UNIVERSITI TEKNOLOGI MARA FAKULTI KEJURUTERAAN KIMIA CHEMICAL ENGINEERING LABORATORY 2 (CHE 523) NAME /STUDENT NO. : SUHAILA BT ASNAWI
(2011242552)
RUHAIDAH BT KAMARUDIN
(2011623726)
NUR SYAZZWANA BT RUSLAN
(2011684876)
NURUL SOFIA BT SAMSUDIN
(2011671816)
HANIS FARHANA BT SHAMSUL AZIZAN (2011447536) GROUP
: EH2203A
EXPERIMENT
:
TRAY DRYER
DATE PERFORMED
: 8 NOVEMBER 2012
DATE REPORT SUBMITTED :
22 NOVEMBER 2012
SEMESTER
:
3
LECTURER
:
PROFF MADYA DR AHMED S IBREHEM
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 Supervisor’s grading TOTAL MARKS
Allocated Marks (%)
Marks
5 5 5 5 5 10 10 10 20 5 5 5 10 100
Comments: Checked by:
0
ABSTRACT The objectives of this experiment are to determine the drying rate for different materials and the moisture content. Also, the experiment was carried out to determine the variation of the drying process with different air speeds and heater powers. Besides that, the experiment was done to determine the relationship between the drying rate and the moisture of content. In this experiment, pandan leaves were used as samples. The mass of the trays were taken and then the pandan leaves were spread out onto the trays, and the total weight was recorded. The time taken for the samples to dry, temperature, humidity, mass of samples and flow speed are recorded during the experiment. The drying experiment is complete when the total mass, m of the samples to be dried is constant. The moisture content and the drying rate was then calculated using the results obtained and graphs were plotted to give a better understanding of the experiment. The experiment was considered a success.
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INTRODUCTION In tray dryers, the pandan is spread out, generally quite thinly, on trays in which the drying takes place. Heating may be 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. Most tray dryers are heated by air, which also removes the moist vapors. Technically, drying is a mass transfer process resulting in the removal of water moisture or moisture from another solvent, by evaporation from a solid, semi-solid or liquid to end in a solid state. To achieve this, there must be a source of heat, and a sink of the vapor thus produced. In the most common case, a gas stream, e.g., air, applies the heat by convection and carries away the vapor as humidity. Other possibilities are vacuum drying, where the source of heat may be by conduction or radiation and the vapor is removed by the vacuum system. Another possibility is drum drying, where a heated surface is used in connection with aspirators to draw the vapor outside the site. The term "drying" is a relative one, and simply means that there is a further reduction in the moisture content from some initial level provided by mechanical dewatering to some acceptable lower level. For example, a moisture content of 10-20% by volume would normally allow particles to flow freely, yet suppress dust formation. The necessity for drying may be to make a product suitable for sale (e.g. paint pigments), or for subsequent processing. When a solid dries, two fundamental and simultaneous processes occur: (1) heat is transferred to evaporate liquid; (2) mass is transferred as a liquid or vapor within the solid and as a vapor from the surface. These factors governing the rates of these processes determine the drying rate. Commercial drying operations may utilize heat transfer by convection, conduction, radiation, or a combination of these. Industrial dryers differ fundamentally by the methods of heat transfer employed. However, irrespective of the mode of heat transfer, heat must flow to the outer surface and then into the interior of the solid.
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Figure 1: Types of dryers
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OBJECTIVES The objectives are as the following: 1. To determine the drying rate for different materials and the moisture content 2. To determine the variation of the drying process with different air speeds and heater powers. 3. To determine the relationship between drying rate and the moisture of content
THEORY
Principles of Drying The purpose of drying is to remove the liquid adhering to a material and contained
within it. The drying curve depends on the form in which the moisture is present in the material to be dried. The surface moisture is evaporated first and carried away by the drying air as it surrounds the material to be dried as a thin film. The drying processes proceed more slowly for the moisture that is located in capillaries and pores within the material. This is because the capillary forces or diffusion resistance must be overcome. The removal of the water of crystallization contained in the material to be dried is even more difficult as it is bonded by relatively strong molecular forces. To expel it, the material to be dried has to be intensely heated. The drying curve is therefore divided into several stages. In the first drying stage, the liquid adhering to the surface of the material to be dried evaporates rapidly at a uniform drying rate. Drying of the capillaries is followed by drying in the pores. To do this, the liquid situated there must be evaporated so that it can diffuse through the material to be dried. This process is relatively slow and thus further reduces the drying rate. Intense heating of the 4
material to be dried over a longer period of time finally expels the liquid bonded within the crystal structure. In most technical dying does not continue to absolute dryness but to an agreed residual moisture level.
Drying Process Drying processes are classified as follows according to the type of heat transfer:
convection drying, contact drying and radiation drying. Depending on whether the drying temperature is higher or lower than the boiling point of the liquid to be separated, an additional distinction is made: Evaporating drying and vaporization drying For the most part, drying is carried out using warm air at atmospheric pressure. In this case, it is referred to as air drying. If drying takes place at significant sub atmospheric pressure, the procedure is referred to as vacuum drying. At drying temperatures below freezing point, it is refer to freeze drying. The experimental stand is designed and intended exclusively for convection drying. In convection drying, the heat necessary for drying is transferred to the material to be dried by a flowing gas through convection. To achieve sufficient heat transfer with loose porous material, the gas flows over several thin layers of material simultaneously. For material that is difficult to dry, the heat transfer is achieved by flowing the gas through a bulk of material to be dried or a fluid bed. The air is not only used to feed in the heat but also to absorb the vapor arising during the drying process. When it flows into the drier, the air must therefore be hot and as possible, so that it can absorb as much moisture as possible.
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The most important key figure in drying is the moisture content V of the material to be dried. This is defined as: ……………………..... Equation [1] = mass of liquid in kg
mST
= mass of solid in dry state in kg
The change in the moisture content during the drying process can be used to derive the drying rate v. …………………..…… Equation [2] mST = Change in moisture content = Drying time for this change
The Mollier h,x diagram The Mollier diagram provides information about the loading of the air with water, depending on the temperature and the relative humidity. This diagram only applies at atmospheric pressure. The loading X describes the mass ratio of water vapour in the air mD to the mass of the dry air mL. …………………. Equation [3]
The axis labels have the following meanings: X
: Loading [g/kg]
φ
: Relative humidity [hPa/hPa]
פּ
: Temperature of moist air [oC] 6
h
: Specific enthalpy of air [kJ/kg]
∆h/∆X
: Change in enthalpy for 1 kg absorbed water vapour [kJ/kg]
The lines in the Mollier diagram have the following meanings: 1.
Lines of constant temperature (isoterms).
2.
Lines of constant specific enthalpy (isenthalps).
3.
Lines of constant relative humidity φ
4.
Lines of constant loading X
As we move along a line in the Mollier diagram, the corresponding variable does not change.
METHODOLGY 1. Drying plates were removed from the support frame and the scale is tare to zero. 2. Drying plates were inserted individually into the support frame. The weight of the individuals drying plates on the digital scale were read and noted. 3. Material to be dried was spread in a thin layer on the drying plates. 4. Drying plates were inserted in the support frame and the total weight was recorded. 5. The fan was switched on and the speed was determined. 6. The flow speed was measured with manual anemometer and the value was recorded. 7. The heating level was switched on and set up. 8. The drying experiment was started and time was measured by using a stopwatch. 9. Temperature and humidity were recorded in 5 minutes interval until total time reached 1.5 hours. 10. The heater was switched off but fan was let on to cool down the channel. 11. After 15 minutes, the drying plates were removed. 12. The Tray Drier Training Unit was shut down.
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APPARATUS
1. Fan 2. Control cabinet 3. Support 4. Compensation screw 5. Channel with panel 6. Material holder with support Digital scale Temperature/ moisture sensor
RESULT First experiment was conducted by using Pandan leaves for each tray. Below were the results recorded: Mass of trays: 1390.3 g Temperature ( oc)
Humidity % rF
Time (min) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
T1 26.5 44.3 46.3 46.9 47.3 47.3 47.4 47.5 47.6 48.5 48.4 48.1 47.8 48.2 48.4 48.5 48.4 47.9 47.7
T2 26.1 42.1 44.7 45.5 45.8 46.1 46.2 46.4 46.5 47.0 47.3 47.1 46.8 47.2 47.3 47.4 47.4 46.9 46.7
H1 28.2 0.78 7.7 7.6 7.6 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5
H2 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
Velocity (m/s) 0 0.96 0.42 0.82 0.34 0.81 1.42 0.55 0.70 0.72 1.59 0.34 0.55 0.35 0.23 1.26 1.18 0.5 1.2
Mass (g) 204.6 193.3 187.5 182.1 177.3 172.1 166.9 164.7 156.1 152.4 146.3 142.1 138.0 134.8 130.7 127.4 123.6 120.5 116.6
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SAMPLE CALCULATION Moisture content can be calculated by using below equation:
V=
V1 =
-
= 0.7547
The drying rate v can be calculated by using the following equation:
v=
v1-2=
=
-
= 0.01938
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For experiment by using Pandanleaves :
Time (min) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
Mass of pandan leaves ( kg ) 0.2046 0.1933 0.1875 0.1821 0.1773 0.1721 0.1669 0.1647 0.1561 0.1524 0.1463 0.1421 0.1380 0.1348 0.1307 0.1274 0.1236 0.1205 0.1166
Moisture content (V)
Drying rate ( 1/min)
0.7547 0.6578 0.6081 0.5617 0.5206 0.4760 0.4314 0.4125 0.3388 0.3070 0.2547 0.2187 0.1835 0.1561 0.1209 0.0926 0.0600 0.0334 0
0.01938 0.00994 0.00928 0.00822 0.00892 0.00892 0.00378 0.01474 0.00636 0.01046 0.0072 0.00704 0.00548 0.00704 0.00566 0.00652 0.00532 0.00668 0
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Moisture content (V) versus time (min) 0.8
Moisture content (V)
0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0
20
40
60
80
100
Time (min)
Graph of moisture content vs tme (min)
Drying rate ( 1/min) versus time (min) 0.025
Drying rate ( 1/min)
0.02
0.015
0.01
0.005
0 0
10
20
30
40
50
60
70
80
90
100
Time (min)
Graph of drying rate vs time
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DISCUSSION Drying is a mass transfer process resulting in the removal of water moisture or moisture from another solvent, by evaporation from a solid, semi-solid or liquid to end in a solid state. To achieve this, there must be a source of heat, and a sink of the vapor thus produced. In the most common case, a gas stream, e.g., air, applies the heat by convection and carries away the vapor as humidity. Other possibilities are vacuum drying, where the source of heat may be by conduction or radiation and the vapor is removed by the vacuum system. Another possibility is drum drying, where a heated surface is used in connection with aspirators to draw the vapor outside the site. In this experiment, pandan leaves are used because pandan leaves requires short drying time and the moisture content will decrease faster with time. Two processes occur simultaneously. One of them is the transfer of energy, mostly as heat from the surrounding environment to evaporate the surface moisture and the other one is the transfer of internal moisture to the surface of the solid and its subsequent evaporation due to the first process. A few types of dryers are used in different fields and they have own specialties. The moisture content of dried products is very important, and if it is too high, moulds and yeasts tend to grow. The moisture content may be checked using scales and an oven.
The objectives of this experiment are to determine the drying rate for different materials and the moisture content, to determine the variation of the drying process with different air speeds and heater powers and lastly to determine the relationship between drying rate and the moisture of content
The mass of pandan leaves also decreases with time and the graph of drying rate versus time was fluctuating. Before the experiment was started the mass of pandan leaves was recorded to see the difference in mass after the pandan leaves was dried. The experiment was conducted for 1 and half hours so that we can make sure that the drying process occurs completely.
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CONCLUSION From this experiment, it can be concluded that the drying rate is varies with time and also it varies with the moisture content inside the substances. A tray dryers is an equipment which can used to determine well the drying rate of a wet substance.
RECOMMENDATIONS From this experiment, there are some recommendation which can be done if necessary to improve the drying rate which are:
Use the most suitable herbs which suits the tray dryers that we use.
Set the tray dryers heating until an appropriate temperature which suits the drying substance.
Make sure your hands are not wet or moist when open the control cabinet or when work on the electrical equipment. Before opening the control cabinet and working on the electrical system, disconnect the unit from the mains.
Before removing the drying plates from the machine, make sure the heater is switch off and allow the fan to continue running for a few minutes. Drying plates can become very hot during operation. So, you have to use gloves to handle the tray and never touched directly immediately after the experiment.
REFERENCE
‘Tray Dryers’ from
http://www.riddhipharma.net/tray-dryer.html ‘Pharmaceutical Tray Dryers’ from
http://www.pharma-machinery.co.in/tray-dryer.html ‘3-Tray Dryers’ from http://catalogs.indiamart.com/products/tray-dryer.html
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APPENDIX
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