UNIVERSITI TEKNOLOGI MARA
FAKULTI KEJURUTERAAN KIMIA
HEAT & MASS TRANSFER LABORATORY
(CHE504)
NAME:
STUDENT NO :
MUHAMAD IBNU HAKIM BIN SHUHAINI
2017632072
MOHAMAD NORAFIQ BIN ZULKEPLI
2017632138
NORHAYATI BINTI AB RAHMAN
2017632114
NURUL NAJIHAH BINTI JAAFAR
2017632056
NURLINA SYAHIIRAH BINTI MD TAHIR
2017632214
GROUP
: EH2204I
EXPERIMENT
: TRAY DRYER (L1) (GROUP REPORT)
DATE PERFORMED
: 29th MARCH 2018
SEMESTER
:4
PROGRAMME / CODE : CHEMICAL ENGINEERING / EH220
SUBMIT TO
: MADAM SYAFIZA BINTI ABD HASHIB
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
Title
Abstract/Summary
Introduction
Aims
Theory
Apparatus
Methodology/Procedure
Results
Calculations
Discussion
Conclusion
Recommendations
Reference
Appendix
TOTAL MARKS
Allocated Marks (%)
Marks
5
5
5
5
5
10
10
10
20
10
5
5
5
100
Remarks:
Checked by:
Rechecked by:
---------------------------
---------------------------
Date:
Date:
TABLE OF CONTENT
1.0
ABSTRACT ................................................................................................................... 2
2.0
INTRODUCTION......................................................................................................... 3
3.0
OBJECTIVES ............................................................................................................... 4
4.0
THEORY ....................................................................................................................... 5
5.0
MATERIALS & APPARATUS ................................................................................... 7
6.0
METHODOLOGY ....................................................................................................... 8
7.0
RESULTS ...................................................................................................................... 9
8.0
CALCULATIONS ...................................................................................................... 12
9.0
DISCUSSION .............................................................................................................. 13
10.0 CONCLUSION ........................................................................................................... 16
11.0 RECOMMENDATIONS............................................................................................ 17
12.0 REFERENCES ............................................................................................................ 18
13.0 APPENDICES ............................................................................................................. 19
LAB REPORT ON TRAY DRYER (L1)
1
1.0
ABSTRACT
Tray dryers are the simplest and least-expensive dryer type which operates by passing hot air
over the surface of a wet solid that is spread over trays arranged in racks. Drying is a mass
transfer process that involves removal of relatively small amounts of water or moisture
contents from a material or a process stream. The purpose of the experiment is to conduct a
drying process on banana fruits in order to determine its drying rate, moisture content, and
the effect of velocity of air on the drying rate of the banana. The banana is sliced thinly and
arranged in the tray. The mass of banana is weighted before and after the experiment. During
the experiment, the mass of banana is recorded every 10 minutes. The moisture content and
the drying rate decreases over time. The drying curve of the banana follows the theoretical
drying curve. Drying times comparison with other types of batch dryers show the trays dryer
as the least effective. The objectives are successfully obtained therefore the experiment is
successfully done.
LAB REPORT ON TRAY DRYER (L1)
2
2.0
INTRODUCTION
Drying is a mass transfer process that involves removal of relatively small amounts of water
or moisture contents from a material or a process stream. In industries, drying process is often
used as the final step operation before packaging and selling products. The final product from
drying process must be in solid form, because all the moisture contents is being dried up.
There are many methods of drying such as application of hot air, contact drying, dielectric
drying, freezing drying and supercritical drying. This method of drying involves with
different type of drying equipment such as Tray dryers, Vacuum-shelf indirect dryers,
Continuous tunnel dryers, Rotary dryers, Drum dryers and Spray dryers.
The common type of dryers uses in many industrial applications involves tray dryers
as their drying operation. The dryers are made of tray held in a cabinet, which is connected to
a source of heated air. The operation mechanism of tray drying is the heat is channelled by an
air current sweeping across the trays, by conduction from heated trays or heated shelves on
which the trays lie, or by radiation from heated surfaces. The tray must be tight-fitting in the
cabinet to air form bypassing the material that needed to be dried. The drying time by using
tray dryers usually need a longer time. In industries, tray dryer operates about 12 to 48 hours
for solids to be dried. This is because tray dryers required low capital and maintenance cost
but it have poor control and chances to produces more variable product quality.
LAB REPORT ON TRAY DRYER (L1)
3
3.0
OBJECTIVES
There were several objectives in conducting the experiment:
1) To determine the drying rate and moisture content of the sample through removal of
water.
2) The effect of velocity of air on drying rate of the sample by performing drying process.
3) To learn how to operate the tray dryer.
4) To compare tray dryers with other types of batch dryers.
LAB REPORT ON TRAY DRYER (L1)
4
4.0
THEORY
Tray dryer operates by passing hot air over the surface of a wet solid that is spread over trays
arranged in racks. Tray dryers are the simplest and least-expensive dryer type. This type is
most widely used in the food and pharmaceutical industries. The advantage of tray dryers,
apart from their low initial cost, is their versatility. With the exception of dusty solids,
materials of almost any other physical form may be dried. Drying times are typically long
(usually 12 to 48 h).
Drying process can be defined as the vaporization and removal of water or other
liquids from a solution, suspension, or other solid-liquid mixture to form a dry solid. It is a
process that involves heat and mass transfer. Drying occurs as a result of the vaporization of
liquid by supplying heat to wet feedstock, granules, and so on. Based on the mechanism of
heat transfer, drying is categorized into direct (convection), indirect or contact (conduction),
radiant (radiation) and dielectric or microwave (radio frequency) drying.
Heat transfer and mass transfer are crucial in drying processes. Heat is supplied to the
product to evaporate the liquid contained, and mass is transferred as a vapor into the
surrounding gas. The drying rate is determined by the set of factors that affect heat and mass
transfer. Solids drying is generally understood to follow two distinct drying zones, known as
the constant-rate period and the falling-rate period. The two zones are demarcated by a break
point called the critical moisture content.
In a typical graph of moisture content versus drying rate and moisture content versus
time (Figure 1), section AB represents the constant-rate period. In that zone, moisture is
considered to be evaporating from a saturated surface at a rate governed by diffusion from the
surface through the stationary air film that is in contact with it. This period depends on the air
temperature, humidity and speed of moisture to the surface, which in turn determine the
temperature of the saturated surface. During the constant rate period, liquid must be
transported to the surface at a rate sufficient to maintain saturation.
LAB REPORT ON TRAY DRYER (L1)
5
Figure 1 - Segment AB of the graph represents the constant-rate drying period,
while segment BC is the falling-rate period (Parikh, 2014)
At the end of the constant rate period, (point B, Figure 1), a break in the drying curve
occurs. This point is called the critical moisture content, and a linear fall in the drying rate
occurs with further drying. This section, segment BC, is called the first falling-rate period. As
drying proceeds, moisture reaches the surface at a decreasing rate and the mechanism that
controls its transfer will influence the rate of drying. Since the surface is no longer saturated,
it will tend to rise above the wet bulb temperature. This section, represented by segment CD
in Figure 1 is called the second falling-rate period, and is controlled by vapor diffusion.
Movement of liquid may occur by diffusion under the concentration gradient created
by the depletion of water at the surface. The gradient can be caused by evaporation, or as a
result of capillary forces, or through a cycle of vaporization and condensation, or by osmotic
effects. The amount of the air (gas) stream to absorb and carry away moisture determines the
drying rate and establishes the duration of the drying cycle. The two elements essential to this
process are inlet air temperature and air flowrate. Theoretically, the higher the temperature of
the drying air, the greater its vapor holding capacity.
LAB REPORT ON TRAY DRYER (L1)
6
5.0
MATERIALS & APPARATUS
5.1
MATERIAL
1) Banana
5.2
APPARATUS
1) Knife
2) Chopping Board
3) Tray Dryer Training Unit CE – 130.
4) Anemometer.
Figure 2 - Tray Dryer Training Unit CE130 used for the Experiment
(a)
(b)
Figure 3 - (a) Digital Balance located as part of the Tray Dryer Unit
used to weight the banana, (b) Anemometer used to determine the
velocity of the air inside the Tray Dryer Unit
LAB REPORT ON TRAY DRYER (L1)
7
6.0
METHODOLOGY
6.1
Start-up procedures:
1) The main switch of the tray dryer machine is opened.
2) Then, the fan power was opened, and the toggle turned to the lowest speed.
3) Lastly, the heater was opened, and the toggle turned to scale 7.
6.2
Preparation procedures:
1) The drying trays has been washed to remove any filthiness.
2) The mass of drying trays is measured by inserted into the support frame. The data
were recorded.
3) The bananas are sliced thinly and been arranged together in the entire tray for all
tray.
4) The tray filled with banana slices then being weight by inserted the tray into the
supporting frame. The data were recorded.
5) The initial temperature and humidity were recorded. Then the initial air flow
inside the tray dryers is measured by using anemometer and the reading were
recorded.
6) Then, all of the data were recorded for every 10 minutes in 90 minutes time of the
drying process.
7) After 90 minutes, all the trays were taken out from the dryer machine and cleaned.
6.3
Shut-down procedures:
1) The heater toggle was turned to scale 0. Then, the heater and fan switch were
turned off.
2) The main switch of the tray dryer machined was turned off.
LAB REPORT ON TRAY DRYER (L1)
8
7.0
RESULTS
Mass of tray (4 Tray)
= 1390.5 g
Mass of tray + banana
= 2399.5 g
Mass of banana
= 1009.0 g
Table 7.1: Temperature, Humidity, Velocity and Mass Properties of Banana at The
Respective Time
Time
Temperature
Humidity
Velocity
Mass of Banana
(min)
(◦C)
(%)
(m/s)
(g)
T1
T2
H1
H2
0
57.2
52.5
07.2
00.5
0.71
1009.0
10
57.1
51.4
07.3
00.5
0.67
966.8
20
56.9
50.7
07.3
00.5
0.79
920.7
30
56.3
50.5
07.3
00.5
0.61
874.5
40
55.6
50.3
07.4
00.5
0.78
839.0
50
55.5
50.1
07.4
00.5
0.96
807.4
60
55.2
50.0
07.4
00.5
0.93
776.3
70
56.1
50.5
07.4
00.5
0.46
753.1
80
56.8
51.5
07.3
00.5
0.79
727.1
90
57.4
52.0
07.3
00.5
0.73
704.9
LAB REPORT ON TRAY DRYER (L1)
9
Table 7.2: Drying Rate and Moisture Content
Time (min)
Mass of banana
Moisture content
Drying rate
(kg)
(v)
(min-1)
0
1.009
0.4314
0.00599
10
0.9668
0.3715
0.00654
20
0.9207
0.3061
0.00655
30
0.8745
0.2406
0.00504
40
0.8390
0.1902
0.00448
50
0.8074
0.1454
0.00441
60
0.7763
0.1013
0.00329
70
0.7531
0.0684
0.00369
80
0.7271
0.0315
0.00315
90
0.7049
0
0
MOISTURE CONTENT
MOISTURE CONTENT VS TIME
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0
20
40
60
80
100
TIME
Figure 4 - Graph of Moisture Content versus Time
The graph shows the moisture content of banana decreases when the time increase.
LAB REPORT ON TRAY DRYER (L1)
10
DRYING RATE
DRYING RATE VS TIME
0.008
0.007
0.006
0.005
0.004
0.003
0.002
0.001
0
0
20
40
60
TIME (MIN)
80
100
Figure 5 - Graph of Drying Rate versus Time
The graph shows slight increase in drying rate from time 0 min to 20 min then
decrease until time 40 min. From time 40 min to 50 min the drying rate is approximately
constant. At time 50 min to 60 min, the graph shows slight increase before drop rapidly at
time 80 min to 90 min.
DRYING RATE VS MOISTURE CONTENT
0.007
DRYING RATE
0.006
0.005
0.004
0.003
0.002
0.001
0
0
0.1
0.2
0.3
MOISTURE CONTENT
0.4
0.5
Figure 6 - Graph of Drying Rate versus Moisture Content (Drying Curve)
The graph shows the drying rate increases when the moisture content increase from
0% moisture up to 0.32% moisture. However, at about 0.07% moisture until 0.1% the graph
shows decrease in the drying rate. At 0.32% until 0.38% moisture the drying rate remains
constant. Before declining until about 0.42% moisture content.
LAB REPORT ON TRAY DRYER (L1)
11
8.0
CALCULATIONS
Provided that the total mass of wet banana and tray are 2.400kg and mass of tray is 1.391kg,
Mass balance:
Mass in = mass out
𝐈𝐧𝐢𝐭𝐢𝐚𝐥 𝐓𝐨𝐭𝐚𝐥 𝐌𝐚𝐬𝐬 (𝐊𝐠)
= 𝐅𝐢𝐧𝐚𝐥 𝐓𝐨𝐭𝐚𝐥 𝐌𝐚𝐬𝐬 + 𝐌𝐚𝐬𝐬 𝐎𝐟 𝐖𝐚𝐭𝐞𝐫 𝐄𝐯𝐚𝐩𝐨𝐫𝐚𝐭𝐞𝐝
Mass Of Water Evaporated = 1.009 − 0.705
= 0.304 kg
𝐌𝐨𝐢𝐬𝐭𝐮𝐫𝐞 𝐜𝐨𝐧𝐭𝐞𝐧𝐭, 𝐯 =
𝐌𝐚𝐬𝐬 𝐨𝐟 𝐰𝐞𝐭 𝐛𝐚𝐧𝐚𝐧𝐚 – 𝐌𝐚𝐬𝐬 𝐨𝐟 𝐝𝐫𝐲 𝐛𝐚𝐧𝐚𝐧𝐚 (𝐟𝐢𝐧𝐚𝐥)
𝐌𝐚𝐬𝐬 𝐨𝐟 𝐝𝐫𝐲 𝐛𝐚𝐧𝐚𝐧𝐚 (𝐟𝐢𝐧𝐚𝐥)
Example:
(1)
=
1.0009 − 0.705
= 0.4314
0.705
(2)
=
0.967 − 0.705
= 0.3715
0.705
By recording the sample weight every 10 minutes;
𝐃𝐫𝐲𝐢𝐧𝐠 𝐫𝐚𝐭𝐞
=
𝐦𝐨𝐢𝐬𝐭𝐮𝐫𝐞 𝐜𝐨𝐧𝐭𝐞𝐧𝐭 (𝐓𝟏) – 𝐦𝐨𝐢𝐬𝐭𝐮𝐫𝐞 𝐜𝐨𝐧𝐭𝐞𝐧𝐭 (𝐓𝟐)
𝐭𝐢𝐦𝐞
Example:
(1)
=
0.4314 − 0.3715
= 0.00599kg/min
10
(2)
=
0.3715 − 0.3061
= 0.00654kg/min
10
LAB REPORT ON TRAY DRYER (L1)
12
9.0
DISCUSSION
Drying basically known as a process of removal of relatively small amounts of water from
material. In the drying process the water is usually removed as a vapor by air. For this
experiment, the drying process classified as batch which is the material was inserted into the
drying equipment and the drying process proceeds for a given period of time. The study of
this experiment is the drying curve based on the moisture content of the banana within the
time taken. Theoretically the dryer occurs in this experiment by the supply of heat into the
banana samples and use the air velocity in order passed over a heated element that act as
mass transfer to evaporate the moisture contain in banana.
From the result, the humidity from the experiment recorded in Table 7.1 according
time taken to dry banana sample for every 10 minutes. Humidity of an air-water can be
defined as kg of water vapor contained in 1kg of dry air. The first humidity that recorded at
the first 10 minutes is 7.3 for H1 and 0.5 for H2 with the temperature of 57.1 and 51.4◦C
respectively. Meanwhile, for this experiment, as we can see that the humidity value only
gives a small amount of changes which is from 7.3% to 7.5% during the drying process of
banana until the end of the experiment. So that, its mean that the water vapor that contain in
1kg dry air does not change. This situation occurs because of the lack of efficiency of
equipment. Noted that in this experiment, the value of H1 and T1 was the humidity and
temperature at early before tray inserted into the dryer while H2 and T2 after the drying
process.
Besides, Table 7.2 shows the moisture content that contain in the banana which is
0.4314 until 0 and drying rate of the banana sample from 0.00599min to 0. The moisture
content of banana decreases proportionally with time taken. Graph in Figure 4 shows the
moisture content of banana will decrease when the time increase. In this experiment, the
initial mass of banana used 1009.0 g, then the weight of banana reduced from the starting of
experiment until the end for every 10 minutes can be used to calculate the moisture contain in
banana. The moisture content decreased as the time increase because the water in the banana
vaporized when the dry air flow through the banana. After the surface of the banana dried
that shows the moisture different, the concentration between upper and bottom of the banana
also different. So that, the transferred of the remaining moisture forms from bottom to the top
of banana sample which is known as diffusion process occur.
LAB REPORT ON TRAY DRYER (L1)
13
Furthermore, the drying rate with time taken also recorded in this experiment and the
result show that the drying rate will take a short time when the time is increasing for every 10
minutes until 90 minutes. Graph in Figure 5 shows the trend of the decreasing of drying rate
of banana. Meanwhile, the drying rate are decreasing fluctuate and not stable because the
error in collecting data from the experiment.
Next, for overall result, the drying rate and moisture content of banana also being
analysed at the end of this experiment. Graph in Figure 6 illustrate the pattern of relation
between drying rate and moisture content of banana. This shows that when the banana
contains high moisture, the drying process will take a longer time to dry it. In this graph, one
part of this graph shows the constant rate and falling rate of drying process. Constant rate is
the rate where the drying at stable and when the banana reaches the critical moisture content
while falling rate take a longer time.
Figure 7 - The Drying Curve for the Banana Fruits
The drying rate and moisture content is also affected by the velocity of the air inside
the system. Although the speed of the fan is set constant at the lowest speed, based on the
results, there are changes in the velocity present. This could happen due to the equipment is
not well maintain making the surrounding air affecting the system in the dryer unit or the
equipment itself is at fault. At the end of the experiment, we can analyse that the result from
the experiment using batch dryer is acceptable. Since over a period of time, the moisture
content is fully removed and the drying curve shows the same pattern as the theoretical one.
LAB REPORT ON TRAY DRYER (L1)
14
Table 9.1: Comparison Between Tray Dryers and Various Types of Batch Dyers
Types of Dryers Mechanism of Drying
Drying Times
Tray Dryers
Hot air passing over the surface of a wet solid that is
Typically, long
spread over trays arranged in racks.
(12 to 48 h)
Heat is supplied by passing steam through hollow
Typically, long
shelves.
(12 to 48 h)
Fluidized-Bed
A preheated stream of air enters from the bottom of
Faster than tray dryer
Dryers
the product container holding the product to be dried with the same feed
Vacuum Dryers
and fluidized it.
Freeze Dryers
Dehydration process. The material is freeze and the
Faster than tray dryer
surrounding pressure is reduced allowing the frozen
with the same feed
water in the material to sublimate directly from solid
to gas phase. (Parikh D. , 2015)
Microwave
High-frequency radio waves are utilized in
Fast (50% reduction
Vacuum Dryers
microwave drying. The radiation from the bulk
in drying times
heating causes the solvent to vaporize in the pores of compared to vacuum
the material.
drying.
However, comparing the batch tray dryer equipment with various other batch dryers,
the tray dryers seems to be less effective compared to the others. Based on references from
(Parikh D. , 2015), (Choudhary, n.d.), and (Parikh D. M., 2014), although vacuum dryers
show the same drying times with tray dryers, the energy consumption and heat required
within the same time is much lesser as compared to tray dryers. Therefore, since microwave
vacuum dryer will reduce as far 50% from the drying times compared to vacuum drying,
similarly could happen when compared to tray dryers. Fluidized-bed dryer also more efficient
because its container equipment with vertical jets of hot gases from the uniform transfer of
thermal energy from a hot gas stream to a moisture product, removed the mixture with
flashed off method that could give an effective drying than tray dryers. Since freeze dryers
using dehydration process which directly involve the item to dried itself making the moisture
content of the item to be removed in anyway faster than tray dryers. Last but not least, the
effectiveness of a drying equipment is however depending on the physical and chemical
properties of the item to be dried such as the moisture content, and the size of the item.
10.0
CONCLUSION
Based on the data and graph plotted, it can be concluded that the objectives of the experiment
were achieved. The results of the drying process performed on the solid sample were
consistent with the theory which is the moisture content and the drying rate decreasing over
time. The velocity of the air highly depends on the fan of the drying unit. Since the speed of
the fan is set constant, the changes in the velocity is due to the outside air or faulty
equipment. The experiment conducted was running smoothly except for a condition where
the equipment was not well-maintained. In fact, troubleshoot the experiments is important as
it yields error in the results obtained. Therefore, since the objective is successfully obtained,
the experiment is successfully done.
11.0
RECOMMENDATIONS
In order to faster the rate of drying, instead of setting the fan at the lowest speed, a higher
speed will yield to a better result. The banana fruits will dry up in a much faster rate. Besides,
increasing the temperature of the air could also be done to increase the rate of drying. Since,
higher rate of drying will make the moisture content to be decreasing faster. The equipment
should undergo maintenance regularly to ensure the accurateness of data. Since, the velocity
of the fan seems to undergoes slight changes though have been set constant. The equipment
should also well-insulated to prevent heat from inside the system to be released to the
surroundings which resulting in slower drying rate. The air circulation within the dryer can be
improved to reduce the drying time and allows the use of lower temperature.
LAB REPORT ON TRAY DRYER (L1)
17
12.0
REFERENCES
Artin Afacan, J. M. (1984). Tray Drying Of Solids. Retrieved April 10, 2018, from University
of Florida Digital Collections:
http://ufdcimages.uflib.ufl.edu/AA/00/00/03/83/00083/AA00000383_00083_132.pdf
Choudhary, A. (n.d.). Principle and Working Of Fluidized Bed Dryer (FBD). Retrieved April
10, 2018, from Pharmaceutical Guidelines:
https://www.pharmaguideline.com/2014/08/principle-and-working-of-fluidized-beddryer-fbd.html
Parikh, D. (2015, April). Vacuum Drying: Basics and Application. Retrieved April 10, 2018,
from Reseacrh Gate:
https://www.researchgate.net/publication/283088611_Vacuum_Drying_Basics_and_
Application
Parikh, D. M. (2014, April 1). Solids Drying : Basic And Applications. Retrieved April 9,
2018, from Chemical Engineering Online: http://www.chemengonline.com/solidsdrying-basics-and-applications/?printmode=1#Figure1
S. M. Zakir Hossain, N. M. (2017, January). Design of a laboratory experiment for the
performance analysis of a retrofitted tray dryer unit. Education for Chemical
Engineers, Volume 18, 35 - 44. Retrieved from
https://www.sciencedirect.com/science/article/pii/S1749772816300173
Suhaila Bt Asnawi, R. B. (2012, November 22). Report Tray Dryer. Retrieved April 10,
2018, from Scribd: http://www.scribd.com/doc/14298479
LAB REPORT ON TRAY DRYER (L1)
18
13.0
APPENDICES
Figure 8 - Students Putting 4 Trays of Banana Slice into the Tray Dryer Training Unit
Figure 9 - Control Panel of The Tray Dryer Unit
LAB REPORT ON TRAY DRYER (L1)
19
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