# Experimental Verification of Yam (_Dioscorea rotundata_) Drying with Solar Adsorption Drying
## 3 Results  
### Performance of SAD Drying  
As the driving force for night drying is the strongest for a wet product, this experiment started with night drying using dried silica gel as an adsorbent. The adsorbent was used on the first night for 5 h and hermetically sealed for assessing whether the drying site was up. On the second and third night, the adsorbent was used again. The adsorbent was then stored for regeneration. The performance of the system was monitored by recording the air inlet and outlet temperatures. During the night the temperature increased by 5.2 \({}^{\circ}\)C through the release of latent heat of adsorption and the rise of temperature indicates active dehumidification by the adsorbent. The SD and OSD started in the next morning. The operational conditions: radiation, ambient temperature, input and outlet air temperatures for SAD, SD, and OSD drying systems are shown in Figure 3. The air temperatures that enter the drying units were significantly higher during the day than the nights, whereas the outlet temperatures were slightly lower. During the day, air temperatures increased from the morning, peaked in the afternoon, and dropped towards the evening. The night temperature increased initially due to adsorption energy (see grey portion of Figure 3). Meanwhile, the air temperature related well with solar radiation. The moisture content of yam particles, averaged over the three trays, is given in Figure 4. The product in the SAD dries immediately in the first night and the water content falls from 1.70 to 1.15 kg water/kg dry matter over the first 5 h of night drying with dehumidified air. SAD is continued the following mornings (day 1). During night 2, SAD is still effective, but, at day 3, the effectivity is no longer significant. The low drying rate during night 3 is a result of the low driving force between the nearly dried the product at the temperatures realized by the dehumidification system. Therefore, adsorption drying the night is most effective at the early stages of drying after which elevated temperatures are required to remove water when the moisture content of the samples are low. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Objective of** & **Start** & **Duration** & **Chemical Analysis** & **Sensors/Probe** & **No. of** \\
**Experiment** & & & & **Analysis** & **Cultivars** \\ \hline Performance of SAD & Night & 3–5 days & Vitamin C in fresh and dried product & K-type & 1 \\ Night & & 6 h & & & thermocouple & \\ Day & & 9 h & & & \\ Drying different & & & & & \\ yam cultivars & & 4–9 days & Vitamin C in fresh and dried product & K-type & 3 \\  & & & Composition & thermocouple & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Major characteristics of experiments. By the end of the second day 90.3%, 84.3% and 76.2% of water was removed for SAD, SD and OSD, respectively. The total time needed for SAD to reach a final moisture content of 0.07-0.08 kg water/kg dry matter is within three evenings and three days compared to four and five days for the SD and OSD, respectively (Figure 4). This result implies that the capacity of a solar adsorption system is higher than that of the SD. Figure 4: Average moisture content over all trays of yam particles (’Dente’) for different drying methods, SAD, SD and OSD. The grey portions represent night drying. Figure 3: Drier cabinet input and output air temperatures T4 and T5 (night), T2 and T3 (day) for SAD (top graph), T2 and T3 (day) for SD (middle graph) and ambient temperature T1 for OSD (See Figure 2) and radiation (bottom graph). The grey portions represent the night drying. increases by a 20%-25% shorter time line compared to a standard solar dryer. Extension to full night drying with an adsorption system, which was not possible in this experimental setting, can further reduce the drying cycle.