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This chapter presents the results and discussion of preliminary experiments and main experiment. Section 4.2 presents the particle size distribution, specific heat capacity determined by lumped system analysis and the results of total heat released from PKC. The results determined using the method of mixture is presented in Section 4.3.
4.2 Preliminary Experiment Results
Particle size distribution was first introduced in this section. Preliminary experiments were carried out to determine the appropriate method and parameter used for main experiments. The result for the experiments were shown and discussed below.
4.2.1 Particle Size Distribution
There are many different sizes of the particle in the sample. The separation of the particle according to the size is required to determine the particle sizes used in the experiment. The particle size distribution is obtained using a sieving machine. The particle size distribution of the PKC sample for each particle size was weighted after sieving process and is shown in Figure 4.1. The respective average particle size obtained for each size range of 0.000-0.212 to >12.500 mm was 9.400, 4.825, 2.675,
1.500, 0.800, 0.513, 0.319, and 0.106 mm respectively. Table 4.1 shows the mass percentages obtained at different sizes.
Figure 4.1: Particle Size Distribution and Average Cumulative Mass Fraction Curve of PKC
Table 4.1: Mass Percentages of PKC at Different Sizes
Mass percentages, %
From table 4.1, the highest mass percentage of PKC fell at the particle size of 0.319 mm while the lowest mass percentage of PKC was at a particle size of >12.500 mm. This result is in agreement with the results of Saw et al. (2010) that the highest mass percentage of PKC was fall in the size range of 4.825, 1.500 and 0.319 mm while for the lowest mass percentage was at >12.500 mm.
The range error of 1.15% for the size of 9.400 mm is respectively high when compared to other size range with each range error less than or equals to 0.60%. This phenomenon shows that the mass percentage of PKC for each size in the particle size distribution was different for every batch of PKC that obtained from IOI Edible Oils Sdn. Bhd. This is caused due to the inconsistent efficiency during oil extraction process that leads to the production of PKC of various size range (Saw et al., 2010). A cumulative analysis was presented in a cumulative mass fraction curves as in Figure 4.1 and a smooth curve was obtained.
From the result obtained, particle size of 1.500 mm is chosen in conduct the experiment for specific heat capacity determination in this study. This is because the water retention capacity of PKC for 1.500 mm was relatively high compared with other sizes. This is important because the experiment carried out in this study was focused on wet PKC. Although the highest mass percentage was fall in the size of 0.319 mm, but the WRC for this size was lower when compare with particle size of 1.500 mm. However, according to Saw et al. (2008), particle size of 0.513 mm has the highest WRC.
Nevertheless, the size of 1.500 mm still being chosen rather than 0.513 mm because it has the higher mass percentage compared with particle size of 0.513 mm. Therefore, a particle size of 1.500 mm is chosen and used in conduct the whole experiment in this study.
4.2.2 Lumped System Analysis
A preliminary experiment for determination of specific heat capacity (Cp) was conducted using sand and dry PKC and analyzed by lump system analysis. The volume of sand and water was fixed at 45 ml using cylinder and immersed into water bath. The final temperature of water bath was set to 35 oC.
The initial temperature for the materials used were measured and recorded for calculation purpose. The experiment was carried out until the temperature for both materials reach steady state at final temperature. The experiment was repeated twice and the average specific heat capacity was calculated. The total surface area, A was calculated as 8.536x10-3 m2 using Equation 3.1.
188.8.131.52 Lumped System Analysis for Sand
Figure 4.2 shows the graph of temperature versus time for water and dry sand. The initial temperature for water and sand were 27.75 oC and 28.23 oC respectively. From the graph above, the temperature of water and dry sand increased from the initial temperature to the final temperature. The time taken to reach steady state is 7 min for water and sand respectively. The specific heat capacity for sand is 0.796 kJ/(kg K) (Science & engineering encyclopedia) while for water is 4.186 (kJ/kg K) (Wilson & Buffa, 2000). Due to the large Cp value of water, a large heat transfer was required for a small change in temperature compare to sand. Therefore, the increase in temperature for sand is faster than water.
A graph of ln T as a function of time for water was plotted and shown in Figure 4.3 while for sand the plot is shown in Figure 4.4. From the graphs, the dimensionless temperature, ln T decreased as the time increased. The slope, M was found as 0.377 and 0.430 min-1 for water and sand respectively
Figure 4.2: Graph of Temperature as Function of Time for Lump System Analysis (Sand)
Figure 4.3: ln T as Function of Time for Water (Sand)
Figure 4.4: ln T as Function of Time for Sand
From Equation 2.15, heat transfer coefficient, h for water is 139 W/(m2 oC). The result obtained for the two replicates and the mean Cp were shown in Table 4.2. The average of Cp of sand was calculated as 2.61Â±0.09 J/(g oC).
Table 4.2: Mean Cp Value for Lump System Analysis for Sand
h, W/(m2 oC)
, J/(g oC)
Mean , J/(g oC)
The convective heat transfer coefficient for water was in the range 500-10000 W/(m2 K) (The Engineering Toolbox.com). However, from the result obtained, it does not fall in this range. The Cp of sand is three times larger than the actual value.
184.108.40.206 Lumped System Analysis for PKC
Lumped system analysis also carried out for the determination of specific heat capacity of dry PKC at various temperatures. A graph of temperature as function of time for PKC was plotted and shown in Figure 4.5. The initial temperature of water and dry PKC were 27.64 oC and 29.40 oC respectively.
From the graph above, the temperature of water and dry sand increased from the initial temperature to the desired final temperature. The time taken to reach steady state is 7 minutes for water. For dry PKC, it takes 9 minutes to reach steady state.
Figure 4.6 and Figure 4.7 shows the plot of ln T as a function of time for water and ln T as a function of time for dry PKC respectively. From the graphs, the dimensionless temperature, ln T decreased as the time increased. The slope, M was found as 0.369 and 0.254 min-1 for water and dry PKC respectively. From Equation 2.15, heat transfer coefficient, h for water is 136 W/(m2 oC). The specific heat capacity of dry PKC was calculated to be 10.09 J/(g oC) which is larger than specific heat capacity of water.
According to Tong (2009), thermal conductivity, K for dry PKC with particle size of 1.500 mm is 0.7230 W/(m oC). By using Equation 2.16, the Biot number is calculated to be 1.29. The calculated Biot number is greater than 0.1, which shows that the lump system analysis is not applicable in this study.
Figure 4.5: Graph of Temperature as Function of Time for Lump System Analysis (Dry PKC)
Figure 4.6: ln T as Function of Time for Water (Dry PKC)
Figure 4.7: ln T as Function of Time for Dry PKC
4.2.3 Method of Mixtures
In this section, sand was used in conduct the experiment for method of mixture. Mass of sand, was fixed to 100g while hot water, was fixed to 400g which is equivalent to 400ml. The temperature of hot water used in this experiment was 65Â±3 oC. The temperature was measured for every minute at a 60 minutes interval. Initial temperature of dry sand, was measured and recorded for calculation purpose. The result of this experiment is shown in Figure 4.8.
From Figure 4.8, the initial temperature for hot water, and the mixture, was 63.23 and 65.25 oC respectively. The temperature for hot water is decreased gradually to 61.91 oC during the 60 minutes interval. The temperature of the mixture first decreased rapidly for 19 min to 61.92 oC, . It decreased gradually after 19 min but the rate of decrease is still more rapid than hot water. This phenomena shows that the Cp of sand is lower than water as the amount of energy needed to heat the sand is smaller.
Figure 4.8: Water and Sand Temperature Change Using the Mixtures Method
As the heat from hot water was assumed to transfer to sand completely, the specific heat capacity was calculated using Equation 3.2. The sample calculation for this method is show in Appendix C. The calculated result is shown in Table 4.3.
Table 4.3: Mean Cp Value for Mixtures Method
, J/(g oC)
Mean , J/(g oC)
From Table 2.2, the mean value for sand was 0.82Â±0.065 J/(g oC) which is approximately 3% less than the actual specific heat capacity of sand (0.796 J/(g oC)). Therefore, by using the method of mixture, the specific heat capacity of sand is more accurate rather than the value using the lump system.
The determination of the specific heat capacity for dry PKC was carried out using this method. The result is shown in Figure 4.9. However, there is temperature increase at the first 3 min. This phenomena shows that dry PKC will produces heat when it first mixes with water. The heat released from dry PKC will affect the temperature of the mixture which will directly affect the analysis of specific heat capacity of dry PKC. Therefore, an experiment to determine the heat produced from PKC was carried out. The result was discussed in next section.
Figure 4.9: Graph of Temperature as Function Time for Hot Water and Dry PKC
4.2.4 Total Heat Released by PKC
The determination of the heat released by dry PKC was carried out using the method of mixtures. The mass of dry PKC was fixed to 40g throughout the experiment and the mass of water was varied. The initial temperature of dry PKC, and the highest temperature of mixture, , was measured and recorded. The heat released is calculated using Equation 2.2. The result of heat released by dry PKC at various mass of water is shown in Appendix A. Figure 4.10 shows the heat released by PKC for various mass of water.
Figure 4.10: Graph of Heat Released by Dry PKC at Various Mass of Water
From the result, the heat released by dry PKC is not consistent at various mass of water. The heat released by PKC for 50 g of water is 15.18 J/g dry PKC. It increases gradually as the mass of water increase. The larger heat released falls in the 250 g of water which is 42.13 /g dry PKC and decreased to 26.06 /g dry PKC for 300 g of water used. However, the heat released increases again from 300 g to 350 g of water used to 28.58 /g dry PKC but decrease again to 28.05 /g dry PKC for 400g of water.
However, heat released for the last three masses is in the range 25 to 30 /g dry PKC. It shows that heat released is consistent in this range. However, the result shown still cannot conclude how much heat is released by dry PKC since the result is not consistent. Therefore, dry PKC will not be included for the determination of specific heat capacity.
4.2.5 Preliminary Experiments Summary
From the preliminary results, it is found that the lump system is not suitable in determining the specific heat capacity. Therefore, method of mixture was chosen to determine the specific heat capacity in this study. A particle size of 1.500mm was chosen in determination of specific heat capacity of PKC. Dry PKC was not chosen in this study as the heat produced by it will affect in analysis for specific heat capacity. Hence, wet PKC with 50, 100 and 150% moisture content were chosen in conduct the experiments. From the preliminary experiments, it is also found out that there will be heat transfer during the transfer of hot water to thermo flask. Therefore, the temperatures used in this study are set to 35Â±5 oC, 45Â±5 oC, 55Â±5 oC and 65Â±5 oC.
4.3 Specific Heat Capacity of PKC
Based on the results determined in preliminary experiments, the following experimental design shown in Table 4.4 was chosen.
Table 4.4: Experimental Design for PKC Specific Heat Capacity Determination
35Â±5 oC (T1)
45Â±5 oC (T2)
55Â±5 oC (T3)
65Â±5 oC (T4)
The specific heat capacity of PKC was measured in J/(g oC ) using method of mixture. The mass of PKC and hot water was fixed at 40g and 400g respectively. The experiments were carried out for 15 minute time period in this study. The specific heat capacity of wet PKC (50, 100 and 150% moisture content) at various temperatures will be discussed below. The calculation of specific heat capacity is shown in Appendix C. The experimental results for moisture content range (50, 100 and 150%) wet PKC at T1, T2, T3 and T4 is shown in Appendix D.
4.3.1 Specific Heat Capacity of 50% Moisture Content
The plot of temperature as function of time for 50% moisture content PKC at 35Â±5 oC (T1) is shown in Figure 4.11. The initial temperature of 50% moisture content PKC, was measured as 25.54 oC. From Figure 4.11, the initial temperature for hot water, in flask A is measured as 38.80 oC. In between the 15 minutes time period, there is not much changes and the last temperature recorded is 38.81 oC. For the temperature of mixture, which starts at 37.99 oC, the figure shows its temperature decreased slowly until 37.88 oC in this 15 minutes time period. A summary for the calculated mean specific heat capacity for the 50% moisture content wet PKC at various temperatures is shown in Table 4.5.
Figure 4.11: Temperature as Function of Time for 50% Moisture Content PKC at 35Â±5 oC
Table 4.5: Mean Cp Value for 50% Moisture Content Wet PKC at Various Temperatures
, J/(g oC)
Mean , J/(g oC)
4.3.2 Specific Heat Capacity of 100% Moisture Content
The experimental result for 100% moisture content wet PKC at 35Â±5 oC is shown in Figure 4.12 below. Temperature of 100% moisture content wet PKC was measured as 26.30 oC before experiment starts.
From the figure, the temperature of hot water and wet PKC decreased continuously throughout the experiment. The initial temperature for hot water, in flask A was 38.31 oC. The temperature of hot water decreased gradually to 38.17 oC during this 15 minutes time period. A small amount of decreased in temperature for the mixture during the experiment is observed which is reduced from 37.06 oC to 36.96 oC. As the temperature of the mixture decreased steadily, the initial temperature of the mixture is set to be in the calculation. The calculated mean value of specific heat capacity for 100% moisture content wet PKC at various temperatures is shown in Table 4.6.
Figure 4.12: Temperature as Function of Time for 100% Moisture Content PKC at 35Â±5 oC
Table 4.6: Mean Cp Value for 100% Moisture Content Wet PKC at Various Temperatures
, J/(g oC)
Mean , J/(g oC)
4.3.3 Specific Heat Capacity of 150% Moisture Content
The 150% moisture content wet PKC is the last moisture content used in determined specific heat capacity in this study and the result for this moisture content at 35Â±5 oC is shown in Figure 4.13.
The initial temperature of the wet PKC was 26.68 oC. The temperature for hot water, in flask A is reduced from 35.89 oC to 35.76 oC. For the mixture, the temperature decreases from 34.53 oC to 34.43 oC. The result shows the temperature of hot water and the mixture is decreasing and is considered to be constant in this 15 minutes time period. As there is no sudden drop of temperature for the mixture, the initial temperature of the mixture is considered as in the calculation. Table 4.7 shows the mean specific heat capacity value for 150% moisture content wet PKC at various temperatures.
Figure 4.13: Temperature as Function of Time for 150% Moisture Content PKC at 35Â±5 oC
Table 4.7: Mean Cp Value for 150% Moisture Content Wet PKC at Various Temperatures
, J/(g oC)
Mean , J/(g oC)
From Figure 4.11, Figure 4.12 and Figure 4.13, the initial temperature of the mixture is lower than hot water. This is because, when hot water was first contact with wet PKC, the heat from hot water will be transfer to the wet PKC. The temperature of mixture decreased steadily with no sudden temperature drop is because the heat from hot water is already absorbed by wet PKC at the moment when it mixed with the mixture. This temperature is then set to be in the specific heat capacity calculation.
4.4 Effect of Moisture Content
The effect of moisture content on specific heat capacity is discuss below. A graph of specific heat capacity versus moisture content is shown in Figure 4.14.
Figure 4.14: Graph of Specific Heat Capacity as Function of Moisture Content
From Figure 4.14, it is observed that the specific heat capacity of PKC increases linearly as the moisture content for each temperature range increased. For a temperature of 35Â±5 oC, the specific heat capacity value for the three moisture content (50, 100 and 150%) increase from 2.80 to 7.09 J/(g oC). The specific heat capacity of PKC at 45Â±5 oC, 55Â±5 oC and 65Â±5 oC also increases from 2.96 to 7.17, 3.09 to 7.18 and 3.30 to 7.32 J/(g oC) respectively for the moisture content ranges.
The increase of specific heat capacity as the moisture content increase is due to the water content in the PKC. As the specific heat capacity of water is relatively large, the amount of energy required to heat the water to increase 1 oC is larger (Wilson & Buffa, 2000). Therefore, the value of specific heat capacity at a higher water content will be greater compared to the one with less water content.
From the results obtained, it shows that specific heat capacity of PKC increased linearly as the moisture content increased. It is found that specific heat capacity of PKC at various moisture content (50, 100 and 150%) was increased from 2.80 to 7.09 J/(g oC), 2.96 to 7.17, 3.09 to 7.18 and 3.30 to 7.32 J/(g oC) at temperature of 35Â±5 oC , 45Â±5 oC, 55Â±5 oC and 65Â±5 oC respectively. This result is in agreement with the findings of other researchers.
Aviara and Haque (2001) reported that the specific heat capacity of sheanut kernel increased linearly with increased in moisture content for each temperature range indicated and the value ranged from 1.792 - 3.172 J/g K. According to Bitra et al. (2010), specific heat capacity of peanut pods, kernels and shells was determined and results reported was increased from 2.1 to 3.3, 1.9 to 2.8, and 2.7 to 4.1 kJ kg-1 oC -1 respectively at different moisture content range. It is reported that Cp of peanut pods, kernels and shells increased linearly as the moisture content increases.
4.5 Effect of Temperature
The effect of temperature on specific heat capacity of PKC at moisture range of 50-150% is shown in Figure 4.15. The result shows that specific heat capacity of PKC increase slightly as the temperature increase from 35Â±5-65Â±5 oC. This increase in temperature is in agreement with Wolfson (2007) which states that specific heat capacity varies slightly with temperature.
Figure 4.15: Graph of Specific Heat Capacity as Function of Temperature
For 50% moisture content, specific heat capacity increased from 2.80 to 3.30 J/(g oC) at temperature ranges of 35Â±5 to 65Â±5 oC. At this temperature ranges, the specific heat capacity for 100 and 150% moisture content is increase from 4.75 to 5.22 J/(g oC) and 7.09 to 7.32 J/(g oC) respectively.
During the heat transfer from hot water to wet PKC, the increase in temperature of hot water will cause the speed of atoms to increase. Therefore, more thermal energy is required in order to increase their speed (Wilson & Buffa, 2000; Heckert, 2008). The specific heat capacity is therefore increased as the thermal energy needed increase.
The specific heat capacity of PKC at various temperatures (35Â±5 to 65Â±5 oC) was found to increases from 2.80 to 3.30 J/(g oC), 4.75 to 5.22 J/(g oC) and 7.09 to 7.32 J/(g oC) for 50%, 100% and 150% moisture contents respectively. This phenomena was in agreement with the work done by other researchers.
Specific heat capacity of sheanut kernel as function of temperature was reported by Aviara and Haque (2001) and found that Cp increases as temperature increased and it shows a linear relationship with temperature. Razavi and Taghizadeh (2007) reported the specific heat capacity of pistachio nuts increase and found a linear relationship between specific heat capacity and temperature.
This chapter presented the results of preliminary experiments and main experiments which were used to determine the specific capacity of PKC at various moisture contents and temperatures.
Several conclusions can be drawn from the experiments:
Particle size of 1.500 mm is chosen in conduct the experiments due to its high mass percentage and water retention capacity.
The method of mixtures is used in determination of specific heat capacity because the accuracy for Cp of sand compare with lump system method.
The experiment for specific heat capacity of dry PKC was not conducted due to the heat released from PKC itself.
Specific heat capacity of wet PKC increase as the moisture content and temperature increases.