for the design of part of the dryer were inculcated in
the design. A graphic user friendly interface and 2D/3D
graphics for the determination of heat load required for
drying , diameter of dryer, length of dryer, design of number
of flights, radial height of flight, the thickness of rotary shell,
the thickness of insulation, air blower power, the power of
motor for feed drive, the power of motor to drive drum of
dryer and the total heat resistance through the dryer were
developed. The data generated from the software developed
was also used to construct a bench scale rotary dryer. This
software developed is a useful tool for engineers, operators,
and designers of rotary dryer for drying ground cassava.
ACKNOWLEDGEMENTS
Thanks to the management of the Raw Materials Research
and Development Council Nigeria (RMRDC) who sponsored
the development of this software and the management of
Tertiary Education Trust Fund, Nigeria (TETFund) who
provide funds for the construction of the Rotary dryer.
Special thanks to Professor M.F.N Abowei , Prof M. J.
Ayotamuno (River State University of Science and
Technology, Port Harcourt) and Professor B. O. Oyelami
(National Mathematics Center, Abuja) for their support.
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