CMT 450 LABORATORY REPORT

Experiment 6B
Title: Tray Drying and Particle Size
Name: MOHAMMAD AMIRUL ALIFF BIN MAHAZAM
Student No: 2018403148
Group: AS245S1
Laboratory Date: 15th November 2018
Submission Date: 22𝑡ℎ November 2018
Lab Partner’s name;
Name Student No
UMMI NASUHA BINTI MOHD ALI 2018288034
NAEMAH BINTI MOHD SALLEH 2018425336
MUHAMMAD SYAFIQ AKMAL BIN 2018425444
ZAMRI

Lecturer`s Name: DR RAJA RAZUAN RAJA DERIS

ABSTRACT

A dry product of the wet sand can be obtained through a process called drying. Drying is
a vaporization and removal of water and/or other liquid from a solution, suspension or other
solid-liquid mixture to form a dry solid. Aim of the conducted experiment is to investigate the
influence of particle size on the drying behaviour of a wet solid in air of fixed temperature and
humidity. Drying of the wet sand are done by using the tray driers. The size of the sand will be
manipulated as it will use two different sizes of sand. The wet sand is spread on shallows trays
resting on the shelves. As the dryer operate, water evaporates from the sand into the air. The
drying rate is the calculated by weighing the initial solid/water mixture and subtracting the
weight of final dry solid and at various times interval. The weight of the sand at))))))))
experiment must be the same at least ± 0000.01 g which indicates that the water content in the
sand is removed. Drying times comparison with others type of batch dryers shows the trays dryer
as the least effective.

INTRODUCTION

Theory/Background

 Theory/background

Drying is a mass transfer process consisting of the removal of water or another solvent by
evaporation from a solid, semi solid or liquid. Drying is differ from that evaporation.
Evaporation is more often applied to the concentration of solution whereby the drying associated
with removal of relatively small quantities of liquid to give a dry product. The drying involve
both heat and mass transfer operations. To dry a material/substance, two steps are needed which
is;

 Heat must be supplied to provide latent heat of vaporisation.

 The liberated vapour must be removed by moving an air stream (presence of air flow)

One of the term associated to drying is total moisture content, which is the total amount of liquid
associated with a wet solid. Also humidity, which is related to amount of water vapour present in
air.
 Drying rate is defined as the amount of water is removed over time. The drying rate of
solids containing internal liquids however depends on

 Internal moisture flow

 Distance it must travel to reach the surface

As the time passes the total moisture content will typically falls.

 Purpose
 To investigate the influence of particle size on the behaviour of a wet solid in air
of fixed temperature and humidity.
 To learn the correct way how to operate the tray dryer.

 Governing equation

In the experiment, the related equation below is involved:

𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑒𝑡 𝑠𝑎𝑚𝑝𝑙𝑒−𝑓𝑖𝑛𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡 𝑑𝑟𝑦 𝑠𝑎𝑚𝑝𝑙𝑒

 Moisture content = 𝑓𝑖𝑛𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑎𝑚𝑝𝑙𝑒

𝑊𝑖 −𝑊𝑓
 Drying rate= 𝑡

Where;

𝑊𝑖 = 𝑊𝑒𝑖𝑔ℎ𝑡 𝑏𝑒𝑓𝑜𝑟𝑒 (Wet Sand)

𝑊𝑓 = 𝑊𝑒𝑖𝑔ℎ𝑡 𝑎𝑓𝑡𝑒𝑟 (Dry Sand)

𝑡 = 𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 𝑖𝑛 𝑚𝑖𝑛𝑢𝑡𝑒

 Discovery question
 How did particle size influence the equilibrium content?
 How was the critical moisture content affected?
 Does the capillary mechanism movement account for the results?
METHODS

 Experiment overview

There are various kind of equipment available associated with drying but the one used in this experiment
is known as tray drier.

Equipment introduction. The equipment used for the best drying results in conventional process.
It is a double walled cabinet with single or two doors. The gap between two walls is filled with
high density fibre glass wool insulation material to avoid heat transfer. Doors are provided with
gaskets. Stainless steel trays are placed on the movable trolleys. Tray Dryer is provided with
control panel board, analog temperature and air velocity (flow rate) controller etc.

Tray dryer theory, stated that tray Dryer is an enclosed insulated chamber in which trays are
placed on top of each other in trolleys. Tray Dryer are used where heating and drying are
essential parts of manufacturing process in industries such as Chemicals, Dye stuff,
Pharmaceutical, Food Products, Colours etc. The material to be dried either wet or solids are
placed in the trays. Heat transfer is by circulation of hot air by electric heaters or steam in
radiator coils. Blower fans are installed inside to ensure proper circulation and transfer of heat. A
control panel to control the temperature and other parameters is fixed outside the dryer. These
dryers are available in Mild Steel, Stainless Steel or construction. Tray dryer is used for drying of
pigments, food, bakery, and electrodes, chemical and plastic powders.

Tray Dryer Working Principle

 In tray dryer hot air is continuously circulated. Forced convection heating takes place
to remove moister from the solids placed in trays.
 Simultaneously the moist air is removed partially.
 Wet solid is loaded in to the trays. Trays are placed in the chamber.
 Fresh air is introduced through in let, which passes through the heaters and gets
heated up.
 The hot air is circulated by means of fans at 2 to 5 metre per second.
 Turbulent flow lowers the partial vapour pressure in the atmosphere and also reduces
the thickness of the air boundary layer.
  The water is picked up by the air. As the water evaporates from the surface, the water
diffuses from the interior of the solids by the capillary action.
 These events occur in a single pass of air. The time of contact is short and amount of
water picked up in a single pass is small.
 Therefore the discharged air to the tune of 80 to 90 % is circulated back through the
fans. Only 10 to 20% of fresh air is introduced.
 Moist air is discharged through outlet. Thus constant temperature and uniform air
flow over the materials can be maintained for achieving uniform drying.
 In case of the wet granules as in tablets and capsules drying is continued until the
desired moister content is obtained.
 At the end of the drying trays or trucks are pulled out of the chamber and taken to a
tray dumping station.

Notes: In this experiment, the temperature used and humidity of the air in the tray dryer are
maintain fixed/constant. Refer to the objective, this experiment purpose is to know whether
the particle size of the solid (sand) effect the drying behaviour or not.

 Apparatus
 Tray drier units
 Digital balance
 Tissue
 Stopwatch
 Materials
  Different particle size of sands
 Water

 Procedure

Throughout the experiment, the temperatures were recorded for both of the experiment (2000
Micron and 600 Micron). The weight also been recorded for the samples that were been dried.

1. Raw dry sand samples were placed in the 2000 Micron sieve stack and been shaken
using mechanical shaker for 10 minutes.
2. The trays been cleaned up and placed in the tray dryer’s rack. Tare the weight.
3. Then, dry sands were making sure to be sufficient enough to fill four trays to a depth
of 10 mm. The dry sands were spread thinly into four trays.
4. The trays with spread sands then were placed into the rack and the mass of the dry
sands were taken.
5. The samples were then saturated with water by spraying little droplets of water.
6. The mass of the wet sand and mass of water contained in the sand were also recorded.
7. In order to operate the dryer, the main switch was turned on and the air flow rate and
air temperature was adjusted to a suitable one by using the main board.
8. The fan speed control was adjusted to 6 (middle position) and the heater power
control to 9. These setups were kept constant till the end of the experiment.
9. The weight of samples and temperatures were recorded for every 5 minutes until the
mass of the samples were constant for at least 3 times and as the same mass as the dry
sand before achieved.
10. Steps 1 to 9 were repeated for different particle size of the sands.

RESULTS

Results Data and Calculation

Results Data

For 2000 Micron:

 Times Mass of the sands Mass of the sands Temperature
(min) before (g) after (g) (⁰C)
5 1114.19 1110.59 33.5
10 1110.59 1106.75 33.8
15 1106.75 1105.31 34.5
20 1105.31 1105.03 35.5
25 1105.03 1105.02 36.0
30 1105.02 1105.02 36.7
35 1105.02 1104.78 36.7
40 1104.78 1103.58 36.8
45 1103.58 1102.32 36.9
50 1102.32 1102.28 37.0
Table 1: Data recorded for experiment 2000 Micron.

For 600 Micron

Times Mass of the sands Mass of the sands Temperature

(min) before (g) after (g) (⁰C)
5 1114.19 1110.59 33.5
10 1110.59 1106.75 33.8
15 1106.75 1105.31 34.5
20 1105.31 1105.03 35.5
25 1105.03 1105.02 36.0
30 1105.02 1105.02 36.7
35 1105.02 1104.78 36.7
40 1104.78 1103.58 36.8
45 1103.58 1102.32 36.9
50 1102.32 1102.28 37.0
Table 2: Data recorded for experiment 600 Micron

Calculations
Moisture content calculated using the following formula:

𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑙𝑖𝑞𝑢𝑖𝑑
 Moisture content = 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑎𝑛𝑑

𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑒𝑡 𝑠𝑎𝑚𝑝𝑙𝑒−𝑓𝑖𝑛𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡 𝑑𝑟𝑦 𝑠𝑎𝑚𝑝𝑙𝑒

= 𝑓𝑖𝑛𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑎𝑚𝑝𝑙𝑒

Drying rates calculated using the following formula:

𝑊𝑖 −𝑊𝑓
 Drying rate= 𝑡

Where;

𝑊𝑖 = 𝑊𝑒𝑖𝑔ℎ𝑡 𝑏𝑒𝑓𝑜𝑟𝑒 (Wet Sand)

𝑊𝑓 = 𝑊𝑒𝑖𝑔ℎ𝑡 𝑎𝑓𝑡𝑒𝑟 (Dry Sand)
𝑡 = 𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 𝑖𝑛 𝑚𝑖𝑛𝑢𝑡𝑒

Overall calculated results,

2000 Micron:
 Table 3: Overall calculated results for experiment 2000 Micron

Times Mass of the sands Mass of the sands after Drying rate Moisture Content
(min) before (g) (g) (g/min)
5 1114.19 1110.59 0.720 0.0032
10 1110.59 1106.75 0.768 0.0035
15 1106.75 1105.31 0.288 0.0013
20 1105.31 1105.03 0.056 0.0025
25 1105.03 1105.02 0.002 0.00009
30 1105.02 1105.02 0.000 0
35 1105.02 1104.78 0.048 0.00022
40 1104.78 1103.58 0.240 0.0011
45 1103.58 1102.32 0.252 0.0011
50 1102.32 1102.28 0.008 0.000036
 600 Micron:

Times Mass of the sands Mass of the sands Drying rate Moisture Content
(min) before (g) after (g) (g/min)
5 1072.35 1069.34 0.602 0.0028
10 1069.34 1066.33 0.602 0.0028
15 1066.33 1063.19 0.628 0.003
20 1063.19 1060.40 0.558 0.0026
25 1060.40 1057.82 0.516 0.0024
30 1057.82 1052.69 1.026 0.0049
35 1052.69 1041.13 2.312 0.011
40 1041.13 1029.12 2.402 0.012
45 1029.12 1016.43 2.538 0.012
50 1016.43 1012.30 0.826 0.0041
55 1012.30 1012.25 0.01 0.00005

Table 4: Overall calculated results for experiment 600 Micron

Graph

Moisture Content Vs Time (mins)

0.014

0.012
Moisture Content

0.01

0.008

0.006 600 Micron

0.004 2000 Micron

0.002

0
5 10 15 20 25 30 35 40 45 50 55
Time (mins)

Chart 1: Moisture Content Vs Time (mins)

 Drying Rate vs Moisture Content 2000 micron
0.9
0.8
0.7
Drying Rate

0.6
0.5
0.4
0.3
0.2
0.1
0

Moisture Content

Chart 2: Drying Rate Vs Moisture Content (2000 Micron)

Drying Rate vs Moisture Content 600 Micron

3

2.5

2
Drying Rate

1.5

0.5

Moisture Content

Chart 3: Drying Rate Vs Moisture Content (600 Micron)

Discussion

These experiment has been done in order to obtain the mass of the wet sand after been
subjected to drying process in the tray drier. From these mass value, the drying rate and moisture
content can be calculated. These drying rate and moisture content was used majorly to answer
the discovery question of these experiment which is the first one is how did particle size
influence the equilibrium content? Secondly how the critical moisture content was affected? And
lastly does the capillary mechanism movement account for the results?

According to the “Equilibrium moisture content” available at

https://en.m.wikipedia.org/wiki/equilibrium_moisture_content (accessed at 19 November) state
that the equilibrium moisture content will be affected by the properties of material used in the
drying affected the equilibrium content. Thus as we used a different size particle the result would
be different as the smaller size has more surface area unit volume. Refer to the Table 3 & 4 there
is a huge difference in the drying rate which is much higher in 600 micron than 2000 micron at
the same time gaps.

For second question, based on the cited reference at “Module 4: Design of Dryer”
available at https://nptel.ac.in/courses/103103027/module4/lec1/2.html (accessed at 18
November 2018) defined the critical moisture content as at which constant rate drying period
ends and the falling rate drying period starts. Referring to the graph below
 Drying Rate vs Moisture Content
2000 micron
1
0.8
Drying Rate

0.6
0.4
0.2
0

Moisture Content
Chart 2: 2000 micron

Drying Rate vs Moisture Content

600 Micron
3
Drying Rate

2
1
0

Moisture Content
Chart 3: 600 Micron)

These 2 graph have the critical moisture content happen where the constant rate period
end at the moisture content of 0.0011 for graph 2 for 2000 micron and for graph 3 the constant
rate ended at 0.012 and falling period happen. This depending on nature and type of solid use.
Depending on the solid nature and type, some can give a better transport of moisture that will
affect the critical moisture content.

Last question is on how does the capillary mechanism movement account for the results?
The answer would be no as the transfer mechanism that in use in this experiment is through the
air flow.

From the experiment, the data was used to plot graph. Compared with the graph at
reference “CMT 450 Laboratory Manual” written by Dr Raja Razuan and the experimental
plotted graph, there seem to be a difference between these two.
 Obtained from the CMT 450 Laboratory Manual

From the left side the graph which should be like that but a different story happen with the
experimental plotted graph.

Moisture Content Vs Time (mins)

0.015
Moisture Content

0.01

0.005 600 Micron

2000 Micron
0
5 10152025303540455055
Time (mins)

Chart 1

The right side though more worse as the plotted graph became like this in the below;

Drying Rate vs Moisture Content

2000 micron
1
0.8
Drying Rate

0.6
0.4
0.2
0

Moisture Content

Chart 2
 Drying Rate vs Moisture Content
600 Micron
Drying Rate 3
2
1
0

Moisture Content

Chart 3

These deviation in the graph that has been plotted to the reference graph was due to many
factors. The reason was due to personal error mainly. First of all when the weigh was taken, there
isn’t sufficient of time was given to stabilize the shelves in the dryer, thus the moved shelves
give incorrect value of the tray with solid. Secondly the “TARE” function at the balance was
didn’t used in the experiment hence the mass obtain was not acceptable.

Conclusion

As a conclusion this experiment was carried out to find out the effect of particle size on
the behaviour of a wet solid in air of fixed temperature and humidity. Based on the data and
graph plotted, it we can concluded that the objective of the experiment has been achieved
although there are some error present that has affected the plotted graph. The results of the effect
of particle size of samples on drying rate were consistent with the theory. The experiment
conducted was running smoothly except for a condition where the data recorded have some
error. 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.
Recommendation

First of all, make sure that the raw sample sand used were totally dry and contain no
water that will affect the process. The raw sand must be sieve first using sieve stack of 2000 and
600 Micron and be shaken using mechanical shaker. Make sure during weighting the sand, the
rack stacks is not shaking or vibrating as it will affecting the reading of the analytical balance.
Hold the stack for a while after filled the tray in to stop the rack stacks from moving too much.
Then try to take the reading of analytical balance.

REFERENCES

1. Retrieved on 31th October 2018 from

http://www.nzifst.org.nz/unitoperatons/traydryer.htm

2. Retrived on 31th October 2018 from

https://en.m.wikipedia.org/wiki/traydryerprocessandconcepts.

3. C.M Vant Land (2011) Drying in the Industry Process, 1st Edition, Wiley Publisher, pp
240-245.