cel drying (marcus poon 004681)
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H83CEL Chemical Engineering Laboratory Marcus Poon Chinn Yoong 004681
H83 CEL
Chemical Engineering Laboratory
Drying of
Rice Noodles
Name : Marcus Poon Chinn Yoong
Student ID : UNIMKL 004681
Group Members : Ler Sin Yee (004669)
Leong Yoong Kit (006414)
Liew Chan Yip (004671)
Supervisor : Professor Law Chung Lim
Date : 30th April 2012
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Declaration Form
I certify that:
1) Apart from the experimental results reported in the lab notebook which are the
joint work of the team, this report is entirely my own work.
2) All information extracted from the literature has been dully attributed.
3) Any material copied verbatim from the literature has been both duly attributed
and enclosed in quotation marks.
Signed:
Date:
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Table of Contents
Contents
Summary ................................................................................................................................................................ 1
Introduction ........................................................................................................................................................... 2
Literature Search................................................................................................................................................. 3
Rice-noodles ...................................................................................................................................................... 3
Freeze Drying.................................................................................................................................................... 4
Heat Pump ......................................................................................................................................................... 7
Comparison........................................................................................................................................................ 8
Future Trend...................................................................................................................................................... 9
Experimental ....................................................................................................................................................... 10
Results ................................................................................................................................................................... 13
Freeze Drying.................................................................................................................................................. 13
Heat Pump Drying......................................................................................................................................... 13
Rice noodles in block................................................................................................................................ 13
Rice noodles in strands ........................................................................................................................... 16
Rehydration ..................................................................................................................................................... 21
Texture Hardness Analyser ....................................................................................................................... 21
Discussion ............................................................................................................................................................ 25
Conclusion ............................................................................................................................................................ 29
Nomenclature...................................................................................................................................................... 30
References ........................................................................................................................................................... 31
Appendix I ............................................................................................................... Error! Bookmark not defined
Appendix II ............................................................................................................. Error! Bookmark not defined
Appendix III ........................................................................................................... Error! Bookmark not defined
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Summary
Rice noodle is one of the most popular Asian noodles consumed in Asia, prepared mainly
from three basic ingredients: rice flour, water and salt. With an increase demand of rice noodles in
Asia especially as instant noodles, two different equipment, freeze drying and heat pump drying
are compared in order to meet the customer expectation and commercial value of rice noodles.
Development of drying technologies is important as dehydration reduces spoilage, decrease
product mass, increase shelf life and gives added value without chemical treatment. The effects of
two different temperatures, 40C and 60C on the rice noodles using heat pump is observed.
Although freeze drying is claimed to be having the highest quality, the high capital and
maintenance cost is the issued that need further research for improvement. Heat pump drying
appears to be more suitable for rice noodles which meet the criteria to judge a raw material qualitywith processing properties, appearance and colour of noodles. However, its batch operation and
shrinkage problem as well as oily surface remain on the rice noodles are issues to be solved
Effective diffusivities, moisture content and activation energy as well as texture hardness analyzer
are performed to investigate the performance of the equipment. The characteristics and kinetics of
sample for both equipment are not precise and data is not clear enough to present the information
of both pro and cons of the equipment. The experiment reliability of result can be improved in the
operation to produce a better quality product at lower energy consumption, environmental impact
and cost.
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Introduction
Drying preserves the product by lowering the amount of moisture in the material. The main
objectives of drying are to decrease moisture content to a level where spoilage due to reactions
can be minimized (Uddin, et al., 2004), prolong shelf life, minimize spoilage, production of higher
value product and reduce transportation cost (Mujumdar, 2008). With the concerned on the
commercial value of rice noodles and to meet customer expectation, two equipment are suggested
heat pump drying and freeze drying to perform the drying process on rice noodles.
The aim of this experiment is to study drying characteristics and kinetics of rice noodles
making use of heat pump drying and freeze drying to compare the influence of different modes of
drying on the dried rice in terms of quality, colour and appearance. This experiment is conducted to
compare the performance of heat pump drying and freeze dryer. The temperature of heat pump
drying is set to 40C and 60C to determine the effect of temperature on the drying rate of the
samples.
The samples are prepared at two different structure, block and strand. Its performance on
drying rate, moisture content, rehydration capacity as well as hardness is carried out to compare
between freeze dryer and heat pump drying on rice noodles.
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Literature Search
Rice-noodles
Introduction
Since ancient time, noodles in various content, formulations and shapes have been the
staple foods for many Asian countries. Rice noodle is one of the most popular Asian noodles
consumed in Asia, prepared mainly from three basic ingredients: rice flour, water and salt
(Samritthisuth & Thammathongchat, 2011). Rice noodles (Kway Teow) or white salted noodles
generally made from flours in range of 8 to 11% protein. The appearance of rice noodles is bright
with clean colour ranging from white to creamy white, with a smooth glossy surface after boiling
Corn starch is added to improve the transparency and chewy texture of the noodles. The noodles
are coated with oil to keep them away from sticking together which will cause problem in storage
of rice noodles (Fu, 2008).
Drying a wet material is achieved by evaporating the liquid water it contains. For food, this
often results in profound changes to appearance and taste. Uniform and straight strands, white and
translucent coloring with absence of broken strands are the characteristics of high quality of rice
noodles. In order for rice noodles to have commercial value for consumer acceptability, increasing
value, improving economic value and edible quality, adding some water to the rice noodles, it must
recover the original state of the rice noodles. The dried rice noodles should retain the color, flavor
and nutrition of the rice noodles (Wang, et al., 2010).
Consumer expectation of noodle product quality is getting higher with the development of
the Asia-Pacific economy. The market of production of instant noodles is expanding. Therefore
porous and spongy structure is needed as they are excellent for rehydration so that it is convenient
for ready-to-eat after adding hot water as instant noodles. The reduction of water content helps to
preserve the food and lower the material weight for convenient transportation. As a result, it can
be used as frozen rice noodles especially target for outdoor usage or food supplies during disasters
(Oikonomopoulou, et al., 2011). High quality noodles should be bright in color, adequate shelf life
without visible microbiological deterioration and appropriate flavor and textual characteristics. It
hydrate with minimum turbidity and surface stickiness when soak into hot water.
The rice noodle industry is now facing problems with overuse of additives to enhance eating
quality. Due to globalization and market expansion, equipment must be designed with emphasize
on product quality to conform to a wide consumer preference (Colak & Hepbasli, 2009). Quality o
dried food products can be assessed by the degree of degradation of the colour, flavor, as well as
texture (Perera & Rahman, 1997). Development of drying technologies is important as dehydration
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reduces spoilage, decrease product mass, increase shelf life and gives added value without
chemical treatment (Chong, et al., 2008).
Freeze Drying
IntroductionFor many years, freeze drying (lyophilization) has been used in a number of applications
most commonly in the food and pharmaceutical industries. It is a techniques wide application to
the preservation of heat-sensitive biological materials, especially foods, and is capable of removing
water without impairing product quality. The first commercial used of freeze drying was during
World War II when it was used to dry blood plasma and penicillin. Freeze drying works through
removal of water or other solvent from a frozen product by sublimation at temperature and
pressure below triple point of water 273.16 K and 611 Pa (Antal & Kerekes, 2007). It occurs when
frozen product goes directly to gaseous state without passing through liquid phase which allows the
preparation of a stable product which is easy to use and aesthetic in appearance, extends products
shelf life and easier to transport as well as storing (Labconco, 2010). It is one of the most
sophisticated dehydration methods (Antal & Kerekes, 2007) and best method of water remova
with final products of highest equality compared to other type of food drying methods (Kudra &
Mujumdar, 2009).
Principles of Vacuum Freeze Drying Operation
Vacuum Freeze drying (VFD) takes place in 3 distinct steps: pre-freezing, primary drying
and secondary drying. Material must first adequately prefrozen to completely solid in order to
control the ice crystals size growth and to avoid possible damage to material. The method of pre-
freezing and the final temperature of the frozen product can affect the ability to successfully freeze
dry the material. At the end of freezing step, about 65 to 90% of initial moisture is in the frozen
state and 10-35% remains at the sorbed (nonfrozen) state (Chen, 2007). The rate of sublimation
of ice from a frozen product depends upon the difference in vapour pressure of the product
compared to the vapour pressure of the ice collector. For primary drying, a vacuum pump is used
to lower the pressure of the environment around the product. This leads to an interconnected
porous structure which can be rehydrated later in an effective way while preserving the nutritiona
and organoleptic properties of the product (Quiroga, et al., 2012). The temperature of the materia
continue to fall below the freezing point and sublimation slow down until the rate of heat gain
through conduction, convection and radiation to the material was equal to the rate of heat loss as
the more energetic molecules sublimed and were removed. For main drying, all the free ice is
removed, leaving an apparently dry material which, contain significant bound water (Baker, 1997)
The products appear dry but residual moisture content may be higher as 7 to 8%. The third and
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final stage is secondary drying. The process called isothermal desorption to desorb bound water
from the water is carried out. Heat is applied to the product under very low pressure (Labconco
2010). The remaining bound water usually amount to below 20% mass basis.
Figure 1: Freezedrying physical phenomena represented on the water phase diagram
(Quiroga, et al., 2012).
A typical vacuum freeze dryer has four principal components: a vacuum pump, a
refrigerated product chamber, a condenser and a control system. A vacuum pump used to force the
air and water vapour out from the system, thereby lowering the air pressure in the chamber
Heating unit applies a small amount of heat to shelves causing ice to change phase. The
refrigerated product chambers contain the material being dried. The condensers trap the water
vapour that sublimes from frozen objects as they dry. The control system shows indicator of
pressure in the product chamber (Cook, 2007).
Figure 2: A Schematic Drawing of the Four Principal Components of a Typical Freeze-
Dryer (Cook, 2007)
http://www.sciencedirect.com/science/article/pii/S0260877412001331 -
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Application on Food Products
VFD mainly employed for drying of pharmaceutical products. The rate of drying is governed
by both temperature and pressure (Cook, 2007). Freeze drying kills active mould and causes
dormancy in spores.
During drying, the drying times and temperature are the most important factors. It is
valuable as a conservation procedure as it does not result in as much shrinkage, distortion, and
collapse as can occur when wet objects are air-dried (Cook, 2007). The temperature of materia
lowering to well below 0 throughout the process reduces the risk of drying damage. The weight
of the freeze object decreases as the moisture sublimes, but stabilizes as soon as it is dried (Cook,
2007).
Shrinkage is eliminated or minimized, and a near-perfect preservation results. Freeze-dried
food can last longer than other preserved food and it is very light (Bellis, 2012). The product of
freeze drying is a stable solid that can reconstituted by simple addition of water (Rao, et al., 2008)
Therefore, it is considered as having a better quality than other dehydrated products. Furthermore
the flavor of freeze dried foods is better than the air dehydrated products (Antal & Kerekes, 2007)
The low temperature employed minimizes the effects of denaturation of proteins and better
retention of flavors and aromas. The solid state protects the primarystructure and the shape of the
products with minimal volume reduction (Mujumdar, 2008). Rehydration ratio of freeze-dried foods
is generally 4 to 6 times higher than air dried foods, making it excellent for ready-to-eat instant
soups or meals (Ratti, 2001). It has 98% of water removed which reduces the food weight by 90%
Among drying methods used in food processing industries, freeze drying is considered as one of
the advanced methods for drying high value products sensitive to heat, prevent shrinkage and
produces materials with high porosity, maintain nutrition quality, superior taste, flavors and color
retention as well as completeness of rehydration. (Oikonomopoulou, et al., 2011)
Unfortunately, freeze drying usually applied to batch process, require pre-freezing, time
consuming and expensive process in both the capital and operating cost as well as high energy cost
(Baker, 1997). Major part of the cost comes from sublimation, maintaining low vacuum and
cryogenic condition (Mujumdar, 2008).
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Heat Pump
Introduction
Heat pump is known as an efficient method of energy recovery with its ability to convert
latent heat of vapor condensation into sensible heat of an air stream passing through the
condenser. Heat pump drying has been used in wood kilns to dehumidify air and control lumber
quality for decades (Kudra & Mujumdar, 2009). With the trend to improve product quality and
reduce energy consumption, many researchers have been focus on the research on heat pump
drying (Kudra & Mujumdar, 2009).
Principles of Heat Pump Operation
It operates according to a basic air conditioning cycle or refrigeration technique which
involves four main components: compressor, condenser, expansion valve and evaporator. It is
attached to a drying chamber with auxiliary heater for better temperature control. Therefore, it is
known as heat pump dryer (HPD). It works through two operating cycles: heat pump and drying
cycles.
Figure 3: A Schematic Illustration of a Heat Pump Drying System
(Colak & Hepbasli, 2009)
For the heat pump drying system, refrigerant (working fluid) at low pressure is evaporates
in the evaporator by heat drawn from the dryer exhaust air. The compressor raises the enthalpy of
refrigerant of heat pump and discharges it as superheated vapor at high pressure. The refrigeran
is condensed in the condenser and heat is transferred to the cool dry air that passes through the
condenser coil. The condensed refrigerant is then expanded in valve and the cycle continues.
In drying system, hot air loses its latent heat to the evaporator and cool to condensation
where moisture is removed. The cool dry air is then heated after passing through the condenser
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coil. Then, heated air is supplied to the drying chamber and the drying cycle continues (Colak &
Hepbasli, 2009). The drying temperature of HPD system can be adjusted from -20C to 60C.
Application on Food Products
Heat pump systems are widely used in space heating and cooling, desalination and drying
Its application can be seen in residential such as existing refrigeration and air conditioning system
(Goh, et al., 2011).
It has advantages of energy saving potential as it consumes 60-80% less energy than
conventional dryers which operates at the same temperature. High energy efficiencies are
achievable through the recovered of sensible and latent heat of vaporization. It is able to control
drying temperature and air humidity which then creates several possibility of a wide range of
drying conditions. It can be carried out at a lower temperature which is suitable for heat sensitive
product. It can be conducted independent of the ambient weather condition. HPDs provide better
quality product, operate independently of outside ambient weather conditions. This technology is
environmental friendly as it requires lower energy and no release of toxic gases and fumes into the
atmosphere. The color and aroma qualities using HPD were better than using conventional hot air
dryer (Colak & Hepbasli, 2009). A combination of both heat pump and drying unit, both latent heat
and sensible heat can then be recovered from exhaust air, hence improving the overall therma
performance and effective control of air conditions at the dryer inlet. It is suitable for high value
products (Goh, et al., 2011).
However, it is limited to batch operation. Its capital cost and maintenance cost are higherthan air drying as it needs to maintain the compressor and it needs refrigerant filter as well as
charging of refrigerant. Another constraint is that too low temperature will limit drying rates which
give rise to microbial growth problems (Perera & Rahman, 1997). Leakages of refrigerant might
occurs and additional floor space requirement (Mujumdar, 2008).
Comparison
Figure 4: General Comparison of Heat Pump with Vacuum and Hot-Air Drying (Mujumdar,
2007).
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Heat pump drying is more economical than freezing drying, in both capital and running cost, by 10
times and 4.5 times less, respectively (Law, et al., 2008).
Future Trend
An application of HPD dryers in combination with fluidized-bed dryers has been investigated
to improve drying efficiency and product quality (Perera & Rahman, 1997). Hybrid technologies
based on heat pumps and vacuum freeze dryer can be achieved through further research and
development.
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Experimental
Figure 5: Freeze Dryer
Figure 6: Front View and Side View of Heat Pump Dryer
Procedures:
1) Material Preparationa) A few packets of rice noodles are bought from market.b) Several sets of rice noodles were prepared in 2 categories, which are strands of rice noodles
and arrangement of rice noodles in block.
c) It was cut into several strands with equal dimensions and the dimension is measured byusing a vernier caliper.
d) Two different equipment, freeze dryer and heat pump dryer, are used to carried out thedrying rice noodles process.
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2) Operating freeze dryera) The initial mass of container is measured.b) The sample is arranged in the container in order to get a block structure and the mass of
container with rice noodles is measured.
c) The water in the freeze dryer is ensured to be empty before operating it to avoid extraenergy needed for vacuum pump to perform the pumping work.
d) The lid is removed and the pump is warmed up for 30 minutes.e) The sample is then placed into the trays.f) The vacuum condition is set to -40C and 0.12 bar.g) Freeze dryer is operated at auto mode and the sample is freeze for 24 hours.h) The vacuum valve is open so that the lid can be removedi) The sample is collected and the mass, dimensions is measured.j) Comparison is made between the initial and final condition of both the sample (strand and
block) of rice noodles.
k) The sample is then placed into the oven for a day.l) The borne dry weight is measured.m)The freeze dryer is cleaned by draining out all the water through a valve.n) Steps b to m is repeated with several samples of strand and block to get average values
from several data.
3) Operating heat pump dryera) Wire mesh is prepared to place the rice noodles in block in the wire mesh to maintain the
structure.
b) The initial mass of wire mesh is measured.c) The sample is arranged in the wire mesh in order to get a block structure and the mass of
wire mesh with rice noodles is measured.
d) The main switch is turned on followed by the compressor.e) The temperature is adjusted to 60C.f) It is allowed to warm up for 30 minutes until the temperature is stable.g) Hygrometer is placed in the drying chamber to measure the temperature and relative
humidity and the values are recorded.h) The samples are then placed into several trays.i) The samples are taken out to measure the mass using electronic balance every 5 minutes
initially then the interval increases to 10 minutes or 15 minutes depends on the drying rate.
j) The mass is recorded accordingly until a constant value is achieved.k) Heat pump is switched off accordingly once the data is collected.
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l) The sample is then placed into the oven for a day.m)The borne dry weight is measured.n) Steps b to m is repeated with samples of strand and block rice noodles at 40C.
4) Texture profile analyzer (TPA)a) It is used to determine the initial texture and final texture of dried noodles.b) The sample is placed at the platform.c) A 2mm stainless steel probe is used to test the hardness of the sample.d) Tables and graphs of sample hardness are obtained electronically through the software
installed.
5) Rehydrationa) A petri dish filled with water is prepared.b) An empty petri dish initial mass is measured.c) Strand of rice noodles after freeze drying is placed in the petri dish filled with water
immediately.
d) The mass of the strand is then placed in the empty petri dish and measured every 5minutes.
e) Steps c and d is carried out until the strand of sample achieving a constant value (no longergaining mass).
f) Steps c to e is repeated by using a stand or rice noodles after heat pump drying.
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Results
Freeze Drying
Table 1: Borne dry weight of samples
Type Initial
Weight (g)
Final Weight
(g)
Borne dry
weight (g)
Change in
weight (g)
Change in
weight (%)
Block 68.95 24.42 23.76 45.19 65.54
Strand 3.83 1.43 1.32 2.51 65.54
Table 2: Change in moisture content of samples
Type Initial Moisture
Content
(g H2O/ g dry solid)
Final Moisture
Content
(g H2O/ g dry solid)
Change in moisture
content
(g H2O/ g dry solid)
Block 1.902 0.0278 1.874
Strand 1.902 0.0833 1.819
Table 3: Shrinkage of samples
Type Initial
Dimension (cm)
Initial
Capacity
(cm3)
Final
Dimension (cm)
Final
Capacity
(cm3)
Shrinkage
(cm3)
Shrinkage
(%)
Block 8.77 x 7.73 x 2.41 163.38 8.01 x 7.55 x 2.38 143.93 19.45 11.90
Strand 8 x 1 x 0.144 1.152 7 x 1 x 0.144 1.008 0.144 12.50
Heat Pump Drying
Rice noodles in block
Table 4: Borne dry weight of block samples at different temperature
Temperature
(C)
Initial
Weight (g)
Final
Weight (g)
Borne dry
weight (g)
Change in
weight (g)
Change in
weight (%)
60 60.878 20.945 19.51 41.368 67.95
40 60.611 21.655 19.73 40.881 67.45
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Table 5: Change in moisture content of block samples at different temperature
Temperature
(C)
Initial Moisture
Content
(g H2O/ g dry solid)
Final Moisture
Content
(g H2O/ g dry solid)
Change in moisture
content
(g H2O/ g dry solid)
60 2.120 0.0736 2.0464
40 2.072 0.0976 1.9744
Table 6: Shrinkage of block samples at different temperature
Temperature
(C)
Initial
Dimension
(cm)
Initial
Capacity
(cm3)
Final
Dimension
(cm)
Final
Capacity
(cm3)
Shrinkage
(cm3)
Shrinkage
(%)
60 7.8 x 7.7 x
2.3
138.14 6.8 x 6.7 x
1.9
86.564 51.576 37.34
40 10.38 x 9.08
x 1.96
184.73 9.28 x 8.0 x
1.8
133.632 51.098 27.66
Graph 1: Graph of moisture content against drying time for block rice noodles
y = -4E-15x6 + 3E-12x5 - 4E-10x4 - 5E-07x3 + 0.0002x2- 0.0346x + 2.0712
R = 0.9992
y = 7E-16x6 - 9E-13x5 + 5E-10x4 - 2E-07x3 + 8E-05x2 -0.0189x + 2.0693
R = 0.9999
0.000
0.500
1.000
1.500
2.000
2.500
0 100 200 300 400 500Moisture
content,MC(gH2O/gdried
solid)
Drying Time. t (min)
Graph of Moisture Content against Drying Time(Block rice noodles)
60 degree with dimension7.8cm*7.7cm*2.3cm
40 degree with dimension
10.38cm*9.08cm*1.96cm
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Graph 2: Graph of drying rate against moisture content for block rice noodles
Graph 3: Graph of moisture ratio against drying time for block rice noodles
y = 24.001x - 2.1112R = 0.8188
y = 7.2619x - 0.0626R = 0.9848
-10.000
0.000
10.000
20.000
30.000
40.000
50.000
60.000
70.000
80.000
90.000
0.000 0.500 1.000 1.500 2.000 2.500
D
ryingrate,
R(gH2O/m2.m
in)
Moisture content, MC (gH2O/g dried solid)
Graph of Drying rate against moisture content(Block rice noodles)
60 degree with dimension7.8cm*7.7cm*2.3cm
40 degree with dimension10.38cm*9.08cm*1.96cm
y = -2E-15x6 + 2E-12x5 - 2E-10x4 - 3E-07x3 +
0.0001x2 - 0.0169x + 0.976R = 0.9992
y = 3E-16x6 - 5E-13x5 + 3E-10x4 - 1E-07x3 + 4E-05x2 - 0.0096x + 0.9986
R = 0.9999
-0.200
0.000
0.200
0.400
0.600
0.800
1.000
1.200
0 100 200 300 400 500
M
oistureRatio,
MR
Drying Time, t (min)
Graph of Moisture Ratio against Drying Time
(Block rice noodles)
60 degree with dimension
7.8cm*7.7cm*2.3cm
40 degree with dimension10.38cm*9.08cm*1.96cm
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Graph 4: Graph of ln MR against drying time for block rice noodles
Rice noodles in strands
Table 7: Borne dry weight of strand samples at different temperature
Temperature
(C)
Initial
Weight (g)
Final
Weight (g)
Borne dry
weight (g)
Change in
weight (g)
Change in
weight (%)
60 1.524 0.463 0.43 1.094 71.78
40 1.507 0.619 0.55 0.957 63.50
Table 8: Change in moisture content of strand samples at different temperature
Temperature
(C)
Initial Moisture
Content
(g H2O/ g dry
solid)
Final Moisture
Content
(g H2O/ g dry
solid)
Change in moisture
content
(g H2O/ g dry solid)
60 2.544 0.0767 2.4673
40 1.74 0.125 1.615
y = -0.0237x + 0.1174
R = 0.9809
y = -0.0182x + 0.5773R = 0.9165
-12.000
-10.000
-8.000
-6.000
-4.000
-2.000
0.000
2.000
0 100 200 300 400 500
lnMR
Drying Time, t (min)
Graph of ln (MR) against Drying Time(Block rice noodles)
60 degree with
dimension7.8cm*7.7cm*2.3cm
40 degree withdimension10.38cm*9.08cm*1.
96cm
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Table 9: Shrinkage of strand samples at different temperature
Temperature
(C)
Initial
Dimension
(cm)
Initial
Capacity
(cm3)
Final
Dimension
(cm)
Final
Capacity
(cm3)
Shrinkage
(cm3)
Shrinkage
(%)
60 8 x 1 x 0.144 1.152 7.2 x 0.7 x
0.144
0.726 0.426 36.98
40 8 x 1 x 0.144 1.152 7.3 x 0.8 x
0.144
0.841 0.311 27.00
Graph 5: Graph of moisture content against drying time for strand rice noodles
y = -2E-12x6 + 1E-09x5 - 2E-07x4 + 1E-05x3 - 0.0002x2 - 0.0339x + 1.7848R = 0.9981
y = 5E-11x6 - 2E-08x5 + 3E-06x4 - 0.0002x3 + 0.0092x2 - 0.2062x + 2.4263R = 0.985
0.000
0.500
1.000
1.500
2.000
2.500
3.000
0 50 100 150 200MoistureContent,MC(gH2O/gdrysolid)
Drying Time, t (min)
Graph of Moisture Content against Time(Strand Rice Noodles)
40 degree with
dimension8cm*1cm*0.144cm
60 degree withdimension8cm*1cm*0.144cm
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Graph 6: Graph of drying rate against moisture content for strand rice noodles
Graph 7: Graph of moisture ratio against drying time for strand rice noodles
y = 27.861x - 4.7219R = 0.9121
y = 6.1802x + 0.3718R = 0.724
-10.000
0.000
10.000
20.000
30.000
40.000
50.000
60.000
70.000
80.000
90.000
0.000 0.500 1.000 1.500 2.000 2.500 3.000
DryingRate,
R(gH2O/m2.m
in)
Moisture Content, MC (gH2O/g dry solid)
Graph of Drying Rate against Moisture Content(Strand Rice Noodles)
60 degree with
dimension8cm*1cm*0.144cm
40 degree withdimension8cm*1cm*0.144cm
y = 2E-11x6 - 8E-09x5 + 1E-06x4 - 9E-05x3 +0.0037x2 - 0.0836x + 0.9522
R = 0.985
y = -1E-12x6 + 7E-10x5 - 1E-07x4 + 9E-06x3 -
0.0001x2 - 0.021x + 1.0278R = 0.9981
-0.2000
0.0000
0.2000
0.4000
0.6000
0.8000
1.0000
1.2000
0 50 100 150 200
MoistureRatio,
MR
Drying Time (min)
Graph of Moisture Ratio against Time(Strand Rice Noodles)
60 degree withdimension
8cm*1cm*0.144cm
40 degree withdimension8cm*1cm*0.144cm
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Graph 8: Graph of ln MR against drying time for strand rice noodles
Table 10: Table for determining constant moisture diffusivity, and activation energy,
DryingTemperature, T
(K)
1/T (1/K)Slope,
9Deff/4L2 (min-
1)
Effectivediffusivity, Deff
(m2min-1)
ln Deff
313 0.0032 0.0446 1.009E-05 -11.503
333 0.003 0.0466 1.055E-05 -11.460
y = -0.0466x - 0.5939R = 0.9626
y = -0.0446x + 0.4472R = 0.9854
-7
-6
-5
-4
-3
-2
-1
0
1
0 20 40 60 80 100 120 140 160
Ln(MR)
Drying Time, t (min)
Graph of ln MR against Drying Time(Strand rice noodles)
60 degree withdimension8cm*1cm*0.144cm
40 degree withdimension
8cm*1cm*0.144cm
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Graph 9: Graph of ln Deffagainst drying time for strand rice noodles
Intercept = ln
Slope =
y = -224.09x - 10.787
R = 1
-11.51
-11.505
-11.5
-11.495
-11.49
-11.485
-11.48
-11.475
-11.47
-11.465
-11.46
-11.455
0.00295 0.003 0.00305 0.0031 0.00315 0.0032 0.00325
ln
(Deff
)
1/T (1/K)
Graph of ln (Deff) against 1/T
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Rehydration
Graph 10: Graph of moisture content against drying time after rehydration for both freeze drying
and heat pump drying
Rehydration capacity of freeze drying is 1.147.
Rehydration capacity of heat pump drying is 1.149.
Texture Hardness Analyser
Figure 7: Initial hardness test of rice noodles (results tabulated)
y = -3E-06x2 + 0.001x + 0.0559R = 0.831
y = -3E-06x2 + 0.0011x + 0.0338R = 0.9368
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0 50 100 150 200 250 300
MoistureContent.
MC
(gH2O/gdriedso
ild)
Drying Time, t (min)
Graph of Moisture Content against Time afterRehydration
Freeze Drying
Heat Pump Drying
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Figure 8: Initial hardness test of rice noodles (graphical representation)
Figure 9: Hardness test of rice noodles after freeze drying (results tabulated)
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Figure 10: Hardness test of rice noodles after freeze drying (graphical representation)
Figure 11: Hardness test of rice noodles after heat pump drying (results tabulated)
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Figure 12: Hardness test of rice noodles after heat pump drying (graphical representation)
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Discussion
The main objective of conducting this experiment were to study the drying characteristics
and kinetics of rice noodles dried in heat pump dryer and freeze dryer. The drying characteristics
such as colour, texture, hardness, shrinkage and rehydration properties are the concerned in thisexperiment. Temperature is manipulated with 40C and 60C of the drying chamber of heat pump
dryer and is observed to determine the effect of temperature on the drying rate. Two different
equipment, heat pump dryer and freeze dryer are used to conduct this experiment to compare the
performance of both the equipment on drying performance of the rice noodles. The weight of rice
noodles are measured using an electronic balance. The experiment for every sample ended when
the weight of the sample decreases until a constant value was obtained. Borne dried weight of each
sample was obtained by placing the sample into the oven for further drying for a day.
For freeze drying, the vacuum is maintained at 0.12 bar and -40C. Vacuum drying is
performed as low pressure, which is an advantage because boiling point of water is lower under
reduced pressure. The internal pressure of the food was greater than the ambient pressure in the
drying chamber and hence, it prevents shrinkage and maintains the structure of the rice noodle.
From table 1 to 3, the percentage change in weight of both block and strand are similar,
which is about 65.5% decrease from the initial weight. The change in moisture content for both
block and strand is about 1.8 g H2O/ g dry solid and shrinkage of sample in block is about 11.9%
while strand is about 12.5%. It shows that the drying characteristics of rice noodles in freezer
drying are about the same in either block or strand. Block is slightly lower for its final moisture
content and shrinkage compared to strand rice noodles.
For heat pump drying, the temperature in the drying chamber is maintained by using a
hygrometer to ensure that it operates at the setting temperature. From table 4 to 9, it shows that
higher temperature has a higher change in weight and lower final moisture content as well as
higher shrinkage of sample. Higher temperature increases the driving force of diffusion process,
speed up the drying rate which cause rice noodle to dry faster which possess a higher moisture
gradient for diffusivity. Shrinkage occurred as the contracting of a hardened concrete mixture due
to the loss of capillary water. Graph 1 and 5 shows the moisture content of both block and strand
of rice noodles decrease exponentially with time until a constant value was obtained. However,
fluctuation of sample occurred during the experiment where reabsorption of water back into the
sample due to moisture gradient between the ambient air and sample when the sample is removed
from the drying chamber and send for weighing.
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From graph 2 and 6, it shows that there is higher drying rate at the beginning for sample at
60C and it fluctuates a little before achieving constant drying rate. For sample at 40C, it shows
constant drying rate throughout the experiment. This discrepancy might due to the sample drying
at 60C exposed to ambient air for too long while waiting the heat pump to start up which cause
the drying rate to be too high which is out of the optimum range for graph plotting. From graph 3
and 7, it shows graph of moisture ratio against drying time. Higher temperature increases the rate
of removal of moisture provided that the higher temperature did not alter the quality of sample
during the experiment.
Graph 8 is plotted to determine the effective diffusivity. At higher operating temperature,
the moisture diffusivity is higher. The effective diffusivities at 40C and 60C are
and respectively. Diffusivity is the rate of water molecules
to diffuse from a material into drying air through a concentration gradient by Ficks law of diffusion
From Arrhenius equation, activation energy and constant moisture diffusivity can be obtained
Activation energy is the minimum energy required by water molecules before diffusion of sample
surface start to occur. The value of activation energy is 1.863 kJ/kmol and constant moisture
diffusivity is .
Generally, there are three stages of drying, constant rate period, first falling period and
second falling rate period. Constant rate period is not obvious which means the surface is not fully
wetted as constant rate period took place only when surface water was removed. Once it passed
the critical moisture content, most of the drying falls on 1st and 2nd falling rate period. Capillary
action occurred by moving liquid to surface from inside solid of sample. Some of the rice noodles
are still wet but other parts have dried in 1st falling rate period while 2nd falling rate occurred when
whole of the surface has dried and interface is completely within the pores of the sample. Hence, it
was clearly shown falling rate period dominates the drying time.
Several errors have been made during the conduction of the experiment which alter the
accuracy and reliability of the experiment. A negative value is obtained for drying rate as shown in
appendix of table of 60C block drying of rice noodles, which is impossible in reality. This is due to
the reabsorption of moisture back into the sample. Arrangement of strand and block of rice noodles
in the trays provided in freeze dryer affect the drying rate. At different tray, the surface exposed to
drying and drying rate is different. The sample exposed to ambient air while transferring from
container into the freezer dryer. Also, the different sets of experiment were not carried out in a
constant period of time. Therefore, it was difficult to compare the experiments results at a certain
period. The drying chamber is not tighten throughout the experiment as the sample is taken out
every few minutes to measure its weight by using electronic balance which causes the air in the
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chamber to mix with the atmospheric air. The accuracy of the experiment can be improved by
repeating the experiment at least two times for each set of sample.
The objective on effect of temperature on the drying rate is achieved where higher temperature
has a higher drying rate with higher shrinkage and lower moisture content and larger change in
term of mass. The performance of heat pump is better compared to freeze dryer for rice noodles
although according to literature, freeze drying should have the best overall quality of product
Heat pump can provide better control of drying conditions which enables drying to perform at lower
temperature and low relative humidity, leading to better retention of appearance. Freeze drying
has the best quality for dried product but lowest energy efficiency (Uddin, et al., 2004). The
characteristics and kinetics of sample for both equipment are not precise and data recorded is not
clear enough to justify the information on pro and cons of heat pump and freeze dryer.
Comparison between freeze drying and heat pump drying are carried out in term of
drying characteristics:
Colour & Appearance
It can be seen in Appendix I, before send to oven for further drying to obtain borne dry weight, the
colour of rice noodles of heat pump is golden brown in color with oily surface while freeze dryer is
coated with white surface. After borne dry, rice noodles from heat pump became transparent while
freeze dryer product is transparent with tiny bubbles formed on the surface.
In term of appearance, borne dried noodles from heat pump dryer is better in term of packaging
for commercial value while freeze dryer product is preferable to be before borne dried rice noodles
as the white coated surface suit customer preference better than the borne dried tiny bubbles
surface.
Texture
Shrinkage in freeze dried noodles is about 11 to 13% while shrinkage in heat pump dryer is about
27 to 37% which is way higher than freeze drying. Hardness defined as the force necessary to
attain a given deformation. The initial force for rice noodles before undergoing any drying
treatment is about 118 N. After freeze dried, rice noodles hardness increases to an average of
4725 N while heat pump drying yield an average of 2810 N of hardness. It shows that freeze dried
product is the strongest which resist to changes.
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Rehydration
Rehydration of dried food play a major role on the quality attributes of the product. Rehydration is
considered as percentage of original weight gained by dried sample during rehydration for a given
time at a given temperature in water. As shown in graph 10, rehydration rate is faster in freeze
dryer compared to heat pump drying. The rehydration capacity for freeze drying is 1.147 while for
heat pump drying is 1.149, which is almost the same for both cases. According to literature, freeze
drying should yield better and faster rehydration properties compared to others. This error might
due to exposure of material to ambient air which indirectly increases its moisture content.
Although freeze drying products are considered to have a better quality than other dehydrated
products and having completeness in term of rehydration, its high capital and operating cost as
well as slow process are issues to be solved. Also, the appearance after rehydration could not
return to the original rice noodles structure. On the other hand, for heat pump dried product, after
rehydration, has a better appearance as in regain the fresh rice noodles original bright, clean
colour and the cost for heat pump is cheaper than freeze drying.
Processing properties, appearance and colour of noodles are the three main important criteria to
judge the quality of rice noodles. Compared to freeze drying, the dried rice noodles of heat pump
drying can retain a better colour, flavour and nutrition of rice noodles. However, the only problem
with heat pump dried product is oily surface and shrinkage problem. Therefore, further research on
removing the oil surface and improving the product quality are needed to improve the commercial
value for consumer acceptability of dried rice noodles in the future.
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Conclusion
In conclusion, the weight of rice noodles sample decreases with time by removing the
moisture it contains until it reaches a phase where constant drying is in equilibrium state. Falling
rate period dominates the drying time throughout the experiment. Comparing freeze drying to heatpump, in term of appearance, heat pump dried noodles has a better commercial value as it
maintains the color of rice noodles and the structure after rehydration is the same as the original
fresh rice noodles. However, the shrinkage in freeze drying is lesser compared to heat pump drying
and freeze dried product is stronger in term of hardness. To improve the commercial value for
consumer acceptability of dried rice noodles, further research on removing the oil surface and
improving the product quality of heat pump product is needed. An increased of temperature of the
drying chamber, increases in drying rate as well as shrinkage of sample. Lower final moisture
content can then be achieved. Rehydration capacity of freeze drying is 1.147 and 1.149 for heat
pump drying. The effective diffusivities at 40C and 60C are and
respectively and activation energy of 1.863 kJ/kmol and constant moisture diffusivity
of . The accuracy of the experiment can be improved by repeating the
experiment at least two times for each set of sample. Although freeze drying products are
considered to have a better quality and completeness in term of rehydration, its high capital and
operating cost as well as slow process are issues to be solved which restricted the popularity of
freeze drying rice noodles. There is potential to improve existing technologies through further
research and development with aim of better quality product, smaller equipment size, safer
operation, higher reliability, lower energy consumption, reduced environmental impact and overal
cost of drying.
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Nomenclature
Symbols & Descriptions Units
Drying time, t
Moisture ratio, MR
Operating temperature, T Effective moisture diffusivity,
Constant moisture diffusivity,
Borne dry weight,
Sample size,
Free moisture content,
Moisture content, MC
Drying rate, R
Activation energy,
Gas constant,
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