Energy and Exergy analyses of the Drying Process of Ghost Chilli and Sliced Ginger
6.4 Exergy Analysis of the Drying Chamber
6.5.2 Drying of sliced ginger
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Fig. 6.8 Change in the exergetic and thermal efficiencies with the drying time.
It should be noted that the exergy efficiency has approached to around 100% towards the last days of the drying processes. This was due to the less moisture content in the products during the last stage of the drying process. The exergy investment during drying of the product was very less. The temperature drop of the drying air between the inlet and outlet of the drying chamber decreases with decrease in the moisture content of the products. As a result, the exergy inflow and outflow of the drying chamber become almost the same. This leads to very high exergy efficiency (98%). Fudholi et al. (2014b), Celma and Cuadros (2009), Midilli and Kucuk (2003), Fudholi et al. (2014a), Akbulut and Durmus (2010), and Akpinar (2010) reported similar results for exergy efficiency for drying red seaweed (47‒97%) olive mill waste water (34.4‒100%) pistachio (15.6‒100%), red chilli (1‒93%) mulberry (21.3‒93.3%), and mint (34.7‒87.7%) in the solar dryer, respectively.
of 55 ºC. The solar radiation intensity was in the range of 207‒944 W/m2 with an average of 695 W/m2. The solar radiation fluctuated throughout the experiment on the second day.
Fig. 6.9 Variation in the moisture content of the ginger with the drying time.
Fig. 6.10 Change in the air temperature with time at different locations of the SAHs.
The thermal efficiencies of the solar air heaters (Fig.6.11) were found to be slightly higher than in the previous experiment which was due to the lower ambient temperature. The average ambient temperature recorded during October was 30 °C while it was 28 °C during November 2015. In the second day, the efficiency fluctuated continuously due to the fluctuation in the solar radiation intensity. The average overall efficiency of the solar air heaters array was found to be 23.3%.
Figure 6.12 shows the variation in the ambient temperature, the solar radiation intensity and the inlet and outlet temperatures of the drying chamber for the five consecutive days. The
0 20 40 60 80 100
09:00 11:00 13:00 15:00 09:00 11:00 13:00 15:00 09:00 11:00 13:00 15:00 09:00 11:00 13:00 15:00 09:00 11:00 13:00 15:00
Moisture content, w.b. (%)
Time (h)
13thNov.
12thNov.
11thNov.
10thNov.
9thNov.
100 300 500 700 900 1100
5 15 25 35 45 55 65 75
09:00 11:00 13:00 15:00 10:30 12:30 14:30 10:00 12:00 14:00 09:30 11:30 13:30 09:00 11:00 13:00 15:00 (W/m2)
Temperature (ºC)
Time (h)
Inlet air temperature of SAH-1 Outlet air temperature of SAH-1 Inlet air temperature of SAH-2 Outlet air temperature of SAH-2 Solar radiation intensity
9thNov. 10thNov. 11thNov. 12thNov. 13thNov.
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ambient temperature varied from 24 C to 31 C with an average of 28 °C. The solar radiation intensity and the drying air temperature were in the range of 207‒944 W/m2 with an average of 695 W/m2 and 37‒57 C with an average of 50 C, respectively.
Fig. 6.11 Variation in the thermal efficiency of SAHs for five consecutive days during ginger drying.
Fig. 6.12 Variations in the ambient temperature, solar radiation intensity, and the inlet and outlet temperatures of the drying chamber during ginger drying.
The exergy inflow and outflow, the exergy losses, and the exergetic efficiency of the drying chamber are shown in Fig. 6.13. The exergy inflow and outflow of the drying chamber were found to be varied from 2.6 W to 23.6 W and 1.1 W to 15.7 W, respectively. The maximum exergy inflow of the drying chamber coincided with the peak sunshine hour. The
0 10 20 30 40 50
09:00 11:00 13:00 15:00 10:30 12:30 14:30 10:00 12:00 14:00 09:30 11:30 13:30 09:00 11:00 13:00 15:00
Efficiency (%)
Time (h)
Thermal efficiency of SAH-1 Thermal efficiency of SAH-2 Overall thermal efficiency of SAH
9thNov. 10thNov. 11thNov. 12thNov. 13thNov.
0 200 400 600 800 1000
0 10 20 30 40 50 60 70
09:00 11:00 13:00 15:00 10:30 12:30 14:30 10:00 12:00 14:00 09:30 11:30 13:30 09:00 11:00 13:00 15:00 Solar radiation intensity (W/m2)
Temperature (ºC)
Time (h)
Ambient air temperature Dryer inlet temperature Dryer outlet temperature Solar radiation intensity
9thNov. 10thNov. 11thNov. 12thNov. 13thNov.
exergetic efficiency was found to be in the range of 4‒94% with an average of 47%, and it increased gradually with advancing in drying time.
Fig. 6.13 Exergy inflow and outflow, exergy loss and the exergetic efficiency change with the drying time.
Fig. 6.14 Change in the thermal and the exergetic efficiencies of the drying process of the ginger for five consecutive days.
Figure 6.14 exhibits the thermal and exergetic efficiencies variation in the drying chamber from 9:00 h to 15:00 h for five consecutive days (9th - 13th November 2015). The thermal efficiency varied from 1% to 77%. The pattern of the thermal efficiency curve of the drying process of the sliced ginger is slightly different from the Ghost chilli one. In the case of the Ghost chilli, the thermal and exergetic efficiency curves on each day for the seven consecutive drying days are almost similar in trend for the whole drying period. However, in
0 20 40 60 80 100
0 5 10 15 20 25
09:00 11:00 13:00 15:00 10:30 12:30 14:30 10:00 12:00 14:00 09:30 11:30 13:30 09:00 11:00 13:00 15:00 Exergy efficiency (%)
Exergy (W)
Time (h)
Exergy inflow Exergy outflow Exergy loss Exergy efficiency
10thNov. 11thNov. 12thNov. 13thNov.
9thNov.
0 10 20 30 40 50 60 70 80 90 100
0 10 20 30 40 50 60 70 80 90 100
09:00 11:00 13:00 15:00 10:30 12:30 14:30 10:00 12:00 14:00 09:30 11:30 13:30 09:00 11:00 13:00 15:00 Exergy efficiency (%)
Thermal efficiency (%)
Time (h)
Thermal efficiency Exergy efficiency 9thNov. 10thNov 11thNov. 12thNov. 13thNov.
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the case of the ginger drying process, the exergetic efficiency increases gradually from the first to the third day, and afterwards the curves are similar in the pattern for the last two days. Thus, the sliced ginger drying process exhibited higher energy efficiency and the lower exergetic efficiency during the first few days of its drying. This may be due to moisture saturated surface of the sliced ginger during the initial period for which more heat is consumed during the initial period. With the elapse of the drying time, the free moisture diminishes from the surface and the moisture starts diffusing from the inner structure of the product to the surface.
The specific energy consumption and the overall thermal efficiency were estimated by applying Eqs. (6.15) and (6.19) for 𝑡𝑑 = 33 h, 𝐼 = 695 W/m2 and 𝑝𝑏𝑙=250 W and found to be 8.8 kW h/kg and 8.5%, respectively.
Table 6.1
Summary of the performance of the solar dryer while drying Ghost chilli and sliced ginger.
Particulars Ghost Chilli Sliced Ginger
Initial mass (kg) 9 13
Initial moisture content, w.b. (%) 85.5 86.3
Final moisture content, w.b. (%) 9.7 10
Total drying time (h) 42 33
Thermal efficiency of the SAH - 1 (%) 22.1‒38.4 26.1‒40.2 Thermal efficiency of the SAH - 2 (%) 9.6‒18.4 10.5‒19.5 Overall thermal efficiency of the air heaters (%) 23 23.3 Specific energy consumption of the product (kW h/kg) 18.7 8.8 Overall thermal efficiency of the drying system (%) 4 8.5 Exergy inflow of drying chamber (W) 4.4‒30 2.6‒23.6
Exergy outflow of drying chamber (W) 2‒22 1‒15.7
Exergy efficiency of the drying chamber (%) 21‒98 4‒94
Average exergy efficiency (%) 64 47
The results show that the overall thermal efficiency of the drying system is comparatively low, and the specific energy consumption is relatively high for both the products. It may be attributed to the longer drying period, the short drying operation per day, and the low loading capacity of the dryer. The dryer was operated daily for six hours because of which more drying days was required for completing the drying process. When the drying
operation was restarted after the interruption, low exergy efficiency and high exergy losses were observed in the first few hours, which indicated that more heat energy was eaten up by the products and the wall material of the drying chamber.
High exhaust air temperature of the drying chamber was recorded during the peak sunshine hours and therefore, meticulous planning for recirculation of the exhaust air, operation of the dryer with the thermal storage to extend the drying time beyond the sunshine hours, and increasing the loading capacity may slightly improve the overall performance of the drying system. It may be also worthwhile to modify the dryer to operate in the mixed mode - type (replacing the top cover of the drying chamber with a transparent cover plate) and to investigate the drying characteristics. The summary of the performance of the solar dryer is presented in Table 6.1.