# The Significance of the Sorption Isotherm on the Simulated Performance of Grain Driers
## 8 Conclusions  
Sorption isotherms provide stored product technologists with indispensable information. They enable the temperature and humidity of process air used to dry agricultural produce to be manipulated to ensure that the desired product moisture content is achieved. Furthermore, information concerning the energy required to remove moisture from the product is subsumed within sorption isotherms. The scientific literature displays a diversity of sorption isotherms for canola and, importantly, a wide range of experimental results. This work highlights that difficulties arise when sorption isotherms are fitted to experimental data with high fidelity. It is shown that steeper-than-anticipated gradients of moisture contents and temperatures may be predicted. Inaccurate isotherms may lead to commercially significant errors when predicting the performance of driers. For example, if isotherms predict equilibrium humidities of the interstitial air that are too high, then the rate of drying will be over-predicted. In this case, driers would be under-sized. This work demonstrates that several widely cited sorption isotherms yield anomalous values of the equilibrium moisture content of canola. For example, it is demonstrated that the modified Chung-Pfost isotherm can yield negative values of moisture contents as the relative humidity of the surrounding atmosphere tends to zero. This is an inherent property of the Chung-Pfost isotherm. It is also shown that the modified Halsey isotherm predicts a sharp drop in the moisture content of canola as the relative humidity of the surrounding air approaches zero. Figure 12: Air in state A enters a bed of canola initially in state B. When Equation (12) is used to calculate the plateau state, P, Equation (29) results in lower values of the temperature and humidity of the air than when the Clausius–Clapeyron Equation (12) is invoked. Grain moisture contents of 0.02, 0.05, 0.08, and 0.11 are shown on the psychometric chart. \begin{table}
\begin{tabular}{l l l l l l l} \hline \hline \multirow{2}{*}{**Variable**} & \multicolumn{2}{c}{**[PERSON]–**} & \multicolumn{2}{c}{**[PERSON]–**} & \multicolumn{2}{c}{**[PERSON]–**} & \multicolumn{2}{c}{**[PERSON]–[PERSON]–**} & \multicolumn{1}{c}{**[PERSON]–[PERSON]**} & \multicolumn{1}{c}{**[PERSON]–[PERSON]**} \\  & \multicolumn{2}{c}{**[PERSON]–Empirical**} & \multicolumn{2}{c}{**[PERSON]–Clausius–Clapeyron**} & \multicolumn{1}{c}{**[PERSON]–[PERSON]**} & \multicolumn{1}{c}{**[PERSON]**} & \multicolumn{1}{c}{**[PERSON]–[PERSON]**} & \multicolumn{1}{c}{**[PERSON]–[PERSON]**} \\ \hline \(T_{r}\) & 27.52 & 28.65 & 29.84 & 28.90 & 29.55 & 29.93 \\ \hline \(w_{p}\) & 0.02346 & 0.02514 & 0.02597 & 0.02550 & 0.02451 & 0.02709 \\ \hline \(W_{p}\) & 0.2551 & 0.2579 & 0.2565 & 0.2566 & 0.2557 & 0.2550 \\ \hline \(\mathcal{V}_{hyp}\) & 7.277 \(\times 10^{-5}\) & 8.195 \(\times 10^{-5}\) & 8.720 \(\times 10^{-5}\) & 8.151 \(\times 10^{-5}\) & 8.514 \(\times 10^{-5}\) & 9.423 \(\times 10^{-5}\) \\ \hline \(\mathcal{V}_{hard}\) & 2.233 \(\times 10^{-3}\) & 1.692 \(\times 10^{-3}\) & 2.504 \(\times 10^{-3}\) & 2.179 \(\times 10^{-3}\) & 2.282 \(\times 10^{-3}\) & 3.635 \(\times 10^{-3}\) \\ \hline \(w_{\text{initial}}\) & 0.01717 & 0.01717 & 0.01651 & 0.01721 & 0.01642 & 0.01713 \\ \hline \(w_{\text{initial}}\) & 0.01717 & 0.01717 & 0.01651 & 0.01721 & 0.01642 & 0.01713 \\ \hline \(W_{\text{init}}\) & 0.01142 & 0.01142 & 0.01037 & 0.00215 & 0.01352 & 0.01023 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: A summary of the performance of a canola drier operating under conditions given in Table 2.  
An empirical expression used by [PERSON] et al. [14] exhibits values of the differential and integral heats of wetting that are considerably higher than those calculated by employing the Clausius-Clapeyron equation. It is also found that the integral heat of wetting cannot be determined by the modified Halsey isotherm when the Clausius-Clapeyron equation is used, because the integral is divergent.