Temperature of Dried SCs
The dryers used in the present study controlled the drying temperature by monitoring the temperature of the air in the drying chamber. Some FIRD procedures control the power instead of the drying temperature, but neither the air tem- perature nor the power provides the temperature of the samples being dried. The temperatures at the center of the SC body wall (denoted as C in Fig. 1) were measured at the drying temperature of 70C (Fig. 4). As shown in Fig. 4, the coming-up-time (CUT) to reach the isothermal tem- perature for FIRD and AD was approximately 25 min. The CUT values of the two methods were nearly identical because the chambers were preheated for 30 min before conducting the experiment. The CUT of both drying methods was relatively short compared with the entire drying process. The CUT may not contribute to the entire drying process, but in the initial drying period, the drying rate is significantly affected by the CUT. The effect of the CUT on the MR in the early drying period is summarized in Table 2. For both FIRD and AD, the MR changes are signifi- cantly higher during CUT, which may be due to the evapo- ration of the free water on the SC surface dominating the drying process during the CUT. The SC temperatures for FIRD and AD at equilibrium were quite different (Fig. 4). At the 70C drying temperature, the SC body temperature with FIRD was approximately 22C higher than the SC body temperature with AD. The SC body temperatures at drying temperatures of 60, 70 and 80C were 67.6, 83.4 and 90.0C, respectively, with FIRD and 54.7, 61.2 and 67.7C, respectively, with AD. These differences may be due to the heating mechanism associated with radiation. The vibration of molecules in the sample that occurs because of the radiation may increase the temperature of the inside of the sample. Thus, the temperature of the samples being dried was higher than that of the air in the drying chamber. For AD, the heat transfer mechanism is simply through the convection of hot air in the drying chamber to the samples. In the present study, the maximum temperature of the SC with AD was approximately 65C. The temperature of dried SC with AD did not reach the air tem- perature of the drying chamber. This result provided an important insight to understand the different drying results from these two drying methods. The sample temperature with FIRD may be higher than the drying temperature set by the dryer as long as the dryer closely monitors and con- trols the air temperature in the chamber. A higher tempera- ture may increase the drying rate, but it may also cause a thermal degradation. The fast drying rate of FIRD observed in the present study may be due to the high SC temperature with FIRD, which implies that the heat transfer mechanism of FIRD is effective. In addition, AD causes surface harden- ing because the heat is transferred from the surface to the inside of the sample, which may also cause the SC quality to degrade.
Temperature of Dried SCs
The dryers used in the present study controlled the drying temperature by monitoring the temperature of the air in the drying chamber. Some FIRD procedures control the power instead of the drying temperature, but neither the air tem- perature nor the power provides the temperature of the samples being dried. The temperatures at the center of the SC body wall (denoted as C in Fig. 1) were measured at the drying temperature of 70C (Fig. 4). As shown in Fig. 4, the coming-up-time (CUT) to reach the isothermal tem- perature for FIRD and AD was approximately 25 min. The CUT values of the two methods were nearly identical because the chambers were preheated for 30 min before conducting the experiment. The CUT of both drying methods was relatively short compared with the entire drying process. The CUT may not contribute to the entire drying process, but in the initial drying period, the drying rate is significantly affected by the CUT. The effect of the CUT on the MR in the early drying period is summarized in Table 2. For both FIRD and AD, the MR changes are signifi- cantly higher during CUT, which may be due to the evapo- ration of the free water on the SC surface dominating the drying process during the CUT. The SC temperatures for FIRD and AD at equilibrium were quite different (Fig. 4). At the 70C drying temperature, the SC body temperature with FIRD was approximately 22C higher than the SC body temperature with AD. The SC body temperatures at drying temperatures of 60, 70 and 80C were 67.6, 83.4 and 90.0C, respectively, with FIRD and 54.7, 61.2 and 67.7C, respectively, with AD. These differences may be due to the heating mechanism associated with radiation. The vibration of molecules in the sample that occurs because of the radiation may increase the temperature of the inside of the sample. Thus, the temperature of the samples being dried was higher than that of the air in the drying chamber. For AD, the heat transfer mechanism is simply through the convection of hot air in the drying chamber to the samples. In the present study, the maximum temperature of the SC with AD was approximately 65C. The temperature of dried SC with AD did not reach the air tem- perature of the drying chamber. This result provided an important insight to understand the different drying results from these two drying methods. The sample temperature with FIRD may be higher than the drying temperature set by the dryer as long as the dryer closely monitors and con- trols the air temperature in the chamber. A higher tempera- ture may increase the drying rate, but it may also cause a thermal degradation. The fast drying rate of FIRD observed in the present study may be due to the high SC temperature with FIRD, which implies that the heat transfer mechanism of FIRD is effective. In addition, AD causes surface harden- ing because the heat is transferred from the surface to the inside of the sample, which may also cause the SC quality to degrade.
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