The Effect of Variety and Drying On the Engineering

International Journal of Scientific Knowledge (Computing and Information Technology) Volume 1 Issue 5, Jan 2013 @2012 IJSK & K.J.A. All rights reserved

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The Effect of Variety and Drying On the Engineering Properties of Fermented Ground Cassava Chukwuneke J.L1, Achebe C.H1, Okolie P.C1 and Okafor E.A2 1

Department of Mechanical Engineering, Nnamdi Azikiwe University, Nigeria School of Engineering, Energy Centre, Robert Gordon University, Aberdeen.

2

E-mail: [email protected] Abstract: - Many food processing industries use cassava as their basic raw material. The existence of improved varieties of cassava demands that the effect of variety on the engineering properties of fermented ground cassava is studied in order to generate data for design and optimum performance of various driers used in cassava processing. This paper attempts to provide data on the engineering properties such as moisture content, specific heat capacity, thermal conductivity, thermal diffusivity, bulk density and mass transfer coefficient of some cultivars as well as determine the effect of variety on the drying and engineering properties of fermented ground cassava using two high yield improved cultivars (Tms 30572 and NR 8082) and one native cultivar (Akpu Bonny). General models were also obtained, which could be used to predict the specific heat and thermal conductivity at different moisture content of the cultivars. The specific heat capacity obtained ranged from 1.53kJ/kgK to 3.49kJ/kgK while the thermal conductivity ranged from 0.24W/moC to 0.51W/moC for dried fermented ground cassava of these cultivars. The highest moisture content of 48.66% was obtained after fermentation with the NR 8082 variety. At same moisture content, the specific heat capacity and thermal conductivity were found to be different for cultivars with different proximate compositions but similar for cultivars with close proximate compositions. The drying rate, thermal diffusivity and mass transfer coefficient of each cultivar varied with proximate composition, hygroscopy, product surface area and change in density after drying. Therefore, the same drying conditions cannot be used for drying the different cultivars except if they have close engineering properties. Keywords: Fermented ground cassava, Specific heat capacity, Thermal conductivity, Thermal diffusivity, Bulk density, Effect of variety, Cultivars, Drying rate, Moisture Content, proximate compositions . 1. INTRODUCTION 1.1. Background of the Study The design, simulation, optimization, operation and control of food processing operations require basic engineering properties of foods. Food technologists require data on engineering properties for various purposes such as process design, quality assessment and evaluation. Cassava is widely grown in Africa and some other parts of the world. It plays a central role in

the diets of most Nigerians. This is why [1] attributed garri (a staple food from drying of fermented cassava flour) as the commonest food amongst the teeming poor West African people. Fermented cassava flour is, therefore, one of the most important cassava products and the methods of processing depend on local customs. However, the industrial utilization of cassava 13


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roots into various food and non-food uses is Consequently, food industries need to understand the various engineering or physical properties of ground cassava in other to use it as a raw material. These properties include;

expanding by the day. 3. The thermal diffusivity determines how fast heat propagates or diffuses through a material. Knowledge of these engineering properties is necessary not only because they are important on their own but they are the commonest indicators of other properties and qualities [3]. These engineering properties are known to be affected by density, moisture content and temperature, and will help the engineer to generate data for the design and operation of driers for cassava processing. Drying is an inevitable unit operation in the food processing industries since dehydrated foods normally last longer due to the absence of microbial activities.

1. Specific heat capacity which is the amount of heat (kJ) needed to raise the temperature of a unit mass (kg) by a unit change in temperature (k). 2. The thermal conductivity which is the amount of energy, in form of heat, "conducted through a body of unit area and unit thickness in unit time when the difference in temperature between the faces causing heat flow is unit temperature difference [2]. 1.2. Aims and Objectives A review of pertinent literature revealed that such data on engineering properties of foods were lacking [3]; Hence the objectives of this study are to determine; at various stages of drying fermented ground cassava into garri:

1. The moisture content. 2. The specific heat capacity. 3. The thermal conductivity. 4. The thermal diffusivity. 5. The bulk density. 6. The mass transfer coefficient. 7. To determine the effect of variety on the drying and engineering properties of fermented ground cassava.

1.3. Significance of Study The significance of this work cannot be overlooked just as cassava itself. Knowledge of the engineering properties is necessary because they are the commonest indicators of other food qualities. Engineering properties are important data needed for quality assessment and evaluation, design, operation and control of driers since drying is an inevitable stage in the production of both food and agricultural products.

Also, knowledge of these properties and how they are affected by drying will enhance better understanding of the heat and mass transfer phenomena for drying of agricultural products. Moreover, it provides an opportunity to apply the principles of chemical and Mechanical engineering processes which will help as a guide to any interested industrialist for future applications taking into account the engineering properties of ground cassava.

1.4. Scope / Limitations The study attempts to determine the various engineering properties such as moisture content, specific heat, thermal conductivity and thermal

diffusivity of fermented ground cassava only. The study is also restricted to three varieties of

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cassava; two improved ones (Tms 30572 and

NR 8082) and a native variety.

2. METHODOLOGY 2.1. Sample Preparation This involved the preparation of cassava cultivars, one native cultivar (Akpu Bonny) and two high yield improved cultivars (Tms 30572 and NR 8082) all obtained from Root-crops Development Centre, Agricultural Research Institute, Igbariam, Anambra State, Nigeia. The cultivars were harvested in the month of April,

peeled, washed, grated and packed in three different sacks for pressing. They were then allowed to ferment for 72 hours. The mashed cassava was sieved with a mesh of 2.4mm. A hot circulating air oven was used to determine the drying rates.

2.2. Determination of Engineering Properties I. Moisture Content The moisture content was determined before and after fermentation. Three different crucibles were washed and dried in an air oven for about 40mins; 5.0g of each sample were carefully weighed into each of the identified crucibles, it is then dried in a hot circulating air oven at Xw 

105°C for 24hours. Further drying was continued until the final weight of dry sample became stable. The initial moisture content of the samples was calculated as the total moisture loss divided by total sample weight and presented in percent wet basis. (1)

W1  W2  100 W1

Where: Xw = moisture content on wet basis, W1 = Initial weight of sample, W2 = Final weight of sample after drying. The moisture content on dry basis was calculated using;

Xd 

W1  W2 100  W1 1

(2)

The moisture content on dry basis at any time‘t’ was also calculated using the equation; Xt (dry basis) =

(3)

Where; W2 is the weight of dried sample and W1 is the weight of sample at any time t. II. Proximate Compositions The Association of Analytical chemists method was used to determine the carbohydrate, moisture, protein, fat, fibre and ash (dry ashing

method in a furnace) content of the samples [4]. The proximate composition was determined after drying in an air oven at 70oC for 24hours.

III. Ash Content Determination 15


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A silica dish was heated at 600oC, cooled and for 3hours. It was then allowed to cool in weighed; 2.0g of the sample was carefully desiccators before taking the final weight. This transferred into the dish. The dish was then procedure was carried out for all the sample placed into a muffle furnace and ashed at 600oC And the ash content was calculated thus; % Ash = (4) IV. Fat Content Determination Soxhlet extractor was used. An extraction flask was thoroughly washed and dried in hot oven for 30mins. It was placed in desiccators to cool. 2.0g· of sample was accurately weighed and transferred into a rolled ashless filter paper and placed inside the extractor thimble. The thimble was placed into soxhlet extractor. Some reasonable quantities of petroleum ether, about three-quarter of the volume of the flask were The percentage fat is thus calculated as;

placed inside the extraction flask. The heater was switched on and the set up was heated for about 3hours at low temperature so that the temperature of the petroleum ether is not exceeded. Finally, the extracted oil was dried at 1000C and weighed. The difference in the weight of empty flask and the flask with oil gives the oil content of the sample. % fat =

(5)

Where; A = weight of empty flask, B = weight of sample, C = weight of flask + oil after drying. V. Moisture Content Determination The sample for proximate analysis was heated at 600C in a hot air circulating oven for 24hours.

The moisture content was determined using 2.0g of sample on dry weight basis.

VI. Fibre Content Determination 2.0g of the sample was collected (W1) 150ml of preheated H2S04 was added and heated to boiling for 30mins. It was then filtered and the residue washed three times with hot water. 150ml preheated KOH was added and heated to

boiling for another 30mins, filtered, washed three time with hot water and three times with acetone before drying at 1300C for 1 hour. The sample was then weighed (W2), ashed at 500oC and the ash also weighed (W3).

The fibre content is thus calculated;

% Fibre  W2  W3  100

(6)

W1

Where; W1 = weight of sample, W2 = weight after pretreatment & drying, W3 = weight after ashing. VII. Protein Content Determination 2.0g of the dried sample was weighed into 30ml kjeldahl flask and 15m1 cone H2S04 and 1.0g of the catalyst mixture (kjeldahl catalyst mixture, a mixture of 20g potassium sulphate, 1.0gram copper sulphate and a pinch of selenium

powder) were added. The mixture was heated until a greenish clear solution appeared (about 30mins), it was heated for more 30mins before allowing to cool. 10ml of distilled water was added to avoid caking. The digested solution 16


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was then transferred to the kjeldahl distillation apparatus. A 50ml receiver flask containing 5ml boric acid indicator solution was placed under the condenser of the distillation apparatus so that the tip is about 2cm inside the solution. The digested sample in the apparatus had10ml of 40% NaOH solution added through the funnel stop-cork. The distillation commenced immediately the steam by-pass was closed and the inlet stop-cork Vol .HCl Calculation follows thus;

on the steam jet arm of the distillation apparatus opened. When distillation reached about 35ml mark on the receiver flask, the process was stopped by closing the inlet stop-cork first, then opening steam by-pass. The resulting solution was then titrated to the first pink colour with 0.1M HCl.

 14 .01  0.1  6.25  50  100 1000  weight of sample  100

(7)

Where; 14.01 = Nitrogen standard, 50 = dilution factor, 6.25 = crude protein factor, 0.1 = concentration of HCI, 1000 - ppm, 100ml distilled. VIII. Carbohydrate Content Determination The carbohydrate content was determined by difference (i.e. by subtracting other constituents in each sample from 100%). IX. Determination of Specific Heat Capacity Specific heat capacities were determined using the various proximate compositions of the samples. These were obtained by applying [5]. Cp = 4.180xw + 1.711xp + 1.929xf + 1.547xc + 0.908xa (8) Where; Cp is the specific heat capacity in kJ/kgK and x are respective mass fractions of water, protein, fat, carbohydrate and ash, present in each cultivar. X. Determination of Thermal Conductivity The thermal conductivities of the samples were obtained by substituting the various proximate composition of the sample in the expression developed by [6]. K = 0.24Xc + 0.155Xp + 0.16Xf + 0.135Xa + 0.54Xw (9) 0 Where; K is the thermal conductivity W/m C of sample. XI. Determination of Thermal Diffusivity Thermal diffusivity ( ) determines how fast heat propagates or diffuses through a material. This was determined from the thermal conductivity K, density ρ, and specific heat Capacity Cp using the dimensionally correct equation developed by [7]. = k/ ρCp (m2/s) (10) XII. Determination of Bulk Density 17


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The bulk density was determined using a centrifuge tube, at intervals of drying until the density becomes constant. The weight of the centrifuge tube and its content (sample) was noted, it was later tapped until there was no longer change in volume, and the centrifuge tube and its content were reweighed. The weight was later obtained. The bulk density was calculated using the expression. Weight of sample Volume of sample

(kg/m3)

(11)

XIII. Determination of Mass Transfer Coefficient This is a function of drying rate. The drying rate per unit area is proportional to the bulk density difference or concentration difference [8]. dm   f   p  Adt (12)

dm  Kc  f   p  Adt 1 dm Kc    f   p Adt

(13)

Where;  f and  p are the bulk density of feed and products respectively, dm = change in mass after each interval of drying, dt = time difference, A = surface area of the particles given as 2

A  N pM p  D p

(14)

Where; Np = Number of particles per unit mass, Mp = Mass of products, D p = Mean particle diameter = Dpd, d = Mass fraction retained on the sieve. A small quantity of about 0.5g of the dried product was counted as accurate as possible to obtain the number of particles per unit mass. The samples were then sieved in sieves of 0.8mm, 1.6mm and 2.0mm respectively to obtain the mean particle size diameter. 3. PRESENTATION OF DATA 3.1. Moisture content at Harvest: Weight of sample used =5.0g in each case Table 1: Weight of sample at harvest Cultivar NR8082

Weight of crucible (g) 29.04

Weight of crucible + wet sample (g) 34.04

Crucible + sample (dried)(g) 30.64

Tms30575 Native

29.17 28.54

34.17 33.54

31.045 30.368

Table 2: Weight of sample at intervals of drying and Weight of dried sample after 48hours 18


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2.1. Weight of sample at intervals of drying Cultivar Weight of Weight of Weight empty petridish + after 10 petridish(g) sample (g) mins (g) NR8082 12.137 26.137 25.367 Tms30575 17.577 22.577 22.464 Native 19.845 24.845 23.648 2.2. Weight of dried sample after 48hours

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Weight after 20 mins (g) 24.347 20.737 22.905




Cultiver

NR 8082

Tms 30572

Native

Weight (g)

1.5385

2.3578

2.9597


Weight after 70 mins (g) 23.704 20.261 -

3.2. Proximate Analysis: Weight of sample used = 2.0g in each case Table 3: Table for Fat, Protein, Ash and Moisture content calculations 3.1. Table for Fat content calculations Cultivar Weight of empty flask (g) Empty flask + extracted oil (g) Weight of oil NR 8082 32.664 32.664 Nil Tms 30572 33.930 33.930 Nil Native 33.724 33.724 Nil 3.2. Table for Protein content calculations Cultivar Initial burette reading (cm3) Final burette reading (cm3) Volume of HCl used (cm3) NR 8082 Tms 30572

20.60 20.40

Native 20.70 3.3. Table for Ash content calculations Cultivar

20.70 20.60

0.1 0.20

20.90

0.20

Weight of empty Silica dish + sample after Weight of sample Sample + silica Weight silica dish (g) treatment (g) after pretreatment (g) dish after ash(g) of ash (g)

NR8082 26.210 26.284 Tms30572 29.062 29.121 Native 28.380 28.483 3.4. Table for Moisture content calculations

0.074 0.059 0.103

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26.22 29.07 28.39

0.01 0.008 0.01


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Cultivar

Weight of crucible + sample (g)

NR 8082 Tms 30572 Native

22.492 16.749 22.098

Table 4: Table for calculation of bulk density during drying Tms 30572 Native Cultivar

NR 8082 Time (min)

Weight of crucible + sample after Weight of moisture (g) drying (g) 22.456 0.036 16.699 0.043 22.059 0.039

10

Mass of Volume of Time Sample Centrifuge (min) (g) Tube (cm3) 3.930 0.006 10

Mass of Volume of Time Sample Centrifuge (min) (g) Tube (cm3) 4.887 0.009 10

Mass of Volume of Sample Centrifuge (g) Tube (cm3) 3.803 0.0060

20

3.210

0.006

20

3.160

0.007

20

3.060

0.0065

30

2.812

0.006

30

2.818

0.0075

30

2.788

0.009

40

2.645

0.007

40

2.744

0.012

40

2.745

0.0095

50

2.574

0.012

50

2.704

0.017

50

2.741

0.017

60

2.567

0.016

60

2.684

0.045

60

2.738

0.025

3.3

Tabulated Results and Simple Calculations: (Mass of sample used = 5.0g in each case)

Cultivars NR 8082 Tms 30572 Native

Table 5: Moisture content of cultivars before fermentation Mass of dried crucible Mass of crucible + sample Weight of + wet sample (g) after drying for 24hours moisture (g) 34.040 30.640 3.40 34.170 31.045 3.125 33.640 30.368 3.172

% moisture content (wet basis) 68 62.5 63.44

Table 6: Moisture content of cultivars after dewatering and fermentation for 72 hours (wet basis) Cultivar NR8082

Mass of petridish Mass of petridish + sample after Weight of moisture % moisture + wet sample (g) drying to stable weight (g) (g) expelled content (wet basis) 26.137 23.704 2.433 48

Tms30572 Native

22.577 24.845

20.261 22.586

2.316 2.559 20

46.32 45.18


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Table 7: Moisture content at intervals of drying (wet basis) Cultivar NR 8082

10mins 53.09

20mins 25.05

30mins 9.54

40mins 3.04

50mins 0.27

60mins -

Tms 30572 Native

82.08 33.74

17.73 11.64

4.99 1.71

2.24 0.15

0.75 -

-

NR8082 2.567 Tms30572 2.684

Table 8: Hygroscopic properties of cultivars MD (g) % water % % % % reabsorbed Ash Fat Protein Fibre 2.892 12.66 1.05 Nil 0.22 3.20 3.039 13.23 1.50 Nil 0.44 2.55

% Moisture 1.80 2.15

% Carbohydrate 93.73 93.36

Native

3.081

1.95

92.86

Cultivar

MC (g)

2.741

12.40

0.15

Nil

0.44

4.60

MC = Mass of cassava after drying to final moisture (g), MD = Mass of dried sample 48 hours later after drying (g) Table 9: Effect of Variety on the surface Area and Mass Transfer Coefficient of the Cultivars Cultivar Surface Area (m2) Density before Density after Mass transfer drying (kg/m3) drying (kg/m3) Coefficient Kc m/s(x10-6) NR 8082 0.897 655 160.44 1.632 x 10-6 Tms 30572 0.415 543 59.64 3.25 x 10-6 Native 0.850 551.2 171.3 2.332 x 10-6

Table 10: Effect of variety on the drying rate of the cultivars Cultivar

Total drying time Drying rate after Drying rate after Drying rate of stable (mins) 20 mins (kg/hr) 40 mins (kg/hr) weight (kg/hr)

NR 8082

50

5.37

3.53

2.61

Tms 30572

60

5.52

3.38

2.32

Native

50

5.82

3.38

3.07

21


% Moisture Content (dry basis)

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90 80 70 60 50 40 30 20 10 0


0

10

20

30

40

50

60

Time (mins)

Specific Heat capacity (kJ/kgK)

Fig. 1: Drying curve for the cultivars

4 3.5 3 2.5 2 1.5 1 0.5 0


0

10

20

30

40

50

% Moisture Content (wet basis)

Fig. 2: Specific Heat of Cultivars at Various Moisture Contents

22

60


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Thermal Conductivity (W/m0C)

0.6


0.5 0.4 0.3 0.2 0.1 0 0

10

20

30

40

% Moisture Content (wet basis)

50

60

Fig. 3: Thermal Conductivity of Cultivars at Various Moisture Contents

Bulk density (kg/m2)

700


600 500

400 300 200 100 0 0

20

40

60


80

Fig. 4: Bulk density variations with Moisture Contents

23

100


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Thermal diffusivity 𝛼(m2/s)

1.00E-03


8.00E-04 6.00E-04 4.00E-04 2.00E-04 0.00E+00 0

20

40

60


80

100

Fig. 5: Thermal Diffusivity Variations with Moisture Contents

4. DISCUSSION 4.1. Moisture Content The moisture contents obtained before and after fermentation by drying the cultivars with a circulating air oven is shown in Tables 6 and 7 respectively. The initial moisture content of cassava at harvest was not stable and may be dependent on season. The cultivars used here were harvested in the month of April. NR 8082

had the highest moisture content of 68% at harvest, but Native cassava had the highest moisture expelled after drying. This suggests that the native cassava was more porous than the improved cassava in agreement with the studies in [9].

4.2. Drying Rate The moisture content (dry basis) decreases as drying time increases for all the cultivars during the drying process as shown in fig.1. The total drying time differed at approximately the same moisture content for all the cultivars, Tms 30572 with almost the same moisture content (wet basis) with the Native cassava after fermentation, had the longest total drying time of 60mins while native cassava had the shortest total drying time of 50mins. Fig.1 suggests that two cultivars with same initial moisture content did not have same drying characteristics. Other properties like the differences in chemical

composition of the cultivars may have contributed to this. The drying rate decreased as the drying time increased for all the cultivars as show in table 2.1. This implies that the drying rate decreased with increase in moisture content (wet basis) as against that reported by [9]. The drying rate of NR8082 and Tms 30572 at stable weight was low compared with native cassava. The native cassava had the highest drying rate of 3.07kg/hr at stable weight with shortest drying time which also confirms its highly porous property, as show in table 2.1. 24


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4.3. Proximate Composition Table 8 shows the proximate composition of the cultivars. The improved cultivars had a slightly higher percentage of carbohydrate (93.36 93.73%) than the native cultivar (92.86%). All the cultivars do not contain fat since there was no oil extract from them. The geographical location of these cultivars as well as time of planting and harvest may have been responsible for this. Tms 30572 and the native cultivar have the same protein content higher than that of

NR8082. The native cultivar ranked highest in fibre content but contains the least percentage of ash. These might have contributed to its shortest drying time. The type of drier used might have equally affected the total drying time as well as the drying rate. Also the differences in the drying rate can be attributed to the difference in their chemical compositions. The same drying condition cannot therefore be used for drying different cultivars.

4.4. Specific Heat Capacity and Thermal Conductivity In order to determine the effect of moisture the same specific heat capacity. The specific content on specific heat capacity and thermal heat capacities of Tms 30572 and NR 8082 were conductivity, the data in table 2.2 and the model high compared with the native cultivars, equations of (8) were used to calculate the probably because of their high carbohydrate and specific heat capacity and (9) was used to ash contents. More heat energy will therefore be calculate the thermal conductivity at various required in other to dry cultivars with high ash range of moisture contents. The specific heat and carbohydrate content. The specific heat capacity increased with moisture content (wet obtained from this work ranged from basis) for all the cultivars. The native cultivar 1.53kJ/kgK-3.49kJ/kgK which compare (fig. 2) had a different specific heat capacity favorably with that of [9]; who obtained up to than the other cultivars. The native cultivar 3.5kJ/kgk. seems to have a lower ash and carbohydrate The thermal conductivity of each of the cultivars content from other cultivars (Table 8) which also increased with moisture content (wet basis). might have contributed to this difference. The The native cultivar from (fig. 3) still exhibited a two improved cultivars exhibited close specific different thermal conductivity relative to other heat capacities probably due to the fact that they cultivars. The two improved cultivars had almost had approximately the same carbohydrate the same thermal conductivity at different content. Tms 30572 and NR 8082 had very close moisture contents. Tms 30572 and NR 8082 still specific heat at different moisture contents exhibited higher thermal conductivity than the showing that cultivars with similar chemical native cultivar. composition (ash and carbohydrate) might have 4.5. Bulk Density The bulk density of each cultivar decreased as the moisture content (dry basis) decreased during drying as shown in fig.4, but it was almost stable with moisture content below 13%

dry basis. This goes to suggest the hygroscopic property of cassava as shown by [8] during the drying of a native cassava cultivar. At particular moisture content under the same drying 25


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conditions the bulk density differed for each cultivar which meant that the mass transfer rate would also differ for all the cultivars, since mass

transfer rate is a function of the density of the sample dried.

4.6. Thermal Diffusivity The thermal diffusivity increased as moisture decreased, but was almost constant below the hygroscopic moisture of about 13%. The thermal diffusivity also differed slightly for each cultivar when determined at the same moisture as shown in fig.5. Thermal diffusivity determines how fast heat propagates or diffuses through a material. From the results, the native cultivar and NR8082

with higher density had low thermal diffusivity while the diffusion of heat is fastest in Tms 30572. NR8082 was the least porous (least thermal diffusivity from fig.5) and also has high carbohydrate and least protein content; this should have contributed to the low thermal diffusivity.

4.7. Hygroscopic Property and Porosity The dried ground cassava from each cultivar was reweighed after 48 hours of drying and the results show that 12.4% - 13.23% moisture was reabsorbed after the drying by the various cultivars. All the cultivars exhibited hygroscopic property. Tms 30572 reabsorbed the highest moisture, indicating that it is more porous and hygroscopic than the other cultivars. Its highest thermal diffusivity also goes to confirm this. This must have also led to the increase in the

rate of mass transfer of moisture from Tms 30572. This is in contradiction with the results of the native cultivar’s porosity, which expelled the highest moisture with the shortest drying time. It can therefore be said that the diffusion of heat and mass through the pores of a cultivar does not depend on porosity alone but can also be affected by the chemical compositions of the cultivar, as reported by [9].

4.8. Surface Area and Mass Transfer Coefficient The surface area was obtained when the fermented ground cassava cultivars were dried to stable weight. Tms 30572, with the least surface area of 0.415m2 has the longest drying time. The Native Cultivar with surface are of 0.85m2 dried faster than Tms 30572 suggesting that the drying time does not entirely depend on the surface are. The proximate composition of

the cultivars has a great effect on the drying rate even when the cultivars surface area is small. Tms 30572 has the highest mass transfer coefficient which was due to its low product surface area and relatively lower density difference.

5. CONCLUSION AND RECOMMENDATION The proximate composition of the cultivars had a very great impact on their engineering properties. The difference in the drying rate could therefore be attributed to the difference in their chemical composition. It can be said that the moisture content, specific heat capacity, and

porosity also affected the rate of diffusion of heat and mass through the cultivars. The specific heat capacity and thermal conductivity of each cultivar varied with the proximate composition, water content and density, indicating that cultivars with similar chemical composition had 26


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same specific heat capacities as could be seen in the improved cultivars. More heat energy would be required to dry cultivars with high carbohydrate and ash content. There was no trace of fat in all the cultivars probably as a result of the geographical location of the samples. Thermal diffusivity of each cultivar varied with the proximate composition, porosity, density as The mass transfer coefficient differed for each cultivar and was highest for cultivars with high protein content and high drying rate.

well as the moisture content. Fermented ground cassava of any of these cultivars should not be dried below their equilibrium moisture content about 13%), else moisture will be reabsorbed from the atmosphere. From all indications, the improved variety is more porous, has high hygroscopic property and exhibited high rate of mass transfer of moisture. Therefore, the same drying condition cannot be used for drying the fermented ground cassava cultivars except if they have close engineering properties.

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