cel drying (marcus poon 004681)

7/28/2019 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


Change in moisture

content


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


Final Moisture

Content


Change in moisture

content


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)



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



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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


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


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)


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


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



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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)


Graph of ln MR against Drying Time(Strand rice noodles)


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)


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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Page | 27

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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