Review on the Application of a Tray Dryer

Review on the Application of a Tray Dryer
World Applied Sciences Journal 22 (3): 424-433, 2013
ISSN 1818-4952
© IDOSI Publications, 2013
DOI: 10.5829/idosi.wasj.2013.22.03.343
Review on the Application of a Tray Dryer System for Agricultural Products
S. Misha, 1S. Mat, 1M.H. Ruslan, 1K. Sopian and 1E. Salleh
Solar Energy Research Institute, Universiti Kebangsaan Malaysia, 43600 Bangi Selangor, Malaysia
Department of Thermal-Fluids, Faculty of Mechanical Engineering,
Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia
Abstract: Application of tray dryer is widely used in agricultural drying because of its simple design and
capability to dry products at high volume. However, the greatest drawback of the tray dryer is uneven drying
because of poor airflow distribution in the drying chamber. Implementing the proper design of a tray dryer
system may eliminate or reduce non-uniformity of drying and increases dryer efficiency. This paper discussed
several design of tray dryer system for drying agricultural products and its performance. Most of the dryer
systems have been developed are using solar energy because the systems run at low operating cost.
Computational fluid dynamics simulation is a very useful tool in the optimization of the drying chamber
configuration by predicting the airflow distribution and the temperature profile throughout the drying chamber.
Key words: Tray dryer
Agricultural drying
Solar dryer
increasing the temperature and velocity shortens the
drying time. However, for heat-sensitive products, such
as food and pharmaceutical products, high temperature
decreases product quality. In this case, drying at low
temperature and humidity is required to maintain the fresh
color of the product using the desiccant system [1-3].
Without the use of the desiccant system, high
temperature is required to obtain low humidity. Several
advantages of using desiccant material in drying
application have been discussed in detail by Misha et al.
[4]. The same product dried with different techniques
produces different levels of product quality [5]. An
example, refractance-window (RW) drying method can
maintain the antioxidant compounds such as L-ascorbic
acid, total flavonoids and lycopene content except in
phenolic compounds which was found to be more in
tomato powder produced by convection drying [6].
Augustus Leon et al. [7] presented the parameters
commonly used to evaluate solar dryers. The parameters
include physical features of the dryer, thermal
performance, quality of dried product, cost of dryer and
payback period. These parameters are also suitable for
any dryer system. Chua and Chou [8] evaluated low-cost
drying methods used in developing countries. The
selection criteria were based on the following
considerations: (1) initial cost is low; (2) system is easy to
Drying has remained one of the popular methods for
preserving food for many years. The drying process
involves reducing water from the product to an acceptable
level for marketing, storage, or processing. Given the
absence of sufficient water, microorganisms are unable to
grow and multiply. Many of the enzymes that cause food
spoilage cannot function without water. The old method
of food drying is executed by spreading the food
material on the ground and exposing the food to sunlight.
This method is practiced until today for certain
products because of the advantages of simplicity and
economy. However, open sun drying has some
drawbacks. Open sun drying requires longer drying time
and product quality is difficult to control because of
inadequate drying, high moisture, fungal growth,
encroachment of insects, birds and rodents and others.
Open sun drying also requires a large space.
Drying is usually conducted by vaporizing water in
the product. Thus, the latent heat of vaporization must be
supplied. Airflow is also required to remove the vapor
away from the product. The lower the humidity of hot air
supplied to the drying chamber is, the better the drying
rate, as the less humid air can carry more moisture from
the product surface than the more humid air. Generally,
Corresponding Author:
S. Misha, Department of Thermal-Fluids, Faculty of Mechanical Engineering,
Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia.
Tel: +60 6 2346712, Fax: +6 06 2346884.
World Appl. Sci. J., 22 (3): 424-433, 2013
install, operate and maintain; and (3) high drying rate and
better product quality are produced. In the selection of
dryer types, each item contributed at a different
percentage to the final score. For most of the cases,
especially food products, they more emphasize on the
product quality characteristic compare to the remaining
Many dryer types have been used in the domestic
and industry sectors. The dryers that are commonly used
are tray dryers, tunnel dryers, drum dryers, fluidized bed
dryers, spray dryers, flash dryers, rotary dryers, belt
dryers, vacuum dryers and freeze dryers. Among these
dryers, the tray dryer is the most extensively used
because of its simple and economic design. The food is
spread out on trays at an acceptable thickness so that the
product can be dried uniformly. Heating may be produced
by hot air stream across the trays, conduction from heated
trays, or radiation from heated surfaces. In a tray dryer,
more products can be loaded as the trays are arranged at
different levels. The key to the successful operation of the
tray dryer is uniform airflow distribution over the trays.
The tray dryer may be applied to a solar dryer or any
conventional dryer that uses fossil fuel or electrical
energy. Good airflow distribution will ensure the final
moisture content of the dried products on the trays are
uniform. Normally the moisture content is determined by
using electronic balance to get the difference between
final and initial mass of the product. Bakhshipour et al. [9]
used a machine vision system integrated with the neural
networks to predict the moisture content of raisin.
Mohanraj and Chandrasekar [10] designed and
fabricated an indirect forced convection solar dryer
combined with heat storage material for chili drying.
The use of heat storage material extends the drying time
by about 4 h per day. The chili moisture content of 72.8%
(wb) was reduced to 9.7% and 9.2% (wb) in the top and
bottom trays, respectively, during the drying process.
The solar dryer thermal efficiency was estimated at about
21% and specific moisture extraction rate was estimated at
about 0.87 kg/kW h. At the initial stages of drying, the
outlet air humidity was higher by about 89% and it
decreased as time increased. At the final stage of drying,
the outlet air humidity became constant at about 60%.
As drying time increased, the drying rate decreased.
Syahrul et al. [11] study the effects of the inlet air
temperature, the air velocity and the initial moisture
content of the corn on the thermal efficiency. It was found
that the thermal efficiencies of the fluidized bed drying
decrease with decreasing moisture content of corn.
Hallak et al. [12] designed and built the staircase
solar dryer for drying fruits and vegetables. The top
surface is covered with a transparent polycarbon sheet to
allow sunlight to pass through. The base of the dryer and
the separation walls between the compartments have four
holes for airflow. The result shows that the temperature
increases in the higher compartment. Therefore, drying at
a higher temperature can be achieved by increasing the
number of dryer compartments, with the uppermost levels
producing higher temperature. Samples can be placed
initially at the lower levels and then moved to the higher
ones later on until the desired moisture content is
achieved. The mass of samples tested was reduced to less
than 20% from the initial mass in around 2.5 days to
3.5 days, whereas samples using open sun drying took
around 12 days to 15 days.
Torres-Reyes et al. [13] investigated the thermal
performance analysis of the cabinet-type indirect solar
dryer for mango slices drying by using semi-empirical
models. A simplified method to design solar collectors
based on the determination of minimum entropy
generation during the thermal conversion of solar energy
was introduced. The results show that the products
positioned at the higher level experience high humidity
compared with those at the lower position. The drying
rate increases by increasing the flow rate of the inlet air.
A hybrid solar dryer was designed and developed by
Amer et al. [14] using direct solar energy and a heat
exchanger for drying ripe banana slices. The drying
chamber is located under the collector. During sunny
Types of Tray Dryer: Generally, a tray dryer consists of
several stacks of trays placed in an insulated chamber in
which hot air is distributed by a fan or natural flow.
Sometimes, part of the exhausted air is re-circulated within
the drying chamber. The tray inside the chamber can be
stationary or moving.
Stationary Tray Dryer: The stationary tray dryer is
widely used because of its simple design. In this system,
the trays are fixed at their positions. The uniformity of
airflow distribution over the trays is crucial to obtain
uniform product quality. The variation of the final
moisture content of the dried product at different tray
positions is commonly encountered because of poor
airflow distribution. This problem also limits the volume
of the product to be loaded in the dryer system. A good
tray dryer system design eliminates or reduces the
non-uniformity of drying throughout the drying chamber.
World Appl. Sci. J., 22 (3): 424-433, 2013
days, the dryer operates as a solar dryer and stores heat
energy in water, whereas during days with less sunlight,
the dryer works as a hybrid solar dryer. At night, the heat
energy stored in water is used to continue drying, with
electric heaters in the water tank supplying sufficient heat
as backup energy. The dryer efficiency was improved by
recycling approximately 65% of the drying air in the dryer
system. The air temperature could increase from 30 °C to
40°C above the ambient temperature. The moisture
content of banana slices was reduced from 82% to 18%
(wb) within 8 h when drying during a sunny day. The use
of open sun drying reduced moisture content by only
62% (wb) with the same duration. The color, texture and
aroma of the products dried with the solar dryer were
better than those of the open sun-dried products.
Gülþah Çakmak and Cengiz Y ld z, [15] designed and
constructed an air solar collector with swirl flow to dry
seeded grape. Additional air-directing elements on the
wall of the drying chamber and a swirl element at the inlet
of the drying chamber produced uniform flow of drying air
over the grapes on a single tray and the dried products
reached the desired moisture conditions more rapidly than
the products subjected to open sun drying. The drying
time of 200 h under open sun was decreased to 80 h with
the developed dryer. The dryer air velocity was about
1.5 m/s. The drying rate increased with the increase in
dryer air velocity. Thus, air velocity has a more significant
effect on the drying process than does air temperature.
Salah et al. [16] investigated and evaluated the
performance of the drying chamber of the forced
convective solar-assisted drying system. The drying
chamber has adjustable shelves to support wire-mesh
trays. The dryer system can operate with or without the
heater. In this work, standard equations of heat transfer
analysis under steady state condition were applied to
determine heat losses from the drying chamber and its
efficiency. The well insulation of the drying chamber was
found to increase the efficiency of the system.
Shawik Das et al. [17] designed and developed a
re-circulatory cabinet dryer using a central air distribution
system. The capacity of the dryer is 5 kg/batch. Hot air is
fed from the center to avoid non-uniform drying and to
reduce the heat loss to the surroundings. A blanched
potato chip was tested in the dryer. The results show that
the velocity of both chambers is in the range of 1.5 m/s to
1.7 m/s. The initial heating time of air is 25 min and 12 min
with no re-circulation and 100% re-circulation,
respectively. The experiments were conducted at loading
capacities of 5, 6 and 7 kg/m2 of potato chips and drying
temperatures of 55, 60 and 65°C. The thermal heat
efficiency and the heat utilization factor are in the range of
21% to 24% and 17% to 20%, respectively. The drying
times of different loading capacities are in the range of
180 min to 225 min. Drying products with a loading
capacity of 7 kg/m2 is more economic because product
quality is maintained despite differences in loading
Pelegrina et al. [18, 19] developed a rotary semicontinuous dryer for drying vegetables and investigated
the effect of air recycling. Recycling of exhaust air and
mixing with fresh air reduced the energy consumption.
However, lower recycle fractions must be applied for
quality retention. Neslihan Colak and Arif Hepbasli [20]
investigated the performance of green olives in a tray
dryer using the exergy analysis method. The drying
process was conducted at four different drying air
temperatures in the range of 40°C to 70°C, with a constant
relative humidity of 15%. Lower exergy loss and higher
exergy efficiency were obtained by decreasing the
boundary temperature of the drying chamber. The drying
process at a temperature of 70°C showed the highest
exergy efficiency.
Sukhmeet et al. [21] designed and constructed a solar
dryer for drying farm products called the “PAU portable
farm solar dryer”. The dryer exhibits high efficiency
because of its inclined absorber and the airflow passing
through the product. Drying can be conducted with or
without shade. All the trays should be fully occupied by
the product. If some spaces are void of the product, the
thermal efficiency drops because of the hot air bypassing
the product. If the amount of the product is less than the
capacity of the dryer, the top tray should be loaded first,
followed by the lower tray. For drying under shade, a
shading plate must be placed over all trays, including the
empty trays if any. During subsequent drying days, if
there are some void spaces in any of the trays, the
product must be transferred from the lower tray to higher
tray to remove the void space.
The drying process can be conducted in batch mode
or semi-continuous mode. In batch mode, the fresh
products are loaded after the dried product from the
previous batch that has been removed. In semicontinuous mode, the partially dried product is transferred
to another tray and the empty tray is filled with fresh
product. The fresh product with high moisture content is
loaded on the top trays, whereas the partially dried
product is transferred to the lower trays. Otherwise,
moisture from the fresh product will be carried by hot air
World Appl. Sci. J., 22 (3): 424-433, 2013
to the partially dried product, potentially increasing the
moisture again. The drying rate is uniform in all the trays
because of air in between the trays being heated by solar
energy. Moisture evaporation on the first, second and
third days of drying fenugreek leaves was 1.4, 0.9 and
0.4 kg/m2, respectively.
Parm Pal Singh et al. [22] designed and constructed
a multi-shelf natural convection solar dryer called the
“PAU domestic solar dryer” which consists of three
perforated trays for drying various products. It has an
adjustable inclination angle to capture more solar energy.
Most of the dryer features and operation are the same as
those of the PAU portable farm solar dryer. Moisture
evaporation on the first, second and third days of drying
fenugreek leaves was 0.23, 0.18 and 0.038 kg/m2 h,
respectively. The drying time for drying chilies and
fenugreek leaves was 86 and 204 drying days,
respectively. A semi-continuous mode was implemented
to maintain the efficiency on all drying days. In open
shade drying, the drying rate was more than double,
causing low-moisture content of the product (7.3% wb).
The drying efficiency is slightly less for indirect mode
dryers, but the quality is good for sensitive products that
require drying under shade. The cost of drying fenugreek
leaves using this solar dryer is approximately 60%
compared with that of the electric dryer. The payback
period is only about two years, but the life of the dryer is
about 20 years. Therefore, the dryer operates at no cost
during almost its entire life period.
Bennamoun and Belhamri [23] investigated a
solar batch dryer for drying agriculture products.
The result shows that increasing the collector surface
area and the temperature of the drying air reduces the
drying time. The capacity of the dried products does
not produce a significant effect. The use of a heater
improves the drying performance. Drying using this
system is more economical. The collector surface with an
area of 3m2 and a heater at 50°C can dry approximately
250 kg per day.
Smitabhindu et al. [24] studied the simulation and
optimization of a solar-assisted drying system for drying
bananas to minimize the drying cost. The drying chamber
consists of 10 trays. The simulation model shows good
agreement with the experimental data. Optimization was
studied on the geometrical and operational parameters of
the drying system. The optimum values of the recycle
factor and collector area are 90% and 26 m2, respectively.
The minimum drying cost obtained is about USD 0.
225 per kg.
Komilov and Murodov [25] designed and developed
a greenhouse-type solar dryer with pebble accumulator.
The walls are constructed from brick except the
south-facing inclined wall, which is covered with window
glass. The heat accumulator in a cylindrical shape filled
with pebbles and an air heater are installed. A black
metallic sheet is mounted under the glass, functioning as
a heat collector and shade. The humid warm air at the top
part of the chamber is directed by a fan to the accumulator
through a pipe. Part of the heat from the humid warm air is
transferred to the pebbles before being exhausted to
ambient. The air pipe below the chamber is connected to
the air heater to provide hot air to the drying chamber. Hot
air flows through the product in each tray to the upper
part. The dryer can be loaded with 500 kg to 600 kg of
apricots, tomatoes, fruits, or vegetables per drying cycle.
A hybrid solar dryer with 3600 kg capacity for drying
fruits and crops was designed and built at the Solar and
other Energy Systems Laboratory of the National Center
for Scientific Research “Demokritos,” as reported by
Belessiotis and Delyannis [26]. The cross section of
the dryer and the air circulation is shown in Figure 1.
The trays are installed at both sides of the drying chamber
wall, with hot air coming from the center. The dryer
system uses propane as an auxiliary energy source.
Al-Juamily et al. [27] designed and developed an
indirect-mode forced dryer for vegetable and fruit drying.
The cabinet consists of five shelves with a distance of
0.3m between the shelves except for the upper one, which
is 0.5m from the roof. Grapes, apricots and beans were
selected as the products to be dried. The moisture content
of apricot was reduced from 80% to 13% in one day and
a half, that of grapes was reduced from 80% to 18% in two
and a half days and that of beans was reduced from 65%
to 18% in 1 day only. The result shows that drying air
temperature is the most important factor in drying rate.
The velocity of air in the drying cabinet has less influence
on the drying rate. The relative humidity of air between
25% and 30% was recorded at an outlet of the cabinet.
The high air velocity in the cabinet is not necessary
because of the low relative humidity at the outlet.
Ayensu and Aseiedu-Bondizie [28] designed and
constructed a mixed-mode natural convection solar dryer
(Figure 2). The dryer is integrated with collector-cum-rock
to store the energy. The drying chamber made of plywood
sides with a glazed top holds three layers of wire-mesh
tray inside it. The chimney, which has a diameter of 30 cm
and height of 1.9 m, is required to increase the airflow
velocity. Hot air passes through the product in each tray
and carries the moisture by natural convection.
World Appl. Sci. J., 22 (3): 424-433, 2013
efficiency can be improved by spreading wet salted
greengages on the two trays from the top and semi-dry
ones on other trays.
Vlachos et al. [30] developed and investigated a
solar-assisted indirect dryer integrated with a heat storage
cabinet. At night, heat is supplied by the heat storage
cabinet with natural convection. The result shows that
the drying process occurs at night but at a lower rate.
Faster drying occurs for products in the lower drawer than
for those in the higher drawer. Therefore, variation occurs
in the moisture removal for the dried product in the drying
chamber. Interchanging the position of the drawer may be
done to avoid this problem.
Tarigan and Tekasakul [31] reported on a natural
convection solar dryer combined with a burner and
bricks for heat storage as back-up energy. The dryer
capacity is about 60 kg to 65 kg of unshelled fresh
groundnuts. The drying efficiency of using solar energy
and a burner with heat storage is 23% and 40%,
respectively. The acceptable thermal efficiency and
uniform drying air temperature through the trays are due
to the insulation and gap enclosing the drying chamber
and bricks that store heat.
Numerous solar dryer systems have been designed
using the tray dryer type, which consists of several
perforated trays arranged at different levels, one above
the other inside the drying chamber [32-42] as reported by
Fudholi et al. [43]. However, the drying air distribution
and the dried product uniformity in the drying chamber
are not described in detail.
Fig. 1: Air circulation inside the hybrid solar dryer [26]
Moving Tray Dryer: The moving tray dryer was designed
to overcome the obstacle of poor drying air distribution,
as encountered in most stationary tray dryer systems.
The movement of the trays helps increase the drying rate
and produce uniform product quality. However, this type
of dryer is more expensive because more energy to move
or rotate the tray and a more complex design are required.
Therefore, the moving tray dryer is seldom used even if it
can produce more uniform drying.
Sarsilmaz et al. [44] developed and investigated the
rotary column cylindrical dryer (Figure 3) for drying
apricots. The rotary column contains holes at the
center of the drying chamber for the flow of outlet air.
The column was rotated by a 12 V DC motor with
adjustable speed through voltage control. The rotary
column is divided into four equal levels and five plates are
attached at each level. Each plate can be loaded with
approximately 2 kg to 3 kg of fresh apricots. The result
shows that the developed dryer system increases the
Fig. 2: Indirect-type natural convection solar dryer [28]
Li et al. [29] designed and constructed a forced
convection dryer for drying salted greengages using the
V-groove air collector absorber. A silica photovoltaic
module is installed to power three fans that are used in the
dryer system. The drying period of salted greengages
using traditional sun drying was reduced from 48 days to
15 days using solar drying. The regained moisture by the
semi-dry product at night or on rainy days can be avoided
during the drying period using a solar dryer. Thermal
World Appl. Sci. J., 22 (3): 424-433, 2013
consists of four stainless steel trays, each with a
dimension of 0.36m x 0.10m. Each tray has 2 mm-diameter
holes for ventilation. An 850W resistor and 10.6W fan
supply circulate hot air through the drying chamber.
Temperature and air velocity can be controlled using a
microcontroller. The use of a rotating tray for tomato
drying significantly increases the drying rate and
improves product quality. Generally, the drying time is
significantly influenced by temperature, tray rotation and
air velocity.
Tunnel dryers are considered as developments of the
tray dryer. The trays are attached on the trolleys and
move through a tunnel. The product direction can be
concurrent or countercurrent to the airflow. Sometimes,
the cross-flow may also be applied. An example of the
tunnel dryer is reported by Kiranoudis et al. [46].
The dryer contains a number of trucks/trolleys, each of
which behaving as a separate batch tray dryer. Products
are placed uniformly on each tray. The air is blown over
the trays in the tunnel. When the first truck reaches the
desired moisture content, it is removed from the dryer and
a new truck is loaded at the end of the train. The tunnel
dryer can produce uniform drying. Re-circulated air is
heated by a conventional burner. The temperature and
humidity of the hot air are controlled by adjusting the fuel
induction valve and fresh air dumper, respectively.
The simple and common design of the tray dryer
consists of several perforated trays or wire mesh arranged
at different levels, one above the other inside the drying
chamber. As the drying air passes over the trays, it carries
more moisture and loses its heat. Thus, the drying air has
low capability of removing moisture from the next product.
Good air flow distribution throughout the drying chamber
can improve the drying uniformity. In some cases, the
semi-continuous mode or exchange of tray position may
be done for the stationary tray dryer to obtain uniform
product quality. For the natural convection solar dryer, a
chimney is required to increase the buoyancy force
imposed on the air stream and to provide higher airflow
velocity. The moving tray dryer produces better flow
distribution of drying air and more even drying.
Fig. 3: Vertical cross-section of the drying chamber [44]
Fig. 4: Rotating tray dryer [45]
drying rate of Sugarpiece-type apricots about twice than
that of drying on an open sheet to achieve a 25% moisture
level. The rotation of the drying chamber produces
uniform and high-quality dried apricots.
Norma Francenia et al. [45] designed and developed
a rotating tray dryer (Figure 4) for tomato drying.
The dryer operates at a temperature range of 20°C to 60°C
and air velocity between 0 ms 1 and 1.2 ms 1. The tray
can be rotated at 20 rpm using a 186.5 W motor. The oven
Design Optimization of the Tray Dryer: Implementing a
better design of tray dryers can eliminate poor drying air
distribution in the drying chamber. The measurement of
drying parameters in the drying chamber is expensive,
difficult and time consuming, as sensors and data loggers
have to be installed in many positions, especially in a
large-scale dryer. Currently, computational fluid dynamics
(CFD) simulation is used extensively because of its
World Appl. Sci. J., 22 (3): 424-433, 2013
capability to solve equations for the conservation of
mass, momentum and energy using numerical methods to
predict the temperature, velocity and pressure profiles in
the drying chamber.
Mathioulakis et al. [47] designed and constructed an
industrial batch-type tray dryer for drying fruits. CFD is
used to simulate the air pressure profiles and the air
velocity distribution in the drying chamber. The result
shows that a variation of final moisture content occurs in
several trays and non-uniformity is present in some areas
of the chamber. Comparison of the simulation result by
the CFD and experimental data shows a strong correlation
between drying rate and air velocity.
Dionissios and Adrian-Gabriel Ghious [48] studied
the numerical simulation inside a drying chamber with
hundreds of trays. A set of measurements was obtained
experimentally above one single tray to validate the
model. The validation between the measured data and the
simulation results by CFD shows that the standard k-e
model is the most adequate turbulence model.
Amanlou and Zomorodian [49] designed, constructed
and evaluated a new cabinet dryer with a side-mounted
plenum chamber for fruit drying. The experimental
results show that the developed dryer produces uniform
airflow and temperature distribution in the chamber.
The experimental and CFD simulation data show very
good agreement with the correlation coefficient of 86.5%
and 99.9% for air velocity and temperature in the drying
chamber, respectively.
Chr. Lamnatou et al. [50] developed and investigated
a numerical model of heat and mass transfer during
convective drying of a porous body using the finitevolume method. The results show that the aspect ratio of
the drying plate and the flow separation influence the flow
field and heat/mass transfer coefficients, affecting the
quality of the dried product. The thinner plate combined
with the blockage effect can lead to better heat/mass
transfer coefficients.
Jacek Smolka et al. [51] investigated a numerical
model of a drying oven using the CFD simulation. The
simulation results show very good agreement with the
experimental data. Several new configurations were
simulated to improve uniformity of temperature
throughout the chamber. A new shape and position of the
heater and baffle directing the airflow were found as the
most effective.
Cronin et al. [52] developed a simulation tool to
analyze industrial batch timber drying. The simulation
result from the integrated model with a customized CFD
code is used to generate a macroscopic representation of
the product. The validated macroscopic model is used as
a component in a drying installation model. The
developed system model can be applied to represent
accurately a new drying material or different drying
conditions. Application of CFD has also been used
extensively in modeling the spray dryers to predict
complex flow patterns and moisture profile. A number of
studies pertaining to the application of CFD in spray
drying have been reported by Rinil Kuriakose and
Anandharamakrishnan [53].
Design optimization of a drying chamber is necessary
to achieve higher heat/mass transfer rates and uniform
drying by avoiding an unfavorable aerodynamic
phenomenon in the chamber. Optimization using CFD can
produce better performance of the tray dryer system, high
quality of dried products and uniform drying at minimum
The objective of this review is to emphasis the
important of tray dryer design in drying of agricultural
product. Several designs can be implemented to improve
tray dryer performance, increases quality of dried product
and produces uniform drying. For the stationary tray
dryer, the semi-continuous mode or exchange of the
position of the tray can be executed to obtain uniform
drying. The rotating/moving tray dryer can also produce
more uniform drying. In general, re-circulation of drying
air and mixing with fresh air reduces energy consumption.
However, for certain products, it may decrease the
product quality and thus appropriate recycle fractions
must be applied. The use of solar energy for drying
agricultural product will make the dryer system run at low
operating cost. Therefore the solar dryer is widely use for
drying agricultural product and will be the future trends.
The drying chamber configuration can be optimized by
CFD simulation to predict the airflow distribution
throughout the drying chamber. Nowadays, given the
increase in computing power, the application of CFD
can be a valuable tool for engineering design and
analysis of solving complex fluid flow, addressing
heat and mass transfer phenomena, aiding in the better
design of tray dryers and produce high quality of dried
The authors would like to thank the Solar Energy
Research Institute, Universiti Kebangsaan Malaysia and
Universiti Teknikal Malaysia Melaka for sponsoring this
World Appl. Sci. J., 22 (3): 424-433, 2013
12. Hallak, H., J. Hilal, F. Hilal and R. Rahhal, 1996.
The staircase solar dryer: Design and characteristic.
Renewable Energy, 7(2): 177-183.
13. Torres-Reyes, E., J.J. Navarrete-Gonzalez and
B.A. Ibarra-Salazar, 2002. Thermodynamic method for
designing dryers operated by flat-plate solar
collectors. Renewable Energy, 26: 649-660.
14. Amer, B.M.A., M.A. Hossain and K. Gottschalk,
2010. Design and performance evaluation of a new
hybrid solar dryer for banana. Energy Conversion
and Management, 51: 813-820.
15. Gül ah Çakmak and Cengiz Y ld z, 2009. Design of a
new solar dryer system with swirling flow for drying
seeded grape. International Communications in Heat
and Mass Transfer, 36: 984-990.
16. Salah, A. Eltief, M.H. Ruslan and B. Yatim, 2007.
Drying chamber performance of V-groove forced
convective solar dryer, Desalination, 209: 151-155.
17. Shawik Das, Tapash Das, P. Srinivasa Rao and
R.K. Jain, 2001. Development of an air recirculation
tray dryer for high moisture biological materials.
Journal of Food Engineering, 50: 223-227.
18. Pelegrina, A., M.P. Elustondo and M.J. Urbicain,
1998. Design of a semi-continuous drier for
vegetables. Journal of Food Engineering, 37: 293-304.
19. Pelegrina, A., M.P. Elustondo and M.J. Urbicain,
1999. Rotary semi-continuous drier for vegetables:
effect of air recycling. Journal of Food Engineering,
41: 215-219.
20. Neslihan Colak and Arif Hepbasli, 2007.
Performance analysis of drying of green olive
in a tray dryer. Journal of Food Engineering,
80: 1188-1193.
21. Sukhmeet Singh, Parm Pal Singh ans S.S. Dhaliwal,
portable solar dryer.
Renewable Energy, 29: 753-765.
22. Parm Pal Singh, Sukhmeet Singh and S.S. Dhaliwal,
solar dryer.
Energy Conversion and Management, 47: 1799-1815.
23. Bennamoun, L. and A. Belhamri, 2003. Design and
simulation of a solar dryer for agriculture products.
Journal of Food Engineering, 59: 259-266.
24. Smitabhindu, R., S. Janjai and V. Chankong, 2008.
Optimization of a solar-assisted drying system for
drying bananas. Renewable Energy, 33: 1523-1531.
25. Komilov, O.S. and Kh.E. Murodov, 1993.
Investigation of kinetics of drying agricultural
products in a solar convective dryer. Applied Solar
Energy, 29(5): 85-88.
Sato, K., M. Katahira and E. Toji, 1997.
Drying characteristics of raw bulb and dehumidified
air and moisture content distribution of different bulb
parts. Journal of Japanese Society of Agricultural
Machinery, Tohoku Branch, 44: 43-46.
2. Miller, W.M., 1983. Energy storage via desiccant for
food agricultural applications. Energy in Agriculture,
3. Okano, H., 1998. Honeycomb rotor type
dehumidifiers: comparison between honeycomb
rotor type dehumidifiers and various dehumidifying
and explanation on their outlines.
Clean Technology, 3: 33-37.
4. Misha, S., S. Mat, M.H. Ruslan and K. Sopian, 2012.
Review of solid/liquid desiccant in drying
applications and its regeneration methods.
Renewable and Sustainable Energy Review,
16: 4686-4707.
5. Hiia, C.L., C.L. Lawb, M. Clokea and S. Suzannah,
2009. Thin layer drying kinetics of cocoa and
dried product quality. Bio Systems Engineering,
102: 153-161.
6. Abul-Fadl, M.M. and T.H. Ghanem, 2011. Effect of
Refractance-window (RW) drying method on quality
criteria of produced tomato powder as compared to
the convection drying method, World Applied
Sciences Journal, 15(7): 953-965.
7. Augustus Leon, M., S. Kumar and S.C. Bhattacharya,
2002. A comprehensive procedure for performance
evaluation of solar food dryers. Renewable and
Sustainable Energy Reviews, 6: 367-393.
8. Chua, K.J. and S.K. Chou, 2003. Low-cost drying
methods for developing countries. Trends in Food
Science and Technology, 14: 519-528.
9. Bakhshipour, A., A. Jafari and A. Zomorodian, 2012.
Vision based features in moisture content
World Applied Sciences Journal, 17(7): 860-869.
10. Mohanraj, M. and P. Chandrasekar, 2009.
Performance of a forced convection solar drier
integrated with gravel as heat storage for chili drying.
Journal of Engineering Science And Technology,
4(3): 305-314.
11. Syahrul, S., F. Hamdullahpur and I. Dincer, 2002.
Thermal analysis in fluidized bed drying of
moist particles. Appllied Thermal Engineering,
22: 1763-1775.
World Appl. Sci. J., 22 (3): 424-433, 2013
26. Belessiotis, V. and E. Delyannis, 2011. Solar drying.
Solar Energy, 85: 1665-1691.
27. Al-Juamily, K.E.J., A.J.N. Khalifa and T.A. Yassen,
2007. Testing of performance of fruit and vegetable
solar drying system in Iraq. Desalination,
209: 163-170.
28. Ayensu, A. and Asiedu-Bondzie, 1986. Solar drying
with convective self-flow and energy storage.
Solar and Wind Technology, 3(4): 273-279.
29. Li, Z., H. Zhoung, R. Tang, T. Liu, W. Goo and
Y. Zhang, 2006. Experimental investigation on solar
drying of salted greengages. Renewable Energy,
31: 837-847.
30. Vlachos, N.A., T.D. Karapantsios, A.I. Balouktsis and
D. Chassapis, 2002. Design and testing of a new solar
tray dryer. Drying Technology, 20(5): 1239-1267.
31. Tarigan, E. and P. Tekasakul, 2005. A Mixed-mode
natural convection solar dryer with biomass burner
and heat storage back-up heater. ANZSES 2005: 1-9.
32. Bolaji,
A.P. Olalusi, 2008.
Performance evaluation of a mixed-mode solar dryer.
AU Journal of Technology, 11(4): 225-231.
33. El-Beltagi, A., G.R. Gamea and A.H.A. Essa, 2007.
Solar drying characteristics of strawberry. Journal of
Food Engineering, 78: 456-464.
34. Farkas, I., I. Seres and C.S. Meszaros, 1999.
Analytical and experimental study of a modular solar
dryer. Renewable Energy, 16: 773-778.
35. Forson, F.K., M.A.A. Nazha, F.O. Akuffo and
H. Rajakaruna, 2007. Design of mixed-mode natural
convection solar crop dryers: application of
principles and rules of thumb. Renewable Energy,
32: 2306-2319.
36. Jain, D., 2005. Modeling the system performance of
multi-tray crop drying using an inclined multi-pass
solar air heater with in-built thermal storage. Journal
of Food Engineering, 71: 44-54.
37. Mohanraj, M. and P. Chandrasekar, 2008. Drying of
copra in
Biosystems Engineering, 99: 604-607.
38. Pangavhane,
P.N. Sarsavadia, 2002. Design, development and
performance testing of a new natural convection
solar dryer. Energy, 27: 579-590.
39. Shanmugam, V. and E. Natarajam, 2007.
Experimental study of regenerative desiccant
integrated solar dryer with and without reflective
mirror. Applied Thermal Engineering, 27: 1543-1551.
40. Tiris, C., M. Tiris and I. Dincer, 1996. Experiments on
the a new solar air heater. International
Communications in Heat and Mass Transfer,
16(2): 183-187.
41. Tiwari, G.N., P.S. Bhatia, A.K Singh and R.F. Sutar,
1994. Design parameters of a shallow bed solar crop
dryer with reflector. Energy Conversion and
Management, 35(6): 542-635.
42. Tiwari, G.N., P.S. Bhatia, A.K. Singih and R.K. Goyal,
1997. Analytical studies of crop drying cum water
Management, 38(8): 751-759.
43. Fudholi, A., K. Sopian, M.H. Ruslan, M.A. Alghoul
and M.Y. Sulaiman, 2010. Review of solar dryers for
agricultural and marine products, Renewable and
Sustainable Energy Reviews, 14: 1-30.
44. Sarsilmaz, C., C. Yildiz and D. Pehlivan, 2000.
Drying of apricots in a rotary column cylindrical dryer
(RCCD) supported with solar energy. Renewable
Energy, 21: 117-127.
45. Norma Francenia Santos-Sánchez, Rogelio ValadezBlanco, Mayra Soledad Gómez-Gómez, Aleyda PérezHerrera and Raúl Salas-Coronado, 2011. Effect of
rotating tray drying on antioxidant components, color
and rehydration ratio of tomato saladette slices.
LWT-Food Science and Technology, 1-7,
doi:10.1016/ j.lwt.2011.09.015.
46. Kiranoudis, C.T., Z.B. Maroulis, D. Marinos-Kouris
and M. Tsamparlis, 1997. Design of tray Dryers for
Food Dehydration. Journal of Food Engineering,
32: 269-291.
47. Mathioulakis,
Karathanos and
V.G. Belessiotis, 1998. Simulation of air movement in
a dryer by computational fluid dynamics: Application
for the drying of fruits. Journal of Food Engineering,
36: 183-200.
48. Dionissios, P., Margaris and Adrian-Gabriel Ghiaus,
2006. Dried product quality improvement by air flow
manipulation in tray dryers. Journal of Food
Engineering, 75: 542-550.
49. Amanlou,
Y. and A. Zomorodian, 2010.
Applying CFD for designing a new fruit cabinet
dryer. Journal of Food Engineering, 101: 8-15.
50. Lamnatou, Chr., E. Papanicolaou, V. Belessiotis and
N. Kyriakis, 2010. Finite-volume modelling of heat
and mass transfer during convective drying of
porous bodies - Non-conjugate and conjugate
formulations involving the aerodynamic effects.
Renewable Energy, 35: 1391-1402.
World Appl. Sci. J., 22 (3): 424-433, 2013
51. Jacek Smolka, Andrzej J. Nowak and Dawid Rybarz,
2010. Improved 3-D temperature uniformity in a
laboratory drying oven based on experimentally
validated CFD computations, Journal of Food
Engineering, 97: 373-383.
52. Cronin, K., B. Norton and J. Taylor, 1996.
Development of a simulation tool to enable
optimisation of the energy consumption of the
industrial timber-drying process. Applied Energy,
53: 325-340.
53. Rinil Kuriakose and C. Anandharamakrishnan, 2010.
Computational fluid dynamics (CFD) applications in
spray drying of food products. Trends in Food
Science and Technology, 21: 383-398.
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